Skip to main content

Full text of "Manual Of Qualitative Chemical Analysis"

See other formats


This book is with 

tight 
Binding 



Carnegie Institute of Technology 
Library 

PITTSBURGH, PA, 
Rulai for Landing Books; 

f. Reserved hook* mav he usd <mfv in rhc 
library until H P. M, Aticr h hnur rbty 
may be requested for outsule iw, Aw <h< fot 
lowing morning ac 9: MX Ask ,u the uk-vk 
at^ut wct?k*eno borrowing pnvilcics, 

2. Boolcfr not of 5rrirMy refcT^nt't* AAtnrr/anH nof 
Oft rescr^i nny bei,flrrovn) tor UiME?r pcn*h, 
on request.\Dt du is K(4m[fdo(t J^r^h^ 
in book. 'V 

Au 

3, A fioe of five ccfHi an ,h'our is <hsraot tvt 
ovfriue reserved bwnfe^TwD cenr* 4 tUy ftn? 
is charged on overdue ttnfw^-mJ buoki 

Artt Braock Ubr*ry 



DATE DUE 



MANUAL OF 



QUALITATIVE CHEMIOAI 



* 



BT TfTB; LATE 

DR 0. BEMIGIUS 



Covnwllor and 
of Uie O'/wmicoZ Ix^oratofj/ at >F*e*&acZen. 



AUTHORIZED TRANSLATION 

BY 



IIOBAOE L. WKLIA M.A., 

Chemistry and Metallurgy in the Sheffield 
tj&cntiflc tictiwl of rate University. 



N&W SMT10N, THOROUGHLY BEV18WD, FROM! 

MM tilXTKKXTX GERMAN 

j* 

KllUKTH THOUSAND, 



TOBK: 



HOHVOB L WELI& 



PBEFACE. 



DURING the fourteen years that have elapsed since the 
apptuiraneo of tho hurt American edition of this work, two 
ruviHod German editions (the fifteenth and sixteenth) have 
IHMM published, embracing so many additions and other 
improvommitH that tho neod of a new translation has been 
folt. With tho contMmt of the author (given only a few 
month** before Inn death), and also with the permission of 
l*rof. H. \V. Johnson, editor of the preceding American 
(ulitioiiH, thin tniuslatiou has therefore been undertaken. 

Except iti regard to nomenclature and chemical formulas, 
th* jmmcmt work faithfully represents the recent sixteenth 
(lurmau adition. The example of the previous American 
tHHua h;iH boon followed in giving modern chemical formulas 
iPwHuniuH, iu recant editions, haw given both old and new), 
and iti modernising tho greater part of the nomenclature, 
Tho few ndditioiiH made to the text are enclosed in brackets, 
hi tioarly nil canon. 

Tho, trannlutor has followed the author in avoiding the 
introihictiou of abbreviated analytical tables, believing that 
imeh tableB are often stumbling-blocks in the way of an intel- 
ligent study of the subject. 

AB far as possible, use has been made of the text of the 
laHfc American edition, but the changes and additions in the 
(tormau work have been BO extensive that it has been neoes- 
*ary to rewrite a large part of the matter, and to reset the 
typo for the whole work. Previous condensations and omis- 
aioiiB have been here restored, and larger and smaller type, 
&lcu>, have been used in the same way as in the German 
edition. 

The translator trusts that the care bestowed upon the 

ill 



IT PBEFAOE. 

work, in the effort to insure accuracy of statement and clear* 
ness of language, will make the present edition satisfactory to 
those who use it ; and he desires to acknowledge the valuable 
assistance, in proof-reading, of Miss Lucy P. Bush, of New 
Haven. 

In view of the recent death of the author, it seems appro- 
priate to give, at this time, some facts concerning the history 
and development of the work, as described in the prefaces to 
the German editions. 

While a student at Bonn, in the winter of 1840-1, Fre- 
senius wrote out a course of qualitative analysis, merely for 
the sake of practice. Following the advice of an experienced 
chemist, whose name is not given, he published these notes, 
thus issuing the first edition of his " Qualitative Analysis." 
In the spring of 1841, he became assistant, and afterwards 
instructor (Privatdocent), in Liebig's laboratory at Giessen, 
and occupied himself there with the instruction of beginners 
in chemical analysis. A second edition of the work appeared 
in 1842, with a preface of recommendation by Liebig. The 
latter stated that the book contained many new and simplified 
methods of separation, so that it would be welcomed eveja by 
those who possessed the larger works on mineral analysis. 
At this time, the systematic course was preceded by a de- 
scriptive part relating to reactions, thus making the treatise 
an independent one. This edition was translated into Dutch, 
English, French, and Italian, and was used in many prom- 
inent laboratories. A third edition was published in 1844, 
while the author was still at Giessen. 

In the autumn of 1845, Fresenius removed to Wiesbaden, 
which was to be his home for the rest of his life. At first he 
was Professor of Chemistry, etc., at the Agricultural Institute, 
and during this period of somewhat more than two years the 
fourth and fifth editions of the book appeared. These issues, 
besides being revised and otherwise improved, contained an 
additional section, devoted to the reactions and detection of 
the more important vegetable alkaloids. 

In the position just mentioned, Fresenius was unable to 
carry on his favorite task of teaching analytical chemistry to 
young men, so that in the spring of 1848, he opened an inde- 
pendent laboratory for instruction. This developed into the 



PREFACE. V 

important institution which is still in operation. The author's 
work now enabled him to observe continually the use of his 
book in the hands of large numbers of students, and, under 
these favorable conditions, the remaining editions, from the 
sixth to the sixteenth, have appeared. 

To tho seventh edition was added a section relating to 
courses of analysis in special cases, thus increasing the 
utility of tlu> work for those engaged in practical investiga- 
tions. In tin* preface to the ninth edition, the author stated 
that he had always remained true to the firm principle, never 
to admit anything into his work without personal verification. 
In the eleventh edition, of 1862, the recently discovered spec- 
troKcopic reactions were included, and, for the first time, the 
work was made to embrace all the known elements. The 
twelfth, thirteenth, and fourteenth editions contained few 
chants, but tho fifteenth, published in 1885, was thoroughly 
revised, and formulas of the new system (in addition to those 
of the old) wore introduced. The last (sixteenth) edition, 
which appeared ten years later, was also completely revised. 
A new feature was introduced at this time by the insertion of 
a much larger number of references to chemical literature, 
relating especially to additional methods. The usefulness of 
tho work was thus considerably enhanced, without unduly 

increasing its size. 

ELL. W. 
Ki:w UAVBN, CONK.', September, 1897. 



NOTE. 

AH temperatures mentioned in this book refer to degrees 
of tho Centigrade thermometer, 



CONTENTS. 



PART I. 
INTRODUCTORY PART. 

PAGE 

IlKMARKH ............................................ 1 

SECTiONT I. 

OPKUATIONS, I ............................................. ,.. 4 

1. Solution, 2 ................................................... 4 

2. OysHlhswiion. 3 ............................................. 6 

3. IVrijutution. 4 ............................... . ............... 8 

4. Kiltnitiim, T> .................................................. 9 

IV IfcuMiitalmn. ................................................ 12 

. Wnhliinir, 7 ................................................... 12 

7. DSrtljhiH, ^8 ..................................................... 14 

H. Kvaporation, 50 ................................................ 1*5 

!. Distillation, 5 10 ................................................ 17 

R Ignition. $11 ...... ............................................ I 8 

H. Stihlhimiitiu, 12 ............................................... 1& 

12. KuMHtn and thuiiif;. 5 13 ......................................... 20 

13. l><*HajL r ruti<n, 14 ............................................... 21 

14. Th uni" of the blowpipe, 15 .................................... 22 

l^. Thi* urn* of lumps, iHirtirulsirly of piw-IampB, 16 .................. 27 

lit. otwrviititm <if tbo (*olor.Hion of flnme and .sjx'Hram analysis, 17. . 30 

17. Th u"* of i Ju inicnwoopf* in qualitative analysis, 18 ............. 43 

tft Flntt NVro, 

anil ul<miK 10 ........................................ 45 



8KCCTON H. 

820 

A. nAGENTP TW THK VET WAT. 

L fllMri.ff ROLVKNTfi. 

1. WriW, |! 

2. Kthyl alcohol, 822 



vli 



VU1 CONTENTS. 

PAGE 

3. Ethyl ether, 23 54 

4. Chloroform 54 

5. Carbon disulphide 54 

II. ACIDS AND HALOGENS, 24 55 

a. Oxygen acids. 

1. Sulphuric acid, 25 57 

2. Nitric acid, 26 60 

3. Acetic acid, 27 61 

4. Tartaric acid, 28 62 

6. Hydrogen acids and halogens. 

1. Hydrochloric acid, 29 63 

2. Chlorine and chlorine-water, 30 65 

3. Nitro-hydrochloric acid, 31 67 

4. Hydrofluosilicic acid, 32 67 

c. Sulphur acids. 

1. Hydrogen sulphide, 33 69 

IU. BASES, METALS, AND SULPHIDES, 34 * 75 

a. Oxygen bases. 
<x. Alkalies. 

1. Potassium hydroxide and sodium hydroxide, 35 76 

2. Ammonia or ammonium hydroxide, 36 79 

ft. Alkali earths. 

1. Banuin hydroxide, 37 , . 81 

2. Calcium hydroxide, 38 82 

y. Heavy metals and their oaidex and hydroxides. 

1. Zinc, 39 83 

2. Aluminium 83 

3. Iron 84 

4. Copper 84 

5. Bismuth hydroxide, 40 84 

&. Sulphides. 

1. Ammonium sulphide, 41 85 

2. Sodium sulphide, 42 87 

IV. PEROXIDER. 

1. Hydrogen peroxide, 43 87 

2, Lead peroxide, 44 88 

V. SALTS. 

a.. Salts of the alkali metals. 

1. Potassium sulphate, 45 89 

2. Sodium phosphate, 46 90 

3. Ammonium oxalate, 47 90 

4. Sodium acetate, 48 9i 

5. Sodium carbonate, 49 02 

6. Ammonium carbonate, 50 93 

7. Hydrogen sodium sulphite, 51 94 

8. PotaBRium nitrite, 52 95 

9. Potassium chromatc, 53 95 

10. Potassium pyroantimonate, 54 96 

11. Ammonium molybdate, 55 , 97 



CONTENTS* il 

PAGB 

12* Ammonium chloride, 56 ...................................... 9S 

13* i'otuhhium cyanide, 57 .......... .. ...... *..... .............. 99 

14 I'otusftium fcrrocyamde, 58 .................. . ................ 101 

lf>, PotuHKium fcnicyunide. 59 .................................... 101 

10. I'otashium sulphooyamde, 60 ................................ ,. 102 

b. NMA tti the alkali-earth metals. 

1. Hun urn chloride, IH .......................................... 103 

ii. Itarium nitrate, 02 .......................... [.] ...... !!.!!..] 104 

;t. Barium carbonate, 63 ........................................ 106 

4. Calcium sulphate, 04 ......................................... 105 

5. Calcium chloride, 05 ................................. . ........ 106 

tf. MagttcHium Htilphule, 66 ..................................... 107 

r. MM* of the heart/ metal*. 

1. Ken cms sulphate, 07 ......................................... 107 

2. Ferric chloride, 68 ............. . ............................. 108 

3< Silver nitrate, 69 ............................................ 109 

4. l*iui acetate, 70,.. .......................................... 110 

5. Mereuroufl nitrate, 71 ........... * ............................ Ill 

0. Mercuric chloride, 72 ....................................... Ill 

7. Cupric Hulpluite, 73 ......................................... 112 

tt. KUnnoiiH chloride, 74 ........................................ 112 

IK Uydrochloroplatinic acid, 75 .................................. 113 

10. Sodium palladioiw chloride, 70 ............................... 114 

11, IlydrcK'hlorauric acid, 77 ...................................... 114 

VI. COLOniNG WATTKBS AND INDIFFERENT VEGETABLE SUBSTANCES. 



1. Twt paperw, 78 .............................................. 115 

2. Solution t>f indigo, 79 ........................................ 117 

B. KKA.(3ENTS IN THE DET WAT. 
1 PM'XKH AND DKCOMPOHINO AGENTS, 

1. Mixture of wuliuzn and potaHsiuni carbonates, 80 ........ . ...... 118 

2. Barium hydroxide, 81 ........................................ 120 

3. Culftum fluoride and other fluoride*, 82 ....................... 121 

4. ftidfiim utirute, 83 ......................................... 121 

5. Potiuwium tlitutlplmte, H4 ..................................... 122 

II, HMWMPK BKAKNTO. 

1. Sodium carlnmatr, 85 ........................................ 122 

2. l*kfdmlttm cyanide, Hfi ........................................ 123 

. Sodium formate, 87 ......................................... 124 

4. Sodium Mraborato, JB8 ........................................ 126 

fi, 1 1 Viirogf'n nodinm ammonium phosphate, 89 ...... , ............. 127 

A Cobalt nitnfcto, 90 ............................................ 127 

SECTION in. 

flKPOHTMENT OF BODIES WtTTt KKAOENTS, 5 91 .......... ...,.... 129 

A. HKArTIONH OF THK METALLIC RADICALS, 92 .................... 130 

cinorp, 593. .......... * .................................. Ml 

94, ............................................... 131 



X CONTENTS. 

PAGE 

6. Sodium, 95 135 

c. Ammonium, 96 1.37 

Recapitulation and remarks, 97 13!) 

Rarer metals. 

1. Csesium, 98 142 

2. Rubidium 142 

3. Lithium 144 

SECOND GROUP, 99 140 

a. Barium, 100 147 

6. Strontium, 101 150 

c. Calcium, 102 153 

d. Magnesium, 103 15ft 

Recapitulation and remarks, 104 159 

THIBD GBOUP, 105 164 

a. Aluminium, 100 lt>5 

6. Chromium, 107 108 

Recapitulation and remarks, 108 170 

Rarer metals. 

1. Beiyllium, 109 172 

2. Thorium, 110 174 

3. Zirconium, 111 175 

4. Yttrium, 112 170 

5. Cerium, 113 178 

6. Lanthanum, 114 17tt 

7. Didymmm, 115 1HO 

Appendix to 112-115, 116 11 

Addenda to 100-116, 117 182 

8. Titanium, 118 183 

9. Tantalum, 119 18tt 

10. Niobium, 120 1H8 

FOUBTH GROUP, 121 189 

a. Zinc, 122 100 

6. Manganese, 123 4 104 

o. Nickel, 124 KH* 

d. Cobalt, 125 202 

e. Iron in ferrous compounds, 126 2041 

f. Iron in ferric compounds, 127 !>01) 

Recapitulation and remarks, 128 212 

Rarer metals. 

1. Uranium, 129 218 

2. Thallium, 130 220 

3. Indium, 131 221 

4. Gallium, 132 223 

5. Vanadium, 133 224 

FIFTH GROUP, 134 226 

First dMsion. 

a. Silver, 135 , 227 

6. Mercury in mercurous compounds, 136 220 

c. Load, 137 032 

Recapitulation and remarks, 138 234 



CONTENTS. XI 

. Mc-zcury in mercuric compounds, 139 .......................... 236 

l>. Copper, 140 ................................................... 240 

i\ Hihinuth, 8MI ................................................. 244 

d. I'udnumn, 14*2 ............................................... 247 

Recapitulation and icinarks, 143 ................................. 240 

/torn- ntttulx. 
1. Palladium, 114 ........................................... 252 

Rhodium, 145 ............................................ 253 

3. Osmium, Htt. ............................................ 254 

4. Ruthenium, 147 ...... ,., ................................. 256 

ouoirr, $148 ........... * ................................. 257 



Flrttt 

tf. liold. 14i) .................................................... 258 

//. I'lutimini, 150 ............................................... 261 

arid remarks, 151 ................................ 263 



(/. Tin and hfaimoua compounds* 152 ............................. 264 

6. Tin and stannic compounds, 153 .............................. 268 

c. Antimony, 154 ....................... * ...................... 271 

</. AtM< k ni<' and arwniouH compounds, 155 ......................... 278 

f, ArMuu compounds. lf>0 ..................................... 291 

Kwapifulation and romarbs, 157 ................................. 295 

Ittinr metal H. 
J. (Sornmnumi, 158 .......................................... 304 

2, Indium, 151) ............................................. 305 

3. Molybdenum, 100 ........................................ 307 

4. TunpMtpn, ll ............................................ 309 

5, IVIIurium, 102 ........................................... 311 

0* Pelwiium, 1U3 ............................................ 313 

B. DKI'OItTMKNT OK ACIDS AND THEIR RADICALS, 104. .............. 314 

I. INORGANIC ACIDS* 

FIRST GROUP, 165 ................. * ........................... 816 



Chromic acid, 166 ...... . ....................................... 317 

Rarer artrtft, 

1. SulphurouB add, 167 ...................... . .............. 321 

2. ThioKU Iph uric odd, 163 .................................... 322 

3. fadfe acid, 169 ........................................... 323 



Sulphuric tidd, 170 ............................................. 824 

HydrofluoftiHeic acid, 1171 ....................................... 827 

Third Jirixton. 
a. rh<wphorlc acid, 172 ......................................... 327 

Pyrophoflphoric and metaphoaphoric acids, 173 .................. 333 



3U1 CONTKKTS, 

FA OR 

b. Boric acid, 174 ............................................... , <l ,l 

C. Oxalic ai'id, 1 175 ............... , .............................. ttr7 

d. Hydrofluoric and. 1715 ............................... , ....... :usi 

Recapitulation and remark*, 177 ........................... ...>,. Ml 

acid, 178 ....... . ......... , ........... . ........ > , , . . ;) W 



Fourth 
a. Carbonic acid. 170 .......................................... :U7 

&. Silicic acid, IHO ........................................... ;ui 

Recapitulation ami remark*, JltiL... ................... , ........ ;j,J 

SKCOND cmoup. 
a. Hydrochloric acid, 182 ..................... **.,, ............. IU' 

I/. Hydrobromie acith 183 ....................................... ;j,7 

c. HydruMlic uciil r 1H4 .......................................... ^iJ 

rf. Hydroi'yttiitO ucid, IK> ......................................... ii>l 

", hytlroferri-, uml hylroHulpho-cynnic <i<U, ItHJ ........ Ml* 

ciiU 187 ................ , ........ , ........... ;i;.i 

and rcinark, 188 ..... . ............. , .......... K7.) 



1. NilruuA acid, 1M ....... , 

2. HyEioc'hl(V(ra*4 add, 8 UK) 

3. Chlonnw add. SUM 

4. Hypophosphoroua acid, $ H 

TUIKP (iiioui*. 
a. Nitric and, 1J3 
&. Chloric acid* $ 191 
R<>cHpi( illation and rvniurkH, 105 
IVvchlonr at-id, $ l!HJ 



11. OKdANZC At 1 IDS. 

FIRHT (iRorr* 
a, Oxalic acid, 107 
ft. Tartiiric add 
a (Uric acid, 1DH 
d, Mjihc acid, { 1M ...................... * 

RHiipiltilntinn and nmark, 
JEUi^mic acid, 8201..., 



a. ftuwimc acid, 
acid, 
and, S^fH ............ . ............................... 1M 

and ronmrkR, 20$,,,.. .......... *, ................ 412 

Tninr> nnonr. 
, AHw ttwd, $20fl .......... ...*...*.... ........ + .*-. ........... -J1J 

. Pormfc add 8*207 ............................................ , *tjr, 



Raw r aHd*. 

1, Tactic arid *>ni> ................................... ....... 417 

& Prnpinnta ftrtd, 210 .............. * ........ *. ........ , ..... 4|fl 

3. Butyric acid ......................... ., ................... 4!H 



CONTENTS. 



PART II. 

SYSTEMATIC COURSE OF QUALITATIVE ANALYSIS. 
PRELIMINARY KEMARKS ............................................ 420 

SECTION I. 

PRACTICAL PROCESS FOB THE ANALYSIS OP COMPOUNDS AND MIXTURES 

IN GENERAL. 

I. I^EUMItfARY EXAMINATION ...................................... 423 

A. The Hulwtance is a solid. 

I. It is neither a metal nor an alloy, 211 ..................... 424 

II. It in a metal or an alloy, 212 .............................. 435 

1*. The HubHtanee is a liquid, 213 .............................. 436 

II. SOLUTION OK HODIKS, 214. ..................................... 437 

A* The substance is neither a metal nor an alloy. 
Simple compounds 215 ..................................... 438 

Complex compounds, 210 .................................... 439 

h The substance w a metal or an alloy, 217 .................... 442 

III. ACTTAI. ANALYSIS 
Kfr/ipfr rufti/joifjftfo. 

A. SutmtunceH soluble in water. 

Dotation of (he metal, 218 .................................. 445 

Detection of one inorganic acid, 219 .............. , ........... 454 

Detection of one organic* acid, 220 ......................... 458 

B. Sulmtuwes taholuble or diflicultly soluble in water, but soluble 

in ucidti. 
Detection of the metal, 221 ................................. 461 

Detection of one inorganic acid, 222 .......................... 465 

Detection of one organic acid, 223 ...................... .... 407 

CV Sulintunctth iiiHoluble or difficultly soluble in acids. 
Detection of the metal and the acid, 224 ..................... 468 



fw/tpfor 

A. Sutmftim'CH Holuble in water or acids. 
Detect if m of the, metaK 

Trenlment with hydrochloric acid: detection of silver, mercury 
iu mereuroiiH compound** (Imd) , 225 ..................... 471 

Treatment with hydrogen aulphido: precipitation of the 
metal** of group V, 2d di\iHion, und group VI, 226 ........ 470 

Treatment of the precipitate produced by hydrogen sulphide 
with ammonium Kulphide: separation of the second division 
of group V from group VI, 227 ........................... 479 

Detection of th? nietute of group VI; awenic, antimony, tin, 
gold ftnd platinum, 228 ................................ 481 

Detection of the mcitalR of group V, 2d division: lead, bismuth, 
copper, cadmium and mercury (in mercuric salts), 229.*.. 487 



CONTENTS. 



Precipitation with ammonia and ammonium sulphide: separa- 
tion and detection ot the metals ot gioupb 111 and IV; 
aluminium, chromium, zmc, manganese, nickel, eolwlt, now, 
and also of those salts ot the alkali-earth metal* *hwk 
are precipitated by ammonia tiom then solutions in hydro- 
chlonc acid, phosphates, borates, oxalatea, bihcates, and 
fiuondes, 230 ........................ .V'YT'" 4<Jl 

' Separation and detection ot those metals of group 11 which me 
precipitated in presence of ammonium chloride, viz., barium, ^ 
stiontium and calcium, 231 ............................. - ; | 

Examination for magnesium, 232 ........................ *j (U J 

Examination for potassium and sodium, 233 ............... ^ 

Examination for ammonium, 234 .......................... 5 < )y 

A. 1. Substances soluble in \\ ater. 
Detection of acids 

I. In the absence of organic acids, 235 ................... > W 

II. In the presence of organic acids, 230 ..... . ............ r>l,"> 

A. 2. Substances insoluble in \vater but soluble in acids. 
Detection of acids 

I. In the absence of organic acids, 237 ................... ; ' 

II. In the presence of organic acids, 238 ............ - ..... -l 

B. Substances insoluble or spaiingly soluble in water and acid*. 

Detection of metals and acids, 239 ......................... 5 ~2 

SECTION II. 

PRACTICAL COUBSE IN PABTICULAB CASES. 

L SPECIAL METHOD FOE THE DECOMPOSITION OF CYANIDES, ferro- 
cyanides, etc., insoluble in water, and also of mixed substance*, in- 
soluble in water, containing such compounds, 240 .............. 52J> 

IL ANALYSIS OF SILICATES, 241 .................................. ww 

A. Silicates decomposable by acids, 242 ......................... #U 

a By hydrochloric or nitric acid ............................ ^ 

d. By concentrated sulphuric acid, but not by hydrochloric acid.. 5rt 

B. Silicates which are not decomposed by acids, 243 ............ 537 

C. Silicates which are partially decomposed by acids, 244 ....... 540 

HL ANALYSIS or NATTTBAL WATERS, 245 .......................... 541 

A. Analysis of ordinary potable waters, 240 .................... 541 

B. Analysis of mineral waters, 247 ........................... 548 

1. Examination of the water. 

a. Operations at the spring, 248 .......................... 549 

6. Operations in the laboratory, 249 ........................ 550 

2. Examination of sinter deposits, 250 ....................... 558 

IV. ANALYSIS OF CTTLTIVATED OR NATURAL SOILS, 251. . . ......... 503 

1. Preparation and examination of the aqueous extract, 252.. . . 565 

2. Preparation and examination of the acid extract, 263 ...... 508 

3. Examination of the inorganic constituents insoluble in water 
and acids, 254 .......................... 5rto 

4. Examination of the organic constituents of the soil, 255 ..... 569 



CONTENTS. XV 

PAGE 

V. DETECTION OP INOBGANIC SUBSTANCES IN PBESENCE OF OBGANIO 

250 ............................................ 570 



1. Gt'uoidl rules lor the detection of inorganic substances in the 
pie^ence of oiganic matters, which by their color, consistence, 
or othei propeities impede the application of the reagents, or 
obacuic the iea,ctions pioduced, 257 ...................... 571 

2. Detection ot inoigamc poisons in articles of food, in dead 
bodies, etc., in cheimeo-legal cases, 258 .................. 579 

I. Method for the detection of arsenic (with due regard to the 

possible presence of othei metallic poisons), 259 ....... 581 

A. Method toi the detection of undibsolved arsemous oxide 

01 metallic aiscmc, 200 .. . ......... 582 

B. Method of detecting soluble aisenical and other metallic 
compounds by dialysib, 201 ........................... 584 

C. Method foi the detection of arsenic m whatever form it 
may exist, which allows also of its quantitative determina- 
tion, and of the detection of other metallic poisons, 262 . 585 

II. Method for the detection of hydiocyanic acid, 263 ........ 603 

III Method ioi the detection of phosphorus, 264 ............ 610 

3 Examination of the inorganic constituents of plants, animals, 
or paits ot the same, of manures, etc. (analysis of ashes) * 265 623 

A. Population of the ash .............................. .. 623 

B. Examination of the ash ................................. 624 

a. Examination of the part soluble in water ....... * ........... 624 

6. Examination of the part insoluble in water ................. 626 



SECTION in. 

EXPLANATORY NOTES AND ADDITIONS TO TEE SYSTEMATIC OOVHEtSE OF 

ANALYSIS. 

I. Additional remarks to the pielimmary examination, 211-213 630 

II. Additional remarks to the solution, etc ,of substances, to 214-217. 631 
TIT. Additional remarks to the actual analysis, to 218-240 634 

A. General review and explanation of the analytical course. 

. Detection of the metals 634 

&. Detection of the acids 639 

B. Special remarks and additions to the systematic course of analysis- 
To 225 643 

226 and 227 646 

jj 228 66 

I m 65 

230 652 

231-234 654 

S 235 

237 and 239 * 

f 240 657 



CONTENTS. 
APPENDIX I. 

PAGB 

Deportment of the most impoitant alkaloids with reagents, and s>b- 
tematic method of efTectmg their detection, 2GG ....... M|l 

A. Geneial leageuts for the alkaloids, 2tS7 .................. IMl - 

B. Propei ties and leactions oi the individual alkaloidb. 

a. Volatile alkaloids ......................................... ullh 

1. Nicotin, 268 ............................................. "*' 

2. Comm, 269 ...................................... ^ 

Recapitulation and remarks, 270 ............................. tu - 

6. N on- volatile alkaloids 

FIBST GROUP. 

1. Morphm, 271 ............................................ * 

2. Cociim. 272 .................................... ^ 

Recapitulation and remarks, 270 ............................. - 



SECOND GROUP. 

1. Narcotin, 274 

2 Quimn, 275 

3 Cmchomn, 276 
Recapitulation and remarks, 277 

THIRD GROUP. 
1. Strychnin, 278 



2. Bruem, 279 ........................................ iil)T 

3 Veratrin, 280 .............................. 7M 

4. Atropin, 281 .................... 7i 

Recapitulation of remarks, 282 ........................... 705 

C Properties and reactions of certain non-nitrogenous bodies allied 
to the alkaloids. 

1. Sahcin, 283 ................................... 707 

2. Digitally 284 ............................. 70** 

3. Picrotoxin, 285 .......................... 710 

D. Systematic course for the detection of the alkaloids under con- 

sideration, and of siliciu, digitahn and picrotoxin. 
a. Detection of the non-volatile alkaloids, etc , in solutions Assumed 

to contain only one of these substances, 280 . . . .... 713 

6. Detection of the non- volatile alkaloids, etc, under consideration 

in solutions which may contain all of these subsiances, 28 / , ... 715 
0. Detection of the alkaloids and of digitalin and picrotoxin in prea- 

ence of vegetable or animal extraction and coloring matters. . . .711) 

1. STAB'S method for the detection of poisonous alkaloids (and 
of. digitahn and picrotoxin), modified by J. and R, OTTO. 

288 . ......................... 720 

2. DRAGENDORFF'S method, 289 .......................... 72fl 

3. SONWENSCHEIN'S method, 290 .......................... 72S 

1 4. Separation by dialysis, 291 ...................... 720 

5. Method used by GRAHAM and A W. HOFMANN for detect- 
ing strychnin in beer, 292 ....... Wft 



CONTENTS. XV11 



APPENDIX II. 

PAfitt 

General plan of the order m which substances should be analyzed for 
piactice, 293 731 

APPENDIX III. 
Record oi the results of the analyses performed for practice, 294 734 

APPENDIX IV. 

Table of solubilities, showing the classes to which the compounds of 
commonly occurring elements belong in rtspect to their solubility in 
water, hydrochloric acid, nitric acid, or aqua regia, 295 737 

INDEX 743 



PARTI. 

INTRODUCTORY. 



PBELIMINAET EEMAUKS. 

IT is well known that chemistry is the science which 
teaches us to understand the substances of which our earth 
consists, their composition and manner of decomposition, and 
especially their behavior towards one another. A special 
branch of this science is designated by the name analytical 
chemistry, inasmuch as it pursues a certain object, which is 
the breaking up (the analysis) of compound bodies and the 
discovery of their constituents. In this investigation of the 
constituents, if consideration is taken only of their kind, the 
analysis is a qualitative one ; but if the amount of each sub- 
stance is investigated, it is a quantitative one. The office of 
qualitative analysis is to exhibit the constituent parts of a 
substance of unhnoim composition in forms of knoivn compo- 
sition, from which the constitution of the body examined, and 
the presence of its several component elements, may be posi- 
tively inferred. The efficiency of its method depends upon 
two conditions, viz., it must attain the object in view with 
unerring certainty and in the most expeditious manner. The 
object of quantitative analysis, on the other hand, is to exhibit 
the elements revealed by the qualitative investigation in forms 
which will permit the most accurate estimate of their weight, 
or to effect by other means the determination of their quan- 
tity. 

The means by which these different ends are reached pre- 
sent wide variations in the two cases. The study of quali* 



2 PRELIMINARY REMARKS. 

tative analysis must, therefore, be pursued separately from 
that of quantitative analysis, and must naturally precede it. 

The idea and aim of qualitative analysis iu general having 
thus been stated, consideration must next be given to the 
preliminary knowledge which warrants its pursuit, the rank 
which it takes in the domain of chemistry, the objects to 
which it is applied, and its use ; then the chief points upon 
which its study depends, and the principal divisions into 
which it is separated must, also be considered. 

For the successful pursuit of qualitative investigations, it 
is absolutely indispensable that the student should possess 
some knowledge of the chemical elements and of their most 
important combinations, as well as of the principles of 
chemistry in general, and that he should combine with this 
knowledge some readiness in the comprehension of chemical 
processes. The practical part of this science demands, more- 
over, strict order, great neatness, and a certain skill in manip- 
ulation. If the student joins to these qualifications the habit 
of invariably ascribing the failures with which he may meet 
to some error or defect in his operations, or, in other words, 
to the absence of some condition indispensable to the 
success of the experiment and a firm reliance on the immu- 
tability of the laws of nature cannot fail to create this habit 
he possesses every requisite to render his study of analyt- 
ical chemistry successful. 

Although chemical analysis is based on general chemistry, 
and cannot be properly pursued without some knowledge of 
the latter, yet we have to look upon it as one of the main 
pillars upon which the entire structure of the science rests, 
since it is of almost equal importance for all branches of 
theoretical as well as of practical chemistry; and the use 
which it affords to the practical chemist, the mineralogist, 
and the metallurgist, to the pharmacist, the physician, the 
rational agriculturist, and others, needs no explanation. 

These considerations would furnish sufficient reason for 
recommending a thorough study of this branch of science, 
even if its cultivation lacked those attractions which it pos- 
sesses for every one who devotes himself ardently to it. The 
mind is constantly striving for the attainment of truth ; it de. 
lights in the solution of problems, and where do we meet with 



PRELIMINARY REMARKS. 3 

a greater variety of them, more or less difficult of solution, 
than in the province of chemistry? But as a problem to 
which, after long pondering, we fail to discover the key wearies 
and discourages the mind, so do chemical investigations, if 
the object in view be not attained, if the results do not bear 
the stamp of unerring certainty. A half-knowledge is, there- 
fore, to be considered worse than no knowledge ; and a super- 
ficial cultivation of chemical analysis is to be particularly 
guarded against. 

A qualitative investigation may be made with either of two 
objects in view, viz., 1st, to prove that a certain body is or is 
not contained in a substance, e.g., lime in well-water ; or, 2d, 
to ascertain att the constituents of a chemical compound or 
mixture. Any substance whatever may, of course, become the 
object of a chemical analysis. 

Since, however, the elements are not all of equal impor- 
tance in practical chemistry (as only a certain number of 
them occur widely distributed in nature, and are important 
in the manufacture of chemical preparations, in metallurgy, 
pharmacy, trade, the arts, manufactures, and agriculture; 
while the others are merely constituents of rare minerals), 
in order to facilitate the study of beginners and the work 
of practical chemists, only the more common elements and 
their more important compounds are treated in full detail 
in the present work. The rarer elements are treated more 
briefly, and in such a manner that they can be studied 
separately without difficulty. 

The study of qualitative analysis may be properly divided 
into four principal parts : 

1. CHEMICAL OPERATIONS. 

2. REAGENTS AND THEIR USES. 

3. DEPORTMENT OF THE VARIOUS BODIES WITH REAGENTS. 

4. SYSTEMATIC COURSE OE QUALITATIVE ANALYSIS. 

It will be readily understood that the pursuit of chemical 
analysis requires practiced skfU and ability, as well as theoreti- 
cal knowledge; and that mere speculative study can as little 
lead to success as purely empirical experiments. To attain 
the desired end, theory and practice must be judiciously com- 
bined. 



4 OPERATIONS. LjjSi 1- a > 

SECTION I. 
OPERATIONS. 

81. 

THE operations of analytical chemistry are essentially the 
same as those of synthetical chemistry, though modified to a 
certain extent to adapt them to the different object in view, 
and to the small quantities operated upon in analytical inves- 
tigations. 

The following are the principal operations in qualitative 
analysis : 

2. 

1. SOLUTION. 

The term solution, in its widest sense, denotes the union of 
a body, whether gaseous, liquid, or solid, with a Haul, result- 
ing in a homogeneous liquid. When the substance dissolved 
is gaseous, the term absorption is more properly made use 
of, and the solution of one fluid in another is generally 
called a mixture. The term solution, in its usual sense, 
means the union of a solid body with a liquid. 

A solution is more readily effected the more minutely 
the body to be dissolved is divided. The fluid by means of 
which the solution is effected is the solvent We call the solu- 
tion cliemical where the solvent enters into chemical combina- 
tion with the substance dissolved; and simple, whero uo 
definite combination takes place. 

In a simple solution, the dissolved body is supposed to 
exist in the free state, and to retain all its original properties 
except those dependent on its form and cohesion, since it 
separates unaltered when the solvent is withdrawn. Common 
salt dissolved in water is a familiar instance of a simple solu- 
tion. The salt imparts its peculiar taste to the liquid. On 
evaporating the water, the salt is left behind in its original 



2.] SOLUTION. 5 

form. A simple solution is called saturated when the solvent 
contains all it can hold of the dissolved substance. But as 
fluids generally dissolve larger quantities of a substance the 
higher their temperature, the term saturated, as applied to 
simple solutions, is only relative, and refers invariably to a 
certain temperature As a general rule, elevation of temper- 
ature facilitates and accelerates simple solution. This rule 
has but few exceptions. 

A chemical solution contains the dissolved substance not 
in the same state nor possessed of the same properties as 
before. The dissolved body is intimately combined with the 
solvent, the latter having also lost its original properties. A 
new substance has thus been produced, and the solution, 
therefore, manifests the properties of this new substance. 
A chemical solution, also, may be usually accelerated by eleva- 
tion of temperature, since heat generally promotes, the action 
of bodies upon each other. The quantity of the dissolved 
body, however, always remains the same in proportion to a 
given quantity of the solvent, the combinpg proportions of 
substances being invariable and independent of the grada- 
tions of temperature. 

The reason of this is that in a chemical solution the 
solvent and the body upon which it acts Iwye mpre or less 
opposite properties, which tend to neutralize each other. 
Solution ceases as soon as this tendency is satisfied. In 
this case, also, the solution is said to be saturated, or, under 
certain conditions, neutralized, and the point which denotes it 
to be so is termed the point of saturation or neutralization. ^ 

The substances which produce chemical solution^ are in 
most cases either acids or alkalies. With few exceptions, 
they have first to be converted to the fluid state by m^anc of 
a simple solvent. When the opposite properties' of acid" and 
base are mutually neutralized, and the new compound is 
formed, the actual transition to the fluid state will ensue only 
if the new compound possesses the property of forming a 
simple solution with the liquid present, e.g., when a solution 
of acetic acid in water is brought into contact with lead oxide, 
there ensues, first, a chemical combination between the acid 
and the oxide, and then a simple solution of the newly formed 
lead acetate in the water present. 



3 OPERATIONS. [ 3. 

In chemical laboratories, solutions are generally made by 
iigesting or heating the substance to be dissolved with the 
fluid in beaker-glasses, flasks, test-tubes, or capsules. In 
the preparation of chemical solutions, the best way usually 
is, in the first place, to mix the body to be dissolved -with 
wrater (or with whatever other indifferent fluid may happen 
to be used), and then gradually add the chemical agent. 
By this course of proceeding, a large excess of the latter is 
avoided, an over-energetic action guarded against, the proc- 
ess greatly facilitated, and complete solution insured which 
is a matter of some importance, as it frequently happens 
in chemical combinations that the product formed refuses to 
dissolve if an excess of the chemical solvent is present. In 
this case, the new salt first formed, being insoluble in the 
liquid present, gathers around and encloses the portion still 
unacted on, weakening thereby or preventing altogether 
further chemical action upon it. Thus, for instance, witherite 
(barium carbonate) dissolves readily when, after being re- 
duced to powder, water is poured upon it and hydrochloric 
acid gradually added; but it dissolves with difficulty and 
imperfectly when projected into a concentrated solution of 
hydrochloric acid in water, for barium chloride will dissolve 
in water, but not in hydrochloric acid. 

CBYSTALUZATION and PRECIPITATION are the reverse of solu- 
tion, since they have for their object the conversion of a fluid 
or dissolved substance to the solid state. As both generally 
depend on the same cause, viz., on the absence of a solvent, 
it is impossible to assign exact limits to either; in ninny 
cases, they merge into one another. We must, however, con- 
sider them separately here, as they differ essentially in their 
extreme forms, and as the special objects which we purpose 
to attain by their application are generally very different. 

3. 

2. CBYSTALLIZAOTON. 

We understand by the term crystallization, in a more 
general sense, every operation or process whereby bodies 



3.] OEYSTALLIZATIOiN. 7 

are made to pass from the fluid to the solid state, and to 
assume certain fixed, mathematically definable, regular forms. 
But as these forms, which we call crystals, are usually more 
regular, and consequently more perfect, the more slowly 
the operation is carried on, we commonly connect with the 
term crystallization the accessory idea of a slow separation, 
of a gradual conversion to the solid state. The formation 
of crystals depends on the regular arrangement of the con- 
stituent particles of bodies (molecules). It can only take place, 
therefore, if these molecules possess perfect freedom of mo- 
tion, and thus, in general, only when a substance passes from 
the fluid or gaseous to the solid state. Those instances in 
which the mere ignition or the softening or moistening of a 
solid body suffices to make the tendency of the molecules to 
a regular arrangement (crystallization) prevail over the dimin- 
ished force of cohesion ; for instance, the turning white and 
opaque of moistened barley-sugar, are to be regarded as 
exceptional cases. 

To induce crystallization, the causes of the fluid or gase- 
ous form of a substance must be removed. These causes are 
either heat (done, e.g., in the case of fused metals ; or solvents 
atone, as in the case of an aqueous solution of common salt ; 
or both combined, as in the case of a hot saturated solution of 
potassium nitrai/e in water. In the first case, we obtain crys- 
tals by cooling the fused mass ; in the second, by evaporating 
off the solvent ; and in the third, by either of these means. 
The case occurring most frequently is that of crystallization 
by cooling hot saturated solutions. The liquids which remain 
after the separation of the crystals are called motfar-liquors. 
The term amorphous is applied to such solid bodies as have 
no crystalline form. 

We generally have recourse to crystallization either to ob- 
tain the crystallized substance in a solid form, or to separate 
it from other substances dissolved in the same liquid. In 
many cases, also, the form of the crystals or their deportment 
in the air, viz., whether they remain unaltered or effloresce or 
deliquesce upon exposure to the air, will afford an excellent 
means of distinguishing between bodies otherwise resembling 
each other ; for instance, between sodium sulphate and potas- 
sium sulphate. The process of crystallization is usually 



8 OPERATIONS. IM 

effected in dishes or, in the case of very small quantities, in 
watch-glasses. 

Where the quantity of fluid to be operated upon is small, 
the surest way of getting well-formed crystals is to let the 
fluid evaporate in the air, or, better, under a bell-glass over 
an open vessel half filled with concentrated sulphuric acid. 
Minute crystals are examined best with a lens or microscope. 

4. 
3. PBECIPITATION. 

This operation differs from the preceding one in that the 
dissolved body is suddenly, or at least more or less quickly, 
converted to the solid state, no matter whether tho substance 
separating is crystalline or amorphous, whether it sinks to 
the bottom of the vessel, or ascends, or remains suspended iu 
the liquid. Precipitation is caused either by a modification 
of the solvent thus, calcium sulphate (gypsum) noparato* 
immediately from its solution in water upon the addition of 
alcohol or in consequence of the separation of a body, 
formed by simple or double decomposition, which IK insoluble 
in the liquid which is present. Thus, metallic copper in pre- 
cipitated when a solution of copper chloride is brought hito 
contact with zinc ; a precipitation of calcium oxalato msults 
when oxalic acid is added to a solution of calcium acetato ; 
one of lead chromate is produced when dissolved potassium 
chromate is mixed with dissolved lead nitrate. In oxcliaugott 
of this kind, one of the products generally remains in solu- 
tion, as the zinc chloride, the acetic acid, and the potassium 
nitrate, in the instances just mentioned. Oases, howover, 
may occur in which the newly formed substances are both 
precipitated, and nothing remains dissolved in the liquid. 
Such is the case, for instance, when a solution of magnesium 
sulphate is mixed with baryta-water, or when a solution of 
silver sulphate is precipitated with barium chloride- 
Precipitation is resorted to for the same purposes as crys- 
tallization,' viz., either to obtain a substance in the solid form, 
or to separate it from other dissolved substances. In qualita- 
tive analysis, however, we have recourse to this operation more 



*>] FILTRATION. 9 

particularly for the purpose of detecting and distinguishing 
substances by the color, properties, and general deportment 
which they exhibit when precipitated either in an isolated 
state or in combination with other substances. The solid 
body separated by this process is called the precipitate, and 
the substance which acts as the immediate cause of the sepa- 
ration is termed the precipitant. Various terms are applied to 
precipitates by way of particularizing them according to their 
different nature, as crystalline, pulverulent, flocculent, curdy, 
gelatinous precipitates, etc. 

Precipitates which appear simply pulverulent to the un- 
aided eye can be seen not infrequently, when observed under 
the microscope, to consist entirely of very small, often very 
regular crystals, and in this manner, precipitates which are 
apparently alike can often be distinguished with ease and 
certainty. 

The terms turbid, turbidity, or dowdy and cloudiness, are 
made use of to designate the state of a fluid which contains a 
precipitate so finely divided and so inconsiderable in amount 
that the suspended particles, although impairing the trans- 
parency of the fluid, cannot be clearly distinguished. The 
separation of flocculent precipitates may be generally pro- 
moted by vigorous shaking ; that of crystalline precipitates, 
by stirring the fluid and rubbing the sides of the vessel in 
contact with the liquid with a glass rod. Elevation of temper- 
ature is also an effective means of promoting the separation 
of most precipitates. The process is conducted, according to 
circumstances, either in test-tubes, flasks, beakers, or dishes. 

The two operations described in 5 and 6, respectively, 
viz., ITLTBAITON and DEOANTATION, serve to effect the mechani- 
cal separation of fluids from matter suspended therein. 

5. 

4. Fn/CRATION. 

This operation consists simply in passing the fluid, from 
which we wish to remove the solid particles mechanically 
suspended therein, through a filtering apparatus formed 



10 



OPEUATIONS. 



usually by a properly arranged piece of unsized paper placed 
in a glass funnel. An apparatus of this description allows the 
fluid to trickle through, while it retains the solid particles. 
We employ smooth filters and plaited fliers ; the former in 
cases where the separated solid substance is to be made use 
of, and the latter where the object is simply to clear Lhe 
solution rapidly. Smooth filters, which are placed in the 
funnel in such a manner that they are everywhere in contact 
with it, are obtained by folding a circular paper twice so that 
the folds are at right angles. The preparation of plaited 
filters, which may be accomplished in various ways, is better 
shown than described. 

In cases where the contents of the filter require washing, 
the paper must not project over the rim of the fuuiiol. lu 
most cases, it is advisable to moisten the filter previously to 
passing the fluid through it, since this not only tends to 
accelerate the process, but also renders the solid particles 
less liable to be carried through the pores of the filter. The 

paper selected for ill tars 
must be as free as possi- 
ble from inorganic sub- 
stances, especially such 
as are dissolved by acids, 
e.g., calcium and iron coin- 
pounds. 

The common filtering- 
paper of commerce seldom 
comes up to our needs in 
this respect, and I would 
therefore recommend al- 
ways washing it carefully 
with dilute hydrochloric 
acid whenever it is in* 
tended for use in accurate 
analyses. For this pur- 
pose, the apparatus shown 
in Fig. 1 will be found 
convenient A is a bottle 
with the bottom taken out; a and i are glass plates, and 
between them lie the filters, which have been previously cut 



a 




FIG. 1. 



6.] FILTEATION. 11 

and folded ; d is a glass tube fitted into the cork c; e is a 
piece of flexible tube, which is closed by a piece of glass rod 
or a clip. The bottle is filled with a mixture of one part 
hydrochloric acid, sp. gr. 1.12, and two parts water, in which 
the filters are allowed to soak from 4 to 8 hours, the acid 
being then run off and replaced by ordinary water. After 
an hour, this is replaced by fresh water, and so on till the 
washings are barely acid. The washing is continued with 
distilled water till the washings are free from hydrochloric 
acid, that is, till they cease to give any turbidity when mixed 
with a few drops of solution of silver nitrate. Finally, the 
filters are drained, turned out upon blotting-paper, covered 
with the same, and dried in a sieve in a warm place. When 
we merely wish to wash two or three filters, we place them 
in a funnel as in filtering, one inside the other, moisten them 
with dilute hydrochloric or nitric acid, and after some time 
wash them well with distilled water. 

Filtering-paper, to be considered good, must, besides 
being pure, also let fluids pass readily through, while com- 
pletely retaining even the finest pulverulent precipitates, 
such as barium sulphate, calcium oxalate, etc. If a paper 
satisfying these requirements cannot be readily procured, it 
is advisable to keep two sorts, 
one of greater density for the 
separation of very finely divided 
precipitates, and one of greater 
porosity for the speedy separa- 
tion of grosser particles. For 
the past few years, cut filters of 
all sizes, both washed and un- 
washed, have been manufact- 
ured on a large scale and can 
be purchased. Quite recently, 
filters hardened by treatment 
with nitric acid have been sold, FIG. 2. 

and these are characterized by 

increased filtering capacity as well as by being but little at- 
tacked by acids and alkalies. 

The funnels must be of glass ( 19, 9). It is best to 
place them upon a stand to insure a firm position. For 




12 OPERATIONS. [S *>, ~- 

smaller filtrations, such as are customary in qualitative 
analysis, a stand of the form shown in Fig. 2 is to be recom- 
mended. 

6. 

5. DEOANTATION. 

This operation is frequently resorted to instead of filtration 
in cases where the solid particles to be removed are of consid- 
erably greater specific gravity than the liquid in which they 
are suspended, as they will in such cases speedily subside to 
the bottom, thereby rendering it easy either to decant tha 
supernatant fluid by simply inclining the vessel, or to draw it 
off by means of a siphon or a pipette. 

Certain slimy or gelatinous precipitates so clog the poros 
of paper as scarcely to admit of filtration. To obtain tlio 
liquid in which they have been formed quite clear, decauta- 
tion is indispensable. Oftentimes the two processes may l> 
advantageously combined by allowing the precipitate to soltle 
as much as possible, and then pouring off the still turbid 
liquid upon a filter. 

7. 

6. WASHING. 

When filtration or decantation has been resorted to for the 
purpose of collecting a solid substance, the latter has to be 
freed afterward from the adhering liquid by repeated wushiny 
or edidcoration. The washing of precipitates collected on a 
filter is usually effected by means of a washing-bottle, such 
as is shown in Fig. 3. 

This consists of a flask or bottle, closed with a twice-per- 
forated, snugly-fitting rubber stopper, through which pass two 
glass tubes, as in the figure. The outer end of the tube a is 
drawn to a moderately fine point. If it is wished to have this 
movable, the tube a is cut in two between the point and the 
bend, and the two parts are united by means of a piece of 
rubber tubing. By blowing into the other tube, a stream of 
water is driven out from a with considerable force, which 



7.] WASHING. 13 

adapts the apparatus to removing precipitates from the sides 
of vessels as well as to washing them on filters. This form of 
washing-bottle serves for washing with warm or even boiling 
water, provided the vessel itself has a uniformly thin bottom, 
so that it can be heated without fear of breaking. By binding 
about the neck a ring of cork, winding it closely with smooth 
cord, or providing it with a handle (Fig. 4), it may be held 
with convenience when its contents are hot Washing by 




FIG. 3, FIG. 4. 

decantation is carried out, after pouring off the liquid, by 
simply stirring up the precipitate with water or any other 
liquid used for washing, allowing it to settle again, and 
decanting anew. 

As the success of an analysis often depends upon the com- 
plete or proper washing of a precipitate, the operator must 
accustom himself to continue the process patiently until he 
is certain that the object in view has been actually accom, 
plished. In general, this is not the case until the precipitate 
has been perfectly freed from the liquor in which it was 
formed. The analyst must not be content with guessing that a 
precipitate is thoroughly washed, but must prove that it is so 
by applying appropriate tests. If the body to be removed is 
aon- volatile, slow evaporation of a few drops of the last por- 
tions of the washings on a clean surface of platinum will 
usually serve to indicate the point at which the process may 
terminate. 



14 



OPEBATIONS. 



8. 

7. DIALYSIS. 

Dialysis is an operation which may be employed for the 
separation of certain dissolved bodies from others. "When 
superficially considered, it appears to possess a certain simi- 
larity to filtration, but in reality it differs essential ly from 
that operation. It was introduced into science by GRAHAM 
(Annal. der Chem. u. Pharm., 121, 1), and depends upon the 
different behavior of bodies dissolved in water towards 
moist membranes. Bodies that are able to crystallize (Crys- 
talloids, GRAHAM) have the power of penetrating certain moin- 
branes with which their solution may be placed in contact, 
while amorphous bodies, or colloids, viz., guin, gelatin, dextrin, 
caramel, tanuic acid, albumen, silicic acid, etc., do not possess 

that property. Hence, the two 
classes may be separated by tak- 
ing advantage of this action. The 
septum must consist of a colloid 
material, as the skin of an animal 
or, best of all, parchment-paper, 
and it must be in contact with 
water on the outer side. Figs. 5 
and 6 exhibit suitable forms of 
apparatus for this operation. In 
Fig. 5, the dialyzer consists of Iho 
upper part of a bottle, closed at 
the base with parchmont-paper ; 
PIG. 5. in Fig. 6, it consists of a hoop of 

wood ox gutta-percha, covered below, like a sieve, with parch- 
ment-paper. 

The disk of parchment-paper should measure about 11) oiu 
more in diameter than the space to be covered. It should 
be moistened, stretched over, and fastened by a string or 
by an elastic band, but should not be secured too firmly. 
The parchment-paper must not be porous, and its soundness 
may be tested by sponging the upper side with wateK 
and observing whether wet spots show on the other aide* 
Defects may be remedied by applying liquid albumen^ 




3.] DIALYSIS. 15 

and coagulating this by heat. When the dialyzer has thus 
been put in perfect condition, the mass to be examined 
is poured into it. If the substance is entirely liquid, the 




FIG. 6. 

bell-shaped dialyzer may be chosen, but if it contains undis- 
solved solid matter, the hoop is preferable. The depth of 
fluid in the dialyzer should not be more than 1.5 cm, and the 
membrane should dip a little below the surface of the 
water in the outer vessel, which should amount to at least 
four times the quantity of the fluid to be dialyzed. The bell- 
shaped dialyzer should be huug in the manner shown in 
Fig. 5, while the hoop may be allowed to float. After twenty- 
four hours, half or three fourths of the crystalloids will be 
found in the external water, while the colloids remain in the 
dialyzer ; at most, only traces pass into the external fluid 
If the dialyzer is brought successively in contact with fresh 
supplies of water, the whole of the crystalloids may be 
finally separated from the colloids. This operation is some- 
times of service in chemico-legal investigations, for the ex- 
traction of poisonous crystalloids from parts of a dead body, 
or from food, vomit, etc. 

There are four operations which serve to separate volatile 
substances from less volatile or from fixed bodies, viz., 

EVALUATION, DISTILLATION, IGNITION, and SUBLIMATION. The 

first two relate to liquids, the others to solids. 



16 OPERATIONS. [ a - 

9. 
8. EVAPORATION. 

This operation is one of those most frequently used. It 
serves to separate volatile fluids from less volatile or from 
fixed bodies (solid or fluid) in cases where the residuary sub- 
stance alone is of importance. Thus, we have recourse to 
evaporation for the purpose of removing from a saline solu- 
tion part of the water, in order to bring about crystallization 
of the salt; also, for removing the whole of the water from 
the solution of a non-crystallizable substance, so as to obtain 
the latter in a solid form. The evaporated water is disre- 
garded in these cases, the only object bohig to obtain in the 
one case a more concentrated fluid, and in tho other a dry 
substance. These objects are attained by converting to tin* 
gaseous state the fluid which is to be removed. This is gener- 
ally done by the application of heat; sometimes by leaving 
the fluid for a time in contact with the atmosphere or with an 
enclosed volume of air kept dry by hygroscopic substances, 
such as concentrated sulphuric acid, calcium chloride, etc. ; 
or lastly, by placing the fluid in rarefied air, with simultji- 
neous application of hygroscopic substances: 

As it is of the utmost importance in qualitative analysos 
to guard against the least contamination, and as an evaporat- 
ing fluid is the more liable to this the longer tho operation 
lasts, the process is usually conducted, with proper expedition, 
in porcelain or platinum dishes, over the flame of a spirit- or 
gas-lamp, in a place free from dust, preferably in a cupboard 
or hood provided with a draught. If the operator has no 
place of this kind, he must have recourse to the inconvenient 
alternative of covering the dish* The best way of doing this 
is to place over it a large glass funnel, secured by a retort- 
holder, in such a manner as to leave sufficient space betwoou 
the rim of the funnel and the border of the dish. The funnel 
should be placed slightly aslant, so that the drops running 
down its sides may be received in a beaker. This end is 
more fully attained by VICTOR MEYER'S protection funnel.* 

*Zeitschr. f. analyt. Ciiem., 23, 539. 




10.] DISTILLATION. 17 

This Las its lower edge bent inward, forming a trough in 
which the condensed liquid collects, and flows through a 
tubulure which is attached to one side. The dish may also 
be covered with a sheet of filter-paper previously freed from 
inorganic substances by washing with dilute hydrochloric or 
nitric acid. Were common and unwashed filter-paper used for 
the purpose, the ferric oxide, lime, etc., contained in it would 
dissolve in the vapors evolved (more especially if acid), and 
the solution dripping down into the evap- 
orating fluid would speedily contaminate 
it. Such precautions are necessary, of 
course, only in accurate analyses. Large 
quantities of fluid are sometimes evapo- p IG . 7 

rated best in flasks standing aslant over a charcoal fire or 
gas flame, or in tubulated retorts with the neck rising 
obliquely upward and with open tubulure. Evaporating proc- 
esses at 100are conducted in a suitable steam apparatus or on 
the water-bath shown in Fig. 7, upon which copper or porce- 
lain rings may be placed, so that it can accommodate smaller 
dishes. Evaporation to dryness is not usually conducted over 
the naked flame, but generally either on the water-bath or 
the sand-bath, or on an asbestus or iron plate. It should be 
remembered that porcelain and glass vessels which we can 
hardly avoid using for the evaporation of large quantities of 
fluids are always somewhat acted upon, so that their contents 
become more or less contaminated. The action is but slight 
in case of most dilute acids or acid liquids, but the student 
should never evaporate alkaline fluids in glass, as, at a boiling 
temperature, they attack it considerably. 

10- 
9. 



This operation serves to separate a volatile liquid from a 
less volatile or a non-volatile substance, where the object is to 
recover the evaporating fluid. A distilling apparatus consists 
of three parts : 1st, a vessel in which the liquid to be distilled 
is heated, and thus converted into vapor ; 2d, an apparatus in 
which this vapor is cooled again or condensed and thus recon- 



18 



OPERATIONS. 



verted to the fluid state ; and 3d, a vessel to receive the fluid 
thus reproduced by the condensation of the vapor (the distil- 
late). For the distillation of large quantities, metallic appa- 
ratus are used (copper stills with head and condenser of tin), 
or large glass retorts; in analytical investigations, we use 
either small retorts with receivers, or more usually an appa- 
ratus like that shown in Fig. 8. The fluid to be distilled is 
boiled in A 9 and the vapor escapes through the tube which 
is fitted into the cork. The tube is surrounded with a wider 




FIG. 8. 



tube, which is filled with cold water, and this is renewed con- 
tinually or occasionally by pouring in fresh water through rf, 
after placing a vessel under g to catch the hot water which 
runs out. A small flask serves as a receiver. 



11- 
10. IGNITION. 

Ignition is, in a certain sense, for solid bodies what evap- 
oration is to fluids, since it serves (at least generally) to sep- 
arate volatile substances from less volatile or from fixed 
bodies, in cases where the residuary substance alone is of 
importance. Ignition always involves the use of a high tem- 
perature, and is thus distinguished from drying. The state 
which the volatilized body assumes upon cooling whether it 



12. J SUBLIMATION. 19 

remains in the gaseous state, as when calcium carbonate is 
ignited ; whether it is liquid, as when calcium hydroxide is 
heated ; or solid, as in the ignition of a mixture containing 
ammonium chloride is quite immaterial as far as the name 
of the operation is concerned. 

The object of ignition already mentioned is the common 
one, but in some instances, substances are ignited simply for 
the purpose of modifying their state, without any volatilization 
taking place, for example, in the conversion of the more 
bulky, more easily soluble form of alumina into the denser 
form which is more difficultly soluble in sulphuric acid. 
Substances are often ignited, also, in order that the operator 
may from their deportment at a red heat draw conclusions 
as to their nature in general, their fixity, their fusibility, the 
presence or absence of organic matter, etc. 

Crucibles are the vessels generally made use of in ignition. 
In operations on a large scale, Hessian or graphite crucibles 
are used, heated by charcoal or gas ; in analytical experi- 
ments, small-sized crucibles or dishes of porcelain, platinum, 
silver, or iron, or glass tubes sealed at one end, are selected, 
according to the nature of the substances to be ignited. 
These crucibles, dishes, or tubes are heated over a spirit- or 
gas-lamp, or a blast-lamp. 

12. 

11. 



The term sublimation designates the process which serves 
to convert solid bodies into vapor by the application of heat, 
and subsequently to recondense the vapor to the solid state 
by refrigeration. The substance thus volatilized and recon- 
densed is called a sublimate. Sublimation is consequently a 
distillation of solid bodies. "We have recourse to this process 
mostly in order to effect the separation of substances pos- 
sessed of different degrees of volatility. It is of great impor- 
tance in analysis for the recognition of several substances, for 
^sample, arsenic. The vessels used for sublimation are of 
variable sizes, according to the volatility of the substance. In 
sublimations for analytical purposes, we generally employ 



20 OPERATIONS. [ 13. 

closed glass tubes. When the sublimation is performed with 
the aid of a current of hydrogen or carbon dioxide, we use open 
glass tubes, which are usually made narrower just in front 
of the part to which the heat is applied. The substance may 
be placed directly in the tube, or it may be contained in a 
boat of platinum or porcelain. 

13. 
12. FUSION AOT> FLUXING. 

Simple fusion is the conversion of a solid substance into 
the fluid form by the application of heat. It is most frequently 
resorted to for the purpose of effecting the combination or the 
decomposition of bodies. The term is also applied in cases 
where substances insoluble or difficult of solution in water 
and acids are by fusion, in conjunction with some other body, 
modified, decomposed, or fluxed in such a manner that they or 
the newly formed compounds will subsequently dissolve in 
water or acids. Fusion is conducted either iu porcolain, silver, 
or platinum crucibles. The crucible is supported on a triangle 
of moderately stout platinum wire (with silver crucibles, iron 
wire), resting on, or attached to, the iron ring of the spirit- 
or gas-lamp. Pipe-stem triangles are also used. Small 
quantities of matter are often fused in glass tubes closed at 
one end. 

Eesort to fusion is especially required for the analysis of 
various insoluble sulphates, silicates, and aluminum coin- 
pounds. The flux most commonly used is sodium carbonate*, 
or potassium carbonate, or, better still, a mixture of both in 
molecular proportions. In certain cases, barium hydroxide is 
employed. For the fusion of aluminates, sodium or potassium 
disulphate is frequently used. A platinum crucible should be 
used for fusions with alkali carbonates, barium hydroxide, 
and alkali disulphates. 

Precautionary rules for the prevention of damage to platinmn 
vessels. "So substance evolving chlorine ought to be treated in 
platinum vessels. No sodium or potassium nitrate or hydrox- 
ide or cyanide, no metals or sulphides of metals, should be 
fused in such vessels ; nor should readily deoxidizable metallic. 



14.] DEFLAGRATION. 21 

oxides, or organic salts of the heavy metals, or phosphates in 
presence of organic compounds, be ignited in them. It is also 
detrimental to platinum crucibles to expose them directly to an 
intense charcoal fire, as this is likely to render them brittle. 
It is always advisable to support these vessels, when used in 
ignition or fusion, on triangles of platinum wire or of pipe-stem. 
When a platinum crucible has been made white hot over the 
bellows blowpipe, it is unwise to cool it too quickly by sud- 
denly turning off the gas, and allowing the cold blast to play 
upon it, since, under these circumstances, the crucible is very 
liable to become slightly cracked. 

Platinum crucibles which have become stained can be 
cleaned by rubbing with moist sea-sand, the grains of which 
are rounded and not inclined to scratch. If the stains or 
impurities in a platinum dish resist this treatment, acid 
potassium sulphate or borax should be heated in it to fusion 
for some time. The vessel is then cleaned with hot water, 
and finally, if needful, is burnished with sand as above de- 
scribed. 

The following operation should also be described as one 
which is related to fusion : 

14. 
13. DEFLAGRATION. 

We understand by the term deflagration, in a more general 
sense, every process of decomposition attended with noise or 
detonation. We use the same term, however, in a more re- 
stricted sense, to designate the oxidation of a substance in 
the dry way, at the expense of the oxygen of another substance 
mixed with it (usually a nitrate or a chlorate), and connect 
with it the idea of sudden combustion attended with incan- 
descence and detonation. 

Deflagration is resorted to either to produce a desired 
body, or it is applied as a means to prove the presence or 
absence of a certain substance. Thus, arsenious sulphide is 
deflagrated with potassium nitrate to obtain potassium arse- 
nate ; and salts are tested for nitric or chloric acid by fusing 



OPERATIONS. 



[15. 



them with potassium cyanide, and observing whether they 
deflagrate, etc. To attain the former object, the perfectly 
dry mixture of the substance and the deflagrating agent is 
projected in small portions at a time into a red-hot crucible. 
Experiments of the latter description are invariably made 
with minute quantities, preferably on a piece of thin iron or 
platinum foil, or in a small spoon. 

15. 

14. THE USE OF THE BLOWPIPE. 

This operation is of paramount importance in many ana- 
lytical processes. We must examine here the apparatus 
required, the mode of its application, and the results of the 
operation. 

The blowpipe, Fig. 9, is a small instrument, usually made 
of brass or German silver. It consists of three parts, viz., 
1st, a tube, 06, fitted, for greater convenience, with a horn or 
ivory mouthpiece, through which air is 
blown from the mouth ; 2d, a small cylin- 
drical vessel, cd, into which oh is screwed 
air-tight, and which serves as an air- 
chamber, and to retain the moisture of the 
air blown into the tube ; and 3d, a smaller 
tube,/<7, also fitted into cd. This small 
tube, which forms a right angle with the 
larger one, is fitted at its aperture either 
with a finely perforated platinum plate, 
or more conveniently with a finely perfo- 
rated platinum cap, h. The construc- 
tion of the cap is shown in Fig. 10* 
This is a little more expensive than a 
simple plate, but it is also much more 
durable. If the opening of the cap 
becomes stopped up, the obstruction may 
generally be removed by heating it to redness before the blow- 
pipe. 

The proper length of the blowpipe depends upon the dis- 
tance at which the operator can see with distinctness. It is 




FIG. 9. 



15.] USE OF THE BLOWPIPE. 23 

usually from 20 to 25 cm long. The form of the mouthpiece 
varies. Some chemists like it of a shape which may be en- 
circled by the lips; others prefer a trumpet mouthpiece, 
which is only pressed against the lips. The latter requires 
less exertion on the part of the operator, and is accordingly 
generally chosen by those who do a great deal of blowpipe 
work. 

The blowpipe serves to conduct a continuous fine current 
of air into a gas flame, or into the flame of a candle or lamp, 
or sometimes into an alcohol flame. The flame of a candle 
or lamp, burning under ordinary circumstances, 
consists of three principal parts, as shown in Fig. 
11, viz., 1st, a dark nucleus, a! a, in the centre ; 
3d, a luminous cone, efg, surrounding this nucleus ; 
and 3d, a feebly luminous mantle, bed, encircling 
the whole flame. The dark nucleus contains the 
gases which the heat evolves from the wax or fat, 
and which cannot burn for want of oxygen. In the 
luminous cone, these gases come in contact with a 
certain amount of air insufficient for their complete 
combustion. In this part, therefore, it is principally 
the hydrogen of the hydrocarbons evolved which 
burns, while the carbon separates in a state of in- 
tense ignition, which imparts to the 'flame the luminous ap- 
pearance observed in the cone. In the outer coat, the access 
of air is no longer limited, and all the matter not yet burned 
is consumed. This part of the flame is the hottest, and 
the extreme apex is its hojbtest point. Oxidizable bodies 
oxidize, therefore, with rapidity when placed in it, since all 
the conditions of oxidation (high temperature and an un- 
limited supply of oxygen) are here united. This outer 
part of the flame is therefore called the oxidising flame. On 
the other hand, oxides having a tendency to yield up their 
oxygen suffer reduction when placed within the luminous part 
of the flame, the oxygen being withdrawn from them by the 
carbon and the still unconsumed hydrocarbons there present. 
'The luminous part of the flame is therefore called the reducing 



The effect of blowing a fine stream of air across a flame 
is, first, to alter the shape of the flame, since, from tending up- 



24 OPERATIONS. [ ir> 

ward, it is now driven sideways in the direction of the blast, 
being at the same time lengthened and narrowed ; and, in the 
second place, to extend the sphere of combustion from the 
outer to the inner part. As the latter circumstance causes 
an extraordinary increase in the heat of the flame, and Hit* 
former, a concentration of that heat within narrower limits, it 
is easy to understand the exceedingly energetic action of the 
blowpipe flame. The way of holding the blowpipe and the 
nature of the blast will depend upon whether the operator 
needs a reducing or an oxidizing flame. The easiest way of 
producing most efficient flames of both kinds is by means of 
coal-gas delivered from a jet, shaped as in Pig. 18, the slit 
being 1 cm long and 1 to 2 mm wide, as, with the use 
of gas, the operator is enabled to regulate not only tho cur- 
rent of air, bnt that of the gas also. The task of keeping 
the blowpipe steadily in the proper position may bo greatly 
facilitated by firmly resting that instrument upon some 
movable metallic support, such as the ring of BCNSHN'S gas- 
larnp intended for holding dishes, etc. Fig. 12 shows the 
flame for reducing ; Fig. 13, the flame for oxidizing. The 




FIG. 13. FIG. 13. 



redwing flame is produced by keeping the jet of the blow- 
pipe just on the border of a tolerably strong gas-flamo, and 
driving a moderate blast across it The resulting mixture 
of the air with the gas is only imperfect, and there remains 
between the inner bluish part of the flame and the outer 
barely visible part a luminous and reducing zone, of which 
the hottest point lies somewhat beyond the apex of the inner 
cone. To produce the oxidizing flame, the gas is lowered, 
the jet of the blowpipe pushed a little farther into the flame, 
and the strength of the current somewhat increased. This 



15.J USE OF THE BLOWPIPE. 25 

serves to effect an intimate mixture of the air and gas, and 
an inner, pointed, bluish cone, slightly luminous towards the 
apex, is formed, and surrounded by a thin, pointed/ light- 
bluish, barely visible mantle. The hottest part of the flame 
is at the apex of the inner cone. Difficultly fusible bodies 
are exposed to this part to effect their fusion, but bodies to 
be oxidized are held a little beyond the apex, that there may 
be no want of air for their combustion. An oil-lamp with a 
broad wick of proper thickness may be used instead of gas ; a 
thick wax-candle also will do. For an oxidizing flame, a small 
spirit-lamp will in most cases answer the purpose. 

The current is produced with the cheek muscles alone, and 
not with the lungs. The way of doing this may be easily 
acquired by breathing quietly, with distended cheeks and 
with the blowpipe between the lips. Practice and patience 
will soon enable the student to produce an even and uninter- 
rupted current. 

The supports on which substances are exposed to the blow- 
pipe flame are generally either wood charcoal, or platinum 
wire or foil. 

Charcoal supports are used principally in the reduction of 
metallic oxides, etc., or in testing the fusibility of bodies. The 
substances to be operated upon are put into small cavities, 
scooped out with a penknife or with a little tin tube. Metals 
that are volatile at the heat of the reducing flame evaporate 
wholly or in part upon the reduction of their oxides. In 
passing through the outer flame, the metallic vapors are re- 
oxidized, and the oxide formed is deposited upon the sup- 
port around the heated substance. Such deposits are called 
coatings or incrustations. Many of these exhibit characteristic 
colors, leading to the detection of the metals. The charcoal 
of pine, linden, or willow, is greatly preferable to that of harder 
woods. Saw the thoroughly burnt charcoal of well-seasoned 
and straight-split pine into rectangular pieces, and brush off 
the dust The blocks may then be handled without soiling the 
hands. The sides alone are used on which the annual rings 
are visible on the edge, as, on the other sides, the fused 
matters are apt to spread over the surface of the charcoal* 
Small supports are sometimes sold, which have been made 



26 OPERATIONS. [ 15. 

from powdered charcoal and pressed into convenient shapes. 
These are very serviceable and clean. 

Charcoal is a valuable material for supports in blow- 
pipe experiments because of 1st, its inf usibility ; 2d, its low 
conducting power for heat, which permits substances to be 
heated more strongly upon a charcoal than upon any other 
support ; 3d, its porosity, which causes it to readily imbibe 
fusible substances, such as boras, sodium carbonate, etc., 
while infusible bodies remain on the surface ; 4th, its reduc- 
ing power, which greatly contributes to the reduction of 
oxides in the inner blowpipe flame. 

We use platinum wire, and occasionally also platinum /W?, 
in all oxidizing processes before the blowpipe ; also when 
fusing substances with fluxes, to test their solubility, to watch 
the phenomena attending the solution, and to mark the color 
of the bead; and lastly, to introduce substances into the 
flame, to see whether they will color it. The wire should be 
cut into lengths of 8 cm, and each length bent at both ends. 



FIG. 14. 

into a small loop (Pig. 14). When required for use, the loop 
is moistened with a drop of water, then dipped into the pow- 
dered flux (where a flux is used), and the portion adhering fused 
in the flame of a gas- or spirit-lamp. When the bead pro- 
duced, which sticks to the loop, is cold, it is moistened again* 
and a small portion of the substance to be examined put on 
and made to adhere to it by the action of gentle heat. The 
loop is then finally exposed, according to circumstances, to 
the inner or the outer blowpipe flame. 

What renders the application of the blowpipe particularly 
useful is the great expedition with which results are attained. 
These results are of a twofold kind, viz., they either afford 
us simply an insight into the general properties of the body, 
and accordingly enable us only to determine whether it is 
fixed, volatile, fusible, etc.; or the phenomena which we ob- 
serve render us able to recognize at once the particular body 
whicfc we have belore us. We shall have occasion to describe 



16.] USE OF LAMPS. 27 

these phenomena when treating of the deportment of the 
different substances with reagents. 

In using the blowpipe, one hand is always occupied ; con- 
tinuous blowing requires practice and some effort, although the 
latter may not be very great, and it is not very easy to main- 
tain a blowpipe flame in such a manner that the substance 
exposed to it is always exactly in the desired part of the 
flame. For these reasons, the efforts of many chemists have 
been directed towards producing automatic blowpipes, and 
many such pieces of apparatus have been recommended and 
used. In some of these, the air-current is produced by means 
of a gasometer, in others by means of a rubber balloon, in 
others still by a species of hydrostatic blast, etc. The simplest 
self-acting apparatus, however, by which most of the objects 
attainable with the blowpipe may be conveniently accom- 
plished, is a BUNSEN gas-lamp, which burns without lumi- 
nosity and without soot. A description of this lamp is given 
in the next paragraph. 

'6. 

15. THE USE OF LAMPS, PARTICULARLY OF GAS-LAMPS. 

As we have to deal mostly with small quantities of matter,, 
we commonly use in processes of qualitative analysis requir- 
ing the application of heat, such as evaporation, ignition, etc., 
either spirit-lamps or gas-lamps. 

Of spirit-lamps, there are two kinds in use, viz., the simple 
kind shown in Fig. 17, and the BERZEIIUS lamp with double 
draught given in Fig. 15. In the construction of the latter, 
it should be borne in mind that the part containing the 
wick and the vessel holding the spirit must be in separate 
pieces, connected only by means of a narrow tube ; otherwise, 
troublesome explosions are apt to occur in lighting the lamp. 
The chimney should not be too narrow, or the stopper fit too. 
tightly on the mouth through which the spirit is introduced. 
A lamp should be selected that will readily slide up and 
down the pillar of the stand, which must be fitted with a 
movable brass ring to support dishes and flasks in processes. 



OPERATION'S. 



[10. 



of ebullition, and a ring of moderately stout iron wire to sup- 
port tlie triangle for holding the crucibles in the processes of 
ignition and fusion. Of the various forms of lamps in use, 
the one shown in Fig. 15 is the most suitable. Fig. 16 rep- 
resents a triangle of platinum wire fixed within an iron-wire 





Fiu 10. 




FIG 15. 



FIG. 17. 



ring. This serves to support crucibles in processes of igni- 
tion. Glass vessels, more particularly beakers, which it is 
intended to heat over the lamp, are most conveniently rested 
on a piece of gauze made of brass wire such as is used in 
making sieves of medium fineness. 

Of the many gas-lamps proposed, BUNSEN'S, as shown in its 
simplest form in Tigs. 18 and 19, is the most convenient, ah 
is a base of cast iron. In the center of this is fixed a brass 
box, cd, which has a cylindrical cavity 12 mm deop and 
10 mm in diameter. In each side of the box, 4 mm from the 
upper rim, is a circular aperture of 8 mm diameter, leading 
to the inner cavity. Pitted into one side, 1 mm below tho 
circular aperture, is a brass tube, which serves for tho 
attachment of the India-rubber supply-tube. This brass tube 
is made in the shape shown in Fig. 18, and has a bore of 
4 mm. The gas conveyed into it passes into a tube in the 
center of the cavity of the box. The latter tube, which is 4 
mm thick at the top and thicker at the lower end, projects 3 
mm above the rim of the box. The gas issues from a narrow 



16.] 



USE 



LAMPS. 



29 



opening which appears to be formed of 3 radii of a circle, in- 
clined to each other at an angle of 120. The length of eacii 
radius is 1 mm, and the opening of the slit is -J- mm wide, ef 
is a brass tube 95 mm long, open at both ends, with a bore of 
9 mm, and the screw at the lower end of this tube fits into 




FIG. 18. 



FIG. 19 



the upper part of the cavity of the box. With this tube 
sere wed in, the lamp is completed. On opening the stop-cock, 
the gas rushes into the tube ef> where it mixes with the air 
coming in through the circular apertures. When this mix- 
ture is kindled at /, it burns with a straight, upright, 
bluish flame, entirely free from soot, which may be regu- 
lated at will by means of the stop-cock. A partial opening 
of the cock suffices to give a flame fully answering the pur- 
pose of the common spirit-lamp ; while with the full stream 
of gas turned on, the flame, which will now rise up to 2 dm 
in height, affords a most excellent substitute for the BEBZE- 
utrs lamp. If the flame is made to burn very low, it will 
often occur that it recedes ; in other words, instead of the 



30 OPERATIONS, [ 1C - 

mixture of gas and air burning at the mouth of the tube </, 
the gas takes fire on issuing from the slit, and burns below 
in the tube. This defect may be remedied by arranging the 
lamp so that not only the stream of gas, but also the air 
which enters, may be regulated, as in the lamp shown 
in Fig. 22; and also in the above described simple lamp, 
by covering the tube ef at the top with a little wire-gauze 
cap. Flasks, beakers, etc., which it is intended to heat over 
the gas-lamp, are supported upon brass or iron gauze, thin 
iron plates, or asbestus board. For blowpipe operations, the 
tube gh must be inserted into ef. This tube terminates iu a 
flattened top, cut off at an angle of 68 to the axis, and having 
an opening 1 cm long and 1| to 2 mm wide. The inser- 
tion of gh into ef serves to close the air-holes in the box, 
and pure gas, burning with a luminous flame, issues from 
the top of the tube. Fig. 19 shows the apparatus complete, 
fixed in the fork of an iron stand. This arrangement permits 
the lamp to bo moved backward and forward between the 
prongs of the fork, and up and down the pillar of the stand. 
The movable ring on the same pillar serves to support the 
objects to be operated upon. The 6 radii around the tube 
of the lamp serve to support a sheet-iron chimney (see Fig. 
23), or a porcelain plate used in quan- 
titative analyses. 

To heat crucibles to the brightest 
red heat or to a white heat, the bellows 
Uotvpipe is resorted to. But even with- 
out this, the action of the gas-lamp 
may be considerably heightened by 
heating the crucible within a small 
clay furnace, as recommended by Enu 
MAKN. Fig. 20 shows the simple con- 
trivance by which this is effected. Tho 
FIG. SO. , 1 1 r T t i 

furnaces are 115 mm high, and meas- 
ure 70 mm in diameter in the clear. The thickness of material 
is 8 mm. If the ordinary BUNSEN burner is not sufficiently 
strong for ay purpose, the three-BuNSEN burner (Fig. 21) 
may be used. A similar purpose is served by the very effect- 
ive gas-furnaces of W. HEMPBL * and H. KoESSLEB.t 
* Zeitschr. f. analyt, Ofceni., 16, 454 aud 18, 404. f Ibid , 25, 95 aud 32, Heft 5* 




16.] 



USE OP LAMPS. 



BUNSEN has demised a more perfect form of this lamp* to 
render the flame a more complete substitute for the blowpipe 
flame, namely, for reducing, oxidizing, fusing, and volatiliz* 
ing, and for the observation of the coloration of flame ( 17). 
This improved form is shown in Fig. 22. a is a sheath, 
which can be turned around for regulating the flow of 
air. When in use, a conical chimney (ddd'd', Fig. 23) is 




Fid 31 




FIG. 




FIG 



placed on ee, and is of such dimensions that the flame will 
burn tranquilly. Fig. 23 shows the flame half its natural size. 
In this, three parts are at once apparent, namely, (1) the dark 
cone, aaa'a', which contains the cold gas mixed with about 
62 per cent of air ; (2) the mantle, a'ca'J, formed by the burn- 
ing mixture of gas and air ; (3) the luminous tip of the dart 
cone, aba, which does not appear unless the air-holes are 
somewhat closed. The last is useful for reductions. 

Such are the three principal parts of the flame, but 

* Annal. d. Ohem. u. Pharm., Ill, 357, and 138, 367. Also, Zeltschr. t 
analyt. Chem., 5, 851. 



32 OPERATIONS. [ 16. 

BUNSEN distinguishes no less than sis parts, which lie names 
as follows : 

1. The lose at a, which has a relatively low temperature, 
because the burning gas is here cooled by the constant cur- 
rent of fresh air, and also because the lamp itself conducts 
the heat away. This part of the flame serves for discovering 
the colors produced by readily volatile bodies when loss vola- 
tile bodies which color the flame are also present. At the 
relatively low temperature of this part of the flame, Hie form or 
volatilize alone instantaneously, and the resulting color im- 
parted to the flame is for a moment visible, unmixed with 
other colors. 

2. TJie fusing zone. This lies at /?, at a distance uf some- 
what more than one third of the height of tlio llama froiu the 
bottom, and equidistant from the outside and the inside of tho 
mantle, which is broadest at this part. This is llio holiest 
part in the flame (about 2300 BUNSEN), and it therefore se.rvos 
for testing substances as to their fusibility, vohitility, emission 
of light, and for all processes of fusion at a high temperature*. 

3. The lower oxidizing flame lies in the outer border of the 
fusing zone at y> and is especially suitable for the oxidation 
of oxides dissolved in vitreous fluxes. 

4. The upper oxidizing zone at e consists of tho non-lumi- 
nous tip of the flame. Its action is strongest wlic.u the air- 
holes of the lamp are fully open. It is used for tho roasting 
away of volatile products of oxidation, and generally for all 
processes of oxidation where the very highest lomporaturc is 
not required. 

5. The lower reducing zone lies at <J, in the inner border of 
the fusing zone next to the dark cone. Tho reducing gasea 
are here mixed with oxygen, and therefore do not POHHUSH 
their full power. Hence, they are without action on many 
substances which are deoxidized in the upper reducing filtuiiQ. 
This part of the flame is especially suited for reduction on 
the charcoal stick (p. 34), or in vitreous fluxes. 

6. The upper reducing flame lies at 77, in the luminous tip of 
the dark inner cone, which, as I have already explained, may 
be produced by diminishing the supply of air. This part of 
the flame must not be allowed to get large enough to blacken 
a test-tube filled with water and held in it. It contains no 



16.] USE OP LAMPS. 33 

free oxygen, is rich in separated incandescent carbon, and 
therefore has a much stronger action than the lower reducing 
zone. It is used more particularly for the reduction of 
metals collected in the form of incrustations. 

With the help of a gas flame of this description, we can 
obtain as high a temperature as with the blowpipe, and even 
higher if the radiating surface of the substance is made as 
small as possible. Moreover, by the use of the different parts 
of the flame, processes of reduction and of oxidation may be 
carried out with the greatest convenience. 

In order to study the deportment of bodies at a high tempera- 
ture, namely, their emission of light, fusibility, volatility, and 
power of coloring flame, they are introduced into the flame in 
the loop of a platinum wire, which should be barely thicker 
than a horse-hair. Should the substance attack platinum, 
a little bundle of asbestus is used, which should be about 
one fourth the thickness of a match. Decrepitating sub- 
stances are first very finely powdered, then placed on a strip 
of moistened filter-paper about a square centimeter in sur- 
face, and this is cautiously burnt between two rings of fine 
platinum wire. The substance now presents the appearance 
of a coherent crust, and may be held in the flame without 
difficulty. Tor testing fluids to see whether they contain a 
substance which colors flame, the round loop of the fine 
platinum wire is flattened on an anvil to the form of a small 
ring. This is dipped into the fluid, and then withdrawn, 
when a drop will be found attached to the ring. This drop 
is held near the flame and allowed to evaporate without boil- 
iiig, after which the residue may be conveniently tested. 

If bodies are to be exposed to the action of the flame for a 
considerable time, the stand shown in Fig. 24 is used. A and 
B are provided with springs, and can be easily turned and 
moved up and down. On A is the arm a, intended for the sup- 
port of the platinum wire fixed in the glass tube (Fig. 25) ; also 
another little arrangement to hold the glass tube 6, with its 
bundle of asbestus fibers, d. B bears a clip for the reception 
of a test-tube, which in certain cases has to be heated for a 
considerable time in a definite part of the flame. G serves 
to hold the various platinum wires fixed in glass tubes. 

Experiments of reduction are performed either with the aid 



34 



OPERATION'S. 



[16. 




of a suitable reducing agent in a small glass tube, or with 
the aid of a little stick of charcoal. In order to prepare the 
latter, BUNSEN recommends holding an uneffloresced crystal 
of sodium carbonate near the flame, and, after having taken 

off the head of a match, 
smearing three fourths of 
its length with the wet mass 
produced by warming the 
crystal. The match-stick is 
then slowly rotated on its 
axis in the fliinie, when a 
crust of solid sodium car- 
bonate will form on the 
carbonized wood, and on 
heating in the fusing zone 
of the flame, this crust will FIO 35 
be melted and absorbed by 
the charcoal. The little stick of 
charcoal will now be protected in 
a measure from combustion. The 
substance to be tested i made 
into a paste, with a drop of melted 
crystallized sodium carbonate, and 
a mass about the size of a millet- 
seed is taken up on the point of tho 
carbonized match. It is then first 
melted in the lower oxidising 
flame, and afterwards moved 
through a portion of the dark cono 
into the opposite hottest part of 
the lower reducing zone. The re- 
duction will be rendered evident 
by the effervescence of the sodium 
carbonate. After a few moments, the action is stopped by 
allowing the substance to cool in the dark cone of the flame. 
If, finally, the point of the carbonized match is cut off and 
triturated with a few drops of water in a small agate mortar, 
the reduced metal will be obtained in the form of sparkling 
fragments, which may be purified by elutriation, and, if neces- 
sary, raore minutely examined. 



FIG 24 



USE OF LAMPS. 35 

Volatile elements which are reducible by hydrogen and 
carbon may be separated as such or as oxides from their com- 
biuations, and deposited on porcelain. These deposits are called 
.incrustations. They are thicker in the middle, and become 
thin towards the edges. They may be converted into iodides, 
sulphides, and other combinations, and thus may be further 
identified. These reactions are so delicate that in many cases 
a quantity of from -^ to 1 mg is sufficient to exhibit them. 

Tla metallic incrustation is obtained by holding in one hand 
a small portion of the substance on asbestus, in the upper 
reducing flame; and in the other a glazed porcelain dish, 
from 1 to 1.2 dm in diameter, filled with water, close over 
the asbestus, in the upper reducing flame. The metals sepa- 
rate as sooty or mirror-like incrustations. 

If the substance is held as just directed, and the porcelain 
dish is held in the upper oxidizing flame, an incrustation of 
oxide is obtained. In order to be sure of getting it, the flame 
must be comparatively small if the portion of substance 
is minute. To tarn the incrusta- 
tion of oxide into an incrustation of 
iodide, let the dish covered with the 
oxide cool, breathe on it, and place 
it on a wide-mouthed bottle (Fig. 
26). This bottle contains phos- 
phorus tri-iodide, which has been 
allowed to deliquesce and become 
converted into fuming hydriodic acid and phosphorous acid. 
It should have an air-tight glass stopper. If the hydriodic 
acid has become so moist that it has ceased to fume, it may be 
restored to its proper condition by the addition of phosphorus 
pentoxide. To turn the incrustation of iodide into an incrusta- 
tion of sulphide, direct a current of air containing ammonium 
sulphide upon it, breathing upon the dish occasionally ; then 
drive off the excess of ammonium sulphide by gentle warming. 

If more considerable quantities of the metallic incrustation 
are required for further experiments, the porcelain dish is 
replaced by a test-tube (D, Fig. 24) half filled with water, in 
which a few pieces of marble should be placed to prevent 
bumping when the water boils. In this case, the asbestus 
*(d, Fig. 24), with the substance on it, is fixed at the same 




36 



OPERATIONS. 



[1Z 



height as the middle of the upper reducing flame ; the test- 
tube is fixed with its bottom close over the asbestus, as shown 
in the figure, and the lamp then is moved just under the test- 
tube. The substance thus comes within tho reducing ilamo, 
and the metallic incrustation forms on the bottom of the test- 
tube. The incrustation may be obtained as thick as is wished 
by renewal of the substance. 

17. 

16. OBSERVATION OF THE COLORATION OF FLAME A>*D 
SPECTRUM ANALYSIS. 

Many substances give characteristic tints to a colorless 
flame, which afford excellent means for their identification. 

For instance, salts of so- 
dium impart to fiamo a yol. 
low, salts of potassium a 
violet, salts of lithium a ear- 
mine tint, and thus may he 
easily distinguished from each 
other. 

The flame of BUNHKV'S gas- 
lamp with chimney, described 
in 16 and shown in Fi#. "23, 
is more particularly suited 
for observations of this kind. 
The substances to he, exam- 
ined are put on tho small loop 
of a fine platinum wire, and 
by means of the holder shown 
in Fig. 2-4, or tho mom simple 
one, Fig. 27, then placed iu 
the fusing zone of tho gas 
flame. A particularly striki n# 
coloration is impartod in tho 
flame by the volatile salts of 
the alkali and alkali-earth 
metals. If different salty of 
one and the same base are 




37. 



compared in this way, it is found that each one of them, if 



17.] FLAME COLORATION SPECTRUM ANALYSIS. 37 

at all volatile at high temperatures, or permitting at least the 
volatilization of the base, imparts the same color to the flame, 
but with different degrees of intensity, the most volatile of 
the salts producing also the most intense coloration. For 
instance, potassium chloride gives a more intense coloration 
than potassium carbonate, and the latter again a more in- 
tense one than potassium silicate. In the case of difficultly 
volatile compounds, the coloration of the flame may often be 
developed by adding some other body which has the power 
of decomposing the compound under examination. Thus, 
in silicates containing only a few per cent of potassium, 
the latter body cannot be directly detected by coloration of 
flame. This detection may be accomplished, however, by 
adding a little pure gypsum, as this will cause formation of 
calcium silicate and potassium sulphate, a salt which is 
sufficiently volatile. 

For continuous observation of the colorations which the 
chlorides of the heavy metals impart to the flame, MITSCEER- 
LIOH'S method can be used. This con- 
sists in passing a stream of hydrogen 
through a bulb-tube, in the bulb of 
which the metallic chloride is heated; 
and the hydrogen issuing from the end 
of the tube, which is bent upward and 
drawn out, is ignited. The following 
apparatus (Fig. 28), described by VOGEL, 
and arranged for the use of illuminating- 
gas, can also be used for this purpose. 
The gas is led in through Tc, passes 
through s 9 and then burns at the top of 
the BUNSEN burner of glass, which is held FIGL 28. 

by the wire u. If the burner is rightly constructed and 
adjusted, the flame will be non-luminous. If the substance 
at p is now heated, the flame will show quickly and con- 
tinuously the coloration corresponding to the intermixed 
chloride. 

But however decisive a test the mere coloration of flame 
affords for the detection of certain metallic compounds, when 
present unmixed with others, this method becomes appar- 
ently useless in the case of mixtures of compounds of several 




88 OPERATIONS. [ 17. 

metals. For instance, mixtures of salts of potassium and 
sodium show only the sodium flame; mixtures of salts of 
barium and strontium, only the barium flame, etc. This 
defect may be remedied, however, in two ways. 

The first way, introduced by CABTMELL,* and afterwards 
perfected by BuNSENf and by MERZ,J consists in looking at 
the colored flame through some colored medium (colored 
glasses, indigo solution, etc.). Such media, in effacing the 
flame coloration of one metal, bring out that of the other 
mixed with it. For instance, if a mixture of a salt of potas- 
sium and a salt of sodium is exposed to the flame, the latter 
will show only the yellow sodium coloration; but if the 
flame be now looked at through a deep-blue cobalt glass, or 
through a solution of indigo, the yellow sodium coloration 
will disappear and be replaced by the violet potassium tint. 
A simple apparatus suflices for every observation and experi- 
ment of this kind, all that is required for the purpose 
being 

1. A hollow prism (Fig. 29) composed of mirror-plates, 
the chief section of which forms a triangle with two sides of 
150 mm and one side of 35 mm length. The indigo solu- 
tion required to fill this prism is prepared by dissolving 1 
part of indigo in 8 parts of fuming sulphuric acid, adding to 




FIG. 29. 

the solution 1500-2000 parts of water, and filtering. When 
using this apparatus, the prism is moved in a horizontal 
direction close before the eye, in such a way that the rays of 
the flame are made to penetrate successively thicker and 
thicker layers of the effacing medium. CORNWALL prefers a 
solution of potassium permanganate to the indigo, since it 



* Phil. Mag., 16, 328 f Annal. d. Chem. u. Pharra., Ill, 257. 

% Journ. f . prakt. Chem , SO, 487. 

American Cliemist, 2, 884; Zeitsclir. f. analyt. Chem., 11, 807. 



17.] FLAME COLORATION SPECTRUM ANALYSIS. 39 

allows the distinct recognition of the potassium flame in the 
presence of compounds of sodium, lithium, and calcium. He 
gives to the sides of the hollow prism a length of 240 mm, 
and to the thick end an interior diameter of 30 mm, and uses 
a solution of potassium permanganate of such strength that, 
at a distance of 45 mm from the thick end, the strongest 
sodium or lithium flame is completely effaced. 

2. A blue, a violet, a red, and a green glass. The blue 
glass is tinted with cobalt oxide ; the violet glass, with man- 
ganese sesquioxide; the red glass (white glass colored red 
superficially), with cuprous oxide ; and the green glass, with 
iron oxide and cupric oxide. The colored glass of commerce 
will generally be found to answer the purpose. In regard to 
the tints imparted to the flame by the different bodies when 
viewed through the aforesaid media, and the combinations 
by which these bodies are severally identified, information 
will be found in Section HI, in the paragraphs treating of 
the several metals and acids. 

The second way, which is called Spectrum Analysis, was 
introduced by KIBCHHOPP and BUNSEN. It consists in letting 
the rays of the colored flame first pass through a narrow slit, 
then through a prism, and observing the rays so refracted 
through a telescope. A distinct spectrum is thus obtained 
for every flame-coloring metal. This spectrum consists either 
of a number of colored lines lying side by side, as in the 
case of barium ; or of two, separate, differently colored lines, 
as in the case of lithium ; or of a single green line, as in the 
case of thallium. These spectra are characteristic in a 
double sense, i*e., the spectrum lines have a distinct color, 
and they also occupy a fixed position. 

It is this latter circumstance which, in the spectrum 
observation of mixtures of flame-coloring metals, enables us 
to identify without difficulty every individual metal. Thus, 
a flame in which a mixture of potassium, sodium, and lithium 
salts is evaporated, will give, side by side, the spectra of the 
several metals in the most perfect purity. 

KIBOHHOFP and BUNSEN have constructed two forms of ap- 
paratus which are adapted for spectroscopic observation, and 
by which measurements of the positions in which the spectral 
lines appear may be made. Both depend upon exactly the 



40 



OPEKATIONS. 



same principles. The larger and more complete apparatus is 
described and figured in POGGENDUI^F'S Aimalou, 113, ;37t, 
and in the Zeitschr. f. analyt. Cheni., 1, 49. The smaller, sim- 
pler, and consequently cheaper apparatus, whii'li sufluvs for 
ordinary purposes, and is used very frequently iti laboratories, 
will be described here. It is shown in Fig 30. 

A is an iron dist, in the center of which a prism, with cir- 




30. 



Fro, Bi 



cular refracting faces of about 25 mm diameter, is fjistouod by 
a clamp and screw. The same disk has also attache! in it the 
three tubes B, C, and I). Each of these tubes is Holdcrod to 
a metal block (Fig. 30a), by which they may bo adjusted in 
the proper position. B is the observation telescope. It has a 
magnifying power of about six, and an objective of about, 20 
mm diameter. The tube G is closed at one end by a bmss 
disk, into which is cut the perpendicular slit through wlrictli 
the light is admitted. The tube 1) carries a photographic 
copy of a millimeter scale, on a glass plate reduced to about 
one fifteenth the original dimensions. This scale is covered 
with tin-foil, with the exception of the narrow strip upou 
which the divisional lines and the numbers are engraved. It 
is lighted by a gas or candle flame placed" before it. 

The axes of the tubes B and D are directed to the center 
of one face of the prism, at the same inclination, while the 



17.] FLAME COLORATION SPECTRUM ANALYSIS. 41 

axis of the tube C is directed to the center of the other face. 
This arrangement makes the spectra produced by the light 
passing through (7, and the image of the scale in D, produced 
by total reflection, appear in one and the same spot, so that 
the positions occupied by the spectrum lines may be read off 
on the scale. The prism is placed in about the position in 
which there is a minimum divergence of the rays of the sodium 
line, and the telescope is set in the direction in which the 
red and the violet potassium lines are about equidistant from 
the middle of the field of view. 

The colorless flame into which the flame-coloring bodies 
are to be introduced is placed 10 cm from the slit. BUNSEN'S 
lamp, shown in Fig. 22, gives the best flame. The lamp is 
adjusted so as to place the upper border of the chimney about 
20 mm below the lower end of the slit. When this lamp has 
been lighted, and a bead of substance say, of potassium sul- 
phate introduced into the fusing zone by means of the holder 
shown in Fig. 27, the iron disk of the spectrum apparatus, 
which, with all it carries, is movable round its vertical axis, 
is turned until the point is reached where the luminosity of 
the spectrum is the most intense. 

To cut off foreign light in all spectrum observations, the 
central part of the apparatus is covered with a black cloth or 
box. 

If reflected sunlight is allowed to pass through the slit of 
the spectroscope, a continuous spectrum showing the rainbow 
colors is obtained, in which a number of dark lines can be 
detected. (Compare 1 in the table of spectra.) These dark, 
FRAUNHOFEK'S lines assume fixed places in the spectrum, and 
therefore serve as definite starting-points for determining the 
positions of other lines. They are due to the fact that the 
rays emanating from the solid or fluid body of the sun pass 
through the sun's atmosphere. The gaseous bodies of which 
this is formed, which would give bright spectrum lines of 
their own accord, absorb out of the white sunlight, exactly 
those parts which they themselves radiate, and thus cause the 
dark lines. 

If reflected sunlight (or also lamplight) which enters the 
slit passes through liquids, it either goes through these 
mnabsorbed, or is partly absorbed. In the latter case, dark 



43 OPER/iTIONS. [ 17. 

stripes or bands are observed in the spectrum, -which, since 
they are caused by the extinction of rays of certain refrangi- 
bility, assume definite positions in the spectrum, and they 
may serve, therefore, for the characterization of many sub- 
stances. For the observation of such absorption-sped w, the 
liquids to be examined are placed in vessels of colorless 
glass, best in such as have straight, parallel walls. 

Besides the spectroscope of BUNSEN and KnicmiOFF, many 
other forms have come into use,* among which I will call 
special attention to the universal spectroscopes of H. W. 
VOGEL t and 0. H. WOLFF, J which are also convenient for the 
observation of flame-spectra and absorption-spectra. 

The spectra yielded by the alkalies and alkali-earths, 
and also those of thallium and indium, are portrayed in Table 
I. The spectra are represented as they appear in instruments 
provided with astronomical telescopes. In Section 111, at- 
tention will be called to the lines which are most character, 
istic for each metal. In this place, I will merely show the 
manner in which the greatest certainty may be attained in 
spectrum analysis. This is done by placing beads of pure 
metallic compounds in the flame, and registering the most 
prominent spectral lines upon a drawn scale, in the position 
which they show upon the scale of the instrument. For the 
sake of an example, this has been done for strontium upon 
the upper scale in the spectral table. It is evident that the 
spectrum of an unknown body can only pass as a strontium 
spectrum when the characteristic lines correspond not only 
in regard to their color, but also to the exact positions iu 
which they have been drawn upon the strontium scalo. 

Such drawings, as is evident, must be prepared by each 
operator for his own apparatus, and they lose their signifi- 
cance if anything is changed in the arrangement of tho prism 
or scale. On this account, it is advisable to give a setting to 
the apparatus which can easily be found again if it should be 
disturbed by accident ; for example, one in which tho loft- 
hand edge of the sodium line corresponds to division 50. 

* Compare Zeitschr. f. analyt. Chem., 2, 64, 190, and 353; 3, 443; 5, 339; 12, 
433, 13, 48, and 442; 14, 335; 16, 468, 17, 187; 19, 72; 20, 99; 21, 182, 241, 
and 554, 22, 540, 25, 879, 26, 124, and 616; 28, 380; 30, 316, and 467; 31, 6& 

I- %VZ. 17, 187. t7Md,20, 99. 



18.] USE OF THE MICROSCOPE. 43" 

In regard to the observation of spark-spectra, I refer to the 
article of R. BUNSEN, which treats this subject fully (Zeitschr. 
f. analyt. Chem., IB, 68). 

With the appearance of spectrum analysis, an era which is 
new in many respects has begun in chemical analysis, for we 
are able by this means to discover much smaller amounts of 
substances than is possible with any other method. At the 
same time, the process gives a certainty which satisfies every 
doubt, and yields results in seconds which formerly, if attain- 
able at all, were only to be obtained in hours or days. 



18. 
17. THE USE OF THE MICBOSOOPE IN QUAIITATTVE ANALYSIS. 

It has already been pointed out in 3 that the microscope 
is used for the observation of very small crystals. While 
this instrument was formerly used only exceptionally, it has 
gained much significance recently through the investigations 
of O. LEHMANN,* K. HAUSHOFER^ A. STBENG,:): H. BEHKENS, 
FEET, || and others. These researches have demonstrated that 
not only occasional substances, but numerous bodies, can be 
detected by the help of microscopic analysis, and in many 
cases even when they are accompanied by other substances. 

The foundation of this method of investigation is the fact 
that bodies which have a tendency to crystallize show the 
same crystalline form under identical conditions of forma- 
tion. Now, since these forms are different with different 
bodies, and in many cases are characteristic for special ones, 
the microscopic observation of the crystals often allows 
the accurate recognition of elements or of certain of their 
compounds. 

* Anual. d. Physik u. Chem. [N F.], 13, 506. Zeitschr. f. analyt. Chem., 
21, 92 

t " Mikroskopische Reactionen " v. K. HATTSHOFER, Braunschweig, 1885. 

t Ber. d. oberhessischen Gesellsch. f . Natur- u. Heilkunde, 22, 258 et seg. 
Zeitschr. f. analyt Chem , 23, 185. 

Ann. de 1'ficole polyt. de Delft, 1891 Zeitschi. f. analyt Chem., 30, 
125 et seq. 

\ Schweitz, Wochenschr. f Phann., 30, 149 Zeitschi, f. analyt. Chem., 
32, 204 



44 OPERATIONS. [ 18. 

As far as the carrying out of work in microscopic analysis 
is concerned, it generally deals with the formation of crystals 
which are produced upon the object-glass, either by mixing a 
drop of the liquid to be investigated with a drop of an ap- 
propriate precipitating agent, or by the careful evaporation 
of a drop of a certain solution of the substance to be recog- 
nized. The resulting crystals are usually observed when 
magnified from 50 to 200 times, sometimes with the help of 
NICOL'S prisms. 

It follows from what has been said that only very small 
amounts of substances are necessary for the performance of 
such microscopic analyses, and that the object is attained 
in a relatively short time. In many cases, reliable results 
are obtained without difficulty, but in others, the task is 
rendered difficult by the circumstance that, with small 
changes in the conditions of formation, regularly formed 
crystals are often not obtained, but instead crystal skeletons 
or aggregations, including many crystals which are mostly 
incompletely developed. 

The advantages which microscopic analysis offers are con- 
sequently obvious, and although this method can scarcely 
replace the usual methods of chemical analysis, yet it often 
supplements them in a very efficient manner. 

However, if reliable results are to be obtained by its use, 
microscopic analysis requires not only a thorough knowledge 
of crystallography, but also extensive practice in the use of 
the microscope. Therefore, those who are taking up analyt- 
ical chemistry cannot readily learn the former subject, in its 
fullest extent, simultaneously with purely chemical methods. 
It should rather be made an object of special study. In the 
present work, I shall limit myself by mentioning only the 
microscopic reactions which have special value for detect- 
ing certain bodies, and shall refer, for the rest, to the treatise^ 
which have beeti citet} above. In HATISHOEEB'S work, the 
descriptions of the microscopic appearance of crystals are 
supplemented by illustrations. 



19.] APPAEATUS AND UTENSILS. 45 



APPENDIX TO SECTION L 

19. 
APPARATUS AND UTENSILS. 

Since it might be difficult for many who are beginning the 
pursuit of chemical analysis to distinguish the most suitable 
from the unnecessary things, in their choice of the apparatus 
and utensils required for the purpose, I here add a list which 
contains the apparatus really necessary for carrying out sim- 
ple investigations. I also take this opportunity to call atten- 
tion to some points which are to be kept in view in buying or 
preparing them. 

1. A BUNSEN BURNER with chimney, and inner tube for 
producing a tiame for blowpiping, together with a LAMDP-STAND 
(16, Pigs. 18, 19, and 22). 

If illuminating-gas is not available, BERZELIUS'S ALCOHOL- 
LAMP ( 16, Fig, 15) and a glass alcohol-lamp ( 16, Fig. IT) 
can be used.* 

2. A BLOWPIPE (see 15). 

3. A PLATINUM CRUOIBLE of about 15 cc capacity, the eover 
of which is in the form of a shallow dish, and which is not 
too deep in proportion to its width. 

4 PLATINUM FOIL, as smooth and clean as possible, and not 
too thin ; length about 40 mm ; width about 25 mm. 

5. PLATINUM WIRE (see pp. 26 and 34). Two larger and two 
finer wires are amply sufficient to begin with. They are kept 
most conveniently in a glass half filled with dilute acid ; the 
wires may thus be kept clean. 

6. A STAND WITH TWELVE OR MORE TEST-TUBES. 16 to 18 cm 

is the proper length of the tubes ; from 1 to 2 cm the proper 
width. The tubes must be made of thin white glass, and well 
annealed. The rim must be quite round, slightly flared, 

* [The dealers supply certain forms of GASOLINE-LAMPS, which give 
non-luminous flame similar to that of the Bunsen gas-burner, and even supe- 
rior to it in heating power. These are recommended as being far cheaper In 
regard to fuel, moie convenient, and moie powerful than alcohol-lamps. J 



46 OPERATIONS. [ 19* 

and without a lip, since this is of no use for pouring, and it 
interferes greatly with corking the tubes, as well as with 
thorough shaking. The stand shown in Fig. 31 will be iound 
convenient. The pegs upon the upper shelf are for hold- 




FIG. 31. 

ing the test-tubes after they are washed . In this position, they 
can drain well, and are always clean and dry. 

7. SEVERAL NESTS OF BEAKERS AND SOME SMALL FLABKH of thin, 
well-annealed glass. 

8. SEVEBAL PORCELAIN EVAVORATINO-DISH^,* AND VAUTOUS 
RMAT.T. PORCELAIN CRUCIBLES. Those of the royal manufacture 
of BERLIN are unexceptionable both in shape and durability. 
Those of MEISSEN and NYMPHENBURG are also very good. 

9. SEVERAL GLASS FUNNELS of various sixes. These must be 
inclined at an angle of 60, and merge into the neck at a deli- 
nite angle. 

10. A WASHING-BOTTLE of a capacity of from 300 to 400 cc 
(see 7). 

11. AN ASSORTMENT OF GLASS TUBES, SOME OLASB RODS, AND A 

GLASS SPATULA. The former may be bent, drawn out, etc., over 
a BERZEUUS lamp or gas-lamp ; the rods are rounded at the 
ends by fusion. 

12. A selection of WATCH-GLASSES. 

* [Porcelain dishes with handles, called CASSEROLES, are very convenient 
for evaporation in qualitative analysis. These can be held by hand over the 
naked gas flame, and the operator, besides securing very rapid evaporation, is 
enabled to stop the process at the proper point. The size most useful for the* 
purpose is SA of the royal Berlin make.] 



19.] APPARATUS AND UTENSILS. 47 

13. A small AGATE MORTAR. 

14. STEEL OR BRASS PINCERS, 10 or 12 cm long. 

15. A WOODEN FILTER-STAND (see 5). 

16. A TRIPOD of thin iron, to support the dishes, etc., which 
are to be heated over the small spirit- or gas-lamp. 

17. WIRE GAUZES OR ASBESTOS BOARDS ( 16). 

18. A PLATINUM TRIANGLE or an iron triangle supplied with 
pipe-stems ( 16, Fig. 16). 

19. Pieces of COLORED GLASS, especially blue and green 

(17). 

20. A PIPETTE holding 10 cc, graduated in half cubic centi- 
meters. 

21. FILTER-PAPEB, or ready-made filters. 



SECTION IL 

BEAGENTS. 
20. 

A VARIETY of phenomena may manifest themselves upon the 
decomposition or combination of bodies. In some cases, 
liquids change their color ; in others, precipitates are formed ; 
sometimes effervescence takes place, and sometimes deflagra- 
tion, etc. Now, if these phenomena are very striking, and 
attend only upon the action of two definite bodies upon one 
another, it is obvious that the presence of one of these bodies 
may be detected by means of the other. If we know, for 
instance, that a white precipitate of certain definite properties 
is formed upon mixing baryta with sulphuric acid, it is clear 
that, if upon adding baryta to any liquid we obtain a precipi- 
tate exhibiting these properties, we may conclude that this 
liquid contains sulphuric acid. 

Those substances which indicate the presence of others by 
any striking phenomena are called reagents. 

According to the different objects attained by the applica- 
tion of these bodies, we make a distinction between general 
and special reagents. By general reagents are meant those 
which serve to determine the class or group to which a sub- 
stance belongs ; and by special reagents, those which serve to 
detect bodies individually. That the line between the two 
divisions cannot be drawn with any degree of precision, and 
that one and the same substance is often made to serve both 
as a general and a special reagent, cannot well be held as valid 
objections to this classification, which is simply intended to 
induce a habit of employing reagents always for a settled 
purpose, viz., either simply to find out the group to which 
the substance belongs, or to determine the latter individually. 

48 



20.] REAGENTS. 49 

While the usefulness of general reagents depends princi- 
pally upon their efficiency in strictly characterizing groups of 
bodies, and often effecting a complete separation of the bodies 
belonging to one group from those belonging to another, that 
of special reagents depends upon their being characteristic and 
sensitive. We call a reagent characteristic if the alteration pro- 
duced by it, in the event of the body tested for being present, 
is so distinctly marked as to admit of no mistake. Thus, iron 
is a characteristic reagent for copper, stannous chloride for 
mercury, because the phenomena produced by these reagents, 
the separation of metallic copper and of globules of mer- 
cury admit of no mistake. We call a reagent sensitive or deli- 
cate if its action is distinctly perceptible, even though only 
a very minute quantity of the substance tested for be present ; 
for instance, starch as a reagent for iodine. 

Very many reagents are both characteristic and delicate ; 
for example, hydrochlorauric acid for stannous salts, potas- 
sium ferro cyanide for ferric and cupric salts, etc. 

I hardly need mention that, as a general rule, reagents 
must be chemically pure, i.e., they must consist purely and 
simply of their essential constituents, and must contain no 
admixture of foreign substances. We must therefore make it 
an invariable rule to test the purity of reagents before we use 
them, whether they be articles of our own production or pur- 
chased. Although the necessity of this is fully admitted, 
yet we find that in practice it is too often neglected. Thus, it 
is by no means uncommon to see aluminium entered among 
the substances detected in an analysis, simply because the 
solution of sodium hydroxide used as one of the reagents 
happened to contain that element ; or iron, because the 
ammonium chloride used was not free from that metal. In 
this section, the directions given for testing the purity of 
the several reagents refer, of course, only to the presence of 
foreign matter resulting from the mode of their preparation, 
and not to mere accidental admixtures. 

One of the most common sources of error in qualitative 
analysis proceeds from missing the proper measure the right 
quantity in the application of reagents. Such terms as 
addition in excess, supersaturation, etc., often induce novicea 
to suppose that they cannot add too much of the reagent. 



50 BEAGENTS. [ 20. 

Consequently, some will Jill a test-tube with acid simply to 
supersaturate a few drops of an alkaline fluid, whereas every 
drop of acid added after the neutralization point has been 
reached is to be looked upon as an excess of acid. On the 
other hand, the addition of an insufficient amount is to be 
equally avoided, since a reagent added in insufficient quantity 
often produces phenomena quite different from those which 
will appear if the same reagent be added in excess. For 
example, a solution of mercuric chloride yields a wA/fr 1 pre- 
cipitate if tested with a small quantity of hydrogen sulphide ; 
but if treated with the same reagent in excess, the precipitate 
is black. Experience has proved, however, that the most 
common mistake beginners make is to add the reagents too 
copiously. One reason why this over-addition must impair 
the accuracy of the results is obvious : we need simply to boar 
in mind that the changes effected by reagents are perceptible 
within certain limits only, and, therefore, that they may be 
the more readily overlooked the nearer we approach these 
limits by diluting the fluid. Another reason lies in the fact 
that a large excess of a reagent will often have a solvent or 
modifying action upon a precipitate or color, and will entirely 
prevent the exhibition of phenomena which a suitable quan- 
tity would produce without difficulty. 

No special and definite rules can be given for avoiding this 
source of error. However, a general rule may be laid down 
which will be found to answer the purpose, if not in all, at 
least in the great majority of cases. It is simply this : JJtfow 
the addition of a reagent, let the student always reflect for what 
purpose he applies it, what are the pJienomena he intends to p/ f o- 
duce, and what are tl\& results of tJte addition of excess. 

We divide reagents into two classes, according to whether 
the fluidity which is indispensable for their action upon 
the various bodies is brought about by the application of 
heat or by means of liquid solvents. We have, consequently, 
1, Heagents in the wet way; and 2, Reagent* in the dry way. For 
greater clearness, we subdivide these two principal olasses as 
follows : 



20.] REAGENTS. 61 

A. REAGENTS IN THE WET WAT. 
L SIMPLE SOLVENTS. 

n. ACIDS and HALOGENS. 

a. Oxygen acids. 

b. Hydrogen acids and halogens. 

c. Sulphur acids. 

HI. BASES, METALS, and SULPHIDES. 
a. Oxygen bases and metals. 
6. Sulphides. 

IV, PEKOXIDES. 

V. SALTS. 

a. Of the alkali metals. 

6. Of the alkali-earth metals. 

c. Of the heavy metals. 

TT. COLORING- MATTERS and INDIFFERENT VEGETABLE SUB* 

STANCES. 

. REAGENTS IN THE DBY WAT. 
I. FLUXES. 
n. BLOWPIPE REAGENTS. 

A. REAGENTS IN THE WET WAT. 

L SIMPLE SOLVENTS. 

Simple solvents are fluids which do not enter into real 
chemical combination with the bodies dissolved in them. 
They will accordingly dissolve any quantity -of matter up to 
a certain limit, which is called the point of saturation, and is 
dependent upon the temperature of the solvent. The essential 
and characteristic properties of the dissolved substances 
(taste, reaction, color, etc.) are not destroyed by the solvent 
(see 2). 



52 REAGENTS. [ 3L 

21. 

1. WATEE, H a O. 

Preparation. Pure water is obtained by distilling well- 
water from a copper still, with head and condenser made of 
pure tin (not as well from a glass retort). The distillation is 
carried to about three fourths of the quantity operated upon. 
If it is desired to have the distilled water perfectly free from 
carbonic acid and ammonium carbonate, the portions passing 
over first must be rejected. In the larger chemical labora- 
tories, distilled water is obtained from the steam apparatus 
which serves for drying, etc. In many cases, rain-water col- 
lected in the open air may be substituted for distilled water.* 

Tests. Water must be colorless, odorless, and tasteless. It 
should not change the color of test-papers, and should not leave 
the smallest residue when evaporated in a platinum vessel. It 
should not be changed by ammonium sulphide (copper, lead, 
iron), nor rendered turbid by baryta-water (carbonic acid). 
Even after long standing, no cloudiness should be caused by 
the addition of ammonium oxalate (lime), of barium chloride 
and hydrochloric acid (sulphuric acid), of silver nitrate and 
nitric acid (chlorides). Tested with potassium iodide, starch 
paste, and dilute sulphuric acid, there should be no blue col- 
oration after standing a short time (nitrous acid), and it should 
not give a yellow color (ammonia) with an alkaline solution of 
potassium mercuric iodide (NESSLER'S reagent). A water which 
is free from reducing inorganic compounds may be tested for 
organic substances by coloring it very pale red with a trace of 
potassium permanganate, heating it to boiling, and observing 
i the reddish color remains, as is the case with pure water. 

Uses. We use water t as a simple solvent for a great 
variety of substances. A supply of it is kept in large glass 
flasks or in stoneware vessels. The most convenient way of 
using it is with the washing-bottle (see 7, Fig. 3 or 4), by 

* As regards the preparation of water absolutely free from organic matter, 
aee STAB, Zeitschr. f. analyt. Chem., 6, 417. 

f In analytical experiments we use ouly distilled water. Whenever, there. 
fore, the term water occurs in the present work, distilled water is meant. 



22.] ETHYL ALCOHOL. 53 

which means, a stronger or finer stream may be obtained. It 
also serves to precipitate substances which are insoluble in it 
from their solution in alcohol, strong acids, and other solvents, 
and also to effect the decomposition of several normal metallic 
salts (more particularly antimony trichloride and the salts of 
bismuth), in which case, the water combines with a part of the 
acid, while the remainder is contained in the basic salt which 
separates. 

22. 
2. ETHYL ALCOHOL, C a H B OH. 

Preparation. For chemical analysis are needed, first, al- 
cohol of .830 to .834 sp. gr. at 15.5, corresponding to 91.17 
to 90 per cent by volume (or the commercial " 95 per cent " 
alcohol) ; and second, absolute alcohol. The latter is most con- 
veniently prepared by digesting in a distilling flask, for two 
or three days, 1 part of fused calcium chloride with 2 parts of 
commercial spirit of about 96 per cent by volume, until solu- 
tion has taken place, then distilling slowly and fractionating. 
As long as the distillate has a lower specific gravity than .8037 
(corresponding to 98 per cent by volume), it may serve as 
absolute alcohol. The subsequent portions are collected 
separately. 

Tests. Alcohol must be colorless, and must completely 
volatilize when heated upon the water-bath. It ought not to 
leave a smell of fusel-oil when rubbed between the hands* 
nor should it alter the color of moist blue or red litmus-paper. 
When kindled, it must burn with a faint bluish, barely per- 
ceptible flame. To test it for traces of tar, it is mixed with 
3 volumes of water, when, after the disappearance of air- 
bubbles, it must remain clear, not opalescent. Hydrogen 
sulphide water should give neither a coloration nor a precipi 
tation. 

Uses. Alcohol serves (a) to effect the separation of 
bodies soluble in this fluid from others which do not dissolve 
in it, e.g., of calcium nitrate from strontium nitrate ; (6) to 
precipitate from aqueous solutions many substances which 
are insoluble in dilute alcohol, e.g., gypsum, calcium malate; 



54 BEAGENT9. L8 ^. 

(c) to produce various kinds of ether, e.g., ethyl acetate, 
which is characterized by its peculiar and agreeable smell ; 

(d) to reduce, usually -with the co-operation of an acid, cer- 
tain peroxides and metallic acids, e.g., lead dioxide, chromic 
acid, etc. ; (e) to detect certain substances which impart a 
characteristic tint to its flame, especially boric acid, stron- 
tium, potassium, sodium, and lithium. 

23. 

3. ETHIL ETHEB, (C tt E,) 4 (X 

4. CHLOBOFOBH, CHOI,. 

5. OABBON DISULPHIDE, CS r 

Of these solvents, ether is the most frequently used. In 
the analysis of inorganic substances, it serves (mixed with 
absolute alcohol) for the separation of the nitrates of barium 
and strontium from calcium nitrate, for the recognition of 
chromic acid by means of hydrogen peroxide, for the detec- 
tion and separation of bromine and iodine, for extracting 
ferric sulpho cyanide from its aqueous solutions, etc. Ether 
is extensively used in the investigation of substances con- 
taining organic compounds, especially in searching for alka- 
loids in cases of poisoning. Chloroform is similarly used, 
but not so frequently. This serves, as does also carbon 
disulphide, especially for the detection and separation of bro- 
mine and iodine, and both these solvents are to be preferred 
to ether for this purpose. 

These preparations are far more readily prepared on a 
large than on a small scale, and are consequently best 
obtained by purchase. 

Tests. Ether must be colorless, must have a specific 
gravity of .720 to .725 at 17.5, and it should require about 
12 parts of water for solution. The solution ought not to 
change the color ct test-papers. Even at the common tem- 
perature, ether must rapidly and completely evaporate on a 
watch-glass, and it is especially important that it should 
leave no residue with an odor when thus treated. When 
shaken with a drop of bright mercury, it ought not to blacken 



24,] AOIDS AND HALOGENS. 55 

this, nor produce the separation of any black, pulverulent 
mercuric sulphide. If some solid potassium hydroxide is 
covered with ether in a test-tube and a little water is added, 
no brown color should appear, even after a long time. If 
ether is poured slowly, with cooling, into concentrated sul- 
phuric acid, it ought to dissolve without coloration. If it 
is shaken with some potassium iodide solution containing 
a few drops of acetic acid, there should be no coloration 
produced, due to the separation of iodine. In keeping ether, 
it should be protected from the action of light 

CUoroform must be transparent and colorless and have a 
specific gravity of from 1.490 to 1.493 at 15. Shaken with 
2 volumes of water, its volume must not be perceptibly 
diminished, and the water should not assume an acid reaction 
nor should it be made turbid by the addition of silver nitrate 
solution. Even at the common temperature, chloroform 
must readily and completely evaporate on a watch-glass. 

Carbon disvlphide should be colorless, completely volatile 
at the common temperature, and exercise no action upon lead 
carbonate or upon moistened, blue litmus-paper. 



II. AOEDS AM) HALOGENS. 
24. 

The acids, at least those of pronounced character, are 
soluble in water. The solutions taste sour and redden lit- 
mus. Acids are divided into oxygen acids, hydrogen acids, 
and sulphur acids. 

The oxygen adds (anhydrides), resulting generally from the 
combination of a non-metallic element with oxygen, combine 
-with water in definite proportions according to the views 
of dualistic chemistry to form acid hydrates. It is with the 
latter that we have most to do. They are contained in the 
aqueous solutions of acid ; they are usually designated by 
the names of the free acids, because the union of the water 
does not take away the acid properties. If they act upon 
metallic oxides, the oxide takes the place of the water of 
bydration, and an oxygen salt results : H a O.SO, + K S O = 



66 REAGENTS. 



[ 24. 



K a O.SO 9 + H a O. If such salts arise from the combination of 
the acid with a strong base, the salts react neutral, provided 
that the acid, also, was a strong one. If, on the other hand, 
the base was a weaker one, for example, the oxide of a heavy 
metal, then the salts react acid. The latter are nevertheless 
called neutral (normal) salts, if the proportion of the oxygen 
of the base to the oxygen of the acid remains the same as 
is observed in the recognized neutral salts of the same acids, 
that is, if it corresponds to the saturating capacity of the 
acid. Sulphate of potash, K 3 O.SO 8 , reacts neutral; blue 
vitriol, CuO.S0 3 .5H 3 O, reacts acid. The latter, however, is 
called neutral (normal) sulphate of copper, because the oxygen 
of the copper oxide is to that of the sulphuric acid in the 
ratio 1 : 3, that is, in the same ratio in which the oxygen of the 
potash stands to that of the sulphuric acid in sulphate of 
potash, which is known to be neutral. 

According to more recent chemical views, it is not the 
acid anhydrides that are called acids, but the compounds- 
which are characterized in dualistic chemistry as acid 
hydrates, and the formation of salts takes place by the 
replacement of hydrogen atoms by metallic atoms : H 9 SO 4 + 
Zn = ZnS0 4 + H 9 . 

The hydrogen acids arise from the combination of the 
halogens with hydrogen. Most of them show the character 
of acids in a pronounced degree. They neutralize oxygen 
bases, forming halogen salts and water : 2H01 + Na a O = 
2Na01 + H a O ; 6H01 + Fe,0 8 = Fe 9 01 6 + 3H a O. The halo- 
gen salts which proceed from the action of strong hydrogen 
acids upon strong bases react neutral, while the solutions of 
those which are produced by the action of strong hydrogen 
acids upon weak bases (for example, alumina and ferric 
oxide) react acid. 

The sulphur adds result more frequently from the combi- 
nation of metallic than of non-metallic elements with sulphur. 
They combine in the sense of dualistic chemistry with sul- 
phur bases to form sulphur salts : As t S B -f- 3Na 2 S = 8Na a S. 
As 4 S a . The sulphur acids are therefore analogous to the 
oxygen acids, and from the standpoints of dualistic and 
modern chemistry, the ways of viewing them vary in the same- 
way from each other as in the case of the oxygen acids di? 



'25.] SULPHURIC AOID. 67 

cussed above. Since the sulphur acids are weak, all the 
sulphur salts which are soluble in water react alkaline. 



a. OXYGEN AOIDS. 
25. 

1. SULPHUEIC Aero, H a SO 4 . 

We use 

a. Concentrated sulphuric acid of commerce, so-called oU of 
vitriol Colorless, sometimes also pale yellowish, oily liquid 
of 1.830 to 1.833 sp. gr. 

b. Concentrated pure sulphuric acid. Colorless, oily liquid 
of 1.836 to 1.840 sp. gr. 

I will here state that pure sulphuric acid is now so easily 
obtained from factories where platinum apparatus is em- 
ployed, that the chemist in the laboratory is seldom required 
to prepare it for himself. Moreover, the preparation from 
glass retorts is disagreeable, and not entirely free from dan- 
ger. For the production of chemically pure sulphuric acid 
from the common acid, however, I recommend the following 
methods : 

a. Put 1000 g of ordinary concentrated sulphuric acid in 
a porcelain dish, add 3 g of ammonium sulphate, and heat 
till copious fumes of sulphuric acid begin to escape, in order 
to destroy the oxides of nitrogen which are present. After 
cooling, add 4 or 5 g of coarsely powdered manganese di- 
oxide, and heat to boiling, with stirring (BLONDLOT), in order 
4o convert any arsenious acid into arsenic acid. When cool, 
pour off the clear fluid, by means of a long funnel-tube, into a 
retort coated with clay. The retort should not be more than 
half full, and is to be heated directly over charcoal. To 
prevent bumping, rest the retort on an inverted crucible cover, 
-so that the sides may be more heated than the bottom. The 
neck of the retort must reach so far into the receiver that the 
acid distilling over drops directly into the body. To cool the 
receiver by means of water is unnecessary and even danger- 
ous. To prevent the receiver coming into actual contact with 
the hot neck of the retort, some asbestus in large fibers is 



8 BEAGENTS. [ 25 ' 

placed between them. When about 10 or 15 g have been 
driven over, change the receiver, and slowly distil off three 
fourths of the contents of the retort. This method depends, 
on the fact discovered by BUSSY and BUIGNET, that, on dis- 
tilling sulphuric acid which contains arsenic in the form of 
arsenic acid, an arsenic-free distillate is obtained. 

# Pour into 4 parts of water 1 part of concentrated sul- 
phuric acid, and conduct into the mixture for some time a 
slow stream of hydrogen sulphide, keeping the fluid heated 
to 70. Let the mixture stand at rest for several days, then 
decant the clear supernatant fluid from the precipitate, which 
consists of sulphur, lead sulphide, perhaps also arsenic sul- 
phide, and heat the decanted fluid in a tubulated retort, with 
upturned neck and open tubulure, until sulphuric acid 
fumes escape with the aqueous vapor. The acid so purified 
is fit for many purposes of chemical analysis. If it is wished, 
however, to free it from non-volatile substances also, it may 
be distilled from a coated retort as in a. As soon as the 
drops in the neck of the retort become oily, the receiver is, 
changed, and the concentrated acid which then passes over is 
kept in a separate vessel. 

c. Common dilute sulphuric acid. To 5 parts of water in 
a lead or porcelain dish add gradually and while stirring, 1 
part of the concentrated sulphuric acid. 

Tests. Pure sulphuric acid must be colorless. When a 
colorless solution of ferrous sulphate ,is poured upon it in a 
test-tube, no brown tint must mark the plane of contact of 
the two fluids (nitric acid, nitrous acid, nitrogen peroxide, 
perhaps also selenium). If the coloration is due to an oxygen 
compound of nitrogen, it will disappear by heating ; if it is 
due to selenium or one of its acids, selenium separates as 
a red precipitate by heating. When diluted with 20 parts 
of water, it must not impart a blue tint to a solution of 
potassium iodide mixed with starch paste (nitrons acid, 
nitrogen peroxide). Mixed with pure zinc and water, it must 
yield hydrogen gas, which on being passed through a red- 
hot tube, must not deposit the slightest trace of arsenic. It. 
must leave no residue upon evaporation on platinum, and 
must remain perfectly clear upon dilution with 4 or 5 
Darts of alcohol (lead, iron, calcium). The presence of small 



25.] SULPHURIC AOID. 59' 

quantities of lead is detected most easily by adding some 
hydrochloric acid to the sulphuric acid in a test-tube. If the 
plane of contact is marked by turbidity (lead chloride), lead 
is present. Sulphurous acid is discovered by the odor after 
shaking the acid in a half-filled bottle, or by finding if the 
acid diluted with water decolorizes water which is colored 
blue with iodized starch. The simplest way to test for am- 
monia is by means of NESSLER'S reagent ( 96), after the acid 
has been largely diluted with water and the solution made 
somewhat alkaline with potassium hydroxide. 

Uses. Sulphuric acid has for most bases a greater affinity 
than almost any other acid. It is therefore used principally 
for the liberation and expulsion of other acids, especially 
phosphoric, boric, hydrochloric, nitric, and acetic acids. The 
great affinity of sulphuric acid for water is the cause of the 
decomposition of many bodies which cannot exist without 
water (e.g., oxalic acid), when they are brought into contact 
with concentrated sulphuric acid. The nature of the decom- 
posed body may in such cases be inferred from the products 
of decomposition. Sulphuric acid is also used for the evolu- 
tion of certain gases, more particularly of hydrogen and hy- 
drogen sulphide. It also serves as a special reagent for the 
detection and precipitation of barium, strontium, and lead. 

The kind of sulphuric acid (whether pure or common 
commercial, whether concentrated or dilute) that should 
be used in each case is shown by a consideration of the 
circumstances, and, moreover, it will be generally stated 
in this book. In using common oil of vitriol, it should be 
borne in mind that where the sulphurous acid used for its. 
manufacture is made from pyrites it may be very much con- 
taminated with the acids of arsenic. Such arseniferous 
sulphuric acid cannot be used for finer analytical purposes, 
and it is not at all adapted for the evolution of hydrogen ; 
for when the diluted acid acts upon zinc, hydrogen arsenide 
is given off with the hydrogen. 



w REAGENTS* 



2. NITKEC ACID, HN0 8 . 

Preparation. a. Take crude nitric acid of commerce, as 
free as possible from chlorine, and of a specific gravity of ai 
least 1.31 (a weaker acid will not answer the purpose), heat 
it to boiling in a glass retort, with addition of some potassium 
nitrate ; let the distillate run into a receiver kept cool, and 
find from time to time whether, after dilution, it still continues 
to precipitate or cloud solution of silver nitrate. As soon as 
this ceases to be the case, change the receiver, and distil 
until a trifling quantity only remains in the retort. Dilute 
the distillate with water until the specific gravity is 1.2. 

b. Dilute crude nitric acid of commerce, of about 1.38 
sp. gr., with two fifths of its weight of water, and add 
solution of silver nitrate as long as a precipitate of silver 
chloride continues to form ; then add a further slight excess 
of solution of silver nitrate, let the precipitate subside, de- 
cant the perfectly clear, supernatant acid into a retort or an 
alembic with a ground head ; add some potassium nitrate free 
from chlorine, and distil until only a small quantity remains, 
taking care to attend to the proper cooling of the vapors dis- 
tilling over. Dilute the distillate, if necessary, with water 
until it has a specific gravity of 1.2. 

Tests. Pure nitric acid must be colorless, and leave no 
residue upon evaporation on platinum foil. Solution of 
silver nitrate or of barium nitrate must not cause the slight- 
est turbidity in it when diluted with at least 3 parts of water. 
To test more accurately for sulphuric acid and to test for iodic 
acid, a somewhat larger amount is evaporated in a porcelain 
dish over an alcohol-lamp (not a gas-lamp) to a small volume. 
This is taken up with water, and a portion of the solution 
is tested with barium nitrate. Some carbon disulphide is 
added to the remainder of the liquid, a very minute quantity 
of 'hydrogen sulphide water or aqueous solution of sulphur- 
ous acid is added, and, after shaking, any violet coloration 
of the carbon disulphide is observed. Lower oxides of 
nitrogen are recognized by the fact that the acid, diluted 



27,] ACETIC ACID. 61 

with 5 parts of water, is instantly made blue by a solution 
of starcli paste and potassium iodide. These lower oxides 
are removed by passing air or carbonic acid through the 
moderately warm acid. The presence of silver is detected 
by the addition of hydrochloric acid to the diluted acid, and 
the occasional presence of selenious acid is detected by 
evaporating off the nitric acid and heating the residue with 
hydrochloric and sulphurous acids. 

Uses. Nitric acid serves as a chemical solvent for metals, 
oxides, sulphides, oxygen salts, etc. With metals and sul- 
phides of metals, the acid first oxidizes the metal present, at 
the expense of part of its own oxygen, and dissolves it as 
nitrate. Most oxides are dissolved by nitric acid at once 
as nitrates, and so are most of the insoluble salts with 
weaker acids, the latter being expelled in the process by the 
nitric acid. Nitric acid also dissolves salts with soluble 
non-volatile acids, as calcium phosphate, with which it 
forms calcium nitrate and acid calcium phosphate, Nitric 
acid is used also as an oxidizing agent, e.g., to convert 
ferrous salts into ferric salts, stannous salts into stannic 
salts, etc.; also for the recognition of certain alkaloids which 
produce characteristic color-reactions with nitric acid, 



27. 
3. AGETIO AOID, HO a H a O fl . 

Since a very concentrated acetic acid is never needed in 
qualitative analysis, the dilute acid of commerce suffices for 
the purpose. This is obtained, by the distillation of pure 
sodium acetate with sulphuric acid and some water, of 1.040 
sp. gr., corresponding to a contents of 29 per cent acetic 
acid. 

Testa. Pure acetic acid must leave no residue upon evap- 
oration, and, after saturation with sodium carbonate, emit 
no empyreumatic odor. Hydrogen sulphide, solution of 
silver nitrate, and solution of barium nitrate must not color 
or cloud the dilute acid, nor must ammonium sulphide after 
neutralization of the acid by ammonia. Solution of indigo 



62 REAGENTS. [ 28* 

must not lose its color when heated with the acid. Empy- 
reumatic matter is best detected by neutralizing the acid 
with sodium carbonate, and adding solution of potassium 
permanganate. If the acid is free from empyreumatic mat- 
ter, no decolonisation takes place in the course of ten 

minutes. 

If the acid is not pure, add some sodium acetate and re- 
distil from a glass retort, not quite to dryness. If it contains 
sulphur dioxide (in which case hydrogen sulphide will pro- 
duce a white turbidity in it), digest it first with lead dioxide 
or finely pulverized manganese dioxide, and then distil, not 
fully to dryness, with sodium acetate. 

Uses. Acetic acid possesses a greater solvent power for 
some substances than for others. It is used, therefore, to 
distinguish the former from the latter. It thus serves to 
distinguish calcium oxalate from calcium phosphate. Acetic 
acid is used also to acidulate fluids where it is wished to 
avoid the employment of mineral acids. 



28. 
4. TABTARIO ACID, H a C 4 H 4 O 6 . 

The tartaric acid of commerce may be sufficiently pure. 
It must dissolve clear in water, and the diluted solution 
should not be colored, made turbid, nor a precipitate be 
formed by the addition of hydrogen sulphide, barium chlo- 
ride, calcium sulphate, or silver nitrate solutions. The solu- 
tion, when made alkaline with ammonia, ought not to be 
colored or made turbid by either ammonium sulphide or 
ammonium oxalate. The tartaric acid should leave no resi- 
due when burnt in a platinum dish. It is kept in powder, 
as its solution suffers decomposition after a time, with the 
formation of mould. For use, it is dissolved in a little water 
with the aid of heat. 

Uses. The addition of tartaric acid to solutions of salts 
of various metals, especially of iron and aluminium, prevents 
the usual precipitation of these metals by an alkali. This, 
non-precipitation is owing to the formation of double tar- 



29.] HYDROCHLOEIO ACID. 63 

trates, which are not decomposed by alkalies. Tartaric acid 
may therefore be employed to effect the separation of these 
metals from other bodies, the precipitation of which it does 
not prevent. Tartaric acid forms a difficultly soluble salt 
with potassium, but not so with sodium. It is therefore one 
of our best reagents to distinguish between the two metals. 
Acid sodium tartrate, HNaC 4 H 4 O 6 , answers the latter pur- 
pose still better than the free acid. This reagent is prepared 
by dissolving one of two equal portions of tartaric acid in 
water, neutralizing with sodium carbonate, then adding the 
other portion of the acid, and evaporating the solution to the 
crystallization point. For use, 1 part of the salt is dissolved 
in about 10 parts of water. 



b. HYDROGEN ACIDS AND HALOGENS. 

29. 
1. HYDBOOHLOBIC ACID, HC1. 

Preparation. Pour a cooled mixture of 7 parts of con- 
centrated sulphuric acid, which contains neither arsenic nor 
oxides of nitrogen (see 25), and 2 parts of water over 4 
parts of sodium chloride in a retort ; expose the retort, with 
slightly raised neck, to the heat of a sand-bath until the 
evolution of gas ceases ; conduct the evolved gas, by means 
of a bent tube, into a flask containing 6 parts of water, and 
take care to keep this vessel constantly cool. To prevent the 
gas from receding, the tube ought to dip but about 2 mm 
into the water of the flask. "When the operation is terminated, 
try the specific gravity of the acid produced, and dilute with 
water until it marks from 1.11 to 1.12. Pure hydrochloric 
acid can also be prepared from the crude acid of commerce, 
which at present usually contains arsenic. For this purpose, 
a concentrated solution of stannous chloride is added to it in 
sufficient amount so that after twenty-four hours a portion of 
the acid will give a white precipitate with mercuric chloride 
an indication that the stannous chloride is present in excess. 
The resulting brown precipitate, containing all the arsenic and 
some tin, is allowed to settle, and the acid is separated from 



64 



BEAGENTS. [ 



the precipitate by decantation or, if necessary, by filtration 
through asbestus. The acid is brought into a retort with the 
addition of from 1 to 5 per cent of sodium chloride, according 
to the amount of sulphuric acid that it contains ; then placing 
60 parts of water in the receiver for every 100 parts of con- 
centrated acid, and without luting the receiver to the retort, 
it is distilled until nearly all the acid has gone over. 

Tests Hydrochloric acid must be perfectly colorless and 
leave no residue upon evaporation. If it turns yellow on 
evaporation, ferric chloride is probably present, but organic 
substances may also give a similar color. It must not impart 
a blue tint to a solution of potassium iodide mixed with starch 
paste (chlorine or ferric chloride), must not destroy indigo- 
blue (chlorine), nor discolor a fluid made faintly blue with 
iodized starch (sulphur dioxide). Barium chloride ought not 
to produce a precipitate in the highly diluted acid (sulphuric 
acid). Small traces of sulphuric acid, however, cannot be 
discovered in this manner. If such are to be tested for, a 
considerable quantity of the hydrochloric acid should be 
evaporated on the water-bath over an alcohol-lamp (not a 
gas-lamp) to a very small residue, and this, after taking it up 
in water, should be tested with barium chloride solution. 
Hydrogen sulphide must leave the diluted acid unaltered 
(arsenious acid, possibly also selenious acid or stannic 
chloride). After neutralization with ammonia, ammonium 
sulphide must produce no change in it (iron, thallium). With 
zinc which is free from arsenic, it must evolve pure (arsenic- 
free) hydrogen. 

Uses. Hydrochloric acid serves as a solvent for many 
substances. It dissolves many metals and sulphides of 
metals as chlorides, with evolution of hydrogen or of hydro- 
gen sulphide. It dissolves metallic oxides and peroxides in 
the form of chlorides, in the latter case usually with libera- 
tion of chlorine. Salts with insoluble or volatile acids are 
also converted by hydrochloric acid into chlorides, with sep- 
aration of the original acid. Thus, calcium carbonate is con- 
verted into calcium chloride, with liberation of carbon di- 
oxide. Hydrochloric acid dissolves salts with non-volatile 
and soluble acids apparently without decomposing them (e.y., 
calcium phosphate); but the fact is that in cases of this kind 



30.] CHLORINE AJSTD CHLORINE WATER. 65 

a metallic chloride and a soluble acid salt of the acid of the 
dissolved compound are formed. For instance, in the case 
of calcium phosphate, calcium chloride and acid calcium 
phosphate are formed. With salts of acids forming no solu- 
ble acid compound with the base present, hydrochloric acid 
forms metallic chlorides, the liberated acids remaining free 
in solution (calcium oxalate). Hydrochloric acid is also ap- 
plied as a special reagent for the detection and separation of 
silver, mercury (of mercurous salts), and lead, and likewise 
for the detection of free ammonia, with which it produces in 
the air dense white fumes of ammonium chloride. 



30. 
2. OHLOETNE (01) AND CHLOBINE WATEB. 

Preparation. Mix 18 parts of coarse common salt with 
15 parts of Jindy pulverized, good manganese dioxide, free 
from calcium carbonate ; put the mixture into a flask, pour a 
completely cooled mixture of 45 parts of concentrated sulphuric 
acid (oil of vitriol) and 21 parts of water upon it, and shake 
the flask. A uniform and continuous evolution of chlorine 
gas will soon begin, which, when slackening, may be easily 
increased again by the application of geritle heat. This 
method of WIGGERS is excellent, and can be highly recom- 
mended. To prepare chlorine water, conduct the chlorine 
gas evolved, first through a flask containing a little water, 
then into a bottle filled with cold water, and continue the 
process until the fluid is saturated. Where it is desired to 
obtain chlorine water quite free from bromine, the washing 
flask is changed after about one half of the chlorine has been 
expelled, and the gas which now passes over is conducted 
into a fresh bottle filled with water. If the chlorine water is 
to be quite free from hydrochloric acid, the gas must be 
passed through a U-tube containing manganese dioxide, or y 
according to HAMPE'S directions, through an aqueous solution 
of potassium permanganate. The chlorine water must be 
protected from the action of light, since, if this precaution is 
neglected, it speedily suffers complete decomposition, being 



36 REAGENTS. [ 30 - 

converted into dilute hydrochloric acid, with evolution of 
oxygen (resulting from the decomposition of water). Smaller 
quantities, intended for use in the laboratory, are best kept 
in a stoppered bottle, protected by a case of pasteboard, or 
else in a black bottle. 

Small quantities of chlorine can be conveniently prepared, 
in an appropriate generating apparatus, by allowing hydro- 
chloric acid, diluted with an equal volume of water, to act 
slowly in the cold upon cubes which are prepared, according 
to the directions of CL, WINELEB, from 1 part of plauter-of- 
Paris and 3 parts of bleaching-powder, with the addition of 
enough water, so that, by mixing, a moist, friable mass is 
produced.* 

Tests. Chlorine water must have a very strong odor of 
chlorine, and must volatilize completely when heated in a 
porcelain dish. It should contain no, or almost no, free 
hydrochloric acid. After having been shaken with some 
metallic mercury until the chlorine odor has disappeared, ^'t 
should therefore give a filtrate which is at most only weakly 
acid. If chlorine water is shaken with carbon disulphide and 
finely divided zinc, the carbon disulphide should not be 
colored brownish red, not even transiently (bromine). 

Uses. Chlorine has a greater affinity for hydrogen and for 
most metals than either iodine or bromine. Chlorine water 
is therefore an efficient agent to effect the expulsion of iodine 
and bromine from their compounds. Chlorine serves, more- 
over, to effect the solution of certain metals (gold, platinum), 
to decompose metallic sulphides, to convert sulphurous acid 
into sulphuric acid, ferrous into ferric compounds, etc., and 
also to effect the destruction of organic substances, as in 
presence of these it withdraws hydrogen from the water, thus 
enabling the liberated oxygen to combine with the vegetable 
matters and to effect their decomposition. For the latter pur- 
pose, it is often advisable to evolve the chlorine in the fluid 
which contains the organic substances, and this is effected by 
adding hydrochloric acid to the fluid, heating the mixture, and 
then adding potassium chlorate. This gives rise to the forma- 
tion of potassium chloride, water, free chlorine, and chlorine 
peroxide, which acts in a manner similar to chlorine. 

* Zeitschr. f . aiialyt. Chem., 26, 352. ~* 



| 31, 32.] HYDROFLUOSILICIC AOID, 67 

31. 

3. NiTBO-HYDEOOHLOEio ACID, or Aqua regia. 

Preparation. Mix 1 part of pure nitric acid with from 3 
to 4 parts of pure hydrochloric acid. 

Uses. Nitric acid and hydrochloric acid decompose each 
other, the decomposition resulting in the formation of free 
chlorine, nitrosyl chloride, and water : 3HC1 -f HNO 3 = 201 + 
NOC1 -j- 2H a O. This decomposition ceases as soon as the 
fluid is saturated with the gases, but it recommences at once 
when this state of saturation is disturbed by heating or by 
combination of the chlorine. The presence of free chlorine, 
and also, in a subordinate degree, that of the nitrosyl 
chloride, make aqua regia our most powerful solvent for 
metals (with the exception of those which form insoluble 
compounds with chlorine). Nitro-hydrochloric acid serves 
principally to effect the solution of gold and platinum, which 
are metals insoluble both in hydrochloric and in nitric acid, 
and also to decompose various metallic sulphides, e.g., cinna- 
bar, pyrites, etc. 

32. 

4. HYBROPLUOSIUOIO AOTD, H a SiF fl , 

Preparation. Take 1 parts of powdered glass, or 1 part 
of powdered, ignited flint, or 1 part of quartz sand. "Whichever 
is used, it must be washed free from every particle of dust, 
and then ignited. Mix intimately with 1 part of perfectly 
dry fluor-spar in powder,* pour 6 parts of concentrated 
sulphuric acid over the mixture in a retort, which it is ad- 
visable to coat with clay, and mix carefully by shaking the 
vessel. As the mixture swells up when getting warm, it 
must at first fill the retort only to one third. The neck of 
the retort is connected air-tight with a small tubulated 
receiver, and the tubulure of the latter again, by means of 

* If the fluor-spar contains organic substances or metallic sulphides, it la 
to be previously iguited with access of air 



68 REAGENTS. [ 

India-rubber, with a wide glass tube bent twice at right angles. 
To the descending limb of the glass tube a funnel is attached 
by means of a rubber tube, and this funnel is lowered into a 
beaker containing 4 parts of water. By moderately heating 
the retort over charcoal or over a gas-lamp, promote the dis- 
engagement of gaseous silicon fluoride, which commences 
even in the cold. Towards the end of the process, a pretty 
strong heat should be applied. Every gas-bubble produces 
in the water a precipitate of silicic acid, with simultaneous 
formation of hydrofluosilicic acid : 3SiF 4 + 2H 3 O= 2H a SiP e + 
SiO a . The precipitated silicic acid renders the liquid gelat- 
inous, and it is for this reason that the aperture of the 
descending limb of the tube cannot be allowed to dip directly 
into the water, since it would in that case speedily be choked. 
It sometimes happens in the course of the operation, espe- 
cially towards the end, that complete channels of silicic acid 
are formed in the gelatinous liquid, through which, if the 
liquid is not occasionally stirred, the gas gains the surface 
without undergoing decomposition. When the evolution of 
gas has completely ceased, throw the gelatinous paste upon a 
linen cloth, squeeze the fluid through, and filter it afterwards. 
It is most advantageously preserved for use in bottles of 
hard rubber. 

Tests. Hydrofluosilicic acid must volatilize completely 
when heated in a platinum dish. Its dilute aqueous solution 
ought not to be precipitated with hydrogen sulphide, and it 
ought to produce no precipitate in the solution of a strontium 
salt (strontium sulphate). 

Uses. Bases decompose with hydrofluosilicic acid, form- 
ing water and metallic silicofluorides. Many of these are 
insoluble, while others are soluble. The latter may therefore- 
be distinguished from the former by means of this reagent. 
In the course of analysis, hydrofluosilicic acid is applied 
simply for the detection and separation of barium. 



33.] 



HYDBOGEN SULPHIDE. 



c. SULPHUE ACIDS. 

33. 

1. HYDROGEN SULPHIDE, Hydrosulphuric Acid, or 
Sulphuretted Hydrogen, H 3 S. 

Preparation. Hydrogen sulphide is usually * evolved from 
iron sulphide, which is broken into small lumps and then 
treated with dilute sulphuric or hydrochloric acid. Fused 
iron sulphide may be purchased cheaply, or may be made by 
heating iron turnings, or iron nails 3 or 4 cm long, in a 
covered Hessian crucible to a bright red heat, and then adding 




FIG. 83 

small lumps of roll-sulphur until the entire contents of the 
crucible are in fusion. As soon as this is the case, pour the 
fused mass upon sand, or into an old Hessian' crucible ; or 
make a hole in the bottom of the crucible, when the iron 
sulphide will run through as fast as it forms, and may be 
received in a shovel placed in the ash-pit ; or introduce an 
intimate mixture of 30 parts of iron filings and 21 parts 

* The evolution of hydrogen sulphide for Judicial purposes will be dis- 
cussed in the section which treats of the detection of poisonous metals in parts 
of dead bodies, etc 



70 REAGENTS. L8 rfrf - 

of flowers of sulphur in small portions into a red-hot 
crucible, awaiting always the incandescence of the portion 
last introduced before proceeding to the addition of a fresh 
one. When the whole mixture has thus been put into the 
crucible, cover the latter closely, and expose it to a more 
intense heat, sufficient to make the iron sulphide fuse more 

or less. 

The evolution of the gas may be effected in the apparatus 
illustrated by Fig. 32. Pour water over the iron sulphide in 
a; add concentrated hydrochloric or sulphuric acid, and 
shake the mixture ; the evolved gas is washed in c. When a 
sufficient quantity of gas is evolved, pour the fluid off the still 
undecomposed iron sulphide, rinse the bottle repeatedly with 
water, then fill it with that fluid, and keep it for the next 
operation. If this precaution is neglected, the apparatus 
soon becomes incrusted with ferrous sulphate, and the proper 
evolution of gas is prevented. 

For large laboratories, or for chemists having to operate 
often and largely with hydrogen sulphide, I recommend, if a 
gasometer is not preferred, the apparatus devised by BBTJG- 
NATELLI, modified as shown in Fig. 33. The bulb 5, which is 
provided with a tubulure* at a, contains coarse pieces of glass 
in its neck with iron sulphide in small pieces in its body. 
The rubber stopper closing the neck carries on one side 
the tube s (which under certain conditions can be omitted ; see 
below), on the other side the short tube c, which must be at 
least a centimeter in inside diameter, and which is united by 
means of a short rubber tube with the tube d of the same 
diameter, leading into the bottle A. The tube e reaches 
nearly to the bottom of A, and is connected at the other end 
by means of the rubber tube /with the bottle M. The latter 
bottle is closed by a stopper, which carries a short tube open 
at both ends. The stopper in the tubulure a of the bulb B 
carries a glass tube, which is united by means of a rubber 
tube to the lead pipe g, which carries the gas to its destina- 
tion, and is provided with brass stop-cocks, 7i 9 b, i, i. To set 
the apparatus in operation, a mixture of 1 volume of crude 

* Flasks with a tubulure At the side, such as are commonly used as re- 
ceivers, as shown in BBITGNATELLI'S original diawing (Zeitschr. f. analyt. 
Chem , 6, 390), can also be used, but uie less appropriate. 



S3.] HYDKOGEN 

hydrochloric acid, as free as possible from arsenic, and 2 
volumes of water is put into M, the cock h being opened. 
The liquid enters A, fills the bottle, and rises through d and 




FIG. 88. 

e into the bulb S. As soon as it has almost filled the neck, 
the cock h is closed, and care is taken that M is only about 
half filled. If the cock 6 and one of the cocks i are now 
opened, the acid rises to the iron sulphide in B, the evolution 
of hydrogen sulphide commences, and continues with great 
regularity, because the wide tubes c and d allow the descent 
of the resulting heavier ferrous chloride solution and the 
ascent of new acid to the iron sulphide. If it is desired to 
increase the contact of the acid with the iron sulphide, one 
or more boards are placed under M, thus increasing the 
pressure of the liquid. The stream of gas can be entirely 



72 REAGENTS. , CS 33. 

regulated by raising and lowering the bottle M, as BBTJONA- 
TELLI recommends. However, if the apparatus is to be em- 
ployed for passing the gas into several liquids at the same 
time, as is the case in large laboratories, cocks become neces- 
sary If the apparatus is not to be used for a considerable 
time the bottle M is lowered. The liquid then falls m B, 
and is not in contact with the iron sulphide, so that the 
evolution of gas gradually ceases. If, under this condition, 
hydrogen sulphide is not evolved fast enough in B to fill the 
space previously occupied by the liquid, air goes in through 
the tube a. This tube, if it is used at all (see below), is made 
rather long in order that liquid cannot escape from it when 
the hydrogen sulphide gas has to overcome the pressure of a 
column of water of considerable height. If the iron sulphide 
which is moistened with acid evolves still more hydrogen sul- 
phide after the liquid has passed down, the only consequence 
is that somewhat more acid flows from A into M. The tube 
a can be omitted when cocks are used. In this case, the liquid 
in B sinks more slowly when Jf is lowered, because the space 
occupied by the acid which flows out is filled solely by hydro- 
gen sulphide. In the absence of a cock, however, the tube a 
is necessary, in order to avoid the sucking back of any liquid 
into which hydrogen sulphide is being passed at the time 
when M is lowered. By the use of cocks, this inconvenience 
can be easily avoided by closing 6 before lowering M, The 
gas passing out of i, i is led through wash-bottles or in 
winter through U-shaped tubes filled with cotton. 

When the acid is finally exhausted, Jf is placed lower than 
A ; while if the tube s has been replaced by the air-cock h, the 
latter is opened. All the liquid then goes into Jf, and can be 
poured out. 

If a WOULFE'S bottle with three necks is used as the vessel 
A, a siphon-tube provided with a pinch-cock can be placed 
in the third tubulure, and the ferrous chloride solution col- 
lecting at the bottom can be allowed to flow off from time to 
time. In this case, the lower branch of the tube e should be 
given such a length that it reaches only half-way to the bottom 
of A, so that the hydrochloric acid flowing in does not mix 
with the ferrous chloride solution. 

I am so well satisfied with the performance of this appara- 



33.] HYDliOGEJir SULPHIDE, 73 

tus that I have given up the large lead generator which I 
had used for many years (see the previous editions), and have 
replaced it by the modified BRUGNATELLI'S generator. A lead 
apparatus of essentially improved construction has recently 
been recommended by CL. WINKLEB.* 

The following apparatus, devised by FR. MOHR, depends 
upon the same principle as the one just described, and is 
especially adapted for the evolution of the gas upon a smaller 
scale (Fig. 34). The glass vessel A (commonly used for des- 
iccating gases) has a perforated disk of lead at 6, and 




FIG. 34. 

above is nearly filled with lumps of fused iron sulphide. 
To the end of d is fixed, by means of the rubber tube a, a 
small piece of wide glass tube, which is filled with cotton, 
and is intended to stop any particles of liquid which may be 
spirted up. c is a glass cock with a long wooden handle 
(which may be replaced by a pinch-cock) ; e contains a solu- 
tion of sodium carbonate to prevent the escape of hydrogen 

* Zeitschr. f . analyt. Chem , 21, 886. 



74 



EE A GENTS. 



B38L 



sulphide. The acid used in B is a mixture of common hydro- 
chloric acid with two measures of water. 

Of the many generators which serve the same purpose, 
I will mention only the one proposed by POHL, which is sim~ 
pie and convenient in operation. It is 
shown in Fig. 35. 

The bottle A, containing dilute sul- 
phuric acid, has a capacity of from 2 to 
2.5 1. In the rubber stopper B is the 
heavy glass rod G, the surface of the 
upper part of which is ground. This 
rod should be of at least 9 mm diameter, 
and should be movable by the use of some 
force. It carries upon its lower end the 
perforated basket ^of so-called hard rub- 
ber or of porcelain. This is lined with 
coarse linen, and filled with pieces oi iron 
sulphide. If the glass rod is pushed down 
so far that the iron sulphide just dips 
into the liquid, a slow stream of hydrogen 
sulphide results, which can be increased 
by pushing the basket down further, and 
can be interrupted by removing it from the liquid. The wide 
tube B connecting with the delivery-tube is filled with cotton, 
and takes the place of a wash-bottle. 

Hydrogen sulphide water is usually prepared by conducting 
the gas into very cold water, which has been previously freed 
from air by boiling. The operation is continued until the 
water is saturated with the gas, which may be readily ascer- 
tained by closing the mouth of the flask with the thumb, 
and shaking it a little. If a pressure is felt from within, 
the operation may be considered at an end. Hydrogen sul- 
phide water must be kept in well-closed vessels, otherwise it 
will soon suffer decomposition, the hydrogen being oxidized 
to water and a small portion of the sulphur to sulphuric acid, 
the rest of the sulphur separating. It keeps for a long time 
if put into small bottles immediately after its preparation, 
and these are well corked and inverted into cups filled with 
water. 

Hydrogen sulphide water must be perfectly clear, must 




PIG 85. 



34.] BASES, METALS, AND SULPHIDES. 75 

strongly emit the odor of the gas, and when treated with ferric 
chloride it must yield a copious precipitate of sulphur. Ad- 
dition of ammonia must not impart a blackish appearance to 
it, and upon evaporation on platinum it must leave no residue. 
Uses. Hydrogen sulphide has a strong tendency to undergo. 
double decomposition with metallic oxides, forming water and 
metallic sulphides, and the latter, being mostly insoluble in 
water, are usually precipitated in the process. By modifying 
the conditions of precipitation, we may divide the whole 
of the precipitable metals into groups, as explained in Section 
III, Hydrogen sulphide is, therefore, a very valuable agent 
for separating the metals into the principal groups. Some 
of the precipitated sulphides exhibit characteristic colors, 
indicative of the individual metals which they contain. The 
great facility with which hydrogen sulphide is decomposed 
renders this substance a useful reducing ^gent for many 
compounds. Thus, it serves to reduce ferric r salts to ferrous. 
salts, chromic acid to chromic oxide, etc. la these reduc- 
tions, the sulphur separates in the form of a fine white 
powder. Whether it is better to apply the hydrogen sul- 
phide in the gaseous form or in aquepus solution dependa 
upon circumstances. ' i 



BASES, METALS, AND SULPHIDES. 
34 

The bases are divided into oxygen bases and sulphur 
bases. The first are formed by the union of metals or com- 
pound radicals similar to them with oxygen, the latter from 
the combination of the same with sulphur. * ' . - 

The oxygen bases are classified into alkalies, altfclt earths, 
earths proper, and oxides or hydroxides of the heavy 'metals. 
The alkalies are readily soluble in water ; the alkali earths 
dissolve with greater difficulty in that liquid ; and magnesia, 
the last member of the class, is only very sparingly soluble in 
it. The earths proper and the oxides and hydroxides of the 
heavy metals are insoluble in water or nearly so (except 
thallious hydroxide). The solutions of the alkalies and 
alkali earths are caustic when sufficiently concentrated ; they 



76 REAGENTS. [ 3fi - 

have an alkaline taste, change the yellow color of turmeric- 
paper to brown, and restore the blue tint of reddened litums- 
paper ; they saturate acids completely, so that even the salts 
which they form with strong acids do not change vegetable 
colors, while those with weak acids generally have an alkaline 
reaction. The earths proper and the oxides of the heavy 
metals likewise combine with acids to form salts, but, as a 
rule, they do not entirely take away the acid reaction of the 
latter. 

The svlphwr bases, which result from the combination of 
the metals of the alkalies and alkali earths with sulphur, are 
more or less soluble in water. The solutions react strongly 
alkaline. The remaining sulphur bases are not soluble in 
water. Many sulphur bases form salts with sulphur acids. 

a. OXYGEN BASES. 



a. 



35. 

1. POTASSIUM HYDROXIDE, or Caustic Potash, KOH, and 
SODIUK HYDROXIDE, or Caustic Soda, NaOH. 

The preparation of perfectly pure caustic potash or soda 
is a difficult operation. In addition to perfectly pure caustic 
alkali, therefore, it is advisable to provide some which is not 
quite pure, and some which, being free from certain impuri- 
ties, may in many cases be safely substituted for the pure 
substance. 

a. Common solution of sodium hydroxide. Put into a clean 
cast-iron kettle furnished with a lid, 3 parts of crystallized 
sodium carbonate of commerce and 15 parts of water ; heat to 
boiling, and add, in small portions at a time, thick milk of 
lime prepared by pouring 3 parts of warm water over 1 part 
of quicklime, and letting the mixture stand in a covered 
vessel until the lime is reduced to a uniform mass. Keep 
the liquid in the kettle boiling while adding the milk of 
lime, and for a quarter of an hour longer; then filter 
off a small portion, and determine whether the filtrate still 



35.] POTASSIUM HYDROXIDE. 77 

causes effervescence in hydrochloric acid. If this is the 
case, the boiling must be continued, and if necessary some 
more milk of lime must be added to the fluid. When the 
solution is perfectly free from carbonic acid, cover the 
vessel, allow the fluid to cool a little, and then, by means of 
a siphon filled with water, draw off the nearly clear solu- 
tion from the residuary sediment, and transfer it to a glass 
flask. Boil the residue a second and a third time with water 
find draw off the fluid in the same way. Close the mouth 
of the flask, and allow the lime suspended in the fluid to 
subside completely. Scour the iron vessel clean, pour the 
clear solution back into it, and evaporate it to 6 or 7 parts. 
The solution so prepared contains from 11 to 13 per cent of 
sodium hydroxide, and has a specific gravity of from 1.13 to 
1.15. If it is wished to filter a solution of caustic soda which 
is not quite clear, a covered funnel should be used, which 
has been charged first with lumps of white marble and then 
with powder of the same, the fine dust being rinsed out with 
water before the filter is used (GEAEGER). Solution of caustic 
soda must be clear, colorless, as free as possible from car- 
bonic acid, and ammonium sulphide must not impart a black 
color to it. If tlie lye is treated with hydrogen sulphide, 
then acidified with hydrochloric acid and heated, it should 
yield only a separation of sulphur and no colored precipitate 
(vanadic acid). 

Traces of silicic acid, alumina, boric acid, and phosphoric 
acid, and small amounts of sodium chloride and sodium 
sulphate are usually found in a solution of caustic soda 
prepared in this manner, on which account it is unfit for use 
in accurate experiments. Commercial caustic soda, and the 
solutions prepared from it, usually contain some nitrate 
and nitrite. Solution of caustic soda is kept best in bottles 
closed with ground-glass caps. In default of capped bottles, 
common ones with well-ground stoppers may be used. In 
this case, the neck must be wiped perfectly dry and clean 
inside and the stopper coated with paraffine. If this pre- 
caution is neglected, it will be found impossible after a 
time to remove the stopper, particularly if the bottle is only 
rarely opened. 

b. Potassium hydroxide purified witTi akohol. Dissolve 



78 REAGENTS. 



[ 



some commercial caustic potash in rectified alcohol, in a 
stoppered bottle, by digestion and shaking ; let the fluid stand, 
decant or filter if necessary, and evaporate the clear fluid in a 
silver dish over the gas- or spirit-lamp until no more vapors 
escape, adding from time to time, during the evaporation, 
some water to prevent blackening of the mass. Place the 
silver dish in cold water until it has sufficiently cooled, 
remove the cake of potash from the dish, break it into coarse 
lumps in a hot mortar, and keep in a well-closed glass bottle. 
When required for use, dissolve a small piece in water. 

The potassium hydroxide thus prepared is sufficiently 
pure for most purposes. It contains a minute trace of 
alumina, but is usually free from phosphoric, sulphuric, and 
silicic acids. The solution must remain clear upon addition 
of ammonium sulphide, and this solution, upon being acidified, 
should behave like the sodium hydroxide (see a) ; hydrochloric 
acid must only produce a barely perceptible effervescence in 
it. Upon evaporation to dryness, the solution acidified with 
hydrochloric acid must leave a residue which dissolves in 
water to a clear fluid, and when mixed with ammonia in 
the least possible excess, it must not show any flocks of 
alumina at least until it has stood in a warm place for 
several houro. The solution acidified with nitric acid must 
not give any precipitate with a nitric acid solution of ammo- 
nium molybdate. 

c. Potassium hydroxide prepared with baryta, Dissolve 
pure crystals of baryta ( 37) by heating with water, and add 
to the solution pure potassium sulphate until a portion of the 
filtered fluid, acidified with hydrochloric acid and diluted, no 
longer gives a precipitate on addition of a further quantity of 
the sulphate (16 parts of crystals of baryta require 9 parts 
of potassium sulphate). Let the turbid fluid clear, decant, 
and evaporate in a silver dish as in &. The caustic potash so 
prepared is pure, except that it contains a trifling admixture 
of potassium sulphate, which is mostly left behind upon 
dissolving in a little water. It is but rarely required, how- 
ever, its use being exclusively confined to the detection of 
minute traces of aluminium. 

Uses. The great affinity which the fixed alkalies possess 
for acids renders these substances powerful agents to effect 



g 3tf.] AMMONIA. 79 

the decomposition of the salts of most bases, and consequently 
the precipitation of those oxides or hydroxides which are in- 
soluble in water. Many hydroxides thus precipitated redis- 
solve in an excess of the precipitant, as those of aluminium, 
chromium, and lead ; while others remain undissolved, as 
those of iron, bismuth, etc. The fixed alkalies, therefore, 
serve as a means of separating the former from the latter. 
Caustic potash and soda also dissolve many salts (e.g., 
lead chromate, sulphur compounds, etc.), and thus aid in 
separating and distinguishing them from other substances. 
Many of tLe hydroxides and oxides precipitated by the action 
of potassium or sodium hydroxide exhibit peculiar colors, or 
possess other characteristic properties that may serve to lead 
to the detection of the individual metal which they respectively 
contain. Such are, for instance, the precipitates of man- 
ganous hydroxide, ferrous hydroxide, and mercurous oxide. 
The fixed alkalies expel ammonia from its salts, and enable us 
to detect that body by its odor, its action on vegetable colors, 
etc. In contact with iron and zinc or with aluminium, 
they cause the evolution of hydrogen, which in the nascent 
state converts the nitrogen of nitric and nitrous acids into 
ammonia, etc. 

36. 
2. AMMONIA, NH a . AMMONIUM HYDROXIDE, NH 4 OEL 

Preparation. For preparing the aqueous solution of am- 
monia on a small scale, the following method answers well : * 
Introduce into a flask 4 parts of ammonium chloride, either 
crystallized or in coarse powder, and the dry slaked lime 
prepared from 5 parts of quicklime ; mix by shaking, and cau- 
tiously add enough water to make the powder agglomerate 
into lumps. Set the flask in a sand-bath and connect it with 
a wash-bottle and delivery-tube. Put a very small quantity 
of water in the bottle, and about 10 parts of water in the 
flask destined to absorb the gas. Place the latter in cold 
water, and then begin to apply heat. Evolution of gas 

* I have described a reliable method for its preparation on a large scale in 
tiie Zeitsclirift filr analytische Chemie, 1, 18ft. 



80 BEAGKENTS. [ 36. 

speedily sets in. Continue to heat until no more bubbles 
appear. Open the cork of the flask to prevent the receding of 
the fluid. The solution of ammonia contained in the wash- 
bottle is impure, but that contained in the receiver is pure ; 
dilute the latter with water until the specific gravity is about 
.96 (= 10 per cent of ammonia). Keep the fluid in bottles 
closed with ground stoppers. 

Tests. Solution of ammonia must be colorless, and ought 
not to leave the least residue when evaporated in a platinum 
dish. When heated with an equal volume of lime-water, it 
should cause no turbidity at least not to a very marked ex- 
tent (carbonic acid). It must remain clear when ammonium 
oxalate is added to it. When supersaturated with nitric acid, 
it should yield a colorless solution (pyridine bases). This 
acidified solution should not be rendered turbid by barium 
nitrate or silver nitrate, nor should hydrogen sulphide im- 
part to it the slightest color. By neutralizing it with dilute 
hydrochloric acid, a colorless, odorless liquid (no ernpyreu- 
matic odor) must result. 

Uses. Ammonia-water is actually only a solution of 
ammonia in water. It is, however, sometimes convenient to 
assume that by the union of ammonia with water, ammo- 
nium oxide or ammonium hydroxide forms (2NH S + H a O = 
(NH 4 ) 9 0, r NH 3 + H fl O = NH 4 OH), and that ammonia-water 
contains one of these. Upon this assumption, solution of 
ammonia may be looked upon as a fluid analogous to solu- 
tions of caustic potash and soda, which greatly simplifies the 
explanation of all its reactions, the salts resulting from the 
neutralization of acids bj solution of ammonia being assumed 
to contain ammonium, NE 4 , instead of NH 3 . Ammonia is one 
of the reagents most frequently used. It is especially applied 
for the saturation of acid fluids, and also to eflect the pre- 
cipitation of numerous metallic hydroxides. Many of these 
precipitates redissolve in an excess of ammonia, as, for in- 
stance, the hydroxides of zinc, cadmium, silver, copper, etc., 
while others are insoluble in free ammonia. This reagent 
may therefore serve to separate and distinguish the former 
from the latter. Some of these precipitates, as well as their 
solutions in ammonia, exhibit peculiar colors, which may at 
once lead to the detection of the metal which they contain. 



-'J BARIUM HYDROXIDE. 81 

Many hydroxides which are precipitated by ammonia 
from neutral solutions are not precipitated by this reagent 
from acid solutions, their precipitation from the latter being 
prevented by the ammonium salt formed in the process* 
Compare 56. 

/?. AT.KAT.T EARTHS. 

37. 
1. BARIUM HYDROXIDE, or JBcvryta y Ba(OH) t . 

Preparation. There are many ways of preparing baryta, 
but as witherite (barium carbonate) is now cheaply procur- 
able, I prefer the following: Mix intimately together 100 
parts of finely pulverized witherite, 10 parts of charcoal in 
powder, and 5 parts of rosin ; put the mixture in an earthen- 
ware crucible, lute on the lid with clay, and expose the cru- 
cible so prepared to the heat of a brick-kiln. Break and 
triturate the baked mass, boil repeatedly with water in an 
iron pot, filter into bottles, stopper, and let them stand in the 
cold, when large quantities of crystals of barium hydroxide, 
Ba(OH) a .8H a O, will make their appearance. Let the crys- 
tals drain in covered funnels, dry rapidly between sheets 
of blotting-paper, and keep in well-closed bottles. For 
use, dissolve 1 part of the crystals in 20 parts of water, with 
the aid of heat, and filter the solution. The 'baryta-water- 
so prepared is purer than the mother-liquor running off from 
the crystals. The residue, which is insoluble in water and 
consists of imdecornposed witherite and charcoal, may be 
turned to account in the preparation of barium chloride. 

Tests. Baryta-water must, after precipitation of the barium 
by pure sulphuric acid, give a filtrate remaining clear when 
mixed with alcohol and leaving no fixed residue upon evapora- 
tion in a platinum crucible. After addition of acetic acid to 
acid reaction, it ought not to be colored nor precipitated by 
hydrogen sulphide. 

Uses. Barium hydroxide being a strong base precipitates 
the metallic hydroxides insoluble in water from the solutions 
of their salts. In the course of analysis, we use it especially 



82 BEAGEJSTTS: [ 38. 

to precipitate magnesia. Baryta-water may also be used to 
precipitate those acids which form insoluble barium com- 
pounds. With this in view, it is applied to effect the detec- 
tion of carbonic acid, the removal of sulphuric acid, phos- 
phoric acid, etc. 

38. 
2. CALCIUM HYDROXIDE, or Lime, Oa(OH),. 

Use is made of 

a. Ccdeium hydroxide in the form of a fine powder. b. Li m& 
water. 

Colcium hydroxide is obtained by slaking lumps of pure 
calcined lime in a porcelain dish with half their weight of 
water. The heat which accompanies the combination of the 
lime and the water is sufficient to evaporate the excess of 
water. Slaked lime must be kept in a well-stoppered bottle. 

To prepare lime-water, digest slaked lime for some time 
with cold distilled water, shaking the mixture occasionally ; 
let the undissolved portion of lime subside, decant, and keep 
the clear fluid in a well-stoppered bottle. If it is wished to 
have the lime-water quite free from all traces of alkalies, 
baryta, and strontia, which are almost invariably present in 
slaked lime prepared from calcined limestone, the liquids ot 
the first two or three decantations must be removed, and the 
fluid decanted afterwards alone used. 

Tests. Lime-water must impart a strongly marked brown 
tint to turmeric-paper, and give a not too inconsiderable 
precipitate with sodium carbonate. It speedily loses these 
properties upon exposure to the air, and is thereby rendered 
totally unfit for analytical purposes. 

Uses. With many acids, lime forms insoluble salts ; with 
others, soluble salts. Lime-water may therefore serve to dis- 
tinguish the former acids, which it precipitates from their 
solutions, from the latter, which it will of course fail to pre- 
cipitate. Many of the precipitable acids are thrown down 
only under certain conditions, e.g., on boiling (citric acid), which 
affords a ready means of distinguishing between them by 
altering these conditions. We use lime-water in analysis 



39.J ZINO. 83 



principally to effect the detection of carbonic acid, and also 
to distinguish between citric acid and tartaric acid. Slaked 
lime is chiefly used to liberate ammonia from ammonium salts. 

X- HEAVY METAIS AND THEIR OXIDES AND HYDROXIDES. 

39. 
1. ZINC, Zn. 

Zinc of good quality should be selected, which dissolves iu 
sulphuric acid completely or leaves only a very slight residue, 
and which contains no arsenic. The latter impurity must be 
tested for by methods given in Section III, under reactions 
for arsenious acid. Fuse the metal and pour it in a thin 
stream into a large vessel of water. Zinc which contains 
arsenic must be rejected, for no practicable process of purifi- 
cation is known (EuoT and STOBER).* 

Uses. In qualitative analysis, zinc serves for the evolution 
of hydrogen, and also of hydrogen arsenide and antimonide. 
It is occasionally used also to precipitate some metals from 
their solutions, in which process the zinc simply displaces 
the other metal: CuSO 4 + Zn = ZnSO 4 -f Cu. Zinc is also 
sometimes used for the detection of sulphurous acid and 
phosphorous acid, and it must then be tested for zinc sulphide 
or zinc phosphide, as the case may be. For the manner of 
using and the testing, see Section TTT, under the reactions for 
sulphurous and phosphorous acids. 

2. ALUMINIUM, Al. 

Aluminium may serve for precipitating many metals from 
their solutions, but is employed especially for the reduction 
of nitric acid, sulphurous acid, and other oxygen salts. It is 
used in the form of fine drillings. It must dissolve in potas- 

* According to GUNNING (Scheikundtge Bijdragen, Deel I, Nr I, p. 113), 
the purification may be effected by repeated fusion with a mixture of sodium 
carbonate and sulphur ; according to SBLMI (Zeitschr 1 analyt. Chem t 22, 76), 
by treating molten zinc with ammonium chloride ; according to LESCOBXTB 
<Compt rend., 116, 58), by first fusing with potassium nitrate, then with zinc 
chloride. 



84 REAGENTS. [ 40 ' 

slum hydroxide without leaving a residue. The hydrogen gas- 
thus evolved ought not to blacken papers moistened with 
silver nitrate or lead acetate. 

3. IEON, Fe. 

Iron reduces many metals, and precipitates them from 
their solutions in the metallic state. We use it especially for 
the detection of copper, which precipitates upon it with its 
characteristic color. Any clean surface of iron, such as a 
knife-blade, a needle, a piece of wire, etc., will serve for this 
purpose. 

4. COPPEE, Cu. 

We use copper to effect the reduction of mercury, and 
sometimes, also, for the deposition of arsenic. Any bright 
copper surface (sheet or wire) can be used for the experiments. 

40. 
5, BISIOJTH HYDROXIDE, BiOOH. 

Preparation. Dissolve bismuth, freed from arsenic by 
fusion with sodium sulphide (hepar sidphuris), in dilute nitric 
acid ; dilute the solution till a slight permanent precipitate is 
produced, filter, and evaporate the filtrate to crystallization. 
Wash the crystals with water containing nitric acid, triturate 
them with water, add ammonia in excess, and let the mixture 
digest for some time ; then filter, wash, dry the white precipi- 
tate, and keep it for use. 

Tests. The bismuth hydroxide (instead of which basic 
bismuth nitrate may be used if it is entirely free from arsenic 
and antimony) is dissolved in dilute nitric acid, and precipi- 
tated with hydrogen sulphide. Part of the precipitated sul- 
phide is treated with ammonia and filtered, and part is treated 
with ammonium sulphide and filtered. These filtrates are 
then mixed with hydrochloric acid in excess. The first 
should give no precipitate, and the second only a white pre- 
cipitate of sulphur. 

Uses. When boiled with alkaline solutions of metallic 



41.] AMMONIUM SULPHIDE. 85 

sulphides, bismuth hydroxide reacts with the latter, giving 
rise to the formation of metallic oxides and bismuth sulphide. 
We use this reagent principally to convert arsenious sul- 
phide and arsenic sulphide into arsenious and arsenic acids. 

b. SULPHIDES. 

41. 
1. AMMONIUM SULPHIDE, (NH^S. 

We use in analysis 

a. Colorless ammonium monosulphide. 

b. Yellow ammonium polysulpliide. 

Preparation. Transmit hydrogen sulphide through 3 
parts of ammonia solution until no further absorption takes 
place, then add 2 parts of the same ammonia solution. The 
action of hydrogen sulphide upon ammonia gives rise to the 
formation, first, of (NH 4 ) a S, then of NH 4 SH. Upon addition 
of the same quantity of solution of ammonia as has been 
saturated, the ammonia reacts with the ammonium hydro- 
sulphide, and ammonium sulphide is formed. The rule, 
however, is to add only two thirds of the quantity of solu- 
tion of ammonia, as it is better that the preparation should 
contain a little ammonium hydrosulphide than that free 
ammonia should be present. To employ ammonium hydro- 
sulphide instead of the simple sulphide is unnecessary, and 
tends to increase the smell of hydrogen sulphide in the labo- 
ratory, for the compound allows that gas to escape when act- 
ing upon acid sulphides. 

Ammonium sulphide should be kept in well-corked phials. 
It is colorless at first, and deposits no sulphur upon addition 
of acids. Upon exposure to the air, however, it acquires a 
yellow tint, owing to the formation of ammonium disulphide, 
which is attended also with formation of ammonia and water : 
2(NE 4 ) a S + = (NH 4 ),S 2 + 2NH 3 + H a O. Continued action 
of the oxygen of the air upon the ammonium sulphide tends 
at first to the formation of still higher sulphides, but after- 
wards the fluid deposits sulphur ; finally all the ammonium 
sulphide is decomposed, and the solution contains noth* 



$6 REAGENTS. [ 41. 

ing but ammonia and ammonium thiosulphate. The forma- 
tion of thiosulphate proceeds as follows : (NH 4 ) fl S a + 3O = 

(NHJJ3.0.- 

The ammonium sulphide which has turned yellow by 

moderate exposure to the air may be used for all purposes 
requiring the employment of yellow ammonium sulphide. 
The yellow sulphide may also be expeditiously prepared by 
digesting the monosulphide with some sulphur. All kinds of 
yellow ammonium sulphide deposit sulphur, and look turbid 
and milky on being mixed with acids. 

Tests. Ammonium sulphide must strongly emit the odor 
peculiar to it, and with acids it must evolve abundance of 
hydrogen sulphide. The evolution of gas may be attended 
by the separation of a pure white precipitate, but no other 
precipitate must be formed. Upon evaporation and exposure 
to a red heat in a platinum dish, it must leave no residue. 
Even on heating, it must not precipitate or render turbid solu- 
tion of magnesium sulphate or solution of calcium chloride 
(free ammonia, ammonium carbonate). 

Uses. Ammonium sulphide is one of the reagents most 
frequently employed. It serves (a) to effect the precipitation 
of those heavy metals which hydrogen sulphide fails to throw 
down from acid solutions, e.g., iron, cobalt, etc. : (NH 4 ) a S + 
FeSO 4 = FeS + (NH 4 ) a S0 4 ; (6) to separate the metallic sul- 
phides thrown down from acid solutions by hydrogen sul- 
phide, since it dissolves some of them to sulphur salts, as 
the sulphides of arsenic and antimony, etc., leaving others 
undissolved for instance, lead sulphide, cadmium sulphide, 
etc. The ammonium sulphide used for this purpose must 
contain an excess of sulphur if the metallic sulphides to 
be dissolved will dissolve only as higher sulphides. For 
example, stannous sulphide, SnS, dissolves with ease only 
after being changed to stannic sulphide, SnS fl . 

From solutions of aluminium and chromium salts, ammo- 
nium sulphide precipitates hydroxides, with escape of hydro- 
gen sulphide, as the sulphur compounds corresponding to 
these hydroxides cannot form in the wet way : Al (SO ) 
4- 3(NH 4 ),S + 6E.O = Al t (OH) 6 + 3(NH 4 ),S0 4 + 3H.S. ' Salts 
insoluble in water are thrown down by ammonium sulphide 
unaltered from their solutions in acids. For instance, calcium 



42, 43.] HYDROGEN PEROXIDE, 87 

phosphate is thus precipitated from its solution in hydro* 
chloric acid. 



42. 
2. SODIUM SULPHIDE, Na a S. 

Preparation* The same as ammonium sulphide, except 
that solution of caustic soda is substituted for solution 
of ammonia. Filter, if necessary, and keep the fluid in 
well-stoppered bottles. If required to contain some higher 
sulphide of sodium, digest with powdered sulphur. When 
hydrochloric acid is added to the solution which has been 
somewhat diluted with water, there must be an abundant 
evolution of hydrogen sulphide. In this case, there ought 
to occur, according to the degree of sulphurization of the 
sodium sulphide, either no precipitate or only a white pre- 
cipitate of sulphur (vanadic acid, bases of the sixth group). 

Uses. Sodium sulphide is sometimes substituted for am- 
monium sulphide to effect the complete separation of cuprio 
sulphide from sulphur compounds soluble in alkaline sul- 
phides, e.g., from stannic sulphide, as cupric sulphide is not 
<quite insoluble in ammonium sulphide. 

IV. PEROXIDES. 

43- 
1. HYDROGEN PEROXIDE, H 8 O a . 

Hydrogen peroxide is best procured by purchase. The 
^clear, colorless liquid employed for medicinal purposes is 
adapted for use in qualitative analysis. It is an aqueous 
solution of hydrogen peroxide which is usually slightly 
.acidified with hydrochloric or sulphuric acid for the sake of 
durability, and it contains about 3 per cent by weight of the 
substance. 

Tests. Hydrogen peroxide must be completely volatilized 
by heating, and when it is mixed with a solution of potassium 
permanganate, the latter should be decolorized, and there 



88 REAGENTS. [ 44. 

should be a large amount of effervescence, due to an abundant 
evolution of oxygen. The last test is to be repeated from 
time to time in order to determine whether the hydrogen 
peroxide has not become decomposed. 

Uses. Hydrogen peroxide is of use in qualitative analysis 
principally as an oxidizing agent, and for this purpose oilers 
the advantage that no elements other than hydrogen and 
oxygen are added to the liquid under treatment, except the 
small amount of acid contained in the reagent. 

44. 
2. LEAD DIOXIDE, PbO a . 

Preparation. The rather small quantity of lead peroxide 
that is used in qualitative analysis is most easily prepared 
by digesting red lead (which should give a clear solution with 
dilute nitric acid and alcohol) with an excess of dilute nitric 
acid. A precipitate of brown lead dioxide and a solution 
containing lead nitrate are thus obtained. The precipitate is 
collected upon a filter, completely washed with hot water, and 
dried at a gentle heat. 

Tests. These are to be directed especially to the detec- 
tion of manganese. To make an accurate test for this, a 
sample is heated with pure concentrated sulphuric acid until 
complete decomposition takes place, and until the excess of 
sulphuric acid has been almost completely removed; then, 
after cooling, a further portion of the lead peroxide is added, 
heated with a mixture of about equal parts of nitric acid (sp. 
gr. 1.2) and water, and allowed to settle. The liquid above 
the precipitate ought to show no red coloration du$ to per- 
manganic acid. 

Uses. Lead dioxide serves especially for the conversion 1 
of manganese compounds into permanganic acid, and on 
account of the high coloring power of the latter, it offers a 
very delicate and characteristic reagent for the detection of 
manganese. 



.] POTASSIUM SULPHATE. 



V. SALTS. 

Of the many salts employed as reagents, those of potassium, 
sodium, and ammonium, are principally used on account of 
their acids. Therefore, salts of sodium may often be substi- 
tuted for the corresponding potassium salts, etc., and it is 
almost always immaterial whether we use sodium carbonate 
or potassium carbonate, potassium ferrocyanide or sodium 
ferrocyanide, etc. I have therefore here classified the salts 
of the alkali metals by their adds. With the salts of the 
alkali-earth metals and those of the heavy metals, however, 
the case is different. These are not used for their acids, but 
for their bases, and we may often substitute for one salt of a 
metal another similar one, as barium nitrate or acetate for 
barium chloride, etc. For this reason, I have classified the 
salts of the alkali-earth metals and of the heavy metals by their 



a. SALTS OP THE AT^AT.T METALS. 

45. 
1. POTASSIUM SULPHATE, K a S0 4 . 

Preparation and Tests. Purify potassium sulphate of com- 
merce by recrystallization, and dissolve 1 part of the pure salt 
in 12 parts of water. The solution should be neutral, and 
should be neither made turbid nor precipitated by hydrogen 
sulphide, ammonium sulphide, ammonium oxalate, or silver 
nitrate. By testing with ferrous sulphate or diphenylamine, 
it must show itself to be free from nitric acid. (See the reac- 
tions of nitric acid in Section III.) 

Uses. Potassium sulphate serves to detect and separate 
barium and strontium. It is in many cases used in prefer- 
ence to dilute sulphuric acid, which is employed for the same 
purpose, as it does not, like the latter reagent, disturb the 
neutrality of the solution. 



90 REAGENTS. [ 46, 47., 



46. 

2. HTDBOGEN DISODIUM PHOSPHATE, or Sodium Phosphate, 
HNa 9 P0 4 .12H a O. 

Preparation. Purify the commercial salt by recrystalliza- 
tion, and dissolve 1 part of the pure salt in 10 parts of water 
for use. 

Tests. Solution of sodium phosphate must not become 
turbid when heated with ammonia. The precipitates which 
solution of barium nitrate and solution of silver nitrate pro- 
duce in it must dissolve completely, and without effervescence* 
upon addition of dilute nitric acid. Even after heating, hydro- 
gen sulphide ought not to color or precipitate the solution,, 
either as it is or after acidifying it with hydrochloric acid. 

Uses. Sodium phosphate precipitates the alkali-earth 
metals and all the heavy metals from solutions of their salts. 
In the course of analysis, after the separation of the heavy 
metals, it serves as a test for alkali-earth metals in general ; 
and, after the separation of barium, strontium, and calcium, as 
a special test for the detection of magnesium. For the latter 
purpose, it is used in conjunction with ammonia, the magne- 
sium precipitating as ammonium magnesium phosphate. In 
the place of sodium phosphate, sodium ammonium phosphate 
( 89) or ammonium phosphate, H(NH 4 ) a P0 4 , can be used. 

47. 
3, AMMONIUM OXALATE, (NB^) i 1 O 4 .H,0. 

Preparation. 1 part of commercial oxalic acid (which 
generally contains potassium) is dissolved in 6 parts of water 
at the boiling temperature. This is allowed to cool, and the 
solution is poured off or filtered from the oxalic acid crystals, 
which usually contain potassium tetra-oxalate ; it is evapo- 
rated further, again cooled, and thus are obtained a second 
and third crop of oxalic acid which are almost or quite free 
from potassium. The mother-liquor, together with the first 
crystallization, may be used for the preparation of potassium 



48.] SODIUM ACETATE. 91 

or sodium oxalate. The pure crystals are dissolved in 2 parts 
of distilled water by warming, ammonia-water is added to dis- 
tinct alkaline reaction, and the solution is then put in a cold 
place. The crystals which form are drained, and a further 
crystallization is obtained by properly evaporating the mother- 
liquor. The crystals are purified by recrystallization. For 
use, 1 part of the pure salt is dissolved in 24 parts of water. 

Tests. The solution of ammonium oxalate must, not be 
precipitated or rendered turbid by hydrogen sulphide, or by 
ammonium sulphide. Ignited on platinum, the salt must 
volatilize without leaving a residue. The precipitates pro- 
duced in the solution by barium chloride and by silver nitrate 
must be completely soluble in nitric acid. 

Uses. With calcium, strontium, barium, lead, and other 
metals, oxalic acid forms insoluble or very difficultly soluble 
compounds. Ammonium oxalate produces, therefore, in the 
aqueous solutions of the salts of these bases, precipitates of 
the corresponding oxalates. In analysis, the reagent serves 
principally for the detection and separation of calcium. 

48. 
4. SODIUM ACETATE, NaO,H I O a .3H a O. 

Preparation. Dissolve crystallized sodium carbonate in a 
little water, add to the solution acetic acid in slight excess, 
evaporate to crystallization, and purify the salt by recrystalli- 
zation. This salt can now be procured very pure in com- 
merce. For use dissolve 1 part of the salt in 10 parts of water. 

Tests. Sodium acetate must be colorless and free from 

empyreumatic matter and inorganic acids. The solution ought 
not to be colored, made turbid, nor precipitated by hydrogen 
sulphide, ammonium sulphide, ammonium oxalate, barium 
chloride, or, after diluting and acidifying with nitric acid, by 
silver nitrate. 

Uses. The stronger acids in the free state decompose so- 
dium acetate, combining with the base and setting the acetic 
acid free. In the course of analysis, sodium acetate is used 
principally to precipitate ferric phosphate (which is insoluble 
in acetic acid) from its solution in hydrochloric acid. It serves, 



92 REAGENTS. [ 49 ' 

also, to effect the separation of ferric oxide and alumina, which 
it precipitates on boiling from the solutions of their salts. 

49- 
5. SODIUM CARBONATE, Na a C0 3 ; crystallized, Na 9 CO,.10H a O. 

Preparation. Finely pulverize " bicarbonate of soda " of 
commerce, put the powder into a funnel stopped loosely with 
cotton, make the surface even, cover it with a disk of thick 
filter-paper with turned-up edges, and wash by pouring small 
quantities of water on the paper disk until the filtrate, when 
acidified with nitric acid, is not rendered turbid by solution 
of silver nitrate, or by solution of barium chloride. Let the 
salt dry, and then convert it by gentle ignition into the normal 
carbonate. This is effected best in a vessel of silver or 
platinum, but it may be done also in a perfectly clean iron 
dish, or, on a small scale, in one of porcelain. Dissolve 1 part 
of the anhydrous, or 2.7 parts of the crystallized, salt in 
5 parts of water for use. 

Tests. Sodium carbonate should be absolutely white, and 
should dissolve in water to a clear solution. Its solution 
should not decolorize water which is colored reddish by potas- 
sium permanganate (sodium thiosulphate). After acidifying 
with nitric acid, neither barium chloride nor silver nitrate 
should cause turbidity in the solution, nor should it become 
yellow or give a precipitate of this color when warmed with 
ammonium inolybdate and nitric acid. When supersaturated 
with hydrochloric acid, evaporated to dryness, and dissolved 
again in water, no residue should be left (silicic acid). The 
solution when acidified with hydrochloric acid ought not to be 
colored nor precipitated by hydrogen sulphide, or, after addi- 
tion of ammonia, by ammonium sulphide. The solution to 
which barium chloride has been added in excess ought not to 
react alkaline (sodium hydroxide). When fused with potas- 
sium cyanide in a porcelain boat within a glass tube through 
which a slow stream of dry carbonic acid gas is passed, it 
ought to give no trace of a dark sublimate (arsenic). (Com- 
pare the reactions of arsenious acid in Section III.) 

Uses. With the exception of the alkali metals, sodium 



50.] AMMONIUM CARBONATE. 93 

carbonate precipitates all the metals in the form of normal or 
basic carbonates. Those metals which form soluble acid 
carbonates require boiling for their complete precipitation 
from acid solutions. Many precipitates produced by the 
action of sodium carbonate exhibit a characteristic color, 
which may lead to the detection of the individual metals 
that they respectively contain. Solution of sodium car- 
bonate also serves for the decomposition of many insoluble 
salts, more particularly of those with organic acids. Upon 
boiling with sodium carbonate, these salts are converted 
into insoluble carbonates, while the acids combine with the 
sodium, and are thus obtained in solution. Sodium carbon- 
ate is often used also to saturate free acids. 



50. 
6. AMMONIUM CABJBONATE, (NH H ) a OO t . 

Preparation. Take commercial "carbonate of ammonia" 
entirely free from any smell of animal oil, such as is pre- 
pared on a large scale by sublimation from a mixture of 
ammonium chloride and calcium carbonate, carefully scrape 
off the outer and inner surface of the mass, if necessary, and 
dissolve 1 part of the salt by digestion with 4 parts of water 
to which 1 part of ammonia solution has been added. 

Teats. Pure ammonium carbonate must completely vola- 
tilize. Its solution ought not to be colored or precipitated 
by ammonium sulphide. It must yield a colorless solution 
When supersaturated with nitric acid (pyridine bases). The 
solution, thus acidified, ought to be colored or precipitated 
neither by barium nor silver solution, nor by hydrogen sul- 
phide. 

Uses. Lite sodium carbonate, ammonium carbonate pre- 
cipitates most metals. It is generally employed in preference 
to the former reagent, because it introduces no non-vola- 
tile body into the solution. Complete precipitation of many 
of the metals takes place only on boiling, and several of 
the precipitates redissolve in an excess of the precipi- 
tant In like manner, ammonium carbonate dissolves many 
hydroxides and sulphides, and thus enables us to distinguish 



94 BEAGENTS. [ 61. 

and separate them from others which are insoluble in this 
reagent. 

Ammonium carbonate, like ammonia solution, and for the 
same reason, fails to precipitate from acid solutions many 
metals which it precipitates from neutral solutions. (Com- 
pare 36.) 'We use ammonium carbonate in analysis princi- 
pally to effect the precipitation of barium, strontium, and 
calcium, and the separation of these substances from magne- 
sium ; also, to separate arsenious sulphide, which is soluble 
in it, from antimonious sulphide, which is insoluble. 



51. 

7. HIDBOGEN SODIUM SULPHITE, ENaSO,. 

Preparation. Heat 5 parts of copper tacks or clippings 
with 20 parts of concentrated sulphuric acid in a flask, and 
conduct the sulphur dioxide gas evolved, first through a 
washing-bottle containing some water, then into a flask con- 
taining 4 parts of purified sodium bicarbonate ( 49), or 7 
parts of pure crystallized, normal sodium carbonate, and 
from 20 to 30 parts of water (this flask should not be much 
more than half full); continue the transmission of the gas 
until the evolution of carbon dioxide ceases. Keep the solu- 
tion, which has a strong smell of sulphurous acid, in a well- 
stoppered bottle. 

Tests. Acid sodium sulphite, when evaporated to dry- 
ness with puro sulphuric acid, while evolving a copious 
amount of sulphurous acid, must leave a residue, the aqueous 
solution of which is not altered by hydrogen sulphide after 
the addition of some hydrochloric acid, nor precipitated yel- 
low by heating with a solution of ammonium molybdate 
mixed with nitric acid. 

Uses. Sulphurous acid has a great tendency to pass to 
the state of sulphuric acid by absorbing oxygen. It is there- 
fore one of our most powerful reducing agents. Acid sul- 
phite of sodium, which has the advantage of being less 
readily decomposed than sulphurous acid, acts in the same 
manner upon addition of acid. We use it principally to 
reduce arsenic acid to arsenious acid, chromic acid to a. 



52, 53.] POTASSIUM OHBOMATE. 95 

chromic salt, and ferric salts to ferrous salts ; also for the 
precipitation of selenium from selenious acid, etc. 



52. 
8. POTASSIUM NITBITE, KNO a . 

Preparation. In an iron pan fuse 1 part of potassium 
nitrate, add 2 parts of lead, and stir constantly with an iron 
rod. Even at a low red heat, the lead becomes for the most 
part oxidized and converted into a yellow powder. To oxi- 
dize the remainder, the heat is increased to visible redness 
and maintained at that point for half an hour. Allow the 
mass to cool, treat with cold water, filter, and pass carbon 
dioxide through the filtrate. This precipitates almost the 
whole of the lead in solution, and the remainder is removed 
with a little hydrogen sulphide. After filtering, concentrate 
the liquid to a small volume, let the undecomposed potassium 
nitrate crystallize out, evaporate to dryness, with stirring at 
the last stage of the process, and heat to fusion in order to 
destroy any potassium thiosulphate that may have been 
formed (AUG. STBOMEYEB). 

Tests. Upon addition of dilute sulphuric acid, potassium 
nitrite must copiously evolve nitric oxide gas. Its dilute 
solution when mixed with ammonia and ammonium sulphide 
ought not to be colored or precipitated. 

Uses. Potassium nitrite is an excellent means to effect 
the detection and separation of cobalt, in the solutions of 
which metal it produces a precipitate of potassium cobaltic 
nitrite. In presence of free acid it also serves to liberate 
iodine from its compounds. 



53. 
9. POTASSIUM CHROMATE, K,Cr0 4 . 

Preparation and Tests. Eecrystallize commercial potas- 
sium dichromate several times, dissolve 60 parts of the dry 
salt in 300 parts of boiling water, add 28.1 parts of pure dry 



96 BEAGENTS, [ 54 

potassium carbonate, and evaporate to crystallization. Dis- 
solve 1 part of the yellow crystals thus obtained in 10 parts 
of water. 

The solution of potassium chromate, when heated with 
hydrochloric acid and some alcohol, must yield a green solu- 
tion, which, after neutralizing the greater part of the free 
acid with ammonia, must not be made turbid by the addition 
of barium chloride (sulphate). The reaction of potassium 
chromate should be only faintly alkaline. 

Uses. Potassium chromate reacts with many of the solu- 
ble metallic salts. Most of the precipitated chromates are 
very sparingly soluble, and often show characteristic colors, 
so that the metals are thereby easily recognized. We make 
use of potassium chromate especially for testing for lead, 
and it is also employed for distinguishing and separating 
barium and strontium. Potassium dichromate can be fre- 
quently used instead of the chromate. 

54 
10. POTASSIUM PYROAOTIMONATE, H^Sb^^O. 

Preparation, Project a mixture of equal parts of pulver- 
ized tartar-emetic and potassium nitrate in small portions at 
a time into a red-hot crucible. After the mass has defla- 
grated, keep it at a moderate red heat for a quarter of an 
hour, It froths at first, but after some time will be in a 
state of calm fusion. Eemove the crucible from the fire, let 
the mass get nearly cold, and extract it with warm water. 
Transfer to a suitable vessel by rinsing, and decant the clear 
fluid from the heavy white powder deposited (BBUNKEB). 
Wash this with some cold water, heat 1 part with 200 parts 
of water for a short time to boiling, cool, and filter. 

Tests and Uses. Acid potassium pyroantimonate is 
sparingly soluble in water, requiring 90 parts of boiling and 
250 parts of cold water for solution. The solution prepared 
according to the above directions keeps for quite a long time 
unchanged. It must be clear and of neutral reaction. It 
ought not to give a precipitate with potassium chloride, nor 
with ammonium chloride, but with sodium chloride solution, 



55.] AMMONIUM MOLYBDATE. 97 

it must yield a crystalline precipitate. When mixed with an 
equal volume of concentrated sulphuric acid and cooled, no 
brown zone ought to form when a solution of ferrous sul- 
phate is placed above the mixture (nitrous or nitric acid). 
Acid potassium pyroantimonate, generally called simply 
potassium antimonate, serves as a very good reagent for 
sodium, but its employment requires great caution (see 94). 



55. 

11. AMMONIUM MOLTBDATE, (NH 4 ) a MoO 4 , DISSOLVED IN 
NITEIO AGED MOLYBDIO AOID SOLUTION. 

Preparation and Tests. Triturate molybdenite with about 
an equal bulk of coarse quartz sand washed with hydrochloric 
acid until it is reduced to a moderately fine powder ; heat to 
faint redness, with repeated stirring, until the mass has 
acquired a lemon-yellow color (which after cooling turns, 
white). With small quantities, this operation may be con- 
ducted in a flat platinum dish; with large quantities, in a 
muffle. Extract with solution of ammonia, filter, evaporate 
the filtrate, heat the residue to faint redness until it appears 
yellow or white, and then digest for several days with nitric 
acid on the water-bath, in order to convert any phosphoric 
acid present to the tribasic state. When the nitric ,acid is 
evaporated, dissolve the residue (in the place of which the 
commercial, pure molybdic acid can also be used) in 4 parts 
of solution of ammonia, filter rapidly, and pour the filtrate into 
15 parts by weight of nitric acid of 1.20 sp. gr. 

To prepare the reagent from ammonium molybdate, dis- 
solve 150 g of the pulverized, pure salt in 1 liter of water by 
heating, and pour the solution into 1 liter of nitric acid of 
1.20 sp. gr. Keep the mixture standing several days in a 
moderately warm place, which will cause the separation of 
any remaining traces of phosphoric acid as ammonium phos- 
phomolybdate. Decant the colorless fluid from the precipi- 
tate, and keep it for use. Heated to 40, the liquid remains 
clear. When heated to boiling, it ought not to give a yellow 
precipitate. The white precipitate which then separates is 
molybdic acid or an acid ammonium molybdate. The yellow 



98 BEAGENTS. [ 56 

precipitate which sometimes separates from the solution upon 
long keeping is a modification of molybdic acid. 

JJses. Phosphoric acid and arsenic acid form with mo- 
lybdic acid and ammonia peculiar, yellow compounds which 
are almost absolutely insoluble in the nitric acid solution of 
ammonium molybdate. The phosphoric acid compound is 
formed in the -cold, but the production of the arsenic acid 
compound requires heat. Ammonium molybdate therefore 
affords an excellent means for detecting these acids, but 
more especially for finding very minute quantities of phos- 
phoric acid in acid solutions containing aluminium and alkali- 
earth metals. 



56. 
12. AJHMONIUM OHLOBIBE, NH 4 C1. 

Preparation. Select sublimed white sal-ammoniac of com- 
merce. If it contains iron it must be purified. For this 
purpose, chlorine-water is added to the boiling solution until 
any ferrous chloride present is changed to ferric chloride. 
Ammonia is then added in slight excess, the whole is heated 
until the liquid is scarcely alkaline, the resulting precipitate 
is allowed to settle, the liquid is then filtered and evaporated 
to crystallization. Dissolve 1 part of the salt in 8 parts of 
water for use. 

Tests. Upon evaporation on platinum, solution of ammo- 
nium chloride must leave a residue, which upon further heat- 
ing volatilizes completely. Ammonium sulphide should have 
no action upon the solution, and barium chloride should not 
cause a turbidity in it. Ferric chloride ought not to redden 
it when acidified with hydrochloric acid (ammonium sul- 
phocyanide). When evaporated with nitric acid upon the 
water-bath, the ammonium chloride solution must leave a 
white residue, not a yellowish or reddish one (pyridine bases). 
Its reaction must be neutral. 

Uses. Ammonium chloride is used very frequently in 
analysis. It serves principally to retain in solution certain 
oxides, e.g., manganons and magnesium oxides, or salts, e.g., 
calcium tartrate, upon the precipitation of other oxides or 



67.] POTASSIUM CYANIDE. 99 

salts by ammonia or some other reagent This application 
of ammonium chloride is based upon the tendency of the 
ammonium salts to form double compounds with other salts. 
Ammonium chloride also serves to distinguish between pre- 
cipitates possessing similar properties in other respects; for 
instance, to distinguish the ammonium magnesium phosphate, 
which is almost insoluble in ammonium chloride, from other 
magnesian precipitates. It is likewise used to precipitate from 
their solutions in potassium hydroxide, various substances 
-which are soluble in that alkali, but insoluble in ammonia, 
e.g., alumina, chromic oxide, etc. In this process, the elements 
of the ammonium chloride transpose with those of the caustic 
potash, and potassium chloride, water, and ammonia are 
formed. Ammonium chloride is also applied as a special 
reagent to effect the precipitation of platinum as ammonium 
platinic chloride. 

57. 
13. PoTASSimi CYANIDE, KCN. 

Preparation. Heat potassium ferrocyanide of commerce 
(perfectly free from potassium sulphate) gently, with stirring, 
until the water of crystallization is completely expelled ; tritu- 
rate the anhydrous mass, and mix 8 parts of the dry powder 
with 3 parts of perfectly dry potassium carbonate ; fuse the 
mixture in a covered Hessian, or, better still, in a covered 
iron, crucible until the mass is at a faint red heat, appears 
clear, and a sample of it, taken out with a heated glass or iron 
rod, looks perfectly white. Eemove the crucible from the 
fire, tap it gently, and let it cool a little until the evolution of 
gas has ceased. Pour the fused potassium cyanide into a 
heated, tall, crucible-shaped vessel of clean iron or silver, or 
into a moderately hot Hessian crucible, using proper care to 
prevent the running out of any of the minute particles of iron 
carbide which have separated in the process of fusion and 
have subsided to the bottom of the crucible. Let the mass 
now slowly cool in a somewhat warm place. The potassium 
cyanide thus prepared is very well adapted for analytical pur- 
poses, although it contains potassium carbonate and cyanate, 



100 BEAGENT8. [ 57* 

the latter upon solution in water being transformed into am- 
znonium carbonate and potassium carbonate : 2KCNO -f- 
4.H A O = K,CO,+ (NH 4 ) a OO t . Keep the potassium cyanide 
(which, as well known, is very poisonous) in the solid form in 
a well-stoppered bottle, and dissolve 1 part of it in 4 parts of 
water, without application of heat, when required for use. 
Instead of potassium cyanide, the sodium-potassium cyanide, 
which is at present extensively prepared, can be used. This 
is made in the same manner as potassium cyanide, by fusing 
together 4 parts of dehydrated potassium ferrocyanide with 
1 part of pure anhydrous sodium carbonate. 

Teats. Potassium cyanide must be of a milk-white color, 
and quite free from particles of iron or charcoal. It must 
completely dissolve in water to a clear fluid. It must con- 
tain neither silica nor potassium sulphide. The precipitate 
which lead salts produce in its solution must accordingly be 
of a white color, and the residue which its solution leaves 
upon evaporation, after previous supersaturation with hydro- 
chloric acid,* must completely dissolve in water to a clear 
fluid. When fused with pure sodium carbonate in a porcelain 
boat within a glass tube through which is passed a slow stream 
of dry carbonic acid, it ought to give no trace of an arsenic 
mirror. (Compare 49.) 

Uses. Potassium cyanide prepared in the manner de- 
scribed produces in the solutions of most metallic salts, pre- 
cipitates of cyanides of metals or of hydroxides or carbonates 
which are insoluble in water. The precipitated cyanides are 
soluble in potassium cyanide, and by further addition of the 
reagent may therefore be separated from the hydroxides or 
carbonates which are insoluble in potassium cyanide. Some 
of the metallic cyanides redissolve invariably in the potassium 
cyanide as double cyanides, even in the presence of free 
hydrocyanic aoid and upon boiling; while others combine 
with cyanogen to new radicals, which remain in solution in 
combination with the potassium. The most common com- 
pounds of this nature are potassium oobalticjanide and potas- 
sium ferro- and ferricyanide. These differ from the double 



*ThIa supersaturation with hydrochloric acid Is attended with disengage* 
meat of hydrocyanic acid. 



58, 59.] POTASSIUM FBRRIOYANIDE. 101 

cyanides of the other kind particularly in this, that dilute 
acids fail to precipitate the metallic cyanides which they con- 
tain. Potassium cyanide may accordingly serve to separate 
the metals which form compounds of the latter description 
from others, the cyanides of which are precipitated by acids 
from their solution in potassium cyanide. In the course of 
analysis, this reagent is of great importance, as it serves to 
effect the separation of cobalt from nickel ; also that of copper, 
the sulphide of which metal is soluble in it, from cadmium, 
whose sulphide is insoluble. 

58. 
14. POTASSIUM FEBBOCYAOTDE, K 4 Fe(ON) e 3H 9 O. 

Preparation. The potassium ferrocyanide found in com- 
merce is sufficiently pure. 1 part of the salt is dissolved in 
12 parts of water for use. 

Uses. Ferrocyanogen forms with most metals compounds 
insoluble in water, some of which exhibit highly characteristic 
colors. These ferrocyanides are produced when potassium 
ferrocyanide is brought into contact with soluble metallic 
salts, the potassium changing places with the other metals. 
The cupric and ferric ferrocyanides exhibit the most charac- 
teristic colors. Potassium ferrocyanide therefore serves par- 
ticularly as a test for cupric and ferric compounds. 

59. 
15. POTASSIUM FEEBIOIANIDE, K e Fe,(ON) ia . 

Preparation. Conduct chlorine gas slowly into a solution 
of 1 part of potassium ferrocyanide in 10 parts of water, with 
frequent stirring, until the solution exhibits a fine deep-red 
color by transmitted light (the light of a candle answers best), 
and a portion of the fluid produces no longer a blue precipi- 
tate in a solution of ferric chloride, but imparts a brownish 
tint to it. Evaporate the fluid in a dish to J of its weight and 
let it crystallize. The mother-liquor will upon further evap- 
oration yield a second crop of crystals fit for use. Dissolve 



10 2 BEACHENTS. [I 60 - 

the whole of the crystals obtained in 3 parts of water, filter if 
necessary; evaporate the solution briskly to half its volume, 
and let it crystallize again. Dissolve some of the magnificent 
red crystals in a little water, preferably just before use. The 
solution, which decomposes under the influence of daylight 
with the deposition of a blue precipitate and the formation of 
potassium ferrocyanide, ought not, as already stated, to pro- 
duce a blue precipitate or coloration with ferric chloride. 

Uses. Potassium ferricyanide reacts with solutions of 
metals in the same manner as potassium ferrocyanide. Of 
the metallic ferricyanides, the ferrous salt is more par- 
ticularly characterized by its color, and we therefore apply 
potassium ferricyanide principally as a test for ferrous com- 
pounds. 

60. 
16. POTASSIUM SULPHOOTAMDB, EONS. 

Preparation. Mix. together 46 parts of anhydrous potas- 
sium ferrocyanide, 17 parts of potassium carbonate, and 32 
parts of sulphur ; introduce the mixture into an iron pan pro- 
vided with a lid, and fuse over a gentle fire ; maintain the 
same temperature until the swelling of the mass which ensues 
at first has completely subsided and given place to a state of 
tranquil and clear fusion,; towards the end of the operation, 
increase the temperature to faint redness, in order to decom- 
pose the potassium thiosulphate which has been formed in the 
process. Pour the mass upon a bright iron plate, break it 
up, and extract it repeatedly with boiling alcohol of from 80 
to 90 per cent. "Upon cooling, part of the potassium sulpho- 
oyanide separates in colorless crystals; to obtain the re* 
mainder, distil the alcohol from the mother-liquor. Dissolve 
1 part of the salt in 10 parts of water for use. 

Testa and Uses. Potassium sulphocyanide serves for the 
detection of ferric compounds, for which it is at once a. most 
characteristic and delicate reagent. It is used further for the 
detection and separation of copper, which it precipitates as 
white cuprous sulphocyanide from cupric solutions, upon 
addition of sulphurous acid. Solution of potassium sulpho- 



$ 61-] BARIUM CHLORIDE. 108 

cyanide must remain colorless when mixed with perfectly 
pure, dilnte hydrochloric acid. It should ba neither colored 
.nor precipitated by ammonium sulphide. 

b. SAI/TS OF THE ALKALI-EARTH METALS. 

61. 
1. BABIUM CHLORIDE, BaCl^E^O. 

Preparation. a. From heavy-spar. Mi* together 8 parts 
-of pulverized barium sulphate, 2 parts of charcoal in powder, 
and 1 part of common rosin. Put the mixture in a crucible 
and expose it in a wind-furnace to a long-continued ignition. 
Triturate the crude barium sulphide obtained, boil about -^ 
of the powder with 4 times its quantity of water, and add 
hydrochloric acid until all effervescence of hydrogen sulphide 
has ceased, and the fluid manifests a slight acid reaction. 
Add now the remaining -^ of the barium sulphide, boil some 
time longer, then filter, treat with hydrochloric acid just to 
acid reaction, heat for a considerable time, filter again, and 
crystallize. Drain the crystals, redissolve them in water, 
and crystallize again. 

b. From witherite. Pour 10 parts of water upon 1 part of 
pulverized witherite, and gradually add hydrochloric add 
until the witherite is almost completely dissolved. Add a 
little more finely pulverized witherite, and heat, with fre- 
quent stirring, until the fluid has entirely or very nearly 
lost its acid reaction ; add solution of barium sulphide as 
long as a precipitate forms, and proceed as in a. For use, 
dissolve 1 part of the barium chloride in 10 parts of water. 

Tests. Barium chloride must not alter vegetable colors ; 
its solution must not be colored nor precipitated by hydrogen 
sulphide (after acidifying with hydrochloric acid), or by 
ammonium sulphide. Pure sulphuric acid must precipitate 
all fixed matter from it, so that the fluid filtered from the 
precipitate formed upon the addition of that reagent leaves 
not the slightest residue when evaporated in a platinum dish. 
Potassium chromate should completely precipitate the solu- 
tion when it has been acidified with a little acetic acid, so that 



104 REAGKENTS, [ 62. 

the liquid, when filtered after standing for two hours in a, 
warm place, remains clear upon the addition of ammonium 
carbonate. Should a precipitate show itself in making this 
test (strontium or calcium carbonate), purify the barium chlo- 
ride by dissolving it in 2 parts of hot water, mixing this 
solution with twice its volume of alcohol, washing the result- 
ing precipitate with alcohol, and drying it. 

Uses. With many acids, barium forms soluble, with others, 
insoluble, compounds. This property of barium therefore 
affords a means of distinguishing the former acids, which 
are not precipitated by barium chloride, from the latter, in 
the solution of the salts of which this reagent produces a 
precipitate. With acids, the precipitated barium salts show- 
varying deportment. By subjecting these salts to the action 
of acids, we are therefore enabled to subdivide the group 
of preoipitable acids, and even to detect certain individual 
ones. This renders barium chloride one of the most im- 
portant reagents for distinguishing between certain groups 
of acids, but more especially for the detection of sulphuric 
acid. 



62. 
2. BARIUM NITRATE, Ba(NO s ),. 

Preparation. Treat barium carbonate (either witherite or 
that precipitated by sodium carbonate from solution of 
barium sulphide) with dilute nitric acid free from chlorine, 
and proceed exactly as directed in the preparation of barium 
chloride from witherite, or else recrystallize the commercial 
salt. For use, dissolve 1 part of the salt in 15 parts of 
water. 

Tests. Solution of barium nitrate must not be made tur- 
bid by solution of silver nitrate. Other tests are the same as 
for barium chloride. 

Uses. Barium nitrate is used instead of barium chloride 
in cases where it is desirable to avoid the presence of & 
metallic chloride in the fluid. 



63, 64.] CALCIUM SULPHATE. 105 

63. 
3. BABIDM CABBONATE, BaOO t . 

Preparation. Dissolve crystallized barium chloride in 
r, heat to boiling, and add a solution of ammonium car- 
bonate mixed with some caustic ammonia, as long as a pre- 
cipitate forms. Let the precipitate subside, decant five or six 
times, transfer the precipitate to a filter, and wash until the 
washing water is no longer rendered turbid by solution of 
silver nitrate. Stir the precipitate with water to the consistence 
of thick milk, and keep this mixture in a stoppered bottle. 
It must, of course, be shaken every time it is required for use. 

Tests. From the dilute solution in hydrochloric acid (not 
-containing too much free acid), pure sulphuric acid must pre- 
cipitate all fixed matter. (Compare barium hydroxide, 37.) 
Hydrogen sulphide and also ammonium sulphide (after pre- 
vious addition of ammonia) ought not to color nor precipitate 
this solution. 

Uses. Barium carbonate decomposes solutions of cer- 
tain metallic salts, e.g., ferric and aluminium salts, precipitat- 
ing from them the whole of the metal as hydroxide and basic 
salt, while some other metallic salts are not precipitated by it. 
It therefore serves to separate the former from the latter, and 
affords an excellent means for effecting the separation of feme 
oxide and alumina from manganese, zinc, calcium, magnesium, 
etc. It must be borne in mind, however, that the salts must 
not be sulphates, as barium carbonate likewise precipitates 
the latter metals from these compounds. 

64. 
4. OALOTDM SUUPHATE, CaS0 4 .2H,O. 

Preparation. Digest and shake powdered, crystallized 
.gypsum (selenite) for some time with water ; let the undls* 
solved portion subside, decant, and keep the clear fluid for 

4136. 

Uses. Oaloium sulphate, being difficultly soluble, is a con. 



106 BEAGENT8. [ 

venient reagent in cases where it is wished to apply a solution 
of a calcium salt or of a sulphate of a definite degree of dilu- 
tion. As dilute solution of a calcium salt, it is used for the- 
detection of oxalic acid ; while as dilute solution of a sul- 
phate, it affords an excellent means for distinguishing between 
barium, strontium, and calcium. 

65. 

i 

6. OALOIDM OHLOEIDB, Oa01 a ; crystallized, CM^Hf). 

Preparation. Dilute 1 part of crude hydrochloric acid 
with 6 parts of water, and add thereto marble or chalk until 
the last portion added remains undissolved ; now add some 
slaked lime, then hydrogen sulphide until a filtered portion 
of the mixture is no longer altered by ammonium sulphide. 
Then let the mixture stand covered for 12 hours at a gentle 
heat, filter, exactly neutralize the filtrate, concentrate by 
evaporation, and crystallize. Let the crystals drain, and 
dissolve 1 part of the salt in 5 parts of water for use. 

Tesfe. Solution of calcium chloride must be neutral, and 
neither be colored nor precipitated by hydrogen sulphide 
(after acidifying with hydrochloric acid), or by ammonium 
sulphide or potassium chromate. When mixed with potas- 
sium or calcium hydroxide, it must liberate no ammonia. 
Calcium chloride can be tested for strontium chloride accord- 
ing to 103. 

Uses. In its action and application, calcium chloride is 
analogous to barium chloride. As the latter reagent is used 
to separate the inorganic acids into groups, so calcium 
chloride serves in the same manner to effect the separation 
of the organic acids into groups, since it precipitates some 
of them, while it forms soluble compounds with others. 
Further, the different conditions under which the various 
insoluble calcium salts are thrown down enable us to sub- 
divide the group of preoipitable acids, as is the case with the 
barium precipitates. 



66, 67.] FEBBOTJS SULPHATE. 107 

66. 
6. MAGNESIUM SULPHATE, MgS0 4 ; crystallized, MgSO 4 .7H,O. 

Preparation. Dissolve 1 part of magnesium sulphate of 
commerce in 10 parts of water. If the salt is not perfectly 
pure, first subject it to recrystallization. 

Tests. Magnesium sulphate must have a neutral reaction. 
Its solution, when diluted with an equal quantity of water 
and mixed with sufficient ammonium chloride, must, after 
the lapse of half an hour, not appear clouded nor tinged 
by ammonia, or by ammonium carbonate, oxalate, or sul- 
phide. 

Uses. Magnesium sulphate serves almost exclusively for 
the detection of phosphoric acid and arsenic acid, which it 
precipitates from aqueous solutions of phosphates and arse- 
nates, in presence of ammonia and ammonium chloride, in the 
form of almost absolutely insoluble, highly characteristic salts 
(ammonium magnesium phosphate or arsenate). Magnesium 
sulphate is also employed to test ammonium sulphide (see 



c. SAUFS OF THE HEAVY METALS. 

67. 
1. FEBBOUS SULPHATE, FeS0 4 ; crystallized, FeS0 4 .7H a O. 

Preparation. Heat an excess of iron nails free from rust, 
or of clean iron wire, with dilute sulphuric acid until the 
evolution of hydrogen ceases; filter the sufficiently concen- 
trated solution, add a few drops of dilute sulphuric acid to 
the filtrate, and allow it to cool. Wash the crystals thus 
obtained with water very slightly acidulated with sulphuric 
acid, dry, and keep for use. 

Ferrous sulphate can also be very readily prepared from 
the solution which is obtained in generating hydrogen sul- 
phide by the action of dilute sulphuric acid upon ferrous 
sulphide. 

Tests. The crystals of ferrous sulphate must have a fine 



108 BEAGENTS. 



[68. 



pale green color. Crystals that have been more or less 
oxidized by the action of the air, and give a brownish-yellow 
solution when treated with water, leaving undissolved basic 
ferric sulphate behind, should be rejected. Hydrogen sul- 
phide must not precipitate solution of ferrous sulphate after 
addition of some hydrochloric acid, nor even impart a black- 
ish tint to it. 

Uses. Ferrous sulphate has a strong tendency to absorb 
oxygen, and to be converted into ferric sulphate. It acts 
therefore as a powerful reducing agent. We employ it prin- 
cipally for the reduction of nitric acid, from which it sepa- 
rates nitric oxide by withdrawing three atoms of oxygen from 
two molecules of it. In this case, the decomposition of the 
nitric acid being attended with the formation of a very pecu- 
liar brownish-black compound of nitric oxide with an unde- 
oomposed portion of the ferrous salt, this reaction affords a 
particularly characteristic and delicate test for nitric acid. 
Ferrous sulphate also serves for the detection of ferri- 
cyanides, with which it produces a kind of Prussian blue. 
It is likewise used to effect the precipitation of metallic gold 
from solutions of that metal 



2. FEBBIO CHLOBJDB, Fe 9 01 fl . 

Preparation. Treat small iron nails in a capacious flask 
with pure hydrochloric acid of 1.11 sp. gr., using heat towards 
the end of the operation, until in the presence of an excess 
of iron no more hydrogen is evolved. Filter the solution into 
another flask, dilute it with about twice its volume of water, 
and conduct into it chlorine gas, with frequent shaking, until 
the fluid no longer produces a blue precipitate in solution of 
potassium ferricyanide. Heat until the excess of chlorine is 
expelled. Dilute until the fluid is 20 times the weight of the 
iron dissolved, and keep for use. 

Tests. Solution of ferric chloride must not contain an 
excess of acid. This may be readily ascertained by stirring a 
diluted sample of it with a glass rod dipped in ammonia, 
when the absence of any excess of acid will be proved by the 



69.] SILVEE NITRATE. 109 

formation of a precipitate which fails to dissolve upon agitat- 
ing the fluid. Potassium ferricyanide must not impart a blue 
color to it. Hydrogen sulphide must give a white precipitate 
of sulphur in the diluted solution to which some hydrochloric 
acid is added. The solution is best tested for arsenic by 
means of MABSH'S apparatus (see the reactions for arsenious 
acid in Section III). When evaporated with nitric acid and 
treated with an abundance of the solution of ammonium 
molybdate in nitric acid, the solution ought not to give a 
yellow precipitate even after long standing (phosphoric acid). 
Uses. Ferric chloride serves to subdivide the group of 
organic acids which calcium chloride fails to precipitate, as 
it produces precipitates in solutions of benzoates and suc- 
cinates, but not in cold solutions of acetates and formates. 
The aqueous solutions of normal ferric acetate and formate 
exhibit an intensely red color. Ferric chloride is therefore 
a useful agent for detecting acetic acid, formic acid, and also 
salicylic acid: It is exceedingly well adapted to effect the 
decomposition of phosphates of the alkali-earth metals (see 
phosphoric acid in Section III). It also serves for the detec- 
tion of ferrocyanides, with which it produces Prussian blue, 
and, with the co-operation of barium carbonate, for the pre- 
cipitation of small amounts of phosphoric and of arsenic 
acids from dilute solutions. 



3. SlLVEB NlTBATE, AgNO,. 

Dissolve 1 part of the crystallized salt, which may be 
purchased in a very pure condition, in 20 parts of water. 

Testa. Solution of silver nitrate should have a neutral 
reaction. Dilute hydrochloric acid must completely precip- 
itate all fixed matter from it The fluid filtered from the 
precipitated silver chloride must accordingly leave no residue 
when evaporated on a watch-glass, and must be neither pre- 
cipitated nor colored by hydrogen sulphide. 

Uses. With many acids, silver forms soluble, and with 
others, insoluble compounds. Like barium chloride, silver 



110 BBAGENTS. [ 70. 

nitrate may therefore serve to effect the separation of acids 
and their arrangement into groups. 

Most of the insoluble compounds of silver dissolve in dilute 
nitric acid, but the chloride, bromide, iodide, and cyanide, 
ferrocyanide, ferricyanide, sulphocyanide, and sulphide of 
silver are insoluble in that reagent. Silver nitrate is there- 
fore an excellent agent to distinguish and separate from all 
others the acids corresponding to the compounds of silver 
just enumerated. Many of the insoluble silver salts exhibit 
peculiar colors (silver ohromate, silver arsenate), or manifest 
a characteristic deportment with other reagents or upon the 
application of heat (silver formate). Silver nitrate is there- 
fore an important agent for the positive detection of certain 
acids. 



70. 
4 LKAD ACETATE, PtyC.H.O,), ; crystallized, Pb(C a E 1 O a ) a .3H,O. 

The best lead acetate of commerce is sufficiently pore. 
For use dissolve 1 part of the salt in 10 parts of water. 

Tests. Lead acetate must completely dissolve in water 
acidified with a drop or two of acetic acid. The solution 
must be quite clear and colorless ; hydrogen sulphide must 
throw down all fixed matter from it, so that the filtrate from 
the lead sulphide is not affected by ammonium sulphide, and 
leaves no residue upon evaporation. On mixing the solution 
with ammonium carbonate in excess, and filtering, the filtrate 
must not show a bluish tint (copper). The solution acidified 
with nitric acid should not be made cloudy or be precipitated 
by silver nitrate. 

Uses. With a great many acids, lead forms compounds 
insoluble in water, which are marked either by peculiarity of 
color or characteristic deportment Lead acetate therefore 
produces precipitates in the solutions of these acids or of 
their salts, and serves for the detection of several of them. 
Thus, lead chromate is characterized by its yellow color, lead 
phosphate by its peculiar deportment before the blowpipe* 
and lead malate by its ready fusibility. 



f 71, 72.] MEBOUEIO CHLORIDE. Ill 



71. 

5. MEBOUBOUS NITRATE, Hg a (N0 8 ), crystdHiwd 9 
Hg,(NO,),.2H fl O. 

Preparation. Pour 1 part of pure nitric acid of 1.2 sp. 
gr. on 1 part of pure mercury in a porcelain dish, and let the 
vessel stand twenty-four hours in a cool place. Separate the 
crystals formed from the undissolved mercury and the mother- 
liquor, and dissolve them in water mixed with ^ part of nitric 
acid, by trituration in a mortar. Filter the solution and keep 
the filtrate in a bottle with some metallic mercury covering 
the bottom. 

Tests. With dilute hydrochloric acid, the solution of 
mercurous nitrate must give a copious white precipitate of 
mercurous chloride ; hydrogen sulphide must produce no 
precipitate in the fluid filtered from this, or, at all events, 
only a trifling black one (mercuric sulphide). This liquid, 
remaining clear or filtered, must be unchanged by ammonia 
and ammonium sulphide, and it should give no residue 
upon evaporation. The solution of mercurous nitrate should 
contain no free acid. It must therefore give a permanent 
black precipitate by the addition of even a very small amount 
of dilute ammonia. 

Uses. Mercurous nitrate acts in a manner analogous to 
the corresponding silver salt. In the first place, it precipi- 
tates many acids, and in the second place, it serves for the 
detection of several readily oxidizable bodies (e.g., of formic 
acid), as the oxidation of such bodies, which takes place at the 
expense of the oxygen of the mercurous salt, is attended with 
the highly characteristic separation of metallic mercury. 

72. 
6. MEBOUBIO CHLOEIDE, HgOl,. 

The corrosive sublimate of commerce is usually sufficiently 

pure. For use dissolve 1 part of the salt in 16 parts of water. 

Uses. With several acids, e.g., with hydriodic acid, mer- 



H2 REAGENTS. [ 73, 74 

<3iiric chloride gives peculiarly colored precipitates, and may 
accordingly be used for the detection of these acids. It is an 
important agent for the detection of tin, where that metal is 
in solution in the state of stannous chloride. If only the 
smallest quantity of the latter compound is present, the addi- 
tion to the solution of mercuric chloride in excess is followed 
by separation of mercurous chloride insoluble in water. In 
a similar manner, mercuric chloride serves also for the detec- 
tion of formic acid. 



73. 

7. OUPBIO SULPHATE, CuS0 4 ; crystallized, OuSO 4 .5H a O. 

Preparation. This reagent may be obtained in a state of 
great purity from the residue remaining in the flask in the 
process of preparing hydrogen sodium sulphite ( 51), by 
treating with water, applying heat, filtering, adding a few 
drops of nitric acid, boiling for some time, allowing to crys- 
tallize, and purifying the salt by re crystallization. For use 
dissolve 1 part in 10 parts of water. 

Tests. After precipitation by hydrogen sulphide, ammonia 
and ammonium sulphide must leave the filtrate unaltered. 

Uses. Copper sulphate is employed in qualitative analysis 
to effect the precipitation of hydriodic acid in the form of 
cuprous iodide. For this purpose, it is necessary to mix the 
solution of 1 part of copper sulphate with 2 parts of ferrous 
sulphate, otherwise half of the iodine will separate in the free 
state. In this process, the ferrous salt changes to ferric salt 
at the expense of the cupric sulphate, and the latter is thus 
reduced to a cuprous salt. Copper sulphate is also used for 
the detection of arsenious and arsenic acids, and likewise 
serves as a test for the soluble ferrocyanides. 

74. 

8. STANNOUS OHLOBTDB, SnCl, ; crystallized, Sn01 s .2H a O. 

Preparation. Beduce grain tin to powder by means of a 
file, or by fusing it in a small porcelain dish, removing from 



76.] HYDROOHLOKOPLATINIO ACID. 113 

the fire, and triturating with a pestle until it has passed again 
to the solid state. Boil the powder for some time with con- 
centrated hydrochloric acid in a flask (taking care always to 
have an excess of tin in the vessel) until hydrogen gas is 
scarcely evolved ; dilute the solution with 4 times the quan- 
tity of water slightly acidulated with hydrochloric acid, and 
filter. Keep the filtrate for use in a well-stoppered bottle 
containing small pieces of metallic tin or some pure tin-foil. 
If these precautions are neglected, the stannous chloride will 
soon change to stannic chloride, with separation of white 
oxychloride, which will render the reagent unfit for use. 

Tests. When added to an excess of solution of mercuric 
chloride, solution of stannous chloride must immediately pro- 
duce a white precipitate of mercurous chloride ; when treated 
with hydrogen sulphide, it must give a dark brown precipitate. 
The liquid filtered from the stannous sulphide ought not to 
be altered (after previous addition of ammonia) by ammonium 
sulphide, and should give no residue upon evaporation. 
Dilute sulphuric acid ought not to cloud or precipitate the 
stannous chloride solution after it has been diluted with 4 
volumes of alcohol (lead). "When 1 volume of the stannous 
chloride solution is heated with about 10 volumes of fuming 
hydrochloric acid, the liquid should not become brown 
(arsenic), 

Uses. The great tendency of stannous chloride to absorb 
oxygen, and thus to form stannic oxide or rather stannic 
chloride, as the stannic oxide at the moment of its formation 
reacts with the free hydrochloric acid present makes this 
substance one of our most powerful reducing agents. It 
is more particularly suited to withdraw part or the whole of 
the chlorine from chlorides. In the course of analysis, we 
employ it as a test for mercury; also to effect the detection of 
gold and arsenic. 

75. 

9. HIDBOOHLOBOPLATINIO ACID, HjPtCl. ; orystaCKzed, 
H,Pt01 6 .6H 1 O. 

Preparation. Treat platinum chips, which have been puri- 
fied by prolonged heating with concentrated nitric acid, with 



114 REAGENTS. [ 76, 77. 

concentrated hydrochloric acid and a little nitric acid, in a 
flask with a narrow neck. Warm gently for a considerable 
time, and add occasionally more nitric acid until all the 
platinum is dissolved. Evaporate the solution with repeated 
additions of hydrochloric acid upon the water-bath, and dis- 
solve the semi-fluid residue in 10 parts of water. 

Tests. Upon evaporation to dryness on the water-bath, 
hydrochloroplatinic acid must leave a residue which dissolves 
completely in alcohol. If this solution is evaporated, the 
residue ignited, treated with warm nitric acid, and the latter 
is evaporated, ixo residue, or only a very small one, should 
>be left. The hydrochloroplatinic acid solution should give 
a pure yellow, not reddish, precipitate with ammonium chlo- 
ride (indium). 

Uses. Hydrochloroplatinic acid forms very sparingly solu- 
ble salts with potassium and ammonium, but a very soluble 
salt with sodium. It serves, therefore, for the detection of 
ammonium and potassium, and for the latter, it is almost the 
best reagent in the wet way. 

76. 

10. SODIUM FALLACIOUS CHLORIDE, Na,Pd01 4 . 

Dissolve 5 parts of palladium in nitre-hydrochloric acid, 
add 6 parts of pure sodium chloride, and evaporate on the 
water-bath to dryness. The double salt thus obtained must 
completely dissolve in very little water without leaving a 
residue of intermixed sodium chloride. Dissolve 1 part of 
the salt in 12 parts of water for use. The brownish solution 
affords an excellent means for detecting and separating iodine. 

77. 

11. HIDBOOHLOBAUBIO Aero, HAu01 4 ; vrystottiwl, 
HAu01 4 .3H,0. 

Preparation. Take fine cuttings of gold, which may be 
alloyed with silver or copper, treat them in a flask with nitro- 
hydrochloric acid in excess, and apply a gentle heat until no 
more of the metal dissolves, then dilute the solution with 10 



78.] TEST-PAPERS. 115 

parts of water. If the gold was alloyed with copper which 
is known by the brownish-red precipitate produced by potas- 
sium ferrocyanide in a portion of the solution diluted with 
water rmix it with solution of ferrous sulphate in excess. 
This will reduce the hydrochlorauric acid to metallic gold, 
Tvhich will separate in the form of a fine brownish-black 
powder. Wash the powder in a small flask, and redissolve it in 
mtro-hydrochloric acid ; evaporate the solution on the water- 
bath, and dissolve the residue in 30 parts of water. If the 
gold was alloyed with silver, the latter metal remains as 
chloride upon treating the alloy with nitro-hydrochloric acid. 
In that case evaporate the solution at once, and dissolve the 
residue in water for use. 

Uses* Hydrochlorauric acid has a great tendency to yield 
up its chlorine. It therefore readily converts lower chlorides 
into higher chlorides, and, with the co-operation of water, 
lower oxides into higher oxides. These chlorinations or oxida- 
tions are usually indicated by the precipitation of pure metallic 
gold in the form of a brownish-black powder. In the course 
of analysis, this reagent is used only for the detection of Stan- 
nous salts, in the solutions of which it produces a brownish- 
jred or purple color or precipitate. 

VI. OOLOBING MATTERS AND INDLETEEENT VEGETABLE SUB- 
STANCES. 

78. 
1. TEST-PAPEBS. 

t 

or. BLUE LITMUS-PAPEB. 

* 

Preparation. Digest 1 part of litmus of commerce with 6 
parts of water, and filter the solution ; divide the intensely 
blue filtrate into 2 equal parts; saturate the free alkali in 
'one part, by repeatedly stirring with a glass rod dipped in 
very dilute sulphuric acid, until the color of the fluid just 
appears red ; add now the other part of the blue filtrate, pour 
the whole fluid into a dish, and draw strips of filter-paper 
ihrough it ; suspend these strips upon strings and leave them 



116 EEAGENTS. [ 78. 

to dry. The color of litmus-paper must be uniform, and 
neither too light nor too dark. It must be easily wet by 
aqueous liquids.* 

Uses, The red coloring matters contained in commercial 
litmus, in its aqueous extract, and in the papers colored with 
it, appear blue only on account of the presence of alkaline 
bases. If one of the blue preparations comes in contact with 
free acid, this combines with the bases, and, in consequence, 
the proper red color of the coloring matters of litmus appears. 
Litmus-paper affords, therefore, an excellent means for detect- 
ing free acids. Weak, volatile acids are capable of only tran- 
siently combining with the bases occasioning the blue colora- 
tion ; consequently the blue color appears again upon their 
volatilization. It must be borne in mind, however, that many 
soluble, normal salts of the heavy metals also effect the change 
of the blue color to red. 

J3. REDDENED LITMUS-PAPEB. 

Preparation. Stir blue solution of litmus with a glass rod 
dipped in dilute sulphuric acid, and repeat this process until 
the fluid has just turned distinctly red. Soak strips of paper 
in the solution, and dry them as in a. The dried strips must 
look distinctly red. 

Uses. Free alkalies and alkali-earths, and also the sul~ 
phides of their metals, give a blue color to red litmus-paper ; 
alkali carbonates and the soluble salts of several other weak 
acids, especially of borio acid, possess the same property. 
This reagent therefore serves for the detection of these bodies 
in general. Ammonia changes the color of red litmus-paper 
to blue only temporarily, for upon the volatilization of the 
ammonia, the red color appears again. 

y, TUEJJCEEIO-PAPEE. 

Preparation. Extract bruised turmeric-root with cold 
water, in order to remove a yellow coloring matter, which 

* The litmus-paper prepared according to the above directions fully suf- 
fices for the purposes of qualitative analysis. In regard to more refined meth- 
ods of preparation, see Zeitschr. f. analyt. Chem., 7, 466; 12, 868, 21, 993;, 
28, 697. 



79.] SOLUTION or INDIGO, 117 

has little delicacy towards alkalies. Dry the residue, digest 
1 part of it with 6 parts of alcohol, and soak strips of fine, 
unglazed paper in the filtered tincture. The dried turmeric- 
paper must have a fine yellow color, and be easily wet by 
aqueous liquids. 

Uses. Like red litmus-paper, turmeric-paper serves for 
the detection of free alkalies, etc., which change its yellow 
color to brown. It is not so delicate a test as the other re- 
agent papers, but the change of color is highly characteristic, 
and is very distinctly perceptible in many colored fluids ; we 
cannot well dispense, therefore, with this paper. When test- 
ing with turmeric-paper, it must be borne in mind that, besides 
the substances enumerated in fi, several other bodies (borio 
acid, for instance) possess the property of turning its yellow 
color to red (especially upon drying). It thus affords an excel* 
lent means for the detection of boric acid. 

All test-papers are cut into strips, which must be kept in 
well-closed boxes or in black bottles, since they are bleached 
by the continued action of light. 



79. 
2. SOLUTION OF INDIGO. 

Preparation. Take from 4 to 6 parts of fuming sulphuric 
acid, add slowly, and in small portions at a time, 1 .part of 
finely pulverized indigo, taking care to keep the mixture well 
stirred. The acid has at first imparted to it a brownish tint 
by the matter which the indigo contains in admixture, but it 
subsequently turns deep blue. Elevation of temperature to 
any considerable extent must be avoided, as part of the indigo 
is thereby destroyed. When dissolving large quantities of 
the substance, it is therefore advisable to place the vessel in 
cold water. When the whole of the indigo has been added to 
the acid, cover the vessel, let it stand forty-eight hours, then 
pour its contents into 20 times the quantity of water, mix, 
filter, and keep the filtrate for use. 



118 REAGENTS. [ 8(X 

B. KEAGKENTS IN THE DET WAT. 

I. FLUXES AHD DECOMPOSING AGENTS. 

80. 

1. MIXTURE OF SODIUM OAEBONATE AND POTASSIUM CARBONATE, 
Na a OO, + ,00,. 

Preparation. Digest for a few hours 10 parts of pow- 
dered, purified cream of tartar with 10 parts of water and 
1 part of hydrochloric acid, with frequent stirring, upon the 
water-bath. Transfer the mass to a funnel provided with a 
small filter in the apex, let it drain, cover it with a double disk 
of thick paper which is turned up around the edge, and wash 
by pouring repeatedly small c[uantities of cold water upon 
this paper, until, after the addition of nitric acid, the wash- 
ings are no longer clouded by silver nitrate solution; dry. 
the hydrogen potassium tartrate thus freed from calcium (and 
phosphoric acid). Prepare also some pure potassium nitrate 
by dissolving the commercial salt in half its weight of water 
at the boiling temperature, filtering the solution into a porce- 
lain or stoneware dish by means of a filter contained in a 
warmed porcelain funnel, and stirring it diligently with a 
porcelain or wooden spatula until cold. Bring the crystalline 
powder upon a funnel which is loosely stopped with, cotton, 
let it drain, press it down firmly, make the surface level, 
cover it with a double disk of slowly permeable paper turned 
up around the edge, and pour water upon this in small por- 
tions and at proper intervals of time until the wash-water 
which comes away is no longer made turbid by silver nitrate. 
Then transfer the contents of the funnel to a porcelain dish, 
dry the salt, and pulverize it finely. 

Mix 2 parts of the pure cream of tartar with 1 part 
of the pure saltpeter. Put the fully dried mixture in por- 
tions into an iron pot which has been brightly scoured and 
heated to low redness. After deflagration has taken place, 
heat it strongly, until a test taken out gives an entirely color- 



80.] SODIUM CARBONATE AND POTASSIUM CARBONATE. 119 

less solution with water. Pulverize the carbonized mass with 
water, filter, wash somewhat, and evaporate the solution in a 
porcelain or, better, in a silver dish until it becomes cov- 
ered with a permanent crust of salt. Let it now cool with 
constant stirring, bring the crystals of potassium carbonate 
upon a funnel, let them drain well, and wash a little. Dry 
the substance completely, best in a platinum or silver dish, 
and preserve in well-closed vessels. Upon evaporation, the 
mother-liquor yields a preparation containing traces of 
alumina and silicic acid, which is serviceable for many 
purposes. 

Pure potassium carbonate can also be obtained without 
difficulty from commercial potassium bicarbonate. Pulver- 
ize this, wash it with small amounts of cold water until, 
after acidifying with nitric acid, the washings are no longer 
clouded by silver nitrate and barium nitrate ; dry the powder 
and convert it by heating (best in a platinum or silver dish) 
into normal potassium carbonate. 

Mix intimately 13 parts of the pure potassium carbonate 
with 10 parts of pure anhydrous sodium carbonate, and pre- 
serve the mixture in well-closed bottles. This mixture can be 
directly prepared by deflagrating 20 parts of pure acid potas- 
sium tartrate with 9 parts of pure sodium nitrate, and evapo- 
rating the solution, obtained as described above, to dryness ; 
or also by igniting pure sodium potassium tartrate (Bochelle 
salt), extracting the carbonaceous mass with water, and evapol 
rating the colorless solution to dryness. 

The salt should be tested like sodium carbonate ( 49). 
The presence of any potassium cyanide is detected by adding 
some ferrous-ferric solution and then an excess of hydrochlo- 
ric acid, when a bluish-green coloration is produced, and a 
blue precipitate which settles after long standing. 

Uses. If silicic oxide or a silicate is fused with about 4 
parts (consequently with an excess) of potassium or sodium 
carbonate, carbon dioxide escapes with effervescence, and an 
alkali silicate is formed, which, being soluble in water, may 
be separated from such metallic oxides as may remain 
undissolved; from the solution, hydrochloric acid separates 
the silicic acid. If sodium or potassium carbonate is fused 
together with sulphates of barium, strontium, or calcium, 



120 KEAGENTS. [ 81. 

there are formed carbonates of the alkali-earth metals and 
sodium or potassium sulphate, which are compounds that can 
"be separated by water, and in which new compounds, both 
the base and the acid of the originally insoluble salt may 
now be readily detected. Instead of potassium carbonate or 
sodium carbonate alone, we use preferably the mixture con- 
sidered above, for fluxing insoluble silicates and sulphates, 
because it has a lower melting-point than either of its con- 
stituents, and thus renders it possible to flux the compounds 
under consideration by the use of a simple gas-lamp or of 
BEBZELIUS'S alcohol-lamp. The fusion with alkali carbonates 
is invariably effected in a platinum crucible, provided no- 
reducible metallic compound is present. 



81. 
2. BABIUM HYDBOXIDE, Ba(OH) a . 

Preparation. Heat the barium hydroxide crystals, ob- 
tained according to 37, in a silver or platinum dish at a 
gentle heat until all the water of crystallization is driven off, 
pulverize the remaining white mass, and keep it for use in 
well-stoppered bottles. 

Uses. Barium hydroxide fuses at a low red heat without 
losing its water. If silicates which are undecomposable by 
acids are fused with about 4 times their weight of this re- 
agent, basic silicates are formed which are decomposable 
by acids. If the fused mass, therefore, is treated with water 
and hydrochloric acid, the solution evaporated to dryness, 
and the residue digested with dilute hydrochloric acid, the 
silicic acid remains undissolved, while the metallic chlorides 
go into solution. Use is made of barium hydroxide for flux- 
ing when it is desired to test silicates for alkalies. It is 
deservedly preferred to barium carbonate or nitrate, which 
may be used for the same purpose, because it does not 
require a very high temperature like the first, and does not 
occasion spattering on account of evolved gas like the latter. 
Fluxing with barium hydroxide is done in a silver or plati- 
num crucible. 



g 82, 83.] SODIUM JNTITBATE. 121 

82. 
3. CALCIUM FLUOBTOE, CaF 15 and other FLUORIDES. 

Select the purest fluor-spar possible, especially such as is 
free from alkalies, pulverize it finely, and keep for use. 

Uses. When used together with sulphuric acid, calcium 
fluoride serves for decomposing silicates which are insoluble 
in acids, and especially for detecting the alkali metals con- 
tained in them. If aqueous hydrofluoric add which is pure 
(leaving no residue when evaporated in a platinum dish) is 
available (this can now to be purchased in wax bottles) or 
pure ammonium fluoride or hydrogen ammonium fluoride, these 
are to be preferred to calcium fluoride for decomposing sili- 
cates. (Compare silicic add, 180.) Hydrogen ammonium 
fluoride, HF.NH 4 F, can be quickly prepared by strongly super- 
saturating hydrofluoric acid or hydrofluosilicic acid with 
ammonia. After warming gently, filter if necessary, best 
with the employment of a funnel of gutta-percha or hard 
rubber, and evaporate the filtrate in a platinum dish to dry- 
ness. The preparation must volatilize without leaving a resi- 
due when heated in a platinum dish (the commercial salt 
sometimes contains lead). It is best prepared directly for 
use, because it can be kept only in platinum vessels, or in 
those of gutta-percha or hard rubber, and it is inclined to 
deliquesce. The solution of this salt, supersaturated with 
ammonia, serves also for the recognition and separation of 
lithium, 

83. 
4. SODIUM NETBACT, NaNO* 

Preparation. Exactly neutralize pure nitric acid with pure 
sodium carbonate, and evaporate to crystallization ; dry the 
crystals thoroughly, triturate, and keep the powder for use. 

Tests. A solution of sodium nitrate must not be made 
turbid by solution of silver nitrate or barium nitrate, nor pre- 
cipitated by sodium carbonate. 

Uses. Sodium nitrate serves as a very powerful oxidizing 



122 BEAGEOTS. [ 84? 85. 

agent, by yielding oxygen to combustible substances when 
heated with them. We use this reagent principally to con- 
vert several metallic sulphides, more particularly the sul- 
phides of tin, antimony, and arsenic, into oxides or acids; 
also to effect the rapid and complete combustion of organic 
substances. For the latter purpose, however, ammonium 
nitrate is sometimes preferable, and is prepared by neutraliz- 
ing nitric acid with ammonium carbonate. 

84. 
5. POTASSIUM DISULPHATE, KaSA- 

Preparation. Mix in a platinum dish or a large platinum 
crucible 87 parts of neutral potassium sulphate with 49 parts 
of pure concentrated sulphuric acid, heat to low redness until 
the mass is uniformly liquid and perfectly clear, then pour it 
into a platinum dish standing in cold water, or upon a frag 
ment of porcelain or something of the kind ; break it up, and 
preserve it for use. 

Tests. The potassium disulphate must dissolve in water 

with ease to a clear fluid with a strong acid reaction. The 
solution must not be rendered turbid nor precipitated by 
hydrogen sulphide or by ammonia and ammonium sulphide. 

Uses.Ai the temperature of fusion, potassium disul- 
phate dissolves and decomposes many bodies which cannot 
be dissolved and decomposed without considerable difficulty, at 
least, by acids in the wet way, such as ignited alumina, titanic 
oxide, chrome ironstone, etc. This reagent, therefore, is of 
service in effecting the solution or decomposition of such 
bodies. The fusion is preferably effected in platinum vessels. 

II. BLOWPIPE BEAGENTS. 

85. 
1. SODIUM OABBONATB, Na,CO $ . 

Preparation. See 49. 

Uses. Sodium carbonate serves, in the first place, to pro- 
mote the reduction of oxidized substances in the inner flame 



86.] POTASSIUM CYANIDE. 128, 

of the blowpipe. In fusing, it brings the oxides into the most 
intimate contact with the charcoal support, and enables the 
flame to embrace every part of the substance under examina- 
tion. With salts of the heavy metals, the reduction is pre- 
ceded by separation of the base. In this process, it also- 
co-operates chemically by the transposition of its constitu- 
ents (according to K. WAGNER, in consequence of the forma- 
tion of sodium cyanide). Where the quantity operated upon 
is very minute, the reduced metal is often found in the 
pores of the charcoal. In such cases, the parts surrounding 
the cavity which contained the substance are dug out with a 
knife, triturated in a small mortar, and the charcoal is then 
washed off from the metallic particles, which now become 
visible either in the form of powder or as small, flattened 
spangles, as the case may be. 

Sodium carbonate serves, in the second place, as a solvent, 
and platinum wire is the most convenient support for testing- 
the solubility of substances in the fused reagent. Only a few 
of the bases dissolve in fusing sodium carbonate, but acids 
dissolve in it with facility. It is also applied as a decompos- 
ing agent and a flux, more particularly to effect the decom- 
position of the insoluble sulphates, with which it exchanges 
acids, the newly formed sodium sulphate being reduced in 
the inner flame to sodium sulphide. It is further employed 
to effect the decomposition of arsenious sulphide, with which 
it forms a double arsenious and sodium sulphide, and sodium 
arsenite or arsenate, thus converting it to a state which 
permits its subsequent reduction by hydrogen. In the dry 
way, sodium carbonate is also the most sensitive reagent for 
the detection of manganese, as when fused in the outer flame 
with a substance containing manganese it produces a green, 
opaque bead, owing to the formation of sodium manganate. 

86. 
2. POTASSIUM OYAMIDB, EON. 



cyanide is an exceedingly powerful 
reducing agent in the dry way, excelling in its action almost 



124 BEAGENTS. 



[87. 



all other reagents, and separating the metals not only from 
most oxygen compounds, but also from many sulphur com- 
pounds. In the former case, this reduction is attended with 
formation of potassium cyanate by the absorption of oxygen, 
and in the latter case, with formation of potassium sulpho- 
cyanide by the taking up of sulphur. By means of this 
reagent, we may effect the reduction of metals from their 
compounds with the greatest facility (usually even in a porce- 
lain crucible over a simple gas or alcohol flame). We may, 
for instance, produce metallic antimony from antimonious 
acid or from antimony sulphide, metallic iron from ferric 
oxide, etc. The readiness with which potassium cyanide 
enters into fusion greatly facilitates the reduction of the 
metals. It is a most valuable and important agent for 
effecting the reduction of stannic oxide, antimonic acid, and 
particularly of arsenious sulphide. It is equally important 
as a blowpipe reagent, its action being exceedingly energetic, 
and substances like stannic oxide, the reduction of which 
by means of sodium carbonate requires a tolerably strong 
flame, are reduced by potassium cyanide with the greatest 
facility. In blowpipe experiments, we invariably use a mix- 
ture of equal parts of sodium carbonate and potassium 
cyanide, the admixture of the former being intended here to 
check in some measure the excessive fusibility of the latter. 
This mixture, besides being a far more powerful reducing 
agent than the simple sodium carbonate, has, moreover, 
this great advantage, that it is absorbed by the pores of 
the charcoal with extreme facility, and thus permits the 
production of the metallic globules in a state of the greatest 
purity. 

87. 
8. SODIUM FOEMA.TB, NaOHO,. 

Preparation. Heat in a tubulated retort connected with a 
condenser and a receiver 200 parts of glycerine and 12 parts 
of crystallized oxalic acid. At 75 a lively reaction begins, 
and at 90 it is in full operation. It consists in the de- 
composition of oxalic acid into carbonic and formic acids: 



88.] SODIUM TETKABOEATE. 125 

H a O a O 4 = CO, -f HCHO,. The glycerine induces the reac- 
tion, but remains unchanged as far as the final result is con- 
cerned. Aqueous formic acid goes over with the liberated 
carbon dioxide. As soon as the evolution of carbon dioxide 
has almost ceased, add 12 parts more of oxalic acid. The 
liquid now going over is richer in formic acid than the 
first distillate. After the reaction has almost stopped, add 
13 parts of oxalic acid, and afterwards again 13 parts. In 
this way, 130 parts of distillate are obtained, which con- 
tains about 56 per cent of formic acid (BEETHELOT, LORIN). 
Neutralize this with sodium hydroxide which is free from 
sulphate, evaporate the solution to dryness, dry the residue 
at 130, and preserve the anhydrous salt thus obtained in 
a well-closed bottle. 

Teats. Sodium formate is, above all, to be tested to find 
if it contains any sulphate. Its aqueous solution ought, 
therefore, to give no turbidity with barium chloride after the 
addition of a few drops of hydrochloric acid. 

Uses* Sodium formate is a powerfully acting reducing 
agent, and can often be used instead of the poisonous potas- 
sium cyanide. Its action depends upon the fact that it goes 
over into sodium carbonate by heating, with the liberation of 
hydrogon and carbon monoxide (F. NELISSEN). 



88. 
4. SODIUM TETRABORA.TE (BORAX), Na a B 4 O t ; wystoIKzed, 



The purity of commercial borax may be tested by adding 
to its solution sodium carbonate, or, after previous addition 
of nitric acid, solution of barium nitrate and of silver nitrate. 
The borax may be considered pure if these reagents fail to 
produce any alteration in the solution ; but if either of them 
causes the formation of a precipitate, or renders the fluid 
turbid, recrystallization is necessary. The pure crystallized 
borax is exposed to a gentle heat in a platinum crucible until 
it ceases to swell. It is then left to cool, and afterwards 
pulverized and kept for use. 



126 REAGENTS. [ 



. Boric acid shows a great affinity for oxides when 
it comes in contact with them in a molten condition. In 
the first place, therefore, it combines directly with oxides ; 
in the second place, it expels weaker acids from their salts ; 
and in the third place, it facilitates the oxidation of metals, 
and of sulphur and halogen compounds in the outer blowpipe 
flame, owing to the fact that it dissolves the resulting oxides. 
The borates which form are usually fusible themselves, but 
they fuse far more readily together with sodium borate, the 
latter acting simply as a flux or forming double salts. In 
sodium tetraborate, we have, first, active boric acid ; second, 
sodium borate ; and, consequently, both conditions com- 
bined, whereby, as stated, oxides, sulphides, metals, etc., are 
brought into a state of solution and fusion. For these reasons, 
borax is of the greatest importance as a blowpipe reagent. 
In the process of fusing with borax, platinum wire is usually 
selected for a support. The loop of the wire is moistened 
or heated to redness, then dipped into the powder, and 
exposed to the outer flame, a colorless bead of fused borax 
being thus produced. A small portion of the substance is 
then attached to the bead, by bringing the latter into con- 
tact with it while still hot or by having previously moistened 
it. The bead with the substance adhering is next exposed 
to the gas or blowpipe flame, and the reactions are observed. 
The following points ought to be more particularly watched : 
(1) Whether the substance dissolves to a transparent bead, 
' and retains its transparency on cooling ; (2) whether the bead 
exhibits a distinct color, which in many cases at once clearly 
indicates the individual metal contained in the substance, as 
is the case, for instance, with cobalt; and (3) whether the 
bead manifests the same or a different deportment in the 
outer and in the inner flame. Beactions of the last kind 
arise from the reduction of higher to lower oxides, or even to 
the metallic state, and are for some substances particularly 
characteristic, 



89, 90. COBALT NITEATB. 127 

89. 

6. HYDROGEN SODIUM AMMONIUM PHOSPHATE, HNaNH 4 P0 4 .8H,O. 
(Microcosmic Salt, Salt of Phosphorus.) 

Preparation. a. Heat to boiling 6 parts of hydrogen diso- 
diuna phosphate and 1 part of pure ammonium chloride with 
2 parts of water, and let the solution cool. Free the resulting 
crystals from the sodium chloride which adheres to them, 
by recrystallization, with addition of some solution of ammo- 
nia. Dry the purified crystals, pulverize, and keep for use. 

b. Take 2 equal parts of pure orthophosphoric acid, and 
add solution of soda to one and solution of ammonia to the 
other, until both fluids have a distinct alkaline reaction ; mix 
the two together, and let the mixture crystallize. 

Tests. Hydrogen sodium ammonium phosphate dissolves, 
in water to a fluid with feebly alkaline reaction. The yellow- 
precipitate produced in this fluid by silver nitrate must com- 
pletely dissolve in nitric acid. Upon fusion on a platinum, 
wire, microcosmic salt must give a clear and colorless bead. 

ZTses. On heating hydrogen sodium ammonium phosphate,, 
two molecules of it give up a molecule of water and two mole- 
cules of ammonia, together with the water of crystallization* 
leaving hydrogen sodium pyrophosphate, B^Na^O,; upon 
heating more strongly, an additional molecule of water escapes* 
and two molecules of readily fusible sodium nwtaplwsp'hate, 
NaPO,, are left behind. The action of sodium metaphos- 
phate is quite analogous to that of sodium tetraborate. How- 
ever, in some oases we prefer it to borax as a solvent or flux, 
the beads which it forms with many substances being more 
distinctly colored than those of borax. Platinum wire is 
also used for a support in the process of fluxing with sodium 
metaphosphate. The loop must be made small and narrow, 
otherwise the bead will not adhere to it The operation 19 
conducted as directed for borax. 

90. 
6. COBALT NITRACT, Oo(NO,) 9 ; crystallized, Oo(NO,) 3 .6H a O. 

Preparation. Dissolve commercial cobalt oxide in hydro- 
chloric acid, evaporate the solution to dryness upon the 



128 REAGENTS. [ 90. 

water-bath, take up the residue with water, add precipitated 
barium carbonate suspended in water, in some excess, let 
it stand for several hours with frequent stirring, filter, and 
wash; add to the filtrate more barium carbonate, pass in 
chlorine, let it stand for some time with frequent agitation, 
separate the precipitate consisting of cobaltic hydroxide and 
the excess of barium carbonate from the solution containing 
the nickel, wash, dissolve in hydrochloric acid, precipitate the 
barium by adding sulphuric acid in only slight excess, and 
then, without previously filtering, pass in hydrogen sulphide 
while the liquid is heated to about 70. Filter, add ammonia 
to alkaline reaction, then ammonium sulphide until this pre- 
dominates ; finally, add acetic acid to distinctly acid reaction. 
Filter off the cobalt sulphide, wash it, dissolve it in aqua 
regia, evaporate off the excess of acid, take up with water, and 
precipitate hot with sodium carbonate. After washing the 
precipitate, mix it while still moist with an excess of oxalic 
acid. Wash the rose-red cobalt oxalate well, dry it, and 
ignite it in a glass tube in a stream of hydrogen, It decom- 
poses in this operation into carbon dioxide, which escapes, and 
metallic cobalt Wash the latter first with water containing 
acetic acid, then with pure water ; dissolve it in dilute nitric 
acid, evaporate the solution on the water-bath to dryness, 
and dissolve 1 part of the residue in 10 parts of water. 

Tests. Solution of cobalt nitrate must be free from other 
metals, especially from salts of the alkali metals ; and when 
precipitated with ammonium sulphide and filtered, the filtrate 
upon evaporation on platinum must leave no fixed residue. 
Treated with potassium cyanide in excess and bromine, with 
the addition, if necessary, of sodium hydroxide, there should 
form no black precipitate of nickelic hydroxide, even after 
about an hour. 

Uses. Upon ignition with certain infusible bodies (zinc 
oxide, alumina), cobalt monoxide forms peculiarly colored 
compounds, and may accordingly serve for their detection 
(see Section III). 



SECTION III. 

REACTIONS, OE DEPORTMENT OF BODIES WITH 

EEAGENTS. 

91. 

IN my introductory remarks, I stated that the operations 
and experiments of qualitative analysis have for their object 
the conversion of the unknown constituents of any given com- 
pound into forms of which we know the deportment, relations, 
and properties, and which will accordingly permit us to draw 
correct inferences regarding the several constituents of which 
the analyzed compound consists. The greater or less value 
of such analytical experiments, like that of all other inquiries 
and investigations, depends upon the greater or less degree 
of certainty with which they lead to definite results, whether 
of a positive or negative nature. But as a question does not 
render us any wiser if the language is unknown in which tha 
answer is returned, so in like manner will analytical investi- 
gations prove unavailing if we do not understand the mode 
of expression in which the desired information is conveyed 
to us ; in other words, if we do not know how to interpret 
the phenomena produced by the action of reagents upon the 
substance examined. 

Therefore, before we can undertake the practical in- 
vestigation of analytical chemistry, it is indispensable that 
we should possess the most accurate knowledge of the de- 
portment, relations, and properties of the new forms into 
which we intend to convert the substances we wish to ana- 
lyze. Now this knowledge consists, in the first place, in a 
clear conception and comprehension of the conditions neces- 
sary for the formation of the new compounds and the mani- 
festation of the various reactions; and in the second place, in 

129 



130 DEPORTMENT OF BODIES WITH REAGENTS. [ 92. 

a distinct impression of the color, form, and physical proper- 
ties which characterize such compounds. This section of 
the work demands, therefore, not only the most careful and 
attentive study, but requires that the student should verify 
the facts by experiment. 

In the present work, those substances which are in many 
respects analogous are arranged in groups, since by compar- 
ing their analogies with their differences, the latter are placed 
in the clearest possible light. 

A, DEPOBTMENT OF THE METALLIC, MOSTLY BASIC, EAJDIOALS. 

92. 

Before proceeding to the special study of the several metals, 
I give here a general view of all of them classified in groups, 
showing which belong to each group. The basis for this 
classification will appear in connection with the special con- 
sideration of each group. 
First group : 

Potassium, sodium, ammonium (owsium, rubidium, 

lithium). 
Second group : 

JBarivm, strontium, calcium, magnesium. 
Third group : 

Aluminium, chromium (beryllium, thorium, zirconium, 
yttrium, cerium, lanthanum, didymium, titanium, 
tantalum, niobium). 
Pourth group : 

Zinc, manganese, nickel, cobalt, iron (uranium, thallium, 

indium, gallium, vanadium). 
Kffli group : 

Silver, mercury, lead, bismuth, copper, cadmium (pal- 
ladium, rhodium, osmium, ruthenium). 
Sixth group : 

Gold, platinum, tin, antimony, arsenic (germanium, irid- 

ium, molybdenum, tungsten, tellurium, selenium). 
Of these metals, only those printed in italics are found dis- 
tributed extensively and in large quantities in that portion of 
the earth's crust which is accessible to investigation. There- 



93, 94] POTASSIUM. 131 

fore, these are most important in chemistry, the arts and 
manufactures, agriculture, pharmacy, etc., and will be dwelt 
upon at greater length. The remainder are more briefly con- 
sidered in paragraphs printed in smaller type, which may be 
passed over when the study of analytical chemistry is first 
taken up. The metals which are still the subject of scientific 
discussion, especially those imperfectly known, such as 
erbium, terbium, davyum, scandium, holmium, ytterbium, 
samarium, philippium, decipium, thulium, etc., are not con- 
sidered in this book. The properties and reactions of the 
metals themselves I have given only in the case of those that 
are more frequently met with in the metallic state. 

93. 

E1BST GROUP. 

More common metals : POTASSIUM, SODIUM, AMMONIUM. 

Barer metals : CESIUM, RUBIDIUM, LITHIUM. 

Properties of the Group. The hydroxides of the metals of 
the first group the alkalies are readily soluble in water, as 
are also the sulphides, carbonates, and phosphates of these 
metals. (Lithium carbonate and phosphate, however, dis- 
solve with difficulty.) Accordingly, the alkalies do not pre- 
cipitate one another, nor do the alkali carbonates or phos- 
phates (in the case of lithium, a high degree of dilution of 
the solutions is presupposed), nor are they precipitated by 
hydrogen sulphide under any conditions. The solutions of 
the hydroxides, as well as of the sulphides and carbonates of 
this group, restore the blue color of reddened litmus-paper, 
and impart an intensely brown tint to turmeric-paper. 

Special fieactions of the More Common Metals of the 
First Group. 

94. 
a. POTASSIUM, K. (Oxide, ,0.) 

1. POTASSIUM HTOBOXTDE and POTASSIUM SAI/TS are not vola* 
idle at a faint red heat. The hydroxide deliquesces in the 



132 DEPORTMENT OF BODIES WITH REAGENTS. [ 94. 

air, and the oily liquid formed absorbs carbon dioxide rapidly, 
but without solidifying. 

2. Nearly all the POTASSIUM SALTS are soluble in water. 
Those with colorless acids are colorless. The normal salts 
of strong acids do not alter vegetable colors. Potassium 
carbonate crystallizes (in combination with water of crystal- 
lization) with difficulty, and deliquesces in the air; while 
potassium sulphate is anhydrous, and suffers no alteration 
upon exposure. 

3. In the neutral and acid solutions of potassium salts,. 
hydrocfdoroplatinic acid produces a yellow, crystalline, heavy 
precipitate of POTASSIUM PLATZNIO CHLOBIDE, K,Pt01 8 . In con- 
centrated solutions, this precipitate separates immediately 
upon the addition of the reagent ; but in dilute solutions, it 
forms only after some time, often after a considerable time. 
Very dilute solutions are not precipitated by the reagent. 
The precipitate consists of octahedrons discernible under the 
microscope. Alkaline solutions must be acidified with hydro- 
chloric acid before the hydrochloroplatinic acid is added. 
The precipitate is difficultly soluble in water, and the presence 
of free acids does not greatly increase its solubility. It is 
insoluble in alcohol. Hydrochloroplatinic acid is therefore 
a particularly delicate test for potassium salts dissolved in 
alcohol. The best method of applying this reagent is to 
evaporate the aqueous solution of the potassium salt with 
hydrochloroplatinic acid nearly to dryness on the water-bath, 
and to pour a little water over the residue (or, better still, 
some alcohol, provided no substances insoluble in that men- 
struum are present), when the potassium platinic chloride will 
be left undissolved. Oare must be taken not to confound this 
salt with ammonium platinio chloride, which greatly resem- 
bles it (see 96, 5). 

4. In neutral or alkaline solutions, tartaric add produces. 
a white, quickly subsiding, granular crystalline precipitate of 
ETOBOGEN POTASSIUM TAETRATE, HE0 4 H 4 O ft . (To alkaline solu- 
tions, the reagent must be added until the fluid shows a 
strongly acid reaction.) In concentrated solutions, this pre* 
cipitate separates immediately, but in dilute solutions, often 
only after the lapse of considerable time. Vigorous shaking 
or stirring of the fluid greatly promotes its formation. Very 



94.] POTASSIUM. 133 

dilute solutions are not precipitated by this reagent. Free 
alkalies and free mineral acids dissolve the precipitate. It is 
sparingly soluble in cold, but pretty readily soluble in hot 
water. In acid solutions, the free acid must, if practicable, 
first be expelled by evaporation and ignition, or the solution 
must be neutralized with sodium hydroxide or carbonate. 

Hydrogen sodium tartrate answers still better than free 
tartaric acid as a test for potassium. The reaction is the same 
in kind, but different in degree, being more delicate with the 
salt than with the free acid. Where the former is used, the 
sodium salt of the acid that was combined with the potas- 
sium is formed, whereas when free tartaric acid is the test 
applied, the acid originally combined with the potassium is 
liberated. This action tends to increase the dissolving power 
of the water present upon the hydrogen potassium tartrate, 
and thus to check the separation of the latter : KNO, + HNa 
4 H 4 O 6 = HK0 4 H 4 6 + NaN0 8 . 

5. If five or six drops of cobalt nitrate solution ( 90) and 
about 1 cc of acetic acid are added to about 2 cc of a 10 per 
cent solution of sodium nitrite, a deep orange-yellow fluid hav- 
ing a strong odor of nitrous acid is obtained. When added 
to the neutral solution of a potassium salt until the color 
becomes yellow, this freshly prepared reagent produces a 
yellow, crystalline precipitate of POTASSIUM OOBALTEO NITRITE, 
K,Co(NC) a ) e . In concentrated solutions, this takes place im- 
mediately, but in more dilute ones, only after some time. 
1 part of potassium chloride dissolved in 1000 parts of water 
will still give the reaction (DE KONINOK). Alkaline solutions 
should be acidified with acetic acid before the test is made. 
Acid solutions should be neutralized with sodium carbonate, 
if the acid cannot be removed by evaporation. The properties 
of the precipitate are given under 125, 14. Ammonium salts 
give a similar reaction, but only in concentrated solutions. 
The salts of the alkaline-earth metals are not precipitated by 
this reagent. 

6. If a potassium salt which is volatile at an intense red 
heat is held on the loop of a fine platinum wire in the fusing 
zone of the BTJNSEN gas-lamp (p. 31), the salt volatilizes, and 
imparts a BLTJISH-VIOLET tint to the part of the flame above the 
sample. Potassium chloride and potassium nitrate volatilize 



134 DEPORTMENT O1P BODIES WITH BEAGENTS. [ 94. 

rapidly, the carbonate and sulphate less rapidly, and the 
phosphate still more slowly; but all distinctly show the reac- 
tion, though in decreasing degree. If it is wished to obtain 
a more uniform manifestation of the reaction, i.e., a manifes- 
tation independent of the nature of the acid that may chance 
to be combined with the potassium, the sample may be 
simply moistened with sulphuric acid, dried at the border of 
the flame, and then introduced into the fusing zone. With 
silicates and other potassium compounds of difficult volatility, 
the reaction may he insured by first fusing the sample with 
pure gypsum, as this serves to form calcium silicate and po- 
tassium sulphate, and the latter salt readily colors the flame. 
Decrepitating salts are ignited in a platinum spoon before 
they are attached to the loop. The sample of potassium 
salt may also be held before the apex of the inner blowpipe 
flame produced with a spirit-lamp. The presence of a sodium 
salt completely obscures the potassium coloration of the 
flame. 

If the potassium flame is observed through the indigo 
prism (p. 38), the coloration appears sky-blue, violet, and at 
last intensely crimson, even through the thickest layers of the 
solution. Admixtures of calcium, sodium, and lithium com- 
pounds do not alter this reaction, as the yellow rays cannot 
penetrate the indigo solution, and the rays of the lithium 
flame are able to pass through the thinner layers of the 
solution, but not through the thicker layers. The exact spot 
where the penetrating power of the rays of the lithium 
flame ceases has to be marked by the operator on his indigo 
prism. But organic substances which impart luminosity to 
the flame might lead to mistakes, and must therefore, if 
present, first be destroyed by heat. Instead of the indigo 
prism, one containing potassium permanganate (p. 38) can be 
used, or also a blue glass. In the presence of lithium, suffi- 
ciently thick layers of the absorbing media should be used, 
so that the red of the lithium cannot penetrate them. 

The spectrum of the potassium flame produced by the 
spectroscope (p. 40) is mapped on Plate L It contains two 
characteristic lines the red line CL and the indigo-blue line ft. 

7. If a potassium salt (potassium chloride is best) is heated 
with a little water, alcohol (burning with a colorless flame) 



Q 5.1 SODIUM. 135 

added, and the liquid heated and kindled, the flame appears 
VIOLET. The reaction is far less delicate than the one men- 
tioned in 6, and the presence of sodium hides it completely. 

95. 

I. SODIUM, Na. (OMe, Na,0.) 

1. SODIUM HYDROXIDE and SODIUM SALTS present in general 
the same properties and reactions as potassium and its corre- 
sponding compounds. The oily fluid which sodium hydroxide 
forms by deliquescing in the air resolidifies speedily by ab- 
sorption of carbon dioxide. Sodium carbonate crystallises 
readily, and the crystals, Na a OO,.10H a O, effloresce rapidly 
when exposed to the air. The same applies to the crystals of 
sodium sulphate, Na a SO 4 .10H a O. Sodium chloride is much 
less soluble in concentrated hydrochloric acid than in water. 

2. If a sufficiently concentrated solution of a sodium salt 
with neutral or alkaline reaction is mixed (conveniently in a 
watch-glass) with a solution of add potassium pyroantimonate 
prepared according to the directions of 54, the mixture 
remains clear at first, or appears only slightly turbid. How- 
ever, upon rubbing with a glass rod the part of the glass wet 
by the fluid, a crystalline precipitate of SODIUM PIBOANTIMONATE, 
Ha!Na a Sb|O 7 .6II fl O, speedily separates, which first makes its 
appearance along the lines rubbed with the rod, and sub- 
sides from the fluid as a heavy, sandy precipitate. From 
dilute solutions of sodium salts, the precipitate separates only 
After some time, e.g., twelve hours. From very dilute solu- 
tions, it does not separate at all. The precipitated sodium 
pyroantimonate is m^ariaJAy crystalline. Where it has separ- 
ated slowly, it occasionally consists of well-formed, micro- 
scopic, tetragonal octahedrons, but more frequently of four- 
sided prisms, terminated by pyramids. Where it has sepa- 
rated promptly, it appears in the form of small boat-shaped 
crystals. Presence of large quantities of potassium salts 
interferes very considerably with the reaction. Acid solu- 
tions cannot be tested with potassium pyroantimonate, as. 
from the latter substance, free acids will separate pyroanti- 
monic acid. Before adding the reagent, it is indispensable. 



136 JD-KPuKlJuENT OF BODIES WITH BEAGENTS, [95* 

therefore, to remove, if possible, the free acid by evaporation 
or ignition, or where this is not practicable, by neutralizing 
the acid solution with a little potassium carbonate until the 
reaction is feebly alkaline. It should also be borne in mind 
that only those solutions which contain no salts other than 
those of sodium, potassium, and perhaps ammonium, can be 
tested with potassium pyroantimonate. 

3. If sodium salts are held in the fusing zone of the BUN- 
SEN gas-lamp or in the inner alcohol Uoivpipe flame, they show, 
with regard to their relative volatility and the action of de- 
composing agents upon them, a similar deportment to the 
salts of potassium. The sodium salts are, however, a little 
less volatile than the corresponding potassium salts. But the 
most characteristic sign of the presence of sodium salts is 
the INTENSE YELLOW COLORATION which they impart to the 
flame. This reaction will effect the detection of the minutest 
quantities of sodium, and is not obscured by the presence of 
large quantities of potassium salts. 

It is characteristic of the sodium flame that a crystal of 
potassium dichromate appears colorless in its light, and that 
a slip of paper coated with mercuric iodide appears white, 
with a faint shade of yellow (BUNSEN) ; also that the flame 
looks orange-yellow when observed through a green glass 
(MERZ). These reactions are not obscured by presence of salts 
of potassium, lithium, and calcium. 

The spectrum (Plate T) shows only a single yellow line a 
in an ordinary spectroscope, but with a very powerful appara* 
tus, two lines will be distinctly visible, although they are ex- 
ceedingly close to each other. The reaction is so delicate 
that the sodium chloride contained in atmospheric dust 
generally suffices to give a sodium spectrum, although a faint 
one. 

4. If a SODIUM SALT (sodium chloride is the best) is treated 
as has been given for potassium under T, the alcohol flame is. 
colored STRONGLY IELLOW. This reaction, also, is not obscured 
by the presence of potassium salts. 

6. HydrocJfaoplatmic add produces no precipitate in neu- 
tral or acid solutions of -sodium salts. Sodium platinio chloride 
dissolves readily both in water and in alcohol, and it ciya* 
tallizes in long, yellow prisms. 



96.] AMMONIUM. 137 

6. Tcvrtcuric add and hydrogen sodium tartrate fail to pre- 
cipitate even concentrated, neutral solutions of sodium salts. 



96. 
AMMONIUM, NH 4 . 

1. AMMONIA, NH 8 , is gaseous at the common temperature ; 
but is most frequently dealt with in its aqueous solution, in 
which it betrays its presence at once by its penetrating odor. 
It is expelled from this solution by the application of heat. 
It may be assumed that the solution contains ammonium 
oxide, (NH 4 ) ft O, or hydroxide, NH.OH (see 36). 

2. All AMMONIUM SALTS are volatile at a low heat, either 
with or without decomposition. Most of them are readily 
soluble in water. The solutions are colorless if the acid 
exerts no coloring influence. The normal compounds of am- 
monium with strong acids do not alter vegetable colors. 

3. If AMMONIUM SAHTS are triturated together with slaked 
lime (best with the addition of a few drops of water), or, 
either in the solid state or in solution, are heated with solution 
of potassium or sodium hydroxide, ammonia is liberated in 
the gaseous state, and betrays its presence 1, by its character- 
istic ODOE ; 2, by its REACTION with moistened test-papers ; and 
3, by giving rise to the formation of WHITE FUMES when any 
object (e.g., a glass rod) moistened with hydrochloric acid, 
nitric acid, acetic acid, or any of the volatile acids, is brought 
in contact with it. These fames arise from the formation of 
solid ammonium salts produced by the contact of the gases in 
the air. Hydrochloric acid is the most delicate test in this 
respect, but acetic acid admits less readily of a mistake. 
If the expulsion of the ammonia is effected in a small beaker, 
best with slaked lime, with addition of a very little water, 
and the beaker is covered with a watch-glass having a strip of 
moistened turmeric- or reddened litmus-paper attached to the 
center of the convex side, the reaction will show the presence 
of even very minute quantities of ammonia. In such cases, 
however, the reaction is not immediate, but requires some 
time for its manifestation. It is promoted and accelerated 
by the application of a gentle heat 



138 DEPORTMENT OF BODIES WITH REAGENTS. [ 96. 

4. If a solution of normal mercurous nitrate is added to a 
solution which contains free ammonia or ammonium carbon- 
ate, a black precipitate results, which in very dilute solutions 
is at first whitish-gray. Therefore, if the ammonia evolved 
according to 3, being set free in a test-tube, is allowed to act 
upon a glass rod which is moistened with mercurous nitrate 
and introduced, or, being liberated in a beaker, is allowed to 
act upon a drop of mercurous nitrate solution spread upon the 
convex side of a watch-glass covering it, or upon a strip of 
paper under the watch-glass, moistened with this solution, the 
moistened part of the rod, the drop, or the paper, becomes 
colored from gray to black. This manner of producing the re- 
action is to be especially recommended, because considerable 
amounts of salts present in the liquid to be tested may retard 
the reaction or prevent it. The precipitate which forms in 
this reaction, the so-called mercurius solubilis HAHNEMANNI, 
is not always of the same composition. The precipitate first 
formed at a great degree of dilution, which produces the com- 
pound in the purest condition, corresponds to the formula 
NH a Hg a NO s (LosoH). The formation is illustrated by the fol- 
lowing equation: Hg a (NO a ) 9 +2NH l = NE^NO.+NI^NO,. 

5. ffydrocJdoroplatinic add shows the same deportment with 
ammonium salts as with salts of potassium. Like the cor- 
responding potassium compound, the yellow precipitate of 
AMiomtfM PLATTNIO CHLORIDE, (NH 4 ) fl Pt01 6 , consists of octahe- 
drons discernible under the microscope. 

6. From highly concentrated solutions with neutral reac- 
tion, tartaric acid throws down after some time part of the 
ammonium as HYDROGEN AMMONIUM TARTRATE, ENH 4 C 4 H 4 0. 
Less concentrated solutions are not precipitated. Hydrogen 
sodium tartrate precipitates concentrated solutions much more 
completely, and produces a precipitate even in more dilute 
solutions. The precipitate is white and crystalline. Its 
separation may be promoted by shaking, or rubbing the glass 
inside with a glass rod. By solvents it is acted upon like the 
corresponding potassium salt, except that it is a little more 
readily soluble in water and in acids. 



97.] KEOAPITULATION AND REMARKS, 13ft 



97. 

Recapitulation and SemarJcs. The potassium and sodium 
salts are not volatile at a moderate red heat, while the am- 
monium salts volatilize readily, and may therefore be easily 
separated from the former by ignition. The expulsion of 
ammonia by slaked lime affords the surest means of ascer- 
taining the presence of ammonium salts. In case of doubt, 
the reaction which ammonia gives with mercurous nitrate is 
more decisive than the alkaline reaction of the gas, for the 
vapors of the volatile alkaloids, such as coniine and nicotine, 
give an alkaline reaction, while they give to the mercurous 
nitrate solution a whitish or yellowish-gray turbidity, but do 
not blacken it. 

Potassium salts can be detected by the aid of hydrochloro- 
platinic acid and of tartaric acid or hydrogen sodium tartrate 
only after the removal of the ammonium salts which may be 
present, because both give exactly similar reactions with these 
reagents. Even in testing for potassium salts with sodium 
nitrite and cobalt solution, the removal of any accompanying 
ammonium salts is to be recommended. After the removal of 
the ammonium compounds, potassium is clearly and positively 
characterized by any one of these three reagents. The reac- 
tions will show with certainty only in concentrated fluids, and 
dilute solutions must therefore first be greatly concentrated. 
A single drop of a concentrated solution will give a positive re- 
sult, which cannot be obtained with a large quantity of a dilute 
fluid. Potassium is most simply detected in potassium platinio 
chloride and in acid potassium tartrate by first decomposing 
these salts by gentle ignition. From the platinum compound, 
the decomposition of which is facilitated by the addition of 
some oxalic acid, the potassium is obtained as chloride, while 
potassium carbonate is obtained from the acid tartrate. When, 
heated with sulphuric acid, potassium cobaltio nitrite yields 
potassium sulphate and cobalt sulphate. For the direct 
detection of potassium in potassium iodide, tartaric acid or 
acid sodium tartrate is better suited than hydrochloroplatinio 
acid or sodium nitrate and cobalt solution, since upon the ad- 
dition of the first, the separation of the potassium platinic 



140 DEPOBTMBNT OF BODIES WITH BEAGETSTfl. [ 97. 

chloride is somewhat obscured by the formation of a deep, 
dark red liquid, containing platinic iodide and some free 
iodine ; while in the second case, nitrous acid and potassium 
iodide react, with the separation of iodine. 

Sodium can be recognized with complete certainty in the 
wet way with acid sodium pyroantimonate, if the reagent has 
been properly prepared ; if the solution of the sodium salt is 
concentrated, neutral, or feebly alkaline, and is free from in- 
terfering bases; and if it is noticed once for all that sodium 
pyroantimonate always separates in a crystalline condition 
and never in a flocculent state. If there is occasion to detect 
in this way small quantities of sodium in the presence of much 
potassium, the latter is first separated by hydrochloroplatinic 
acid, the platinum is removed from the filtrate by means of 
hydrogen sulphide and filtration, the solution is evaporated to 
dryness, gently ignited, taken up in very little water, and then 
tested with acid potassium pyroantimonate. 

Potassium and sodium can be detected by flame coloration 
much more easily and more quickly, and also with far greater 
delicacy, than in the wet way. We have seen, indeed, that the 
sodium coloration completely obscures that of potassium, 
even when only a small amount of a sodium salt is present 
with a large quantity of a potassium salt ; but if the spectro- 
scope is made use of, the spectra of both appear so clearly 
and beautifully that no error is possible. The presence of 
sodium chloride actually increases the strength of the potas- 
sium lines up to a proportion of 100 parts of sodium chloride 
to 1 part of potassium -chloride, but with greater proportions 
of sodium chloride, the delicacy of the spectroscopic detection 
of potassium again decreases (Qooon and HART). Where a 
spectroscope is not available, the potassium coloration can be 
distinctly recognized in a flame colored strongly yellow by 
sodium, by means of a glass prism filled with a solution of 
indigo or of potassium permanganate, or by the use of a blue 
glass ; while the sodium coloration can be more accurately 
tested, if necessary, by the use of mercuric iodide paper, or of 
a green glass, in the manner already described.* 

* Cotu ernlng tlie detection of very small amounts of potassium and sodium 
by the microscopic observation of crystallized potassium and sodium com- 
pounds, compare HAUSHOFEB'S " Mikioskopische React ionen," pp. 55 and 98; 
BBHBBNS, Zeitschr. f. analyt Chem., 30, 184 and 135; FRET, ibid., 32, 204. 



97.] RECAPITULATION AND REMARKS. 141 

The following methods serve for the detection of am- 
monium in exceedingly minute quantities, as, for instance, in 
natural waters ; they depend upon the separation of certain 
mercury compounds which are insoluble in water, and which 
contain the nitrogen or the nitrogen and part of the hydrogen 
of the ammonia : 

a. If water containing a trace of ammonia or ammonium 
carbonate is mixed with a few drops of solution of mercuric 
chloride, a white precipitate is formed, even in a very dilute 
solution. The precipitate consists of rnercurammonium chlo- 
ride, NH,E g Cl, thus: 2NH, + HgCl 3 =NH a HgCl + NH.Gl. If 
the solution is extraordinarily dilute, no turbidity occurs, but 
on the addition of a few drops of solution of sodium carbon- 
ate, the fluid will become turbid or opalescent in a few 
minutes, even after very extensive dilution. This reaction takes 
place when water containing a trace of a neutral ammonium 
salt is mixed with a few drops of solution of mercuric chloride 
and a few drops of solution of sodium carbonate. The pre- 
cipitate which separates on the addition of sodium carbonate 
consists of one molecule of the previously mentioned precipi- 
tate with one molecule of mercuric oxide: 2NH l + 4Hg01 9 
+ 3K a OO t = 2(NH a HgCl + HgO) + H a O + 6K01 + 300.. 
'Too much mercuric chloride and sodium carbonate must not 
be added, otherwise a yellow precipitate of mercuric oxy- 
chloride would be formed (BoHiia, SOHOIEN). 

b. Upon adding to a solution of potassium mercuric 
iodide containing potassium hydroxide,* a little of a fluid 
containing ammonia or an ammonium salt, a reddish-brown 
precipitate is formed if the ammonia is present in some 
quantity; but there is always a yellow coloration pro- 
duced, at least after some time, even if only most minute 
traces of ammonia are present. The precipitate consists 
of dimercurammonium iodide, NHg,LH,O, and the reaction 

* This (NESSLBR'S reagent) is prepared by heating to boiling, with stirring, 
85 g of potassium iodide and 13 g of mercuric chloride with 800 cc of water. 
When a clear solution results, a cold saturated solution of mercuric chloride 
is added drop by drop until a permanent precipitate just begins to form. Then 
160 g of potassium hydroxide or 120 g of sodium hydroxide are added, the 
volume is brought to 1 liter by addition of water, a little more mercuric chlo- 
ride solution is added, and the liquid is allowed to become clear by settling. 
The solution has a very pale, yellowish color. 



142 DEPORTMENT OF BODIES WITH EEAGENTS. [ 98. 

is as follows: 2(2KLHgI a ) + NH, + 3KHO = NHg fl I.H fl O 

+ 7KI -f 2H a O. Application of heat promotes the separation 
of the precipitate. Presence of chlorides of the alkali metals, 
or of their salts with oxygen acids, does not interfere with the 
reaction ; but presence of alkali-metal cyanides and sulphides,, 
as well as free carbonic acid and alkali-metal acid carbonates, 
will prevent it (J. NESSLEE). In the presence of the latter, 
potassium or sodium hydroxide is therefore to be added. If 
bicarbonates or any other soluble salts of the alkali-earth 
metals are present, these are precipitated from the solution 
by the addition of an exactly sufficient quantity of a freshly 
boiled and subsequently cooled solution containing about 
1 part of sodium hydroxide to 2 parts of sodium carbonate. 
The precipitate is allowed to settle in a closed cylinder, and 
the decanted, clear solution is tested with NESSLER'S reagent. 
For the recognition of small amounts of ammonia by the- 
microscopic method, an appropriate means is offered by the 
production and testing of ammonium magnesium phosphate 
crystals (see HAUSEOEEB, p. 13 ; BEHBENS, Zeitschr. f . analyt. 
Ohem., 30, 166). 

98. 
SpecM/l Reactions of the Barer Metals of the First Groti/p. 

1. CAESIUM, Os ; 2. BUBIDIUM, Bb. 

The caesium and rubidium compounds, especially the latter, occur 
rather widely disseminated in nature, but in very minute quantities only. 
They have hitherto been found chiefly in the mother-liquors of mineral 
waters, and in a few minerals (lepidolite, carnallite, etc.). Caesium has also 
been found in considerable quantities in pollux, and traces of rubidium 
have been detected m beet-molasses and in the ashes of plants. In general, 
the caesium and rubidium compounds bear great resemblance to those of 
potassium, more particularly in this, that their aqueous solutions, even 
when moderately concentrated, are precipitated by hydrochloroplatmic 
acid, and also that those compounds that are volatile at a red heat tinge 
the flame violet. The most notable characteristic differences, on the 
other hand, are that the precipitates produced by hydrochloroplatmic acid, 
are far more insoluble in water than potassium platinic chloride. At 10, 
100 g of water will dissolve 900 mg of potassium platinic chloride, but only 
154 mg of the rubidium platmio chloride, and as little as 50 mg of the 
caesium platinic chloride. Again, the alums show great differences as 



98.] CLESIUM. 143 

regards their solubility in cold water. Thus, 100 parts of water at 17 dis- 
solve 13.5 parts of potassium alum, 2 27 parts of rubidium alum, and .619 
parts of caesium alum. Moreover, the flames colored by caesium and 
rubidium compounds give spectra quite different from the potassium spec- 
trum (see Plate I). The caesium spectrum is especially characterized by 
the two blue lines a and fi, which are remarkable for their wonderful 
intensity and sharp outline ; also by the line r, which, however, is less 
strongly marked. In the rubidium spectrum, the splendid indigo-blue lines 
marked a and ft strike the eye by their extreme brilliancy. Less brilliant, 
but still very characteristic, are the lines 5 and y t To detect both alkalies 
m presence of each otitier by the spectroscope, the chlorides and not the 
carbonates should be taken, since with the latter salts, the rubidium 
spectrum is not always distinct in the presence of that of caesium (ALLEN, 
HEINTZ). It should also be mentioned that caesium carbonate is soluble m 
absolute alcohol, while rubidium carbonate is insoluble in that liquid. Still, 
a separation of the two metals is effected only with difficulty by this means, 
as they seem to form a double salt which is not absolutely insoluble in 
alcohol It is more easy to separate them when they are in the form of 
acid tartrates, for the hydrogen rubidium tartrate dissolves in 8.5 parts of 
boiling water and 84,57 parts of water at 25, while the corresponding 
salt of caesium dissolves in 1 02 parts of boiling water and 10.32 parts 
of water at 25 (ALLEN). (Hydrogen potassium tartrate requires 15 parts 
of boiling water and 89 parts of water at 25.) 

The following methods are recommended as the most reliable ones 
for separating caesium from rubidium as well as from potassium : (a) Add 
stannic chloride to the hot, concentrated solution containing a rather 
large amount of strong hydrochloric acid, filter the precipitate of caesium 
stannic chloride upon a hardened filter, wash it with concentrated hydro- 
chloric acid, dissolve it m boiling water containing some hydrochloric acid, 
precipitate with concentrated hydrochloric acid, filter again, and wash 
with concentrated hydrochloric acid. The filtrate contains the rubidium, 
also any potassium that was present, as well as stannic chloride. Any 
ammonium present, however, is found in the precipitate as ammonium 
stannic chloride, and ammonium salts are, therefore, to be previously 
removed (F. STOLBA). (6) Add a solution of antimonious chloride in 
strong hydrochloric acid to the concentrated solution of the salt, filter 
the precipitate of caesium antimonious chloride, 30s01.2Sb01s, which 
separates immediately, upon a hardened filter, and wash it with strong 
hydrochloric acid. All the other alkali metals, as well as ammonium, 
are not precipitated, and are found with antimony trichloride in the 
filtrate (GODEFFBOY). 

Concerning the microscopic detection of caesium and rubidium, com- 
pare HAUSHOFEB, p. 81; and BEHEBNS, Zeitschr. f. analyt Ohem., 30, 187, 



144 DBPOETMENT OF BODIES WITH BEAGENTS. [ 98. 



3. LITHIUM, Li. 

Lithium is found rather widely disseminated in. nature, but not in 
large quantities. It is often met with in the analysis of mineral waters 
and ashes of plants, less frequently m the analysis of minerals, and only 
rarely in that of technical and pharmaceutical products. Lithium forms 
the transition from the first to the second group of metals. Its hydroxide 
dissolves with difficulty in water, and it does not attract moisture from 
the air. Most of its salts are soluble in water, while some of them are 
deliquescent (lithium chloride). Lithium carbonate is difficultly soluble, 
particularly in cold water. It is more soluble in water containing carbonic 
acid. Upon boiling, hydrogen sodium pJiosphate produces in not too 
dilute solutions of salts of lithium, a white, crystalline precipitate of lithium 
phosphate, SLi 3 P0 4 .H a O, which quickly subsides to the bottom of the 
vessel. This reaction, which is characteristic of lithium, is rendered 
much more delicate by adding with the sodium phosphate a little sodium 
hydroxide solution, just sufficient to leave the reaction alkaline, evapo- 
rating the mixture to dryness, treating the residue with a little water, and 
adding an equal volume of ammonia solution. By this course, even very 
minute quantities of lithium will be separated as 2LiaP0 4 .H 2 0. The pre- 
cipitate fuses before the blowpipe, upon fusion with sodium carbonate 
gives a clear bead, and when fused upon charcoal, it is absorbed by the 
pores of the latter. It dissolves in hydrochloric acid to a fluid which, 
when diluted and supersaturated with ammonia, remains clear in the 
cold, but upon boiling gives a heavy, crystalline precipitate of the com- 
pound mentioned above. (Reactions by which the lithium phosphate dif- 
fers from the phosphates of the alkali-earth metals.) If pure ammonium 
fluoride (free from ammonium silicofluoride) is added to a not too dilute 
solution of a lithium salt, together with an excess of ammonium hydroxide, 
a white, gelatinous precipitate of lithium fluoride gradually separates. 
Since potassium, rubidium, and csssium fluorides are easily soluble in 
water, even when it is ammoniacal, and since sodium fluoride requires 
only 70 parts of a mixture of equal parts of ammonia solution and water 
to dissolve it, while lithium fluoride requires 3500 parts of the same for its 
solution, it is evident that lithium can be separated from the other alkali 
metals in the form of lithium fluoride, especially if the amount of sodium 
salts present is not too great. Very small amounts of lithium are best 
separated by evaporating the solution of alkali salts, after adding ammo- 
nium fluoride, to dryness in a platinum dish upon the water-bath, and 
treating the residue with dilute ammonia solution (A. OABNOT).* [If 
several volumes of amyl alcohol are added to a very concentrated solution 
of the chlorides of lithium, sodium, and potassium, best after making 
slightly acid with hydrochloric acid, and the whole is boiled until the 
water has disappeared, and the boiling is then continued until about one 

* Zeitschr. f. analyt. Ohem , 29, 33B. 



98.] LITHIUM. 145 

half of the remaining amyl alcohol has been removed in order that the 
remainder may become anhydrous, the lithium chloride, being* very soluble 
in the liquid, may be separated from the almost absolutely insoluble sodium 
and potassium chlorides by filtering the hot liquid through a dry filter 
(Goocfl).] 

Tartaric acid and hydrochloroplatinic add fail to precipitate even con* 
centrated solutions of lithium salts. If salts of lithium are exposed to the 
gas or 'blowpipe flame, in the manner described for potassium (g 94, 6), they 
tinge the flames carmine-red. Silicates containing lithium require addition 
of gypsum to produce this reaction, or, better still, gypsum and pure fluor- 
spar in the proportion 2:1. Lithium phosphate will tinge the flame 
carmine-red if the fused bead is moistened with hydrochloric acid. The 
sodium coloration conceals that of lithium. In presence of sodium, 
therefore, the lithium tint must be viewed through a blue glass, or through 
a thin layer of indigo solution. Presence of a small proportion of potas- 
sium will not conceal the lithium coloration. In presence of a large 
proportion of potassium, the lithium may be detected by placing the sub- 
stance in the fusing zone, viewing the colored flame through the indigo 
prism, and comparing it with a pure potassium flame produced in the 
opposite part of the fusing zone. Viewed through thin layers, the lithium 
colored flame now appears redder than the pure potassium flame ; viewed 
through somewhat thicker layers, the flames appear at last equally red, if 
the proportion of the lithium to the potassium is only trifling ; but when 
lithium predominates in the sample examined, the intensity ot the red col- 
oration imparted by lithium decreases perceptibly when viewed through 
thicker layers, while the pure potassium flame is scarcely impaired 
thereby. By this means, lithium may be detected in potassium salts, even 
though present only in the proportion of one part in several thousand 
parts of the latter. Unless present m very large quantities, sodium inter- 
feres but little with these reactions (OABOMELL, BUNSKN). 

The lithium spectrum (Plate I) is most brilliantly characterized by the 
splendid carmine-red line a and the very faint, orange-yellow line ft. The 
flame of a BUNSEN burner yields only these two lines, but if lithium chloride 
is introduced into a hydrogen flame, a dull blue line is perceptible, which 
becomes brilliant if the oxyhydrogen flame is used. Its position nearly 
coincides with the weaker of the two blue lines of caBsium (TYNDALL, 
FRANELAND). If alcohol is poured over lithium chloride and then ignited, 
the flame also shows a carmine-red tint. Presence of sodium salts will 
mask this reaction. 

Concerning the detection of lithium by microchemical methods, com- 
pare HAUSHOFKB, p. 89; and BBHRKNS, Zeitschr. f. analyt. Chem., 30, 186. 



To detect small quantities of csBsium, rubidium, and lithium, in pres- 
ence of very large quantities of sodium or potassium, as is necessary, for 
example, in the analysis of mineral waters, extract the dry chlorides, with 
addition of a few drops of hydrochloric acid, with alcohol of 90 per cent, 



146 DEPORTMENT OF BODIES WITH BEAGKNTS. [ 99. 

which leaves behind the far larger portion of the sodium and potas- 
sium chlorides, Evaporate the solution to dryness, dissolve the residue 
m very little water, and precipitate with hydrochloroplatinic acid. Filter 
off the precipitate, boil it repeatedly with small quantities of water to 
remove the potassium platinic chloride present, and in the course of 
this process examine repeatedly by the spectroscope. For this purpose 
place a slight amount of the precipitate upon a small piece of moistened 
filter-paper, wind a very fine platinum wire about the folded paper, car- 
bonize it at the top of the flame, avoiding too high a temperature, and then 
place the sample in the fusing zone of the flame, which is in front of the 
sht of the spectroscope. The potassium spectrum will now be found to 
grow fainter and fainter, while the spectra of rubidium and caesium will 
become visible, if these metals are present. Evaporate to dryness Uic 
fluid filtered from the platinum precipitate, with the addition of some 
oxalic acid, ignite the residue gently to decompose the sodium platmic 
chloride and the excess of hydrochloroplatinic acid, moisten with hydro- 
chloric acid, drive off the acid again, and finally extract the lithium chloride 
with a mixture of absolute alcohol and ether. The evaporation of the 
solution obtained leaves the lithium chloride behind m a state of almost 
perfect purity, and it may then be further examined and tested. Before 
concluding from the simple coloration of the flame, that lithium is present, 
it is advisable, m order to guard against the chance of error, to test a 
portion of the residue, dissolved in water, with sulphuric acid and alcohol, 
to make sure that strontium or calcium is not present. The addition of 
hydrochloric acid, which is repeatedly prescribed m the above process to 
precede the extraction of the lithium chloride with alcohol, is necessary, for 
the reason that lithium chloride, even by moderate ignition, is converted 
by the action of aqueous vapor into lithium hydroxide, which then attracts 
carbonic acid, forming lithium carbonate, which is insoluble in alcohol. 
Lithium chloride can be separated from considerable amounts of sodium 
and potassium chlorides by adding fuming hydrochloric acid to the con- 
centrated solution of the salts, and pouring off the solution containing 
lithium chloride and small amounts of the other chlorides from the sepa- 
rated potassium and sodium chlorides. 

99. 

SECOND GKROUP. 
BABIUM, STBOOTIUM, OALOIDM, MAGNESIUM. 

Properties of the Group. The oxides of the metals of this 
group, the alkali earths, unite with water to form hydroxides 
which are more or less soluble in that liquid. Magnesium 
oxide and hydroxide, however, dissolve but very sparingly in 
water. The solutions manifest alkaline reaction, which in the 



I 100.] BARIUM, 147 

case of magnesia is most clearly apparent when that earth is 
laid upon moistened test-paper. The neutral carbonates and 
phosphates of the alkali-earth metals are insoluble in water. 
The solutions of their salts are therefore precipitated, even in 
dilute solution, by carbonates and phosphates of the alkali 
metals. This property distinguishes the metals of the second 
group from those of the first. From the metals of the follow- 
ing groups, they are distinguished by the solutions being pre- 
cipitated neither by hydrogen sulphide nor by ammonium 
sulphide. The alkali earths and the salts of their metals are 
white or colorless (if the acid radical of the salt does not im- 
part a color to it), and not volatile at a moderate red heat. 
The solutions of the nitrates and chlorides of this group are 
w>t precipitated by barium carbonate. 



Special Reactions. 

100. 
a. BABIDM, Ba. (Oxide, BaO.) 

1. BABITOC HTOBOXEDE, Ba(OE),, is readily soluble in hot 
water, but rather sparingly so in cold water. It dissolves 
freely in dilute hydrochloric or nitric acid. It fuses at 
a red heat without losing water, but upon stronger ignition 
the water is lost (BBtaELMAEN). 

2. Host of the BAEIUM SALTS are insoluble in water. The 
soluble salts do not affect vegetable colors, and with the 
exception of chloride, bromide, and iodide of barium, are de- 
composed upon, ignition in a glass tube. The insoluble salts 
dissolve in dilute hydrochloric acid, except barium sulphate 
and barium silicofluoride. BABIUM CHLORIDE and NITRATE are 
almost insoluble in alcohol, insoluble in a mixture of equal 
parts of absolute alcohol and ether, and do not deliquesce in 
the air. Concentrated solutions of barium salts are precipk 
tated by hydrochloric or nitric acid added in large propor- 
tions, as barium choride and nitrate are not soluble in the 
concentrated aqueous solutions of these acids. 

3. Ammonia, produces no precipitate in aqueous solutions 
of barium salts. From highly concentrated solutions only, 



148 DEPOBTMENT OF BODIES WITH REAGENTS. [ 100. 

potassium or sodium hydroxide (free from carbonic acid) pre- 
cipitate crystals of BABIUM HYDBOXIDE, Ba(OH) a .8H a O, which 
redissolve in water. 

4 Soluble carbonates throw down BABIUM OABBONATE, BaCO, , 
in the form of a white precipitate. If the solution was pre- 
viously acid, complete precipitation takes place only upon 
heating the fluid. In ammonium chloride, the precipitate is 
soluble to a trifling, yet clearly perceptible, extent, and there- 
fore ammonium carbonate produces no precipitate in very 
dilute barium solutions containing much ammonium chloride. 

5. Sulphuric acid and all the soluble sulphates, more 
particularly solution of ccdciwn sulphate, produce, even in very 
dilute solutions, a heavy, finely pulverulent, white precipitate 
of BABIUM SULPHATE, BaSO 4 . This is generally formed im- 
mediately upon the addition of the reagent, but from highly 
dilute solutions, especially when strongly acid, it separates 
only after some time. The precipitate is insoluble in alkalies, 
nearly so in dilute acids, but perceptibly soluble in con- 
centrated hydrochloric and nitric acids, especially upon 
heating, as well as in concentrated solutions of ammonium, 
potassium, sodium, calcium, and magnesium salts. The 
solvent action of the acids and also of the salts is counter- 
acted, or at least very much diminished, if sulphuric acid 
or a sulphate is present in considerable excess. Bather 
large quantities of calcium chloride may completely prevent 
the precipitation of small amounts of barium by means of 
calcium sulphate (LtJPEKTNa *). 

6. JHydrofluosilicic acid throws down BABIUM SJXIOOFLUOB- 
H>E, BaSiF, , in the form of a colorless, crystalline, quickly 
subsiding precipitate. In dilute solutions, this precipitate is 
formed only after the lapse of some time. Very dilute solu- 
tions are not precipitated, for barium silicofluoride is not 
entirely insoluble in water. With the addition of an equal 
volume of alcohol, the precipitation takes place quickly, and 
so completely that the filtrate remains clear upon the addi- 
tion of sulphuric acid. Hydrochloric and nitric acids and 
ammonium salts increase its solubility in water as well as 
in alcohol. 

* Zeitachr. f . analyt. Chem., 29, 566. 



100.] BAEIUM. 149 

7. In neutral or alkaline solutions, sodium phosphate pro- 
duces a white precipitate of HYDBOGKEN BABIUM PHOSPHATE, 
HBaPO 4 , which is soluble in free acids. Addition of ammonia 
only slightly increases the quantity of this precipitate, a 
portion of which is converted into barium phosphate, 
Ba 8 (PO 4 ) a , in this process. Ammonium chloride dissolves 
the precipitate to a clearly perceptible extent. 

8. In moderately dilute solutions, ammonium oxcdate pro- 
duces a white, pulverulent precipitate of BABIUM OXALAIE, 
BaC a O 4 .H a O, which is soluble in hydrochloric and nitric acids, 
"When recently thrown down, this precipitate also dissolves 
in oxalic and acetic acids, but the solutions speedily deposit 
acid barium oxalate, HjBa^jOJa.aH^O, in the form of a crys- 
talline powder. 

9. Potassium chromate and dichromate produce a bright 
yellow precipitate of barium chromate, BaOr0 4 , even in very 
dilute solutions of barium salts. This is very difficultly sol- 
uble in cold water, somewhat more readily in boiling water, 
while ammonium salts increase its solubility very noticeably. 
But all these conditions of solubility are completely changed 
when potassium chromate is added in excess in making the 
precipitation, so that in the case of acid solutions, no free 
acid is present, but in the place of this, potassium dichromate 
is formed. Under these conditions, the precipitation of barium 
is complete. Hydrochloric or nitric acid dissolves barium 
chromate, and ammonia precipitates it again from the reddish- 
yellow solution. 

10. Soluble barium salts, when triturated and heated with 
dilute alcohol, give to its flame a GBEBNISH-IBLLOW OOLOB. 

11. If barium salts are held 01* the loop of a platinum 
wire in the fusing zone of the BUNSEN gasjftame, the part of 
the flame above the sample is colored YELLOWiSH-aBBEN ; or if 
the barium salts are held in the inner (alcohol) ttourpipe flame, 
the same coloration is imparted to the part of the flame 
beyond the sample. With the soluble barium salts, and also 
with barium carbonate and sulphate, the reaction is immediate 
or takes place very soon. The phosphate, however, requires 
previous moistening of the sample with sulphuric or hydro- 
chloric acid, by which means barium may be detected by 
the flame coloration in silicates decomposable by acids. 



150 DEPORTMENT OF BODIES WITH EEAGBNTS. [ 101. 

Silicates which hydrochloric acid fails to decompose must 
be fused with sodium carbonate, when the barium carbonate 
produced will show the reaction. It is characteristic of the 
yellowish-green barium coloration of the flame that it appears 
bluish-green when viewed through the green glass. If _the 
sulphates are used for the experiment, presence of calcium 
and strontium will not interfere with the reaction. The 
barium spectrum is shown in Plate I. The green lines a and 
./? are the most intense ; y is less marked, but still character- 
istic. Since platinum wire sometimes contains barium (KBAUT), 
it is well to find first whether it will give a barium spectrum 
by itself. 

12. Barium sulphate is not, or, more correctly, scarcely at 
all, decomposed by cold solutions of the bicarbonate* of the 
alkali metals or of ammonium carbonate. It behaves in the 
same way with a boiling solution of 1 part of potassium carbon- 
ate and 3 parts of potassium sulphate, but its behavior towards 
all these reagents is essentially different when strontium sul- 
phate or calcium sulphate is mixed with it (see p. 162). 
Eepeated action of boiling solution of sodium or potassium 
carbonate upon barium sulphate succeeds in the end in com- 
pletely decomposing that salt. Barium sulphate is readily 
decomposed by fusion with sodium carbonate, with the for- 
mation of sodium sulphate, which is soluble in water, and of 
barium carbonate, insoluble in that liquid. 



101. 
I. STRONTIUM, Sr. (Oxide, SrO.) 

L STRONTIUM HYDROXIDE and the STRONTIUM SAUTS have 
nearly the same general properties and reactions as the 
corresponding barium compounds. Strontium hydroxide is 
more sparingly soluble in water than barium hydroxide, and 
it loses its water only upon strong ignition. SIBOOTTUM CHLO- 
RIDE dissolves in absolute alcohol and deliquesces in moist air. 
STRONTIUM NITRATE is almost insoluble in absolute alcohol, and 
is insoluble in a mixture of equal volumes of absolute alcohol 
and ether. Strontium nitrate does not deliquesce in the air. 



101.] STRONTIUM. 151 

2. With, ammonia, potassium hydroxide, sodium hydroxide, 
also -with the alkali carbonates, and with sodium phosphate, the 
strontium salts show nearly the same reactions as the barium 
salts. In ammonium chloride, strontium carbonate dissolves 
to a less marked degree than barium carbonate. 

3. Sulphuric adds and sulphates throw down STBONTTDM SUL- 
PHATE, SrSO 4 , in the form of a white precipitate. When 
thrown down from concentrated solutions, it is at first floc- 
culent and amorphous, afterwards pulverulent and crystalline ; 
but from dilute solutions, it is immediately pulverulent and 
crystalline. Application of heat promotes the precipitation. 
Strontium sulphate is less insoluble in water than barium 
sulphate ; hence it separates from rather dilute solutions only 
after some time. Calcium sulphate solution causes no imme- 
diate precipitation except in very concentrated, and especially 
in hot, strontium solutions; yet it precipitates more dilute 
.solutions after some time. Potassium, sodium, calcium, and 
magnesium salts increase the solubility of strontium sul- 
phate, so that, for example, strontium cannot be precipitated 
by calcium sulphate solution in the presence of much cal- 
cium chloride (LUDEKING). In Hydrochloric and nitric acids, 
strontium sulphate dissolves perceptibly. Presence of large 
quantities of these acids will accordingly most seriously im- 
pair the delicacy of the reaction. An excess of sulphuric 
acid tends to counteract the solvent action of acids and salts. 
Strontium sulphate is insoluble in alcohol, so that the addi- 
tion of the latter promotes its precipitation very greatly. 
Strontium sulphate does not dissolve in a concentrated solu- 
tion of ammonium sulphate, even by boiling, but if mixed 
with calcium sulphate, it dissolves with the latter to a marked 
degree in this reagent. 

4. Hydrqfiuosibidc add fails to produce a precipitate, even 
in rather concentrated solutions of strontium salts, because 
strontium siuooiTiUOBrDB, SrSLF fl , is moderately soluble in 
cold water. Hot water dissolves it somewhat less easily. It 
dissolves in small amount in dilute alcohol, but the stronger 
the alcohol the less readily it dissolves. Hydrochloric acid 
greatly increases the solubility of the salt in water, and also 
-in alcohol, but to a somewhat less degree. 

5. Even from rather dilute solutions, ammonium oxdlate 



152 DEPORTMENT OF BODIES WITH KE AGENTS. [101. 

precipitates STBONTITOI OXAIATE, 2SrO fl O 4 .5H a O, in the form of 
a white powder, which dissolves readily in hydrochloric and 
nitric acids, and perceptibly in ammonium salts, but is only 
sparingly soluble in oxalic and acetic acids. 

6. Potassium dichromate does not precipitate solutions of 
salts of strontium, even when they are concentrated. Potas- 
sium chromate at first produces no precipitate, but on long 
standing, if the solution is neutral and not very dilute, bright 
yellow STEONTTDM CHBOMATE, SrCrO 4 , is precipitated in a crys- 
talline condition. This does not take place, however, in solu- 
tions acidified with acetic acid. The precipitate dissolves 
rather difficultly in pure water, more abundantly in water 
containing acetic acid or ammonium salts, but hydrochloric, 
nitric, and chromic acids dissolve it easily. None of these 
solutions are precipitated by the addition of potassium chro- 
mate in excess. Alcohol does not dissolve strontium chro- 
mate, and even dilute alcohol scarcely dissolves it at all. 
Neutral solutions of strontium salts to which potassium chro- 
mate is added are therefore precipitated by the addition of 
even small amounts of alcohol. Warming to 70 facilitates 
the precipitation. 

7. If strontium salts which are soluble in water or alcohol 
are heated with dilute alcohol, and the latter is ignited, they 
impart to the flame, especially upon stirring, an intense 

OABMINB-EED OOLOB. 

8. If a strontium salt is held in the fusing zone of the 
BTOTSEN gas flame, or in the inner alcohol blowpipe flame, an 
INTENSELY BED COLOB is imparted to the flame. The reaction 
is most distinct with strontium chloride, less clear with the 
hydroxide and carbonate, fainter still with the sulphate, 
and scarcely appears with strontium salts of fixed acids. 
Therefore, after its first exposure to the flame, the sample is 
moistened with hydrochloric acid, and again thus exposed. 
If strontium sulphate is likely to be present, the sample is 
first exposed a short time to the reducing flame (to produce 
strontium sulphide), before it is moistened with hydrochloric 
acid. Viewed through the UIM glass, the strontium flame 
appears purple or rose (difference between strontium and 
calcium, the latter showing a faint greenish-gray color when 
treated in this manner). This reaction also is most clearly 



102.] CALCIUM. 153 

apparent if the sample is moistened with hydrochloric acid 
when brought into the flame. In presence of barium, the 
strontium reaction shows only upon the first introduction 
into the flame of the sample moistened with hydrochloric 
acid. The strontium spectrum is shown in Plate L It con- 
tains a number of characteristic lines, more especially the 
orange line or, the red lines /? and y, and the blue line tf, the 
latter being more particularly suited for the detection of 
strontium in presence of barium and calcium. 

9. Strontium sulphate is completely decomposed by di- 
gestion with solution of sodium or potassium carbonate. It 
is also decomposed even by digestion with solutions of ammo- 
nium carbonate or of alkali-metal bicarbonates, but much more 
rapidly by boiling with a solution of 1 part of potassium car- 
bonate (wd 3 parts of potassium sulphate. Its decomposition 
by ammonium carbonate, by the alkaline bicarbonates, and 
also by potassium carbonate and sulphate is, however, not 
complete when it is mixed with barium sulphate ; for in 
presence of the latter, a certain amount of strontium sulphate 
always remains undecomposed. 

102. 
c. CALCIUM, Oa. (Oxide, lame, OaO.) 

1. CALCIUM OXIDE (quicklime), CALCIUM HIDBOXTDE (slaked 
lime), and CALCIUM SALTS, in their general properties and re- 
actions, present a great similarity to the corresponding barium 
and strontium compounds. Calcium hydroxide is far more 
difficultly soluble in water than the barium and strontium 
hydroxides, and dissolves more sparingly in hot than in cold 
water. Calcium hydroxide loses its water upon ignition. 
CALCIUM OHLOBEDE and NITBATE are soJable in absolute alcohol, 
and also in a mixture of equal volumes of alcohol and ether, 
and deliquesce in the air. 

2. Ammonia, potassium hydroxide, sodium hydroxide, aLkdH 
carbonates, and sodium, phosphate show nearly the same reac- 
tions with calcium as with barium salts. Eecently precipitated 
CALCIUM CARBONATE, OaCO,, is bulky and amorphous, but after 
a time, or immediately upon the application of heat, it shrinks 
=and assumes a crystalline form. Becently precipitated calcium 



154 DEPORTMENT OF BODIES WITH REAGENTS. [ 102. 

carbonate dissolves somewhat readily in solution of ammo- 
nium chloride ; but the solution speedily becomes turbid, and 
deposits the greater part of the dissolved salt in a crystalline 
form. 

3. In highly concentrated solutions, sulphuric add and 
sodium sulphate immediately produce white precipitates of 
CALCIUM SULPHATE, CaSO 4 .2H a O, which redissolve completely 
in a large proportion of water, and are far more soluble in 
acids. In less concentrated solutions, the precipitates are 
formed only after the lapse of some time, and no precipita- 
tion whatever takes place in dilute solutions. Solutions of 
calcium sulphate, of course, cannot produce a precipitate in 
calcium salts ; but even a cold saturated solution of potas- 
sium sulphate, mixed with 3 parts of water, produces a pre- 
cipitate only after standing from twelve to twenty-four hours. 
In solutions of calcium salts which are so very dilute that 
sulphuric acid has no apparent action on them, a precipitate 
will form upon addition of 2 volumes of alcohol, either 
immediately or after the lapse of some time. Calcium sul- 
phate dissolves in a large amount of a concentrated solution 
of ammonium sulphate, but this takes place completely only 
when it is not mixed with barium or strontium sulphate. 

4. Hydroftuosilidc acid does not precipitate calcium salts, 
even when an equal volume of alcohol is added. 

5. Ammonium oxalate produces a white, pulverulent pre- 
cipitate of CALCIUM OXALATE. If the Cuids are in any degree 
concentrated or hot, the precipitate, OaO a 4 .H 9 O, forms at 
once ; but if they are very dilute and cold, it forms only after 
some time, in the latter case being more distinctly crys- 
talline and consisting of a mixture of the above salt with, 
CaOjO^SH^O. Calcium oxalate dissolves readily in hydro- 
chloric and nitric acids, but acetic and oxalic acids fail to. 
dissolve it to any considerable extent. 

6. Potassium chromate produces no precipitate at first, even- 
in very concentrated solutions of calcium salts. Only after 
long standing does CALCIUM OHROMATE, CaGrO^H^O, separate 
as a yellow, crystalline precipitate. Solutions which are 
at all dilute do not give a precipitate, but if 2 or 3 volumes, 
of alcohol are added, an immediate precipitation follows in 
solutions which are not extremely dilute. Calcium solutions 



102.] CALCIUM. 155- 

containing free acetic acid are not precipitated, even upon the 
addition of alcohol. Potassium dichromate does not precipi- 
tate even very concentrated solutions. 

7. Soluble calcium salts when heated with aqueous alcohol 
impart to its flame a YELLOWISH-BED color, which may be mis- 
taken for that produced by strontium. 

8. If calcium salts are held in the fusing zone of the BUN- 
SEE gas flame, or in the inner akoM blowpipe flame, they impart 
to the flame a YELLOWISH-RED color. This reaction is most 
distinct with calcium chloride, while calcium sulphate shows it 
only after its incipient decomposition, and calcium carbonate 
most distinctly after the escape of the carbonic acid. Com- 
pounds of calcium with fixed acids do not color flame, but 
those which are decomposed by hydrochloric acid will show 
the reaction after being moistened with that acid. In such 
cases, the reaction is promoted by flattening the loop of the 
platinum wire, placing a small portion of the calcium com- 
pound upon it, letting it frit, adding a drop of hydrochloric 
acid, which remains hanging to the loop, and then thrusting 
the latter in the fusing zone. The reaction appears most 
distinctly at the instant when the drop disappears, having, 
evaporated without boiling as in LETDEOTBOST'S phenomenon 
(BOTSEN). Yiewed through green glass, the calcium color- 
ation of the flame appears siskin-green on bringing the sample 
moistened with hydrochloric acid into the flame (difference 
between calcium and strontium, the latter substance under 
similar circumstances showing a very faint yellow (MERE). In 
presence of barium, the calcium reaction shows only upon 
the first introduction of the sample into the flame. The calr 
dum spectrum is shown in Plate I. The intensely green 
line ft is particularly characteristic, also the intense orange 
line <x. It requires a very good apparatus to show the indigo- 
blue line to the right of Gr in the solar spectrum, as this is 
much less luminous than the others. 

9. With carbonates and arid carbonates of the alkalies, also 
with a solution of potassium carbonate cmd sulphate, calcium 
sulphate shows the same behavior as strontium sulphate. 



166 DEPORTMENT OF BODIES WITH BEAGENTS. [ 103. 

103. 

MAGNESIUM, Mg. (Oxide, Magnesia, MgO.) 

1. MAGNESIUM is silver- white, hard, malleable, of 1.743 sp. 
gr. It melts at a moderate red heat, and volatilizes at a white 
heat. When ignited in the air, it burns with a dazzling white 
flame to magnesium oxide. It preserves its luster in dry air, 
but gradually becomes coated with hydroxide when exposed 
to moist air. Pure water is not decomposed by magnesium 
at the ordinary temperature, but in water acidulated with 
hydrochloric or sulphuric acid, magnesium dissolves rapidly 
with evolution of hydrogen. 

2. MAGNESIUM OXEDE and HYDBOXEDE are white powders of far 
greater bulk than the other oxides and hydroxides of this 
group, and are nearly insoluble in both cold and hot water. 
The hydroxide loses its water upon ignition. 

3. Some of the SALTS OF MAGNESIUM are soluble in water, 
while others are insoluble in that fluid. The soluble salts 
have a nauseous, bitter taste, and the normal salts do not 
alter vegetable colors. With the exception of the sulphate, 
they undergo decomposition when gently ignited, and the 
grearer part of them, even upon simple evaporation of their 
solutions. Magnesium sulphate loses its acid at a white 
heat. Nearly all the magnesium salts which are insoluble 
in water dissolve readily in hydrochloric acid. 

4. Ammoma throws down from the solutions of normal 
-salts part of the magnesium as HYDBOXEDE, Mg(OH) a , in the 
form of a white, bulky precipitate. The rest of the magnesium 
Te mains in solution as a double salt, i.e., in combination with 
the ammonium salt which is formed by the reaction. It is 
owing to this tendency of magnesium salts to form such 
double salts with ammonium compounds that ammonia fails 
to precipitate them in presence of a sufficient proportion of 
an ammonium salt with neutral reaction ; or, what amounts 
to the same thing, that ammonia produces no precipitate in 
solutions of magnesium containing a sufficient quantity of 
free acid, and that precipitates produced by ammonia in 
neutral solutions of magnesium are redissolved upon the 
addition of ammonium chloride. It should be borne in mind 



; 103.] MAGNESIUM. 157 

that in solutions containing only 1 equivalent of an ammonium 
salt (ammonium chloride or sulphate) to 1 equivalent of 
magnesium salt, although no precipitate is produced by the 
addition of a slight excess of ammonia, a portion of the 
magnesium is, however, thrown down on the addition of a 
large excess of ammonia. 

5. Potassium, sodium, barium, and calcium hydroxides 
throw down MAGNESIUM HYDBOXIDE. The separation of this 
precipitate is greatly promoted by boiling the mixture. Am- 
monium chloride and similar ammonium salts redissolve the 
washed hydroxide. If the ammonium salts are added in 
sufficient quantity to the magnesium solution before the 
addition of the precipitant, small quantities of the latter fail 
-altogether to produce a precipitate. However, upon boiling 
the solution afterwards with an excess of potassium or 
sodium hydroxide, the precipitate will, of course, make its 
appearance, since this process causes the decomposition of 
the ammonium salt, thus removing the agent which retains 
the magnesium hydroxide in solution. It should be remem- 
bered that magnesium hydroxide is more soluble in solutions 
of potassium chloride, sodium chloride, potassium sulphate, 
and sodium sulphate, than in water, and on this account, its 
precipitation is less complete when these salts are present 
in large quantities. From such solutions, however, the mag- 
nesium is thrown down, for the most part, by an excess of 
solution of potassium or sodium hydroxide. 

6. Potassium carbonate and sodium carbonate produce in 
neutral solutions a white precipitate of BASIC MAGNESIUM OAB- 
BONATE, 4MgC0 8 .Mg(OH) 4 .0H a O. One fifth of the carbonic 
acid of the decomposed alkali carbonate is liberated in the 
process, and combines with a portion of the magnesium car- 
bonate to form bicarbonate, which remains in solution.^ This 
acid carbonate is decomposed by boiling, and an additional 
precipitate formed, consisting of MgOO a .3H a O, while carbon 
dioxide escapes. Application of heat, therefore, promotes the 
.separation, and increases the quantity of the precipitate. 
Ammonium chloride and other similar ammonium salts, when 
present in sufficient quantity, prevent this precipitation also, 
and readily redissolve the precipitates after they have been 
washed. 



168 DEPORTMENT OF BODIES WITH REAGENTS. [ 103*. 

7. If magnesium solutions are mixed with ammonium car. 
lonate, the liquid always remains clear at first; but after 
standing, it deposits a crystalline precipitate, more or less, 
quickly according to the concentration of the solution. 
When the ammonium carbonate is in slight excess, the pre- 
cipitate consists of magnesium carbonate, MgCO.-SHj.O ; but 
when the ammonium carbonate is in large excess, it consists 

Of AMMONIUM MAGNESIUM OABBONATE, (NH 4 ) 9 Mg(00 8 ) a .4H a O. 

In highly dilute solutions, this precipitate will not form. 
Addition of ammonia and of excess of ammonium carbonate 
promotes its separation. Ammonium chloride prevents the 
formation of the precipitate, except in concentrated solutions* 

8. Sodium phosphate precipitates from magnesium solu- 
tions, if not too dilute, HTOBOGEN MAGNESIUM PHOSPHATE, 
HMgP0 4 .7H s O, as a white powder. Upon boiling, magne- 
sium phosphate, Mg,(PO 4 ) 9 .7H a O, separates even from 
rather dilute solutions. But if the addition of the precipitant 
is preceded by that of ammonium chloride and ammonia, a. 
white, crystalline precipitate of AMMONIUM MAGNESIUM PHOS- 
PHATE, NH 4 MgPO 4 .6H a O, will separate even from very dilute- 
solutions. Its formation in dilute solutions may be greatly 
promoted and accelerated by stirring with a glass rod, and 
should the solution be so extremely dilute as to forbid the 
formation of a precipitate, yet the lines of direction in which 
the glass rod has moved along the inside of the vessel will, 
after the lapse of some time, appear distinctly as white streaks, 
(soluble in hydrochloric acid). Water and solutions of am- 
monium salts dissolve the precipitate but very slightly, yet 
it is readily soluble in acids, even in acetic acid. In water 
containing ammonia, it may be -considered practically in- 
soluble. Instead of hydrogen sodium phosphate, hydrogen 
sodium ammonium phosphate is a very good reagent to use. 

9. Ammonium oxalate produces no precipitate in highly 
dilute solutions of magnesium salts. In less dilute solutions, 
no precipitate is formed at first, but after standing some time, 
crystalline crusts of various double oxdlates of ammonium and 
magnesium make their appearance. In highly concentrated 
solutions, ammonium oxalate very speedily produces precipi- 
tates of magnesium oxalate, MgC,O 4 .2H 9 0, which contain 
small quantities of the double salts previously mentioned. 



104.] RECAPITULATION AND REMARKS. 169 

Ammonium chloride, especially in presence of free ammonia, 
interferes with the formation of these precipitates, but in 
general will not absolutely prevent it. 

10. Sulphuric add, hydrofluosttidc add, and potassium chro 
mate do not precipitate salts of magnesium. 

11. Salts of magnesium do not color flames. 

104. 

Recapitulation and Remarks. The difficult solubility of 
magnesium hydroxide, the ready solubility of the sulphate 
(unless present in the natural form, i.&, as kieserite, which 
contains one molecule of water), and the disposition of mag- 
nesium salts to form double salts with ammonium compounds, 
are the three principal points in which magnesium differs, 
from the other alkali-earth metals. To detect magnesium in 
solutions containing all the alkali-earth metals, we always first 
remove the barium, strontium, and calcium. This is effected 
most conveniently by means of ammonium carbonate, with 
addition of some ammonia and ammonium chloride, and 
application of heat ; since by this process, the barium, stron- 
tium, and calcium are obtained in a form of combination 
suited for further examination. If the solutions are some- 
what dilute, and the precipitated fluid is filtered after about 
an hour, the carbonates of barium, strontium, and calcium 
are obtained on the filter, while all the magnesium is found in 
the filtrate. But as ammonium chloride dissolves a little 
barium carbonate, and also a little calcium carbonate, though 
much less of the latter than of the former, trifling quantities 
of these metals are found in the filtrate. Moreover, where 
only traces of them are present, they may remain wholly in 
solution. In accurate experiments, therefore, the complete 
separation is effected in the following way : Divide the filtrate 
into three portions, test one portion with a few drops of dilute 
sulphuric acid for the trace of barium which it may contain* 
and another portion with ammonium oxalate for the minute 
trace of calcium which may have remained in solution. If the 
two reagents produce no turbidity, even after some time, test 
the third portion with sodium phosphate and ammonia for 
MAGNESIUM. If, however, one of the reagents causes turbidity. 



160 DEPORTMENT OF BODIES WITH KEAGENTS. [ 104. 

filter off the gradually subsiding precipitate, and test the fiL 
trate for magnesium. Should both reagents produce precipi- 
tates, mix the first two portions together, which in any case 
must still be alkaline, filter after some time, and then test 
the filtrate for magnesium. To make sure that the precipitate 
thrown down by ammonium oxalate is actually calcium oxa- 
late, and not, as it might be, oxalate of ammonium and mag* 
iiesium, dissolve it in a very little hydrochloric acid, and add 
dilute sulphuric acid, and then alcohol. 

To show the presence of barium, strontium, and calcium 
in the precipitate produced by ammonium .carbonate, dissolve 
the precipitate in an exactly sufficient amount of dilute nitric 
acid, evaporate the solution in a small porcelain dish to dry- 
ness, heat this upon an iron plate for 10 or 15 minutes rather 
strongly (the temperature may rise to 180 without injury) 
until the residue no longer has an odor of nitric acid, and a 
cold glass plate, placed upon the dish for a few seconds, no 
longer shows a coating of moisture. Triturate the contents 
of the dish immediately after cooling, at first dry, then after 
the addition of about 6 to 10 cc of a mixture of equal 
volumes of absolute alcohol and ether. Filter the solution 
after a few minutes, and wash the residue four times with 
small quantities of the ether-alcohol mixture. The residue 
now contains the barium and strontium nitrates, to which a 
small amount of calcium nitrate may still adhere ; while the 
filtrate contains the calcium nitrate, with which there may be 
a slight trace of strontium nitrate if the operation has not 
been performed with sufficient care. 

Add 2 drops of dilute sulphuric acid to the ether-alco- 
hol solution. If a considerable amount of precipitate results, 
this must be calcium sulphate, and it is unnecessary to test 
further for calcium. If, however, the precipitate should be 
very small, it might originate from the traces of strontium 
which had possibly gone into the ether-alcohol solution. In 
this case, therefore, add about 4 cc of water to the solu- 
tion, evaporate off the ether and alcohol, add a few drops of 
ammonia and about 1 g of solid ammonium sulphate, heat 
to boiling, filter through a small filter, add to the filtrate 
a drop of acetic acid, so that it just reddens litmus-paper, 
then a few drops of ammonium oxalate. If CALCIUM is present, 



104.] RECAPITULATION AND REMARKS. 161 

a precipitate of calcium oxalate is formed immediately, or, if 
only very small amounts are present, after standing for some 
time. Any error on account of the very small amount of 
strontium possibly present is excluded, because the traces of 
strontium sulphate which dissolve in a concentrated solution 
of ammonium sulphate are not precipitated by ammonium 
oxalate in the presence of a little free acetic acid. 

Dissolve the barium and strontium nitrates with the aid 
of heat in 70 to 100 parts of water, filter if necessary, acidify 
with 3 or 4 drops of acetic acid, heat to boiling, add gradu- 
ally potassium chromate until the solution shows a yellow 
color, and boil up once more. If an odor of acetic acid 
then appears, add some more potassium chromate. If BABIUH 
is present, a bright yellow precipitate appears at once, or if 
only very small amounts are present, after^tftending a short 
time. Let it stand for about an hour, filte^/^and add some 
ammonia to a portion of the filtrate, then addW&ponium car- 
bonate. If a considerable amount of precipitate results, this 
can only be strontium carbonate, and J>as unnecessary, there- 
fore, to make further tests for stronwoa. If, on the other 
hand, no precipitate or only a very saj&U onfe is produced, 
add 1 or 2 drops of nitric acid to tfejnaiix part of the 
filtrate, concentrate to 10 or 20 cc, anddjjten jjwild ammonia 
and ammonium carbonate. If no precipitate is now found, 
strontium is not present ; but if there is a small ^precipitate, 
this may be strontium, but it may possibly be dne 1 t9 traces 
of calcium which are still present here. Filteifoff the smafy 
precipitate, wash it, dissolve it in a few drops ofcdilut^ftiycfaro- 
chloric acid, and evaporate the solution to drynesk.',. Dissolve 
the small residue of neutral chloride or chlorides ^1 or 2 co ( 
of a mixture of 3 parts of water and 1 part of alcotfirfl (which 
should be kept on hand), add a drop of potassium tf&romate 
solution, and heat until boiling just begins. If STRONTIUM: is 
present, a finely divided, yellow precipitate of strontium chro- 
mate separates immediately or after standing a short time in 
a warm place (W. EBESENITTS and F. BTJPPERT). 

The separation is accomplished just as well but less 
simply as follows : Dissolve the precipitate consisting of ba- 
rium, strontium, and calcium carbonates in acetic acid, remove 
most of the excess of this by evaporation, and after addition. 



DEPORTMENT OF BODIES WITH REAGENTS. [ 104. 

of water precipitate the barium from the solution, which must 
always contain some free acetic acid, by adding an excess of 
potassium chromate. In order to effect a good separation of 
strontium from calcium, it is then necessary to precipitate 
both these metals with ammonium carbonate, to convert the 
carbonates into dry nitrates, and to separate these with ether- 
alcohol, thus making the whole process less simple than the 
previous one. 

For the detection of small amounts of calcium in the 
presence of large amounts of barium and strontium, the fol- 
lowing method can also be used : Precipitate the solution, to 
-which some hydrochloric acid is added, while hot with dilute 
sulphuric acid, filter off the precipitate, first make the filtrate 
alkaline with ammonia, then acidify it with acetic acid and 
add ammonium oxalate. A resulting precipitate, often 
formed only after long standing, shows the presence of cal- 
-cium, because the traces of strontium sulphate which have 
remained in solution upon its precipitation with sulphuric 
acid are not precipitated by ammonium oxalate from the 
solution containing some free acetic acid. 

The methods formerly practised for the separation of 
barium, strontium, and calcium, or for the recognition of one 
of these metals in the presence of another, being based 
upon the varying deportment of the solutions of their salts to 
calcium sulphate solution, upon the separation of the dry 
chlorides by alcohol, and upon the separation of strontium 
and calcium sulphates by ammonium sulphate, are much less 
exact than those described, as is already evident from what 
has been stated in relation to the reactions of the separate 
metals. The separation of barium from strontium, which is 
based upon the varying deportment of the sulphates to a 
solution of ammonium carbonate or to a mixture of potassium 
carbonate and sulphate, is also not to be recommended, since 
in the predominance of barium sulphate, a portion of the 
strontium sulphate remains undecomposed, while in the pre- 
dominance of strontium sulphate, barium sulphate is also 
converted into carbonate. The separation of barium from 
calcium succeeds better upon this basis, but even this is not 
fully exact. 

If the sulphates of the alkali-earth metals present them- 



104.] KECAPITULATIOtf AND KEMABKS. 163 

selves for investigation, the mass is first extracted with small 
quantities of boiling water. The solution contains the whole 
of the magnesium sulphate, if this is not present as kieserite, 
besides a small quantity of calcium sulphate. The residue 
is fused with 4 parts of potassium-sodium carbonate in a 
platinum crucible, the mass is treated with boiling water, and 
the resulting carbonates are filtered and washed. In order 
to detect the alkali-earth metals in their phosphates, it is 
most advantageous to decompose these by means of ferric 
chloride with the addition of sodium acetate (see Section III, 
under phosphoric acid). They are detected in their oxalates 
after changing them by ignition into carbonates. The fluor- 
ides and silicofluorides of the alkali-earth metals are first 
converted into sulphates by heating with concentrated sul- 
phuric acid. 

The detection of barium, strontium, and calcium by the wet 
way, as above described, is somewhat tedious, but it gives an 
approximate idea of the relative quantities. By means of the 
spectroscope, these metals are much more readily detected 
even when all three are present together. According to the 
nature of the acid, the sample is either introduced into the 
flame directly, or after previous ignition in the reducing 
flame and moistening with hydrochloric acid. To detect 
very minute quantities of barium and strontium in presence 
of large quantities of calcium, ignite a few grams of the 
mixed carbonates for several minutes in a platinum crucible 
strongly over the blast-lamp (whereby barium and stron- 
tium carbonates become caustic much more readily than 
would be the case in the absence of calcium carbonate), 
extract the ignited mass by boiling with a little distilled 
water, filter, evaporate with hydrochloric acid to dryness, 
and examine the residue by spectrum analysis (ENGEL- 
BAOH). If traces of calcium and strontium are to be 
detected in barium minerals, convert the metals into 
chlorides, extract these with very small amounts of abso- 
lute alcohol, and examine by spectrum analysis the residue 
left upon evaporation* In dealing with the detection of 
traces of calcium and barium in strontium minerals, extract 
the chlorides, first with cold, then with hot alcohol. In 
the first extract, the calcium is to be found ; in the succeed- 



163 DEPORTMENT OF BODIES WITH EEAGENTS. [ 104. 

of water precipitate the barium from the solution, which must 
always contain some free acetic acid, by adding an excess of 
potassium chromate. In order to effect a good separation of 
strontium from calcium, it is then necessary to precipitate 
both these metals with ammonium carbonate, to convert the 
-carbonates into dry nitrates, and to separate these with ether- 
alcohol, thus making the whole process less simple than the 
previous one. 

For the detection of small amounts of calcium in the 
-presence of large amounts of barium and strontium, the fol- 
lowing method can also be used : Precipitate the solution, to 
which some hydrochloric acid is added, while hot with dilute 
sulphuric acid, filter off the precipitate, first make the filtrate 
alkaline with ammonia, then acidify it with acetic acid and 
add ammonium oxalate. A resulting precipitate, often 
formed only after long standing, shows the presence of cal- 
cium, because the traces of strontium sulphate which have 
remained in solution upon its precipitation with sulphuric 
acid are not precipitated by ammonium oxalate from the 
solution containing some free acetic acid. 

The methods formerly practised for the separation of 
barium, strontium, and calcium, or for the recognition of one 
of these metals in the presence of another, being based 
upon the varying deportment of the solutions of their salts to 
calcium sulphate solution, upon the separation of the dry 
chlorides by alcohol, and upon the separation of strontium 
and calcium sulphates by ammonium sulphate, are much less 
exact than those described, as is already evident from what 
has been stated in relation to the reactions of the separate 
metals. The separation of barium from strontium, which is 
based upon the varying deportment of the sulphates to a 
solution of ammonium carbonate or to a mixture of potassium 
carbonate and sulphate, is also not to be recommended, since 
in the predominance of barium sulphate, a portion of the 
strontium sulphate remains undecomposed, while in the pre- 
dominance of strontium sulphate, barium sulphate is also 
converted into carbonate. The separation of barium from 
calcium succeeds better upon this basis, but even this is not 
fully exact. 

If the sulphates of the alkali-earth metals present them- 



104.] RECAPITULATION AND REMARKS. 163 

selves for investigation, the mass is first extracted with small 
quantities of boiling water. The solution contains the whole 
of the magnesium sulphate, if this is not present as kieserite, 
besides a small quantity of calcium sulphate. The residue 
is fused with 4 parts of potassium-sodium carbonate in a 
platinum crucible, the mass is treated with boiling water, and 
the resulting carbonates are filtered and washed. In order 
to detect the alkali-earth metals in their phosphates, it is 
most advantageous to decompose these by means of ferric 
chloride with the addition of sodium acetate (see Section III, 
tinder phosphoric acid). They are detected in their oxalates 
after changing them by ignition into carbonates. The fluor- 
ides and silicofluorides of the alkali-earth metals are first 
converted into sulphates by heating with concentrated sul- 
phuric acid. 

The detection of barium, strontium, and calcium by the wet 
way, as above described, is somewhat tedious, but it gives an 
approximate idea of the relative quantities. By means of the 
spectroscope, these metals are much more readily detected 
even when all three are present together. According to the 
nature of the acid, the sample is either introduced into the 
flame directly, or after previous ignition in the reducing 
flame and moistening with hydrochloric acid. To detect 
very minute quantities of barium and strontium in presence 
of large quantities of calcium, ignite a few grams of the 
mixed carbonates for several minutes in a platinum crucible 
strongly over the blast-lamp (whereby barium and stron- 
tium carbonates become caustic much more readily than 
would be the case in the absence of calcium carbonate), 
extract the ignited mass by boiling with a little distilled 
water, filter, evaporate with hydrochloric acid to dryness, 
and examine the residue by spectrum analysis (ENGEL- 
BACH). If traces of calcium and strontium are to be 
detected in barium minerals, convert the metals into 
chlorides, extract these with very small amounts of abso- 
lute alcohol, and examine by spectrum analysis the residue 
left upon evaporation. In dealing with the detection of 
traces of calcium and barium in strontium minerals, extract 
the chlorides, first with, cold, then with hot alcohol. In 
the first extract, the calcium is to be found ; in the succeed- 



164 DEPORTMENT OP BODIES WITH REAGENTS. [ 105. 

ing ones, strontium, while barium is in the last or in the 
residue. (The tests should be ignited in the reducing flame, 
then moistened with hydrochloric acid, and brought into 
the flame.) (BuNSEN.) 

Concerning the detection of magnesium by means of an 
absorption-spectrum, compare H. W. VOGEL and F. YON 
LEPEL, Zeitschr. f. analyt. Ohem., 17, 89. Barium, stron- 
tium, calcium, and magnesium can also be detected by 
microchemical methods, even when only small amounts 
are present. (Compare HAITSHOFEB, pp. 15, 32, 92, and 121, 
and BEHEENS, Zeitschr. f. analyt. Chem., 30, 139, 145, 146,. 
and 148.) 

105. 

TEDDRD GBOUP. 

More common metals : ALTBONIUM, CHBOMUM. 

Barer metals : BEBILLIUM, THOETDM, ZntooNiUM, YOTPBIUM;, 
CEBIUM, LAOTHANUM, DIDBJIUM, TITAOTDM, TANTALUM, NIOBIUM. 

Properties of the Group. The oxides and hydroxides 
of the third group are insoluble in water. The sulphides 
cannot be produced in the wet way. Hydrogen sulphide, 
therefore, fails to precipitate the solutions of the salts. From 
solutions of the salts in which the metals of the third group 
constitute the base,* ammonium sulphide throws down the 
hydroxides in the same way as ammonia. The reaction with 
ammonium sulphide distinguishes the metals of the third 
group from those of the two preceding ones. 

* The oxides of almost all the metals of the third group are able to com- 
bine with acids as well as with bases to form salts; for example, alumina with 
potassium oxide forms potassium aluminate, while with sulphuric acid, alu- 
minium sulphate is formed. Some of these elements, therefore, stand upon 
the boundary between acid-forming and basic elements. The oxides of tita- 
nium, tantalum, and niobium are called acids, because they stand neartha 
adds in their properties. 



106.] ALUMINIUM. 165 

Special Reactions of the More Common Metals of the Third Group. 

106. 
a. ALUMINIUM, Al. (Oxide, Alimina, Al a O,.) 

1. ALUMINIUM is nearly -white. It is not oxidized by the 
action of the air, in compact masses scarcely even upon igni- 
tion. It may be filed, is very malleable, and its specific 
gravity is only 2.67. It is fusible at a bright red heat. It 
does not decompose boiling water. Aluminium dissolves 
readily in hydrochloric acid, as well as in hot solution of 
potassium hydroxide, with evolution of hydrogen. Nitric 
acid dissolves it but slowly, even with the aid of heat. 

2. ALUMINIUM OXIDE is non-volatile and colorless, and the 
HYDKOXTDE is also colorless. Alumina dissolves in dilute 
acids slowly and with very great difficulty, but more readily 
in concentrated, hot hydrochloric acid. In fusing potassium 
disulphate, it dissolves readily to a mass soluble in water. 
In the amorphous condition, the hydroxide is readily sol- 
uble in acids, but in the crystalline state, it dissolves in 
them with very great difficulty. By ignition with alkalies* 
an aluminate is formed which readily dissolves in acids. By 
igniting alumina mixed with carbon in a current of chlorine, 
or by the action of carbon tetrachloride, 001 4 , upon alumina 
below a red heat (DEMABgAY), aluminium chloride, A101,, is. 
obtained as a sublimate. 

3. The ALUMINIUM OXYGEN SALTS are colorless and non-vol- 
atile ; some of them are soluble, others insoluble. The an* 
hydrous chloride is solid, colorless, crystalline, volatile, and 
easily soluble in water. The soluble oxygen salts have a sweet- 
ish, astringent taste, redden litmus-paper, and lose their acid 
upon ignition. With the exception of certain native com- 
pounds, the salts insoluble in water are dissolved by hydro- 
chloric acid, while the aluminium compounds which are 
insoluble in hydrochloric acid are made soluble by ignition 
with sodium-potassium carbonate or potassium disulphate. 
Their decomposition and solution may be also effected by 
heating them, reduced to a fine powder, with hydrochlorio 



166 DEPORTMENT OF BODIES WITH KEAGENTS. [ 106. 

acid of 25 per cent, or with, a mixture of 3 parts by weight of 
sulphuric acid and 1 part by weight of water, in sealed glass 
tubes, from 200 to 210 for two hours (A. MITSOHEE IICH). 

4 From solutions of aluminium salts, potassium and sodium 
hydroxides throw down a bulky precipitate of ALUMINIUM HY- 
DROXIDE, A1(OH) S , which contains alkali and generally also an 
admixture of basic salt, and redissolves readily and com- 
pletely in an excess of the precipitant The solution of 
alkaline aluminate thus formed remains clear upon boiling, 
but the aluminium hydroxide is precipitated again by the ad- 
dition of sufficient ammonium chloride (compare 56). This 
precipitation takes place even in the cold, but is more com- 
plete upon heating. The precipitate does not dissolve in 
excess of ammonium chloride, and ammonium salts do not 
interfere with the precipitation by potassium or sodium 
hydroxide. 

5. Ammonia and ammonium sulphide also produce a pre- 
cipitate of ALUMINIUM HTDBOXIDE, which contains ammonia and 
an admixture of basic salt. The precipitate redissolves to 
some extent in a large excess of the precipitant, but this solu- 
bility is lessened by ammonium salts. Boiling promotes the 
precipitation, as it drives off the excess of ammonia. This 
deportment accounts for the complete precipitation of alu- 
minium hydroxide from solution in potassium or sodium 
hydroxide by an excess of ammonium chloride, especially 
when the solution is boiled. 

6. Alkali carbonates precipitate BASIC ALUMNIUM OAEBONATE, 
which is slightly soluble in excess of fixed alkali carbonate, 
and still less soluble in excess of ammonium carbonate. 
Boiling promotes precipitation by the latter. 

7. If the solution of an aluminium salt is digested with 
finely divided barium carbonate, the greater part of the acid of 
the aluminium salt combines with the barium, the liberated 
carbonic acid escapes, and the aluminium precipitates com- 
pletely as HIDBOXIDE MIXED WITH BASIC SALT. Even digestion 
in the cold suffices to produce this reaction. 

N.B. to 4, 5, 6, and 7. Tartaric, citric, and other non-vola- 
tile organic acids completely prevent the precipitation of 
aluminium as hydroxide or basic salt, when they are present 
in considerable quantity. The presence of sugar and similar 



106.] ALUMINIUM. 167 

organic substances interferes with the completeness of the 
precipitation. 

8. Sodium phosphate precipitates ALUMINIUM PHOSPHATE, 
AlPO 4 .4H a O, from solutions of aluminium salts. The bulky, 
white precipitate is readily soluble in potassium or sodium 
hydroxide solution, but difficultly so in ammonia, and 
scarcely at all when ammonium salts are present. Ammo- 
nium chloride, therefore, precipitates it from its solution in 
potassium or sodium hydroxide. The precipitate is readily 
soluble in hydrochloric or nitric acid, but not in acetic 
acid (difference from aluminium hydroxide). Therefore, 
sodium acetate precipitates it from its solution in hydro- 
chloric acid if the latter is not too predominant. Tartaric 
acid, sugar, etc., do not prevent the precipitation of alu- 
minium phosphate, but citric acid does prevent it (GBOTEE). 

9. Oxalic add and its salts do not precipitate solutions of 
aluminium. 

10. Potassium sulphate, added to very concentrated solu- 
tions of salts of aluminium, occasions the gradual separation 
of aluminium potassium sulphate, ~K t S0 4 .AlJ[S0 4 \.24S.j0 9 in 
the form of crystals or a crystalline powder. 

11. If aluminium oxide or a compound of it is ignited 
upon charcoal before the blowpipe, and afterwards moistened 
with a solution of cobalt nitrate, and then again strongly 
ignited, an unfused mass of a deep SKY-BLUE color is pro- 
duced, which consists of a compound of the two oxides. The 
blue color becomes distinct only upon cooling. By candle- 
light it appears violet This reaction is to be relied on, in a 
measure, only in the case of infusible or difficultly fusible 
compounds of aluminium nearly free from other metals. ' It is 
never quite decisive, since cobalt solution may give a blue 
color under similar circumstances, not only with readily fusi- 
ble compounds, but also with certain infusible compounds 
free from aluminium, such as the normal phosphates of the 
alkali-earth metals. 



168 DEPORTMENT OF BODIES WITH REAGENTS. [ 107. 

107. 

J. CHROMIUM, Or. (Chromic oxide, 01,0,.) 

1. CHROMIC OXIDE is a green, OHROMIO HYDROXIDE, usually 
a bluish gray-green powder. The hydroxide dissolves 
readily in acids, while the non-ignited chromic oxide dissolves 
more difficultly, and ignited chromic oxide is almost 
insoluble. When chromic oxide mixed with carbon is 
ignited in a stream of chlorine, or when it is heated 
below redness in the vapor of carbon tetrachloride (DE- 
MARgAY), it yields crystalline, reddish-violet chromium chlo- 
ride, CrCl a . 

2. The CHROMIC SALTS have a green or violet color. Many 
of them are soluble in water, and most of them dissolve 
in hydrochloric acid. The solutions exhibit a fine green 
or a dark violet color, the latter, however, changing to 
green upon heating. The chromic oxygen salts with volatile 
acids are decomposed upon ignition, the acids being ex- 
pelled. The chromic salts which are soluble in water redden 
litmus. Anhydrous chromic chloride is crystalline, violet- 
colored, insoluble in water and in acids, and volatilizes with 
difficulty. * 

3. In the green as well as in the violet solutions, potassium 
and sodium hydroxides produce a bluish-green precipitate of 
CHROMIC HYDROXIDE, which dissolves readily and completely in 
an excess of the precipitant, imparting to the fluid an emer- 
ald-green tint. Upon long-continued ebullition of this solu- 
tion, the whole of the hydroxide separates again, and the 
supernatant fluid appears perfectly colorless. The same 
reprecipitation takes place if ammonium chloride is added 
to the alkaline solution. Application of heat promotes the 
separation of the precipitate. 

4. Ammonia and also ammonium sulphide produce in 
green solutions a grayish-green, in violet solutions a grayish- 
blue, precipitate of OHEOMIO HYDROXIDE. The former precipi- 
tate dissolves in cold hydrochloric acid to a reddish-violet 
fluid, the latter to a bluish- violet fluid. Other circumstances 
(concentration, way of adding the ammonia, etc.) also exer- 
cise some influence upon the composition and color of these 
hydroxides. In the cold, a small portion of the hydroxide 



107.] CHROMIUM. 169 

redissolves in an excess of the precipitant, imparting to the 
liquid a peach-blossom red tint ; but if, after the addition of 
ammonia in excess, heat is applied to the mixture, the pre- 
cipitation is complete. 

5. Alkali carbonates precipitate BASIC CHROMIC CARBONATE, 
which redissolves with difficulty and slowly in an excess of 
the precipitant. 

6. Barium carbonate precipitates the whole of the chro- 

mium as a GREENISH HYDROXIDE MIXED WITH BASIC SALT. The 

precipitation takes place in the cold, but is complete only 
after long-continued digestion. 

7. Sodium phosphate when added to neutral or weakly acid, 
either green or violet solutions of chromic salts (but not 
chromic oxalate solutions), to which sodium acetate has been 
added in excess, upon boiling precipitates all the chromium 
as chromium, phosphate, CrP0 4 .3H 9 0, in the form of a light 
green precipitate (A CARNOT). 

N. B. to 4, 5, 6, and 7. The precipitation of chromium 
hydroxide by ammonia, both in green and violet solutions, is 
interfered with more or less by tartaric acid, citric acid, and 
sugar, as well as by oxalic acid. After long standing, the 
precipitates resulting .at first occasionally redissolve com- 
pletely, forming violet or green solutions. The precipitation 
,by sodium carbonate, as well as by sodium phosphate, is 
often wholly prevented by the acids which have been men- 
tioned, and in their presence, the precipitation by barium 
carbonate is incomplete. A solution of a chromic salt which 
has been boiled for a considerable time with the addition of 
sodium acetate is not precipitated in the cold either^ by 
alkali-metal hydroxides, carbonates, or phosphates, barium 
carbonate or ammonium sulphide, but precipitation does take 
place by boiling (E 



8. If a solution of chromic hydroxide in caustic potash or 
soda is mixed with some lead dioxide in excess, and the mixture 
is boiled a short time, the chromic hydroxide is oxidized to 
chromic acid. A yellow fluid is therefore obtained on filter- 
ing, which consists of a solution of LEAJD CHROMATE in caustic 
potash or soda. Upon acidifying this liquid with acetic acid, 
the lead chromate separates as a yellow precipitate (CHANCEL), 

9. If a solution containing a chromic salt is allowed to flow 



170 DBPOBTUBNT OF BODIES WITH BBAGKENTS. [ 108. 

into a hot sodium carbonate solution to which potassium per- 
manganate has been added, and the whole is boiled for a short 
time, chromic oxide is changed to chromic acid. If a few- 
drops of alcohol are now added in order to reduce the excess 
of the permanganate, and the resulting hydrated manganese 
dioxide is filtered off, any considerable amount of chromium 
can be recognized by the yellow coloration of the filtrate, due 

to SODIUM OHBOMATE (DONATE). 

10. The fusion of chromic oxide or of any chromic com- 
pound with sodium nitrate and carbonate, or still better, with 
potassium chlorate awl sodium carbonate or with sodiwn peroxide 
(HEMPEL), gives rise to the formation of yellow AT.KATT OHBO- 
ILATE, which dissolves in water to an intensely yellow fluid. 

K B. to 8, 9, and 10. If the amount of chromium is so 
minute that the filtrates do not show a yellow color, any trace 
of chromic acid they contain may often be detected by con- 
centrating the liquid, and applying the methods recom- 
mended under chromic acid for the detection of the smallest 
amounts of that substance. 

11. In both the oxidizing and reducing flames of the blow- 
pipe, sodium metaphospJiate dissolves chromic oxide and 
chromic salts to clear beads of a faint yellowish-green tint, 
which upon cooling change to la.MTgRAi.'n GBEEN. Chromic com- 
pounds show a similar reaction with torass. The BTJNSEN gas 
flame ( 16) or the blowpipe flame is used for the experiment. 

108. 

JSecapitulation and RentMwks. The solubility of aluminium 
hydroxide in sodium and potassium hydroxide solutions (or 
also in barium hydroxide solution, which should be used 
when no alkali-metal hydroxides free from silicic acid and 
alumina are available, BECKKAKN), and its reprecipitation from 
the alkaline solutions by ammonium chloride, afford a safe 
means of detecting aluminium in the absence of chromium. 
But if the latter is present, which is seen either by the color of 
the solution or by the reaction with sodium metaphosphate, it 
must be removed before aluminium can be tested for. This 
separation of chromium from aluminium is effected most com- 
pletely by fusing 1 part of the mixed oxides with 2 parts of 
sodium carbonate and 2 parts of potassium chlorate (which 



108.] EEOAPITULATION ANJL> REMARKS. 171 

may be done in a platinum crucible), and the yellow mass. 
obtained is boiled with water. By this process, the whole of 
the chromium is dissolved as potassium chromate, and part, 
of the aluminium as potassium aluminate, the rest of the alu- 
minium remaining undissolved. If the solution is acidified 
with nitric acid, it acquires a reddish-yellow tint ; and if 
ammonia is then added to feebly alkaline reaction, the dis- 
solved portion of the aluminium separates. 

If it is preferred to change the chromium oxide to chromic 
acid in the wet way in order to make the separation from alu- 
minium, the solution of both in potassium or sodium hydrox- 
ide may be boiled with potassium permanganate, then after 
reduction, (by means of some alcohol), of the permangan- 
ate added in excess, filtering off the hydrated manganese di- 
oxide and acidifying the filtrate with nitric acid, aluminium 
hydroxide can be precipitated by ammonia. The chromic 
oxide can also be readily converted into alkali-metal chromate 
by gently warming the alkaline solution of both oxides with 
hydrogen peroxide. 

The precipitation of chromic hydroxide, effected by boil- 
ing its solution in potassium or sodium hydroxide, is also suf- 
ficiently exact if the ebullition is continued long enough. 
Still it is often liable to mislead in cases where only little 
chromic salt is present, or where the solution contains organic 
matter, even though in small proportion only. Attention 
should here be called to the fact that the solubility of 
chromic hydroxide in an excess of cold solution of potassium 
or sodium hydroxide is considerably impaired by the presence 
of other hydroxides (manganous, nickelous, cobaltous, zinc, 
ferric, lead, calcium, magnesium hydroxides, etc.). If these 
happen to be present in large excess, they may altogether 
prevent the solution of the chromic hydroxide in caustic 
potash or soda. Lastly, the influence of non-volatile organic 
acids, sugar, etc., upon the precipitation of aluminium and 
chromium hydroxides by ammonia, etc., must be remembered. 
If organic substances are present, therefore, ignite, fuse the 
residue with sodium carbonate and potassium chlorate, and 
proceed as directed before. 

Concerning the detection of very small traces of aluminium 
by means of cochineal tincture, compare LTOKOW, Zeitschr. 1 



1 12 DEPORTMENT OF BODIES WITH EEAGENTS. [109. 

analyt. Chem., 3, 362 ; by means of an alcoholic solution of 
morin and the fluorescence produced in it, compare GOPPELS- 
BODEB, ibid., 7, 208; by means of tincture of logwood, see 
HOBSLET and SomjutA-OHEB-Kopp, fbid., 31, 222; in respect to 
the detection of aluminium by an absorption-spectrum, see 
H. W. VOGEL, ibid., 15, 332, and 17, 89. Concerning the micro- 
chemical detection of aluminium and chromium, see HAUS- 
EOFEB, pp. 12 and 47, and BEHBENS, Zeitschr. f. analyt. Chem., 
30, 159 and 161. 

Special Heactions of the Barer Metals of fh& Third Group. 

109. 

1. BEBYLLIUM, Be, or GLUCTNOM, Gl. (Oxide, BeO.) 

Beryllium is a rare metal found in the form of a silicate in phenacite, 
and with other silicates m beryl, euclase, and some other rare minerals. 
Beryllium oxide is a white, tasteless powder, insoluble in water. The ig- 
nited earth dissolves slowly but completely in acids, and is readily soluble 
after fusion with potassium disulphate. The hydroxide dissolves readily 
in acids. The compounds of beryllium very much resemble those of alu- 
minium. The soluble beryllium salts have a sweet, astringent taste, 
their reaction is acid, and the solutions are colorless. The native silicates 
of beryllium are completely decomposed by fusing with 4 parts of sodium- 
potassium carbonate, and most of them also by heating with concentrated 
sulphuric acid. Anhydrous beryllium chloride, obtained by igniting beryl- 
lium oxide mixed with carbon in a stream of chlorine, also by moderate 
ignition in carbon tetrachloride (L. METER and R. WILKBNS), is white, 
crystalline, capable of being sublimed, and easily soluble in water. From 
solution of beryllium salts, potassium and sodium hydroxides, ammonia, 
and ammonium sulphide throw down the white, flocculent hydroxide, 
which is but slightly soluble in ammonia, yet dissolves readily in solution 
of caustic potash or soda, from which solution it is precipitated again by 
ammonium chloride. The concentrated, alkaline solutions remain clear on 
boiling, but from more dilute, alkaline solutions, the whole of the beryllium 
separates upon continued ebullition (difference between beryllium and alu- 
minium,* but this is only a means for complete separation when pure potas- 

* [This test may fall when precipitated beryllium phosphate, which dissolves 
readily in caustic alkalies, is so treated. To apply the test, fuse the beryllium 
phosphate with sodium carbonate, treat the mass with hot water, and filter. 
The whole of the beryllium oxide, free from phosphoric acid, is thus obtained. 
Dissolve this in hydrochloric acid, evaporate to very small bulk to remove 
practically all the free acid, add pure potassium hydroxide slowly to the 
cold, concentrated solution until the beryllium hydroxide has redissolved, 
filter if necessary, dilute very largely, and boll.] 



109.] BERYLLIUM. 173 

slum, not sodium hydroxide, is used, aud the dilution is not too great*). 
Tartaric add prevents the precipitation by alkalies. By continued boiling 
with ammonium chloride, the freshly precipitated hydroxide dissolves as 
beryllium chloride, driving off ammonia (difference from aluminium). 
Alkali carbonates precipitate white beryllium carbonate, which redissolves 
in a great excess of sodium or potassium carbonate, and in a much less con- 
siderable excess of ammonium carbonate (especially characteristic difference 
between beryllium and aluminium, but they cannot be completely separated 
in this way, as m the presence of beryllium, a certain quantity of aluminium 
dissolves in ammonium carbonate, JOY). Upon boiling these solutions, 
basic beryllium carbonate separates readily and completely from the solution 
in ammonium carbonate, but only upon dilution and imperfectly (as hy- 
droxide) from the solutions in sodium and potassium carbonate If the so- 
lution of a beryllium salt is treated with ammonium phosphate m consider- 
able excess (sodium phosphate does not answer), the resulting precipitate 
is dissolved in hydrochloric acid, then, while the liquid is constantly heated, 
ammonia is added drop by drop to neutral reaction (an excess being avoided) 
and the liquid is then heated to boiling for some time, the precipitate, 
ammonium beryllium phosphate, which is slimy at first, assumes a crystal- 
line condition, and subsides rapidly. Citric acid does not prevent this reac- 
tion (difference from aluminium, which never yields a crystalline precipitate 
under these conditions, and which is not precipitated at all in the presence 
of citric acid). The presence of much aluminium prevents the separation 
of the beryllium precipitate in the presence of citric acid (0. ROSSLEB). 
Barium carbonate precipitates beryllium completely upon boiling, but not 
upon cold digestion. Oxalic acid and oxalates do not precipitate beryllium 
(difference from thorium, zirconium, yttrium, cenum, lanthanum, didym- 
lum). "When fused with 2 parts of hydrogen potassium fluoride, beryl- 
lium oxide yields a mass which dissolves in water acidified with hydrofluoric 
acid. (This reaction serves as a means of separating beryllium from alu- 
minium, for when the latter is similarly treated, it remains insoluble as 
potassium aluminium fluoride.) For the detection of small amounts of 
.beryllium when present with much aluminium, dissolve the hydroxides 
in hydrochloric acid, evaporate to dryness, take up the residue with a little 
water, using a very little hydrochloric acid if necessary, transfer to a tube 
of strong Bohemian glass which is closed at one end, add potassium sul- 
phate (about 12 parts for 1 part of alumina) and also enough water so that 
the salt can dissolve upon heating, seal the tube by fusion, warm until 
everything has dissolved, and heat for half an hour to 180. After cooling, 
open the tube, filter off the basic potassium aluminium sulphate, precipitate 
the solution with ammonia, dissolve the filtered precipitate in hydrochloric 
acid, add enough citric acid so that ammonia produces no precipitate, and 
then separate beryllium as crystalline ammonium beryllium phosphate 

* A. ZIMUEBKAXK succeeded in making a complete separation where 0.8 
g of the oxides were dissolved in 300 cc of dilute potassium hydroxide. With 
greater dilution, aluminium hydroxide precipitates with the beryllium. 



174 DEPORTMENT OF BODIES WITH REAGENTS. [ 110* 

(0. EOSSLEB). Moistened with solution of cobalt nitrate, the beryllium com- 
pounds give gray masses upon ignition. Concerning the microchemical 
detection of beryllium, see HAUSHOFER, p. 33, and BEHRENS, Zeitschr. f. 
Analyt. Ohem., 30, 189; in regard to the spectroscopic detection, see 
HARTLEY, Jahresbencht d. Ohem., 1887, 1, 346. 

110. 
2. THOBIUM, Th. (Thoria, ThO a .) 

Thorium is a very rare metal, found in thorite, monazite, etc. The 
oxide is white or gray. Ignited thoria is soluble upon heating with a 
mixture of 1 part of concentrated sulphuric acid and 1 part of water ; but 
it is not soluble m other acids, even after fusion with alkalies. When thoria, 
produced by gently igniting the oxalate, is evaporated with hydrochloric or 
nitnc acid, the corresponding salts are left in a varnish-like form, and 
at once dissolve completely in water, giving colorless solutions. Hydro- 
chloric and nitric acids precipitate the chloride or nitrate from such solu- 
tions, and even sulphuric acid may produce a precipitate in them (B^m). 
The moist hydroxide dissolves readily in acids, the dried hydroxide only with 
difficulty. Thorium chloride is volatile at a nearly white heat. Thorite 
(thorium silicate) is decomposed by moderately concentrated sulphuric acid, 
and also by concentrated hydrochloric acid. From solutions of thorium 
salts, potassium hydroxide, ammonia, and ammonium sulphide precipi- 
tate the white hydroxide, which is insoluble in an excess of the precipitant, 
even of potassium hydroxide (difference from aluminium and beryl- 
lium.). Tartanc acid prevents the precipitation. Potassium carbonate and 
ammonium carbonate precipitate basic thorium carbonate, which readily 
dissolves in an excess of tbe precipitant in concentrated solutions, but with 
difficulty in dilute solutions (difference from aluminium). From the solu- 
tion in ammonium carbonate, the basic salt separates again even at 50. 
Harium, carbonate precipitates thorium completely. Hydrofluoric acid 
precipitates the fluoride, which at first appears gelatinous, but after a 
little while, pulverulent. The precipitate is insoluble in water and hydro- 
fluoric acid (difference from aluminium, beryllium, zirconium, and tita- 
nium). Oxalic acid causes a white precipitate (difference from aluminium 
and beryllium). The precipitate is not soluble in oxalic acid, and is very 
slightly soluble in dilute mineral acids (BERZELIUS), but it does dissolve in 
a solution of ammonium acetate containing free acetic acid (difference from 
yttrium and cerium). It also dissolves in a boiling, concentrated solution 
of ammonium oxalate, and is not reprecipitated when the solution is 
diluted and allowed to cool (difference from cerium, lanthanum, didym- 
ium, and yttrium, BUNSEN). A concentrated solution of potassium 
sulphate precipitates thorium slowly but completely (difference from 
aluminium and beryllium). The precipitate consists of potassium thorium 
sulphate, which is insoluble in concentrated solution of potassium sulphate, 
dissolving with difficulty in cold and easily in hot water. Anhydrous, 



111-] ZIRCONIUM. 175 

normal thorium sulphate dissolves in ice-water, but upon wanning e^en 
to the temperature of the room, it separates in a hydrated, very difficultly 
soluble condition (difference from aluminium, beryllium, cerium, yttrium). 
If the hydrated salt is converted by heating into the water-free condition, 
it dissolves again in ice-water (difference from titanic acid, KBTJSS and 
NILSON). If thorium hydroxide is suspended m potassium hydroxide 
solution and Marine is led in, it does not dissolve (difference from many 
other earths, but not from cerium oxide, J. LAWRENCE SMITH). From neutral 
or slightly acid solutions, on boiling, sodium thiosulphate precipitates tho- 
rium thiosulphate mixed with sulphur, but the precipitation is not quite 
complete (difference from yttrium and didymmm). Concerning the micro- 
chemical detection of thorium, see HAUSHOFER, p. 127, and BEHBENS, Zeit- 
schr. f. analyt. Ohem., 30, 157. 

111. 

3. ZIRCONIUM, Zr. ( Zirconia, ZrO r ) 

Zirconium occurs in zircon, eudialite, and some other rare minerals. 
Zirconia is a white, infusible powder, which glows upon ignition, and is 
insoluble in hydrochloric acid, but is soluble upon addition of water after 
long-coiitinued heating with 2 parts of concentrated sulphuric acid and 1 
part of water. Soluble zirconium salts are also obtained by fusion with 
alkali-metal disulphates or with hydrogen potassium fluoride. The hy- 
droxide resembles aluminium hydroxide, dissolving readily in hydrochloric 
acid when precipitated cold and still moist, but with difficulty when pre- 
cipitated hot or after drying. The zirconium salts soluble in water redden 
litmus, and their solutions are colorless. The native zirconium silicates 
may be decomposed by fusion with sodium carbonate. The finely elutriated 
silicate is fused at a high temperature, together with 4 parts of sodium car- 
bonate. The fused mass gives sodium silicate to water, a sandy sodium 
zirconate being left behind, which is washed and dissolved m hydrochloric 
acid. Zircon may be easily decomposed by fusion with hydrogen potas- 
sium fluoride at a red heat, potassium silicofluoride and potassium zirco- 
nium fluoride being produced. When zirconia is mixed with carbon and 
ignited in a stream of chlorine, or is treated for a long time below redness 
with carbon tetrachloride (DraARgAY), zirconium chloride, ZrCU , IB pro- 
duced, which is solid, white, capable of being sublimed, and soluble in 
water. Potassium and sodium hydroxides, ammonia, and ammonium sul- 
phide precipitate from solutions of zirconium salts a white, flocculent hy- 
droxide, which is insoluble in an excess of the precipitant, even of caustic 
soda and potash (difference from aluminium and beryllium), and is also not 
dissolved by boiling solution of ammonium chloride (difference from beryl- 
lium). Tartaric acid prevents the precipitation by alkalies. Carbonates 
of potassium, sodium, and ammwtium gradually throw down basic zir- 
conium carbonate as a white, flocculent precipitate, which redissolves in a 
large excess of potassium carbonate, more readily in potassium bicarbonate. 



176 DEPORTMENT OF BODIES WITH BEAGENTS. [ 112. 

and most easily m ammonium carbonate (difference from aluminium). 
From the latter solution, a gelatinous hydroxide is precipitated by boiling. 
Oxalic acid precipitates fine, crystalline zirconium oxalate (difference from 
aluminium and beryllium), which is soluble in excess of oxalic acid, espe- 
cially upon warming, and m hydrochloric acid as well as in an excess 
of ammonium oxalate solution even in the cold (difference from thorium). 
The solution is completely precipitated again by ammonia. A concentrated 
solution of potassium sulphate soon yields a white precipitate of potas- 
aium zirconium sulphate, which is insoluble in an excess of the reagent 
<difference from aluminium and beryllium), and which, if precipitated 
cold, dissolves readily m a large proportion of hydrochloric acid, but is 
almost absolutely insoluble in water and in hydrochloric acid if precipi- 
tated hot (difference from thorium and cerium). Barium carbonate does 
not precipitate zirconium completely, even upon boiling. Hydrofluoric 
acid does not precipitate zirconium solutions (difference from thorium 
and yttrium). Sodium tUosulphate precipitates zirconium salts upon boil- 
ing (difference from yttrium and didymium). The separation of the zirco- 
nium thiosulphate takes place on boiling even in the presence of 100 parts 
of water to 1 part of the oxide (important in regard to the complete sep- 
aration from cerium). A concentrated solution of hydrogen peroxide pre- 
cipitates from solutions of zirconium salts all the zirconium in the form of 
a white, voluminous precipitate, a hydrate of zirconium pentoxide, ZraOa. 
The precipitate is insoluble in 1 per cent sulphuric acid, and also in dilute 
acetic acid. By boiling with acids, it is partly dissolved with decomposition 
(BAILEY). (Means of separating zirconium from titanic acid, niobic acid, 
ferric oxide, alumina, but not from thoria.) From neutral or very weakly 
acid solutions, an alkali-metal iodate precipitates zirconium completely 
as zirconium iodate. Heating facilitates the precipitation (Tn. DAVIS, Jr.). 
(Means of separating zirconium from aluminium,) Turmeric-paper dipped 
into zirconium solutions slightly acidified with hydrochloric or sulphuric 
acid acquires a brownish-red color after drying (difference from the other 
earths). In the presence of titanic acid, which also has the effect of turn- 
ing turmeric-paper brown, first treat the acid solution with anc to reduce 
the titanic acid to titanic oxide, the solution of which does not affect tur- 
meric-paper (PiSANi). la relation to the microchemical detection of zir- 
conium, see HAUSHOFER, p. 156, and BEHEENS, Zeitschr. f. analyt. Ohem,, 
30, 156. 

112. 
YTTBIUM, Y. (Yttria, Y fl O a .) 

Yttrium is a rare metal found in gadolinite, orthite, yttro-tantalite, and 
fergusonite. Yttria when pure is white, and when ignited in the oxidizing 
flame, it emits a white light without fusing or volatilizing. In nitric, hydro- 
chloric, and dilute sulphuric acids, it is difficultly soluble in the cold, but on 
warming, it dissolves completely after some tune (BAHB and BUNSEN). The 
solutions and likewise the salts of yttrium are colorless, and have an acid 



112.] YTTBIUM. 177 

reaction and a sweetish, astringent taste. Yttrium under no circumstances 
yields a direct spectrum, nor do the solutions of its salts show any absorp- 
tion-bands (BAHR and BUNSEN). However, when strongly ignited, yttria 
shows a phosphorescence spectrum (OROOKES). Anhydrous yttrium chlo- 
ride is not volatile (difference from aluminium, beryllium, and zirconium). 
Potassium hydroxide precipitates the white hydroxide, which is insoluble 
in an excess of the precipitant (difference from aluminium and beryllium). 
Ammonia and ammonium sulphide give the same reaction. Alkali 
carbonates produce a white precipitate, which dissolves with difficulty in 
potassium carbonate, but more readily in hydrogen potassium carbonate 
and in ammonium carbonate, though by no means so readily as the cor- 
responding beryllium precipitate. On boiling, the solution of the pure hy- 
droxide in ammonium carbonate deposits the whole of the yttrium ; and if 
ammonium chloride is present at the same time, this is decomposed upon 
continued heating, with separation of ammonia, the precipitate redis- 
solvmg as yttrium chloride. Saturated solutions of yttrium carbonate in 
ammonium carbonate have a tendency to deposit yttrium carbonate, 
which should be borne in mind. Oxalic acid produces a white precipi- 
tate (difference from aluminium and beryllium). The precipitate does not 
dissolve in oxalic acid, it dissolves with difficulty in dilute hydrochloric 
acid, and is partially dissolved by boiling with ammonium oxalate, but 
by diluting and cooling, the oxalate separates again almost completely 
(difference from thorium). Potassium yttrium sulphate dissolves readily 
in water and in solution of potassium sulphate (difference from thorium, 
zirconium, and the metals of cerite). Barium carbonate produces no pre- 
cipitate in the cold (difference from aluminium, thorium, cerium, lan- 
thanum, and didymium), and even on boiling, the precipitation is incomplete. 
Turmeric-paper is not altered by acidified solutions of yttrium salts (differ- 
ence from zirconium). Tartaric acid does not interfere with the precipi- 
tation of yttrium by alkalies (characteristic difference between yttrium and 
aluminium, beryllium, thorium, and zirconium). The precipitate is yttrium 
tartrate. The precipitation ensues only after some time, but it is complete. 
Sodium thiosidphate does not precipitate yttrium (difference from alumin- 
ium, thorium, zirconium, and titanium). Hydrofluoric acid produces a 
precipitate (here yttrium differs from aluminium, beryllium,, zirconium, 
and titanium) which is gelatinous, Insoluble in water and hydrofluoric 
acid ; before ignition, it will dissolve in mineral acids, but after ignition 
it is decomposed only by strong sulphuric acid. Yttrium gives clear, color- 
less beads with borax and sodium, metaphosptMte, in both the outer and 
inner flames (difference from cerium and didymium). In relation to the 
microchemical detection of yttrium, see HAUSHOJUSR, p. 148, and BEHHENS, 
Zeitschr. f. analyt. Ohem., 30, 145. 

Besides yttrium, there occur in gadolinite, etc., a number of similar ele- 
ments, such as erbium, terbium, ytterbium, scandium, thulium, decipium, 
philippium, etc. (see 117). 



178 DEPOBTMENT OF BODIES WITH BEAGENT8. [ 113. 

113. 
6. CESIUM, Ce. (Owidea; Oerous, 06,0,, and Ceric, OeO a .) 

Oeriam occurs sparingly in nature, principally as oerous silicate in 
cente and orthite, as cerous phosphate in monazite, and in combination 
with fluorine in fluooente. It combines With oxygen in two proportions, 
forming cerous oxide, Oe fl O a , and cenc oxide, OeOa , called also cerium di- 
oxide and peroxide. Cerous oxide, which is obtained by igniting either 
cenc oxide or cerous carbonate or oxalate in a stream of hydrogen, is a 
white or bluish-gray powder. It absorbs oxygen rapidly from the air, 
and by ignition in the same is changed into cenc oxide. The cerous 
salts are white or colorless, and some of them are soluble in water. The 
solutions are colorless, have a sweet, astringent taste, and show no absorp- 
tion-spectrum. Cerous chloride, Ce01 8 , easily obtained by heating cerous 
oxide in carbon tetrachloride vapor (L. MEYER and B WILKENS), is white, 
fusible, and not volatile (difference between cerium and aluminium, beryl- 
lium and zirconium) It is soluble in water. By boiling a solution of 
cerous sulphate, a salt is precipitated, which dissolves again upon cooling. 
Cente (hydrous cerous silicate) is decomposed by fusion with sodium car- 
bonate, and concentrated sulphuric acid also decomposes it. Potassium 
hydroxide precipitates white cerous hydroxide, which turns yellow in the 
air from the absorption of oxygen, and does not dissolve in an excess of 
the precipitant (difference from aluminium and beryllium). Ammonia 
precipitates basic salts, which are insoluble in an excess of the precipitant. 
Tartanc acid prevents the precipitation (difference from yttria). Am- 
monium carbonate precipitates white cerous carbonate, which is at first 
amorphous, but gradually becomes crystalline, and dissolves to some extent 
in an excess of the precipitant. Oxalic acid precipitates white cerous 
oxalate, which is amorphous at first, but gradually becomes crystalline. 
The precipitation is complete, even from moderately acid solutions (differ- 
ence from aluminium and beryllium). The precipitate does not dissolve in 
oxalic acid, but it does dissolve in a very large quantity of hydrochloric 
acid, and to a slight extent in a boiling, concentrated solution of ammo- 
nium oxalate. In* the last case, it separates out almost completely again 
upon diluting and cooling (difference from thorium). Even from somewhat 
acid solutions, a saturated solution of potassium sulphate precipitates white 
potassium oerous sulphate (difference from aluminium and beryllium), 
which is difficultly soluble in cold water, more readily in hot water (BAHE), 
and altogether insoluble in a saturated solution of potassium sulphate (dif- 
ference from yttrium). The precipitate may be dissolved by boiling with a 
large quantity of water, to which some hydrochloric acid has been added. 
Jiartum carbonate does not produce a precipitate in the cold, but precipi- 
tates cerous salts completely upon heating. Sodium thiowlphate does not 
precipitate cerium, even on boiling with very concentrated solutions. The 
precipitated sulphur only carries down traces of the salt with it. From 



114.] LANTHANUM. 179 

solutions of cerous salts, alkali-metal hypocUorites precipitate bright yel- 
low eerie hydroxide. If a cerous salt is dissolved in nitric acid with the 
addition of an equal volume of water, a small amount of lead peroxide 
as added, and the solution is then boiled for a few minutes, the liquid 
assumes a yellow color in consequence of the formation of a cenc salt, even 
if only a small amount of cerium is present. On evaporating this solution 
to dryness, heating the residue till a portion of the acid escapes, and treat- 
ing it with water acidified with nitric acid, no cerium will be dissolved, 
but any didymium and lanthanum present will be dissolved (GIBBS). If 
potassium or sodium hydroxide is added to the solution of a cerous salt to 
distinct alkaline reaction (after having evaporated off any free, volatile acid, 
if such is present in large quantity), the solution evaporated to dryness, 
and a solution of strychnine in concentrated sulphuric acid (about 1 : 1000) 
poured over this residue, a magnificent bluish-violet liquid results, the 
color of which soon changes into red (PLUGGE). 

Ceric oxide, obtained by igniting cerous hydroxide, carbonate, or 
oxalate in the air, or by heating cerous nitrate, forms a powder of an 
oramge-yellow color when hot, but yellowish- white when cold. It is soluble 
in concentrated sulphuric acid upon heating, usually with the evolution of 
oxygen, to a yellow solution containing eerie and cerous sulphates. Nitric 
or hydrochloric acids scarcely dissolve it upon heating, but the latter acid 
dissolves it easily when potassium iodide is added, forming cerous chloride, 
e01 a , with the liberation of iodine, or also when alcohol or hydrogen 
peroxide is added to the acid. Oenc hydroxide is soluble in nitric and 
sulphuric acids. Hydrochloric acid dissolves it, with evolution of chlorine 
and formation of cerous chloride. The cenc salts are yellow or red, and their 
solutions are yellow. Sulphurous add decolorizes the solutions, producing 
'Cerous salts. Solutions of eerie salts are precipitated slowly but completely 
by barium carbonate in the cold. Sodium thwsulphate precipitates a 
solution of cenc nitrate. 

In the outer flame, borax and sodium metaphosphate dissolve cerium 
oxides to yellowish-red beads (difference from the preceding earth metals). 
The coloration gets fainter on cooling, and often disappears altogether. In 
the inner flame, colorless beads are obtained. 



114. 
6. LANTHANUM:, La. (Oxide, La s O t .) 

This element is generally found associated with cerium. Lanthanum 
oxide is white, and remains unaltered by ignition in the air (difference 
from cerous oxide). In contact with cold water, it is slowly converted into 
a milk-white hydroxide; while with hot water, the conversion is rapid. The 
oxide and hydroxide change the color of reddened litmus-paper to blue, and 
they dissolve in boiling solution of ammonium chloride, as well as in dilute 
jacids. In this, lanthanum oxide resembles magnesia. The salts of Ian- 



180 DEPOBTMENT OF BODIES WITH REAGENTS. [ 116* 

thanum are colorless. The saturated solution of lanthanum sulphate in 
cold water deposits a portion of the salt even at 80 (difference from cerium). 
Potassium sulphate, oxalic add, and ammonium oxalate (acting upon lan- 
thanum oxalate) give the same reactions as with cerous salts. Potassium 
hydroxide precipitates the hydroxide, which is insoluble in an excess of 
the precipitant, and does not turn brown in the air. Ammonia precipi- 
tates basic salts, which pass milky through the filter on washing. The 
precipitate produced by ammonium carbonate is entirely insoluble in an 
excess of the precipitant (difference from cerous salts). If a cold, dilute 
solution of lanthanum acetate is supersaturated with ammonia, the slimy 
precipitate repeatedly washed with cold water, and a little iodine in pow- 
der added, a blue coloration makes its appearance, which gradually per- 
vades the entire mixture (characteristic difference between lanthanum and 
the other earth metals). Barium carbonate precipitates solutions of lan- 
thanum salts completely, even in the cold. 

115. 
7. DIDYMIUM, Di. (Oxide, Di a O,.) 

This element, like lanthanum and in conjunction with it, is found 
associated with cerium. After intense ignition, didymium oxide appears 
white; but when moistened with nitric acid and feebly ignited, a dark brown 
peroxide is formed, which after intense ignition is converted into the white 
oxide. In contact with water, the oxide is slowly converted into hydroxide; 
it rapidly attracts carbon dioxide; its reaction is not alkaline; it dissolves 
readily in acids and also in a boiling solution of ammonium chloride. The 
salts soluble in water and their concentrated solutions have a reddish or a 
faint violet color. On heating, the nitrate is first converted into a basic 
salt (difference from lanthanum), which is gray when hot and also when 
cold. The chloride is not volatile. The saturated solution of the sulphate 
deposits salt, not at 30, but upon boiling. Potassium hydroccide precipi- 
tates the hydroxide, which is insoluble in an excess of the precipitant, and 
does not alter in the air. Ammonia precipitates a basic salt, which is 
insoluble in ammonia, but somewhat soluble in ammonium chloride. 
Alkali carbonates produce a copious precipitate, which is insoluble in an 
excess of the precipitant, even in an excess of ammonium earbonate (dif- 
ference from cerous salts), but dissolves slightly in concentrated solution 
of ammonium chloride. Tartario acid prevents the precipitation by the 
alkalies. Oxalic add precipitates salts of didymium almost completely. 
The precipitate is difficultly soluble in cold hydrochloric acid, but dissolves 
upon application of heat. It behaves towards ammonium oxalate like 
cerous oxalate. Barium carbonate precipitates didymium solutions slowly 
but completely. A concentrated solution of potassitm sulphate precipi- 
tates didymium solutions more slowly and less completely than cerous 
solutions. The precipitate (potassium didymium sulphate) is insoluble in 
solution of potassium sulphate and in water (DELAFONTAINB), but it dis- 



116.] APPENDIX. 181 

solves in hot hydrochloric acid, although with difficulty. Sodium thiosul* 
phate does not precipitate solutions of didymmm. DIDTMTUM PEROXIDE is 
brown, soluble in hydrochloric acid, with evolution of chlorine, and in 
oxygen acids, with evolution of oxygen. With borax, in both flames, didym- 
ium oxide gives a nearly colorless bead, which in the presence of large 
quantities has a faint amethyst-red tmge. Sodium metaphosphate dissolves 
the oxide in the oxidizing flame to an amethyst-red bead inclining to violet. 
The color disappears m the reducing flame. With sodium carbonate m 
the outer flame, a grayish-white mass is obtained (difference from man- 
ganese). The absorption-spectrum given by the solutions of the salts is 
peculiarly characteristic for didymium. This was first described by GLAD- 
STONE, and afterwards by 0. L. ERDMANN and DELAFONTAINE. BASE aud 
BUNSEN have laid down the exact position of the bands (Zeitschr. f. analyt. 
Ohem., 5, 110). 

APPENDIX TO 112-115. 

116. 

Eegarding the microscopic detection of cerium, lanthanum, and didym- 
ium, see HAUSHOFER, p. 40, and BEHBENS, Zeitschr. f. analyt. Ohem., 30, 
144. 

For separating the metals under consideration, one of the following 
methods may be used : a. Neutralize the solution of the three bases 
almost completely, if it is acid, without, however, allowing a permanent 
precipitate to form ; Add a sufficient amount of sodium acetate and an 
excess of sodium hypochlorite, and boil for some time; cerium is thus 
precipitated as cenc hydroxide (Popp), or as basic acetate which should 
be washed with sodium acetate (ERK) while lanthanum and didymium 
remain in solution (Popp, Ann. Ohem. Pharm., 131, 860). b. Precipitate 
the bases with potassium hydroxide, suspend the washed precipitate in 
potassium hydroxide solution, and pass m chlorine. Lanthanum and 
didymium oxides dissolve, while eerie oxide remains behind (DAMOtJH and 
ST. OLAIRE DEVILLE, Oompt. rend., 69, 272). c. Evaporate the solution of 
the nitrates to dryness, and heat the residue until the brown mass has be- 
come light yellow. If, after cooling, this is treated with boiling, dilute nitric 
acid, lanthanum and didymium go into solution, while cerium remains 
almost completely undissolved as basic nitrate (ROBINSON), d. Dissolve in 
an excess of strong nitric acid, boil with lead peroxide, evaporate the 
orange-yellow solution to dryness, and heat the residue until a part of its 
acid has been removed, treat with water which is acidified with nitric acid, 
and separate the undissolved basic eerie nitrate from the solution contain- 
ing all the lanthanum and didymium (GteBS, Zeitschr. f. analyt. Ohem., 3, 
396). In using the last method, it must be remembered that in the further 
treatment of the solution and the residue, lead is to be first removed by 
hydrogen sulphide* e. Heat the chromates to 110 a and extract with hot 
-water the lanthanum and didymium compounds, which remain xmdecom* 



182 DBPOETMBNT OF BODIES WITH REAGENTS. [ 117. 

posed. Cerium remains behind as insoluble dioxide (PATTCNSON and GLARE, 
Ohem. News, 16, 259). 

From the solution of lanthanum and didymium obtained by one or the 
other of the foregoing methods, the bases are precipitated with ammonium 
oxalate, the oxalates are ignited, and the oxides thus obtained are treated 
with dilute nitric acid. If the separation of cerium was incomplete, the 
remainder of the cerium will be left behind. The solution is evapo- 
rated to dryness in a dish with a flat bottom, and heated to 400 or 500. 
The salts fuse, and nitrous fumes escape. The residue is treated with hot 
water, which dissolves the lanthanum, leaving behind gray basic didym- 
ium nitrate. By many repetitions of the evaporation, etc., the two 
bases may be satisfactorily separated (DAMOUE and ST. CLAIBE DEVILLE). 
MOSANDER recommends converting the didymium and lanthanum into 
sulphates, making a saturated solution of the dry salts in water at 5 or 6, 
and heating the solution to 80, when the lanthanum sulphate is for the 
most part thrown down, and the didymium sulphate is mostly held in 
solution. For other methods of separating lanthanum and didymium, 
compare CL. WINKLER, Zeitschr, f. analyt. Ohem., 4, 417; ZSOHIESCHE, 
ibid., 9,541; FBERIOHS, ibid., 13, 317. 



ADDENDA TO 109-116. 

117. 

The chemistry of the rare-earth metals has recently been studied by many 
investigators,* and the views which were held concerning them at the time 
of the appearance of the 15th (Gterman) edition of this book have been con- 
siderably modified. It has been found that a number of the bodies which 
were previously thought to be elements are mixtures of several, or even of 
many, very similar elemente. According to OBOOKES, yttrium consists of a 
complex of five, or, more probably, of eight, distinct elements. Didymium 
contains two elements. An actual separation of all these bodies has not, as 
yet, been accomplished, at least completely, although evidence has been ob- 
tained in regard to their diversity in spectroscopic properties and atomic 
weight. 

In addition to the elements just considered, a large number of others 
belonging to the rare-earth metals are to be mentioned ; as erbium, ter- 
bium, ytterbium, scandium, thulium, deoipram, philippinm, samarium, 
holmium, mosandrium, dysprosium, austrium, gadolinium, neodymium, 
and praseodymium. 

* The following should receive special mention here : CEOOEES, AUHR v. 
WBLSBACH, LBOOQ DB BOIBBATTDRAN, KRUSS, NELSON, RAMHBLSBBRG, BBT- 

TBNDOKF, SCHOTTLlLNDER, BRATJNER, LAWRENCE SMITH, DlDEfflR, OliBVE, 

DBMAROAY, BEOQUBRBL, THOMPSON, and BLOMSTRAND. 



TITANIUM. 183 

Since the study of these elements cannot yet be considered as finished, 
and an exact characterization of many of them is not yet possible, I cannot 
attempt to give their behavior and reactions, and have therefore treated 
the complex yttrium and didymium as simple metals. 

118. 
8. TITANIUM, Ti. 

Titanium forms three oxides ; titanious oxide, TiO (only known in the 
form of the hydroxide), titanic oxide, Ti fl O s , and titanic acid (anhydride), 
TiOa. The latter is more frequently met with in analysis. Titanic acid is 
found in the free state m rutile,* brookite, and anatase, and in combination 
with bases in titanite, titaniferous iron, etc. It also occurs in small propor- 
tions in bauxites, in many iron ores, m clays, and generally in silicates, 
consequently also m cast-iron and in blast-furnace slags. The small, copper* 
colored cubes which are occasionally found in such slags consist of a com- 
bination of titanium cyanide with titanium nitride. Feebly ignited titanic 
acid is white, but it transiently acquires a lemon tint when heated. Accord- 
ing to the manner of preparation, very intense ignition may give it a yel- 
lowish-white color, or if it previously contained ammonium chloride, a 
brownish color, due to the formation of titanium nitride (v. D. PFOBDTEN). 
It is infusible, insoluble in water, and its specific gravity is 3.9 to 4.25. 
"When strongly ignited in hydrogen for a long time, it is converted into the 
indigo-blue compound, Ti 7 0ia , which is to be considered as a combination 
of titanic acid with titanic oxide (v. D. PFOBDTEN t). Titanium tetrachlo- 
ride, TiOU , is a colorless, volatile liquid, which fumes strongly in the air, 
and decomposes very violently with water. Alcohol dissolves it more quietly 
to a clear fluid, which also remains clear upon mixing it with water. Upon 
the addition of ether, the alcoholic solution which has been diluted with 
water becomes yellow. Upon mixing titanium tetrachloride with concen- 
trated hydrochloric acid, a yellow compound is formed, while much heat 
is produced and hydrogen chloride is given off. This compound dissolves 
in an excess of hydrochloric acid to a clear, bright yellow liquid, which 
does not fume, and can be diluted with water as much as desired without 
becoming turbid (v. D. PFOBDTEN). 

a. Deportment with Acids, and Reactions of Add Solutions of Titanic 
Acid. Ignited titanic acid is insoluble in acids, except in hydrofluoric 
and concentrated sulphuric acids. If the solution in hydrofluoric acid 
is evaporated with sulphuric acid, no titanium tetrafluoride will vola- 
tilize (difference from silicic acid). When evaporated with hydrofluoric 

* Concerning the preparation of pure titanic acid from rutile, the most 
Important compounds of titanium, and the reactions of the solutions-of the 
three titanium oxides, compare v D PFORDTEN, Ann. d. Chem., 234, 857, et 
-W0., and especially 237, 201, etaeg. 

j Ann. d. Chem., 237, 280. 



184 DEPORTMENT OF BODIES WITH REAGENTS. [118. 

acid alone, titanic acid is volatilized. Upon sufficiently long-continued 
fusion with potassium disulphate, titanic acid gives a clear mass, which 
is completely soluble in a large proportion of cold or lukewarm water. 
Titanic acid is very easily brought into a clear solution by fusing with 
hydrogen potassium fluoride, and dissolving the fusion in dilute hydro- 
chloric acid. Potassium titanium fluoride is difficultly soluble in water, 
1 part requiring 06 parts at 14. Both when moist and when it has been 
dried without the aid of heat, hydrated titanic acid is soluble m dilute 
acids, especially in hydrochloric and in sulphuric acids. All solutions of 
titanic acid in hydrochloric or sulphuric acids, especially the latter, and 
consequently also solutions obtained by treating acid potassium sulphate 
fusions with water, when subjected in a highly dilute state to long-con-* 
tinned boiling, deposit metatitanic acid as a white powder, insoluble in 
dilute acids. Presence of much free acid retards the separation and 
diminishes the quantity of the precipitate. The precipitation is most com- 
plete when the mass obtained by fusion with potassium disulphate is dis- 
solved with the addition of some sulphuric acid, the solution neutralized 
with potassium hydroxide, and then, after the addition of .5 g of sul- 
phuric acid for each 100 cc of liquid, it is boiled for six hours with renewal 
of the water lost by evaporation (L&VY). The precipitate which separates 
from hydrochloric acid solutions may be filtered, but it will pass milky 
through the filter on washing, unless an acid or ammonium chloride 
is added to the washing water. From solutions of titanic acid in hydro- 
chloric or sulphuric acid, solution of potassium hydroxide throws down 
titanic acid as a bulky, white precipitate, which is insoluble in an excess of 
the precipitant ; ammonia, ammonium sulphide, and "barium carbonate 
act in the same way. The precipitate, thrown down cold and washed 
with cold water, is soluble in hydrochloric and in dilute sulphuric acids, 
and presence of tartaric acid prevents its formation. In acid solutions 
of titanic acid, potassium ferrocyanide produces a bright reddish-yellow 
precipitate; potassium ferricyanide, a yellow ; and infusion of galls, a 
brownish precipitate, which speedily turns orange-red. On boiling a solu- 
tion of titanic acid with sodium thiosulphate, all the titanic acid is thrown 
down. Sodium phosphate throws it down almost completely as phospho- 
titanic acid, even from solutions containing^muoh hydrochloric acid. The 
washed precipitate consists of P a Ti a O fl (MBRZ). Titanic acid is also precip- 
itated by sodium phosphate in the presence of a large excess of formic 
add; also by boiling with much sodium acetate and acetic acid. Both 
methods of precipitation, especially the latter, accomplish a complete sepa^ 
ration from alumina if the operation is repeated (Goocra*). Hydrogen per- 
oxide colors titanic acid solutions orange-yellow (SCH6N). [The solution 
used for this test should contain no fluorides.] When the colored solution 
is shaken with ether, the colored substance does not go into that solvent 
(HEPPB). Stannous chloride or zinc dust decolorize the solution. The 
reaction is not applicable in the presence of vanadic, molybdio, and chromic? 

* Chem. Centralbl , 1887, p. 15& 



118.] TITANIUM. 185 

acids, nor in the presence of large amounts of ferric salts. [When iron is 
present, a solution in sulphuric acid should be used for the test, because 
ferric sulphate gives far less color than ferric chloride. The reaction in 
this case is delicate, even in the presence of a large amount of iron.] The 
yellow solution which is obtained by the action of aqueous sulphurous acid 
upon granulated zinc (hydrosidpJiurous acid, according to SCHCJTZEN- 
BEEGKR; hyposulphwrous acid, H 3 SaO*, according to BERNTHSEN) produces 
a red coloration in titanic acid solutions, even when extremely dilute. The 
red coloring matter is not taken up by ether when the solution is shaken 
with that liquid (R. FRESENIUS). Metallic zim or tin produces, after some 
time, a pale violet to bluish coloration of the solution, in consequence of 
the reduction of titanic acid to titanic oxide. Subsequently, a blue precipi- 
tate separates, which gradually becomes white. If potassium hydroxide 
or ammonia is added to the solution which has become blue but is still 
clear, blue titanic hydroxide separates, which, by the decomposition of 
water, gradually changes into white, hydrated titanic acid. The reduction 
of titanic acid in hydrochloric solution takes place also in the presence of 
potassium fluoride (difference from niobic acid), the fluid in this case be- 
coming light green. The solutions of titanium tetrachloride in water have 
properties which vary according to their preparation. If, for example, the 
chloride is dissolved in water in such a manner that no heating takes 
place, a slightly opalescent liquid is obtained, which is only slightly clouded 
by boiling (titanium tetrachloride solution), while the same solution, if 
kept for a few weeks, gives a large precipitate by boiling (metatitanic acid 
solution). The solutions are also distinguished by the fact that the first 
remains clear upon the addition of sulphuric or oxalic acids, while the 
other is precipitated by each of these. If the mass obtained by fusing 
titanic acid with potassium disulphate is dissolved in cold water, a precipi- 
tation is made with ammonia, the precipitate is washed with cold water 
and dissolved in as little hydrochloric acid as possible, a solution of meta- 
titanic acid is obtained; i e., it is precipitated by boiling as well as by sul- 
phuric and oxalic acids.* 

b. Reaction wth Alkalies. Recently precipitated titanic acid is almost 
absolutely insoluble in solution of potassium hydroxide. If titanic acid 
is fused with potassium hydroxide and the mass treated with water, 
the solution contains a little more titanic acid. By fusion with alkali 
carbonates, normal alkali titanates are formed, with expulsion of carbon 
dioxide. From the fused mass, cold water extracts alkali and alkali car- 
bonate, leaving behind acid titanate of the alkali metal, soluble in hydro- 
chloric acid with the production of a clear solution or the formation of a 
precipitate, according to the concentration of the acid. When hydro- 

*The statements concerning the formation and properties of titanic 
chloride solutions and metatitanic chloride solutions, by B. WEBEB, Fogg. 
Ann., 120, 287, and 0. RAJOTKLSBEBG, Berlin Monatsber., 1874 p. 490, and 
Zeitschr. f. analyt. Chem., 13, 447, differ from each other. This subject, 
therefore, needs a new investigation. 



186 DBPOBTMENT OP BODIES WITH BEAGEOTS. [ 119* 

chloric acid of about 86 per cent is used, titanic acid separates in a gelat- 
inous form (H. KOSE, v. D. PFORDTBN), 

"When titanic acid is mixed with charcoal and ignited in a stream of 
chlorine, or is exposed to the vapor of carbon tetrachloride below a red 
heat (DEMARgAY), it gives titanium tetrachloride as a volatile liquid, which 
emits copious fumes m the air (see above). At the point of the outer blow- 
pipe flame, sodium metaphospTiate dissolves titanic acid to a colorless bead, 
but with difficulty ; while in the outer flame, yet near the point of the inner 
flame, it dissolves readily and in considerable quantity. If the clear and 
colorless bead is again held in the point of the outer flame, it becomes 
opaque if sufficiently saturated, and by continued action of the flame, 
titanic acid will separate in microscopic crystals of the form of anatase 
(G. ROSE). According to A. KNOP, the crystals are a compound of titanic 
and phosphoric acids ; according to G. WUNDER, they are composed of 
sodium phosphate and titanate, and are rhombohedral. If the bead is held 
in a good reducing flame for some time, it will appear yellow while hot, 
red while cooling, and violet when cold. The reduction is promoted by 
the addition of a little tin. If some ferrous sulphate is added, the bead 
obtained in the reducing flame will appear blood-red. If a substance 
containing titanium is fused upon the loop of a fine platinum wire with a 
little sodium carbonate, in the inner flame of a BUNSEN Jmrner, which is 
made somewhat luminous, and is heated until all the sodium carbonate 
has volatilized, there is formed the copper-red compound composed of tita- 
nium cyanide and nitride, STi 3 N a .TiO a N a , in consequence of the action of 
the cyanogen contained in the gas (LUDEKING). In order to detect tita- 
nium m minerals, .1 g of the finely pulverized substance is fused with 
.2 g of sodium fluoride and 3 g of acid sodium sulphate. By treating 
the mass with cold water, the titanic acid is obtained in solution, in which 
it can be detected (A. NOTES). In regard to the microscopic detection of 
titanium, compare HATTSHOFER, p. 130; BEHRENS, Zeitschr. f. analyt. 
Ohem., 30, 156. 



119. 
9. TANTALUM, Ta. 

With oxygen, tantalum forms tantalous oxide, TaO , and tantalic acid 
(anhydride), Ta a 6 . Tantalum occurs in columbite and tantalite (almost 
always in conjunction with niobium). Tantalic acid is white, and is only 
pale yellowish when hot. When separated in the wet way, the acid contains 
hydroxyl-water. The water-free acid has a specific gravity of 7 to 8 25. 
Tantalio acid is not reduced by ignition in a current of hydrogen. It 
combines with acids as well as with bases. 

a. Add Solutions. When tantalic acid is intimately mixed with char- 
coal and ignited in a current of dry chlorine, and also by the action of car- 
bon tetrachloride vapors below a red heat (DEMARgAY), tantalum chloride,, 



119.] TANTALUM. 187 

Tad* , is formed. The latter is yellow, solid, fusible, and can be sub- 
limed, and is completely decomposed by water, with separation of tantalio 
acid (hydroxide). The chloride is entirely soluble in sulphuric acid, nearly 
so in hydrochloric acid, and partially soluble in potassium hydroxide solu- 
tion. If titanium is present, on treating the mixtures of oxides and char- 
coal with a current of chlorine, titanium chloride will be formed, which 
fames strongly in the air. Hydrated tantalic acid dissolves in hydrofluoric 
add; and the solution, when mixed with potassium fluoride, yields a very 
characteristic salt in fine needles, 2KF.TaF B , which is distinguished by its 
difficult solubility in water acidified with hydrofluoric acid (1 part of the 
acid to 150 or 300 of water). (Distinction and method of separation from 
niobium.) Hydrochloric and concentrated sulphuric acids do not dissolve 
ignited tantabc acid. With potassium disulphate, it fuses to a colorless 
mass ; and if this is treated with water, tantalic acid combined with sul- 
phuric acid remains undissolved (difference between tantalic acid and titanic 
acid, but it cannot be made the ground of a method of separation). "When 
ignited in an atmosphere of ammonium carbonate, the tantalic sulphate 
is converted into tantalic acid. If a solution of alkali tantalate is mixed 
Trith hydrochloric acid in excess, the precipitate first formed redissolves to 
an opalescent fluid. From this liquid, ammonia and ammonium sulphide 
precipitate tantalic acid or an acid ammonium tantalate, but tartaric acid 
prevents the precipitation. Sulphuric acid precipitates tantalic sulphate 
from the opalescent fluid. When acid solutions of tantalic acid are 
brought into contact with zinc, no blue coloration is observed (difference 
between tantalic acid and niobic acid). 

6. Behavior to Alkalies. By continued fusion with potassium hydrox- 
ide, potassium tantalate is formed, and the fused mass will dissolve in 
water. By fusion with sodium hydroxide^ a turbid mass is obtained, and 
a little water poured on this will dissolve out the excess of sodium hy- 
droxide, leaving the whole of the sodium tantalate undissolved. The latter 
salt is insoluble in solution of caustic soda, but the sodium tantalate will 
dissolve in water after the removal of the excess of soda. Solution of 
sodium hydroxide throws down from this solution the sodium tantalate, 
and if the precipitant is added slowly, the form of the precipitate is 
crystalline. From solutions of alkali tantalates, carbon dioxide throws 
down acid salts not soluble in boiling solution of sodium carbonate, and 
even from the dilute solutions, sulphuric acid throws down tantalic sul- 
phate. Potassium ferrocyani&e and infusion of galls produce precipi- 
tates only in acidified solutions, the precipitate produced by the former 
being yellow, and by the latter, light brown. 

Sodium metaphosphate dissolves tantalic acid to a colorless bead, 
which is colorless also when hot, remains colorless even in the inner flame, 
and does not acquire a blood-red tint by addition of ferrous sulphate 
(difference between tantalum and titanium). The microscopic detection 
of tantalum is based npon the observation of the crystals, in which potas- 
sium tantalum fluoride and sodium tantalate can be obtained (BEHRENS 
Zeitschr. f. analyt. Ohem., 30, 163; HAITSHOFBE, p. 105). 



188 DEPOBTMBNT OF BODIES WITH EBAGBNTS. [ 120. 

120. 
10. NIOBIUM, Nb, or COLUMBIOT, Ob. 

Niobium combines with oxygen in several proportions, viz., NbO, 
NbOa, and NbaOs. It is rare, being found in oolumbite, samarskite, etc., 
and it is usually accompanied by tantalum. Niobic acid (anhydride), 
NbaOs , is white, can be obtained in a crystallized condition (EBELMEN, A. 
KNOP), and turns transiently yellow when ignited (difference from tantalio 
acid). Its specific gravity lies between 4.37 and 4.53 (difference from tan- 
tahc acid). By strong ignition in hydrogen, the niobic acid is converted 
into black Kb0 3 . Niobic acid combines both with bases and with acids. 

a. Add Solutions of JVtobic Acid. Concentrated sulphuric add dis- 
solves the acid on heating, unless it has been too strongly ignited. On the 
addition of much cold water, a clear solution is obtained. On fusing with 
potassium disulphate, it dissolves readily to a colorless mass, and on 
treating the fusion with boiling water, niobic acid containing sulphuric 
acid remains undissolved, but is readily soluble in hydrofluoric acid (see 
below). By mixing niobic oxide intimately with charcoal and treating 
with a current of Marine, and also by heating it in the vapor of carbon 
tetrachlonde at about 440 (DEMAR9AY), a mixture is obtained of white, 
infusible, difficultly volatile niobic oxychlonde, N"b001a , and yellow more 
volatile niobic chloride, Nb01 B . Treated with water, both compounds give 
turbid fluids, in which a part of the niobium is separated as niobic acid, 
but the larger portion remains dissolved. By boiling with hydrochloric 
acid and afterwards adding water, the compounds give clear solutions, 
which are not precipitated by boiling or by sulphuric acid in the cold (dif- 
ference from tantalum chloride). By igniting niobic oxide in the vapor of 
niobium chloride, the oxychloride is formed (difference from tantalic 
oxide). From the acid solutions of niobic acid, ammonia and ammonium 
sulphide throw down niobic acid containing ammonia, which, as well as 
any niobic acid that has not been ignited, dissolves in hydrofluoric acid. 
When mixed with potassium fluoride, the hydrofluoric solution gives potas- 
sium niobium fluoride, SKF.ltfbFi , if hydrofluoric acid is in excess ; other- 
wise it gives potassium niobium oxyfluoride, 2KF.M>OF. The latter 
salt is also obtained when potassium niobate is dissolved in hydrofluoric 
acid ; it is readily soluble in cold water, 1 part dissolving in 13.5 parts 
(difference from potassium titanium fluoride, which requires 96 parts of 
water, and from potassium tantalum fluoride, which requires 200 parts of 
water). If the solution of potassium niobium oxyfluoride is boiled for a 
long time, with renewal of the evaporated water, niobium dioxyfluoride 
separates in microscopic crystals (Kuttss and NIMON*). If very dilute 
potassium hydroxide is added to a very dilute, boiling solution of niobic 

* Jahresber. uber die Fortschritte d. Ohemie, 1887, p. 557, 



121-] FOURTH GROUP. 189 

acid in hydrofluoric acid until reddish litmus-paper begins to change its 
color a little, and then ammonia is added to neutralization, all the niobic 
acid is precipitated (difference and means of separation from titanic acid, 
DEMAB^AT*). On digesting a hydrochloric or sulphuric acid solution of 
niobic acid with sine or tin, it acquires a blue and generally also a brown 
color, in consequence of the reduction of the niobic acid to lower oxides. 
In the presence of alkali-metal fluorides, the reduction does not take place 
{difference from titanic acid). 

6. Alkaline Solutions. With potassium hydroxide, niobic acid fuses to 
A clear mass, soluble in water. To sodium hydroxide, niobic acid shows 
the same deportment as tantalic acid. From the solution of potassium 
mobate, sodium hydroxide precipitates an almost insoluble sodium niobate. 
On boiling a solution of potassium niobate with hydrogen potassium car- 
bonate, an almost insoluble acid potassium niobate is thrown down. On 
fusing niobic acid with sodium carbonate and boiling the fusion with 
water, a crystalline acid sodium niobate remains undissolved. Carbon 
dioxide when passed into solution of sodium niobate precipitates all the 
niobic acid as an acid salt. 

Bodiwm metaphosphate dissolves niobic acid readily. The bead held in 
the outer flame appears colorless as long as it is hot, but in the inner flame, 
it has a violet, blue, or brown color, according to the quantity of the acid 
present, and a red color on the addition of ferrous sulphate. The micro- 
scopic detection of niobium is accomplished by observing the crystals of 
sodium niobate (see HAUSHOFER, p. 104 , BEHBENS, Zeitschr. f . analyt. 
Chem., 30, 161). 

For the best methods of detecting several, or possibly all, of the 
members of the third group in presence of each other, see Fart II, 
Section IH 



121. 

FOUETH 0BOUP. 

More common metals : ZINO, MANGANESE, NICKEL, COBALT, 
IBON. 

Barer elements: UKANIUM, THALLIUM, INDIUM, GAUIUM, 
VANADIUM. 

Properties of the Group. II they contain a stronger free 
acid in sufficient amount, solutions of the metals of the fourth 
group are not precipitated at all by hydrogen sulphide, nor 
are neutral solutions at least not completely. Alkaline solu- 
tions, however, are completely precipitated by hydrogen sul- 

* Jahresber. Uber die Fortschrltte d. Chemie, 1885, p. 1920. 



190 DEPOBTMETTT OF BODIES WITH EEAGBNTS. [ 122. 

phide ; and so are other solutions, if a sulphide of an alkali 
metal is used as the precipitant instead of hydrogen sul- 
phide.* The precipitates are hydrated sulphides correspond- 
ing to the oxides of the metals.t They are insoluble in water. 
Some of them are easily soluble in dilute acids, but others 
(nickel and cobalt sulphides) are very difficultly soluble. In 
alkali-metal sulphides, most of them are insoluble, while 
others are soluble, either slightly under certain circumstances, 
(nickel), or even completely (vanadium). 

The metals of the fourth group differ, accordingly, from 
those of the first and second groups in this, that their solutions, 
are precipitated by ammonium sulphide ; and from those of 
the third group, inasmuch as the precipitates produced by 
ammonium sulphide are sulphides, and not hydroxides, as is 
the case with aluminium, chromium, etc. 



SpeM Reactions of the More Common Metals of t7& Fourth. 

Growp. 

122. 
a. ZINO, Zn. (OMe, ZnO.) 

1. METAUJO ZINC is bluish-white and very bright. When- 
exposed to the air, a thin coating of basic zinc carbonate forms 
gradually on its surface. It is of medium hardness, malleable 
at a temperature of between 100 and 150, but otherwise 
more or less brittle. It fuses readily on charcoal before the 
blowpipe, boils afterwards, and burns with a bluish-green 
flame, giving off white fumes, and coating the charcoal sup- 
port with oxide. Pure zinc scarcely dissolves in dilute hy- 
drochloric and sulphuric acids ; in very dilute nitric acid, it. 
dissolves with evolution of nitrous oxide ; and in more con- 
centrated nitric acid, with evolution of nitric oxide. Impure 

* Vanadic acid behaves in a very peculiar way with ammonium sulphide* 
(see 138). 

f Alkali-metal sulphides precipitate a mixture of ferrous sulphide and 
sulphur, from solutions of ferric salts. It is only when a ferric salt solution is* 
allowed to flow slowly into an excess of a sulphide solution that a hydrated 
sulphide corresponding to ferric oxide is obtained (BEBZELTUS). 



122.] ZINC. 191 

zinc, or zinc which is in contact with electro-negative metals, 
dissolves in dilute hydrochloric or sulphuric acid, -with evolu- 
tion of hydrogen gas. 

2. ZINO OXIDE and ZINC EYDBOXEDE are usually white pow- 
ders, which are insoluble in water, but dissolve readily in 
hydrochloric, nitric, and sulphuric acids. Zinc oxide acquires 
a lemon-yellow tint when heated, but resumes its original, 
white color upon cooling. When ignited before the blowpipe, 
it glows with considerable brilliancy. 

3. The zmo SALTS are colorless or white if the acid causes 
no coloration. Part of them are soluble in water, and the 
rest in acids. The normal salts of zinc which are soluble in 
water redden litmus-paper, and those containing volatile 
oxygen acids are readily decomposed by heat, with the excep- 
tion of zinc sulphate, which can bear a dull red heat without 
undergoing decomposition. Zinc chloride is volatile at a red 
heat. 

4. From neutral solutions of zinc salts of strong acids, 
hydrogen sulphide precipitates a portion of the metal as white, 
hydrated ZINC SULPHIDE, ZnS. From solutions of neutral 
zinc salts of weak acids, however (e.g., from zinc acetate 
solutions or from solutions of zinc salts of strong acids which 
contain normal salts of weak acids in sufficient amount, as 
sodium acetate, sodium formate, ammonium sulphocyanide)* 
hydrogen sulphide precipitates all the zinc upon warming* 
In acid solutions, no precipitate is formed if the free acid pres- 
ent is one of the stronger ones, and if it is present in sufficient 
amount Alkali-metal acid sulphates only prevent the pre- 
cipitation when they are present in large amount. When they 
are present in smaller' quantities, a part of the zinc is pre- 
cipitated. From a sufficiently dilute solution of zinc in acetic 
acid, formic acid (DELMS, HAMPE), monochloracetic acid 
(v. BERG), or succinic acid (ALT and J. SOHULZE), the zinc ia 
also precipitated, even if the acid is in excess. Wanning to 
50 or 60 facilitates the precipitation. 

5. From neutral solutions, ammonium sulphide, and from 
alkaline solutions, hydrogen sulphide, throw down the whole 
of the metal as hydrated ZING SULPHIDE, in the form of a white 
precipitate. Ammonium chloride greatly promotes the separa- 
tion of the' precipitate, which from very dilute solutions sepa- 



192 DEPORTMENT OF BODIES WITH REAGENTS. [ 122. 

rates only after long standing. This precipitate is not dis- 
solved by an excess of ammonium sulphide, nor by potassium 
hydroxide or ammonia; but it dissolves readily in hydro- 
chloric, nitric, and dilute sulphuric acids. It is insoluble in 
acetic acid. 

6. Potassium and sodium hydroxides throw down ZINO HT- 
DKOXIDE, Zn(OH) a , in the form of a white, gelatinous precipi- 
tate, which is readily and completely redissolved by an excess 
of the precipitant. Upon boiling these alkaline solutions, they 
remain, if concentrated, unaltered ; but from dilute solutions, 
nearly the whole of the zinc hydroxide separates as a white 
precipitate. Ammonium chloride, added to alkaline solutions 
containing only a very small excess of potassium or sodium 
hydroxides, produces a white precipitate of zinc hydroxide, 
which, however, redissolves on addition of more ammonium 
chloride. Solutions which contain larger amounts of potassium 
or sodium hydroxides are not precipitated by ammonium 
chloride (difference from aluminium). 

7. In zinc solutions, if they do not contain a large excess 
of free acid, ammonia also produces a precipitate of ZINO 
EYDBOXIDE, which readily dissolves in an excess of the pre- 
cipitant. The concentrated solution turns turbid when mixed 
with water. On boiling the concentrated solution, a part of 
the zinc hydroxide separates, while on boiling the dilute 
solution, all of it precipitates. Ammonium salts interfere 
with or prevent these precipitations. 

8. Sodium carbonate produces a precipitate of BASIC ZINO 
OABBONATE, which is insoluble in an excess of the precipitant. 
The composition of the precipitate varies according to the 
concentration and temperature of the solution and the excess 
of the precipitant. Presence of ammonium salts in great 
-excess prevents the formation of this precipitate. 

9. Ammonium carbonate also produces a precipitate of BASIC 
ZINC CABBONATE, but this redissolves upon further addition of 
the precipitant. On boiling the dilute solution, a white pre- 
cipitate is produced. Ammonium salts hinder or prevent 
this precipitation. 

N.B. Non-volatile organic acids interfere more or less with 
the precipitation of solutions of zinc by the caustic and car- 
bonated alkalies. Sugar does not prevent the precipitations. 



122.] ZING. 193 

10. In the cold, barium carbonate fails to precipitate solu- 
tions of zinc salts, with the exception of the sulphate. 

11. Potassium cyanide precipitates white ZINO CYANIDE, 
Zn(ON) a . This dissolves in an excess of the precipitant. If 
the excess of potassium cyanide is not too great, potassium 
sulphide or sodium sulphide precipitates hydrated zinc sul- 
phide at once from this solution, while hydrogen sulphide or 
ammonium sulphide precipitates it slowly and incompletely. 

12. Potassium ferrocyanide throws down ZINC FEKROCYANIDE, 
Zn a Fe(ON) fl , as a white, slimy precipitate, somewhat soluble 
in excess of the precipitant, but difficultly soluble in hydro- 
chloric acid. It is formed even in a solution to which tartaric 
acid and an excess of ammonia have been added. 

13. Potassium ferricyanide throws down ZINO EEBRIOYANIDE, 
Zn.Fe^CNXa , as a brownish orange-yellow precipitate, soluble 
in hydrochloric acid and in ammonia. 

14. If a mixture of a zinc compound with sodium carbonate 
is exposed to the reducing flame of the blowpipe, the char- 
coal support becomes covered with a coating of ZINO OXIDE, 
which presents a yellow color while hot, and turns white 
upon cooling. This coating is produced by the reduced 
metallic zinc volatilizing at the moment of its reduction, and 
being reoxidized in passing through the outer flame. The 
METALLIC INCRUSTATION, obtained according to p. 35, is black, 
with a brown edge ; but the INOEUSTATION OF OXIDE is white, 
and therefore invisible upon porcelain. They may be dis- 
solved in a little nitric acid and examined according to 15. 

15. If zinc oxide or one of the zinc salts is moistened 
with solution of cobalt nitrate, and then heated before the 
blowpipe, an unfused mass of a beautiful GBEEN color is ob- 
tained, which is a compound of zinc oxide with cobalt oxide. 
If, therefore, in the first experiment described in 14, the coat- 
ing on the charcoal is moistened with cobalt solution and 
ignited, it appears green when cold. This test may be applied 
with great delicacy by mixing the solution to be tested with 
a very little of the cobalt solution (not enough to give a 
bright red color), adding sodium carbonate in slight excess, 
boiling, filtering off, washing, and igniting on platinum foil. 
On 'triturating the residue, the green color may be distinctly 
and readily observed (BLOXAM), 



194 DEPORTMENT OF BODIES WITH REAGENTS. [ 123. 

16. In relation to the microscopic detection of zinc, see 
HAUSHOEEB, p. 151 ; BEHBENS, Zeitsohr. f. analyt. Ohem., 30, 
142. 

123, 
b. MANGANESE, Mn. (Mangan&ua Oxide, MnO.) 

1. METALLIC MANGANESE is whitish-gray, dull, very hard, 
brittle, and fuses with very great difficulty. It oxidizes rap- 
idly in moist air, and in water with evolution of hydrogen, 
,and crumbles to a dark green powder. It dissolves readily 
in acids, forming manganous salts. 

2. MANGANOUS OXIDE is light green, and manganous hy- 
droxide, Mn(OH) a , is white. The former smoulders to brown 
mangano-manganic oxide, Mn a 4 , when heated in the air ; the 
latter, even at the ordinary temperature, rapidly absorbs oxy- 
gen from the air and passes into brown mangano-manganic 
hydroxide. Both are readily soluble in hydrochloric, nitric, 
and sulphuric acids. The brownish-black manganic oxide, 
MuaO^and the black manganese dioxide, MnO 9 , dissolve to 
manganous chloride, with evolution of chlorine, when heated 
with hydrochloric acid; and to manganous sulphate, with 
evolution of oxygen, when heated with concentrated sul- 
phuric acid. 

3. The MANGANOUS SALTS are colorless or pale red if their 
acid produces no coloration. Part of them are soluble in 
water, and the rest in acids. The salts containing volatile 
oxygen acids are readily decomposed at a red heat, with the 
exception of the sulphate, which withstands a red heat with- 
out decomposition. The solutions do not alter vegetable colors. 

4. Hydrogen sulphide does not precipitate acid solutions, 
even if the weaker acids, such as acetic, formic, monochlor- 
-acetic, or succinic acids, are present. Neutral solutions, also, 
are not precipitated, or are precipitated very imperfectly. 

5. From neutral solutions, ammonium sulphide, and from 
alkaline solutions, hydrogen sulphide, throw down the whole 
of the metal as hydrated MANGANOUS SULPHIDE, MnS.HjO, in 
form of a light flesh-colored, or (with small quantities) yellow- 
ish-white precipitate, which acquires a dark brown color in 



123.] MANGANESE. 195 

the air, on account of oxidation. This precipitate is insol- 
uble in ammonium sulphide and in alkalies, but readily sol- 
uble in hydrochloric, nitric, and acetic acids. The separation 
of the precipitate is materially promoted by addition of a 
moderate amount of ammonium chloride. From very dilute 
solutions, the precipitate separates only after standing some 
time in a warm place. Ammonium oxalate, tartrate, but 
especially citrate, retard the precipitation, the latter salt also 
interfering with its completeness. In the presence of ammonia 
and ammonium sulphide in large excess, the flesh-colored hy- 
drated precipitate occasionally passes into the green, crystal- 
line sulphide, SMnS^B^O, even in the cold, the change being 
greatly facilitated by boiling, and being hindered more or 
less by the presence of ammonium chloride- Solutions con- 
taining much free ammonia should be nearly neutralized 
with hydrochloric acid before precipitating with ammonium 
sulphide. 

6. Potassium and sodium hydroxides produce whitish pre- 
cipitates Of MAtfGANOTJS EYDBOXEDE, Mn(OH) 3 , which UpOU eX- 

posure to the air speedily acquire a brownish and finally a 
^deep blackish-brown color, owing to the conversion of the 
manganous hydroxide into mangano-manganic hydroxide by 
the absorption of oxygen from the air. Ammonia also pre- 
cipitates manganous hydroxide, but the precipitate never 
contains more than about half the manganese present (com- 
pare the analogous behavior of magnesium salts). Ammonia 
and ammonium carbonate do not redissolve this precipitate ; 
but presence of ammonium chloride in sufficient amount 
entirely prevents the precipitation by ammonia, and renders 
incomplete that by potassium and sodium hydroxides. Of 
precipitates already formed, solution of ammonium chloride 
redissolves only those parts which have not yet undergone 
oxidation. The solution of the manganous hydroxide in am- 
monium chloride is due to the tendency of the manganous 
salts to form double salts with ammonium salts. The am- 
moniacal solutions of these double salts turn brown in the 
air, and deposit dark brown mangano-manganic hydroxide. 
This dissolves in a solution of acid potassium oxalate to a 
beautiful red solution containing potassium manganic oxalate. 



196 DEPORTMENT OF BODIES WITH BEAGENT8. [ 123 

7. If potassium or sodium hydroxide or ammonia is added 
to a solution of a manganous salt, and a solution of bromine 
or of hydrogen peroxide is then added, all the manganese 
separates as brownish-black, hydrated MANGANESE DIOXIDE, 
MnO fl .H a O. Heating facilitates the separation. Solutions of 
manganous salts containing sodium acetate are also precipi- 
tated by bromine upon heating. 

N.B. Non-volatile organic acids may interfere with or 
prevent the precipitation of manganous hydroxide or man- 
ganese dioxide. Sugar interferes with or prevents the pre- 
cipitation as manganous hydroxide, but not as manganese 
dioxide. 

8. Ammonium carbonate precipitates white MANGANOUS CAB- 
BONATE, MnCOa-HjO. After a considerable time, the precipi- 
tation is complete, even in presence of ammonium chloride. 
Sodium or potassium carbonate produces a white precipitate, 
which, according to circumstances, is HIDEOUS MANGANOUS CAB- 

BONATE, MANGANOUS HYDROXIDE, or a MIXTUBE OF BOTH. When 

freshly precipitated, this dissolves in ammonium chloride 
solution, but it is insoluble in an excess of the precipitant. 

N.B. Non-volatile organic acids hinder or prevent the 
precipitations by the fixed alkali carbonates. The precipita- 
tion by ammonium carbonate is retarded but not prevented 
by them. 

9. Potassium ferrocyanide precipitates MANGANOUS EEBBOOT- 
ANEDE, Mn s Fe(CN) e , as a white precipitate, which is rather dif- 
ficultly soluble in hydrochloric acid. The precipitation also 
occurs in a freshly prepared, ammoniacal solution of a man- 
ganous salt, which contains ammonium tartrate (difference 
from iron, L. BLUM). 

10. Potassium ferricyanide precipitates MANGANOUS EEBBI- 
OYANIDE, MnaFe a (C:N) 19 , as a brown precipitate, which is but 
slightly soluble in cold hydrochloric acid and insoluble in 
ammonia. By boiling with a large excess of concentrated 
hydrochloric acid, the precipitate dissolves with decomposi- 
tion. 

11. If a few drops of a fluid containing a manganous salt, 
and free from chlorine, are sprinkled on lead dioxide, and nitric 
acid free from chlorine is added, the mixture boiled and 



123.] MANGANESE. 197 

allowed to settle, the fluid acquires a deep red color, from the 
formation of permanganic acid, HMnO 4 * (HoppE-SEYLEB). 

12. Upon digestion in the cold, barium carbonate does not 
precipitate aqueous solutions of manganous salts, with the 
exception of manganous sulphate. 

13. If a manganese compound is treated with phosphoric 
aaid, evaporated to syrupy consistence, and then (after the 
addition of a little potassium nitrate if a manganous com- 
pound is under experiment) it is heated more strongly, a 
violet mass is obtained, which is semi-liquid while hot and 
solid upon cooling, due to the formation of MANGANIC PHOS- 
PHATE. This reaction is very delicate. 

14. If any compound of manganese in a state of minute 
division is fused with 2 or 3 parts of sodium carbonate on a 
platinum wire, or on a small strip of platinum foil (heated by 
directing the flame against the lower surface), or upon the 
cover of a platinum crucible in the outer flame of the BUNSEN 
lamp, blowpipe, or blast-lamp, SODIUM MANGANATE, Na a Mn0 4 , 
is formed, which makes the fused mass appear GREEN while 
hot, and of a BLUISH-GBEEN tint after cooling, the mass at the 
same time losing its transparency. This reaction enables us 
to detect the smallest traces of manganese. It also succeeds 
very well with sodium peroxide (HEMPEL). 

15. In the outer gas or blowpipe flame, borax and sodium 
metaphosphate dissolve manganese compounds to clear VIOLET- 
BED beads, which upon cooling acquire an AMETHYST-RED tint 
They lose their color in the inner flame, owing to a reduction 
of manganic borate or phosphate to manganous salts. The 
borax bead appears black when containing a considerable 
portion of manganic borate, but that formed by sodium meta- 
phosphate never loses its transparency. The latter bead, 
also, loses its color in the inner flame of the blowpipe far 
more readily than the former. 

16. In relation to the microscopic detection of manganese, 
see HAUSHOEEB, p. 96; BEKBENS, Zeitschr. f. analyt Ohem., 30, 
140. 

* The lead dioxide should first he tested to find whether it is free from 
manganese, hy evaporating with sulphuric acid until most of the excess of thia, 
is removed, and hoiling with dilute nitric add and more of the lead dioxide. 



19S DEPORTMENT OF BODIES WITH REAGENTS. [124. 

124 
c. NICKEL, Ni. (NicMous Oxide, NiO.) 

1. Metallic nickel, when it has been fused, is yellowish- 
white, inclining to gray. It is bright, hard, malleable, dif- 
ficultly fusible, and does not oxidize in the air at the com- 
mon temperature, but oxidizes slowly upon ignition. It is 
attracted by the magnet, and may itself become magnetic. 
Upon the application of heat, it slowly dissolves in hydro- 
chloric and dilute sulphuric acids, with evolution of hydrogen 
gas, but it dissolves readily in nitric acid. The solutions con- 
tain nickelous salts. 

2. NICKELOUS HYDBOXEDE is light green, and remains unal- 
tered in the air, but is converted by ignition at a white heat 
into amorphous, green NIOEELOUS OXIDE (NiO). Both nickelous 
oxide and the corresponding hydroxide are readily soluble in 
hydrochloric, nitric, and sulphuric acids. The nickelous 
oxide which crystallizes in octahedrons is insoluble in acids, 
but dissolves in fusing potassium disulphate. NIOKEUO 
OXIDE, Ni,O f , is black, and dissolves in hydrochloric acid to 
nickelous chloride, with evolution of chlorine. By gentle igni- 
tion of the nitrate, nickelous oxide of a grayish-green color, 
and containing a little nickelic oxide, is obtained. 

3. Most of the NIOKELOUS SALTS are yellow in the anhydrous, 
and green in the hydrated, state, their solutions being light 
green. They are decolorized by the addition of a certain 
amount of a cobaltous salt solution, 3Ni : ICo. The soluble, 
normal salts slightly redden litmus-paper. Generally, the 
oxygen salts containing volatile acids are readily decomposed 
by ignition, but nickelous sulphate withstands a low red heat. 

4 Hydrogen sulphide does not precipitate solutions of 
nickel salts with strong acids in presence of free acids. In 
the absence of the latter, a small portion of the nickel gradu- 
ally separates as black, hydrous NICKEL SULPHIDE, NiS. Nickel 
acetate is not, or is scarcely at all, precipitated in presence of 
free acetic acid, but in the absence of the free acid, the greater 
part of the nickel is thrown down by long-continued action of 
hydrogen sulphide. If the solution, however, contains a suf- 



124.] NICKEL. 199 

ficient amount of alkali-metal acetate, the nickel is all pre- 
cipitated, even in the presence of free acetic acid, especially 
by the action of hydrogen sulphide with the aid of heat Free 
formic and monochloracetic acids also prevent the precipita- 
tion, but if their alkali-metal salts are present, the precipita- 
tion, upon heating, is only prevented by considerable amounts 
of the free acids. 

5. Ammonium sulphide in neutral, and hydrogen sulphide 
in alkaline, solutions produce a black precipitate of hydrous 
araoKEL SULPHIDE, NiS, which is not altogether insoluble in 
ammonium sulphide, especially if the latter contains free am- 
monia. The fluid from which the precipitate has been thrown 
down usually exhibits, therefore, a brownish color, and upon 
neutralizing with acetic acid and warming, gives a slight 
precipitate of nickel sulphide. The presence of ammonium 
chloride, and especially of ammonium acetate, considerably 
promotes the precipitation. Ammonium sulphide which has 
been decolorized by sodium sulphite precipitates the nickel 
completely in the presence of ammonium salts and the absence 
of large amounts of free ammonia (LECRENIEB). Nickel sul- 
phide dissolves scarcely at all in acetic acid, with great diffi- 
culty in dilute hydrochloric acid, but readily in nitric and in 
nitro-hydrochloric acid upon application of heat. 

6. Potassium and sodium hydroxides produce a light green 
precipitate of NIOKELOUS HYDROXIDE, Ni(OH) a , which is insolu- 
ble in an excess of the precipitants, and unalterable in the 
air and on boiling (even in the presence of hydrogen peroxide, 
iodine, or alcohol). Ammonium carbonate dissolves this pre- 
cipitate, when filtered and washed, to a greenish-blue fluid, 
from which caustic potash or soda reprecipitates the nickel as 
apple-green hydroxide. 

7. Ammonia added in small quantity produces a trifling 
greenish turbidity, but upon further addition of the reagent, 
this redissolves readily to a blue fluid containing a compound 
of NIOKELOUS SALT AND AMMONIA. From this solution, potassium 
and sodium hydroxides precipitate nickelous hydroxide. 
Solutions containing ammonium salts or free acid are not 
rendered turbid by ammonia. 

8. If the solution of a nickelous salt is treated with potas* 
tium or sodium hydroxide, and bromine-water or a solution of 



200 DEPORTMENT OF BODIES WITH REAGENTS. [ 

*odiim hypocMorite is added in sufficient quantity, but not 
lijdrogen peroxide or iodine (difference from cobalt), and heat 
is applied, all the nickel separates as black NICKELIC HYDROX- 
IDE, which dissolves immediately upon the addition of potas- 
sium cyanide, in the form of potassium nickelous cyanide. It 
is also reduced by a mixture of ammonia and ammonium 
chloride, going into solution as an ammonia-nickelous salt. 
The mixture just mentioned should be allowed to act upon 
the precipitate after the latter has been separated from the 
liquid. The solution takes place somewhat slowly in the 
cold, but quickly by heating. 

N.B. The presence of non-volatile, organic acidr \nd also 
of sugar prevents or interferes with the precipitation ui nickel 
as nickelous or nickelic hydroxide. 

9. Potassium, ferroeyanide precipitates from solutions 
of nickelous salts, greenish-white NICKEL EERROOTANEDE, 
NyEXCN),, which is difficultly soluble ii hydrochloric 
acid. 

10. Potassium ferricyanide precipitates yellowish-brown 
NICKEL FEBRICIANEDE, which is difficultly soluble in hydro* 
chloric acid. In the presence of ammonium chloride or 
tartario acid and an abundant excess of ammonia, a clear 
liquid is obtained, which is brownish-yellow or, if very dilute, 
pale yellow. 

11. Potassium cyanide produces a greenish precipitate of 
NICKEL CYANIDE, Ni(ON) a , which in an excess of the precipitant 
redissolves readily as a double nickel potassium cyanide, 
Ni(CN) 9 .2KC]Sr. The solution is brownish-yellow, and does; 
not acquire a darker color on exposure to the air. If sul- 
phuric or hydrochloric acid is added to this solution, the 
potassium cyanide is decomposed, and the nickel cyanide 
reprecipitated, although from highly dilute solutions, it sep- 
arates only after some time. It is very difficultly soluble 
in an excess of the precipitating acids in the cold, but more 
readily DO upon boiling. If the solution of the double cyanide 
is rendered alkaline by sodium hydroxide, being also kept la 
this condition by a further addition of the latter if necessary, 
and chlorine is passed into it without warming, or bromine 
is added, the whole of the nickel gradually separates as black 
nickelic hydroxide. 



124] NICKEL. 301 

12. On adding a solution of potassium thiocarbonate* to sola- 
tions which are not too dilute and which have been rendered 
alkaline by ammonia, a deep brownish-red fluid is obtained* 
which is barely translucent, and appears almost black by 
reflected light. If the solution of nickel is extremely dilute, 
the addition of the reagent will produce a yellowish-red color 
(0. D. BBAUN). The occurrence of this color in highly dilute 
solutions is characteristic of nickel. In the presence of cobalt, 
this reaction is almost or completely hidden, and it is more 
or less obscured in the presence of manganese and zinc. 

13. On digestion in the cold, barium carbonate does not 
precipitate solutions of nickel salts, solution of sulphate alone 
excepted. 

14. Potassium nitrite with acetic acid does not throw down 
nickel, even from concentrated solutions. In the presence of 
calcium, barium, or strontium, however, a yellow, crystalline 
nitrite of potassium, nickel, and the alkali-earth metal is pre- 
cipitated from not too dilute solutions. The precipitate is 
difficultly soluble in cold water, but more readily so in hot 
water to a green fluid (KiJNZEL, 0. L. EKDMANN). 

15. In the outer flame, borax and sodiwn mstapho^phate 
dissolve compounds of nickel to clear beads. The borax bead 
is violet while hot, and reddish-brown when cold. The sodium 
metaphosphate bead is reddish or brownish-red while hot, 
and yellow or reddish-yellow when cold. Small amounts of 
cobalt hide the colorations. In the inner flame, the sodium 
metaphosphate bead remains unaltered, but the borax bead 
becomes gray and cloudy from reduced metal. On continued 
heating, the particles of nickel collect together without fusing, 
and the bead loses its color. 

16. By the reduction in the stick of charcoal, according to 
p. 34, the compounds of nickel yield, after trituration, white, 
shining, ductile spangles, which attach themselves to the point 
of a magnetic Inife in the form of a brush. With nitric acid, 
they give a green solution, which can be further examined. 

To prepare potassium thiocarbonate, KCS , saturate one half of a solu- 
tion of potassium hydroxide containing about 5 per cent of this substance 
with hydrogen sulphide, add the other half, and digest at a gentle heat with 
Vr of its volume of carbon disulphide ; separate the dork red liquid from the 
Tindissolved carbon disulphide and preserve It in well-closed bottles. 



202 DEPORTMENT OF BODIES WITH REAGEOTS. [ 125. 

17. In relation to the microscopic detection of nickel, se<* 
HAUSEOFEE, p. 63 ; BEHKENS, Zeitschr. f. analyt. Chem., 30^ 
141. 

125. 
d. COBALT, Co. (Cdbaltoua Oxide, OoO.) 

1. METALLIC COBALT which has been fused is steel-gray, 
rather hard, capable of taking a polish, malleable, difficultly 
fusible, and magnetic. It does not oxidize in the air at the 
common temperature, but it oxidizes at a red heat. With 
acids it behaves like nickel, and the solutions contain cobalt* 
ous salts. 

2. CoBAi/rotJS OXIDE, CoO, is light brown ; cobaltous hy- 
droxide is a pale red powder. Both dissolve readily in 
hydrochloric, nitric, and sulphuric acids. COBALTTO OXIDE,, 
Co a O,, is black, and dissolves in hydrochloric acid to cobalt* 
ous chloride, with evolution of chlorine. 

3. The OOBALTOUS SALTS containing water of crystallization 
are red; the anhydrous salts are mostly blue. Moderately 
concentrated solutions appear of a light red color, which they 
retain when considerably diluted. The soluble normal salts 
redden litmus slightly ; the salts containing volatile oxygen 
acids are generally readily decomposed at a red heat, although 
cobaltous sulphate can bear a moderate red heat without 
suffering decomposition. When a solution of cobaltous 
chloride is evaporated, the light red color changes to blue 
toward the end of the operation, but addition of water restores 
the red color. 

4. Hydrogen sulphide does not give precipitates in solutions 
of salts with strong acids, if they contain free acid, but from 
neutral solutions, it gradually precipitates part of the cobalt 
as black, hydrous cobaltous sulphide, CoS. Gobaltous acetate 
does not give a precipitate, or gives only a very slight one, in 
presence of free acetic acid ; but in the absence of free acid, 
the metal is almost or completely precipitated. If the solu- 
tion, however, contains an alkali-metal acetate in sufficient 
amount, all the cobalt is thrown down, even in the presence- 
of free acetic acid, especially by the action of hydrogen. 



125.] COBALT. 203 

sulphide with the aid of heat. Free formic and monochlora- 
cetic acids also prevent the precipitation ; but if alkali-metal 
salts of these acids are present, the precipitation is prevented 
only by larger amounts of the acids. 

5. Ammonium sulphide from neutral, and hydrogen sul- 
phide from alkaline, solutions precipitate the whole of the 
metal as black, hydrous OOBALTOUS SULPHIDE, CoS. Ammo- 
nium chloride promotes the precipitation most materially. 
Oobaltous sulphide is insoluble in alkalies and ammonium 
sulphide, scarcely soluble in acetic acid, very difficultly so 
in hydrochloric acid, and almost not at all if the cobalt sul- 
phide has been precipitated at a boiling temperature. Nitric 
acid, as well as nitro-hydrochloric acid, dissolve cobalt, 
sulphide upon heating. 

6. Potassium and sodium hydroxide produce blue precipi- 
tates of BASIC COBALTOUS SALTS, which are insoluble in an 
excess of the precipitant when the dilution is sufficient 
They become dirty green and afterwards grayish-yellow in 
the air, in consequence of the absorption of oxygen. Upon 
boiling, they are converted into pale red COBALTOUS HYDROXIDE, 
which contains alkali, and generally appears rather discolored 
from cobaltic hydroxide formed in the process. If, before 
boiling, alcohol is added, the precipitate is rapidly converted 
into dark brown cobaltic hydroxide. Ammonium chloride, if 
present in sufficient amount, prevents the precipitation by 
caustic alkalies. Normal ammonium carbonate completely 
dissolves the washed precipitates of cobaltous basic salts or 
cobaltous hydroxide to intense violet-red fluids, in which a 
somewhat large proportion of caustic potash or soda pro- 
duces blue precipitates, the liquids still retaining their violet 
colors. However, if very wncentrated potassium Jiydro&ide 
solution is added in excess to the solution of a cobaltous 
salt, or if cobaltous hydroxide is heated with very little 
water and a piece of solid potassium hydroxide, the cobaltous 
hydroxide dissolves as such (DONATE) to a blue liquid. 

7. Ammonia produces the same precipitate as potassium 
hydroxide, but this redissolves in an excess of the ammonia, 
(leaving behind green flocks) to a brownish-yellow fluid, which 
turns brownish-red on exposure to the air, and from which 
caustic potash or soda throws down a portion of the cobalt 



204 DEPORTMENT OF BODIES WITH KEAGENTS. [ 125. 

as blue basic salt Ammonia produces no precipitate in solu- 
tions containing ammonium salts or a free acid 

8. If the solution of a cobaltous salt is treated with potas- 
sium or sodium hydroxide, and then Iromine-ivater, a solution 
of sodium hypochlorite, hydrogen peroxide, or iodine is added, 
and the solution is boiled, all the cobalt separates (if the 
dilution is sufficient) as brownish-black OOBALTIO HYDROXIDE. 
This is not soluble either in a mixture of ammonia and 
ammonium chloride or in potassium cyanide, but if nickelic 
hydroxide is present at the same time in large amount, 
potassium cyanide dissolves the cobaltic hydroxide with the 
nickelic hydroxide. 

N.B. The presence of non-volatile organic acids or of 
sugar interferes with or prevents the precipitation of cobalt 
as cobaltous or cobaltic hydroxide. 

9. From cobaltous solutions, potassium ferrocyanide throws 
down green OOBALTOUS FEBROOYAOTDE, Co a Fe(ON) a , which is 
difficultly soluble in hydrochloric acid. 

10. Potassium ferricyanide throws down COBALTOUS FEBEI- 
OTANIDE, which is hardly soluble at all in hydrochloric acid. 
If the cobaltous solution is first treated with tartaric acid or 
ammonium chloride, and then with ammonia in excess, so 
that a clear, strongly ammoniacal liquid is produced, and 
potassium ferricyanide is then added, a deep yellowish-red 
solution is obtained with rather concentrated cobalt solu- 
tions, the color of which can be recognized even at a great 
degree of dilution (SKEY, GINTL). The reaction is very deli- 
cate, and well adapted for detecting cobalt in presence of 
nickel* 

11. Addition of potassium cycmide gives rise to the forma- 
tion of a brownish-white precipitate of COBALTOTJS CYANIDE, 
Co(ON) a , which dissolves readily in excess of the precipitant 
as a double potassium cobaltous cyanide. Acids precipitate 
cobaltous cyanide from the solution, but if the latter is 
boiled with potassium cyanide in excess, in presence of free 
hydrocyanic acid (liberated by addition of a drop or two of 
hydrochloric acid), or if it is mixed with potassium or sodium 
hydroxide and chlorine is passed through it without warm- 
ing, or bromine water is added, the double cyanide is con- 
verted into potassium cobalticyanide, K e Co a (CN) 1S , and acids 



125.] COBALT. 205 

will now produce no precipitate (essential difference from 
nickel). Potassium nitrite and acetic acid added to the unal- 
tered solution of the double cyanide produce a blood-red 
color, in consequence of the formation of cobalt potassium 
nitrocyanide, but when the liquid is very dilute, the color is 
merely orange-red. Solution of sodium hydroxide added to 
the potassium cobaltous cyanide solution occasions a brown 
color when the fluid is shaken, oxygen being absorbed (O.D. 
BBAUN) ; while if it is treated with yellow ammonium sulphide, 
it assumes a blood-red color (TATTEBSALL and PAPASOGLI). By 
the latter reaction, cobalt is essentially distinguished from 
nickel. 

12. Potassium tkiocarbonate, added to solutions which 
have been rendered alkaline by ammonia, produces a dark 
brown, almost black, color, but if the solution is extremely 
dilute, a wine-yellow color. 

13. Barium carbonate behaves to cobaltous solutions in the 
same way as to solutions of nickelous salts. 

14. If potassium nitrite is added in not too small propor- 
tion to the solution of a cobaltous salt, then acetic acid to 
strongly acid reaction, and the mixture put in a moderately 
warm place, all the cobalt separates (from concentrated solu- 
tions very soon and from dilute solutions after some time) in 
the form of a crystalline precipitate of a fine yellow color 
(FiscHEB, STBOMEYEB). This is called FISOEEB'S SALT, or, 
according to STBOMEYEB, POTASSIUM OOBALHO NITEITE. Various 
views prevail concerning its composition, the following being 
the most probable formula: 9E,Oo(NO v ) 1 .8H l O. The pre- 
cipitate is very perceptibly soluble in pure water, scarcely so 
in concentrated solutions of potassium salts and in alcohol, 
and insoluble in the presence of potassium nitrite. When 
boiled with water, it dissolves, though not copiously, to a red 
fluid, which remains clear upon cooling, and from which 
alkalies throw down cobaltous hydroxide. This is an excel- 
lent reaction, which serves well to distinguish and separate 
cobalt from nickel. 

Iff. Upon adding an equal volume of hydrochloric aoid of 
20 per cent hydrogen chloride to a solution containing cobalt 
as sulphate or chloride, warming, and adding a hot solution 
of rMroso-P-vwphthol in 60 per cent acetic acid, a voluminous, 



306 DEFOBTMEin? OF BODIES WITH REAGENTS. [ 126* 

purple-red precipitate of cobalti-nitroso-/?-naphthol is formed 
(essential difference and means of separating cobalt from 
nickel, the salts of the latter not being precipitated in the 
presence of a sufficient amount of hydrochloric acid). Care 
should be taken not to confuse with cobalti-nitroso-/?- 
naphthol a slight separation of nitroso-yff-naphthol, which 
may take place upon adding an abundant amount of its acetic 
acid solution to hot water containing hydrochloric acid. 
Cobalti-nitroso-/?-naphthol, (O^H.ONOJ.Oo, is stable in the 
highest degree towards acids, alkalies, and oxidizing and 
reducing agents. By warming it with ammonium sulphide > 
however, cobalt sulphide is formed (IiiNSEi and VON KNOBBE). 

16. In the inner and outer flames, borax dissolves com- 
pounds of cobalt to clear beads of a magnificent blue color, 
which appear violet by candle-light, and are almost black in 
the presence of a large quantity of cobalt. This test is as 
delicate as it is characteristic. Sodium metaphoajphate gives 
the same reaction, but it is less delicate. 

17. In the reduction with the stick of charcoal, according 
to p. 35, compounds of cobalt behave in the same way as 
compounds of nickel. The solution with nitric acid is red. 

18. Concerning the microscopic detection of cobalt, see 
HAUSHOEEB, p. 63; BEHBENS, Zeitschr. f. analyt. Chem., 30,, 
140. 

126. 
e. IRON, Fe, IN FERROUS COMPOUNDS. (Ferrous Oaride t FeO.) 

1. METALLIC IBON in the pure state has a light whitish- 
gray color (iron containing carbon is more or less gray). The 
metal is hard, lustrous, malleable, ductile, exceedingly diffi- 
cult to fuse, and is attracted by the magnet In contact with 
air and moisture, a coating of rust (ferric hydroxide) forms on 
its surface, and upon ignition in the air, a coating of black 
ferrous-ferric oxide, Fe 8 O 4 ,is produced. Hydrochloric and 
dilute sulphuric acids dissolve iron, with evolution of hydro- 
gen ; if the iron contains carbide, the hydrogen is mixed with 
hydrocarbons. The solutions contain ferrous salts. Dilute 
nitric acid dissolves iron (according to its relative quantity,, 
the degree of dilution, and the temperature) either without. 



126.] IEOK IN FERROUS COMPOUNDS. 207 

the evolution of gas, but with the formation of ammonium 
nitrate, to ferrous nitrate, or with the evolution of nitrous or 
nitric oxide, to ferric nitrate. If the iron contains carbide, 
some carbon dioxide is also evolved, and there is leTt undis- 
solved a brown substance resembling humus, which is soluble 
in alkalies; when graphite is present, it, also, is left behind. 

2. FEBBOUS OXIDE is black; ferrous hydroxide is white, 
and in the moist state absorbs oxygen and speedily acquires 
a grayish-green and ultimately a brownish-red color. Both 
ferrous oxide and ferrous hydroxide are readily dissolved by 
hydrochloric, sulphuric, and nitric acids. 

3. In the anhydrous state, the FERROUS SALTS have a white, 
in the hydrated state a greenish, color, but their solutions look 
greenish only when concentrated. The solutions absorb oxy- 
gen when exposed to the air, and are converted more or less 
completely into ferric salts, with precipitation of basic ferric 
salts. Chlorine, bromine, hydrogen peroxide, or nitric acid, 
upon boiling, convert them quickly and completely into fer- 
ric salt solutions. In relation to the brownish-black colora- 
tion of the solution, which appears transiently during the 
oxidation by nitric acid, compare nitric acid, Section III. 
The soluble, normal ferrous salts do not redden litmus-paper, 
but this is the case only when they are entirely pure and 
free from ferric salts. Ferrous salts which contain volatile 
oxygen acids are decomposed by ignition. 

4. Solutions of ferrous salts made acid by strong acids 
are not precipitated by hydrogen sulphide; nor are neutral 
solutions or solutions acidified with weak acids precipitated 
by this reagent, or at the most but very incompletely. Solu- 
tions containing sodium acetate and some free acetic acid 
are only very incompletely precipitated, even upon heating. 
Monochloracetic or formic acid, added in sufficient amount, 
prevents the precipitation, even when alkali-metal salts of 
these acids are present. 

5. Amwowum sulphide from neutral, and hydrogen sul- 
phide from alkaline, solutions, precipitates the whole of the 
metal as black, hydrous PEREOUS SULPHIDE, FeS, which is insol- 
uble in' the hydroxides and sulphides of the alkali-metals, but 
dissolves readily in hydrochloric and nitric acids. This black 
precipitate turns reddish-brown in the air by oxidation. Ta 



DEPORTMENT OF BODIES WITH REAGENTS. [ 126. 

highly dilute solutions, ammonium sulphide imparts a green 
color, and it is only after some time that the ferrous sulphide 
separates as a black precipitate. Ammonium chloride pro- 
motes the precipitation most materially. 

6. Potassium hydroxide, sodium hydroxide, and ammonia 
produce a precipitate of FEBBOUS HYDROXIDE, Fe(OH) a , which 
at the first moment looks almost white, but acquires after a 
very short time a dirty green and ultimately a reddish-brown 
color, owing to absorption of oxygen from the air. Presence 
of ammonium salts partly prevents the precipitation by potas- 
sium hydroxide, and wholly prevents that by ammonia. If 
alkaline ferrous solutions thus obtained by the agency of 
ammonium salts are exposed to the air, ferrous-ferric and 
ferric hydroxides precipitate. Non-volatile organic acids, 
sugar, etc., check or prevent the precipitation by alkalies. 

7. Potassium ferrooyanide produces a bluish- white precipi- 
tate of POTASSIUM FEBBOUS EEBBOCYAEIDE, K a Fe a (FeC 6 N a ) a , which 
by absorption of oxygen from the air speedily acquires a 
blue color. Nitric acid or chlorine converts it immediately 
into Prussian blue : 3K a Fe,(Fe0 6 N a ) 9 + 901 = 6K01 + FeCl, + 
aFe^FeCaN,^. The precipitate also forms in an ammoniacal 
solution containing ammonium tartrate. 

8. Potassium ferricyanide produces a magnificent, blue 
precipitate of EEBBOOT FEBBICYANTDE (TUBNBULL'S blue), Fe,(Fe 
C 6 N fl ) B . This does not differ in color from Prussian blue. It 
is insoluble in hydrochloric acid, but is readily decomposed 
by potassium hydroxide. In highly dilute solutions, the re- 
agent produces simply a deep blue-green coloration. 

9. Potassium sulphocycmde does not alter solutions of fer- 
rous salts when free from ferric salts. 

10. In the cold, barium carbonate does not precipitate solu- 
tions of ferrous salts, with the exception of the sulphate. 

11. Borax dissolves ferrous compounds in the oxidizing 
flame, giving beads varying in color from yellow to a dark 
red ; when cold, the beads vary from colorless to dark yel- 
low. In the inner flame, the beads change to bottle-green, 
owing to the reduction of the previously formed ferric borate 
to ferrous-ferric borate. Sodium Tnetaphosphate shows a simi- 
lar reaction. Upon cooling, the beads produced with this 
reagent lose their color still more completely than those pro* 



127.] IRON IN FEBBIO COMPOUNDS. 209 

duced with borax, and the signs of the ensuing reduction in 
the reducing flame are also less marked. 

12. When reduced in the stick of charcoal (p. 34), ferrous 
compounds give a dull black powder, which is attracted by a 
magnet. When dissolved in a few drops of aqua regia, the 
reduced metal gives a yellow fluid, which can be further 
tested according to 127. 

13. Concerning the microscopic detection of ferrous iron, 
compare HAUSEOFEB, p. 49. 



127. 
/. IRON, Fe, IN FEBBIO COMPOUNDS. (Ferric Oxide, Fe a O 8 .) 

1. Native, crystallized KEBBIO OXIDE, Fe fl O a , is steel-gray. 
Upon trituration, the native as well as the artificially pre- 
pared ferric oxide gives a brownish-red powder. The color 
of the ferric hydroxides is more inclined to reddish-brown. 
Ferric hydroxide dissolves in hydrochloric, nitric, and sul- 
phuric acids. The oxide is more difficultly soluble, but 
dissolves upon long digestion with the aid of heat, especially 
in hydrochloric acid, and by fusion with potassium disul- 
phate. FEBBOUS-EEBBia OXIDE, Fe,0 4 , is black, and dissolves 
in hydrochloric acid to ferrous and ferric chlorides, and in 
aqua regia to ferric chloride. 

2. The normal, anhydrous FEBBIO SALTS are nearly white, 
but the basic salts are yellow or reddish-brown. The color of 
the solutions is brownish-yellow, and becomes reddish-yellow 
upon the application of heat. The soluble, normal salts redder 
litmus-paper. The ferric salts of volatile oxygen acids are 
decomposed by ignition. 

3. In solutions made acid by stronger acids, hydrogen 
sulphide produces a milky-white turbidity, proceeding from 
separated SULPHUB, the ferric salt being at the same time 
converted into ferrous salt: ' Fe a (S0 4 ) $ + H,S = 2FeSO 4 + 
HJ30. + S. 

If a solution of hydrogen sulphide is rapidly added to 
neutral solutions, a transient bluiug of the fluid also occurs. 
From solution of normal ferric acetate, hydrogen sulphide 



210 DEPORTMENT OF BODIES WITH REAGENTS. [ 127. 

throws down the greater part of the iron ; but in presence of 
a sufficient quantity of free acetic acid, sulphur alone sepa- 
rates. Upon treatment with hydrogen sulphide in the cold, 
a solution of a ferric salt containing sodium acetate and 
much free acetic acid gives scarcely anything but a separation 
of sulphur, but when warm, a part of the iron may precipitate 
as ferrous sulphide. Monochloracetic acid and formic acid, 
when present in sufficient amount, prevent the precipitation, 
even when the alkali-metal salts of these acids are present, 
and when the liquids are heated. 

4 Ammonium sulphide from neutral, and hydrogen sul- 
phide from alkaline, solutions precipitate the whole of the 
metal as black FERROUS SULPHIDE, FeS, mixed with sulphur : 
2Fe01, + 3(NH 4 ) a S = 6NH 4 01 + 2FeS + S. In very dilute 
solutions, the reagent produces only a blackish-green colora- 
tion, and in such cases, the minutely divided ferrous sulphide 
subsides only after long standing. Ammonium chloride 
most materially promotes the precipitation. The properties 
of ferrous sulphide have been given under ferrous com- 
pounds. 

5. Potassium hydroxide, sodium hydroxide, and ammonia pro- 
duce bulky, reddish-brown precipitates of FERBIO HYDBOXTDE, 
Fe(OH),, which are insoluble in an excess of the precipitant 
as well as in ammonium salts. Non-volatile organic acids or 
sugar, when present in sufficient quantity, entirely prevent 
the precipitation. 

6. Even in highly dilute solutions, potassium ferrocycmide 
produces a magnificent blue precipitate of FERRIC FERROOY- 
ANIDE (Prussian blue), Ee^eOJST.), : Fe01, + 3K 4 Fe(ON) a 
= 12KC1 + Fe^FeC.N,,),. This is insoluble in hydrochloric 
acid, but is decomposed by potassium hydroxide, with sepa 
ration of ferric hydroxide. Prussian blue is somewhat soluble 
in an excess of potassium ferrocyanide. In solutions contain- 
ing very much hydrochloric acid, or in neutral solutions con- 
taining very much ammonium chloride, small amounts of 
ferric compounds cannot be detected by means of potassium 
ferrooyanide. In the solutions containing ammonium chlo- 
ride, the reaction makes its appearance only upon the addi- 
tion of some hydrochloric acid (Vuu?ius). Solutions of ferric 
salts which have been made ammoniacal after the addition 



127.] IRON IN FERRIC COMPOUNDS. 211 

of tartaric acid are not precipitated by potassium ferrocyanide 
(difference from manganese, L. BLUM). 

7. Potassium ferricyanide deepens the color of solutions of 
ferric salts to reddish-brown, but it fails to produce a pre- 
cipitate. 

8. Potassium sulptocyanide, if not added in too small a 
quantity, imparts to acid solutions a most intense, blood-red 
color, arising from the formation of a soluble POTASSIUM FERRIC 
SULPHOCTAOTDE (KEuss and MOBAHT). This color does not 
disappear on the addition of a little alcohol and warming 
(difference from the analogous reaction of nitrous acid, 189). 
Solutions of ferric salts containing sodium acetate (which con- 
sequently are more or less red from ferric acetate) do not 
show the blood-red color of the sulphocyanide till after the 
addition of much hydrochloric acid. The same is the case 
when the solution contains oxalic, tartaric, citric, malic, iodic, 
phosphoric, arsenic, and hydrofluoric acids. In the presence 
of nitric acid, the reaction must be carried out in the cold. 
'This test will indicate the presence of iron, even in fluids 
"which are so highly dilute that every other reagent fails to 
produce in them the slightest visible alteration. In such 
-cases, the red coloration may be detected most distinctly by 
resting the test-tube upon a sheet of white paper, and looking 
through it from the top. The delicacy of the reaction may be 
also increased by shaking gently with ether, after the addition 
of hydrochloric acid and of excess of potassium sulphocyanide 
solution freshly prepared from the crystals. The ferric sul- 
phocyanide dissolves in the ether, and the layer of the latter 
.acquires a more or less red color. 

9. If a small amount of the solution of a ferric compound 
is added to the blue liquid obtained by adding a little cobatt 
^KLoride or mtrate to fuming TiydrocKloric arid, the blue color 
changes to GREEN. The reaction is especially adapted for 
recognizing ferric compounds in acids or in the presence of 
ferrous salts (VENABLE). 

10. Even in the cold, barium carbonate precipitates all the 
iron as FEBBIO HYDROXIDE *rmim WITH A BASIC SALT. 

11. The reactions before the Uowpipe are the same as with 
4;he ferrous compounds. 

12. In reference to the microscopic detection of ferric 



212 DEPORTMENT OF BODIES WITH REAGENTS. [ 128. 

compounds, see HAUSHOFEB, p. 48 ; BEHEENS, Zeitschr. f. 
analyt. Chem., 30, 160. 

128. 

Recapitulation and fiemarfo. In carrying out analyses, the 
members of Group IV are generally obtained as hydrated 
sulphides by precipitating their solution with ammonium sul- 
phide. We shall first consider the methods by which the 
metals contained in such a precipitate can generally be best 
separated from each other and detected when all are present, 
on the basis of the reactions which have been described in 
the preceding paragraphs, and then we shall mention some 
further methods, which offer special advantages in certain 
cases. 

1. Since cobalt and nickel sulphides are but slightly 
soluble in dilute hydrochloric acid, especially if it contains 
hydrogen sulphide, while ferrous sulphide and manganese 
and zinc sulphides are readily soluble in it, it is generally 
most convenient to separate cobalt and nickel, or at least by 
far the greater portion of them, upon this basis. For this 
purpose, the moist precipitate of the sulphides is treated with 
a mixture of 5 parts of hydrogen sulphide water and 1 part 
of ordinary hydrochloric acid of 1.12 sp. gr.,* with active 
stirring, but without warming. Nickel and cobalt sulphides 
then remain almost completely undissolved, while the other 
sulphides dissolve as chlorides, with the evolution of hydro- 
gen sulphide. The precipitate is filtered off and washed with 
water, to which it is best to add a little hydrogen sulphide 
water. 

We shall next consider the precipitate which remained 
undissolved and afterwards the liquid which was filtered 
from it. 

2. Since cobalt can be separated from nickel only by 
having both in solution, it is first necessary to dissolve the 
precipitate. It is therefore best to dry the filter containing 

* If the precipitate contains a considerable amount of other sulphides, the 
hydrochloric acid may be diluted with water instead of hydrogen sulphide 
water, in this case, because a sufficient amount of hydrogen sulphide fa 
evolved during the treatment. 



128.] EEOAPITULATION A2TD REMARKS. 213 

the precipitate, then ignite it with access of air in a porce* 
lain crucible, until the carbon of the filter has been consumed, 
and warm the residue with hydrochloric acid with the 
addition of a few drops of nitric acid. If much iron was 
present, this solution usually contains a small amount of this 
metal, together with the cobalt and nickel. After the addition 
*>f water, therefore, it is treated with ammonia in moderate 
excess, and filtered if necessary. The ammoniacal solution is 
evaporated to dryness in a small porcelain dish, the ammo- 
nium salts are driven off by gentle ignition, the residue is 
dissolved in hydrochloric acid with a few drops of nitric acid, 
the solution is evaporated to a small volume, sodium car- 
bonate is carefully added to alkaline, then acetic acid to 
strongly acid, reaction, and finally potassium nitrite ( 125, 14). 
By allowing the liquid to stand at a gentle heat, the cobalt 
separates quickly if it is present in considerable amount, or 
after a longer time if only a little is present, in the form of 
yellow potassium cobaltic nitrite. A filtration is made after 
about 12 hours, and the nickel in the filtrate is precipitated 
with potassiuip or sodium hydroxide. For the sake of cer- 
tainty, both precipitates should be tested in the borax bead 
( 125, 16, and 124, 15). The separation of cobalt from nickel 
by means of nitroso-jff-naphthol more readily gives occasion 
for mistakes. 

3. The solution filtered from the precipitate of cobalt and 
nickel sulphides contains the iron as ferrous chloride, also 
manganous and zinc chlorides, as well as small amounts of 
cobalt and nickel chlorides. Since iron can be easily sepa- 
rated from the other metals only when it is present as a ferric 
compound, the liquid is first boiled in order to drive off the 
hydrogen sulphide, and nitric acid is added to the gently 
boiling solution until the ferrous chloride is completely con- 
verted into ferric chloride. In case of doubt, the testing of 
a few drops with potassium ferricyanide leads to certainty. 
The solution is now allowed to cool, and the iron is separated 
as a basic ferric salt. For accomplishing this end, one of the 
following methods may be chosen : 

a. The free acid is almost neutralized by the careful addi- 
tion of sodium .carbonate ; barium carbonate, suspended in 
water, is then added until a small portion of it remains undis* 



214 DEPOBTMENT OF BODIES WITH BEAGENTS. [ 128. 

solved; it is well stirred, allowed to settle, and filtered, 
i. The solution is diluted sufficiently, a rather large quantity 
of ammonium chloride is added, then ammonium carbonate 
carefully, using at last a dilute solution of it, until the liquid, 
while still showing an acid reaction, begins to be turbid. The 
liquid is then heated to boiling for a short time, allowed to 
settle somewhat, and filtered hot. c. The solution is diluted, 
sodium carbonate is added until the acid is almost neutral- 
ized, sodium acetate is added to the solution, which should 
be clear and have a distinct acid reaction ; it is then heated 
to boiling, allowed to settle a little, and filtered hot. 

Whichever of these methods is used, the ochre-like color 
of the precipitate generally allows the presence of iron to be 
recognized conclusively. In case of doubt, a portion of the 
precipitate may be dissolved in hydrochloric acid, and the 
diluted solution tested with potassium ferrooyanide or sul- 
phocyanide. 

4. The liquid filtered from the basic ferric salt now con. 
tains manganous chloride, zinc chloride, and small amounts of 
cobalt and nickel chlorides. For the separation of manganese 
from the other metals, the solubility of manganous sulphide 
in acetic acid offers a good means. Upon this basis, the 
separation may be made according to one of the following 
methods : 

a. To the solution contained in a small flask, after the 
addition of ammonium chloride, ammonia is added to alka- 
line reaction, then ammonium sulphide; it is allowed to 
stand at a gentle heat, filtered, the precipitate is washed with 
water, to which a little hydrogen sulphide water is added ; 
the filter containing the precipitate is then spread out in a 
small porcelain dish ; a mixture of about equal parts of acetic 
acid of 1.04 sp. gr. and water is poured over it ; this is allowed 
to act about five minutes, when it is diluted with water, fil- 
tered, and the precipitate is washed, b. (This is a more exact, 
but somewhat more complicated method.) If barium car- 
bonate has been used for separating the iron, it is best, in 
the first place, to remove the barium from the solution by 
means of sulphuric acid. Ammonia is added in excess to the 
solution, then acetic acid to acid reaction ; sodium acetate is 
next added, and hydrogen sulphide is passed into the solu- 



128.] RECAPITULATION AND REMARKS. 215 

tion while hot ; it is now allowed to settle, filtered, and the 
precipitate washed. 

In either case, the manganese, in the form of manganous 
acetate, is now in a solution which contains some free acetic 
acid and hydrogen sulphide, and may be separated from it, 
or, by adding ammonia and ammonium sulphide, so as to pre- 
cipitate the manganese as sulphide; ft, by evaporating the 
solution and precipitating the manganese as manganous or 
mangano-manganic hydroxide by the addition of potassium 
hydroxide ; y, by adding some bromine in hydrochloric acid 
to the solution until it is colored strongly yellow, then pre- 
cipitating the manganese as hydrated dioxide by adding an 
excess of ammonia and boiling. Of these methods, the latter 
possesses greater delicacy, as well as the additional advantage 
that the brownish-black color of the precipitate generally 
makes further testing unnecessary. For confirmation, a small 
portion of the precipitated manganese compound may be 
fused with sodium carbonate according to 123, 14 

5. The precipitate left undissolved by treating with acetic 
acid according to 4, a, or produced by hydrogen sulphide 
from the solution acidified with acetic acid according to 4, 6, 
contains zinc sulphide, the white color of which is more or 
less concealed by the small quantities of cobalt and nickel sul- 
phides which are mixed with it. In order to detect the zinc, 
.the filter containing the precipitate is spread out in a porcelain 
'dish, and a mixture of about 5 parts of hydrogen sulphide 
water and 1 part of ordinary hydrochloric acid of 1.12 sp t 
gr. is poured over it, allowed to act for a few minutes, and 
then the liquid containing the zinc as chloride is filtered 
from the nickel and cobalt sulphides remaining undissolved. 
If an excess of sodium acetate is now added to the filtrate, 
sodium chloride and acetic acid are formed by its action upon 
the hydrochloric acid ; and since the liquid already contains 
hydrogen sulphide, the zinc separates as white zinc sulphide. 
The latter is free from the minute traces of nickel and cobalt 
which had gone into solution in hydrochloric acid, because 
~4heir sulphides are not precipitated in the cold, tinder the 
prevailing conditions. If so little cobalt and nickel had been 
present that they were not found in 2, the sulphides remain- 



216 DEPORTMENT OF BODIES WITH BEAGENTS. [ 12& 

ing behind in 5 should be tested for these metals according ta 
the method given in 2. 

"We now pass on to other methods which offer advantages 
in certain cases. If it is desired to separate small amounts 
of iron in the ferric condition from the other metals of the 
fourth groi'~% the end is readily reached by adding ammo- 
nium chloriue and ammonia in moderate excess in the cold, 
and quickly filtering off the small amount of ferric hydroxide 
which separates. By delaying the filtration, a part of the 
manganese would separate with the iron as manganic hydrox- 
ide, in consequence of the action of the oxygen of the air. If 
this precitate is dissolved again in hydrochloric acid, the 
solution heated to boiling for some time, and then another 
precipitation made in the cold with an excess of ammonia, 
the separation of iron from the other metals is almost com- 
plete. In the presence of more considerable quantities of 
iron, the method is not to be recommended, because certain 
amounts of other hydroxides always precipitate with the 
ferric hydroxide, so that by the use of this process small 
quantities of other metals may be entirely overlooked. 

If it is desired to separate zinc from the other metals of the 
fourth group, one of the following methods may also be used r 
ct. The solution is sufficiently diluted, the greater part of any 
free acid that may be present is neutralized with ammonia, 
ammonium monochloracetate and a little free monochloracetio 
acid are added, and a precipitation of zinc with hydrogen sul- 
phide is made at a temperature of from 50 to 60. The. other 
metals remain in solution. 6. Sodium carbonate is added to* 
the solution until a permanent precipitate just begins to form, 
this is redissolved in a few drops of dilute hydrochloric acid, 
sodium thiosulphate is added in not too small amount, the 
solution is : '-rgely diluted, and hydrogen sulphide is passed 
in in the cold. Zinc precipitates as zinc sulphide, while 
the other metals remain in solution (J. EIBAN). c. If large 
amounts of zinc are to be separated from small amounts of 
the other metals, the solution may also be treated with 
potassium or sodium hydroxide. If an excess of this is 
added, the precipitated zinc hydroxide redissolves, while the 
hydroxides of the other metals remain behind. Zinc can be 
precipitated from the solution with ammonium sulphide*. 



128.] EEOAPITULATION AND BEMARKS. 217 

This method seldom offers special advantages, because not 
inconsiderable quantities of zinc remain behind in the un- 
dissolved precipitate. The process would be entirely in- 
admissible if chromic hydroxide were present at the same 
time, since solutions of the latter and of zinc hydroxide 
in potassium or sodium hydroxide mutually precipitate each 
other. 

Since a brown coloration of the liquid (which may occur 
in the presence of nickel when the precipitate obtained by the 
addition of ammonium chloride, ammonia, and ammonium 
sulphide to the solution of the metals of the fourth group is 
filtered) is a sufficient indication of the presence of nickel; 
and since it is often possible to recognize cobalt with cer- 
tainty in the presence of nickel, by testing a little of the 
residue obtained after removing the ammonium salts accord- 
ing to 2, by means of the borax bead in the reducing flame, 
the separation of cobalt from nickel given above in 2, which 
requires considerable time, may sometimes be omitted. If it 
is desired to recognize small amounts of nickel in presence 
of large quantities of cobalt, the use of the solution of the 
cyanides of the metals in potassium cyanide, to which sodium 
hydroxide is, added, is to be recommended. The red colora- 
tion produced in a portion of this liquid by the addition of 
yellow ammonium sulphide shows the presence of cobalt, 
while the separation of black nickelic hydroxide obtained by 
treatment with chlorine or bromine allows the nickel to be 
detected ( 125, 11, and 124, 11). The varying behavior of 
nickelic and cobaltic hydroxides to potassium cyanide 
solution, and also to ammonium chloride and ammonia 
( 124, 8, and 125, 8), is more appropriate for distinguishing 
than for separating nickel and cobalt* 

In the presence of non-volatile organic substances, the 
method depending upon the preliminary precipitation of all 
the metals as sulphides must be used for the separation of the 
members of the fourth group, because such organic substances 
would hinder or prevent the precipitation of iron as hydroxide 
or as a basic salt. In the presence of citric acid, even this 

* Concerning the detection of nickel beside cobalt, see also HEBUBN- 
CHMXDT and OAPELLE, Zeitschr. f. analyt Chem., 32, 608. 



218 DBPOBTMEKT OF BODIES WITH REAGENTS. [ 129.. 

method does not suffice, because alkali-metal citrates prevent 
tlie precipitation of manganese as manganous sulphide; 
aiid therefore the solution should, in the first place, be 
evaporated with sodium carbonate, and ignited with the 
addition of potassium nitrate, in order to destroy the organic 
substances. 

Ferrous and ferric salts may be detected in presence of 
each other by testing for the former with potassium ferricy- 
anide, and for the latter with potassium ferrooyanide or sul- 
phocyanide. 

Spedd Reactions of the Barer Metals of the Fourth Group. 

129. 
1. UEANIUM, U. 

This metal is found only sparingly, in pitchblende, uranium-ochre, etc. 
Its oxides are used for the production of a yellowish-green glass. Ura- 
nium forms three oxides, viz., uranous oxide, UOa , uranic oxide, U0 
(also called uranic acid), and peruranic acid, UOe ; the latter, however, is- 
not known in the free state. Uranous oxide is brown or black, and dis- 
solves in nitric acid to uramo nitrate. Uranic oxide is brick-red ; uranie 
hydroxide, UO a (OH) 9 , is yellow. Both are converted by ignition into the 
dark blackish-green urano-uranic oxide, U0 8 . The uranic salts are yellow. 
Most of them dissolve in water, and those which are insoluble in that 
liquid, almost without exception dissolve in hydrochloric acid. The 
solutions are yellow. If uranic salts in sulphuric acid solution are 
warmed with zinc, the color of the solution changes into the green color 
of uranous salts. Hydrogen sulphide does not alter solutions of uranic 
salts ; but after neutralization of the free acid, ammonium sulphide throws 
down from them a slowly subsiding precipitate, which is readily soluble in 
acids, even acetic acid. The precipitation is promoted by ammonium 
chloride. The precipitate, when formed in the cold, is chocolate-brown, 
and contains uranic oxysulphide, ammonium sulphide, and water. It is 
insoluble in pure ammonium sulphide; but in that which is colorless 
and contains some ammonium carbonate, or in yellow ammonium sul- 
phide, it dissolves to a brown liquid (CL. ZIMMBRMANN). On being washed, 
the precipitate is gradually converted into yellow uranic hydroxide. On 
boiling the mixture of uranium solution and ammonium sulphide, the oxy- 
sulphide at first thrown down decomposes into sulphur and black uranous 
oxide, the latter being insoluble in the excess of ammonium sulphide (KEM- 
BLfi). The uranic oxysulphide (but not the precipitate which has been 
converted into uranous oxide and sulphur) dissolves readily in ammonium 



129.] URANIUM. 219> 

carbonate (essential difference, and means of separating uranium from 
zinc, manganese, iron, etc.). If the oxysulphide remains long in contact 
with an. excess of ammonium sulphide, it is converted, when air has access 
to it, into a red modification in consequence of the formation of ammo- 
nium thiosulphate ; but when air is excluded, a black modification is formed. 
Ammonia and potassium and sodium hydroxides produce yellow precipi- 
tates containing uranic oxide and alkali, which are insoluble in excess of 
the precipitants, e g., KJJ a 07. Tartanc acid prevents or interferes with 
the precipitation, and ammonium chloride facilitates the precipitation 
by ammonia. Ammonium carbonate and potassium or sodium bicar- 
bonate produce yellow precipitates of ammonium, sodium, or potassium 
uranic carbonate, e.g, 9 SKaOOLUOaOOs , which readily redissolve in an 
excess of the precipitants. Potassium and sodium hydroxides throw down 
from such solutions the whole of the uranium. Hydrogen peroxide pro- 
duces a yellowish-white precipitate, soluble in hydrochloric acid, which 
may be regarded as the hydroxide of a compound of one molecule of per- 
uranic acid with two molecules of uranio oxide, or as uranium tetroxide > 
TJ04 (FATTUJCY). Ammonium carbonate dissolves this to an intensely yel- 
low liquid. The reaction is very delicate. From" acetic acid solutions, or 
from solutions to which sodium acetate is added, sodium phosphate pre- 
cipitates yellowish-white uranyl phosphate, HU0 3 P04.a?H a O, which is, 
soluble in the mineral acids. In the presence of much ammonium salts, 
similarly colored ammonium uranyl phosphate, NHJJOaPC^.ajHaO, is 
formed. Heating facilitates the separation of both precipitates. Solu- 
tions of uranio salts (that of the nitrate to a marked degree) color tur- 
meric-paper brown, even m the presence of a little free hydrochloric acid, 
but in that case with less delicacy. Larger amounts of free mineral 
acids prevent the reaction (OL. ZIMMERMANN). When the turmeric-paper 
which is colored brown by uranium solution is dotted with a solution of 
sodium carbonate, more deeply colored brown spots are formed. Barium 
carbonate completely precipitates solutions of uranic salts, even in the cold 
(essential difference from nickel, cobalt, manganese, and zinc, and means 
of separating uranium from these metals). 

Mercuric oxide, made into a slime with water, precipitates uranic solu- 
tions completely when they are boiled with it in the presence of ammo- 
nium chloride (means of separating uranium from strontium, calcium, and 
the alkali-metals, but not as good for barium, AUBBGOFP). Potassium 
ferrocyanide produces a reddish-brown precipitate, or at least a coloration 
(a most delicate test). The precipitate dissolves in ammonium carbonate, 
giving a pale-yellow color. Upon heating, it is also soluble in dilute hydro- 
chloric acid. "With uranium compounds, in the inner flame of the blow- 
pipe, boraas and sodium metaphosphate give green beads ; in the outer 
flame, yellow beads, which acquire a yellowish-green tint on cooling. 

Concerning the microscopic detection of uranium, see 
p. 180 ; BBHRENB, Zeitschr. f. analyt Chem., 30, 160. 



220 DEPORTMENT OF BODIES WITH REAGENTS. [ 130. 

130. 

2. THALUUM, Tl. 

Thallium occurs in minute quantities, in many kinds of copper, in iron 
pyrites, and crude sulphur, and accumulates in the flue-dust of the lead 
chambers where the furnaces are fed with thalliferous pyrites. It is 
occasionally found in commercial sulphuric and hydrochloric acids, and 
has been discovered in lepidolite, preparations of cadmium and bismuth, 
in ores of zinc, mercury, and antimony, in the ashes of plants, and in 
some saline waters. Thallium is a metal resembling lead, of 11.8 to 11.9 
sp. gr., soft, fuses at 285 to 290, volatile at a white heat, crackling like 
tin when bent, and does not decompose water, except upon addition of 
acid. Dilute sulphuric and nitric acids readily dissolve it, but hydro- 
chloric acid dissolves it with difficulty. It forms two oxides ; thallious 
oxide, Tl a O, and thallic oxide, TUOa. THALLIOUS OXIDE is black, fusible, 
and when in the melted state, it attacks glass or porcelain. It dissolves 
in water to hydroxide, and the solution is colorless, alkaline, caustic, and ab- 
sorbs carbonic acid. It also dissolves in alcohol. THALLIC OXIDE is dark 
violet, and insoluble in water ; thallic hydroxide is brown. Thallic oxide 
is scarcely acted on by concentrated sulphuric acid in the cold ; but on 
heating, they combine. On continued heating, oxygen escapes, and thal- 
lious sulphate is formed. Treated with hydrochloric acid, thalhc oxide 
yields the corresponding chloride, which may be obtained in the form of 
colorless, easily soluble crystals. When this is heated, chlorine escapes, 
while compounds of thallious and thallic chlorides result. Thallic salts are 
decomposed by water, with the separation of thallic hydroxide. In acid 
solutions of THALLIO SALTS, alkalies throw down thallic hydroxide. Hydro- 
gen sulphide produces thallious salts, with separation of sulphur, potassium 
iodide yields thallious iodide and iodine, while hydrochloric acid produces 
no precipitate. The THALLIOUS SALTS are colorless ; some are readily soluble 
in water (sulphate, nitrate, neutral phosphate, tartrate, acetate), others 
difficultly soluble (carbonate, tri-basic phosphate, chloride), while a few- 
are almost insoluble (iodide, etc.). On boiling solutions of thallious salts 
with nitric acid, they are not converted into thallic salts, but they are so 
converted entirely by boiling with aqua regia. Potassium hydroxide, 
sodium hydroxide, and ammonia do not precipitate aqueous solutions of 
thallious salts. Alkaline carbonates throw down thallious carbonate, but 
only from very concentrated solutions (for 100 parts of water dissolve 6.28 
parts at 18). If the solutions are not extremely dilute, hydrochloric acid 
throws down thallious chloride in the form of a white, readily subsiding 
precipitate, unalterable when exposed to light, and still less soluble in dilute 
hydrochloric acid than in water. Even from the most dilute solutions, 
potassium iodide precipitates light yellow thallious iodide, which is almost 
insoluble in water (1 : 17000), and far less soluble in an excess of potassium 
iodide. In the cold, it dissolves difficultly in sodium thiosulphate solution 



131.] INDIUM. 221 

{difference from lead iodide, E. A. WERNER). From solutions which are 
not extremely dilute* hydrochloroplatimc acid precipitates pale orange 
thallious platimo chloride, ThPtCle, which is very difficultly soluble. 
Hydrogen sulphide does not precipitate solutions rendered strongly acid 
by mineral acids (unless arsenious acid or antimonious oxide are present, 
in which case compounds of thallium sulphide with sulphides of arsenic or 
antimony separate as more or less orange-colored precipitates). Neutral or 
very slightly acid solutions are incompletely precipitated by this reagent, 
-and from acetic acid solutions, the whole of the thallium is thrown down 
as black thallious sulphide. Colorless ammonium sulphide precipitates 
the whole of the thallium as black sulphide, which readily collects into 
lumps, especially on warming ; and hydrogen sulphide added to alkaline 
solutions has the same effect. The sulphide thrown down is insoluble in 
ammonia, alkali-metal sulphides, and potassium cyanide, rapidly oxidizes 
in the air to thallious sulphate, dissolves readily in dilute hydrochloric, 
sulphuric, and nitric acids, but is acted on only with difficulty by acetic 
.acid. On heating, it first fuses and then volatilizes. Zine throws down 
the metal in the form, of black, crystalline laminae. Colorless flames are 
tinged intensely green by compounds of thallium. The spectrum of thal- 
lium exhibits only one line (compare the spectrum plate) of a magnificent, 
extremely characteristic, emerald-green color. If the quantity of metal is 
small, the line soon disappears. The spectroscope generally affords the 
best means of detecting thallium. Thalliferous pyrites often give the green 
line at once. To look for thallium in crude sulphur, it is best to remove 
the greater part of the sulphur with carbon disulphide, and then to test 
the residue. In the presence of much sodium with very small quantities 
of thallium, the green line will not be seen, unless the substance is moist- 
ened, and the spectrum examined which is first produced. If a precipitate 
obtained by hydroohloroplatinic acid is to be tested for traces of thallium 
platmic chloride in the presence of much potassium, rubidium, and caesium 
platinic chlorides, it is boiled repeatedly with small quantities of water, 
and the residue remaining at last is tested spectrosoopically for thallium. 
Tor the detection of thallium in the wet way, potassium iodide is the most 
-delicate reagent ; if a ferric salt is present, it should be previously reduced 
by sodium sulphite. Concerning the microscopic detection of thallium, 
flee HATTBHOFER, p. 125, and BEHRENS, Zeitscor. f. analyt, Chem., 30, 138. 



131. 
3. IKDIUM, In. (Oxide, L^O,.) 

Indium has hitherto been discovered only in the blende of Freiburg, in 
the zinc prepared from the same, and in wolfram. It is a white, highly lus- 
trous metal, and resembles platinum in color. It is very soft, ductile, makes 
a mark on paper, is capable of receiving a polish, and is oxidized slowly 



322 DEPOBTMENT OF BODIES WITH REAGENTS. [ 131. 

upon contact with air and water less easily than zinc. Indium melts at 
176. On charcoal before the blowpipe, it melts with a shining metallic 
surface, colors the flame blue, and yields an incrustation, which is dark 
yellow while hot, light yellow when cold, and cannot be easily dispersed by 
the blowpipe flame. Indium dissolves in dilute hydrochloric and sulphuria 
acids, with evolution of hydrogen, slowly in the cold, but more rapidly on 
heating. In contact with cold, concentrated sulphuric acid, it also gives 
off hydrogen, while anhydrous indium sulphate separates. In nitric acid, it 
dissolves with ease even when the acid is cold and dilute. Indium oxide, 
In a Oa, is reddish-brown when hot, very light yellow when cold, and doea 
not color vitreous fluxes. When ignited in hydrogen or with charcoal, it 
is readily reduced, and if a flux is used, metallic globules are obtained. 
The ignited oxide dissolves slowly in acids in the cold, but readily and com* 
pletely by the aid of heat. The salts are colorless, and the sulphate, nitrate, 
and the volatile, hygroscopic chloride dissolve readily m water. Alkalies 
throw down the hydroxide in the form of a white, bulky precipitate 
resembling aluminium hydroxide, but tartanc acid prevents the precipi- 
tation. Potassium or sodium hydroxide dissolves the precipitate, giving 
a liquid which soon becomes turbid. By boiling the solution, or by the 
addition of ammonium chloride, the indium separates as hydroxide. 
Ammonia does not dissolve it. Alkali carbonates precipitate a white, 
gelatinous carbonate, which, when recently thrown down, dissolves iu. 
ammonium carbonate, but not in potassium or sodium carbonate. If the 
solution in ammonium carbonate is boiled, the indium carbonate separates 
again. Sodium phosphate throws down a white, bulky precipitate. 
Alkali-metal Mediates produce a crystalline precipitate in concentrated, 
neutral solutions. Sodium acetate added to the nearly neutral solution 
of the sulphate throws down, on boiling, a basic sulphate. On digestion 
in the cold, barium carbonate precipitates the whole of the indium in the 
form of basic salt. (Means of separating indium from zinc, manganese, 
cobalt, nickel, and ferrous compounds.) From neutral or acetic acid 
solutions (even in the presence of a large excess of acetic acid), hydrogen 
sulphide precipitates all the indium as yellow indium sulphide. Solutions 
made strongly acid with mineral acids, if moderately concentrated, are 
not precipitated, but by large dilution with water, indium sulphide sepa- 
rates. Hydrogen sulphide in alkaline solutions, and ammonium sulphide 
in neutral solutions, produce a white precipitate (perhaps a compound 
of indium sulphide with hydrogen sulphide). If yellow indium sulphide 
is boiled with yellow ammonium sulphide, it also becomes white, and 
is partly dissolved. Upon cooling, white, voluminous indium sulphide (Q 
separates from the solution. Potassium ferrocyanide produces a white- 
precipitate. Potassium ferricyanide, sulpTiocyanide, and dichromate give 
no precipitates. Potassium chromate, however, produces a yellow pre- 
cipitate. Zinc precipitates the metal in the form of white, shining laminae. 
Indium compounds produce a peculiar bluish-violet tinge in a colorless 
flame. The spectrum has two characteristic blue lines (see the spectrum 
plate). They appear brightest, especially a, with the chloride, but they 



132.] GALLIUM. 223 

are very transient. For obtaining more persistent lines, the sulphide is the 
most suitable compound, 



132. 

4. GALLIUM, Ga. (Oxide, Ga,0 t .) 

Up to the present time, gallium has been found only in some zinc 
blendes, and in very small amount. The metal is white ; in the molten 
condition, silver-white ; upon cooling, crystalline, bluish-white, and duller. 
It fuses at 30.16, and its specific gravity is 5.956. It is hard, but slightly 
malleable, unchanged in the air at ordinary temperatures, and even when 
heated to redness is but little oxidized, and not volatilized. Water, even 
when boiling, is not decomposed by metallic gallium. In the cold, gallium 
is not noticeably attacked by nitric acid, but upon heating, it dissolves, 
with the evolution of red vapors. It also dissolves readily in hydrochloric 
acid, potassium hydroxide, and ammonia, with the evolution of hydrogen. 
Gallium oxide, Ga a 3 , and gallium hydroxide are white. "When the oxide 
is heated in a stream of hydrogen to a red heat, it sublimes with partial 
reduction, probably forming a lower oxide. Gallium salts are colorless or 
white. The sulphate and the nitrate dissolve in water easily, and are 
decomposed by ignition. Gallium sulphate combines with ammonium sul- 
phate to form an alum. From solutions of the sulphate and also c f the 
alum, a basic salt separates upon boiling. Gallium combines with chlorine 
to an easily oxidizable chloride, Ga01 a , and to a chloride, Ga01 3 , cor- 
responding to the oxide. The latter chloride is a colorless, deliquescent 
mass, melting at 75, and boiling at 215'-220. The volatility of gallium 
chloride shows itself even in the evaporation of hydrochloric acid solu- 
tions, but if sulphuric acid is added to them, no loss of gallium takes 
place, either upon evaporating the solution or upon heating the residue to 
a dark red heat (Lsooq DE BOISBAUDRAN). From aqueous solutions of gal- 
lium salts, the alkalies precipitate a white, flocculent hydroxide, which is 
easily soluble in an excess of the precipitant ; but if a solution supersatu- 
rated with ammonia is boiled for a considerable time, all the gallium is 
precipitated as hydroxide. Tartaric acid prevents the precipitation by 
ammonia. Alkaline carbonates produce white precipitates, and that pro- 
duced by ammonium carbonate dissolves in an excess of the precipitant. 
Bariim carbonate precipitates the gallium completely, even in the cold. 
Hydrogen sulphide does not give a precipitate in gallium solutions which 
are made acid with hydrochloric acid ; but, on the other hand, in solu- 
tions containing both free acetic acid and ammonium acetate, it produces 
a white precipitate of gallium sulphide. Ammonium sulphide also pre- 
cipitates white gallium sulphide, which is insoluble in an excess of the 
precipitant. Tartaric acid prevents the precipitation. From dilute toln 
tions made acid with acetic acid, upon boiling, ammonium iicrtMte pre- 
cipitates almost all the gallium, but only when ihc precipitant is not used 



224 l>JPOKTMJttrT OF BODIES WITH KEAGEITTS. [ 133. 

in too large amount. Potassium ferrocyanide produces a precipitate 
which has a bluish color (probably on account of a contamination with 
iron), and which is less soluble in hydrochloric acid than in water (very 
delicate reaction). Gallium compounds show a spectrum consisting of 
two violet lines (between G and H). The spectrum is not very distinct 
except as a spark-spectrum. If a gallium compound is brought into the 
flame of the BUNSEN burner, only one indistinct line is to be observed. 



133. 
5. VANADIUM, V. 

Vanadium occurs rarely in the form of vanadates, occasionally in 
email quantities in iron and copper ores, and in the slags obtained by 
smelting the same. There are four oxides of vanadium: vanadious oxide, 
VO; the sesquioxide, V a O; the dioxide, Y0 a ; and vanadiq acid, VaOs. 
Vanadious oxide is gray, possesses metallic luster, is insoluble in water, 
but is soluble in dilute acids, with evolution of hydrogen, to blue fluids 
which bleach organic coloring matters by reducing them. The sesquioxide 
is black, insoluble, not reduced by ignition in hydrogen, and when exposed 
to the air is gradually converted into tbe dioxide. Acid solutions of the 
sesquioxide are green. Vanadium dioxide is dark blue, and acid solutions 
of it are pure blue. All the lower oxides pass into vanadic acid, on heating 
with nitric acid or aqua regia, on fusing with potassium nitrate, or on 
igniting in oxygen or air. Vanadic acid is non-volatile, fusible, and solidi- 
fies to a crystalline mass of a dark red to orange-red color. Heated to 
redness in a current of hydrogen, it is changed to the sesquioxide. By 
exposure to moist air, anhydrous vanadic acid is converted into the dark 
red hydroxide. In contact with a little water, it forms a pasty mass, 
which dissolves in a large amount of cold water, but more readily in warm 
water to a blood-red liquid (A, DITTE). Vanadio acid reddens moist 
litmus-paper strongly, aud combines with acids and with bases. 

a. Acid Solutions. Ths stronger acids dissolve vanadic acid to red or 
yellow liquids, which gradually turn green in the air (evidently on account 
of reducing dust). If ammonia is slowly added to a cold, acid solution 
of vanadio acid, the liquid becomes continually more distinctly yellow up to 
the moment when the reaction becomes alkaline (OARNOT). If sine is in- 
troduced into the warm, dilute sulphuric acid solution, the color goes at 
first through green to blue (reduction to dioxide), then through greenish- 
blue to green (reduction to sesquioxide), and finally through violet to laven- 
der-blue (reduction to vanadious oxide) From the lavender-blue solution, 
ammonia precipitates brown, readily oxidized vanadious-vanadic hydrox- 
ide. Sulphurous add, hydrogen sulphide, oxalic acid, etc., also reduce 
acid solutions of vanadic acid, but only to the dioxide, and therefore the 
solutions become only blue. In the case of hydrogen sulphide, the reduc- 



133 -] VANADIUM. 225 

tion is accompanied with the separation of sulphur. When vanadic acid is 
boiled with concentrated hydrochloric acid, chlorine is given off, and an 
oxide or a corresponding chloride is formed, which is intermediate between 
V a Oa and V0 fl (KOSENHEIM). In vanadic acid solutions, alkalies produce 
brown precipitates, which are soluble in an excess of the precipitants giv- 
ing solutions of a yellowish-brown color. Ammonium sulphide produces a 
brown precipitate of vanadium sulphide, V a S. , which dissolves rather dif- 
ficultly m an excess to a reddish-brown liquid. From this, acids precipi- 
tate brown vanadium sulphide. Potassium ferrocyanide throws down a 
green, floccnlent precipitate which is insoluble in acids. In solutions which 
contain but little free acid, tannic acid produces a bluish-black precipi- 
tate. If an alkaline carbonate is added to an acid solution of vanadic acid 
until the free acid is almost completely neutralized, and then mercurous 
nitrate and an excess of precipitated mercuric oxide, the vanadic acid is 
completely precipitated as mercurous vanadate. By igniting the precipi- 
tate, vanadic acid is obtained. 

ft. Vanadates (with vanadic acid as the acid). Yanadic acid forms 
ortho-, pyro : , and metavanadates. The vanadium minerals generally con- 
tain ortho salts. When their solutions are allowed to stand, the ortho- 
vanadates soluble in water, and those insoluble in water upon the addition 
of acid, are converted into pyro- and metavanadates. Alkaline pyrovana- 
dates also easily yield metavanadic acid, even by leading carbonic acid 
into their solutions. Alkali-metal metavanadates are obtained by dis- 
solving vanadic acid in potassium or sodium hydroxide, also by fusing 
vanadic acid with alkaline caibonates and nitrates. The solutions are col- 
orless. If solid ammonium chloride is added to the neutral or alkaline 
solution warmed to 80-40 e 5 all the vanadic acid separates as ammonium 
metavanadate, which is insoluble in ammonium chloride solution, crys- 
talline and colorless, and which when ignited in oxygen gives pure vanadic 
acid (especially characteristic reaction). Solutions of alkaline metavana- 
dates become red with strong acids, but after a time, colorless again. 
Barium cTdoride (but not strontium chloride and calcium chloride, distinc- 
tion from phosphoric and arsenic acids, OAENOT), silver nitrate, and lead 
acetate, in solutions of alkaline metavanadates, produce yellow precipitates, 
which become colorless upon standing, and more quickly upon warming. 
Soluble uranium satis precipitate the vanadic acid from solutions containing 
ammonium acetate when they are ammoniacal (or even weakly acid with 
acetic acid) as ammonium nranyl vanadate, iNHtTTOaVC^ ,H 9 (means of 
separating vanadic acid from alkali and alkali-earth metals, and from man- 
ganese, zinc, and copper). From boiling solutions containing ammonia and 
ammonium chloride, a boiling solution of manganous chloride containing 
ammonium chloride precipitates manganese pyrovanadate, MnaVaOr 
(means of separating vanadic acid from molybdic acid, CARNOT). In 
contact with aniline hydrochloride, the alkaline metavanadates yield the 
vanadium chloride corresponding to the dioxide and aniline-black. Am- 
monium sulphide acts as in the acid solutions mentioned above under a, as 
does also tannic acid upou the addition of acetic acid. If an acidified sola- 



226 DEPORTMENT OF BODIES WITH BEAGENTS. [ 134 

tion of an alkaline metavanadate is shaken with hydrogen peroxide, it 
assumes a red color, or when very dilute, a brownish rose-red color. If 
ether is added and the whole is shaken, the solution retains its color, the 
ether remaining colorless (very delicate reaction, WHETHER). An excess of 
hydrogen peroxide produces a partial decolorization (A. WBLLEB). Borax 
dissolves vanadium compounds in the inner and outer flames to clear 
beads. The bead produced in the outer flame is colorless, or, with large 
quantities of vanadium, yellow ; while that produced in the inner flame 
has a beautiful green color, but with large quantities of vanadium, it looks 
brownish while hot, and turns green only on cooling. Concerning the 
microscopic detection of vanadium, see HAUSHOEER, p. 183; BEHRENS, 
Zeitschr. f. analyt. Chem., 30, 161.* 



134. 

BTPTH GROUP. 

More common metals : SILVER, MERCURY, LEAD, BISMUTH, 
COPPER, CADMIUM. 

Barer metals: PALLADIUM, EHODIDM, OSMIUM, EUTHENIUM. 

Properties of the Group. The sulphides are insoluble both 
in dilute acids and in alkali-metal sulphides. \ The solutions 
of these metals are therefore completely precipitated by 
hydrogen sulphide, whether they are neutral, or contain free 
acid (in moderate amount) or free alkali. The fact that the 
solutions of the metals of this group are precipitated by 
hydrogen sulphide in presence of a free, strong acid, distin- 
guishes them from the metals of the fourth group and also 
from the metals of all the preceding groups. 

For the sake of greater clearness, the more common metals 
of this group are divided into two classes, as follows : 

1. METALS PREOIPITABLB BY EIDROOHLOBIO AOID, viz., silver, 
mercury in mercurous salts, lead. 

2. METALS NOT PREOIPITABLE BY HYDROCHLORIC AGED, viz., 
mercury in mercuric salts, copper, bismuth, cadmium. 

* A full summary of the most recent articles concerning the detection and 
determination of vanadic acid is found in the Zeitschr. f. anaJyt. Chem., 32, 
217-232. 

t Consult, however, the paragraphs on copper and mercury, as the latter 
remark applies only partially to them. 



135.] SILVER. 227 

Lead must be considered in both classes, since the spar- 
ing solubility of its chloride might lead to confounding it 
with silver and mercury in mercurous salts, without affording 
a means of effecting its perfect separation from the metals of 
the second division. 

Special fieactions of the More Common Metals of the Fifth Group. 



FIEST DIVISION : METALS PRECIPITATED BY HYDROCHLORIC ACID. 

135. 

a. SILVER, Ag. (Ovide, Ag a O.) 

1. METALLIC SILVER is white, very lustrous, moderately 
hard, highly malleable, and rather difficultly fusible. It is 
not oxidized by fusion in the air. Nitric acid dissolves silver 
readily, and the metal is somewhat soluble in dilute sulphuric 
acid (1 : 4) upon heating, if the silver is finely divided (OABY 
LEA). It is insoluble in hydrochloric acid. 

2. SILVER OXIDE, Ag a O, is a grayish-brown powder, which is 
not altogether insoluble in water, and dissolves readily in 
dilute nitric acid. There is no corresponding hydroxide. Sil- 
ver oxide is decomposed by heat, as is also SILVER PEROXIDE, 
Ag a O fl , into metallic silver and oxygen gas. 

3. The SILVER SALTS are non-volatile and usually colorless, 
but many of them acquire a black tint upon exposure to light 
'The soluble normal salts do not alter vegetable colors, and 
are decomposed at a red heat. 

4. Hydrogen sulphide and ammonium sulphide precipitate 
black SILVER SULPHIDE, Ag a S, which is insoluble in dilute 
acids, alkalies, and alkali sulphides, but soluble in potassium 
cyanide. Boiling nitric acid decomposes and dissolves this 
precipitate readily, with separation of sulphur. 

5. Potassium and sodium hydroxides precipitate SILVER 
OXIDE in the form of a grayish-brown powder, which is insolu- 
"ble in an excess of the precipitants, but dissolves readily in 
.ammonia. 

6. Ammonia, if added in very small quantity to neutral 
solutions, throws down SILVER OXIDE as a brown precipitate, 



228 DEPORTMENT OF BODIES WITH REAGENTS. [ 135* 

which readily redissolves in an excess of ammonia. Acid 
solutions are not precipitated. 

7. Hydrochloric add and soluble metallic chlorides produce a 
white, curdy precipitate of SILVER CHLORIDE, AgOL In very 
dilute solutions, these reagents impart at first simply a bluish- 
white, opalescent appearance to the fluid; but after long 
standing in a warm place, the silver chloride collects at the 
bottom of the vessel. By the action of light, the white silver 
chloride loses chlorine, first acquiring a violet tint, and ulti- 
mately turning black. Silver chloride is insoluble in nitric 
acid, but dissolves readily in ammonia as a compound of 
silver chloride with ammonia, from which double compound 
the former is again separated by acids. Concentrated hydro- 
chloric acid and concentrated solutions of chlorides of the 
alkali metals dissolve silver chloride to a very perceptible 
extent, more particularly upon application of heat ; but the 
dissolved chloride separates again upon dilution. Potassium 
cyanide dissolves silver chloride easily. Upon exposure to 
heat, it fuses without decomposition, giving upon cooling a 
translucent, horny mass. 

8. In solutions of silver salts which are not too dilute, 
potassium chromate produces a dark brownish-red precipitate 
of SILVER OHROMA.TE, Ag a Or0 4> which is easily soluble in nitric 
acid, dilute sulphuric acid, and also in ammonia. 

9. If a clear solution of ferrous sidphate, containing tartaric 
acid and an excess of ammonia, is added to a neutral or am- 
moniacal solution of a silver salt, a fine, black, pulverulent 
precipitate separates, even at a great dilution of the silver 
solution. Whether this is argentous oxide, Ag 4 O, or, as the 
investigations of FRIEDHEIM indicate, a mixture of silver oxide 
and finely divided silver, contaminated with organic sub- 
stances, requires further investigation. Ferrous sulpJuzte alone 
precipitates metallic silver from neutral solutions of silver 
salts, in the form of a gray precipitate. This separation takes 
place gradually in the cold, but more quickly by hea-ting. The 
separated silver is sometimes deposited in the form of a 
mirror upon the walls of the glass vessel. 

10. If compounds of silver mixed with sodium carbonate 
are exposed on a charcoal support to the INNER flame of the 
Uoivpipe, white, brilliant, malleable, metallic globules are 



136.] MERCURY. 229 

obtained, with or without a slight, dark red incrustation of 
the charcoal. The metal is also readily reduced in the stick 
of charcoal (p. 34). 

11. In relation to the microscopic detection of silver, see 
HA.USHOEEE, p. 117 ; BEHEENS, Zeitschr, f. analyt Chem., 30, 
138. 

136. 

b. MEEOUBY, Hg, IN MEEOUBOUS COMPOUND**. 
(Mercurous Oxide, Hg 2 O.) 

1. METALLIC MEBCUEY is grayish-white, lustrous, fluid at 
the common temperature, solidifies at 39.4, and boils at 
360. It dissolves in cold, dilute nitric acid to mercurous 
nitrate, and in the hot, concentrated acid to mercuric nitrate. 
It does not dissolve in hydrochloric acid, and only very dif- 
ficultly even upon the addition of potassium chlorate (LEGCO). 
Mercury vapors, if such are present even iii minute traces, 
can be readily detected by allowing them to act upon paper 
which has been marked with an ammoniacal silver nitrate 
solution. They quickly produce a blackening of the marks, 
in consequence of a reduction of the silver salt which takes 
place (MEBGET). They may be detected, also, by allowing 
them to act upon solution of gold chloride whifch is free from 
nitric acid. They are then absorbed, with the formation of 
mercuric chloride and the liberation of metallic gold. The 
latter separates in the form of a pellicle or in spots and 
streaks (BABFOED). 

2. MEBCUBOUS OXIDE, Hg,0, is a black powder, readily 
soluble in nitric acid. It is decomposed and volatilized by 
the action of heat. There is no corresponding hydroxide. 

3. The MEEOUBOUS OXTGEN SALTS volatilize upon ignition, 
suffering decomposition in this process. Mercurous chloride 
and mercurous bromide volatilize unaltered. Most of the 
mercurous salts are colorless. The soluble normal salts 
redden litmus-paper. Mercurous nitrate is decomposed by 
addition of much water into a light yellow, insoluble basic salt 
and a soluble acid salt. 

4. Hydrogen sulphide and ammonium sulphide produce a 



230 DEPORTMENT OF BODIES WITH REAGENTS. [ 136. 

black precipitate, which is insoluble in dilute acids, ammo- 
mum sulphide, and potassium cyanide. The precipitate is 
not mercurous sulphide, as was formerly believed, but con- 
sists of MERCURIC SULPHIDE MTYT?.T> WITH HOTLY DIVIDED MERCURY. 
In presence of some caustic soda, sodium monosulphide dis- 
solves this precipitate, with separation of metallic mercury, 
but sodium disulphide dissolves it without the separation of 
the metal. The solutions contain mercuric sulphide, HgS, 
which is precipitated upon the addition of ammonium chlo- 
ride. The precipitate produced by hydrogen sulphide gives 
up mercury to boiling, concentrated nitric acid, with forma- 
tion of a white, double mercuric compound, 2HgS.Hg(NO 8 ) a . 
It is readily dissolved by aqua regia. 

5. Potassium and sodium hydroxides precipitate MEBOUROUS 
OXIDE, which contains MBROURIO OXIDE and METAUJO MERCURY, 
and is insoluble in an excess of the precipitant. Ammonia 
in very dilute solutions produces gray, in concentrated solu- 
tions black, precipitates, which are partially dissolved with 
decomposition, in an excess of the precipitant. In the pres- 
ence of an excess of ammonia, these precipitates are mixt- 
ures of exceedingly finely divided mercury and of the white 
precipitates produced by ammonia in solutions of the corre- 
sponding mercuric salts (LEFORT, BARFOED.) 

6. Hydrochloric add and soluble metallic chlorides precipitate 
MERCUROUS CHLORIDE, HgCl, as a fine powder of dazzling 
whiteness. Cold hydrochloric and cold nitric acids fail to 
dissolve this precipitate, but it dissolves, although very 
difficultly and slowly, upon long-continued boiling with 
these acids, being resolved by hydrochloric acid into mer- 
curic chloride and metallic mercury which separates, and 
being converted by nitric acid into mercuric chloride and 
mercuric nitrate. Nitro-hydrochloric acid and chlorine- water 
dissolve mercurous chloride readily, converting it into mer- 
curic chloride. Ammonia and potassium hydroxide decom- 
pose mercurous chloride, the former producing a black mixt- 
ure of very finely divided METALLIC MERCURY and the so-called 
infusible WHITE PBEOIPITA.TE ( 139, 5), while the black substance 
produced by potassium hydroxide is MEROUROUS OXIDE mixed 
with finely divided MERCURY and MERCURIC OXIDE (BABFOED). 

7. If a drop of a neutral or slightly acid solution of a mer- 



136.] MERCUBY. 231 

curous salt is put on a clean and smooth surface of copper, and 
washed off after some time, the spot will afterwards, on being 
gently rubbed with cloth, paper, etc., appear white and 
lustrous like silver. The application of a gentle heat to the 
copper causes the METALLIC MERCURY precipitated on its sur- 
face to volatilize, and thus removes the apparent silvering. 

8. When added in very dilute solution and in very small 
amount, stannous chloride produces a white precipitate of 
MERCUROUS CHLORIDE. By the addition of larger quantities 
of stannous chloride, the white precipitate forming at the 
first instant is converted into a gray MIXTURE OF MERCUROUS 

CHLORIDE AND FINELY DIVIDED MERCURY. With an excess of 

stannous chloride, the gray precipitate is converted into a 
black one of finely divided MERCURY. This may be united 
into globules, after allowing it to settle and decanting the 
liquid, by boiling it with hydrochloric acid, to which a little 
staimous chloride may also be added. 

9. From solutions of mercurous salts which are not ex- 
tremely dilute, potassium chromate throws down a bright red 
precipitate of BASIC MEROUROUS GHROMATE, 3Hg fl CrO 4 .Hg t O, 
which is rather difficultly soluble in nitric acid. 

10. If an intimate mixture of a dry compound of mercury 
with anhydrous sodium carbonate is introduced into a glass 
tube which is closed at the bottom, and covered with a 
layer of sodium carbonate, and the tube is then strongly 
heated, the mercury compound invariably undergoes decom- 
position, and METALLIC MERCURY is liberated, forming a gray 
sublimate above the heated part of the tube. By means 
of a lens or a microscope, the sublimate will be seen to 
consist of globules of metal. Larger globules may be ob- 
tained by rubbing the sublimate with a glass rod. If, after 
cooling, a very small fragment of iodine is brought into the 
vicinity of the sublimate, and a very gentle heat is applied, it 
is converted into a mercuric iodide coating. This is generally 
red at first, and in that case easily visible, but sometimes 
it is yellow at first, and thus less easily recognized. If the 
tube is allowed to stand a while, the yellow iodide changes 
into the red. The conversion of sublimates of mercury into 
iodide can also be accomplished by hanging the tube with 
the open end down, in a small beaker having iodine upon its 



DEPOBTMENT OF BODIES WITH BEA0ENTS. [ 137* 

bottom, using for this purpose a perforated cardboard cover 
upon the beaker (NEQA). 

11. In regard to the microscopic detection of mercurous 
compounds, see HAUSHOEER, p. Ill; BEHEENS, Zeitschr. f. 
analyt Ohem., 30, 151. 

137. 
c. LEAD, Pb. (Oxide, PbO.) 

1. METALLIC T.TCAT> is bluish-gray, and a recently cut surface- 
exhibits a metallic luster. It is soft, malleable, readily 
fusible, and evaporates at a white heat. Fused upon charcoal 
before the blowpipe, it forms a coating of yellow oxide on the 
support Hydrochloric acid and moderately concentrated 
sulphuric acid act upon it but little, even with the aid of 
heat ; but dilute nitric acid dissolves it readily, more particu- 
larly on heating. 

2. LEAD MONOXIDE, PbO, is a yellow or reddish-yellow 
powder, appearing brownish-red while hot, and fusible at a. 
red heat Lead hydroxide is white. Both the oxide and 
hydroxide dissolve readily in nitric and acetic acids. LEAD 
DIOXIDE, PbO a , is brown, is converted into lead oxide by 
ignition, and is not dissolved by nitric acid upon heating, but 
is easily dissolved in that acid upon the addition of some 
alcohol or sugar. The solution contains lead nitrate. MINIUM, 
or red lead, Pb a 4 , may be considered as a compound of lead 
oxide with lead dioxide. It is red in color, and nitric acid 
dissolves the oxide from it, leaving the dioxide. 

3. The OXYGEN SALTS OP T;RAT> are non- volatile, and most of 
them are colorless. The normal soluble salts redden litmus- 
paper, and are decomposed at a red heat. Only a few of 
the insoluble salts are decomposed by ignition, for example, 
lead carbonate. If lead chloride is ignited in the air, part of 
it volatilizes, and leaves behind a compound of lead oxide and 
lead chloride. 

4. Hydrogen sulphide and ammonium sulphide produce black 
precipitates of T^AT* SULPHIDE, PbS, which are insoluble in 
cold dilute acids, in alkalies and alkali sulphides, and cya- 
nides. Lead sulphide is decomposed by hot nitric acid, if 



137.] LEAD. 233 

the acid is dilute, the whole of the lead is obtained in solu- 
tion as lead nitrate, and sulphur separates ; but if the acid Is 
fuming, the sulphur is also completely oxidized, and insoluble 
lead sulphate alone is obtained ; while if the acid is of medium 
concentration, both processes take place, a portion of the 
lead being obtained in solution as nitrate, while the remain- 
der separates as sulphate, together with the unoxidized sul- 
phur. In solutions of lead salts containing a large excess of 
a concentrated mineral acid, hydrogen sulphide produces a 
precipitate only after the addition of water or after partial 
neutralization of the free acid by an alkali. If a lead solu- 
tion is precipitated by hydrogen sulphide in presence of a 
large quantity of free hydrochloric acid, a red precipitate is 
occasionally formed, consisting of lead chloro-sulphide, which, 
however, is gradually converted by an excess of hydrogen 
sulphide into black lead sulphide. 

5. Potassium and sodium hydroxides and ammonia throw 
down BASIO SALTS in the form of white precipitates, which are 
insoluble in ammonia, but soluble in potassium and sodium 
hydroxides. In solutions of lead acetate, ammonia (free from 
carbonate) does not immediately produce a precipitate, owing 
to the formation of soluble basic lead acetates, containing 
one half or one third of the normal amount of acetic acid. 

6. Sodium carbonate throws down a white precipitate, in 
the cold, of normal, when boiling, of more or less basic, LEAD 
CARBONATE, which is not quite insoluble in a large excess of 
the precipitant, especially on heating, but is insoluble in 
potassium cyanide. 

7. Hydrochloric add and soluble chlorides produce in con- 
centrated solutions, heavy, white precipitates of LEAD CHLORIDE, 
Pb01 fl , which are soluble in a large amount of water, espe- 
cially upon application of heat. Lead chloride is converted 
by ammonia into lead oxychloride, PbCl^SPbO.^H/), which 
is also a white powder, but almost absolutely insoluble in 
water. In dilute nitric and hydrochloric acids, lead chloride 
is more difficultly soluble than in water. 

8. Sulphuric add and sulphates produce white precipitates 
of T.TCAji STJLPHATE, PbSO 4 , which are nearly insoluble in water 
and dilute acids. From dilute solutions, especially from 
such as contain much free acid, the lead sulphate precipitates 



234 DEPORTMENT OP BODIES WITH REAGENTS. [ 138. 

only after some time, frequently only after a long time. It is- 
advisable to add a considerable excess of dilute sulphuric 
acid, as this tends to increase the delicacy of the reaction, 
lead sulphate being more insoluble in dilute sulphuric acid 
than in water. The separation of small quantities of lead sul- 
phate is best effected by evaporating as far as practicable 
on the water-bath, after the addition of the sulphuric acid, 
and then treating the residue with water, or, if allowable, 
with alcohol. Lead sulphate is slightly soluble in concen- 
trated nitric acid. It dissolves with difficulty in boiling, con- 
centrated hydrochloric acid, but more readily in solution of 
potassium hydroxide. It also dissolves pretty readily in the 
solutions of some ammonium salts, particularly in solution of 
ammonium acetate upon moderate heating, and dilute sul- 
phuric acid precipitates it again from these solutions. 

9. Potassium chromate produces a yellow precipitate of 
TF.AT) OHEOMATE, PbCr0 4 , which is readily soluble in potassium 
and sodium hydroxides, but difficultly so in dilute nitric acid, 
and insoluble in ammonia. 

10. If a mixture of a compound of lead with sodium car- 
bonate is exposed on a charcoal support to the reducing flame 
of the bloivpipe, soft, malleable, METALLIC GLOBULES OP LEAD are 
readily produced, the charcoal becoming covered at the same- 
time with a yellow incrustation of LEAD OXIDE. The reduction 
may be also readily effected by means of the stick of charcoal. 

11. The metallic incrustation, obtained according to p. 35, 
is black with a brown edge ; the incrustation of oxide is light 
ochre-yellow ; the incrustation of iodide varies from the yellow 
of a lemon to that of the yolk of an egg ; while the incrustation 
of sulphide varies from brownish-red to black, and is not dis- 
solved by ammonium sulphide (BrasEN). 

12. Concerning the microscopic detection of lead, see 
HAUSHOEEB, p. 25 ; BEHBENS, Zeitschr. f. analyt. Ohem., 30, 149, 

138. 

Reca/pitulation and Bemarks. The metals of the first divi- 
sion of the fifth group are most distinctly characterized in 
their chlorides, since the different reactions of these chlorides 
With water and ammonia afford a simple means both of 



138.] RECAPITULATION AND REMARKS. 235 

detecting them and of effecting their separation from one 
another. If the precipitate containing the three metallic 
chlorides is boiled with a somewhat large quantity of water, 
or boiling water is repeatedly poured over it on the filter, the 
lead chloride dissolves, while the silver chloride and the 
mercurous chloride remain undissolved. In the aqueous 
solution of lead chloride,* the metal may be readily detected 
by sulphuric acid. 

If the silver and mercurous chlorides are then treated, 
with ammonia, the mercurous chloride is converted into the 
black precipitate, more fully described above, which is insolu- 
ble in an excess of ammonia, while the silver chloride dis- 
solves readily in ammonia, and reprecipitates from this solu- 
tion upon addition of nitric acid. (When operating upon 
small quantities, it is advisable first to expel the greater part 
of the ammonia by heat.) If the chlorides are precipitated, 
Iiowever, from a solution containing very much mercurous 
salt and only a little silver, the silver chloride cannot be 
completely extracted by ammonia, and in presence of a great 
excess of the mercurous chloride, it may happen that all 
the silver chloride remains behind with the mercury resi- 
due (MoEOK). If very much mercury is present, therefore, 
and if no silver has been found in the ammoniacal solution,, 
the black mercury product should be ignited in a porcelain 
crucible under a good hood until all the mercury has vola- 
tilized. Any residue remaining is then ignited with som& 
crystals of oxalic acid until these have been also volatilized, 
the residue is treated with nitric acid with the aid of heat, 
and this solution, after diluting somewhat with water, is tested 
for silver with hydrochloric acid. 

For separating silver from lead, or for detecting small 
amounts of silver in the presence of much lead, the following 
methods may also be used : a. Add to the solution some nitric 
acid, and then a mixture of equal parts of ammonia and solu- 
tion of hydrogen peroxide, and a little ammonium* carbonate. 
The lead then separates from the ammoniacal liquid, as a com- 
pound of lead dioxide and monoxide, in the form of a reddish- 
yellow precipitate, while the silver remains in solution. If 
the precipitate is filtered off, the filtrate acidified with nitria 
acid, and a little hydrochloric acid added, the silver sepa. 



236 DEPORTMENT OF BODIES WITH BEAGEKTS. [339. 

rates as silver chloride (P. JANNASOH). b. Acidify the solution 
containing lead and silver with a little nitric acid, heat, add a 
small excess of potassium chromate or dichromate, heat fur- 
ther, add an excess of dilute ammonia, warm for some time, and 
filter. Lead chromate is then obtained upon the filter, while 
silver chromate is contained in the ammoniacal filtrate. If 
the latter is acidified with nitric acid and some hydrochloric 
acid is added, the silver separates as silver chloride (P. 
JAJNNASCH).* 

SECOND DIVISION: COMMONLY OOOUBBING- METALS WHICH ARE NOT 

PBEOIPITATED BY KIDBOOELOBIO ACID. 

139. 
a. MERCURY, Hg, IN MERCURIC COMPOUNDS. (Oxide, HgO.) 

1. MERCURIC OXIDE, HgO, is generally crystalline, and has 
a bright red color, which upon reduction to powder changes 
to a dull yellowish-red. The oxide precipitated from solutions 
of mercuric nitrate or chloride forms a yellow powder. It is 
not quite insoluble in water, and gradually turns gray in sun- 
light. Upon exposure to heat, it transiently acquires a 
deeper tint ; and at a dull red heat, it is resolved into metallic 
mercury and oxygen. Mercuric oxide dissolves readily in 
hydrochloric acid and in nitric acid. 

2. The MERCURIC SALTS volatilize upon ignition ; the oxygen 
salts suffer decomposition in this process; while mercuric 
chloride, bromide, and iodide volatilize unaltered. On boiling 
a solution of the chloride, some of the salt escapes with the 
steam. Most of the mercuric salts are colorless. They are 
very poisonous. The soluble normal salts redden litmus- 
paper. The nitrate and sulphate are decomposed by a large 
quantity of water into soluble acid and insoluble basic salts. 

3. Addition of a very small quantity of hydrogen svbphide 
or of ammonium sulphide to mercuric salt solutions produces, 
After shaking, a perfectly white precipitate; addition of a 

* Concerning further methods "for detecting little silver In presence of 
much lead, compare RRUTWIG, Zeitschr. f analyt. Ohem., 22, 428 ; JOHN* 
STONE, Chem. Centralbl,, 1890, 1, 298. 



139.] MERCURY. 287 

somewhat larger quantity of one of these reagents causes the 
precipitate to acquire a yellow, orange, or brownish-red color ; 
while an excess of the precipitant produces a black pre- 
cipitate of MEBOTJRIC SULPHIDE, HgS. This progressive variation 
of color from white to black, which depends on the proportion 
of the hydrogen sulphide or ammonium sulphide added, 
distinguishes the mercuric salts from all others. The white 
precipitate which forms at first consists of a double com- 
pound of mercuric sulphide with the still undecomposed por- 
tion of the mercuric salt (in a solution of mercuric chloride, 
for instance, Hg01 4 .2HgS). The gradually increasing admixt- 
ure of black sulphide causes the precipitate to pass through 
the several gradations of color above mentioned. Ammonium 
sulphide dissolves only the smallest traces of mercuric sul- 
phide, and the least amount of mercury is dissolved when the 
precipitate is digested hot with yellow ammonium sulphide. 
Potassium hydroxide and potassium cyanide do not dissolve 
mercuric sulphide. Potassium sulphide and sodium sulphide 
in the presence of some caustic potash or soda dissolve the 
precipitate completely (difference from silver, lead, bismuth, 
and copper), but it is insoluble in potassium hydrosulphide 
and in sodium hydrosulphide. Ammonium chloride precipi- 
tates the mercuric sulphide from its solutions in sodium or 
potassium sulphide. Mercuric sulphide dissolves in potas- 
sium thiocarbonate (difference from silver, lead, bismuth, and 
copper). It is reprecipitated from this solution by carbonic 
acid (difference from palladium, ROSENBLAIKF). Mercuric sul- 
phide is entirely insoluble in nitric acid, even upon boiling. 
By the long-continued action of hot, concentrated nitric acid, 
it is converted, without dissolving, into the white compound, 
2HgS.Hg(N0 8 ) a . Concentrated hydrochloric acid dissolves 
it rather readily when hot, but more difficultly when cold, yet 
it is insoluble or nearly so in dilute hydrochloric acid in the 
cold, but upon boiling, the latter dissolves it a little. Aqua 
regia decomposes the precipitate and dissolves it with ease. 
In mercuric solutions containing a large excess of con- 
centrated mineral acid, hydrogen sulphide produces a pre- 
cipitate only after the addition of water. 

4 Potassium hydroxide, and also sodium hydroxide, added 
in small quantity, produce in neutral or slightly acid solu- 



388 DEPORTMENT OF BODIES WITH BEACKENTS. [ 139* 

tions of mercuric salts (but not of mercuric cyanide) a reddish- 
brown precipitate, which acquires a yellow tint if the reagent 
is added in excess. The reddish-brown precipitate is a BASIC 
SALT, while the yellow precipitate consists of MEBOHBIO OXIDE, 
HgO. An excess of the precipitant does not redissolve these 
precipitates. In very acid solutions, this reaction does not. 
take place at all, or at least the precipitation is very incom- 
plete. In presence of ammonium salts, potassium hydroxide 
produces neither reddish-brown nor yellow, but white, precipi- 
tates. The precipitate thrown down by potassium hydroxide 
from a solution of mercuric chloride containing an excess of 
ammonium chloride is of nearly the same composition as that 
produced by ammonia (see 5). 

5. Ammonia causes white precipitates quite analogous 
to those produced by potassium or sodium hydroxide in 
presence of ammonium chloride. For instance, from solu- 
tions of mercuric chloride, ammonia precipitates the so-called 
infusible white precipitate, NH 9 HgCl, which may be regarded 
as mercurammonium chloride, or as mercuric amido-chlo- 
ride. If the solution of the mercuric salt contains very much 
free acid, no precipitate is produced by ammonia. The white 
precipitates do not dissolve in ammonia, but are easily soluble 
in hydrochloric acid. 

6. Btannous chloride added in small quantity to solution of 
mercuric chloride, or to solutions of other mercuric salts in 
presence of hydrochloric acid, throws down MEBOUBOTJS OHLO- 
WDE : 2Hg01 fl + SnOl, = 2Hg01 + Sn01 4 . By addition of a 
larger quantity of the reagent, the precipitated mercurous 
chloride is reduced to METAL : 2Hg01 + SnCl a = Hg a + Sn01 4 . 
The precipitate, which was white at first, therefore now ac- 
quires a gray tint, and, after it has subsided, may be readily 
united into globules of metallic mercury by boiling with 
hydrochloric acid and a little stannous chloride. 

7. If a little galvanic demerit, made from a strip of plati- 
num foil and one of tin-foil, joined at one end with a wooden 
clamp, but otherwise apart from each other, is introduced 
into a mercuric solution acidified with hydrochloric acid, 
all the mercury will gradually be precipitated, chiefly upon 
the platinum. On removing the platinum foil, drying, roll- 
i i it up, and heating strongly in a glass tube, a sublimate- 



139.] MERCUBY. 290 

of globules of mercury will be obtained, which may be more 
distinctly seen under the microscope (VAN DEN BBOEE*). 
Upon the electrolytic separation of mercury depends also 
the method of MAYEN^ON and BEEGEBET,t and that of C. H. 
WOLFF, J which is to be highly recommended, but requires 
a special apparatus. In relation to the conversions of sub- 
limates of mercury into the iodide, compare 136, 10. 

8. For the deposition of small traces of mercury from 
acidified solutions upon metals (gold, platinum, copper, zinc), 
various other methods besides the foregoiDg may be used. 
One of the most convenient of these, given by FURBBINGEK, 
consists in bringing a little (.25 to .50 g) shredded brass- 
wool or imitation gold-leaf (TEUBNEE d ) (which is -first rolled 
together and then pulled apart), into the liquid, which is 
distinctly acidified with some hydrochloric, sulphuric, or 
acetic acid, and heated to 60 or 80, and allowing it to act for 
five or ten minutes with frequent stirring. The metal, now 
amalgamated, is washed with water (in presence of organic 
matter, also with alcohol and ether), dried between blottiug- 
papers, formed into the shape of a spindle, and introduced into 
a piece of difficultly fusible glass tube which is drawn out to 
a capillary tube at one end ; the other end of the tube near 
the metal is then also drawn out into a capillary tube, and 
the amalgamated metal is uniformly heated, just to an incipi- 
ent red heat, by rotating the tube over a quietly burning gas 
flame. The mercury is then deposited in both capillary ends 
in the form of rings. If zinc rings also form, as is often the 
case, these are always nearer the heated part than those of 
mercury. The conversion of mercury coatings into mercuric 
iodide coatings may be carried out according to 136, 



* Zeltschr. f. analyt. diem., 1, 512. f Pharmac. Centralhalle, 14, 317. 

f Pharmac. Centralhalle, 24, 315, and 29, 342. 

Zeitschr f. analyt. Ohem., 17, 526. I Zeitschr. f. analyt Chem., 19, 199. 

If Upon a similar basis are founded the methods of LTTDWIG, who uses 
zinc-dust (Pharmac. Centralhalle, 22, 436) f ITsaA, who precipitates with brass 
foil (Chem. Centralbl., 1884, p. 498); A. WOLFF and J NBGA, FK. MILLER, 
EIELBIG, MBRQBT, who precipitate with copper filings, foil, or wire (Zeitscjir. 
1 analyt Chem., 26, 116 and 670 ; Chem. Centralbl. f 1888, p. 1248 ; Zeitscbr. 
f analyt. Chem., 29, 113) ; K. ALT, who separates the mercury by means of 
a leaf of aitiflcial gold-tinsel (Chem. Centralbl, 1887, p. 1573); ALsdSN, who 



240 DEPORTMENT OF BODIES WITH REAGENTS. [ 140. 

9. Mercuric salts show the same reaction as mercurous 
salts with metallic copper, and when heated with sodium car- 
bonate in a glass tube. 

10. The microscopic detection of mercury is carried out 
by observing mercuric sulphate, mercuric iodide, and also 
cobalt mercuric sulphocyanide. (Compare HA.USHOEEB, p. 112 ; 
BEHRENS, Zeitschr. f. analyt Chem., 30, 151.) 



140. 
6. COPPER, Cu. (Cupric Oxide, CuO.) 

1. METALLIC COPPER has a peculiar red color, and a strong 
luster ; it is moderately hard, malleable, and rather difficultly 
fusible. In contact with water and air, it becomes covered 
with a green crust of basic cupric carbonate ; while upon igni- 
tion in the air, it becomes coated with cuprous and cuprio 
oxides. In hydrochloric acid and dilute sulphuric acid, it 
is insoluble or nearly so when air is excluded, even upon 
boiling. Nitric acid dissolves the metal readily. Concen- 
trated sulphuric acid converts it into cupric sulphate, with 
evolution of sulphur dioxide. 

2. CUPROUS OXIDE, Ou,O, is red, and CUPROUS HYDROXIDE is 
yellow, both changing to cupric oxide upon ignition in, the 
air. On treating cuprous oxide with dilute sulphuric acid, 
metallic copper separates, while cupric sulphate dissolves ; on 
treating it with hydrochloric acid, white cuprous chloride 
is formed, which dissolves in an excess of the acid, but is re- 
precipitated from this solution by water. 

3. CUPRIO OXIDE, CuO, is a black powder which withstands 
a red heat without decomposition, but by very strung ignition 
it loses oxygen and is converted into cuprous oxide. Its 
hydroxide, Cu(OH) a , is light blue. Both the oxide and 
hydroxide dissolve with ease in hydrochloric, sulphuric, and 
nitric acids. 

uses copper or brass wire (Zeitschr. f. analyt. Chem., 26, 669), MEEGBT 
presses the amalgamated copper wire, after drying, between papers soaked 
with ammoniacal silver nitrate solution Dark spots result upon the latter 
after a few minutes 



140.] COPPER 241 

i. Many of the normal CUPEIO SALTS are soluble in water. 
The soluble salts redden litmus, and those containing volatile 
oxygen acids suffer decomposition when heated to gentle 
redness, with the exception of the sulphate, which can bear a 
somewhat higher temperature. They are usually white in 
the anhydrous state, while the hydrated salts are generally of 
a blue or green color, which their solutions continue to exhibit 
even when much diluted. 

5. In alkaline, neutral, and acid solutions, "hydrogen sul* 
phide and ammonium sulphide produce brownish-black precipi- 
tates of OUPBIO SULPHIDE, CuS.* This sulphide is insoluble 
in dilute acids and caustic alkalies. Hot solutions of potas- 
sium and sodium sulphides take sulphur from it, but do 
not dissolve the copper sulphide, or dissolve it only to a 
very trifling extent However, it is a little more soluble in 
ammonium sulphide, especially if this is very yellow and acta 
hot. This reagent is therefore less appropriate for separat- 
ing copper sulphide from other metallic sulphides. Ouprio 
sulphide is readily decomposed and dissolved by boiling 
nitric acid, bat it remains altogether unaffected by boiling, 
dilute sulphuric acid. When freshly precipitated, it dissolves 
easily and completely in solution of potassium cyanide. In 
solutions of cupric salts which contain a very large excess of 
a concentrated mineral acid, hydrogen sulphide produces a 
precipitate only after the addition of water. 

6. Potassium or sodium hydroxide produces a light blue, 
bulky precipitate of OUPBIO HIDBOXEDE, Ou(OH) s . If the 
solution is highly concentrated and the precipitant is added 
in excess, the precipitate turns brownish-black after the 
lapse of some time, and loses its bulkiness, even in the cold, 
but the change takes place immediately if the precipitate 
is boiled with the fluid (diluted if necessary) in which it is 
suspended. The blue hydroxide is thereby converted into a 
brownish-black hydroxide, SCuO.HaO, containing less water. 
In a large excess of very concentrated potassium or sodium 
hydroxide, the light blue precipitate dissolves to a blue 
liquid. 

7. Sodium carbonate precipitates HYDROUS, BASIC COPPER 

* According to J. THOMSKN, the precipitate is CiuS. + 8. 



243 DEPORTMENT OF BODIES TVITH REAGENTS. [ 140. 

CABBOXATE, CuC0 8 .Cu(OE) a , as a greenish-blue precipitate, 
which dissolves in ammonia to an azure-Hue and in potas- 
sium cyanide to a colorless fluid. Upon boiling, the pre* 
cii/iluto loses the greater part of the carbonic acid contained 
in it. and becomes brownish-black. 

8. Ammonia added in small quantity to solutions of 
normal cupiic salts produces a greenish-blue precipitate, 
consisting of a BASIC CUPRIC SALT. This redissolves readily, 
upon further addition of ammonia, to a perfectly clear fluid 
of a magnificent azure-blue, which owes its color to the for- 
mation of a basic corPEE-AMMONiA SALT. For instance, in a 
solution of cupric sulphate, excess of ammonia produces 
(XH,) a CuO.(NH 4 ) a SO i . In solutions containing a certain 
amount of free acid, ammonia produces no precipitate, but 
this azure-blue coloration makes its appearance the instant 
the ammonia predominates. The blue color ceases to be per- 
ceptible oiily in very dilute solutions. After the lapse of 
some time, potassium or sodium hydroxide produces iu 
such blue solutions in the cold, a precipitate of blue cnprio 
hydroxide, but upon continued boiling, all the copper is 
precipitated as brownish-black hydroxide. 'With cuprio 
salts, ammonium carbonate shows the same behavior as 
ammonia. 

N.B. In the presence of non-volatile organic acids, the 
cuprie salts are not precipitated by caustic or carbonated 
alkalies, the resulting alkaline solutions having a deep blue 
color. In presence of sugar or similar organic substances 
caustic alkalies produce precipitates which are soluble in 
excess of the precipitants, but sodium carbonate produces a 
permanent precipitate. 

9. In moderately dilute solutions, potassium ferrocyanide 
produces a reddish-brown precipitate of OUPEIO EEBROOYANIDE, 
Cn a Fe(CN) e , insoluble in dilute acids, but decomposed by 
potassium or sodium hydroxide. In very highly dilute solu- 
tions, the reagent merely produces a reddish coloration. 

10. If the solution of a cupric salt is mixed with sulphur- 
ous acid or with hydrochloric acid and sodium sulphite, and 
potassium sulphocyanide is then added, CUPROUS SULPHOOTAKIDE, 
OuONS, is thrown down. The precipitate is pale reddish- 
white, and is practically insoluble in water and dilute acids. 



140,] COPPEB. 343 

"With insufficient sulphurous acid, black cupric sulphocyanide 
is precipitated. 

11. If 2 cc of a cold, saturated potassium bromide solution 
is mixed with 1 cc of pure, concentrated sulphuric acid, and a 
few drops of a solution containing a cupric salt are added 
immediately, there is lormed at first above the more dense 
lower liquid a beautiful bluish-red zone. Upon shaking, the 
whole liquid is colored red. The color disappears upon the 
addition of water. The reaction is very delicate, and permits 
the detection of copper in the presence of other metals (DiEKl- 

GES). 

12. When brought into contact with concentrated solu- 
tions of salts of copper, metallic iron is almost immediately 
covered with a coating of METALLIC COPPEB, yet very dilute solu- 
tions produce this coating only after some time. Presence of 
a little free acid accelerates the reaction. Instead of the iron 
a small galvanic element may be made use of, constructed 
from a strip of platinum foil and one of bright sheet zinc, 
or even of tin-foil. These are fastened together at the upper 
end, then a flat piece of cork is put between them, and this 
place is also tied. The strips are given an almost parallel 
position, and are put into the weakly acidified copper solu- 
tion in such a manner that the part which is tied together 
does not dip below the surface. The copper then precipitates 
(in the case of very dilute solutions, only after about twelve 
hours) principally upon the platinum, which thereby assumes 
a copper-red to blackish color. The advantage of this sepa- 
ration of copper upon platinum consists in the fact that it can 
be readily dissolved in nitric acid, and the resulting solution 
can be subjected to further tests. For this purpose, it is 
almost entirely evaporated, and a few drops of water and a 
drop of potassium ferrocyanide solution are added. Traces of 
copper deposited upon platinum or iron may be confirmed by 
moistening them with hydrochloric acid and making a test 
according to 14 SALET recommends using the hydrochloric 
acid by moistening a bundle of fine platinum wires with it, 
and introducing this into the flame under the iron wire or 
platinum strip. The delicacy of the reaction is decidedly 
increased by this means. 

13. If a mixture of a compound of copper vith sodium 



244 DEPOBTMENT OF BODIES WITH KEA0ETTTS. [ 141. 

carbonate is exposed on a charcoal support to the inner ftam& 
of fl& bloivpipe, METALLIC COPPER is obtained without incrusta- 
tion of the charcoal. The reduction may be also very con- 
veniently effected in the stick of charcoal (p. 34). The best. 
method of freeing the copper from the particles of charcoal 
is to triturate the fused mass in a small mortar with water, 
and then cautiously wash off the charcoal powder, when the 
copper-red metallic scales will be left behind. 

14. If copper, some alloy containing copper, a trace of a 
salt of copper, or even simply the loop of a platinum wire 
dipped in a highly dilute copper solution, is introduced 
into the fusing zone of the gas flame or exposed to the inner 
Uowpipe flame, the upper or outer portion of the flame shows 
a magnificent emerald-green tint. Addition of hydrochloric 
acid to the sample considerably heightens the beauty of this 
extremely delicate reaction. The flame then has an azure 
color. 

15. Borax readily dissolves oxides of copper in the outer 
gas or blowpipe flame. The beads are green while hot, and 
blue when cold. In the inner flame, the bead is colorless. 
nnless a very large quantity of copper is present, but when 
cold, it is red and opaque. In the lower reducing flame of 
the BUNSEN gas flame, the bead does not become reddish- 
brown until the addition of stannic oxide, when this change- 
rapidly takes place, owing to the production of cuprous oxide. 
If a bead is introduced alternately into the lower oxidizing: 
zone an< the lower reducing zone, it becomes ruby-red and 
transparent. 

16 In relation to the microscopic detection of copper, see 
HAUSHOFEB, p. 87; BEEEENS, Zeitschr, i analyt Chem., 30,, 
150. 



a BISMUTH, Bi. (Oxide, Bi,0,.) 

1. BISMUTH has a reddish tin-white color and moderate 

etallic luster. It is of medium hardness, brittle, unchange- 

able in the air at ordinary temperatures, and melts at 264. 

Fused upon a charcoal support it forms an incrustation of 

yellow oxide- It dissolves readily in nitric acid, but is nearly 



141.] , BISMUTH. 245 

insoluble in hydrochloric acid, and altogether so in dilute 
sulphuric acid. Concentrated sulphuric acid converts it into 
bismuth sulphate, with evolution of sulphur dioxide. 

2. BISMUTH OXIDE, Bi a O 9 , is a yellow powder, which tran- 
siently acquires a deeper tint when heated. It fuses at a 
red heat. Bismuth hydroxide, BiOOH, is white. Both the 
oxide and hydroxide dissolve readily in hydrochloric, sul- 
phuric, and nitric acids. By fusion with potassium cyanide, 
they yield the metal. The grayish-black BISMUTHOUS OXIDE, 
Bi ft O a , and the red BISMUTHIO ACID, Bi a 6 , are converted into 
bismuth oxide by ignition in the air, and by heating with 
nitric acid, they are converted into bismuth nitrate. 

3. The BISMUTH OXYGEN SALTS are non-volatile, and those 
containing volatile acids are decomposed at a red heat Bis- 
muth chloride is volatile at a moderate heat. The bismuth 
salts are colorless or white if the acid causes no coloration. 
Some of them are soluble in water, others insoluble. The 
soluble salts redden litmus-paper, and are decomposed by 
a large quantity of water into insoluble basic salts, which 
separate, wfrile the greater portion of the acid remains in 
solution together with some bismuth. 

4. In neutral and acid bismuth solutions, hydrogen sul- 
phide and ammonium sulphide produce black precipitates of 
BISMUTH SULPHIDE, Bi 9 S, , which is insoluble in dilute acids, 
alkalies, alkali sulphides, and potassium cyanide, but is 
readily decomposed and dissolved by boiling nitric acid. In 
solutions of salts of bismuth which contain a very consider- 
able excess of hydrochloric or nitric acid, hydrogen sulphide 
produces a precipitate only after the addition of water. 

5. Potcbssiwn hydroxide, sodium hydroxide, and ammonia 
throw down BISMUTH HTDBOXIDE, BiOOH, as a white precipi- 
tate, which is insoluble in an excess of the precipitant If 
a little hydrogen peroxide is added to the liquid containing 
an excess of the precipitant, the white precipitate is converted 
upon warming into a yellow one of BISMUTHIO ACID. By this 
means, the reaction is made more delicate (HASEBBOEE). 

6. Sodium carbonate and ammonium carbonate throw down 
BASIC BISMUTH OABBONATE, Bi,O a G0 8 , as a white, bulky pre- 
cipitate, which is insoluble in excess of the precipitant, and 
in potassium, cyanide. Warming assists the precipitation. 



246 DEPOKTMENT OF BODIES WITH REAGENTS. [ 141. 

7. Potassium dicliromate precipitates BASIC BISMUTH CHBO- 
MATE, Bi a O(Cr0 4 ) fl , as a yellow powder. This substance dif- 
fers from lead chromate in being readily soluble in dilute 
nitric acid, and insoluble in potassium or sodium hydroxide, 

8. Dilute sulphuric acid fails to precipitate moderately 
dilute solutions of bismuth nitrate. On evaporating with an 
excess of sulphuric acid on the water-bath until no more acid 
vapors escape, a white, saline mass of bismuth sulphate, 
Bi,fSO 4 ) Jf is left, which always dissolves readily to a clear 
fluid in water acidified with sulphuric acid (characteristic 
difference between bismuth and lead). After long stand- 
iug (several days occasionally), a basic bismuth sulphate, 
Bi a O(SO 4 ) a .3H a O, separates from this solution in white, micro- 
scopic, needle-shaped crystals, which dissolve in nitric acid. 

9. The reaction which more particularly characterizes 
bismuth is the decomposition of its normal salts by water, 
which is attended with the separation of insoluble basic salts. 
The addition of a large amount of water to solutions of 
bismuth salts causes the immediate formation of a dazzling 
white precipitate, provided there is not too much free add 
present. This reaction is most sensitive with bismuth chlo- 
ride, as the BASIC BISMUTH CHLORIDE or oxychloride, BiOOl, 
is almost absolutely insoluble in water. Where water fails 
to precipitate nitric acid solutions of bismuth, owing to the 
presence of too much free acid, a precipitate will almost in- 
variably make its appearance immediately upon addition of 
solution of sodium chloride or ammonium chloride. Presence 
of tartaric acid does not interfere with the precipitation of 
bismuth by water. 

10. On mixing a solution of bismuth with an excess of 
solution of stannous chloride in potassium or sodium hydroxide, 
a black precipitate of BISMUTHOUS OXIDE, Bi a 9 , will fall. This 
is a very characteristic and delicate reaction: Bi^O.-f- 
K,SnO a = Bi a O fl + K fl SuO a . 

11. If a mixture of a compound of bismuth with sodium 
carbonate is exposed on a charcoal support to the reducing 
flame, brittle GLOBULES OF BISMUTH are obtained, which fly 
into pieces under the stroke of a hammer. The charcoal be- 
comes covered at the same time with a slight incrustation of 
3ISKUTH OXIDE, which is orange-colored while hot, and yellow 



142.J CADMIUM. 247 



cold. The reduction may be also conveniently effected 
in the stick of charcoal (p. 34). On triturating the end of 
the charcoal stick containing the reduced metal, yellowish 
spangles will be obtained. 

12. The METALLIC COATING of bismuth obtained according 
to p. 35 is black with a brown border ; the OXIDE COATING is 
yellowish-white, but becomes black with stannous chloride and 
sodium hydroxide (compare 10, distinction from lead oxide 
coating) ; the iodide coating is bluish-brown with a red bor- 
der, transiently disappearing when breathed upon ; while the 
sulphide coating is umber-brown with a coffee-brown border, 
and is not removed by ammonium sulphide (BuKSEN). 

13. If a compound of bismuth is heated (in case it is free 
from sulphur) with a mixture of equal parts of potassium 
iodide and flowers of sulphur, upon charcoal, before the blow- 
pipe (if the substance already contains sufficient sulphur for 
the decomposition of the potassium iodide, then potassium 
iodide alone suffices), there is formed a very volatile, scarlet 
coating of bismuth iodide. When treated in the same way, 
compounds of lead yield a deep yellow coating, and their 
presence does not interfere with the bismuth reaction (v, 
KOBELL). The reaction also succeeds by heating the mixture 
in a glass tube open at both ends (COBSTWALL). 

14. Begarding the microscopic detection of bismuth, see 
HAUSHOEEB, p. 138 ; BEEBENS, Zeitschr. 1 analyt. Oliem., 
30, 162. 

142. 
d. CADMIUM, Od. (Oxide, CdO.) 

1. METALLIC CADMIUM has a tin-white color, is lustrous, 
not very hard, and is malleable. It fuses at 315 to 316, boils 
at about 770, and may therefore be sublimed in a glass tube. 
Heated on charcoal before the blowpipe, it takes fire and 
burns, emitting brown fumes of cadmium oxide, which form 
a coating on the charcoal. Hydrochloric acid and dilute sul- 
phuric acid dissolve it, with evolution of hydrogen, but nitric 
.acid dissolves it most readily. 

2. CADMIUM OXIDE, OdO, is a fixed powder of a brown 



248 DEPORTMENT OF BODIES WITH REAGENTS. [ 142. 

color, sometimes lighter and sometimes darker in shade ; but, 
its HYDBOXIDE is white. Both dissolve readily in hydrochloric, 
nitric, and sulphuric acids. 

3. The CADMIUM SALTS are colorless or white when their 
acids produce no coloration, and some of them are soluble in 
water. The soluble normal salts redden litmus-paper, and 
those containing volatile oxygen acids are decomposed at a. 
red heat. 

4. In alkaline, neutral, and acid solutions, hydrogen sulphide 
and ammonium sulphide produce bright yellow precipitates 
of CADMIUM SULPHIDE, OdS, which are insoluble in dilute acids, 
alkalies, alkali-metal sulphides, and potassium cyanide (differ- 
ence from copper). They are readily decomposed and dis- 
solved by boiling nitric acid, as well as by boiling hydro- 
chloric acid and by boiling dilute sulphuric acid (difference- 
from copper). In solutions of cadmium containing a large 
excess of acid, hydrogen sulphide produces a precipitate only 
after dilution with water- By the action of hydrogen sulphide 
upon moderately acid, hot solutions, orange-yellow to dark 
red cadmium sulphide is precipitated. 

5. Potassium and sodium hydroxides produce white precipi- 
tates of CADMIUM HYDEOXIDE, Od(OH) s , which are insoluble 
in an excess of the precipitants, 

6. Ammonia likewise precipitates white CADMIUM HTDBOXEDE, 
which, however, redissolves readily and completely to a color- 
less fluid in an excess of the precipitant. The ammoniacal 
solution becomes turbid upon boiling, and also by diluting 
with much water, but this happens only when no ammonium 
salts are present. Potassium hydroxide as well as sodium 
hydroxide precipitate cadmium hydroxide from the ammo* 
niacal solution. 

7. Sodium carbonate and ammonium carbonate produce white 
precipitates of CADMIUM OABBONATE, CdOO a , which are insoluble 
in an excess of sodium carbonate, and very slightly soluble in 
an excess of ammonium carbonate. The presence of ammo- 
nium salts impedes and interferes with the precipitation in 
the cold, but the precipitate is formed npoc heating ; and 
free ammonia hinders it The precipitate is readily soluble 
in potassium cyanide. It separates slowly from dilute sohu 
tions, but warming assists the separation greatly. 



143.] RECAPITULATION AND REMARKS. 249 

8. Potassium sidphocyanide does not cause a precipitate in 
solutions of cadmium, even after the addition of sulphurous 
acid (difference from copper). 

9. If a mixture of a compound of cadmium with sodium 
carbonate is exposed on a charcoal support to the reducing 
flame, the charcoal becomes covered with a deep yellow to 
reddish-brown coating of CADMIUM OXIDE, owing to the instant 
volatilization of the reduced metal and its subsequent reoxi- 
dation in passing through the oxidizing flame. The coating 
is seen most distinctly after cooling. 

10. The metallic incrustation, obtained according to p. 35, is 
black with a brown edge ; the incrustation of oxide is brownish- 
black, the edge passing from brown to white ; the incrustation 
of iodide is white ; while the incrustation of sulphide is lemon- 
yellow, and is not dissolved by ammonium sulphide (BUNSEN). 

11. Concerning the microscopic detection of cadmium, see 
HAUSHOEEB, p. 52 ; BEHBENS, Zeitschr. f. analyt Ohem., 30, 
143. 

143. 

jRecapitulation and JSemarks. As already stated, the perfect 
separation of the metals of the second division of the fifth 
group from silver and mercurous salts may be effected by 
means of hydrochloric acid, but this agent fails to separate 
them completely from lead. Traces of mercuric salt, which 
are at first retained by the precipitated silver chloride by sur- 
face attraction, are dissolved out completely by washing (G. 
J. MULDEB). MEEOTJEIO compounds are distinguished from 
'Compounds of the other metals of this division by the insol- 
ubility of mercuric sulphide in boiling nitric acid. This 
property affords a convenient means for its separation from 
copper, lead, bismuth, and to a certain extent from cadmium. 
Cadmium sulphide, in fact, remains behind with the mer- 
curic sulphide partly, and if a very small quantity is pres- 
ent, it may remain behind wholly (BffLOW). Oare must 
always be taken to free the sulphides comptetdy by washing 
from all traces of hydrochloric acid or chlorides that may 
happen to be present, before proceeding to boil them 
with nitric acid. The mercuric sulphide is readily dis- 



250 DEPORTMENT OF BODIES WITH TCEAGENTS. [ 

solved by heating it with hydrochloric acid to which 
a very small amount of potassium chlorate is added. In a 
part of this solution, mercury can be detected with great ease 
by means of stannous chloride. The cadmium which has 
remained with the mercuric sulphide may be found by evapo- 
rating another portion of the solution to dryness in a porce- 
lain crucible, and volatilizing the mercuric chloride under a 
good hood at a gentle red heat. If the residue is treated with 
a drop of hydrochloric acid and a little water, the cadmium is 
obtained in solution, and may be precipitated with hydrogen 
sulphide. From the remaining metals, LEAD is separated by 
sulphuric acid. The separation is most complete if the fluid, 
after addition of dilute sulphuric acid in excess, is evaporated 
on the water-bath, the residue diluted with water containing 
some sulphuric acid, and the uudissolved lead sulphate filtered 
off immediately. The latter may be further examined in the 
dry way by the reaction described in 137, 10, or also as fol- 
lows : Pour over a small portion of the lead sulphate a little 
solution of potassium chromate, and apply heat, which will 
convert the white precipitate into yellow lead chromate ; 
Wash this, add a little solution of potassium or sodium hy- 
droxide and heat ; the precipitate will now dissolve to a clear 
Cttid, and by acidifying this with acetic acid, a yellow pre- 
cipitate of lead chromate will again be produced. After the 
Removal of mercury and lead, BISMUTH may be separated from 
jopper and cadmium by addition of ammonia in excess, as the 
fcydroxides of the last two metals are soluble in an excess of 
this agent. If the precipitate, after being filtered off, is dis- 
solved in a drop or two of hydrochloric acid on a watch-glass, 
and water added, the appearance of a milky turbidity is a 
confirmation of the presence of bismuth. The reaction given 
in 141, 10, which is based upon the production of bismuth- 
ous oxide, is also well adapted for a confirmatory test. The 
presence of a notable quantity of COPPER is revealed by the 
blue color of the ammoniacal solution ; while smaller quan- 
tities are detected by evaporating the ammoniacal solution, 
nearly to dryness, adding a little acetic acid, and then potas- 
sium ferrocjauide i The separation of copper from CADMIUM: 
may be effected by evaporating the arnmoniaca.1 solution to a 
small bulk, acidifying faintly with hydrochloric acid, adding 



143.] RECAPITULATION AND REMARKS. 251 

a little sulphurous acid and potassium sulphocyanide, filtering 
off the cuprous sulphocyanide after allowing it to stand in a 
warm place, and precipitating the cadmium in the filtrate by 
hydrogen sulphide after the removal of any sulphurous acid 
still present (an unnecessarily large excess of sulphurous acid 
should, of course, be avoided). The separation of copper 
from cadmium may also be effected by acting on the sulphides 
with potassium cyanide, or with boiling dilute sulphuric acid 
(5 parts of water to 1 part of concentrated acid). In tho latter 
methods, the solution of copper and cadmium somewhat 
acidified with hydrochloric acid is precipitated by hydrogen 
sulphide, and the precipitate is separated from the fluid by 
decantation or filtration, and is then washed. On treating the 
precipitate now with some water and a small lump of potas&ium 
cyanide, the cupric sulphide will dissolve, leaving the yellow 
cadmium sulphide undissolved. On the other hand, by boil- 
ing the precipitate of the mixed sulphides with dilute sul- 
phuric acid, the cupric sulphide remains undissolved, while 
the cadmium sulphide is obtained in solution. Hydrogen 
sulphide will therefore now throw down from the filtrate,, 
yellow cadmium sulphide (A. "W. HOFBIANN).* 



* In legard to the detection of small traces of mercury, see the communica- 
tions of TBUHNER (Zeitschr f. analyt. Ohem., 19, 198) ; BIEWEND (ibid,, 22, 
89) , J. KLEIN (#&, 29, 186) ; G. KROUPA (Chem Centralbl , 1886. p. 250). 
Concerning the detection of traces of copper, see WILDENSTEIN (Zeitschr. f. 
analyt Ohem., 2, 9) , SOHAER(W&, 9, 100) t Sandra (ibid., 9, 310) ; BELLAMY 
(ibid , 9, 382) , PUBGOTTI (ibid., 18, 476) ; ENDEMANN and PROCHAZKA (ibid.^ 
21, 265) , v. KNOBKE(t5fcL, 28, 284) ; H. TnoMsfPharmac. Oentralhalle, 1890| 
p 31). In regard to the detection of bismuth, see TRESH (Zeitschr. f. analyt. 
Chem., 22, 483) ; E. LEOER (ibid., 28, 847). Further, concerning the detection 
of these metals in the presence of organic substances, see V (detection of in- 
organic poisons in food, etc.), in the second division of Part II. In regard to 
other methods for the separation of the metals of the fifth group, see especially 
the communications of ROSENBLATT (Zeitschr f. analyt Chem , 26, 15) ; 
KOHNER (&W&, 27, 217) ; PoLSTORFF and Bt7Low(Chem Centralbl., 1891, 2 
327) ; JAKHASOH and Erz (Zeitschr. f. analyt. Chem,, 33, 67). 



252 DEPORTMENT Off BODIES WITH EEAGEtfTS. [ 144. 

Special Seactions of the Rarer Metals of the Fifth Group. 

144. 

1. PALLADIUM, Pd. (Palladious Ossicle, PdO.) 

PALLADIUM is found in the metallic state, occasionally alloyed with 
gold and silver, but more particularly with or in platinum ores. It greatly 
resembles platinum, but is somewhat darker in color. It fuses with great 
difficulty. Heated in the air to dull redness, it becomes covered with a 
blue film, but it recovers its light color and metallic luster upon more 
intense ignition. It is difficultly soluble in pure nitric acid, but dissolves 
somewhat more readily in nitric acid containing nitrous acid. It dis- 
solves very slightly in boiling concentrated sulphuric acid, but is soluble 
in fusing potassium disulphate, and readily soluble in nitre-hydrochloric 
acid. There are three oxides: the suboxide, PcUO; palladious oxide, 
PdO; and palladia oxide, PdOa. PALLADIOUS OXIDE is black, the cor- 
responding hydroxide dark brown, and both are decomposed by intense 
ignition, leaving a residue of metallic palladium. PALLADIO OXIDE is 
black. By heating with dilute hydrochloric acid, it is dissolved to palla- 
dious chloride, Pd01 a , with evolution of chlorine. The FALLACIOUS SALTS 
are mostly soluble in water, and are brown or reddish-brown. Their con* 
oentrated solutions are reddish-brown, but their dilute solutions are yellow. 
From a solution of palladious nitrate containing a slight excess of acid, 
water precipitates a brown basic salt. The oxygen salts as well as pal- 
ladious chloride, are decomposed by ignition, leaving metallic palladium 
behind. Hydrogen sulphide and ammonium sulphide throw down from 
acid or neutral solutions, black palladious sulphide, which does not dis- 
solve in ammonium sulphide, but is soluble in potassium thiocarbonate 
(difference from lead, copper, bismuth), and is not precipitated from the 
solution by carbonic acid (difference from mercury, BOSENBLADT). Ifc is 
also soluble in boiling hydrochloric acid, and readily soluble in aqua regia. 
From the solution of palladious chloride, potassium hydroxide precipitates 
a brown basic salt, which is soluble in a large excess of the precipitant. 
Ammonia precipitates a flesh-red compound of palladious chloride and 
ammonia, which is soluble in an excess of ammonia (rather rapidly by 
heating, slowly in the cold) to a colorless liquid from which hydrochloric 
acid precipitates yellow, crystalline palladammonium chloride, PdfNHOaOlj. 
Mercuric cyanide throws down from neutral or slightly acid solutions, yel- 
lowish-white palladious cyanide as a gelatinous precipitate, slightly soluble 
in hydrochloric acid, and readily soluble in ammonia (especially character- 
istic). In the absence of free hydrochloric acid, stannvus chloride pro- 
duces a brownish-black precipitate; but in presence of free hydrochloric 
acid t a red solution, which speedily turns brown, and ultimately greon, RI<* 
becomes brownish-red upon addition of water. Sodium fvrmate precipitates 



EHODIUM, 263 

at 50' all the palladium in the metallic state as palladium-black. Potas- 
sium iodide precipitates black palladious iodide, which is soluble in an 
excess of the precipitant, giving a dark brown color (especially char- 
actenstio). Potassium chloride precipitates from highly concentrated 
solutions, potassium palladious chloride, 9ECl.PdCl, in the form of 
golden-yellow needles, which dissolve readily in water to a dark red fluid, 
but are insoluble in absolute alcohol Potassium nitrite produces in not 
too dilute solutions, a yellowish, crystalline precipitate, which becomes 
reddish on long standing, and is soluble in much water. Potassium 
sulphocyanide does not precipitate palladium, even after the addition of 
sulphurous acid (difference from copper, and best means of separating 
from the same). On treatment with sodium cartonate in the upper 
oxidizing flame (p. 82), all the compounds of palladium yield a gray, 
metallic sponge. When this is triturated in an agate mortar, silver- white, 
ductile, metallic spangles are obtained. Concerning the microscopic detec- 
tion of palladium, see HAUSHOI-EE, p. 107; BEHBENS, Zeitschr. f. analyt. 
Chem., 30, 153. 



145. 
2. EHODIUM, Eh. (fihodw Oxide, Eh a O t .) 

BHODIUM is found in small quantity in platinum ores. It is almost 
silver-white, malleable, and very difficultly fusible. When prepared in 
the wet way, it is a gray powder. Compact rhodium is insoluble in all 
acids. Even in aqua regia, it dissolves only when alloyed with platinum, 
copper, etc., and not when alloyed with gold or silver. Precipitated 
rhodium, on the other hand, is somewhat soluble in nitric acid and in 
hydrochloric acid in presence of air. Fusing znetaphosphoric acid and 
fusing potassium disulphate dissolve it, forming rhodio salts. Heated 
in chlorine, it yields a chloride of variable composition (GLAUS, LEIDE). 
Heated with potassium or sodium chloride in a stream of chlorine, double 
-chlorides are formed. Sodium rhodic chloride is insoluble in alcohol 
(means of separation from platinum and other metals). There are three 
oxides: rhodious oxide, EhO; rhodio oxide, Rh a O a ; and the dioxide, Rh0 3 . 
KHODIO OXIDE is gray or black, and yields a yellow and a brownish-black 
hydroxide. It is insoluble in acids, but dissolves in the fluxes mentioned 
in connection with the metal. The solutions have a beautiful red color. 
Upon prolonged action, especially by the aid of heat (but even then com- 
plete precipitation is difficult), hydrogen sulphide precipitates brown 
rhodium sulph-hydrate, Bh a (SH} ? which is not dissolved by acids or alkali- 
metal sulphides, but is easily soluble in bromine and aqua regia. When it is 
boiled with much water, it is decomposed into rhodium sulphide and hydro- 
gen sulphide, with contraction in volume. Normal alkali-metal sulphides 
precipitate compounds of rhodium sulphide with alkali-metal sulphides in 
the form of brownish-black precipitates, which are insoluble in an excess 



254 DEPORTMENT OF BODIES WITH EEAGEITTB, [ 146* 

of the precipitant, and are decomposable by water (Irani). Potassium 
hydroxide, added in not too great excess to solutions of rhodic oxygen 
salts, produces immediately a yellow precipitate of the hydroxide, 
Rh(OH),.H,0, which is soluble at the ordinary temperature in an excess of 
pota&smm hydroxide, and by boiling the yellow solution, the blackish- 
brown hydroxide, Ilh(OH) 3) is precipitated. In solutions of rhodic chlo- 
ride, no 'precipitation is produced at first by potassium hydroxide, but 
upon the addition of alcohol, a black hydroxide soon separates (OLAUS). 
Ammonia produces, after some time, a yellow precipitate, soluble in 
hydrochloric acid. Zinc precipitates black metallic rhodium. Upon heat- 
ing with potassium nitrite, a solution of rhodic chloride becomes yellow 
and an orange-yellow powder separates, which is but little soluble in 
water, although easily soluble in hydrochloric acid; while at the same 
time, another part of the rhodium is converted into a yellow salt, soluble 
in water, which may be precipitated by alcohol. The insolubility of potas- 
sium rhodio nitrite in alcohol permits a separation of rhodium from 
ruthenium (GiBBS). If a slight excess of a freshly prepared solution of 
sodium hypochlonte is added to a not too dilute, neutral, or weakly acid 
solution of ammonium rhodium chloride, a yellowish precipitate is ob- 
tained. If dilute acetic acid (1 : 5) is now added drop by drop, with con- 
tinual stirring, the precipitate dissolves, and the liquid assumes an intense 
orange color; then it quickly becomes decolorized, gives a gray precipitate^ 
and finally an intense sky-blue color (DEMAB^AY) . On ignition in hydrogen , 
or on ignition on a platinum wire with sodium carbonate in the upper 
oxidizing flame, all solid compounds of rhodium yield the metal, which is 
well characterized by its insolubility in aqua regia, and its solubility in 
fusing potassium disulphate. The fused mass obtained with the latter is 
yellow after cooling, and dissolves in water with a yellow color. By- 
adding hydrochloric acid, the solution becomes red (BuNSEN). The micro- 
scopic detection of rhodium depends upon an examination of potassium. 
rhodic nitrite, of rhodic oxalate (BEHRBNS, Zeitschr. f. analyt. Chem,, 30 > 
154), or of ammonium rhodic chloride (WiLM, Ber. der deutch. chem. 
GesellsoL, 1885, p. 3547). 

146. 
3. OSMIUM, Os. 

OSMIUM is found rarely in platinum ores as a native alloy of osmium 
and indium, etc. It is generally obtained as a black powder, or gray 
with metallic luster, and is infusible. The metal. OSMIOUS OXIDE, OsO, 
the SESQUIOXIDE, OssOa, and OBMIC OXIDE, OsOa, oxidize readily when heated 
to redness in the air, and give PBROSMIC AOID, OsO* , which volatilizes and 
makes its presence speedily known by its exceedingly irritating and offen- 
sive smell, resembling that of chlorine and iodine (highly characteristic). 
If a little osmium on a strip of platinum foil is held in the outer mantle of 



146.] OSMIUM. ^5 

a gas or alcohol flame, at half its height, the flame becomes most strik- 
ingly luminous. By this reaction, even minute traces of osmium may be 
detected in alloys of indium and osmium, but the reaction in that case 
is only momentary, still it may be reproduced by holding the sample first 
in the reducing flame, and then again in the outer mantle. Nitric acid, 
more particularly red fuming nitric acid, and aqua regia dissolve osmium 
to perosmic acid. Application of heat promotes the solution, -which is, 
however, attended with volatilization of perosmic acid. Very intensely 
ignited osmium is insoluble in acids. On fusing with potassium nitrate 
and distilling the dissolved mass with nitric acid, perosmic acid is found 
in the distillate (characteristic reaction for all osmium compounds). By 
heating osmium m dry chhrltw free from air, bluish-black OSMIOCS CHLO- 
RIDE, OsCla , is first formed, but always only in small quantity, theu the 
more volatile and red osmo CHLORIDE, OsOh ; while if moist chlorine is 
used, a green mixture of both chlorides is formed. The osmious chloride 
dissolves with a blue color, the osmic chloride with a yellow color, and both 
together with a green color, which turns red. The solutions are soon 
decomposed, perosmic acid, hydrochloric acid, and a mixture of osmious 
and osmic oxides being formed, while the mixed oxides separate as a black 
powder. On heating a mixture of powdered osmium or osmium sulphide 
and potassium chloride, in chlorine, a double salt, POTASSIUM OSMIC 
CHLORIDE, is produced, which is somewhat difficultly soluble in cold water, 
but more readily so in hot water. From the yellow solution, alcohol 
precipitates the salt as a red, crystalline powder. Potassium hydroxide 
precipitates a black hydroxide upon heating. Upon fusing potassium osmic 
chloride with sodium carbonate, blackish-gray osmic oxide, insoluble in 
water and in hydrochloric acid, is formed. The double salt, 3KC1 OsCla . 
3H a O, dissolves in water very easily. The deep cherry-red solution is 
decomposed readily, especially when warm, with separation of black oxy- 
chloride. Potassium hydroxide precipitates from this solution a reddish- 
brown hydroxide. Anhydrous PEROSMIC ACID is white, crystalline, fusible 
at a gentle heat, and boils at about 100. The fumes possess an unendur- 
able odor, and attack the nose and eyes powerfully. Heated with water it 
fuses and dissolves slowly. The solution is colorless, gives no acid reaction, 
and has a strong, irritating, unpleasant smell. Concentrated potassium 
hydroxide solution colors the solution yellow, and upon distilling, the greater 
part of the osmium passes over as perosmic acid (very characteristic), the 
remainder gives off oxygen, forming potassium osmate, KaOsO* , and upon 
continued boiling forms perosmic acid, osmio hydroxide, and potassium 
hydroxide. Perosmic acid decolorizes indigo solution, separates iodine from 
potassium iodide, and converts alcoliol into aldehyde and acetic acid. Potas- 
sium nitrite readily reduces it to potassium osmate, which separates out in 
garnet-red crystals. Hydrogen sulphide colors the aqueous solution of 
perosmic acid dark brown, and upon the addition of acid, a dark brown 
precipitate of osmium sulphide is produced, which is insoluble in alkaline 
hydroxides and carbonates, as well as in ammonium and alkali-metal sul- 
phides. Sulphurous acid, added in increasing amount, produces a yellow, 



266 DEPORTMENT OF BODIES WITH KEAGEFTS. [ 147- 

reddish-brown, green, and finally an indigo-blue color. Ferrous sulphate 
causes a black precipitate of osmic oxide. 8tanw>us chloride gives a 
brown precipitate, soluble in hydrochloric acid to a brown fluid. Zinc 
and many other metals, in the presence of a strong acid, precipitate 
metallic osmium. All the compounds of osmium yield the metal on igni- 
tion in a current of liydrogm; but upon ignition in the oxidizing flame, 
volatile perosmic acid is formed, recognizable by its odor, etc, Concern- 
ing the microscopic detection of osmium, compare BEHRHSNS, Zeitschr. f. 
analyt. Chem., 30, 154. 



4 EUTHENIUM, Ell. 

RUTHENIUM is found in small quantity in platinum ores. It is a gray- 
ish-white, brittle, and exceedingly difficultly fusible metal. The powder is 
grayish-black. It is barely acted upon by aqua regia, and fusing potassium 
disulphate fails altogetber to affect it. It combines with oxygen, forming 
ratheuious oxide, RuQ, the sesquioxide, Ru a 3 , ruthenic oxide, BuO, 
ruthemc acid, RuO a (only known in compounds), and perruthenic acid, 
BuO By ignition m the air, the pulverulent metal forms the black 
sesqmoxide,* which is insoluble in acids. 

By igoition of the metal mixed with potassium chloride in a stream 
of chlorine, the double salt, SKCLRuOls , is formed, which dissolves in 
water with an orange-yellow color. From the solution, there separates 
gradually upon standing, but at once upon heating, a black, volumi- 
nous precipitate, which remains suspended for a long time, and has the 
property of staining very strongly (delicate reaction). Potassium hydrox- 
ide, sodium hydroxide, and also ammonia throw down the blackish-brown, 
hydrated sesquioxide, which is insoluble m an excess of the fixed alkalies, 
but is soluble in an excess of ammonia, with a greenish-brown color, and 
dissolves in hydrochloric acid to an orange- colored solution. Hydrogen 
sulphide produces, only after some time, a light-colored precipitate, per- 
haps a mixture of black ruthenium sulphide and sulphur. The precipi- 
tate gradually becomes darker, while the b'quid assumes a deep blue color. 
Ammonium sulphide gives a brownish-black precipitate, which is scarcely 
soluble in an excess of the precipitant. Zinc gives at first an indigo-blue 
color, in consequence of a reduction from ruthemc to ruthenious chloride, 
and afterwards metallic ruthenium is deposited. Potassium sulpha- 
cyanide produces (in absence of other metals of platinum ores) after some 
time, a red coloration, gradually becoming purplish-red, and upon heating, 
a beautiful violet coloration (very characteristic). Potassium iodide pre- 
cipitates gradually in the cold, but at once upon heating, black ruthenio 

* According to DBBBAT and Jor/r, the product thus obtained is, in all 
probability, only a mixture of ruthenic oxide with metallic ruthenium. 



148.] SIXTH GROUP. 257 

iodide. ' If potassium nitrite is added to the solution which is made 
weakly alkaline with sodium carbonate, it is then heated to boiling, 
allowed to cool, and a very little colorless ammonium sulphide is added, 
the liquid becomes colored a beautiful crimson-red, afterwards brown 
(even in the presence of other metals occurring in the platinum ores). 
More ammonium sulphide produces a brown precipitate. If to a solution 
of sodium thiosu1p?tate containing ammonia, a few drops of a solution 
of ruthenium trichloride are added, the liquid assumes an intense purple- 
red color. 

Ruthenic oxide is a blackish-blue powder, insoluble in acids, and dis- 
solving in fusing potassium hydroxide with a brown color. Its hydroxide 
has a dark ochre color, and is soluble an acids to light yellow liquids. By 
fusing metallic ruthenium with potassium hydroxide and potassium 
nitrate or chlorate, an orange-red mass results, containing potassium 
wth&nate) which dissolves in water, forming an orange-yellow solution. 
It colors organic bodies black. Acids or alcohol precipitate from it the 
hydrated sesquioxide. Perruthenic acid forms a yellow, crystalline mass, 
which evaporates even at the ordinary temperature. It fuses easily, and 
boils somewhat above 100. The golden-yellow gas has an odor similar to 
that of nitrous acid. Perruthenic acid dissolves slowly and difficultly in 
water. Upon being heated with hydrochloric arid, ruthenium sesqni- 
chloride is formed, with evolution of chlorine. Sulphurous acid colors it 
purple-red at first, then violet-blue. Hydrogen sulphide precipitates 
a black oxysulphide, with a transitory red coloration of the liquid. In 
relation to the microscopic detection of ruthenium, see BEHRENS, Zeitschr. 
f. analyt. Ohem., 30, 164. 



148. 
SIXTH GROUP. 

More common metals: GOLD, PLATINUM, TIN, ANTIMONY, 
ARSENIO. 

Barer metals: GEBMANIUM, IRIDIUM, MOLYBDENUM, TUNG- 
STEN, TELLURIUM, SELENIUM. 

The higher oxides of the elements belonging to the sixth 
group all have more or less strongly pronounced acid char- 
acters. They are included here, however, as they cannot well 
be separated from the lower oxides of the same elements, 
to which they are very closely allied in their reactions with 
hydrogen sulphide. 

Properties of tJie Group. The sulphides of the metals of 
the sixth group are insoluble in dilute acids. These sulphides 
combine with alkali-metal sulphides (either directly, or with 



258 DEPOIITMENT OF BODIES WITH REAGENTS. [ 149. 

the addition of sulplmr) to soluble sulphur salts, in which they 
take the part of the acid. From acidified solutions, therefore, 
hydrogen sulphide precipitates these elements completely, 
like those of the fifth group. The precipitated sulphides differ, 
however, from those of the fifth group in this, that they dis- 
solve 111 ammonium sulphide, potassium sulphide, etc., and are 
precipitated from these solutions by the addition of acids. 

The more common metals of this group are divided into 
two classes, as follows: 

1. The noble metals, GOLD and PLATINUM. Their oxides 
are decomposed by ignition into the metal and oxygen, and 
their chlorides, into the metal and chlorine. The precipitates 
formed by hydrogen sulphide, especially if the precipitations 
have been made from hot solutions, are not soluble in boiling 
hydrochloric acid, and dissolve scarcely or not at all in boil- 
iug nitric acid. The sulphides are more difficultly soluble in 
alkali-metal sulphides, especially in ammonium sulphide, 
than are the sulphides of the ignoble metals of this group. 
When heated in a stream of chlorine, or with a mixture of 5 
parts of ammonium chloride and 1 part of ammonium nitrate, 
the sulphides give the metals. 

2. The ignoble metals, TIN, ANTIMONY, and ABSENIO. The 
oxides of these elements are not decomposed into metal and 
oxygen by ignition, and their chlorides are volatile upon heat- 
ing. The sulphides dissolve in boiling hydrochloric acid 
(with the exception of the sulphides of arsenic), and are dis- 
solved or decomposed by boiling nitric acid. When ignited 
in a stream of chlorine, or with a mixture of 5 parts of am- 
monium chloride and 1 part of ammonium nitrate, the sul- 
phides are completely volatilized. 

FIEQT DIVISION. 

Special Reactions. 

H9. 
a. GOLD, An. (Auric Oxide, Au,O,.) 

1. METALLIC GOLD has a yellow color, a very high luster, 
is rather soft, and exceedingly malleable. When precipi- 



149 '] GOLD. 2S9 

tated in the form of powder, it is brown and dull It is 
difficultly fusible, does not oxidize upon ignition in the air, 
and is insoluble in hydrochloric, nitric, and sulphuric acids. 
It dissolves somewhat in hot concentrated sulphuric acid 
containing nitric acid, and readily in fluids containing or 
evolving chlorine, e.g., in mtro-hydrochloric acid. The solu- 
tions contain auric chloride. Liquids which contain free 
bromine and iodine also dissolve gold. Fusing potassium 
disulphate does not attack it. Alkali-metal hydroxides with 
access of air, and also the nitrates, oxidize it at the temper- 
ature of fusion. It dissolves slowly in potassium cyanide 
solution, with access of air. 

2. AUEIO OXIDE (Au a O 3 ) is a blackish-brown, and its 
hydroxide is an ochre-brown or also a blackish-brown, pow- 
der. Both are reduced by light and heat, and dissolve readily 
in hydrochloric acid, but not in dilute oxygen acids. Con- 
centrated nitric and sulphuric acids dissolve a little auric 
oxide, but water reprecipitates it from these solutions. 
AUEOUS OXIDE, Au a O, is violet-black, and is decomposed by 
heat into gold and oxygen. 

3. OXYGEN SALTS of gold are practically unknown. ATIEIO 
OHLOBIDE, Au01 8? is red to brownish-red, loses chlorine at 
150 to 200, and leaves yellowish-white AUBOUS CHLOBTDE, 
AuOl, which is decomposed by stronger heating into chlorine 
and gold, and by treatment with water, into metallic gold and 
auric chloride. Auric chloride solution is brownish-red when 
concentrated, and reddish-yellow when more dilute. It shows 
a yellow coloration to a great degree of dilution. Solution of 
auric chloride reddens litmus. Hydrogen gold chloride (hy- 
drochlorauric acid), HCl.Au01,.4H 9 0, crystallizes in light 
yellow crystals, which with water give a bright yellow solu- 
tion, the so-called acid gold chloride solution. 

4. Hydrogen, sulphide precipitates the whole of the metal 
from neutral or acid solutions. The brownish-black precipi- 
tate, when precipitated cold, is GOLD SUEPEIDE, Au 9 S a (L. 
HoiMAflN and GK KBUSS). Precipitated under somewhat 
-different conditions, it is often mixed with metallic gold or 
sulphur (v. SOHBOTTEB and PBIWOZNIK). The precipitate is in- 
soluble in hydrochloric and in nitric acids, even upon heating, 
but is soluble in nitro-hydrochloric acid. It is also soluble in 



260 DEPORTMENT OF BODIES WITH REAGENTS. [ 149. 

colorless and in yellow ammonium sulphide, especially by 
heating, and more readily still in sodium sulphide or potas- 
sium sulphide, sometimes leaving behind a residue of black, 
pulverulent gold. It leaves metallic gold when ignited in a 
stream of chlorine, or with a mixture of 5 parts of ammonium 
chloride and 1 part of ammonium nitrate. 

5. Ammonium sulphide precipitates brownish-black GOLD 
SULPHIDE, Au a S a , which redissolves in an excess of the pre- 
cipitant, especially upon heating. 

6. Ammonia produces, though only in concentrated solu- 
tions of gold, reddish-yellow precipitates of AUBIC OXIDE 
combined with AMMONIA (fulminating gold). The more acid 
the solution and the greater the excess of ammonia added,, 
the more gold remains in solution. 

7* Stannous chloride, containing an admixture of stannic- 
chloride (which may be easily prepared by mixing a solution 
of stannous chloride with a little chlorine-water) produces, 
even in extremely dilute solutions of gold, a purple-red pre- 
cipitate or at least coloration, which sometimes inclines 
rather to violet or to brownish-red. This precipitate, which 
has received the name of PURPLE OF OASSIUS,* is decomposed 
by hydrochloric acid, with the separation of gold. 

8. Ferrous salts reduce auric chloride in its solutions, and 
precipitate METALLIC GOLD in the form of a most minutely 
divided, brown powder. The fluid in which the precipitate is 
suspended appears of a blackish-blue color by transmitted 
light. The dried precipitate shows metallic luster when 
pressed with the blade of a knife. If, before a small amount 
of ferrous sulphate solution is added, the auric chloride 
solution is made alkaline by a few drops of potassium or 
sodium hydroxide, a black precipitate is obtained instead 
of a dirty green one, even at a great dilution ("FT, BOSE, 
EUDOBFF). 

9. Potassium nitrite produces, even in highly dilute solu- 
tions, a precipitate of METALLIC GOLD. In very dilute solutions, 

* The much-discussed question, whether the purple of Cassias is a gold 
compound, or whether its color Is due to metallic gold contained in it in a. 
state of the finest division, has been decided in favor of the latter view, by the 
comprehensive experiments of MAX MULLBB, Journ. 1 prakt. Chem., 30 



160.] PLATINUM. 261 

the fluid at first shows only a blue color. Sulphurous acid 
also precipitates GOLD slowly in the cold, but rapidly by heating. 

10. If oxalic add is added to a gold solution which is free 
from nitric acid, and which contains little or no hydrochloric 
acid or alkali-metal chloride, the GOLD separates upon warm- 
ing, with evolution of carbonic acid, either in the form of 
brilliant scales or as a golden metallic mirror upon the sur- 
face of the glass vessel, according to the concentration of the 
solution : 2AuCl, + 3H S C 9 4 = 2Au + 6HC1 + 6CO a . 

11. All compounds of gold are reduced in the stick of 
cJiarcoal (p. 34). By triturating the charcoal afterwards, yel- 
low spangles of metal may be obtained, which are insoluble 
in nitric acid, but readily soluble in aqua regia. 

150. 
6. PLATINUM, Pt. (Plalinic Oxide, PtO t .) 

1. METALLIC PLATINUM in the compact condition has a 
light steel-gray color. It is very lustrous, moderately hard, 
very malleable, very difficultly fusible, and does not oxidize 
upon ignition in the air. Platinum sponge is dull gray, and 
precipitated platinum (platinum-black) is black and finely pul- 
verulent. Platinum is insoluble in hydrochloric, nitric, and 
sulphuric acids, but dissolves in nitro-hydrochloric acid, 
especially upon heating. When hydrochloric acid is in ex- 
cess, the solution contains hydrogen platinio chloride (hydro- 
chloroplatinic acid). Fusing potassium disulphate does not 
attack platinum, but alkali-metal nitrates oxidize it at a red 
heat, as do also the hydroxides with access of air. 

2. PLATTNIO OXIDE, PtO, , is a black powder, while ILATESIO 
EVDBOXIDE, Pt(OH) 4 , is a reddish-brown powder. Both are 
reduced by heat. The hydroxide is easily soluble in dilute 
acids and in sodium hydroxide. PLATINOUS OXIDE, PtO, is dark 
violet, its hydroxide is black, and they are both reduced by 
ignition to the metallic state. 

3. The PLATINIO OXYGEN SALTS are decomposed by ignition. 
They have a yellow or a brown color. Platinic chloride, 
PtClj.SHjO, forms red crystals, while hydrogen platinic chlo- 
ride, 2HOLPt01 4 .6H,O, forms brownish-red ones. What ia 



262 DEPORTMENT OF BODIES WITH REAGENTS. [ 150. 

usually called platinic chloride solution is the solution of 
hydrogen platinic chloride (hydrochloroplatinic acid). This 
has an acid reaction. Platinic chloride and also hydrogen 
platiuic chloride are converted into platinous chloride, Pt01 a , 
at a low red heat, and upon stronger ignition, into metallic 
platinum. A platinic chloride solution containing platinous 
chloride has a deep, dark brown color. 

4 Hydrogen sulphide gradually colors acid or neutral solu- 
tions brown, and upon continued action, black PLATINIC SUL- 
PHIDE, PtS a , is precipitated, but even after prolonged action, 
the precipitation is not complete. If the solution containing 
hydrogen sulphide is heated, the precipitate is formed at once. 
Many bodies precipitate with it readily, which by themselves 
are not precipitated in acid solutions by hydrogen sulphide, 
especially ferrous sulphide (WiLM). Alkali-metal sulphides, 
particularly when containing an excess of sulphur, dis- 
solve platinic sulphide when they are employed in large 
excess, and act with the aid of heat, but always very slowly, 
and complete solution is attained only with great difficulty. 
Hot nitric acid dissolves platinic sulphide which has been 
precipitated in the cold to a dark brown liquid, while it scarcely 
dissolves that which has been precipitated hot. Hydrochloric 
acid does not dissolve platinic sulphide, even upon heating. 
When it is ignited in a stream of chlorine or with a mixture 
of 5 parts of ammonium chloride and 1 part of ammonium 
nitrate, metallic platinum is left behind. 

5. Ammonium sulphide also produces blackish-brown pla- 
tiirie sulphide. This redissolves slowly and with difficulty in 
a large excess of the precipitant (especially if the latter con- 
tains an excess of sulphur), somewhat more readily upon heat- 
ing, but completely, only with difficulty. Acids reprecipitate 
the platinic sulphide unaltered from the reddish-brown solu- 
tion. 

6. Potassium cMoride and ammomwm chloride (and accord- 
ingly also potassium hydroxide and ammonia in presence of 
hydrochloric acid) produce in not too highly dilute solutions 
of platinic chloride, yellow, crystalline precipitates of POTAS- 
SIUM and AMMONIUM PLATINIC OHLOETDE. From dilute solutions, 
these precipitates are obtained by evaporating the fluid mixed 
with the precipitant, on the water-bath, and treating the resi- 



151.] RECAPITULATION AXD REMARKS. 263 

due with a little water or with dilute alcohol. The precipi- 
tates dissolve in acids somewhat more readily than in water, 
.and dissolve in concentrated potassium or sodium hydroxide 
upon warming. Upon ignition, ammonium platinic chloride 
leaves spongy platinum behind, while potassium platinic 
chloride leaves platinum and potassium chloride. The de- 
composition of the latter is complete only if the ignition is 
effected in a current of hydrogen gas, or with addition of 
some oxalic acid. 

7. Stannous chloride imparts to platinic solutions contain- 
ing much free hydrochloric acid, an intensely dark red to 
brownish-red color, owing to a reduction of platinic chloride 
to platinous chloride, but the reagent produces no precipi- 
tate in such solutions. 

8. Ferrous sulphate does not precipitate solution of platinic 
chloride except upon very long-continued boiling, in which 
case, the chloride ultimately suffers reduction, with the sepa- 
ration of platinum. If, however, sodium hydroxide is added 
to the platinic chloride solution after the addition of ferrous 
sulphate, and hydrochloric acid is then added, PLATINUM-BLACK 
is precipitated. 

9. If potassium iodide in excess is added to a solution of 
hydrogen platinic chloride, there is obtained a very charac- 
teristic, deep, dark red coloration, or, with very dilute solu- 
tions, a rose-red color. 

10. Oxalic acid and sulphurous acid throw down no plati- 
num from platinic chloride solutions, even upon heating. 

11. On igniting a compound of platinum mixed with sodium 
^carbonate on the loop of a platinum wire, in the upper oxidissinp 
Jlcme, a gray, spongy mass is obtained, which on trituration in 
an agate mortar yields silver-white, ductile, metallic spangles, 
insoluble in hydrochloric and in nitric acids, but soluble in 

regia. 

151. 

and SemarJcs. The reactions of gold and 
rplatinum enable us, in many cases, to detect these two metals 
^directly in the presence of many others, and especially in 
solutions containing the two metals alone. In the latter 



264 DEPOETMENT OF BODIES WITH REAGENTS. [ 162. 

case, it is best to evaporate the solution almost to dryness- 
upon the water-bath, evaporating with repeated additions of 
hydrochloric acid if nitric acid is present. The residue is 
then taken up with water, oxalic acid is added to the solution 
(which should now contain almost no hydrochloric acid), and 
it is warmed for a long time, so that the gold is completely 
precipitated. The liquid filtered from the gold is treated 
with ammonium chloride, evaporated almost to dryness, and 
the residue is treated with weak alcohol. The excess of the 
ammonium chloride and oxalic acid is thus dissolved, while 
the platinum remains behind as ammonium platinic chloride. 
If very little platinum is present, it is better to evaporate the 
liquid filtered from the gold to dryness, and to ignite the res- 
idue in order to remove the oxalic acid. The platinum re- 
mains behind in the metallic state. This is dissolved in a few 
drops of aqua regia, and the resulting solution is subjected to* 
further tests. Concerning the microscopic detection of gold 
and platinum, see HAUSHOFEB, pp. 50 and 100; BEHBENB > 
Zeitschr. f. analyt. Chem., 30, 152. 



SECOND DIVISION. 

Special Reactions. 

152. 
a. TIN, Sn, AND STANNOUS COMPOUNDS. (Stwwow Oxide, SnO.) 

1. TIN has a light grayish-white color and a high metallic 
luster. It is soft and malleable, and when bent it produces a 
crackling sound. It melts at 228.5, and boils at a white heat. 
Heated in the air, it is oxidized (but this takes place com- 
pletely only after long heatiDg), and is converted into white 
stannic oxide ; and heated on charcoal before the blowpipe, 
it forms a white incrustation. Concentrated hydrochloric 
acid dissolves tin to stannous chloride, with evolution of 
hydrogen gas ; nitro-hydrochloric acid dissolves it, according 
to circumstances, to stannic chloride or to a mixture of Stan- 
nous and stannic chlorides. Tin dissolves with difficulty in 



152.] TIN AND STANNOUS COMPOUNDS. 366 

dilute sulphuric acid ; but with the aid of heat, concentrated 
sulphuric acid in excess converts it into stannic sulphate. 
Moderately dilute nitric acid oxidizes it readily, particularly 
with the aid of heat ; but the white hydroxide formed, meta- 
stannic acid, Sn(OH) 4 , does not redissolve in an excess of the 
nitric acid. 

2. STANNOUS OXIDE, SnO, is a black or grayish-black 
powder, while stannous hydroxide is white. Stannous oxide is 
reduced to metal by fusion with potassium cyanide. It is 
readily soluble in hydrochloric acid, but nitric acid converts 
it into metastannic acid, which is insoluble in an excess of 
the acid. 

3. The STANNOUS SALTS are colorless. The oxygen salts of 
volatile acids are decomposed by heat, with the formation 
of stannic oxide where there is access of air. The soluble, 
normal salts redden litmus-paper, while those which are insol- 
uble in water dissolve in hydrochloric acid, if they have not 
been ignited. The stannous oxygen salts rapidly absorb 
oxygen from the air, and are partially or entirely converted 
into stannic salts. Stannous chloride, whether in crystals 
or in solution, also absorbs oxygen from the air, which leads 
to the formation of insoluble stannous oxychloride and stan- 
nic chloride. Hence, a solution of stannous chloride becomes 
speedily turbid if the bottle is often opened, and there is only 
little free acid present ; and none but quite recently prepared 
stannous chloride will completely dissolve in water free from 
air, while crystals of the salt that have been kept for any 
time will dissolve to a clear fluid only in water containing 
hydrochloric acid. 

4. Hydrogen sulphide throws down from neutral and acid 
solutions, a dark brown precipitate of STANNOUS SULPHIDE, SnS, 
which contains water. This reagent does not precipitate 
.alkaline solutions, at least not completely. The precipita- 
tion may be prevented by the presence of a very large quan- 
iity of free hydrochloric acid. The precipitate is insoluble, 
or nearly so, in colorless ammonium sulphide, but dissolves 
readily in the yellow sulphide. From this solution, acids pre- 
cipitate yellow stannic sulphide mixed with sulphur. Stan- 
nous sulphide also dissolves in solutions of sodium and 
potassium hydroxides. Warming accelerates the complete 



DEPORTMENT OF BODIES WITH REAGENTS. [ 152, 

solution. Acids reprecipitate it unaltered from these solu- 
tions- Boiling hydrochloric acid dissolves it, with evolution 
of hydrogen sulphide ; and boiling nitric acid converts it into 
insoluble metastannic acid. Stannous sulphide, when ignited 
in a stream of chlorine or with a mixture of 5 parts of ammo* 
mum chloride and 1 part of ammonium nitrate, is decomposed 
and completely volatilized. If the latter operation is per- 
formed in a glass tube closed at one end, the tin is found aa 
stannic chloride in the sublimate. 

5. Ammonium sulphide also precipitates hydrous STANNOU& 

SULPHIDE. 

6. Potassium hydroxide, sodium hydroxide, ammonia, and 
carbonates of the alkali metals produce a white, bulky precipi- 
tate of STANNOUS HYDROXIDE, Sn(OH) s , which redissolvea 
readily iii an excess of potassium or sodium hydroxide, but ia 
insoluble in an excess of the other precipitants. If the solu- 
tion of stannous hydroxide in potassium hydroxide is briskly 
evaporated, potassium stannate is formed, which remains in 
solution, while metallic tin precipitates ; but upon evaporat- 
ing slowly, crystalline stannous oxide separates. 

7. If a few drops of Irixmuth nitrate solution are added to a 
solution of stannous oxide in potassium or sodium hydroxide, 
there results a white precipitate, which rapidly changes into 
black bismuthous oxide (compare 141, 10). The reaction ia 
very delicate. 

8. In solutions of stannous chloride and in those of other 
stannous salts mixed with hydrochloric acid, auric chloride 
produces a precipitate which varies in color between brown, 
reddish-brown, and purple-red, according to the presence of 
more or less stannic chloride and the state of concentration 
(compare 149, 7). In very dilute solutions, merely a more- 
or less brown or red coloration is produced. 

9. Solution of mercuric chloride added in excess to solu- 
tions of stannous chloride, or of stannous oxygen salts mixed 
with hydrochloric acid, produces a white precipitate of MEB- 
CUBOUS OHLOBIDE, owing to the stannous salt withdrawing half 
the chlorine from the mercuric chloride. 

10. If a fluid containing a stannous salt and hydrochloric 
acid is added to a mixture of potassium ferrivyanide and ferric 
chloride, a precipitate of PBUSSIAN BLUE separates immediately, 



352.] TIN AND STANNOUS COMPOUNDS. 

on account of the reduction of ferric ferricyanide to ferrio 
ferrocyanide : 2Fe,(Fe a C ia N ia ) + 4HC1 + 2SnCl a = Fe 4 (FeO, 
N e ) a + H 4 Fe0 6 N fl +2Sn01 4 This reaction is extremely deli- 
cate, but it can be regarded as decisive only in cases where 
no other reducing agent is present. 

11. From neutral or slightly acid solutions of stannous 
salts, oxalic add precipitates a white, granular, quicklj- sub- 
siding precipitate of STANNOUS OXALATE, SnC,O 4 (difference 
from stannic salts). Concentrated solutions are precipitated 
immediately, but when more dilute, only after some time. 
Ammonium chloride prevents the precipitation. A solu- 
tion of a stannous salt containing ammonium chloride 
and much oxalic acid is not precipitated by hydrogen sul- 
phide. 

12. From a solution of a staimous salt which is neutral- 
ized as far as possible with potassium hydroxide, hydrogen 
peroxide, upon warming, throws down all the tin as white, 
flocculent stannic hydroxide (TV. FEEXOH). 

13. From solutions mixed with hydrochloric acid, zinc 
precipitates METALLIC TIN in the form of gray laminae or of 
a spongy mass. If the experiment is made in a platinum 
capsule, the latter is not colored black (difference from 
antimony). 

14. If stannous compounds mixed with sodium carbonate 
and some borax, or, better still, with a mixture of equal parts 
of sodium carbonate and potassium cyanide 9 or with sodium for- 
mate, are exposed on a charcoal support to the inner Uoicpipe 
flame, malleable grains of METALLIC TIN are obtained on cut- 
ting out and forcibly triturating the surrounding parts of 
charcoal with water in a small mortar, and washing off the 
charcoal from the metallic particles. Upon strongly heating 
the grains of metallic tin on a charcoal support, the latter 
becomes covered with a coating of white stannic oxide. The 
stick of charcoal (p. 34) is also admirably adapted for the 
reduction of tin. 

15. If a trace of a stannous compound is added to a borax 
bead colored slightly blue by copper, and the bead is heated 
in the lower redwing zone of the non-luminous gas-lamp flame 
(p. 32), it will become reddish-brown to ruby-red, in conse- 
quence of the formation and separation of cuprous oxide 



268 DEPORTMENT OF BODIES WITH REAGENTS. [ 

(compare 140, 15). A compound of tin is essential to this 
reaction. The blowpipe flame cannot replace that of the 
gas-lamp, since in the former, cupric oxide can be reduced to 
cuprous oxide without the presence of tin. 

16. Concerning the microchemical detection of stannous 
compounds, see HAUSHOFEB, p. 153; BEHBENS, Zeitschr. f. 
analyt. Chem., 30, 155 ; STBENG, Ber. d. deutsch. chem. Ge- 
aellsch., 1889, Kef., p. 34 



153. 
b. TIN, Sn, IN STANNIC COMPOUNDS. (Stannic Omde, Sn0 9 .) 

1. STANNIC OXIDE is a powder varying in color from white 
to straw-yellow, which upon heating transiently assumes a 
brown tint. When heated with concentrated sulphuric acid 
or fused with potassium disulphate, it gives compounds from 
which water separates all the stannic oxide. Other acids do 
not attack stannic oxide. When it is ignited with ammonium 
chloride, the tin volatilizes as stannic chloride. Stannic oxide 
forms with acids, bases, and water, two different series of 
compounds: the stannic oxide or stannic acid compounds, 
and the metastannic acid compounds. The chlorides (stan- 
nic chloride and metastannic chloride) correspond to the 
compounds with oxygen acids. The hydroxide precipitated 
from stannic chloride solution by alkalies dissolves easily in 
hydrochloric acid, but that produced by the action of nitric 
acid upon tin, metastannic hydroxide, does not dissolve in 
that acid. If the latter, however, is boiled a short time with 
hydrochloric acid, metastannic chloride, slightly soluble in 
hydrochloric acid, is formed, and if the excess of acid is now 
poured off and water is added, a solution of metastannic 
chloride, usually somewhat opalescent, results. 

2. The STANNIC OXYGEN SALTS are colorless. The solutions 
of the normal salts redden litmus. The oxygen salts with 
volatile fccids are easily decomposed by ignition. Anhy- 
drous STANNIC CHLOBIDE, SnCI 4 , is a volatile liquid, strongly 
fuming in the air. It dissolves in cold water to stan- 
nic chloride solution. This is not precipitated by concen- 



163.] TIN IW STANNIC COMPOUNDS. 

trated hydrochloric acid nor by sulphuric acid, unless it 
is very dilute, and it does not become yellow upon the 
addition of stannous chloride. The aqueous solution of 
metastannic chloride, on the other hand, is precipitated by 
concentrated hydrochloric acid and by sulphuric acid, and 
is colored yellow by stannous chloride. The dilute solutions 
of both chlorides are precipitated by boiling, and this takes 
place very rapidly with metastannic chloride, 

3. By fusing stannic oxide, stannic hydroxide, or meta- 
stannic hydroxide with alkali-metal hydroxides, STANN^TBS 
soluble in water are formed, from the solutions of which, 
acidc (even carbonic acid) separate stannic hydroxide. By 
fusing with alkaline carbonates, only a part of the stannic 
oxide is converted into stannate. 

4u In stannic chloride solutions containing a moderate 
amount of free hydrochloric acid, hydrogen sulphide acting in 
excess produces a light yellow precipitate of STANNIC SULPHIDE, 
SnS a , which contains stannic hydroxide, and does not 
change in color. In more dilute or less acid solutions, the 
precipitate is not always formed immediately, and it gradu- 
ally becomes more intensely yellow. In very dilute solu- 
tions containing no free acid, the precipitate produced after 
some time is at first white, but afterwards yellow. Warming 
facilitates the precipitation. Alkaline solutions are not pre- 
cipitated, and a great amount of free hydrochloric acid like- 
wise prevents the precipitation. Oxalic acid, also, added in 
sufficient amount (35 to 40 parts of oxalic acid to 1 part of 
tin), prevents the precipitation (difference from antimony 
and arsenic, CLABKE, LESSEE). The precipitate dissolves 
with some difficulty in ammonia, is nearly insoluble in am- 
monium carbonate, and insoluble in hydrogen potassium 
sulphite. It dissolves readily in potassium and sodium 
hydroxides, in alkaline sulphides, in concentrated, boiling 
hydrochloric acid, and also in aqua regia. The precipitate 
produced in metastannic chloride solutions by hydrogen 
sulphide, viz., stannic sulphide containing metastannic hy- 
droxide, is formed slowly, especially in dilute solutions. 
It becomes more or less brown upon long standing under 
the liquid. An excess of sodium hydroxide dissolves the 
stannic sulphide out of it, leaving behind undissolved sodium 



270 DKl'OUTMKIMT Otf BODIES WITH REAGENTS. [ 15& 

rnetastannate (BABFOED). Concentrated nitric acid converts 
all the precipitates produced by hydrogen sulphide into 
metastannic hydroxide. When ignited with a mixture of 5 
parts of ammonium chloride aad 1 part of ammonium 
nitrate, the precipitates behave in the same way as stannous. 
sulphide ( 152, 4). Upon deflagrating them with sodium 
nitrate and carbonate, sodium sulphate, stannic oxide, and 
some sodium stannate are obtained. If a solution of stannic 
sulphide in potassium hydroxide or sodium hydroxide is 
boiled with bismuth oxide or cupric oxide, sulphides of the 
latter metals are formed, while an alkaline stannate remains, 
in solution. 

5. Ammonium sulphide produces yellow, hydrous STANNIC 
SULPHIDE, which dissolves readily in an excess of the precip- 
itant. Prom this solution, acids reprecipitate the stannic 
sulphide unaltered. 

6. Potassium and sodium hydroxides give, in stannic 
chloride solutions, white precipitates of STANNIC ETDBOXIDE, 
which dissolve readily in an excess of the precipitant. From 
metastannic chloride solutions, potassium hydroxide throws 
down METASTANNIO HYDROXIDE, which dissolves in a moderate 
excess of the precipitant. With a larger excess, potassium 
metastannate separates, which is difficultly soluble in potas- 
sium hydroxide, but soluble in water. From metastannic 
chloride solutions, sodium hydroxide precipitates white 
SODIUM METASTANNATE, which does not dissolve in an excess of 
sodium hydroxide. Stannic hydroxide as well as metastannic 
hydroxide, when dried over sulphuric acid, have a composi- 
tion corresponding to the formula SnO(OH),. 

7. Potassiwn carbonate gives a white precipitate in a 
stannic chloride solution. The precipitate, STANNIC HIDBOX- 
XDE, containing potassium, dissolves in an excess of the 
reagent, but separates again upon standing. The pre- 
cipitate by sodium carbonate does not dissolve in an excess of 
the precipitant The white precipitates which alkali-metal 
carbonates produce in metastannic chloride solutions dissolve 
scarcely or not at all in an excess of the precipitants. 

8. Sodium sulphate or ammonium nitrate (in fact, most 
normal alkali-metal salts, when added in excess) throws down 
from both kinds of stannic solutions, provided they are not too 



154.] ANTIMONY. 271 

add, the whole of the tin as STANNIC or METASTANKIC HYDROXIDE. 
Heating promotes the precipitation : Sn01 4 + 4Na 9 S0 4 + 
4H,O = Sn(OH) 4 + 4NaCl + 4NaESO 4 . 

9. From solutions of stannic chloride, in the presence of 
free acid, metallic zinc precipitates METALLIC TIN in the shape 
of small, gray scales or as a spongy mass. If the operation 
is conducted in a platinum dish, no blackening of the latter 
is observed (difference from antimony). 

10. If a stannic chloride solution is boiled for a long time 
with metallic copper,* the stannic chloride is reduced to 
stannous chloride, and .the solution then precipitates mer- 
curous chloride from mercuric chloride solution (PATTTSON 
Mum). 

11. Before the 'blowpipe or in the gas flame, the stannic 
compounds show the same reactions as the stannous com- 
pounds (compare 152, 14 and 15). Stannic oxide is also 
readily reduced when fused with potassium cyanide in a glass 
tube or in a crucible. 

12. In relation to the detection of stannic compounds by 
microchemical methods, see HAUSHOFER, p. 156; BEHBENS, 
Zeitschr. f. aaalyt. Chem., 30, 155; STBENG, Ber. d. deutsch. 
chem. Qesellsch. 1889, Ref., p. 34. 

154 
c. ANTIMONY, Sb. (Antimonious Oxide, Sb,O t .) 

1. METALLIC ANTIMONY has a bluish tin-white color, is 
lustrous, hard, brittle, fusible at 430, and volatile at a very 
high temperature. When heated on charcoal before the 
blowpipe, it emits thick, white fumes of antimonious oxide, 
which form a coating on the charcoal. This combustion con- 
tinues for some time, even after the removal of the metal 
from the flame; and is most distinctly visible if a strong 
current of air is thrown by the blowpipe directly upon the 
sample on the charcoal. But if the fames ascend straight, 
the hot, metallic bead becomes surrounded with a net of 
brilliant, acicular crystals of antimonious oxide. Nitric acid 
oxidizes antimony readily. The dilute acid converts it aJmo,c+ 
entirely into antimonious oxide, while the more concentrated 



272 DEPORTMENT OF BODIEd WITH REAGENTS. [ Jft4. 

the acid the more antimonic oxide (metantimonic acid) is 
formed, and the boiling, concentrated acid converts it almost 
completely into antimonic oxide. Neither of the two oxides 
is altogether insoluble iu nitric acid ; consequently, traces of 
antimony are always found in the acid fluid filtered from the 
precipitate- Even boiling hydrochloric acid, with exclusion 
of air, does not attack antimony. In nitro-hydrochloric acid, 
the metal dissolves readily, the solution containing antimoni- 
ous chloride, Sb01 3 , or antimonic chloride, SbCl B , according 
to the degree of concentration of the acid and the duration 
of the action. 

2. According to the mode of its preparation, ANTIMONIOUS 
OXIDE, Sb,0 3 , occurs in white and brilliant crystalline needles, 
or as a white powder. It fuses at a moderate red heat out 
of contact with air, and at a higher temperature, it volatilizes 
without decomposition. It is insoluble in water, almost 
insoluble in nitric acid, but dissolves readily in hydrochloric 
and tartaric acids* No separation of iodine takes place on 
boiling it with hydrochloric acid free from chlorine and 
potassium iodide free from iodic acid (BuNSEN). Antimoni- 
ous oxide is easily reduced to metal by fusion with potassium 
cyanide. 

3. ANTIMONIO OXIDE (or AGED), Sb 9 6 , is pale yellow. It 
forms three hydroxides with water: orthoantimonic acid, 
H,Sb0 4 ; pyroantimonic acid, H 4 Sb,0,; and metantimonic acid, 
HSbO,. These hydroxides are white, and they redden moist 
litmus-paper. The anhydrous acid and its hydrates scarcely 
dissolve in water, they are almost insoluble in nitric acid, 
but they dissolve rather readily in hot, concentrated" hydro- 
chloric acid, forming a solution containing antimonic chlo- 
ride, SbCl , which becomes turbid upon the addition of water. 
On boiling antimonic acid with hydrochloric acid and potas- 
sium iodide, iodine separates, which dissolves in the hydriodic 
acid present to a brown fluid (BTOBEN). Upon ignition, anti- 
monic acid loses oxygen, and is converted into infusible 
JLNTCMONIOUS ANTEMONATE, Sb a 4 . The potassium antimonates, 
pyroantimonates, and metantimonates are only partly soluble 
in water. Acids precipitate from the solutions the correspond- 
ing antimonic acids, and sodium chloride precipitates acid 



164.] ANTIMONY. 273 

sodium pyroantimonate from a solution of acid potassium 
pyroantimonate ( 95, 2). 

4. The ANTIMONIOUS SALTS of volatile oxygen acids are 
decomposed by ignition. The halogen salts are readily vola- 
tile without decomposition. The soluble, normal antimoni- 
ous salts redden litmus-paper. With a large quantitv of 
water, they are decomposed, with formation of insoluble basic 
salts and acid solutions containing antimony. Thus, water, 
when added in considerable amount, throws down from 
solutions of antimonious chloride in hydrochloric acid, 
a white, bulky precipitate of ANTIMONIOUS OXYCHLORIDE, 
Sb 4 B Cl, (powder of Algaroth), which soon becomes heavy 
and crystalline. Tartaric acid dissolves this precipitate 
readily, and therefore prevents its formation if mixed with 
the solution previously to the addition of the water. It 
is this property that distinguishes this antimony compound 
from the basic bismuth salts formed under similar cir- 
cumstances. 

5. From acid solutions of antimonious salts (if the quantity 
of free mineral acid present is not too large), hydrogen sulphide 
precipitates the whole of the metal as orange-red, amor- 
phous ANTIMONIOUS SULPHIDE, Sb 9 S,. In alkaline solutions, 
this reagent fails to produce a precipitate, or, at least, it pre- 
cipitates them only imperfectly ; and in neutral solutions, also, 
the metal is only partially thrown down by it. The antimoni* 
ous sulphide produced is readily dissolved by potassium or 
sodium hydroxide and by alkali sulphides, especially if the 
latter contain an excess of sulphur. It is dissolved to a 
slight extent by ammonia, but if free from antimonic sulphider 
it is almost insoluble in ammonium bicarbonate. It is in. 
soluble in cold, dilute acids and in acid potassium sulphite. 
Concentrated hydrochloric acid of 1.18 sp. gr. dissolves it 
even in the cold, with evolution of hydogen sulphide, and, 
upon heating, it dissolves even in the acid of 1,12 sp. gr. 
Upon heating in the air, the precipitate gives a mixture of 
antimonious antimonate and antimony sulphide. If it is 
deflagrated with sodium nitrate, sodium sulphate and pyro- 
antimonate are obtained. Ignited in a stream of chlorine or 
with a mixture of 5 parts of ammonium chloride and 1 part 
of ammonium nitrate, antimony sulphide is decomposed and 



274 DEPORTMENT OF BODIES WITH KEAGEOTS. [ 154. 

completely volatilized. If the latter operation takes place in 
a glass tube closed at one end, antimonious chloride is found 
in the sublimate. % If the solution of antimonious sulphide in 
potassium hydroxide or potassium sulphide is boiled with 
bismuth oxide, bismuth sulphide is formed, and antimonious 
oxide remains dissolved in potassium hydroxide ; and if the 
alkaline solution is boiled with cupric oxide, cuprous sulphide 
is produced, and the solution then contains potassium 
pyroantimonate. On fusing antimoiiious sulphide with po- 
tassium cyanide, metallic antimony and potassium sulpho- 
'cyaiiide are formed. If the operation is conducted in a 
small tube expanded into a bulb at the lower end, or in a 
stream of carbon dioxide (see 105, 13), no sublimate of anti- 
aiony is produced. But if a mixture of antimonious sul- 
phide with sodium carbonate or with potassium cyanide and 
sodium carbonate is heated in a glass tube in a stream of 
hydrogen gas (compare 155, 4), a mirror of antimony is 
deposited in the tube, immediately beyond the spot occu- 
pied by the mixture. 

From a solution of antimonio acid in hydrochloric acid, 
hydrogen sulphide throws down ANTIMONIC SULPHIDE, Sb 9 S , 
mixed with antimonious sulphide and sulphur. The precipi- 
tate dissolves readily when heated with solution of caustic 
soda or ammonia, and easily in concentrated, boiling hydro- 
chloric acid, with evolution of hydrogen sulphide and separa- 
tion of sulphur, but it dissolves only very sparingly in a cold 
solution of hydrogen ammonium carbonate. 

6. Ammonium sidphide produces in solutions of antimoni- 
ous salts, an orange-red precipitate of ANTIMONIOUS SULPHIDE, 
which readily redissolves in an excess of the precipitant if 
the latter contains an excess of sulphur. Acids throw down 
from this solution antimonic sulphide, Sb 3 S 6 . However, in 
that case, the orange color usually appears of a lighter tint, 
owing to an admixture of sulphur. 

7. If aqueous sulphurous acid is added to a solution of 
sodium thiosulphate (whereupon the solution becomes yellow- 
ish), and then some solution of an antunonious salt is also 
added, and the liquid is heated to boiling, it at first becomes 
turbid from the separation of sulphur, then the antimony 
separates as red ANTIMONY CINNABAR, Sb,8,O. 



154] ANTIMONY. 275 

8. From solutions of antimonious chloride, and also of 
other simple antimonious salts but far less completely, and 
mostly only after some time, from solutions of tartar emetic or 
analogous compounds -potassium hydroxide, sodium hydroxide, 
ammonia, sodium carbonate, and ammonium carbonate throw down 
a white, bulky precipitate of ANTEKONIOUS EYDBOXIDE, which re- 
dissolves rather readily in an excess of potassium or sodium 
hydroxide, but requires the application of heat for its resolu- 
tion in sodium carbonate, and is almost insoluble in ammonia. 

9. From all solutions of antimonious salts, if they contain 
no free nitric acid, metallic zinc and likewise metallic tin 
(PIESZOZEE) precipitate METAT.T.TO ANTIMONY as a black powder. 
If a few drops of a solution of antimony containing some free 
hydrochloric acid are put into a platinum capsule (the lid of a 
platinum crucible), and a fragment of zinc or tin is introduced, 
hydrogen containing hydrogen antimonide is evolved, and 
antimony separates, staining the part of the platinum covered 
by the liquid brown or black, even in the case of very dilute 
solutions. This reaction is to be highly recommended as 
equally delicate and characteristic. Cold hydrochloric acid 
of 1.12 sp. gr. soon removes the stain if it is very faint, but it 
removes it slowly and only upon warming if it is strong, 
while heating with nitric acid removes it immediately. 

10. If the solution of an antimonious salt containing some 
hydrochloric acid is warmed with bright iron, e.g., a piece of 
-wire, all the antimony separates in a short time, with evolu- 
tion of hydrogen, in the form of heavy, black flocks (difference 
from tin). 

11. If a solution of antimonious oxide in potassium or 
sodium hydroxide is mixed with a solution of silver nitrate, a p 
deep black precipitate, which was formerly believed to be 
argentous oxide, forms with the grayish-brown precipitate of 
argentic oxide. Upon now adding ammonia in excess, the 
latter is redissolved, while the black precipitate is left nndis- 
solved (H. BOSH). According to the investigations of PTLUTZ, 
this is a variable mixture of antimony and silver, which may 
perhaps contain a chemical compound of both. This exceed- 
ingly delicate reaction affords an excellent means of detecting 
Antimonious oxide in presence of antimonio acid. 

12. If any solution of antimony in hydrochloric or sul- 



276 DEPORTMENT OP BODIES WITH REAGENTS. [ 164. 

phuric acid is introduced into a flask in which hydrogen gas. 
is being evolved from pure zinc and dilute sulphuric acid, the 
zinc produces a reduction of the antimony compound in ad- 
dition to the evolution of hydrogen. Antimony separates in 
the metallic state, but another portion pf the metal combines 
with hydrogen, forming HIDEOGEN AMIMONIDE GAS, SbH,. If 
this operation takes place in the apparatus which is used 
for MABSH'S test for arsenic ( 155, 10), and after all the air 
has been expelled, the gas which is escaping from the fine 
opening is ignited,* the flame appears bluish-green from the 
antimony, separated by the decomposition of the hydrogen 
antimonide, burning in the flame. White fumes of antimoni- 
ous oxide rise from it, which are readily deposited upon cold 
bodies and do not dissolve in water. However, if a cold 
body (a porcelain dish is best) is held in the flame, METALLIC 
ANTIMONY f is deposited upon it in an extremely fine state of 
division, forming a deep black and almost lusterless spot. If 
the middle part of the tube through which the gas is passing 
is heated to redness, the bluish-green tint of the flame decreases 
in intensity, and a metallic mirror of antimony of silvery lus- 
ter is formed within the tube, on both sides of the heated part. 
As compounds of arsenic give under the same circum- 
stances similar stains or mirrors ( 155, 10), it is always 
necessary to examine carefully the spots produced, in order 
to ascertain whether they really consist of antimony or con- 
tain any of that metal. With stains deposited on a porcelain 
dish, the object in view is most readily attained by treating 
them with a solution of sodium hypochlorite and sodium chlo- 
ride (prepared by mixing a solution of calcium hypochlorite 
with sodium carbonate in some excess, and filtering), which 
will immediately dissolve arsenical stains, leaving those pro- 
ceeding from antimony untouched, or at least removing them 
only after a very protracted action. A mirror within the glass. 
tube, on the other hand, may be tested by heating it while 
the current of hydrogen gas still continues to pass through 
the tube. If the mirror volatilizes only at a rather high tem- 

* The coloration of the flame appears especially distinct and puie when the 
gas escapes from a platinum jet. 

f Whether this is actually antimony or perhaps solid hydrogen antimonide 
requires further investigation (J. W. RKTOEHS) 



154.] ANTIMONY. 377 

perature, and the hydrogen gas then issuing from the tube 
does not smell of garlic, and if it is only with a strong current 
that the ignited gas deposits spots on porcelain, and the 
mirror before volatilizing fuses to small, lustrous globules dis- 
tinctly discernible through a magnifying glass, the presence of 
antimony may be considered certain. Moreover, the metals 
may be distinguished with great certainty by conducting 
through the tube a very sloiv stream of dry hydrogen sulphide, 
and heating the mirror moderately, proceeding in an opposite 
direction to that of the current. The autimonial mirror is by 
this means converted into antimonious sulphide, which ap- 
pears of a more or less reddish-yellow color, but looks black if 
it becomes crystalline. If a feeble stream of dry hydrochloric 
acid gas is now transmitted through the glass tube, the anti- 
monious sulphide, if present in thin layers only, disappears 
immediately; while if the incrustation is somewhat thicker, 
it takes a short time to dissipate it. The reason for this is 
that the antimonious sulphide decomposes readily with hydro- 
chloric acid, and the antimonious chloride formed is exceed- 
ingly volatile in a stream of hydrochloric acid gas. If the 
gaseous current is now conducted into some water, the pres- 
ence of antimony in the latter fluid may be readily proved by 
means of hydrogen sulphide. By this combination of reac- 
tions, antimony may be distinguished with positive certainty 
from all other metals. The reactions which hydrogen gas 
containing hydrogen antimonide shows with solutions of sil- 
ver nitrate and mercuric chloride, and with solid potassium 
hydroxide, will be found in 157, 7. 

13. If a solution of antimonious oxide in potassium or 
sodium hydroxide is heated with aluminium or with amc and a 
little magnesium, all the antimony separates, and hydrogen is 
evolved. Hydrogen antimouide does not go off iu this case 
(difference from arsenious acid, which gives hydrogen arsen- 
ide when subjected to this treatment, HAGEB, GACTHOUSE). 

14 If a mixture of a compound of antimony with sodium 
carbonate and potassium cyanide or with sodium formate is 
exposed on a charcoal support to the reducing flame of tfa 
bloiopipe, brittle globules of METALLIC ANTIMONY are produced, 
which may be readily recognized by the peculiar reactions 
that mark their oxidation (compare 154, 1). 



S78 DEPORTMENT OF BODIES WITH BEAGENTS. [ 155. 

15. In the upper reducing flame of the gas-lamp (p. 32), 
compounds of antimony give a greenish-gray color, and no 
odor. The metallic incrustation is black, sometimes dull, 
sometimes bright. The incrustation of oxide is white. When 
moistened with entirely neutral silver nitrate and then blown 
on with ammonia, it gives a black spot (ButfSEN). 

16. In relation to the microchemical detection of anti- 
mony, see HAUSHOFER, p. 14; BEELRENS, Zeitschr. L analyt. 
Chem., 30, 163, 



155. 

d. ARSENIC, As, and ARSENIOUS COJIPOTODS. 
(Arsenious Oxide or Add, 



1. jMETAUic ARSENIC, in a microcrystalline condition, is 
black (J, W. BETGERS), but when it is in distinct crystals, it is 
steel-gray, and has a high luster, which it retains in dry air, 
hut loses in moist air by becoming superficially oxidized. 
The metallic arsenic of commerce is therefore commonly 
dull, with a dim, bronze luster on the planes of crystallization. 
Arsenic is not very hard, but very brittle, and at a dull red heat, 
under ordinary pressure, it volatilizes without fusion. The 
fumes escaping into the air have a most characteristic odor 
of garlic, which is ascribed to a suboxide of arsenic occurring 
in a state of vapor. Heated with free access of air, arsenic 
burns at an intense heat, with a bluish flame emitting 
white fumes of arsenious oxide, which condense on cold 
bodies. If arsenic is heated in a glass tube sealed at the 
lower end, the greater part of it volatilizes unoxidized ; and 
if it is heated in a stream of carbonic acid, it volatilizes wholly 
unoxidized, and recondenses above or beyond the heated spot 
as a sublimate (arsenical mirror). This is usually brilliantly 
gray next to the heated part (crystalline), and beyond this it is 
black (microcrystalline). Upon heating in a stream of hydro- 
gen, in addition to the arsenic mirror, a more volatile, Jbrown 
sublimate of solid hydrogen arsenide is formed (BETGERS). In 
contact with air and water, arsenic oxidizes slowly to arseni- 
<OUH acid. Weak nitric acid converts it, with the aid of heat, 



$ 155,] ARSENIC AND ARSENIOUS COMPOUNDS. 

into arsenious oxide, winch dissolves only sparingly in an ex- 
cess of the acid ; but strong nitric acid converts it partially 
into arsenic acid. It is insoluble in hydrochloric acid and 
dilute sulphuric acid, while concentrated, boiling sulphuric 
acid oxidizes it to arsenious oxide, with evolution of sulphur 
dioxide. It dissolves in aqua regia easily to arsenic acid. 

2. ABSENIOUS OXIDE or ACID, in the amorphous condition, is a 
colorless, transparent, glassy mass. In the crystalline con- 
dition, it forms a white, porcelain-like mass or occurs also 
in well-formed crystals. When pulverized, it appears as a 
heavy, white, gritty powder. When heated, it volatilizes in 
white, inodorous fumes. If the operation is conducted in a 
glass tube, a sublimate is obtained, consisting of small, 
brilliant octahedrons and tetrahedrons. Arsenious acid is 
only difficultly moistened by water, and comports itself in 
this respect like a fatty substance. It is sparingly soluble in 
cold, but more readily in hot water. It is copiously dissolved 
by hydrochloric acid, as well as by solutions of potassium 
and sodium hydroxides. Upon boiling with nitro-hydro- 
chloric acid, it dissolves to arsenic acid. It is highly 
poisonous. 

I a small fragment of arsenious oxide is placed in the 
point of a drawn-out glass tube (Fig. 36), and a splinter of 
diwcoal, broken from a piece that has been freshly ignited, 




Fio. 36. 



is placed above it, and the latter is first heated to redness 
and then the arsenious oxide is also heated, the vapors 
of the arsenious oxide are reduced by the red-hot charcoal, 
and a MIBROB OF METALLIC ABSBNIO is obtained. If the tube 



280 DEPORTMENT OF BODIES WITH REAGENTS. [ 

is now cut off between a and c, and is heated in an inclined' 
position (with c at the top), the arsenic is volatilized, giving 
the garlic-like odor. This is the simplest as well as the 
surest method of detecting pure arsenious acid. 

3. The ABSENITES are mostly decomposed upon ignition, 
either into arsenates and metallic arsenic which volatilizes,, 
or into arsenious oxide and the base with which it was com- 
bined. Of the arsenites, only those with alkali bases are 
soluble in water. The insoluble arsenites are dissolved, or 
at least decomposed, by hydrochloric acid. Anhydrous 
ABSENIOUS CHLOBIDE, AsCl a , is a colorless volatile liquid, fum- 
ing in the air, which will bear the addition of a little water, 
but is decomposed by a larger amount into arsenious oxide, 
which partly separates, and hydrochloric acid, which retains 
the rest of the arsenious oxide in solution. If a solution of 
arsenious oxide in hydrochloric acid is evaporated by heat, 
arseuious chloride escapes along with the hydrochloric acid. 
Wlieu such a solution is heated in a distilling apparatus, the 
arsenic is obtained in the form of arsenious acid in the 
distillate, which also contains hydrochloric acid. If the 
distillation is repeated with renewed additions of fuming 
hydrochloric acid, all the arsenious acid is obtained iu 
the distillate. 

4. Hydrogen sulphide colors aqueous solutions of arsenious 
acid yellow, but produces no precipitate in them. It fails 
equally to give a precipitate in aqueous solutions of normal 
alkali arsenites, but upon addition of a strong acid, a bright 
yellow precipitate of ABSENIOUS SULPHIDE, As a S t , forms at once. 
The same compound forms in like manner in the hydro- 
chloric acid solution of arsenites insoluble in water. Even 
a large excess of concentrated hydrochloric acid does not 
prevent complete precipitation. Alkaline solutions are not 
precipitated. Arsenious sulphide is readily and completely 
dissolved by alkalies, normal alkali carbonates, and also by 
alkali sulphides. Freshly precipitated arsenious sulphide 
is also soluble in alkali-metal acid sulphites. It is nearly 
insoluble in hydrochloric acid, even though concentrated and 
boiling. Boiling nitric acid decomposes and dissolves the 
sulphide readily. 

The deflagration of arsenious sulphide with sodium car- 



155.] ARSENIC AND ARSENIODS COMPOUNDS. 281 

bonate and nitrate gives rise to the formation of sodium 
arsenate and sulphate. "When it is heated with a mixture of 
5 parts of ammonium chloride and 1 part of ammonium 
nitrate, in a glass tube, complete volatilization takes place. 
The arsenic is found in the sublimate as arsenious chloride. 
When a solution of arsenious sulphide in ammonia is heated 
with an excess of hydrogen peroxide, a clear liquid is pro- 
duced, containing ammonium sulphate and arsenate. Upon 
boiliug a solution of arsenious sulphide in sodium sulphide, 
or, also, in potassium or sodium hydroxide, with bismuth 
hydroxide, carbonate, or basic nitrate, bismuth sulphide and 
potassium (or sodium) arsenite are produced. By boiling 
such a solution with cupric oxide, cuprous sulphide and 
sodium (or potassium) arsenate are formed. 

If arsenious sulphide is mixed with 3 or 4 parts of sodium 
carbonate, with the addition of a little water, the pasty mass 
is then spread out upon small fragments of glass, and after 
this has been well dried, it is quickly heated to redness in a 
glass tube through which dry hydrogen is being passed, the 
greater part of the arsenic will be reduced and driven off if 
the temperature is high enough. A part of that which is 
driven off is obtained as a metallic mirror in the tube, and the 
more volatile, brown sublimate of solid hydrogen arsenide is 
likewise formed. The rest of the arsenic escapes as gaseous 
hydrogen arsenide with the hydrogen, and when the latter is 
ignited, it gives a bluish color to the flame, and, when a porce- 
lain dish is held in the latter, causes the production of 
brownish-black stains of solid hydrogen arsenide (KETOERS). 
This method of reduction gives accurate results, but does not 
permit the distinction of arsenic from antimony with suf- 
ficient certainty, or the detection of the former in the pres- 
ence of the latter (compare 154, 5), and the method is there- 
fore generally replaced by the reducing operation described 
in 155, 13. 

5. Ammonium sulphide also causes the formation of ABSENI- 
ous SULPHIDE. In neutral and alkaline solutions, however, 
the arsenious sulphide does not precipitate, but remains 
dissolved as ammonium sulpharsenite, yet from this solu- 
tion, it precipitates immediately upon the addition of a free 
acid. 



282 DEPORTMENT OF BODIES WITH REAGENTS. [ 155: 

6. Silver nitrate, added in slight excess, leaves aqueous, 
solutions of arsenious acid perfectly clear, or at least pro* 
duces onlj a trifling yellowish-white turbidity in them ; but if 
a little ammonia is added, a yellow precipitate of SILVER ARSEN- 
ITE, Ag a AsO, , separates. Upon the addition of silver nitrate 
to the solution of a normal alkali-metal arsenite, an almost 
white precipitate is formed, which becomes yellow only upon 
the addition of a little potassium hydroxide. Silver arsenite 
dissolves readily in nitric acid as well as in ammonia when 
some alkaline nitrate is present, and is not insoluble in ammo- 
nium nitrate. If, therefore, a small quantity of the precipitate 
is dissolved in a large amount of nitric acid, and the latter is 
afterwards neutralized with ammonia, the precipitate does not, 
make its appearance again, since it remains dissolved in the 
ammonium nitrate formed. The reaction is produced most 
delicately by adding a layer of ammonia upon the top of the 
liquid to which silver nitrate has been added. The precipi- 
tate then appears at the point of contact of the two liquids as 
a yellowish zone. If a solution of arsenious acid is heated to 
boiling after the addition of a small excess of silver nitrate- 
and a moderate excess of ammonia, METALLIC SILVER separates,, 
while the arsenious acid is converted into arsenic acid. 

7, ' Gupric sulphate does not produce a precipitate in 
aqueous solutions of arsenious acid, but upon the addition of' 
an alkali, a yellowish-green precipitate of OUPRIO ARSENITE, 
CuHAsO, , is produced. This dissolves in potassium hydrox- 
ide as well as in sodium hydroxide to a blue liquid, from which 
cuprous oxide separates upon boiling (^compare 8). 

8. If arsenious acid is dissolved in an excess of potassium 
or sodium hydroxide, or if potassium or sodium hydroxide is 
added in excess to the solution of an alkaline arsenite, and a 
small amount of a very dilute solution of eupric sulphate is 
then added, a clear, blue solution is obtained, which upon 
boiling gives a red precipitate of CUPROUS OXIDE. The solu- 
tion contains potassium or sodium arsenate. This reaction 
succeeds easily, and is exceedingly delicate provided not too, 
much of the eupric sulphate is used. Even should the red 
precipitate be so exceedingly minute as to escape detection 
when looking across the tube, yet it will always be discerni- 
ble with great distinctness upon looking down the test-tube^ 



155.] ARSENIC AND AKSENIOUS COMPOUNDS. 

Although this reaction is really of great importance in certain 
instances as a confirmatory proof of the presence of arsenious. 
acid, and more particularly, also, as a means of distinguish- 
ing that acid from arsenic acid, yet it is entirely inapplicable 
for the direct detection of arsenic, since grape-sugar and other 
organic substances produce cuprous oxide from cupric salts 
in the same manner. 

9. If a solution of arsenious oxide mixed with hydrochloric 
acid is heated with a perfectly clean strip of copper or copper 
wire, an iron-gray, metallic film is deposited on the copper, 




FIG. 87. 

even in highly dilute solutions; and when this film increases 
in thickness, it peels off in black scales. If after washing off 
the free acid, the coated copper is heated with solution of am- 
monia, the film peels off from the copper, and separates in 
the form of minute spangles (EEINSOH). These are not pure 
arsenic, but consist of COPPBE AESENIDE, CU.AS,. If the sub- 
stance, either simply dried or oxidized by ignition in a cur- 
rent of air (which is attended with escape of some arsenious 
acid), is heated in a current of hydrogen, there escapes rela- 
tively but little arsenic, alloys richer in copper being left 
behind (FBBSENira, LIPPEBT). Only after the presence of ar- 
aenic in the alloy has been fully demonstrated, can this 



284 DEPORTMENT OF BODIES WITH KEAGEiNTS. [ 155. 

tion be considered a decisive proof of the presence of that 
metal, as under the same circumstances, antimony and other 
metals ^rill also precipitate in a similar manner upon copper, 
and a black coating is formed upon the copper in the presence 
of sulphurous acid. 

10. If an acid or neutral solution of arsenious acid or any 
of its compounds is mixed with zinc, water, and dilute svdphuric 
odd or hydrochloric acid, HYDEOGEN ARSENIDE, AsH, , is formed, 
in the same manner that compounds of antimony give hy- 
drogen antimonide under analogous circumstances (compare 
154, 12). This reaction affords a means for the detection of 
even the most minute quantities of arsenic. The operation 
is conducted in the apparatus illustrated in Fig. 37, or in one 
of similar construction.* a is the evolution-flask; 4, a bulb 
intended to receive tbe water carried with the gaseous cur- 
rent ; c, a tube filled with cotton wool and small lumps of 
calcium chloride for drying the gas.t This tube is connected 
with 6 and d by rubber tubes which have been boiled in 
a solution of sodium hydroxide; d should have an inner 
diameter of 7 mm (Fig. 38), and must be made of 
difficultly fusible glass, free from lead and as free as 
possible from arsenic. In experiments requiring 
great accuracy, the tube should be drawn out as shown 
FIG. 88. . - ,r sma ji a q uan tity of zinc, as pure 




as possible, but in any case entirely free from arsenic,:): is 
placed in the evolution-flask, water is poured through the 
funnel-tube until the end of it is covered, and then pure sul- 
phuric acid diluted with 3 parts of water is added gradually 
through the funnel-tube, so that a uniform and moderate 
stream of hydrogen is produced. As soon as it is certain 

*I prefer tbe very convenient form of MARSH'S apparatus, which IB 
recommended by F. J. OTTO. 

t A bulb-tube containing a little concentrated sulphuric add may also be 
used for drying the gas (LYTTKBNS, LENZ). 

J Since zinc which Is entirely free from other metals evolves hydrogen 
with dilate sulphuric acid only very slowly, it was formerly customary to add 
a trace of platinic chloride to the liquid, which causes a lively evolution of 
hydrogen to take place at once But since, according to TBOTELE, the delicacy 
of tbe arsenic reaction is thus diminished, it is more advisable to use zinc con- 
taining a trace of iron, such as is obtained when molten zinc is stirred with 
an iron rod (L. L'H&rs). 



155.] ARSENIC AND ARSENIOUS COMPOUNDS. 286 

that all the air has been driven out of the apparatus, the gas 
escaping from the tube d is ignited. It is advisable to wrap 
a towel around the flask before kindling the gas, to guard 
against accidents in case of an explosion. It is first abso- 
lutely necessary to ascertain whether the zinc and the sul- 
phuric acid are quite free from any admixture of arsenic. This 
is done by depressing a porcelain dish horizontally upon the 
flame, in order to make it spread over the surface ; and if the 
hydrogen contains hydrogen arsenide, brownish or brownish- 
black stains of solid hydrogen arsenide will appear on the 
porcelain. If this is not the case, in addition to the above 
test, in accurate experiments, the part of the tube d shown in 
the figure is heated to redness for some time, to see whether 
the arsenic coating does not show itself at the narrowed part 
of the tube. When it is certain that the hydrogen is pure, 
the liquid to be tested for arsenic is poured through the 
funnel-tube, and the latter is rinsed with water. It is to be em- 
jphaticaHy recommended that only a very little of the liquid to 
be tested should be put in at first, since in cases where the 
quantity of arsenic present is considerable, and a somewhat 
large supply of the fluid is poured into the flask, the evolution 
of gas often proceeds with such violence as to stop the further 
progress of the experiment 

Now if the fluid which is added contains an oxygen or 
halogen compound of arsenic, there is immediately evolved, 
along with the hydrogen, the exceedingly poisonous hydrogen 
arsenide, which at once imparts a bluish tint to the previously 
colorless flame of the kindled gas. At the same time, white 
fumes of arsenious acid arise, which condense upon cold 
objects. If a porcelain dish is now depressed upon the flame, 
solid hydrogen arsenide condenses upon the dish in black 
stains in a manner similar to antimony (see 154, 12). The 
stains formed by arsenic, however, incline more to a blackish- 
brown tint, and show a bright luster ; while the antimonial 
stains are dull and of a deep black color. The arsenical 
stains may be distinguished, moreover, from those of anti- 
mony by solution of sodium hypochlorite with sodium chlo- 
ride (compare 154, 12), which will at once dissolve arsenical 
stains, leaving antimonial stains unaffected, or removing them 
only after a considerable time. The stains may also be recog- 



286 DEPORTMENT OJF BODIES WITH REAGENTS. [ 155. 

nized as those of arsenic by warming them with a few drops 
of concentrated nitric acid. They dissolve to arsenic acid, 
which may then be easily detected with ammonium molyb- 
date (see 156, 9, DENIGES). 

If the tube d is strongly heated at the place indicated in 
the figure, a brilliant arsenical mirror makes its appearance 
in front of or in the narrowed portion of the tube, beyond the 
heated part This mirror is of a darker and less silvery-white 
hue than that produced by antimony under similar circum- 
stances. It is distinguished, moreover, from the latter by the 
facility with which it may be driven forward in a current of 
hydrogen gas without previous fusion, and also by the charac- 
teristic odor of garlic emitted by the escaping (unkindled) gas. 
If the gas is kindled while the mirror in the tube is being 
heated, the flame, even with a very slight current of gas, will 
deposit arsenical stains on a porcelain plate. 

The reactions and properties just described are amply 
sufficient to enable us to distinguish between arsenical and 
antimonial stains and mirrors; but they will often fail to 
detect arsenic, with positive certainty, in presence of anti- 
mony. In cases of this kind, the following process will serve 
to set at rest all possible doubt as to the presence or absence 
of arsenic : Heat to redness in several places the long tube 
through which the gas to be tested is passing, in order to 
produce metallic mirrors which are as strong as possible; 
then transmit through the tube a very slow stream of dry 
hydrogen sulphide, and heat the metallic mirrors with a 
gas- or simple alcohol-lamp, proceeding in a direction oppo- 
site to that of the current of gas. If arsenic alone is pres- 
ent, yellow arsenious sulphide is formed inside the tube ; if 
antimony alone is present, an orange-red or black antimo- 
nious sulphide is produced ; and if the mirror consisted of 
both metals, the two sulphides appear side by side, the 
arsenious sulphide, as the more volatile, lying invariably be- 
yond the antimonious sulphide. If dry hydrogen chloride 
gas is now transmitted through the tube containing either 
sulphide or both sulphides, without applying heat, no alter- 
ation will take place if arsenious sulphide alone is pres- 
ent, even though the gas be passed through the tube for & 
considerable time. If antimonious sulphide alone is present,. 



I 155.] ARSENIC AND ARSENIOUS COMPOUNDS. 287 

this will entirely disappear, as already stated (see 151, 
12); and if both sulphides are present, the antimonious 
sulphide will immediately volatilize, while the yellow ar- 
senious sulphide will remain. If a small quantity of ammo- 
nia solution is now drawn into the tube, the arseuious 
sulphide dissolves, and thus may be readily distinguished 
from sulphur which may have separated. Personal expe- 
rience has convinced me of the infallibility of these combined 
tests for the detection of arsenic. The following method of 
distinguishing stains depends upon the same chemical proc- 
esses : The stains are obtained upon a glass plate, they are 
moistened with ammonium sulphide, this is allowed to evapo- 
rate by the aid of heat, then the glass plate is placed, with the 
stains turned downward, upon a beaker containing a little 
fuming hydrochloric acid. If antimony only is present, the 
orange-colored residue disappears, while in presence of ar- 
senic, yellow arsenious sulphide remains behind (J. T. ANDER- 
SON). 

The reaction of hydrogen containing hydrogen arsenide 
with solution of silver nitrate and of mercuric chloride will be 
found in 157, 7. 

MA BSE was the first to suggest the method of detecting 
arsenic by the production of hydrogen arsenide. 

11. If a few drops of stannous cKloride solution are added 
to about 5 cc of fuming hydrochloric acid, and a few drops of 
a solution of arsenious acid or of an arsenite are added, the 
arsenious acid is reduced, and a brownish-black precipitate 
is obtained (BETXENDOBF).* The reaction, which takes place 
slowly in the cold, but rapidly by heating, is very delicate, 
and occurs only in the presence of an excess of fuming hydro- 
chloric acid If the hydrochloric acid has a lower specific 
gravity than 1,123, the precipitation is incomplete, or does 
not occur at all. If one has occasion to make frequent tests 
for arsenic by this method, it is convenient to keep on hand 
a solution of stannous chloride in extremely concentrated 
hydrochloric acid (38 per cent). Antimonious acid is not 
reduced under the same conditions. 

* Whether the precipitate is arsenic or solid hydrogen arsenide require* 
further investigation (RBTGBBS). 



288 DEPORTMENT OF BODIES WITH REAGENTS. [ 155. 

12. If to a solution of arsenious acid or of an arsenite an 
equal or double amount of concentrated hydrochloric acid 

and a little sodium hypophosphite are added, and it is heated 
to boiling, a brownish-black precipitate like that mentioned 
in 11 separates, if the quantity of arsenic is not very small. 
With very small amounts of arsenic, only a yellowish-brown 
to brown coloration of the liquid results, even after long 
heating. The addition of a crystal of potassium iodide con- 
siderably heightens the delicacy of the reaction, but this 
cannot be used in the presence of such substances as give 
precipitates with potassium iodide or which separate iodine 
from it (Loop, TOTBLE). 

13. If arsenites, arsenious acid, or arsenious sulphide are 
fused with a mixture of 3 parts of dry sodium carbonate and 
1 part of potassium cyanide, all the arsenic is reduced, and 
certain bases present at the same time may also be reduced, 
the oxygen converting a part of the potassium cyanide 
into cyanate. In the reduction of arsenious sulphide, potas- 
sium sulphocyanide is formed. While all the arsenic is 
Tolatilized upon the reduction of arsenious acid and arsenious 
sulphide, and is obtained as a mirror if the reduction is 
curried out in an appropriate apparatus, still mirrors are 
obtained from arsenites only when their bases are not 
reduced to arsenides at all, or are reduced to such arsenides 
as lose their arsenic wholly or partly by heating. This 
method of reducing arsenic compounds with potassium 
cyanide deserves special attention on account of its sim- 
plicity, the certainty of its results even in the presence of 
very small amounts of arsenic, and because of the neat- 
ness with which it can be performed. It is excellently 
adapted for the direct production of metallic arsenic from 
arsenic sulphide, in which respect it undoubtedly excels 
all other methods in simplicity and accuracy. Formerly, 
when glass tubes were free from arsenic, the experi- 
ment could be made with complete safety in a glass tube 
blown into a small bulb at the lower end, or better, with 
the use of a slow stream of carbonic acid, directly in a 
glass tube drawn out to a long point. Now, however, 
-since nearly all the glass tubes of commerce contain 



155.] ARSENIC AND ABSENJOUS COMPOUNDS. 289 

arsenic,* the reduction must take place in such a manner 
that the fusing mixture of potassium cyanide and sodium 
carbonate does not come in contact with the glass. The 
apparatus described by myself and L. v. BABO, therefore, 
requires a slight modification of the form in which it was 
described in previous editions, and is given that shown in 
Pig. 39. 




FIG. 89. 



a 6 is a KIPP'S apparatus charged with pieces of marble 
and pure, dilute hydrochloric acid, for the evolution of car* 
bonic acid ; f c is a wash-bottle which contains some pure, coiu 
centrated sulphuric acid for the purpose of drying the car- 




FIG. 40. 

bonic acid ; d is a tube of difficultly fusible glass, free from 
lead, which is made over the blast-lamp from a piece of 

* Compare W. EBBSEHTOS, " Der Arsengehalt des Glases als cine Fehler- 
quelle bei der Nachweisung von Arsen," Zeitechr. f. analyt. Chera., 22, 397. 

f Instead of this, any other carbonic acid generator with which the stream 
of gas mny be accmately regulated by means of a stop-cock will, of course, 
serve the purpose. 




290 DEPORTMENT OF BODIES WITH REAGENTS. [ 155. 

tubing like that used for the elementary analysis of organic 
substances. This is shown in Fig. 40, one half natural 
size. The tube must be large enough so that the porcelain 
boat (shown in Fig. 41, natural size) used for the purpose 

of heating the mixture may be 
t>| pushed into it. 

TVhen the apparatus is set up, 

and filled with carbonic acid, the 
FlG ' tt ' completely dry arsenious sulphide 

or other arsenious salt which is to be reduced is triturated 
111 a slightly warmed mortar with 12 parts of a completely 
arsenic-free, well-dried mixture ( 49 and 57), consisting of 
3 parts of sodium carbonate and 1 part of potassium cyanide. 
The powder is transferred to the porcelain boat and is 
introduced into the reduction-tube in the position shown in 
Fig. 39. The tube is then connected with the wash-bottle, a 
moderate stream of carbonic acid is allowed to escape by 
opening the stop-cock e (Fig. 39), and the mixture is dried in 
the most careful manner by gently warming the boat and also 
the tube throughout its whole length, by means of a flame. 
TVhen every particle of deposited water has disappeared from 
the tube, the stream of carbonic acid is moderated so that 
single bubbles go through the sulphuric acid at intervals of 
about one second. The end of the thick part of the tube, 
where it begins to narrow, is now heated to redness by 
means of the lamp /. When this temperature has been 
reached, the boat is heated by the lamp g, at first moderately 
so that the fusing mass does not spatter, afterwards strongly 
and persistently until all the arsenic is driven out. If any of 
the latter should have deposited in the wider part of the 
tube, this is also heated, progressing towards the drawn-out 
end. The whole amount of the reduced arsenic is then found 
as a metallic mirror (Fig. 42) beyond the part of the tube 



FIG. 42. 

heated to redness by the burner /, which is kept in place 
during the whole operation. A small part of the arsenic 
escapes from the point of the tube, and imparts to the air a 



156.] AKSENIO COMPOUNDS. 291 

garlic-like odor. The point of the tube may be finally closed 
by fusion, and the mirror may be driven together towards the 
thicker part by carefully heating the small end of the tube, 
by which means, it assumes an especially fine and pure 
metallic appearance. In this manner, even -j-J-^ of a milligram 
of arsenious acid gives a recognizable arsenic mirror.* Anti- 
mony sulphide and other antimony compounds give no 
metallic mirror when treated in this way. 

14 If arsenious oxide or an arsenite is exposed on char- 
coal to the reducing /lame of the blowpipe, the frequently men- 
tioned, highly characteristic odor resembling garlic is emitted, 
more especially if some sodium carbonate is added. This 
odor has its origin in the reduction and reoxidation of the 
arsenic, and enables us to detect very minute quantities. 
This test, however, like all others that are based upon the 
indications of the sense of smell, cannot be implicitly relied 
on. 

15. Concerning the detection of arsenic in the micro- 
chemical way, see HAUSHOEEB, p. 15; BEHBENS, Zeitschr. f. 
analyt. Ohem., 30, 164; EMIOH, ibid., 32, 167. 



156. 
e. ABSENIC COMPOUNDS. (Arsenic Add, AS.OB.) 

1. ABSENIO ACID free from water (arsenic anhydride) forms 
a colorless or white, glassy, fusible mass, which dissolves 
slowly in cold water, more rapidly in hot water, and decom- 
poses into oxygen and arsenious acid at a strong red heat. 
ARSENIC KSDBOXEDE (orthoarsenic acid) containing water of 
crystallization, aHjAsO^H^O, is deposited from the solutions 
at a low temperature, in the form of perfectly colorless and 
transparent, prismatic crystals, which deliquesce in moist air 
and lose their water at 100. At 180, PTBOABSENIC ACID, 
H 4 Afi,O T ,'i8 obtained; at 206, METABSENIO AGED, HAsO,, is 
formed ; and at a temperature near redness, the anhydride 

* Compare W. FBESENIUS, "Ueber die richtige Ausfohrung und der 
Bmpfindlichkeit der FRESBNius-BABo'schen Methode zur NachweisaDg des 
Arsens " Zeitschr. f. analyt Chern., 20, 581. 



292 DEPORTMENT OJP BODIES WITH REAGENTS. [ 156 r 

Is left. All the acids dissolve in water to orthoarsenic acid. 
Arsenic acid acts as a poison. 

2. The arsenates correspond in composition to the acids, 
and it is therefore customary to distinguish orthoarsenates, 
pyroarsenates, and metarsenates, The orthoarsenates, cor- 
responding to the orthophosphates, are (according to the old 
nomenclature) either basic, neutral, or acid salts, respectively, 
as they contain 3 equivalents of the base and no hydroxyl, 
2 equivalents of the base and 1 equivalent of hydroxyl, or 
1 equivalent of the base and 2 equivalents of hydroxyl. The 
salts of the alkali metals and the acid salts of the alkali- 
earth metals are soluble in water, while almost all the other 
arsenates dissolve in hydrochloric or nitric acid. The anhy- 
drous arsenates of fixed bases are not decomposed by heat. 

A solution of arsenic acid or of an arsenate in hydro, 
chloric acid may be boiled for a long time without losing 
arsenious chloride by volatilization, if it does not contain too 
much hydrochloric acid. It is only when the residue con- 
sists of about equal parts of hydrochloric acid of 1.12 sp. gr. 
and water that traces of arsenious chloride escape with the 
hydrochloric acid. If, on the other hand, arsenic acid is 
heated with concentrated hydrochloric acid, some arsenious 
chloride and chlorine escape. If arsenic acid is distilled re- 
peatedly with concentrated hydrochloric acid and ferrous 
chloride, all the arsenic is volatilized as arsenious chloride 
and obtained in the distillate. 

3. Hydrogen sulphide fails to precipitate alkaline and neu- 
tral solutions, and in moderately acid solutions, it occasions 
no precipitate at first in the cold. Upon long standing, a 
partial reduction of arsenic acid to arsenious acid takes 
place, accompanied by the separation of colloidal arsenic 
sulphide, As 9 S B , and sulphur ; then there is a precipitation of 
yellow ABSENIO SULPHIDE and ABSENIOUS SULPHIDE. This proc- 
ess continues until all the arsenic is finally precipitated 
(BBAUNEB and TOMIGEE, THIELE). From solutions which con- 
tain at least 2 parts of concentrated hydrochloric acid of 
1.2 sp. gr. to 1 part of water, hydrogen sulphide precipitates 
ABSENIO SOTPHIDE very quickly (Fa. NEEEB.) 

If hydrogen sulphide is conducted into a moderately acid 
solution of arsenic acid, which is warmed to about 70, ABSENIO 



156.] AKSENIC COMPOUNDS. 291:* 

SULPHIDE, As a S B , is also obtained if hydrogen sulphide is 
largely in excess (BUNSEN;, but otherwise the precipitate con- 
sists of a mixture of arsenic sulphide, arsenious sulphide, and 
sulphur. If sulphurous acid, or sodium sulphite with hydro- 
chloric acid, is added to a solution of free arsenic acid or of 
an arsenate, the sulphurous acid reacts with the arsenic 
acid (most quickly by heating), and arsenious acid and sul- 
phuric acid are formed. If hydrogen sulphide is now added, 
the whole of the arsenic is immediately precipitated as 

ARSENIOUS SULPHIDE. 

4. In neutral and alkaline solutions, ammonium sulphide 
changes arsenic acid into arsenic sulphide, which remains in 
solution as ammonium sulpharsenate. This compound is 
decomposed by the addition of an acid, and arsenic sulphide 
separates. The separation takes place more quickly than that 
by hydrogen sulphide from cold, moderately acid solutions. 
It is facilitated by warming. The precipitate is not a mixture 
of arsenious sulphide and sulphur, but is ARSENIC SUI^PHTDE. 

5. In solutions of arsenic acid and of alkali-metal arsenates, 
silver nitrate prod aces a very characteristic, reddish-brown 
precipitate of SILVER ARSENATE, Ag 8 As0 4 , which is readily sol- 
uble in dilute nitric acid and in ammonia, and dissolves also 
slightly in ammonium nitrate. Accordingly, if the precipitate 
is dissolved in some nitric acid, and a layer of dilute ammonia 
is brought above the solution, a precipitate is produced at the 
surface of contact of the two liquids and forms a ring. The 
addition of some sodium acetate increases the delicacy of 
the reaction. If, however, but little of the precipitate is dis- 
solved in very much nitric acid, the precipitate often does not 
form again upon neutralizing with ammonia, on account of 
the solvent action of ammonium nitrate. The ammoniacal 
solution of silver arsenate does not deposit silver upon boiling 
(difference between arsenic and arsenious acids). 

6. Cuprio sulphate does not produce a precipitate in aque- 
ous solutions of arsenic acid. Upon the addition of an alkali, 
a bluish-green precipitate of COPPER ABSENATE is formed. Upon 
the addition of more potassium or sodium hydroxide, the color 
changes to a beautiful, light blue, while the precipitate does 
not dissolve. Upon boiling, no cuprous oxide is formed (dif- 
ference between arsenic and arsenioiis acids). 



394 DBPOKTMENT OF BODIES WITH REAGENTS. [ 156. 

7. If a dilute solution of arsenic acid mixed with some 
hydrochloric acid is heated with a clean strip of copper, the 
metal remains perfectly bright (WEBTHEE, BEINSCE) ; but if 
to 1 volume of the solution 2 volumes of concentrated 
hydrochloric acid are added, a gray film is deposited on the 
copper, as in the case of arsenious acid. Under these cir- 
cumstances, the reaction is just as delicate as with arsenious 
acid (REINSCH). 

8. If a solution of arsenic acid, or of an arsenate soluble in 
water, is added to a clear mixture of magnesium sulphate, am- 
monium cJdoride, and not too little ammonia, a crystalline pre- 
cipitate Of AMMTOMIUM MAGNESIUM ARSENATE, NH 4 MgAsO 4 .6H,O, 

separates from concentrated solutions immediately, from 
dilute solutions after some time. If a small portion of the 
precipitate is dissolved on a watch-glass in a drop of nitric 
acid, a little silver nitrate added, and the solution touched 
with a glass rod dipped in ammonia, brownish-red silver 
arsenate is formed. Or, if a small portion of the precipitate 
is dissolved in hydrochloric acid, and hydrogen sulphide is 
passed into the solution with warming, a yellow precipitate 
is formed. (Differences between ammonium magnesium 
arsenate and phosphate.) 

9. If a small amount of a solution of arsenic acid or of an 
arsenate is added to a few cubic centimeters of the solution 
of ammonium molytdate in nitric acid, no precipitate is formed 
in the cold, even after long standing. Upon heating, how- 
ever, a bright yellow precipitate of AMMONIUM ABSENO-MOLYB- 
DATE separates, which under the microscope is shown to 
consist of needles grouped in star-shaped forms. The precip- 
itate is soluble in ammonia. In the colorless solution thus 
obtained, the magnesia mixture mentioned in 8 produces the 
reaction there described. 

10. Arsenic compounds deport themselves in the same way 
as those of arsenious acid, with stannous chloride, with sodium 
hypopJtospJiite and hydrochloric add, with zinc in the presence 
of sulphuric acid, with potassium cyanide, and before the tiow- 
pipe. If the reduction of arsenic acid is effected by means of 
zinc in a platinum dish, the platinum is not colored black 
(difference from antimony). 

11. In relation to the detection of arsenic in the micro- 



157.] RECAPITULATION AND REMARKS. 295 

chemical way, see HAUSHOPEB, p. 15 ; BEHRENS, Zeitschr. f. 
analyt. Ohem,, 30, 164. 



157. 

Jleoapitulatian and Remarks. Various methods may be 
used for the detection of the metals of the second division of 
the sixth group, in mixtures or solutions containing all or 
several of them, and it is not possible to decide at once 
which process is the best. On the contrary, sometimes one 
method and sometimes another deserves preference, accord- 
lug to the relative amounts of the metals present, and 
whether it is a question of the greatest possible convenience 
or of rapidly attaining the end without demanding the high- 
est degree of exactness. 

The different ways of effecting the detection or separa- 
tion of tin, antimony, and arsenic, when present together, will 
be described first, and afterwards the means of distinguish- 
ing between the several oxides and acids of the three metals, 
a.nd also the methods of separating gold and platinum from 
tin, antimony, and arsenic. 

1. If a dry mixture of sulphides of tin, antimony, and 
arsenic is to be examined, triturate 1 part of it with 1 part of 
dry sodium carbonate and 1 part of sodium nitrate, and trans- 
fer the mixed powder gradually to a small porcelain crucible 
containing 2 parts of sodium nitrate kept in a state of fusion 
at a not too strong heat. Oxidization of the sulphides en- 
sues, attended with slight deflagration. The fused mass con- 
tains stannic oxide, sodium arsenate and antimonate, witt 
sodium sulphate, carbonate, nitrate, and nitrite. Care must 
be taken not to raise the heat to such a degree, nor continue 
the fusion ao long, as to lead to decomposition of the sodium 
nitrite, producing caustic soda, for this will cause the forma- 
tion of sodium stannate soluble in water. Upon treating the 
mass with a little cold water, stannic oxide and acid sodium 
pyroantimonate remain undissolved, while sodium arsenate 
and the other salts are dissolved. If the filtrate is acidified 
with nitric acid, and heat is applied to remove carbonic and 
nitrous acids, the arsenic acid may be detected and sepa- 
Tated, either with silver nitrate, according to 156, 5, or with 



296 DEPORTMENT OF BODIES WITH HEAGEtfTS. [ 157. 

a mixture of magnesium sulphate, ammonium chloride, and 
ammonia, according to 156, 8, or as ammonium arseno- 
molybdate, as described in 156, 9. 

If the undissolved residue, consisting of stannic oxide and 
acid sodium pyroantimonate, after being washed once with 
cold water and three times with dilute alcohol, is digested 
with a little hydrochloric acid at a gentle heat in the hollow 
of a platinum crucible cover, the mass is either completely 
dissolved or, if the tin is present in a large proportion, a 
white residue is left undissolved. If, disregarding the latter,, 
a fragment of zinc is now added, the compounds are re- 
duced to the metallic state, and the antimony will at once 
reveal its presence by blackening the platinum. After the 
evolution of hydrogen has nearly stopped, if the remainder of 
the zinc is taken away, the zinc chloride solution is removed 
by careful decautation, and the contents of the cover are 
heated with some hydrochloric acid, the tin dissolves to stan- 
nous chloride, while the antimony, if present in considerable 
quantity, is left undissolved, partly in the form of black 
flakes. The tin may then be detected in the solution with 
mercuric chloride or with a mixture of ferric chloride and 
potassium ferricyanide, and the antimony, after solution in a 
little tartaric and nitric acids, may be tested with hydrogen 
sulphide. If the antimony has not been found with certainty 
by the foregoing reactions, a part of the hydrochloric acid 
solution obtained by treating the metals is evaporated to a 
small volume, a drop of hydrochloric acid is added, and a 
test is made with tin upon the platinum cover (see 154, 9). 
As this method of detecting arsenic, tin, and antimony, in pres- 
ence of each other, is adopted in the systematic course of 
analysis, the principle upon which it is based is here simply 
explained, and the details of the process will be found in the 
second part. 

2. If the mixed sulphides, after being freed from the 
greater part of the adhering water by laying the filter con- 
taining them on blotting-paper, are treated with fuming 
hydrochloric acid, with application of a gentle heat, the 
sulphides of antimony and tin dissolve, while the sulphide- 
of arsenic is left undissolved. The warming is continued until 
the hydrogen sulphide has escaped, then some water ia 



157.] RECAPITULATION AND REMARKS. 297 

added, and the liquid filtered. If the sulphide of arsenic 
is treated (together with the filter, if very little is present/ 
with concentrated nitric acid with the aid of heat, the result- 
ing arsenic acid in the solution may be easily detected by 
means of ammonium molybdate (see 156, 9). If the sulphide 
of arsenic is treated with ammonia, and the solution is evapo- 
rated to dryness, with the addition of a little piece of sodium 
carbonate, an arsenic mirror is readily obtained from the 
residue by treatment with potassium cyanide and sodium 
carbonate, in a stream of carbonic acid (see 155, 13). The 
hydrochloric acid solution containing the tin and antimony 
is warmed for a short time with a bright rod of iron wire, and 
allowed to stand for ten or fifteen minutes. The antimony 
is thereby precipitated in the form of black flakes, while the 
stannic chloride is reduced to stannous chloride. A filtra- 
tion is then made, and the filtrate is tested for tin, with mer- 
curic chloride. The precipitated antimony may be further 
tested by dissolving it, after complete washing, in nitric acid 
containing a small amount of tartaric acid, and adding 
hydrogen sulphide water to the solution. 

3. If the mixed sulphides are digested at a gentle heat with 
some solid, ordinary ammonium carbonate and water, arsenious 
sulphide dissolves, while the antimony and tin sulphides 
remain undissolved. But this separation is not quite abso- 
lute, as traces of antimony and tin sulphides are apt to pass 
into the solution, while some arsenious sulphide remains in 
the residue. The arsenious sulphide precipitating from the 
alkaline solution, upon acidifying the latter with hydro- 
chloric acid, must, therefore (especially if consisting only of a 
few flakes), after washing, be treated with ammonia, the solu- 
tion evaporated, with addition of a small quantity of sodium 
carbonate, and the residue fused with potassium cyanide in a 
stream of carbon dioxide, to make sure of the presence 
of arsenic by the production of an arsenical mirror. The 
residue, insoluble in ammonium carbonate, should be treated 
as directed in 2. 

4 In the analysis of metallic alloys, stannic oxide and 

< oxides of antimony and arsenic are often obtained together 

as a residue insoluble in nitric acid* It is best to fuse these 

with sodium hydroxide in a silver crucible, then soften the 



298 DEPORTMENT OF BODIES WITH REAGENTS. [ 1S7. 



mass with water, add one third of the volume of alcohol, 
filter off the acid sodium pyroantimonate remaining un- 
dissolved, and wash it with weak alcohol to which a few 
drops of a solution of sodium carbonate have been added. 
In the presence of much tin, it is advisable to treat the 
residue again in the same way, in order to extract all the tin. 
The filtrate is acidified with hydrochloric acid, then tin and 
arsenic are precipitated as sulphides in the heated solution, 
and these are most conveniently separated according to 2. 

5. If very small amounts of arsenic are to be detected in 
the presence of much tin and antimony, it is advisable to 
distil the solution which contains the chlorides of the metals 
with not too small an amount of fuming hydrochloric acid and 
ferrous chloride or sulphate* (using a cooled receiver con- 
taining a little water), until about one fourth of the liquid haa 
gone over, and to test the distillate with hydrogen sulphide 
(E. FISCHEB, P. HUFSCHMIDT, A. CLASSEN). This method is 
less well adapted for detecting tin and antimony at the 
same time, because the distillation must then be continued 
and repeated until all the arsenic has been driven off, in 
which case, small quantities of antimony and tin may readily 
go over into the distillate; also, because the tin and antimony 
sulphides, precipitated with hydrogen sulphide from th& 
residue from the distillation, are obtained mixed with much 
sulphur. A solution adapted for distillation is obtained from 
the sulphides of the metals by warming them with hydro- 
chloric acid, with the addition of some potassium chlorate, or, 
still more conveniently, by suspending them in water and 
adding sodium peroxide (Tn. POLECK). 

6. Arsenic and antimony may be easily separated also by 
adding to 1 part of the solution 2 parts, or even a larger 
quantity, of hydrochloric acid of 1.2 sp. gr., and passing 
in hydrogen sulphide. The arsenic then separates as arseni- 
ous or arsenic sulphide, according to circumstances, while 
the antimony remains dissolved, and, after diluting with 
water, may be precipitated from the solution with hydro- 
gen sulphide (0. KOEHLEB, NEHEB). Antimony may be 

* Before tbese reagents can be used for the detection of minute amounts 
of arsenic, they should be put to test by the distillation method, to ascertain, 
whether they are entirely fiee from arsenic. 



157.] BEOAPITULATION AND KBMABKS. 29& 

separated from tin in a similar manner by diluting the 
liquid containing the tin as a stannic compound, with con- 
centrated hydrochloric acid of 1.18 sp. gr., so that 1 part of 
this acid is present to 1 part * of water ; because hydrogen 
sulphide precipitates from such a solution the antimony 
only, and not the tin (LovrroN). These two methods may be 
utilized for the separation of the three metals (NEHEB). 

7. It should be noted here that arsenic and antimony 
may be separated and distinguished by treating the mirror 
produced by MARSH'S process, with hydrogen sulphide, and 
separating the resulting sulphides by means of hydrochloric 
acid gas (see 155, 10) ; but when antimony and arsenic are 
mixed as hydrogen compounds, they may also be separated by 
the following methods : a. First conduct the gases, mixed 
with an excess of hydrogen, through a tube containing glass 
splinters moistened with a dilute solution of lead acetate, to 
retain the hydrochloric acid and hydrogen sulphide gases, then 
in a slow stream into a solution of silver nitrate. Almost 
all the antimony in the gas falls down as black silver anti- 
monide, Ag,Sb, while the arsenic passes into the solution as 
arsenious acid, with reduction of the silver, and may be de- 
tected in the fluid as silver arsenite, by cautious addition of 
ammonia, or, after precipitating the excess of silver by 
hydrochloric acid, by means of hydrogen sulphide. Since, 
however, a little antimony always passes into the solution, the 
precipitate by hydrogen sulphide must not be considered as 
arsenious sulphide without further examination. The test 
may be made according to 157, 2. In the precipitated 
sijver antimonide, which is often mixed with much sil- 
ver, the antimony may be most readily detected by heat- 
ing the precipitate thoroughly freed from arsenious acid 
and silver nitrate by boiling with water with tartarie 
acid and water to boiling* This will dissolve the anti- 
mony alone, which may then be readily detected by means 
of hydrogen sulphide, in the solution acidified with hydro- 
chloric acid (LASSAIGNE, A. "W. HOFMAEN). b. Conduct the 
gases, mixed with an excess of hydrogen, through a rather 
wide glass tube, 10 cm at least of which are filled witk 
caustic potash in small pieces. The potash decomposes 
the hydrogen antimonide entirely, becoming coated witk a 
* TrTr H. A- Harper of Chicago advises using 2 parts of water. H. L. W. 



300 DEPOBTMENT OF BODIES WITH REAGENTS. [ 157, 

lustrous film of metal. The hydrogen arsenide is, on the 
contrary, scarcely at all decomposed, and may be detected 
readily on its exit from the tube by the production of stains 
or rings (see 155, 10), or by its action on solution of silver 
nitrate (DBAGENDORFF). c. The stream of gas, very slowly 
evolved, is conducted through a mixture of 2 cc of silver 
solution (1 part silver nitrate and 24 parts water), 2 cc concen- 
trated nitric acid, and 8 to 10 cc of water. When the black 
precipitate produced in the solution settles, the action may 
be considered as finished. Bromine-water in excess is now 
put into the flask containing the liquid and precipitate, or it 
is treated with hydrochloric acid with the addition of enough 
potassium chlorate so that chlorine is in excess. After some 
time, it is filtered, then tartaiic acid, ammonium chloride, and 
ammonia are added in excess, and the arsenic, now present as 
arsenic acid, is precipitated as ammonium magnesium arse- 
nate (see 156, 8). After long standing, this is filtered off, 
the filtrate is acidified with hydrochloric acid, and the anti- 
mony is precipitated with hydrogen sulphide (E. EEIOHABDT). 
(If the liquid brought into contact with zinc in the presence 
of dilute sulphuric acid in the methods a, 6, and c, also con- 
tained tin, the latter separates in the metallic state upon 
prolonged action of the zinc. If, therefore, the zinc solu- 
tion is poured off, the residue is heated with hydrochloric 
acid, this is filtered, and mercuric chloride solution is added, 
the resulting precipitate of mercurous chloride shows the 
presence of tin), d. If a solution containing arsenious acid 
(but not arsenic acid) is brought into an apparatus evolving 
hydrogen from an alkaline solution (e.g., one which contains 
potassium hydroxide, and arsenic-free aluminium foil or 
wire), and the gas is conducted through silver nitrate solution, 
any blackening taking place is decisive for arsenic alone, for 
under these conditions, hydrogen antimonide cannot form. 
e. If hydrogen arsenide or antimonide is allowed to act upon 
pure filter-paper which is moistened with a solution of silver 
nitrate, the moistened parts of the paper are colored. If, 
according to GUTZEEP, a solution is used which contains 1 
part of silver nitrate to 1 part of water, a lemon-yellow stain 
is produced by hydrogen arsenide, which becomes black by 
being touched with water, while hydrogen antimonide colors 



167.] KECAPITULATION AND REMARKS. 301 

the periphery of the place touched with the silver solution, 
dark brownish-red to black. The inner part shows no color, 
or only a slight, gray coloration. Paper moistened with more 
dilute silver solution (&g., in the proportion 1 : 4) is blackened 
by both gases. These reactions, concerning which it must be 
remembered that hydrogen sulphide and phosphide give 
similar colorations, have undergone various criticisms and 
modifications since they were introduced into the German 
pharmacopoeia. EITSEET recommends the use of an ammoni- 
acal silver solution. A paper moistened with this becomes 
dull brown to black from the most minute amount of hydrogen 
arsenide. The reaction is not influenced by aqueous or acid 
vapors nor by the action of the paper, but it is interfered with 
by the presence of hydrogen sulphide and phosphide, as well 
as by that of hydrogen antimonide, the latter also giving brown 
to black stains. A complete summary and critical testing of 
the methods referred to have been given by H. BEOKUBTS.* It 
must suffice to mention this here. /. If pure filter-paper is 
spotted with a drop of a saturated alcoholic solution of mer- 
curic chloride, this is allowed to dry superficially, the 
operation is repeated four or five times, and hydrogen 
arsenide is allowed to act upon paper thus prepared, a stain, 
at first light yellow, but becoming orange-colored upon longer 
action, is produced. Hydrogen antimonide produces no stain 
when acting in very small quantity, but it gives a brown to 
grayish-black color when the amount is larger. If the stain 
is occasioned by both hydrogen compounds, that formed 
by hydrogen arsenide may be detected, if not too much 
hydrogen antimonide has acted, by moistening the stain, after 
cutting it out, with 80 per cent alcohol in a watch-glass. The 
coloration produced by hydrogen antimonide disappears after 
standing for a while, and allows the yellow color produced by 
hydrogen arsenide to be recognized (FLUCKIGER, LOHMANNV 

8. If saturated hydrogen sulphide water is added to a 
solution acidified with hydrochloric acid which contains 
arsenic and arttimonic acids, and after a few minutes, a stream 
of air is passed through the liquid in order to remove the ex- 
cess of hydrogen sulphide, the precipitate contains all the 

Pharmac Ontralkalle, 1884, No. 17. 



302 DEPORTMENT OF BODIES WITH REAGENTS. [ 157. 

antimony as antimonic sulphide, but no arsenic. The latter 
can then be precipitated from the filtrate, when warmed to 70, 
by passing in hydrogen sulphide (BuNSEN). 

9. The attention of chemists who are expert in flame- 
reactions should also be called to the method of BUNSEN,* which 
is designed to detect all three metals in the precipitate of their 
sulphides, by means of flame-reactions and blowpipe tests. 
Bef erence only will be here made to the methods, partly micro- 
scopic, of H. BAGER,t which are chiefly intended for the 
rapid detection of arsenic in pharmaceutical preparations J 

10. Stannous and stannic compounds may be detected in 
presence of each other, by testing one portion of the solution 
for the first, with mercuric chloride, auric chloride, or a mix- 
ture of potassium ferricyanide and ferric chloride, and another 
portion for stannic compounds, by pouring it into a concen- 
trated, hot solution of sodium sulphate. For the last test, the 
solution must not contain much free acid. 

11. Antimonious oxide in presence of antimonic a&id may be 
identified by the reaction described in 154, 11. Antimonic acid 
in presence of antimonious oxide is detected by heating the oxide 
(which must be free from other bodies) with hydrochloric acid 
and potassium iodide (see 154, 2 and 3), or by adding to the 
solution, mixed with concentrated sulphuric acid, after cool- 
ing, a drop of a solution of diphenylamine in concentrated 
sulphuric acid, whereby, in presence of antimonic acid, a 
deep blue coloration of the liquid results. This reaction, 
however, is only conclusive for antimonic acid when other sub- 
stances giving the same coloration with diphenylamine, such 
as nitric acid, chromic acid, etc., are not present. 

12. Arsenious add and arsenic add in the same solution 
may be distinguished by means of silver nitrate. If the pre- 
cipitate contains little arsenate and much arsenite of silver, it 



* Zeitschr f. analyt. Chem.. 5, 878. 

fPharmac. Centralhalle, 1884, p. 265 and p 277. 

j In relation to other methods proposed for the separation of antimony, tin, 
and arsenic, see F W. CLARKE, Zeitschr. f. analyt. Chem., 9, 487; BEBODTJND, 
*W, 23, 587, and 24, 221; LEBSEK, iW&, 27, 318; J. OLAUK, Chem. Centralbl. 
1893, I, 965. See also, for the separation of antimony and tin, LTTOKO-W, 
Zeitschr. f, analyt. Chem., 26, 18; CABHOT, ML. 27, 651; WABBBN, Qhem. 
Centralbl., 1888, p. 645. 



157.] RECAPITULATION AND REMARKS. 303 

is necessary, in order to identify the former, to add cautiously, 
drop by drop, most highly dilute nitric acid, which dis- 
solves the yellow silver arsenite first. A still safer way to 
detect small quantities of arsenic acid in presence of arsenious 
acid is to precipitate the former with a mixture of magnesium 
sulphate, ammonium chloride, and ammonia ( 156, 8), by 
which means an actual separation of the two acids is effected 
Arsenious acid may be recognized in presence of arsenic acid 
by the immediate precipitation by hydrogen sulphide of the 
moderately acidified solution in the cold, which is not the case 
with arsenic acid ; also, by the fact that arsenious acid alone 
evolves hydrogen arsenide when brought into solution of 
sodium hydroxide which is acting upon aluminium. Arseziious 
acid is also readily detected by its reduction of cupric oxide 
in alkaline solution, and by the separation of metallic silver, 
by boiling the ammoniacal solution of the silver salts. To 
ascertain the degree of sulphuration of arsenic in a sulphur 
salt, boil the alkaline solution of the salt under examination 
(after the extraction with carbon disulphide of any sulphur 
that may be present) with bismuth hydroxide, filter off the 
bismuth sulphide formed, and test the filtrate for arsenious 
and arsenic acids. , To distinguish between the arsenious and 
arsenic sulphides, first completely extract the sulphur which 
may be present, by means of carbon disulphide, then dissolve 
the residue in ammonia, add immediately silver nitrate in 
excess, filter off the silver sulphide, and observe whether 
arsenite or arsenate of silver is formed upon addition of 
ammonia. It should be observed that a portion of the arsenic 
is to be found with the bismuth sulphide and silver sulphide 
in the two tests last mentioned (WAirz). 

13. GOLD and PLATINUM may be separated from TIN, 
ANTIMONY, and ABSENIO, by boiling their solutions in an excess 
of sodium hydroxide with chloral hydrate. The resulting 
precipitate contains all the gold and platinum free from 
the other metals. 



304 DEPORTMENT OF BODIES WITH BEAGENTS. [ 158* 

Special Heactions of the Barer Metals of the Sixth Group. 

158. 

1. GEBMAXEU3I, Ge. (Germanic Oxide, G-eO,.) 

Up to the present time, GERMANIUM has been found only in argyrodita, 
euxinite, and canfieldite, and in very small quantity. It forms two oxides; 
gennanious oxide, GeO, and germamc oxide. The metal is obtained as a 
powder by igniting the oxides in hydrogen, and this may be fused under 
borax to a grayish-white regulus with a metallic luster. This has * 
specific gravity of 5.469, is easily pulverized, and is permanent in the air 
Germanium volatilizes at a bright red heat, yielding a sublimate consist* 
ing of small crystals. It is insoluble in hydrochloric acid, and it is con- 
verted by nitric acid into white germanic oxide, and by concentrated suk 
phuric acid, upon heating, into a white sulphate soluble in water. Aqua 
regia dissolves the metal readily to chloride ; concentrated potassium 
hydroxide solution does not attack it, but it gives potassium germanio 
oxide upon fusion with potassium hydroxide, the action being accom- 
panied by deflagration. Germanic oxide is formed by burning the metal 
in oxygen, by roasting germanic sulphide, by treating the metal with 
nitric acid, and by decomposing the chloride with water, etc. It is a white, 
dense powder, difficultly soluble in water, which may be heated to bright 
redness without undergoing any change, and dissolves but slightly in 
acids. The alkali-metal hydroxides and carbonates dissolve it when 
they are fused with it, and convert it into compounds that are soluble in 
water. Germanic chloride, GeCU , obtained by igniting the metal or the 
sulphide in a stream of chlorine, forms a mobile, colorless liquid, boiling 
at 80, which is volatile even at ordinary temperatures, and is de- 
composed by water, with formation of the oxide, which partially sepa- 
rates. If the aqueous solution of the chloride is acidified with hydrochloric 
acid, and evaporated to dryness upon the water-bath, the chloride vola- 
tilizes completely. 

From acid solutions containing germanic salts, hydrogen sulphide 
precipitates germanic sulphide, GeBa, in the form of a white, voluminous 
precipitate. This is somewhat soluble in water, even in hydrogen sul- 
phide water. In order to obtain it pure, therefore, it should first be 
washed with hydrochloric or sulphuric acid saturated with hydrogen 
sulphide, then with alcohol saturated with the same gas, and finally with 
ether. After drying, it forms a soft, white powder. If it is heated in a 
stream of carbonic acid, an odor is produced resembling very dilute 
aorolein, and the sulphide shrinks greatly and assumes a yellowish or 
grayish-yellow color. It volatilizes upon being heated to a bright red 
heat. Germanic sulphide dissolves readily in ammonium sulphide ; and 



159.] IBIDITJM. 305 

a sufficient excess of acid precipitates it unchanged and white in color 
from the solution (characteristic reaction). Germanic sulphide is also 
readily dissolved by potassium hydroxide and by ammonia. Aqua 
regia dissolves it, with separation of sulphur. Nitric acid changes 
it into oxide containing sulphuric acid and mixed with sulphur. If 
germanic sulphide is heated in a stream of hydrogen, germanious sul- 
phide, GeS, is produced at first, with the formation of hydrogen 
sulphide. Upon further heating, this is partly reduced to germanium. 
From solutions of germanium salts, zinc separates the metal slowly in the 
form of a dark brown slime. Before the Uowpipe, when heated without 
an alkaline flux in the reducing flame, germanic oxide gives the fused 
metal, with the formation at the same time of a white coating of the oxide. 
Borax and salt of phosphorus dissolve the oxide abundantly, both in the 
oxidizing and the reducing flames, giving colorless glasses which are not 
changed even by heating with tin. Non-luminous flames are not colored 
by germanium compounds, and consequently they cannot be detected by 
means of the spectroscope. The detection of the small amount of germa- 
nium in argyrodite may be effected by heating the mineral in an atmos- 
phere of hydrogen sulphide or illuminating-gas. A sublimate is thus 
obtained, similar to antimony sulphide, which shows very characteristic 
forms under the microscope, and which may be subjected to further tests 
in the wet way 



159. 
2. IETOIUM, Ir. (Iridic Oxide, IrO a .) 

IETDIUM occurs in combination with platinum and other metals in 
the platinum ores, but more especially as osmiridium. Alloyed with 
platinum, it has of late been employed for crucibles, etc. Indium resem- 
bles platinum, but it is brittle, fuses with extreme difficulty, and its 
specific gravity is 22.4. In the compact state, or reduced at a red heat by 
hydrogen, it dissolves in no acid, not even in aqua regia (difference from 
gold and platinum). Reduced in the moist way, e.#., by formic acid, Ob 
largely alloyed with platinum, it dissolves in aqua regia to tetrachloride, 
IrOl*. In a state of fusion, potassium disulphate oxidizes, but does not 
dissolve it (difference from rhodium). It oxidizes by fusion with sodium 
hydroxide with access of air, or by fusion with sodium nitrate. The 
compound of iridious oxide, Ir 3 0s, with soda which is formed in this 
process, dissolves partially in water ; and by heating with aqua regia, it 
gives a deep black-red solution of indie chloride, IrCU, and sodium 
chloride. 

If iridium powder is mixed with sodium chloride, the mixture heated 

*Sitzungsber. der Mflnchener Akademie, 1887, p. 138; Chem. Gentralbl.., 
1888, p. 867. 



806 DEPORTMENT OF BODIES WITH BEAGENTS. [ 159. 

to incipient redness, and treated with chlorine gas, sodium Jridic chloride 
is formed, which dissolves in water to a deep red-brown fluid. Potassium 
hydroxide, added in excess, colors the solutions greenish, a little brownish- 
black potassium iridic chloride precipitating at the same time. If the solu- 
tion is heated, and exposed some time to the air, it acquires at first a red- 
dish tint, then becomes violet, and with absorption of oxygen, it changes 
afterwards to blue (GLAUS, characteristic difference from platinum). If the 
solution is now evaporated to dryness, and the residue treated with water, 
a colorless fluid is obtained, while a blue deposit of indie oxide, IrO a , is 
left undissolved. If the solution of indie chloride is heated with sulphuric 
acid until vapors of sulphuric acid escape, and the residue is treated with 
water at the boiling temperature, a clear solution of a green or sometimes 
blue or violet color is usually obtained. If this is neutralized with potas- 
sium hydroxide and boiled from fifteen to thirty minutes, finally with the 
addition of an excess of potassium hydroxide, an oxide separates, which 
dissolves in dilute sulphuric acid with a bright violet color. If solid 
ammonium nitrate is added in small portions to the indium salt heated 
with sulphuric acid, as mentioned above, as soon as the vapors of sul- 
phuric acid have stopped coming off, after removing the dish from 
the source of heat, a blue or sometimes an emerald-green mass is 
obtained, which, if the operation is interrupted before all the ammo- 
nium nitrate has been decomposed, dissolves in water to a blue liquid. 
The presence of foreign metals naturally interferes with the delicacy of 
the reaction. If iridic chloride is heated directly with ammonium nitrate 
and ammonium chloride, added at intervals, a rose-red mass, instead of a 
blue one, is obtained, from which a rose-red powder separates upon treat- 
ment with very little water (LECOQ DB BOISBAUDRAN). Hydrogen sulphide 
at first colors solutions of iridic chloride olive-green, and iridious chloride, 
IraCh , is formed, with separation of sulphur ; afterwards, brown iridious 
sulphide, Ir a Si , is precipitated. Ammonium sulphide produces the same 
precipitate, which redissolves readily in an excess of the precipitant. 
Potassium chloride precipitates potassium iridic chloride as a blackish-red 
crystalline powder, insoluble in a concentrated solution of potassium 
chloride. Ammonium chloride precipitates from concentrated solutions, 
ammonium iridic chloride in the form of a dark red powder, consisting of 
microscopic octahedrons, insoluble in concentrated solution of ammonium 
chloride. This double salt, and also the corresponding potassium com- 
pound, especially when in hot solution, are turned olive-green by potassium 
nitrite, owing to the formation of potassium or ammonium iridious 
chloride : SKJrCls + 2KN"0 = 6K01.Ir01e + 2KO. This double salt 
crystallizes out on cooling. On heating or evaporating the green solution 
with an excess of potassium nitrite, it turns yellow, and when boiled 
deposits a white precipitate, which is hardly soluble in water and hydro, 
chloric acid (essential difference and basis of a method of separation 
from platinum, GIBBS). If the iridic ammonium chloride is dissolved in 
water by boiling, and oxalic acid is added, a reduction to the iridious salt 
takes place, and on this account, the solution remains clear on cooling 



160.] MOLYBDENUM. 307 

(difference from platinum, 0. LEA). If stannous chloride is added to 
iridic chloride and the solution is boiled, then an excess of potassium 
hydroxide is added and the mixture is boiled again, a leather-colored 
precipitate is formed. Ferrous sulphate, oxalic acid, and sulphurous acid 
do not precipitate iridium (means of separating indium from gold) ; but zino 
separates black indium. If indie oxide is suspended in a solution of 
potassium sulphite, and this is saturated with sulphurous acid and boiled, 
with renewal of the evaporating water, till all the free sulphurous acid is 
expelled, the whole of the iridium is converted into insoluble iridic sul- 
phite (any platinum which may be present will remain dissolved as plati- 
nous potassium sulphite, C. BIBNBAUM). Ignited with sodium carbonate 
in the upper oxidizing fame, compounds of iridium yield the metal, which 
when triturated is gray, devoid of luster, and without ductility. Concern- 
ing the microscopic detection of iridium, see BEHRKNS, Zeitschr. f. analyt, 
Chem., 30, 154. 



160. 
3. MOLYBDENUM, Mo. (Oxides of Molyldenum.) 

MOLYBDENUM is not largely disseminated iu nature, and is found only 
in moderate quantities, more especially as molybdenum sulphide and as 
lead molybdate (yellow lead ore). From the use of ammonium molybdate 
as a means of detecting and determining phosphoric acid, molybdenum 
has acquired considerable importance in practical chemistry. MOLYBDE- 
NUM is tin-white and hard; when heated in the air, it oxidizes; and it is easily 
soluble in nitric acid and in aqua regia, as well as in concentrated sulphuric 
acid. It fuses with extreme difficulty. The MONOXIDE, MoO, and the SESQFI- 
OXIDE, MoaOa , are black ; while the dioxide, MoOa , is dark brown or dark 
violet. When heated in the air or treated with nitric acid, all of these are 
converted into MOLYBDIC AGED, Mod. This is a white, porous moss, 
which separates into fine scales in water, and dissolves to a slight extent. 
It fuses at a red heat; in close vessels, it volatilizes only at a very high tem- 
perature; while in the air, it volatilizes easily at a red heat, and sublimes to 
transparent laminae and needles. On igniting it in a current of hydro- 
gen, it is first converted into the dioxide, and afterwards, by strong and 
long-continued heating, into the metal The non-ignited acid dissolves in 
acids. When heated to redness in vapor of carbon tetrachloride or in a 
mixture of chlorine and carbon monoxide, molybdic acid yields volatile 
chlorides (QUAKTIS>. The solutions are colorless ; but the hydrochloric solu- 
tion is colored by contact with zinc soon, and on addition of stannous chlo- 
rwfe immediately, the color being blue, green, or brown, according to the pro- 
portion of reducing agent and the concentration of the fluid. Digested 
with copper, the sulphuric acid solution turns blue, and the hydrochloric acid 
solution, brown. The reaction often requires some time. A solution of 
ferrous sulphate acidified with sulphuric acid colors acid solutions per- 



308 DEPORTMENT OF BODIES WITH REAGENTS. [$ 160. 

manently blue. If sodium Jtypophosphite and sulphurous acid are added 
to an acid solution of molybdic acid, a blue precipitation or only a blue 
coloration of the liquid results, according to the amount of molybdenum 
present. Slight warming hastens the appearance of the reaction (MILLABD). 
In solutions acidified with hydrochloric acid, potassium ferrocyanide 
produces a reddish-brown precipitate. Tincture of galls as well as 
tannin color solutions of alkaline molybdates deep red with a brown tint, 
and if hydrochloric acid is now added, a brown precipitate or coloration 
results. A little hydrogen sulphide colors acid solutions blue, while more 
gives a brownish-black precipitate. The fluid over the latter at first appears 
green, but after being allowed to stand for some time, and heated, addi- 
tional quantities of hydrogen sulphide being repeatedly conducted into it, 
the whole of the molybdenum present separates ultimately, though slowly, 
as brownish-black molybdenum trisulphide, MoS 8 . The precipitate dis- 
solves in sulphides of the alkali metals. Acids reprecipitate molybdenum 
trisulphide from the sulphur salts thus formed, and the application of heat 
promotes the separation. Boiling oxalic acid solution does not attack 
molybdenum sulphide (means of separation from tin sulphide produced in, 
the wet way, which dissolves m it, CLARKE). By heating to redness in the 
air, or by heating with nitric acid, molybdenum sulphide is converted into 
the acid. If potassium sulphocyanide and a little hydrochloric acid are 
added to a solution containing molybdic acid, it is not colored; but if some 
ffinc is added, reduction takes place, and in consequence of the formation of 
a sulphocyanide corresponding to the dioxide or also to the sesquioxide, 
the liquid is colored carmme-red. The addition of phosphoric acid does 
not destroy the reaction (difference from ferric sulphocyanide) Upon 
shaking the red liquid with ether, the sulphocyanides are dissolved in 
the latter, and there is consequently formed a red layer of ether (0. D. 
BRAUN). If hydrogen peroxide is added to an acid solution of molybdic 
acid, a yellow-colored liquid results, the color of which is not taken tip by 
ether upon shaking with the latter (ScnoN, WHETHER, BARWALD;. When 
vanadium or titanium compounds are present at the same time, the re- 
action is not applicable, 

Holybdic acid dissolves readily in solutions of alkalies and alkali car- 
lonates. From concentrated solutions, nitric acid or hydrochloric acid 
throws down molybdic acid, which redissolves in a large excess of the pre- 
cipitant. The solutions of molybdates of the alkali metals are colored 
yellow by hydrogen sulphide, and give afterwards, upon addition of acids, 
a brownish-black precipitate. If a solution of molybdic acid in excess of 
ammonia is mixed with yellow ammonium sulphide, and boiled for some 
time, a dark red liquid of great depth of color is formed, in addition to a 
brownish-black precipitate unless a very large excess of ammonium sul- 
phide is present. For the deportment of molybdic acid with orthophos- 
phoric acid and ammonia, see 172, 10. 

If a little concentrated sulphuric acid is dropped upon a trough- 
shaped piece of platinum foil, a small amount of molybdic acid or 
of a molybdate is added in the form of powder, and the mixture is 



161.] TUNGSTEN. 309 

then heated to copious fuming, allowed to cool, and a little alcohol 
is added or the platinum foil breathed upon repeatedly, an intense 

BLUB COLORATION OF THE SULPHUBIO ACID is produced (V. KOBELL, 

SCH'ON, MASGHEE). In the presence of antimonie acid or of much 
stannic oxide, the mixture must be evaporated with phosphoric acid 
before it is heated with sulphuric acid (&ASCHKE). TThen molybdic 
acid is heated on charcoal in the oxidising flame, it is volatilized, and 
the charcoal becomes coated with a yellow powder, often crystalline, 
which becomes white upon cooling. In the reducing flame* metallic 
molybdenum is produced, which is obtained as a gray powder npon wash- 
ing away the carbon. In the oxidizing flame, molybdenum sulphide 
yields sulphurous acid, and molybdic acid which coats the charcoal. If 
molybdic acid or a molybdate is heated for a short time with sodium car- 
bonate in a spiral of platinum, the mass is dissolved in a few drops of water 
with the aid of heat, and the solution is soaked up with strips of filter- 
paper, these allow the recognition of molybdenum by touching them with 
hydrochloric acid and potassium f errocyanide, with stannous chloride, and 
also with ammonium sulphide and hydrochloric acid OUKSEN). K 
molybdic acid is heated with an equal quantity of sulphur iodide * upon 
an artificially prepared gypsum plate, in the oxidizing flame of the blow- 
pipe, an ultramarine-blue coating is obtained (WHEELER and LUDEKING). 
Concerning the microchemical detection of molybdenum, compare EAUS- 
HOFER, p. 97 ; BEHBENS, Zeitschr. f. analyt. Ohem., 30, 168. 



161. 
4 TUNGSTEN, W. (Oxides of Tungsten.) 

TUNGSTEN does not occur widely disseminated in nature, and only in 
moderate amount. The most common tungsten minerals are scheelite 
(calcium tungstate) and wolframite (ferrous and manganous tungstate). 
Tungsten, produced by the reduction of tungstic acid by hydrogen at a 
strong red heat, is an iron-gray powder, which is very difficultly fusible. 
The powder when ignited in the air gives tungstic acid, VOi. When 
heated in dry chlorine gas, free from air, it is converted into the blackish- 
violet tungstic chloride, WClo, which may be sublimed, and gener- 
ally contains lower chlorides and sometimes oxychlorides. This chloride 
is decomposed by heating with water, forming hydrated tungstic acid. 
Tungstic chloride is also obtained by heating tungstic acid to red- 
ness in the vapor of carbon tetrachloride or in a mixture of chlorine and 
carbon monoxide (QUANTIN). Acids, even aqua regia, dissolve metallic 
tungsten but little or not at all. It is also insoluble in potassium hydroxide 
solution, but it is dissolved by this reagent when an alkaline hypochlorite 
is mixed with it. TUNGSTEN DIOXIDE, "WO. , is brown, and by intense igni- 

*This is prepared by fusing together 40 parts of iodine and 60 parts of 
sulphur, and pulverizing the mass. 



310 DEPOBTMENT OF BODIES "WITH BEAGEKTS. [ 161. 

tion, with free access of air, it is converted into tungstic acid. TTTNGSTIC 
ACID is lemon-yellow when cold, dark orange when hot, fixed, and insoluble in 
water and acids. With water and with bases, it forms two series of com- 
pounds : tungstates and metatungstates. By fusing tungstic acid with potas- 
sium disulphate, and treating the fused mass with water, an acid solution is 
obtained, which contains no tungstic acid. After the removal of this solu- 
tion, the residue, consisting of potassium tungstate and a large excess of 
tungstic acid, completely dissolves in water containing ammonium carbon- 
ate (difference and means of separating tungstic from silicic acid). ALKALI- 
METAL TUNGSTATES soluble in water are formed readily by fusion with 
alkali-metal carbonates, but with more difficulty by boiling with solutions 
of the same. Hydrochloric acid, nitric acid, and sulphuric add, when 
added in sufficient quantity, produce in solutions of these tungstates 
white precipitates, which turn yellow on boiling, and are insoluble in an 
excess of the acids (difference from molybdic acid), but soluble in ammo- 
nia. They also dissolve, after pouring off the acid, upon protracted treat- 
ment with water. Upon evaporating with an excess of nitric acid to dry- 
ness, heating the residue to 120, and treating the latter, without warming, 
with a solution of ammonium nitrate containing some nitric acid, the 
tungstic acid remains almost entirely undissolved (K J. TRAM, A. ZEEGLEB). 
PJiosphoric acid does not produce precipitates, but rapidly changes tung- 
stic acid into metatungstic acid, in consequence of which, it prevents 
the precipitation by other acids, barium chloride, calcium chloride, lead 
acetate, silver nitrate, and mercurous nitrate produce white precipitates. 
Potassium ferrocyanide, with addition of some acid, colors the fluid deep 
brownish-red, and after some time produces a precipitate of the same 
color. Tincture of galls and also tannin, with a little acid added, pro- 
duce a brown color or precipitate. Hydrogen sulphide scarcely precipitates 
acid solutions. Ammonium sulphide fails to precipitate solutions of 
alkali-metal tungstates, but upon acidifying the solution containing an 
excess of ammonium sulphide, light brown trisulphide, TO* , mixed with 
sulphur, precipitates, which is slightly soluble in pure water, but is practi- 
cally insoluble in water containing salts. JSftannous cJiloride produces 
a yellow precipitate, which on acidifying with hydrochloric acid, and 
applying Heat, acquires a beautiful blue color (highly delicate and 
characteristic reaction). If solutions of alkali tungstates are mixed with 
hydrochloric acid, or better still, with an excess of phosphoric acid, and 
zinc is added, the fluid acquires a beautiful blue color. The blme color 
produced in the hydrochloric acid solution changes transiently into red, 
and then becomes brownish-black. Also, upon the addition of sodium 
hypophosphite and sulphurous acid to a solution of an alkaline tang- 
state somewhat acidified with sulphuric acid, a solution colored deep blue 
is obtained upon gentle warming. Ferrous sulphate gives an ochre* 
colored precipitate, which does not become blue with acids (difference from, 
molybdic acid). The METATUNGSTATES are mostly soluble in water. Upon 
protracted boiling, sulphuric, hydrochloric, and nitric acids separate from 
the solutions the hydrate of ordinary tungstic acid. Fusing sodium meta- 



162.] TELLUETCnff. 311 

pJwsphate dissolves tungstic oxide. The bead, exposed to the oxidizing flame, 
appears clear, varying from colorless to yellowish ; while in the reducing 
flame, it acquires a pure blue color, and upon addition of ferrous sulphate, a 
blood-red color. By mixing tungstic acid with very little sodium carbonate, 
and exposing in the cavity of the charcoal support to the reducing flame, 
tungsten in powder is obtained, which may be separated by washing. If 
tungstic acid is fused in the platinum spiral with sodium carbonate, the 
mass is warmed with a few drops of water, and the solution soaked up with 
strips of filter-paper, the latter give a means of detecting tungstic acid by 
the yellow color produced by moistening them with hydrochloric acid and 
wanning, and by the blue color produced by touching them with stannous 
chloride and warming. Ammonium sulphide does not color the paper, 
either alone or after the addition of hydrochloric acid, but it assumes a 
blue or green color upon wanning (BUNSEN). Upon heating with sulphur 
iodide upon a gypsum tablet in the oxidizing blowpipe flame (compare 
160), tungstic acid yields a pale greenish-blue coating (^HEELER and 
LTJDEKING). The tungstates which are insoluble in water may, most of 
them, be decomposed by digestion with acids. Wolframite, which strongly 
resists the action of acids, is fused with alkali-carbonate, when water will 
dissolve from the mass the alkali tungstate formed. Concerning the 
microohemical detection of tungstic acid, see HAUSHOFEE, p. 141; BEHBENS, 
Zeitschr. f. analyt. Ohem., 30, 109* 



162. 

5. TELLUBIUM, Te. (Oxides of Tellurium.) 

TELLURIUM is not widely disseminated, and is found in small quantities 
only, in the native state or alloyed with other metals, or as tellurous acid. 
It is a white, brittle, readily fusible metal, which may be sublimed in ? 
glass tube. Heated in the air, it burns with a greenish-blue flame, emit* 
ting thick, white fumes of tellurous acid. Tellurium is insoluble in hydro* 
chloric acid, but dissolves readily in nitric acid to tellurous acid, TeO* 
Tellurium in powder dissolves in cold, concentrated sulphuric acid to a 
purple-colored fluid, from which it separates again upon addition of water. 
If the concentrated solution is heated, it becomes decolorized, and the 
greater part of the sulphate of tellurons acid, which is formed, separates. 
TELLUBQUB ACID is white; at a gentle red heat, it fuses to a yellow fluid, 
and it is volatilized by strong ignition in the air, forming no crystalline 
sublimate. The anhydrous acid dissolves readily in hydrochloric acid, 
sparingly in nitric acid and dilute sulphuric acid, freely in solution of 
potassium hydroxide, slowly in ammonia, and barely in water. Hydrated 
tellurous acid is white, perceptibly soluble in cold water, and dissolves 
easily in hydrochloric acid and in nitric acid. Addition of water to 
the acid solutions throws down the white hydroxide, and from the undi- 
luted nitric acid solution nearly all the tellurous acid separates after some 



312 DEPOBTMEtfT OF BODIES WITH REAGENTS. [ 162, 

time as a crystalline precipitate. From the hydrochloric acid solution, 
alkalies and alkali carbonates throw down a white hydroxide, which is 
soluble in an excess of the precipitant. Hydrogen sulphide produces in 
acid solutions a brown precipitate of tellurous sulphide, TeSa (in color 
like stannous sulphide), which dissolves very freely in ammonium sulphide. 
From acid solutions, stannous chloride and also zinc precipitate black, 
metallic tellurium. Sulphurous add and sodium sulphite precipitate the 
metal in this way only in the presence of hydrochloric acid. If a solution 
of tellurous acid in an excess of potassium or sodium hydroxide is heated 
with addition of grape-sugar, there is also a precipitation of metallic 
tellurium (STOLBA). Tellurous acid produces a white precipitate in a mix- 
ture of magnesium chloride, ammonium chloride, and ammonia. This 
precipitate is not crystalline (difference from selenious acid, HILGER, v. 
GERICHTEN). TELLURIC ACID, TeO s , is formed by fusing tellurium or com- 
pounds of tellurous acid with mixtures of alkaline nitrates and carbonates. 
The mass is soluble in water, the solution remains clear upon acidifying it 
frith hydrochloric acid in the cold, but upon boiling, it evolves chlorine, 
and tellurous acid is formed, which may be precipitated by water if the 
excess of acid is not too great. 

If tellurium, its sulphide, or an oxygen compound of the metal, is 
fused with potassium cyanide in a stream of hydrogen, potassium telluro- 
cyamde is formed. The fused mass dissolves in water, but a current of 
air throws down from the solution the whole of the tellurium (difference 
and means of separation from selenium). If finely pulverized tellurium 
or tellurium ore, e.g., gold telluride, is covered with a little water in a 
porcelain dish, a little mercury is added, and then a little sodium amalgam 
is brought upon this, the water is immediately colored beautifully violet 
in consequence of sodium telluride going into solution (G. KUSTBL). "When 
tested in the dry way by BTOSEN'S method (p. 31), the compounds of tellu- 
rium give a grayish-blue color in the upper reducing flame, while the 
upper oxidizing flame appears green. The volatilization is unaccom- 
panied by any odor. The incrustation produced l?y reduction is black, with 
a blackish-brown edge, and gives a crimson solution when heated with con- 
centrated sulphuric acid. The incrustation of oxide is white, and scarcely 
visible; but stannous chloride colors it black, metallic tellurium being 
separated. When heated with sodium carbonate in the stick of charcoal, 
compounds of tellurium yield sodium tellunde, which when placed on 
dean silver and moistened produces a black stain, and when treated with 
hydrochloric acid (in the presence of enough tellurium) gives an odor of 
hydrogen telluride, with separation of tellurium. Concerning the micro- 
scopic detection of tellurium, see HAUBHOFEB, p. 124 ; BEHBENS, Zeitschr. 
f. analyt Chem., 30, 167. 



168.] SELENIUM. 813 

163. 
6. SELENIUM, Se. (Oxides of Selenium.) 

SELENIUM occurs rarely in nature, in the form of selenides of metals. It 
is found occasionally in pyrites, and, in consequence of this, also in sul- 
phuric and hydrochloric acids. It resembles sulphur in some respects, and 
tellurium m others. Fused selenium is grayish-black, volatilizes at a high 
temperature, and may be sublimed. Heated in the air, it burns taselemous 
oxide, SeOa , exhaling a characteristic smell of decaying radish. Selenium 
is soluble in carbon disulphide. The solution m contact with mercury pro- 
duces black selenide of mercury. Cold concentrated sulphuric acid dis- 
solves selenium to a dark green liquid, without oxidizing it, and upon 
diluting the solution, the selenium falls down in red flakes. Upon boiling 
with concentrated sulphuric acid, it dissolves with oxidation to SELENIOUS 
ACID. Nitric acid aud aqua regia also dissolve selenium to SELEXIOUS ACID. 
This volatilizes at about 200, forming a deep yellow gas. Sublimed 
selenious acid appears in the form of white, four-sided needles, and 
hydrated selenious acid, in the form of crystals resembling those of potas- 
sium nitrate. Both the anhydride and the hydrated acid dissolve readily 
in water, forming strongly acid fluids. Of the normal salts, only those 
with the alkali metals are soluble in water ; the solutions have alkaline 
reactions. Most of the selenides dissolve readily in nitric acid, but the 
lead and silver salts dissolve with difficulty. In solutions of selenious acid 
or of selenites in the cold (in presence of free hydrochloric acid), hydrogen 
sulphide produces a yellow precipitate of a mixture of finely divided 
selenium and sulphur, which upon heating turns reddish-yellow, and is 
soluble in ammonium sulphide. Barium chloride produces (after neutral- 
ization of the free acid, should any be present) a white precipitate of 
barium selenite, which is soluble in hydrochloric acid and in nitric acid. 
Sulphurous add precipitates red selenium from acid solutions, and also 
even from sulphuric acid solutions (difference from tellurium). Stannous 
chloride gives the same precipitate in hydrochloric and sulphuric acid solu- 
tions. Metallic copper, when placed in a warm solution of selenious acid 
containing hydrochloric acid, immediately becomes coated black ; and if 
the fluid remains long in contact with the copper, it turns light red from 
separation of selenium (BEINSOH). Selenious acid produces in a mixture of 
magnesium chloride, ammonium chloride, and ammonia, usually only after 
some time, a colorless, crystalline precipitate of magnesium selenite, which 
is soluble in acids (HELGER, v. GERICHTEN). SELENIO ACTO, SeOs, is pro- 
duced by heating selenium or its compounds with mixtures of alkaline car- 
bonates and nitrates. The mass is soluble in water, and the solution remains 
clear upon being acidified with hydrochloric acid. "When boiled with the 
latter, it evolves chlorine, selenic acid being converted into selenions acid. 
If selenium or one of its compounds is fused with potassium cyanide in a 



314 DEPORTMENT OP BODIES WITH REAGENTS. [ 163. 

stream of hydrogen, potassium selenocyanide is obtained, from which the 
selenium is not eliminated by the action of the air (as is the case with 
tellurium). It separates, however, upon long-continued boiling, after 
addition of hydrochloric acid. When tested according to p. 31, compounds 
of selenium give a blue color to the flame, and by volatilisation and com- 
bustion of the vapor, the characteristic odor of decaying radish is emitted. 
The incrustation produced by reduction is brick-red to cherry-red, and 
gives a dirty green solution with concentrated sulphuric acid. The 
incrustation of oxide is white, and when moistened with stannous chloride 
becomes red from separated selenium. In the charcoal stick with sodium 
carbonate, sodium selenide is formed, which when placed on silver and 
moistened produces a black stain, and when treated with acids yields 
hydrogen selenide. Heated with sulphur iodide in the oxidizing flame of 
the blowpipe, upon a gypsum tablet (compare 160), setenious acid gives 
a reddish-brown coating (WHEELER and LUDEKING). Concerning the 
microscopic detection of selenium, see HAUSHOFEE, p. 116; BEHBENS, 
Zeitschr. f. analyt. Chem., 30, 167. 

To separate selenium from tellurium, heat the solution of tellurous and 
selenious acids in concentrated sulphuric acid with a fourfold volume of 
a moderately strong, aqueous solution of sulphurous acid, warm for some 
time, filter off the separated selenium, and heat with hydrochloric acid 
with the addition of more sulphurous acid, in order to precipitate the 
tellurium (DiVEBS and SGHDIOSE). 



B, DEPORTMENT OF THE AOTDS AND THEIR RADICALS. 

164. 

The reagents which serve for the detection of the acids are 
divided, like those used for the detection of the metals, into 
GENERAL REAGENTS, i.e., such as indicate the GROUP to which 
the acid nnder examination belongs; and SPECIAL REAGENTS, 
<?., such as serve to effect the identification of the INDIVIDUAL 
AOTDS. The groups of acids cannot be defined with the same 
degree of precision aa those into which the bases are divided. 

The two principal groups are the INORGANIC and OR- 
GANIC AOIDS. This division is based npon those characteristics 
by which the ends of analysis are most easily attained, regard- 
less of theoretical considerations. In fact, this distinction is 



164.] DEPOBTMENT OP THE ACIDS. 315 

based upon the behavior at a high temperature, and those acids 
are called organic of which the salts (particularly those of an 
alkali or an alkali-earth metal) are decomposed upon ignition, 
with separation of carbon. This criterion has the advantage, 
that a most simple preliminary experiment at once determines 
the class to which an acid belongs. The salts of organic acids 
with alkali or alkali-earth metals are converted into carbonates 
when heated to redness. 

Before proceeding to the special study of the several acids, 
a general view of all of them, classified in groups, is here 
given. 

I. INOBGANIO ACIDS. 

FIRST GROUP: 

Division a. Chromic acid (sulphurous and thiosulphuric 
acids, iodic acid). 

Division 5. Sulphuric acid (hydrofluosilicic acid). 

Division c. Phosphoric add, loric acid, oxatic add, hydro- 
fluoric acid (phosphorous acid). 

Division d. Carbonic acid, silicic acid. 

SEOOJSTD GEOTJP: 

Chlorine and hydrochloric acid/ bromine and Kydrobromio 
acid; iodine and Kydriodic acid; cyanogen and hydro- 
cyanic acid, together with hydrqferro- and hydroferri- 
cyanic acids, as well as hydrosulphocymic acid; 
sulphur and hydrosvl/phuric add (hydrogen sulphide) 
(nitrous acid, hypochlorous acid, chlorous acid, hypo- 
phosphorous acid). 

TBDDKD GBOUP: 
Nitric acid, chloric acid (perchloric add). 

IL OBGAOTO Aoros. 

FIRST GBOTTP: 

Oxalic acid, tartaric acid, citric add, mdKc acid (racemie 
acid). 



816 DEPORTMENT OF BODIES WITH KEAGENTS. [ 165. 



GKOUP: 
Succinic add) ~bemoic acid, salicylic acid. 

THIED GROUP: 

Acetic acid) fonmo acid (lactic acid, propionic acid, butyric 
acid). 

The acids printed in italics are more frequently met with in 
the examination of minerals, waters, ashes of plants, industrial 
products, articles of food and luxury, medicines, etc. ; while 
the others occur more rarely. 

L INOEGAJSIO ACIDS. 
first Group. 

ACIDS WHICH AT?-"tt PRECIPITATED FROM NEUTRAL SOLUTIONS BY 

BAKIUM CHLOBIDE. 
165. 

For the sake of distinctness, this group is subdivided into 

four divisions, as follows : 

a. Acids which are decomposed in acid solution by hydrogen 
sulphide, and to which attention has therefore been directed 
already in the testing for bases, viz., CHROMIC ACID (sul- 
phurous acid, and thiosulphuric acid, the latter because it is 
idecomposed and detected by the mere addition of hydro- 
chloric acid, to the solution of one of its salts; and also 
iodic acid).* 

8. Acids which are not decomposed in acid solution by hydrogen 

* To this first division of the first group of inorganic acids belong properly 
also all the oxygen compounds of a distinctly pronounced acid character, 
which have been discussed already with the Sixth Group of the metals (acids 
of arsenic, antimony, selenium, etc.). But as the reaction of these compounds 
with hydrogen sulphide leads to confounding them with other metals rather 
than with other acids, it appears the safer course to class these compounds, 
which stand, to a certain degree, upon the border-line between bases and 
acids, with the metallic radicals. 



166.] CHROMIC ACID. 317 

sulphide, and the barium compounds of which are insoluble 
or scarcely soluble in hydrochloric acid, viz., SCLPHURIO 
ACID (hydrofluosilicic acid). 

o. Acids which are not decomposed in acid solution by hydrogen 
sulphide, and the barium compounds of which dissolve in 
hydrochloric acid, apparently without decomposition, inas- 
much as the acids cannot be completely separated from the 
hydrochloric acid solution by heating or evaporation, viz., 

PHPOSHOBIC ACID, BORIC ACID, OXALIC ACID, HYDBQFLD )RIC ACID 

(phosphorous acid). (Oxalic acid, although it will albo be 
considered with the organic acids, is included here, because 
its salts are decomposed upon ignition, without actual car- 
bonization, and this fact may lead to its being overlooked as 
an organic acid.) 

d. Acids which are not decomposed in acid solution by hydrogen 
sulphide, and the barium salts of which are soluble in 
hydrochloric acid, with separation of the acid, viz., CARBONIC 

ACID, SILICIC ACID. 

First Division of the First Orowp of Inorganic Acids. 

166. 

CHROMIC ACID (Anhydride\ CrO,. 

1. CHROMIUM TRIOXIDE forms a scarlet, crystalline mass, or 
distinct acicular crystals. Upon ignition, it is resolved into 
chromic oxide, Cr a O,, and oxygen. It deliquesces rapidly upon 
exposure to the air. It dissolves in water, imparting to the 
fluid a deep reddish-yellow tint, which remains visible in very 
dilute solutions. 

2. The OHROMATBS are all red or yellow, and for the most 
part insoluble in water. Part of them are decomposed upon 
ignition. Those with alkali bases are soluble in water, and 
when normal are not decomposed by ignition; the solutions of 
the normal alkali-metal chromates are yellow, those of the acid 
chromates are reddish-yellow. These tints are visible in highly 
dilute solutions. The yellow color of the solution of a normal 
salt changes to reddish-yellow on the addition of an acid. 



318 DEPORTMENT OF BODIES WITH REAGENTS. [ 166. 

3. Hydrogen sulphide, acting upon the acidified solution, 
produces first a brownish coloration of the fluid, then a green 
color, arising from the formation of a chromic salt. This- 
change of color is attended with separation of sulphur, which 
imparts a milky appearance to the fluid : K a Cr a O T + 4JE a SO 4 -|_ 
3H a S = K.SO. + Cr 9 (SO 4 ) 8 + 38 + 7H a O. Heat promotes 
the reaction, part of the sulphur being in that case converted 
into sulphuric acid. 

4. Ammonium sulphide, when added in excess to a solu- 
tion of an alkali dichromate, immediately produces a bluish 
gray-green precipitate, consisting essentially of chromic hydrox- 
ide and sulphur. In a solution of normal potassium chromate, 
at first a dark brownish coloration alone is produced, but the 
bluish gray-green precipitate above mentioned soon separates. 
The precipitations are complete only upon boiling. After being 
washed, the precipitate dissolves in hydrochloric acid, giving off 
an odor of hydrogen persulphide. 

5. Chromic acid may also be reduced to chromic oxide by 
means of many other substances, and more particularly by 
wd/phurous add) by heating with concentrated kydrocMoriG 
acid, or with the dilute acid and alcohol (in which case ethyl 
chloride and aldehyde are evolved); by stcwwiouB cKloride or 
metallic amo in the presence of hydrochloric or sulphuric acid,, 
by heating with tartarie add, oxalic add, etc. All these 
reactions are clearly characterized by the change of the red or 
yellow color of the solution to the green or violet tint of the 
chromic salt. Alkaline solutions of chromates are not reduced 
by alcohol, even upon heating (difference from manganic and 
permanganic acids). 

6. In aqueous solutions of chromates, larium chloride pro- 
duces a yellowish-white precipitate of BABIUM OHROMA.TB, 
BaOrO 4 , soluble in dilute hydrochloric and nitric acids. This 
dissolves very slightly in cold water, but somewhat more in hot 
water. Ammonium salts increase the solubility very notice- 
ably, and acetic acid increases it considerably. The solu- 
bility in these weaker solvents disappears completely, however, 
if normal potassium or ammonium chromate is added. 

7. In aqueous solutions of normal chromates, silver nitrate 
produces a dark brownish-red precipitate of SILVBE OHBOMATB, 



166.] CHROMIC ACID. 310 

Ag,OrO 4 , easily soluble in nitric acid and in ammonia. In 
slightly acid solutions, it produces a dark red to reddish-brown, 
crystalline precipitate of SILVER DICHEOMATE, Ag,Cr 9 O 7 , which 
dissolves easily in ammonia, and somewhat less readily in nitric 
acid. 

8. In an aqueous or acetic add solution of a cliromate, 
lead acetate produces a yellow precipitate of LEAD CHROJIATE, 
PbCrO 4 , insoluble in ammonia, soluble in potassium hydroxide 
and sodium hydroxide solutions, sparingly soluble in dilute 
nitric acid, and insoluble in acetic acid. Upon heating with 
alkalies, the yellow normal salt is converted into a red basic 
chromate, PbCrO.PbO. 

9. If a very dilute, acid solution of hydrogen peroxide* 
(about 6 or 8 cc) is covered with a layer of et^ej? (about half a 
centimeter thick), and a fluid containing chromic acid is added, 
the solution of hydrogen peroxide acquires a flue ''blue color. 
By closing the test-tube with the thumb, and inverting it repeat- 
edly, without much shaking, the solution becomes colorffess, while 
the ether acquires a blue color. The latter reaction ie. jwirtieu- 
larly characteristic. One part of potassiuity ehromate in ^0,000 
parts of water suffices to produce it distinctly (Sratim) ; bat the 
presence of vanadic acid materially impairs th&gdlic&qy of th6 test 
(WERTHER).t This blue coloration is caused by perchromic 
acid, Cr a 7 . After some time, it is reduced to a chromic salty 
and the ether is decolorized, 

10. If insoluble chromates are fused with sodium ca&onats 
with the addition of some potassium chlorate, and the mass is 
treated with water, a solution is obtained which IB colored 
yellow from the alkali chromate dissolved in it, and which 
becomes reddish-yellow upon the addition of an ao^L, The 



* If a solution of hydrogen peroxide is not at hand, a solution which V 
adapted for making the experiment may be easily prepared by triturating c. 
fragment of barium dioxide (about the size of a pea) with some water, and 
adding it with stirring to a mixture of about 80 cc hydrochloric add and 130 
cc water. The solution keeps a long time without Buffering decomposition. 
In default of barium dioxide, impure sodium dioxide may be used, which ia 
obtained by heating a fragment of sodium in a porcelain capsule until it takes 
fire, and. letting it burn. 

f Journ. f prakt. Chem., 83, 195. 



320 DEPORTMENT OF BODIES WITH REAGENTS. [ 

i 

metals of the original insoluble chromates remain undissolved 
as oxides or carbonates, when the mass is treated with water. 

11. In the blowpipe flame, the chromates show the same 
reactions with sodium metaphosphate and with borax as chromic 
oxide compounds. 

12. Very minute quantities of chromic acid may be detected 
in aqueous solution by one of the following methods : a. Mix 
with the fluid, slightly acidified with sulphuric acid, a little 
tincture of guaiacum (1 part of the resin to 100 parts of alcohol 
of 60 per cent), when an intense blue coloration of the fluid will 
at once make its appearance, speedily vanishing again, however, 
where mere traces of chromic acid are present (H. SOHIFF). 
I. Dissolve a little diphenylamine in concentrated sulphuric 
acid, and add a drop of the solution containing chromic acid. 
A distinct blue coloration shows the presence of chromic acid. 
<?. Moisten a small piece of starch with a freshly prepared 
potassium iodide solution, and drop upon it some of the chromic 
acid solution which . is acidified with dilute hydrochloric or 
sulphuric acid, or add a small amount of carbon disulpMde 
to a freshly prepared potassi'um iodide solution, add the chromic 
acid solution acidified with hydrochloric or sulphuric acid, and 
shake. The occurrence of a violet coloration of the starch or of 
the carbon disulphide allows the detection of even the minutest 
traces of chromic acid. With the reactions mentioned in 12, 
the presence of chromic acid is shown only when it is certain 
that other substances which give the same or similar reactions 
(and there are many of them) are absent. 



Chromic acid being reduced by hydrogen sulphide to 
a chromic salt, the element is always found in the course of 
analysis in the examination for bases. The intense color of the 
solutions containing chromic acid, the excellent reaction with 
hydrogen peroxide, and the characteristic precipitates produced 
by solutions of lead and of silver salts, afford, moreover, ready 
means for its detection. For the discovery of traces of chro- 
mium present in many minerals, for instance in serpentine, the 
reactions in 12 may be used after the mineral has been fused 
with sodium carbonate and potassium chlorate. Concerning 
the detection of normal alkaline chromates in the presence of 



167.] SULPJU 1101> ACID. 321 

dicziromateSj of dichromates in the presence of normal chromates, 
and of free chromic acid in alkaline dichromates, compare E. 
DONATH, Zeitschr. f. analyt. Chein., 18, 78. In regard to the 
microchemical detection of chromic acid, see 108. 



Harer Acids of the First Division. 
167. 

1. SULPHUROUS ACID, HJSO,. (Sulphurous Anhydride, SO,.) 

SULPHUR DIOXIDE or SULPHUROUS ANHYDRIDE, S0, is a colorless, non- 
inflammable gas, which has the stifling odor of burning sulphur. It dis- 
solves copiously in water. The solution has the odor of the gas, reddens 
litmus-paper, and bleaches Brazil-wood paper. It gradually absorbs oxygen 
from the air, and is thereby converted into dilute sulphuric acid. The salts 
are colorless. Of the normal sulphites, only those with alkali bases are 
zeadily soluble in water; while many of the sulphites insoluble or spanngly 
soluble in water dissolve in an aqueous solution of sulphurous acid, but fall 
down again on boiling. All the sulphites evolve sulphur dioxide when 
treated with sulphuric acid, and this can be readily distilled from the solu- 
tions. Chlorine-water changes sulphites to sulphates, and consequently 
dissolves most of them. Barium chloride precipitates normal sulphites, but 
not free sulphurous acid. The precipitate dissolves in hydrochloric acid. 
Alkali-metal acid sulphites yield, besides the precipitate of normal barium 
sulphite, free sulphurous acid, which remains in solution. Hydrogen 
sulphide decomposes free sulphurous acid, water and pentathionic aewk 
being formed, with separation of sulphur. If to a solution of sulphurous 
acid mixed with an equal volume of hydrochloric acid, a piece of clean 
copper wire is added, and the mixture is boiled, the copper appears black, 
as if covered with soot, if mnch sulphurous acid is present; but only dull 
if little is present (H. BEINBCH). If a trace of sulphurous acid or of a sul- 
phite is introduced into a flask in which hydrogen is being evolved from 
Bulphnr-free zinc or aluminium and hydrochloric acid free from sul- 
phurous acid, hydrogen sulphide is immediately evolved along with the 
hydrogen and the gas BOW produces a black coloration or a black pre- 
cipitate in a solution of lead acetate to which has been added a sufficient 
quantity of caustic soda to redissolve the precipitate which forms at first 
(Sulphurous acid is a powerful reducing agent. It reduces chromic acid, 
permanganic acid, iodic acid, mercurons nitrate, and upon heating (in 
the presence of a considerable amount of alkali-metal chloride), it reduces 
mercuric chloride (to mercurous chloride). It decolorizes iodized starch, 



323 DEPORTMENT OF BODIES WITH REAGENTS. [ 168* 

and produces a blue pi capitate in a mixture of potassium ferricyanide and 
ferric chloride, etc. It, therefore, filter-paper is wet with a dilute starch 
solution* containing some pure potassium iodate (A. FRANK), or with a 
solution of ferric chloride and potassium ferricyanide (0. BROWN), and the 
paper is dried, very delicate test-papers for sulphurous acid are obtained. 
The resulting blue colorations are conclusive tests for sulphurous acid only 
when other reducing agents are certainly not present. The papers, in a 
moistened condition, are therefore especially adapted for the detection of 
minute amounts of gaseous sulphurous acid. Silver nitrate precipitates, from 
a solution of sulphurous acid, white silver sulphite, soluble in nitric acid. 
With a hydrochloric acid solution of sta?mous chloride, a yellow precipitate 
r of STANNIC SULPHIDE is formed after some time. If an aqueous solution of 
an alkali-metal sulphite is mixed, if not neutral, according to circum- 
stances, with acetic acid to give it an exactly neutral reaction, or with 
hydrogen sodium carbonate (an excess of which is without disadvantage, 
while an excess of alkaline hydroxide, normal carbonate, or ammonium 
carbonate may prevent the reaction), and is then added to a rela- 
tively large amount of solution of zinc sulpfiate mixed with a very 
small quantity of sodium ntti opncsside, the fluid acquires a red color it 
the quantity of sulphite present is not too inconsiderable. When, however, 
the amount of sulphite is very minute, the coloration makes its appear- 
ance only after addition of some solution of potassium ferrocyanide. 
If the quantities are not altogether too small, a purple-red precipitate 
will form upon the addition of the potassium ferrocyanide (B6DEKER). 
Thiosulphates of the alkalies do not show this reaction. Concerning the 
microchemical detection of sulphurous acid, compare DENIGES, Phannac* 
OentralhaUe, 1892, p. 98. 



168. 

2. THIOSTJLPHUBIO Aon>, 

Thiosulphuric anhydride, S0, does not exist in the free state. 
Most of its salts are soluble in water. The solutions of most thiosul- 
phates may be boiled without suffering decomposition ; but upon boil- 
ing its solution, calcium tbiosulphate is resolved into calcium sulphite 
and sulphur. The alkali-metal thiosulphates, when heated out of con- 
tact with air, decompose into water, sulphur and hydrogen sulphide, 
which escape, and a mixture of sulphide and sulphate of the alkali metal, 
which remains behind. If sulphuric or hydrochloric acid is added 
to the solution of a thiosulphate, the liquid at first remains clear and 
odorless, but after a short time (the shorter, the more concentrated and 
warmer the solution), it becomes more and more turbid, owing to the sep- 

* 3 g of wheat starch, 100 g of water, and .2 g- of potassium iodate 



169.] IODIC ACID. 323 

aration of sulphur, and exhales the odor of sulphur dioxide. Silver nitrate 
produces a white precipitate of SILVER THIOSCLPHATB, which is soluble in 
an excess of the thiosulphate, and after a little while (upon heating, 
almost immediately) turns black, being decomposed into silver sul- 
phide and sulphuric acid. Sodium thiosulphate dissolves silver chloride; 
upon the addition of an acid, the solution remains clear at first, but after 
some time, and immediately upon boiling, silver sulphide separates. 
Barium chloride produces a white precipitate, which is soluble in much 
water, more especially hot water, and is decomposed by hydrochloric acid. 
Ferric chloride colors the solutions of alkali thiosulphates reddish-violet 
(difference from alkali sulphites); but on standing, the liquid loses its color, 
especially when heated, ferrous chloride being formed. Acidified solution 
of tfiromic acid is immediately reduced by thiosulphates to green chromic 
salt solutions. When the chromic acid solution is not acidified, it turns 
brown, and upon heating, it yields brown chromic chrornate. ' Iodized 
starch solution and an acidified solution of potassium permanganate are 
decolorized at once. With zinc or aluminium and hydrochloric acid the 
thiosulphates behave like the sulphites. Treated with potassium or sodium 
hydroxide and aluminium, sulphides of the alkali metals are obtained 
(DE KONINOK, difference from sulphites). 



Where it is required to find sulphites and thiosulphates of the alkali 
metals in presence of alkali-metal sulphides, as is of ten the case, solution of 
sine sulphate is first added to he fluid until the sulphide is decomposed; the 
zinc sulphide is then filtered off, and one part of the filtrate is tested for 
thiosulphuric acid by addition of hydrochloric acid or with aluminium and 
potassium hydroxide, another portion for sulphurous acid with sodium 
nitroprusside, etc. 



169. 

8. IODIO Aero, BIO,. (lodic Anhydride, I.O..) 

IODIO ANHYDRIDE forms a white, crystalline powder, while the acid forms 
-colorless, rhombic crystals. Both are readily soluble in water, and are de- 
composed at a moderate heat into iodine vapor and oxygen, and, in the case 
of the hydrated acid, water also. The salts are decomposed upon ignition, 
being resolved either into oxygen and a metallic iodide, or into iodine, 
-oxygen, and metallic oxide. Only the iodates of the alkali metals dissolve 
readily in water. From solutions of alkali-metal iodates, barium chloride 
throws down a white precipitate of barium iodate, which is soluble 
in nitric acid. Silver nitrate gives a white, granular, crystalline precipitate 
of silver iodate, which dissolves readily in ammonia, but only sparingly iii 
nitric acid. Lead acetate precipitates white lead iodate, which is scarcely 



824 . DEPORTMENT OF BODIES WITH BEAGENTS. [ 170. 

soluble in water, and difficultly so in nitric acid. Hydrogen sulphide 
precipitates iodine from solutions of iodic acid, with the simulta- 
neous separation of sulphur. Upon further addition of hydrogen sulphide, 
the iodine dissolves in the hydriodic acid formed, and with an excess of 
hydrogen sulphide, the liquid becomes decolorized with further separation 
of sulphur, while the iodine is completely converted into hydriodic acid. 
Iodic acid when combined with bases is also decomposed by hydrogen sul- 
phide. Sulphurous acid throws down iodine, which is converted into 
hydriodic acid by an excess of the sulphurous acid. A boiling, 
saturated solution of oxalic add expels all the iodine from salts of lodio 
acid. Phosphorus (colorless as well as red, the latter with especial energy) 
reduces free and combined iodic acid even in very dilute solutions, with 
the formation of phosphoric acid and the separation of iodine (POLAooi). 
To detect iodio acid in nitric acid, it is best to dilute the latter with about 
2 volumes of water, to add a little carbon disulphide or chloroform and 
one drop of an aqueous solution of sulphurous acid, and to shake the mix- 
ture. If iodic acid was present, the carbon disulphide or chloroform is 
colored violet in consequence of taking up the iodine set free. An excess 
of sulphurous acid is, of course, to be avoided. 



Second Division of the First Ghrowp of Inorgamo Acids. 

170. 
SULPHUEIO AOTD, HJS0 4 . (Sulpkurio Anhydride, SO,.) 



1. SULPHUB TRIOXEDB Or SUUHUEIC AtfHYDMDE, SO, 

forms a white, feathery, crystalline mass, which fumes strongly 
upon exposure to the air ; while OONOENTBATED SULPHUBIO ACID 
(which contains a little more water than the f onnulaH a SO 4 requires) 
forms an oily liquid, colorless and transparent like water. Both 
the anhydride and the acid char organic substances, and combine 
with water in all proportions, the process of combination being 
attended with considerable elevation of temperature, and in the- 
case of the anhydride, with a hissing noise. 

2. The normal STTLPHATES are readily soluble in water, with 
the exception of the sulphates of barium, strontium, calcium, 
and lead. The basic sulphates of the heavy metals which are 
insoluble in water diss6lve in hydrochloric or in nitric acid. 
Most of the sulphates are colorless or white. Those of the> 



170.] ^ SULPHURIC ACID. 323 

alkali and alkali-earth metals are not decomposed by moder- 
ate ignition, but are more or less easily decomposed at very high 
temperatures. The other sulphates are variously acted upon by 
a moderate red heat, some of them being readily decomposed, 
and many others resisting decomposition. 

3. Even in exceedingly dilute solutions of sulphuric acid 
and of the sulphates, "barium chloride produces a finely pulver- 
ulent, heavy, white precipitate of BARIUM SULPHATE, BaSO 4 , 
scarcely soluble in dilute hydrochloric and nitric acids. From 
very dilute solutions, the precipitate separates only after stand- 
ing for some time. Concentrated acids and concentrated solutions 
of many salts impair the delicacy of the reaction, while a certain 
excess of barium chloride increases it. 

4. Lead acetate produces a heavy, white precipitate of LEAD 
SULPHATE, PbSO 4 , which is but slightly soluble in water, still 
less so in dilute sulphuric acid, insoluble in alcohol, and spar- 
ingly soluble in dilute nitric acid, but dissolves completely in 
hot concentrated hydrochloric acid. It is dissolved by hot solu- 
tions of ammonium tartrate or acetate. 

5. The sulphates of the alkali-earth metals which are in- 
soluble in water and acids are converted into CARBONATES by 
fusion with alkali-metal carbonates; but lead sulphate yields 
LEAD OXIDE when treated in this manner. In both cases, alkali- 
metals sulphates are formed. The sulphates of the alkali-earth 
metals and of lead are also resolved into insoluble carbonates and 
soluble alkali sulphates, by digestion or boiling with concentrated 
solutions of carbonates of the alkali metals. In the case of 
barium sulphate, however, repeated boiling with renewal of the 
solution is necessary for complete decomposition. 

6. Upon fusing sulphates with sodium, carbonate on charcoal 
in the inner flame of the blowpipe, or heating them in the stick 
of charcoal (p. 34) in the lower reducing flame, the sulphuric 
acid is reduced, and sodium sulphide formed, which may be 
readily recognized by the odor of hydrogen sulphide emitted 
upon moistening the sample and the part of the charcoal into which 
the fused mass has penetrated, and adding a small quantity of an 
acid. If the fused mass is transferred to a clean silver plate, or 
a polished silver coin, and then moistened with water, a black 
stain of silver sulphide is immediately produced. (Compounds 



326 DEPORTMENT OF BODIES WITH REAGENTS. [ 170. 

of tellurium and selenium give foe same reaction.) Since the 
gas flame contains sulphur, these experiments by fusion should 
be made by the help of an alcohol-lamp. 

7. Concerning the microchemical detection of sulphuric acid, 
sec HAUSHOFEB, p. 115; BEHRENB, Zeitschr, f. analyt. Chem., 
30, 166. 

Remarks. The characteristic and exceedingly delicate reac- 
tion of SULPHUEIO AOID with barium salts renders the detection 
of this acid an easier task than that of almost any other. It is 
simply necessary to take care not to confound with barium 
sulphate, precipitates of barium chloride, and particularly of 
barium nitrate, which are formed upon mixing aqueous solu- 
tions of these salts with fluids containing a large proportion of 
free hydrochloric acid or free nitric acid. It is very easy to dis- 
tinguish these precipitates from barium sulphate, since they re- 
dissolve immediately upon diluting the acid fluid with water. To 
tilute the fluid largely is a rule that should never be de- 
parted from in testing for sulphuric acid with barium chloride. 
A little hydrochloric acid should also be added, which counter- 
acts the adverse influence of many salts for instance, citrates 
of the alkali metals. Where very minute quantities of sulphuric 
acid are to be detected, the fluid, after the addition of a suffi- 
cient excess of barium chloride, should be allowed to stand sev- 
eral hours at a gentle heat. The trace of barium sulphate formed 
will in that ease be found deposited at the bottom of the vessel. 
When the least uncertainty exists about the nature of the pre- 
cipitate produced by barium chloride in presence of hydrochloric 
acid, the reaction in 6 will at once remove all doubt. In 
testing for very small quantities of sulphuric acid in the presence 
of much hydrochloric or nitric acid, the greater part of the lat- 
ter should first be evaporated off or neutralized with an alkali 
before adding barium chloride. To detect free sufyJiwric <tdcl 
in presence of a sulphate, the fluid is mixed with a very little 
cane-sugar, and evaporated to dryness in a porcelain dish at 
100. If free sulphuric acid was present, a black residue re- 
mains, or in the case of most minute quantities, a blackish-green 
residue. Other free acids do not decompose cane-sugar in this 
way. The reaction may be also carried out by adding a very 



171, 172.] PHOSPHORIC ACID, 827 

minute amount of cane-sugar (about .2 to .3 per cent) to the 
solution, and allowing the lower end of a strip of filter-paper 30 
or 40 cm long to dip into it. After 24 hours, the strip of papei 
is dried and heated to 100. In the presence of free sulphuric 
acid, the paper becomes brown or black, and often very brittle, 
at the upper limit of the moistened part (XESSLEB). 



HYDBOFLUOSILIOIC AOID, H,SiF 6 . 

HYDROFLUOSHJOIO ACID forms a white, deliquescent mass, which fuses at 
19', and is easily soluble in water. The aqueous solution is a very acid 
fluid, which volatilizes completely upon evaporation in platinum, as silicon 
fluoride and hydrofluoric acid. When evaporated in glass, it etches the lat- 
ter. With bases, it forms water and sihcofluorides, most of which are 
soluble in water, redden litmus-paper, and upon ignition are resolved into 
metallic fluorides and silicon fluoride. Barium chloride forms a crystal- 
line precipitate with hydrofluosilicic acid ( 100, 6). Strontium chloride 
forms no precipitate with this acid, while lead acetate added in excess 
gives a white precipitate. Potassium salts precipitate transparent, gelat- 
inous potassium silicofluonde. Ammonia in excess throws down hydrated 
silicic acid, with formation of ammonium fluoride. By heating metallic 
silicofluorides with concentrated sulphuric acid, dense fumes are emitted 
in the air, arising from the evolution of hydrofluoric acid and silicon flu- 
oride. If the experiment is conducted in a platinum vessel covered witli 
glass, the fumes etch the glass ( 176, 5), while the residue contains the 
sulphates formed. 



Third JDwision of the Mrst Group of Inorgwiio 



0. PHOSPHOMO Acn>, H,PO 4 . (Phosphoric Anhydride, P.O..) 

1. COMMON PHOSPHOBUB is a colorless, transparent, solid body, 
of 1.83 sp. gr., with a waxy appearance. It is insoluble in 
water, somewhat soluble in alcohol and in ether, and easily sol- 
uble in carbon disnlphide. Taken internally, it acts as a virulent 
poison. It fuses at 44.3, and boils at 290, but it volatilizes in 



328 DEPORTMENT OF BODIES WITH REAGENTS. [ 

small amount even upon distillation with water. By the influ- 
ence of light, phosphorus kept under water turns first yellow, 
then red, and is finally covered with a white crust. If 
exposed to the air at the common temperature, it exhales 
a highly characteristic and most disagreeable odor, copious 
fumes being evolved, which are luminous in the dark. These 
fumes are formed by oxidation of the vapor of phosphorus, and 
consist of phosphoric and phosphorous acids and phosphorus 
vapor. When the air is moist, ozone, hydrogen dioxide, and 
ammonium nitrite are produced at the same time. Phospho- 
rus very readily takes fire, burning with a luminous flame to- 
phosphoric anhydride, the greater part of which appears in the 
form of white fumes. By the protracted influence of light, or by 
heating to 250 out of contact with air, phosphorus is converted 
into BED (so-called amorphous) PHOSPHOEUS. Red phosphorus 
does not alter in the air, is not luminous, its inflammability is 
much decreased, it is not poisonous, has a specific gravity of 
2.1, and does not dissolve in carbon disulphide. Nitric acid 
and nitre-hydrochloric acid dissolve colorless phosphorus rather 
readily upon heating. Besides phosphoric acid, the solutions at 
first also contain phosphorous acid. Hydrochloric acid does, 
not dissolve phosphorus. If phosphorus is boiled with solution 
of potassium or sodium hydroxide, or with milk of lime, hypo- 
phosphites and phosphates are formed, while spontaneously- 
inflammable hydrogen phosphide gas escapes. If a substance 
containing colorless phosphorus is placed at the bottom of a flask, 
and a strip of paper moistened with solution of silver nitrate is 
suspended inside the flask by means of a cork loosely inserted 
into its mouth, and a gentle heat applied (from 30 to 40), the 
paper will turn black, in consequence of the reducing action 
of the phosphorus fumes, even though only a most minute quan- 
tity of the phosphorus is present. If, after the termination of 
the reaction, the blackened part of the paper is boiled with 
water, the undecomposed portion of the silver salt precipitated 
with hydrochloric acid, the fluid filtered, and the filtrate evap- 
orated as far as practicable on the water-bath, the presence of 
phosphoric acid in the residue may be shown by means of the 
reactions described below (J. SCHEKER). It must be borne in 
mind that the silver salt is also blackened by hydrogen sulphide, 



1 172.] PHOSPHORIC ACID. 329 

formic acid, volatile products of putrefaction, etc., and, moreover, 
that the detection of phosphoric acid in the strip of paper can be 
of value only where the latter and the filtering-paper were per- 
fectly free from phosphoric acid. As regards the deportment 
of phosphorus upon boiling with dilute sulphuric acid, and in a 
hydrogen evolution apparatus supplied with zinc and dilute sul- 
phuric acid, see the detection of phosphorus, Part II, Division II. 

2. ANHYDBOUS PHOSPHORIC ACID, P a O 6 , is a white, siiow- 
like mass, which rapidly deliquesces in the air. When treated 
with water, it hisses, and is at first only partially dissolved ; in 
time, however, the solution is complete. "With water and bases, 
it forms three series of compounds; viz., with 3 molecules of 
water or with an equivalent amount of base, orthopliosphoric 
acid or common phosphates ; with 2 molecules of water or the 
corresponding amount of base, pyrophosphoric acid or pyro- 
phosphates; with 1 molecule of water or its equivalent of base, 
metaphosphoric acid or inetaphospliates. Since compounds of 
orthophosphorie acid only are usually encountered in nature and 
in analysis, these alone will be discussed in a comprehensive 
manner, while pyro- and metaphosphoric acids will be treated 
more briefly in a supplementary paragraph. 

3. OETHOPHOSPHOEIO ACID, H,PO 4 , forms colorless and pellu- 
cid crystals, which deliquesce rapidly in the air to a syrupy, non- 
<3austie liquid. The action of heat changes it into meta- or pyro- 
phosphorie acid, according to whether one or two molecules of 
-water are expelled from 2H,P0 4 . Heated in an open platinum 
dish, orthophosphorie acid, if pure, volatilizes completely, though 
with difficulty, in white fumes. 

4. The action of heat fails to decompose the ORTHOPHOS- 
PHATES with fixed bases, but converts them into pyrophosphates 
if they contain one hydrogen or one ammonium, and into meta- 
phosphates if they contain two hydrogens or other volatile radi- 
caJs. Of the normal orthophosphates, only those with alkali 
bases are soluble in water. The solutions manifest alkaline 
reactions. If pyro- or metaphosphates are fused with excess of 
sodium carbonate, the fused mass contains only orthophosphates. 

5. In aqueous solutions of alkaline phosphates having a 
neutral or alkaline reaction, but not in those having an acid 
inaction (dihydrogen phosphates), barium chloride produces white 



330 DEPOBTMENT OF BODIES WITH REAGENTS. [ 172. 



precipitates of BARIUM PHOSPHATE, HBaP0 4 or 

which are soluble in hydrochloric and nitric acids, but difficultly 

soluble in ammonium chloride. 

6. In neutral or alkaline solutions of phosphates, but not 
in solutions of phosphoric acid, solution of calcium sulphate 
produces a white precipitate of HYDROGEN CALCIUM PHOSPHATE,. 
ECaPO 4 .2H,0, or of TEICALCITJM PHOSPHATE, Ca,(PO 4 ) 9 , which 
dissolves readily in acids, even in acetic acid if it is still in an 
amorphous condition, and in this state, it is soluble also in am- 
monium chloride. 

7. In concentrated solutions of dimetallic alkali phosphates,. 
magnesium sulphate produces a white precipitate of HTDEOGEK 
MAGNESIUM PHOSPHATE, HMgPO^TH.O, which of ten separates 
only after some time ; but upon boiling, a precipitate of TRIMAGNE- 
SIUM PHOSPHATE, Mg a (P0 4 ),.7H a O, is thrown down immediately. 
The latter precipitate forms also upon addition of magnesium 
sulphate to the solution of a trimetallic alkali phosphate. But if 
a mixture of magnesium sulphate and sufficient ammonium chlo- 
ride to keep it clear when it contains ammonia is added to a solution 
of phosphoric acid or of an alkali-metal phosphate, and then an 
excess of ammonia is also added, a white, crystalline and quickly 
subsiding precipitate of AMMONIUM MAGNESIUM PHOSPHATE, 
NH 4 MgP0 4 .6H a O ? is formed, even in highly dilute solutions. 
This precipitate is almost entirely insoluble in ammonia, and 
most sparingly soluble in ammonium chloride, but dissolves 
readily in acids, even in acetic acid. It makes its appearance 
often only after the lapse of some time, but stirring promotes its 
separation ( 103, 8). The reaction can be considered decisive 
only if no arsenic acid is present ( 156, 8). 

8. Silver nitrate throws down from solutions of di- and tri- 
metallic alkali phosphates, a light yellow precipitate of SILVER 
PHOSPHATE, Ag,P0 4 , which is readily soluble in nitric acid and 
in ammonia. If the solution contained a trimetallic phosphate,. 
the fluid in which the precipitate is suspended manifests a neu- 
tral reaction, while the reaction is acid if the solution contained 



* A precipitate corresponding to the first formula is produced when the so- 
lution contains an alkaline phosphate with one hydrogen and two alkali-metal 
atoms or ammoniums, while a precipitate corresponding to the second formula 
ifl formed where the phosphate is tribaric. 



172.] PHOSPHORIC ACID. 

a dimetallic phosphate. The acid reaction in the latter ca&e 
arises from the circumstance that the nitric acid radical receives 
only 2 atoms of alkali metal for the 3 atoms of silver which it 
yields to the phosphoric acid : HK fl P0 4 + SAgZS'O, = Ag.PO, 
+ 2KNO.+ HNO,. 

9. If a tolerably large amount of sodium acetate is added 
to a solution containing phosphoric acid and little or no free acid, 
and then a drop of ferric chloride, a yellowish-white, fluccu- 
lent, gelatinous precipitate of FERBIC PHOSPHATE, FePO 4 .2E a O, is 
produced. An excess of ferric chloride must be avoided, as ferric 
acetate (of a red color) would thereby be formed, in which the 
precipitate is not insoluble. This reaction is of importance, a* 
it enables us to detect phosphoric acid in phosphates of the alkali- 
earth metals; but it can be held to be decisive, only if no arsenic 
acid is present, as this shows a very similar reaction. To effect 
the complete separation of phosphoric acid from the alkali-earth 
metals, a sufficient quantity of ferric chloride is added to impart 
a reddish color to the solution, which is then boiled (whereby the 
whole of the iron is thrown down, partly as phosphate, partly a& 
basic acetate), and filtered hot. The filtrate contains the alkali- 
earth metals as chlorides. In order to detect, by means of 
this reaction, phosphoric acid in presence of a large proportion 
of ferric salts, boil the hydrochloric acid solution with sodium 
sulphite until the ferric chloride is reduced to ferrous chloride, 
as indicated by decoloration ; add sodium carbonate until the 
fluid is nearly neutral, then sodium acetate, and finally one drop 
of ferric chloride. The reason for this proceeding is that fer- 
rous acetate does not dissolve ferric phosphate. 

10. If a few cubic centimeter: of the solution of ammonium 
molybdate in nitric acid ( 55) are placed in a test-tube, and a 
little of a liquid containing phosphoric acid in neutral or acid 
solution is added, there is formed immediately or in a short time, 
even in the cold, if the amount of phosphoric acid is at all 
considerable, a pulverulent, pale yellow precipitate of AMMONICM 
PHOSPHOMOLYBDATE, which gathers upon the sides and bottom 
of the test-tube. When the phosphoric acid is present in ex- 
ceedingly minute quantity, 0.^., 0,00002 g, it is necessary to wait 
some hours and to apply a gentle heat, not to exceed 40, 
before the precipitate appears. When other coloring matters 



832 DEPORTMENT OF BODIES WITH REAGENTS. [ 172. 

are not present, the liquid above the precipitate is colorless after 
the complete separation of the precipitate. More of the solution 
to be tested for phosphoric acid than a third, at the most, of the 
molybdenum solution used should never be added, and a mere 
yellow coloration of the liquid should not be considered as a 
reaction for phosphoric acid. 

The yellow precipitate under consideration, ammonium phos- 
phomolybdate, contains MOLTBDIO ACID, AMMONIUM, WATEE, and 
a little PHOSPHORIC AOTD (3 per cent). Since it is insoluble in 
dilute acids, only in the presence of an excess of molybdic acid, 
it may not form at all if an excess of phosphoric acid is added, 
a fact which should be well heeded. Hydrochloric acid, if 
present in considerable amount, interferes with or prevents the 
reaction. It may be readily removed by evaporation with nitric 
acid. Certain organic substances also (e.ff. 9 tartaric acid and 
reducing agents) exert a disturbing influence, and consequently 
are to be removed, when necessary, by fusion with sodium car- 
bonate and potassium nitrate. The precipitate is easily recog- 
nized, even in dark-colored liquids, after allowing it to settle. 
If the precipitate is washed with the molybdenum solution which 
serves to precipitate it, then dissolved in ammonia, and a 
mixture of magnesium sulphate, ammonium chloride, and am- 
monia is added, ammonium magnesium phosphate is obtained. 

If one operates in the manner given above, phosphoric acid 
cannot be confused with any other acid ; for arsenic acid gives 
no precipitate m the cold with the molydenum solution in ques- 
tion, although it gives one upon heating, and especially upon 
boiling (the fluid above this appears yellow for a considerable 
time); while silicic acid gives no reaction in the cold, although 
upon heating, it gives a strong yellow coloration but no pre- 
cipitate. 

11. If & finely powdered substance containing phosphoric acid 
(or a metallic phosphide) is intimately mixed with 5 parts of a 
flux consisting of 3 parts of sodium carbonate, 1 part of sodium 
nitrate, and 1 part of silicic add, the mixture then fused in a plati- 
num spoon or crucible, the mass boiled with water, the solution 
obtained decanted, ammonium carbonate added to it, the fluid 
"boiled again, and the silicic acid which is thereby precipitated 
filtered off, the filtrate now holds in solution alkali phosphate, 



173.] APPEXDIX. 333 

and accordingly may be tested for phosphoric acid as directed in 
7, 8, 9, or 10. 

12. On igniting and pulverizing a substance containing 
phosphoric acid, placing it into a tube of the thickness of a 
straw and sealed at one end, adding a fragment of magnesium 
wire about i mm long (or a small piece of sodium), which should 
be covered by the sample, and then heating, a vivid incandes- 
cence is observed, and magnesium (or sodium) phosphide is 
formed. When the black contents of the tube are crushed and 
moistened with water, they exhale the characteristic odor of 
hydrogen phosphide (WINKELBLECH, BrasEx). 

13. White of egg is not precipitated by solution of ortho- 
phosphoric acid, nor by solutions of orthophosphates mixed with 
acetic acid. 

14. In relation to the microchemical detection of phosphoric 
acid, see HAUSHOFEB, p. 108; BEHKEXS, Zeitschr. 1 analyt. 
Chern., 30, 165. 

ITS. 
Appendix. 

a. Pyrop7u)sphoric acid, H 4 PaOT. The solution of pyrophosphoric acid 
is converted by boiling into solution of orthophosphoric acid. The solu- 
tions of the salts bear heating without suffering decomposition ; but upon 
boiling with a strong acid, the pyrophosphorio acid is converted into ortho- 
phosphoric acid. If the salts are fused with sodium carbonate m excess, 
orthophosphates are produced. Of the tetrametallic pyrophosphates, only 
those with alkali bases are soluble in water. The acid salts, e.g., H 3 Na 9 P*07, 
are converted by ignition into metaphosphates, e.g., NaPO*. Barium 
'chloride fails to precipitate the free acid; but from solutions of the salts, it 
precipitates white BARIUM PYRQPHOSPHATE, BasPaO?, soluble in hydro- 
chloric acid. Silver nitrate throws down from a solution of the acid, 
especially upon addition of an alkali, a white, earthy-looking precipitate of 
SILVER PYRQPHOSPHATE, AgiPaO?, which is soluble in nitric acid and in 
ammonia. Magnesium sulphate precipitates MAGNESIUM FTROPHOSPHATE, 
MgaPaO-. The precipitate dissolves in an excess of the pyrophosphate, as 
well as in an excess of magnesium sulphate. Ammonia fails to precipitate 
it from these solutions (difference from metaphosphoric acid). Upon 
boiling the solution, it separates again. A concentrated solution of ItUeo- 
cobaltic chloride, added to a uot too dilute solution of an alkali pyrophos- 
phate, produces an immediate precipitation of pale reddish-yellow spangles 
(difference from phosphoric and metaphosphoric acids, 0. D. BRAUN). 
White of egg is not precipitated by solutions of the acid, nor by solutions 
of the salts mixed with acetic acid. Ammonium molybdate, with addition 



334 DEPORTMENT OF BODIES WITH REAGENTS. [ 174 

of nitric acid, fails to produce a precipitate at first, but afterwards yellow 
ammonium phosphomolybdate separates to the extent to which pyrophos- 
phoric acid is converted into orthophosphoric acid. 

6. Mefaptosphoric acid. Five sorts of metaphosphates are known at 
present, and the acids, also, corresponding to most of these have been pre- 
pared. The several reactions by which these may be distinguished will 
not be entered upon here, but mention should be made of the fact that the 
metaphosphoric acids differ from the pyro- and orthophosphoric acids in 
this, that the solutions of the metaphosphoric acids, and the solutions of 
their salts after addition of acetic acid, precipitate white of egg at once. 
Those acids and salts which are precipitated by silver nitrate produce with 
that reagent a white precipitate. Magnesium sulphate produces no pre- 
cipitate, but one forms when ammonia is also added, which dissolves in 
much ammonium chloride. All metaphosphates yield sodium orthophos- 
phate upon fusion with sodium carbonate. 

174. 
0. BORIO Aom, H.BC,, (Boric Anhydride, B,O 8 .) 

1. BOEIO ANHYDRIDE forms a colorless, fixed glass, which is 
fusible at a red heat. -The hydrate, HB0 9 [metaboric acid], 
forms a porous, white mass. The compound HBO,.H,O [or 
HjBOu orthoboric acid], crystallizes in scale-like plates. Boric 
acid is soluble in water and in alcohol, and upon evaporating the 
solutions, a large portion of it volatilizes along with the aqueous 
and alcoholic vapors. The solutions redden litmus-paper, and 
impart to turmeric-paper a faint brown-red tint, which acquires 
intensity upon drying. The BOBA.TES are not decomposed upon 
ignition ; and only those with alkali bases are readily soluble in 
water. The solutions of berates of the alkali metals are color- 
less, and all, even those of the acid salts, manifest an alkaline 
reaction. 

2. In solutions of alkali-metal borates, if not too highly 
dilute, Iwrium chloride produces white precipitates of BAJBIUM 
BORA.TE, which are soluble in acids and ammonium salts. The 
formula for the precipitate when produced from solutions of 
normal borates is Ba(BO a ) s .2H 9 O, and from solutions of aoid 
borates it is Ba,B 10 O ia .6H,O (H. EOSE). 

3. Silver mtrate, when mixed with concentrated solutions 
of normal alkali-metal borates, gives a white precipitate, colored 
somewhat yellowish from free silver oxide, of 2AgB0 9 .H s O; 



174.] BOEIC AGIO. 335 

while from concentrated solutions of alkali-metal acid borates, it 
throws down white Ag^O,,. Dilute solutions of alkali-metal 
borates give with silver nitrate a brown precipitate of silver oxide 
(H. ROSE). All these precipitates dissolve in nitric acid and in 
ammonia. 

4. If dilute sulphuric acid or hydrochloric acid is added to 
highly concentrated, hot solutions of alkali boratea, (OETHO)BOBIO 
ACID separates upon cooling, in the form of shining, crystalline 
scales. 

5. If a solution of boric acid, or of a borate of an alkali 
metal or of an alkali-earth metal, is mixed with hydrochloric 
acid to slight, but distinct, acid reaction, and a slip of turmeric- 
paper is half dipped into it, and then dried on a watch-glass at 
100, the dipped half shows a peculiar BED tint (H. ROSE;. 

This reaction is very delicate. Care must be taken not to 
confound the characteristic red coloration with the blackish- 
brown color which turmeric-paper acquires when moistened 
with rather concentrated hydrochloric acid and then dried, nor 
with the brownish-red coloration which ferric chloride, or a 
hydrochloric acid solution of ammonium molybdate or of zir- 
conia gives to turmeric-paper, more particularly upon drying. 
By moistening turmeric-paper, reddened by boric acid, with a 
solution of an alkali or an alkali carbonate, the color is changed 
to bluish-black or greenish-black ; but a little hydrochloric acid 
will at once restore the brownish-red color (A. VOGBL, H. 
LTOWIG). 

6. If alcohol is poured over free boric acid or a borate 
with addition, in the latter case, of concentrated sulphuric acid 
to liberate the boric acid, and the alcohol is kindled, the flame 
appears of a very distinct YELLOWISH-GBEKN color, especially 
upon stirring the mixture. This tint is imparted to the flame by 
the boric acid separated from the boric etiber which volatilizes 
with the alcohol- The delicacy of this reaction may be consid- 
erably heightened by heating the dish which contains the alco- 
holic mixture, kindling the alcohol, allowing it to burn for a 
short time, then blowing out the flame, and afterwards rekin- 
dling it. At the first flickering of the flame, its borders will now 
appear green, even though the quantity of the boric acid be so 
minute that it fails to produce a perceptible coloring of the 



836 DEPORTMENT OF BODIES WITH REAGENTS. [174. 

"flame when treated in the usual manner. Concentrated sul- 
phuric add in not too small a/mount should be used. As salts of 
copper likewise impart a green tint to the flame of alcohol, any 
copper which may be present must first be removed by menus 
of hydrogen sulphide. Presence of metallic chlorides may also 
lead to mistakes, as the ethyl chloride formed in that case colors 
the borders of the flame bluish-green. 

7. For the following very characteristic reaction for boric 
acid, a short, wide test-tube is required, which is provided with 
a doubly perforated stopper : Into the two holes, glass tubes 
bent at right angles are inserted, one of which reaches almost to 
the bottom of the test-tube, while the end of the other is just 
below the stopper. The limb of the latter tube, projecting 
about 5 cm, is contracted at the end to about 1 mm. If a small 
amount of a substance containing boric acid is placed in the test- 
tube, a little concentrated sulphuric acid added, and, after 
cooling, some methyl alcohol is gradually added, then pure hy- 
drogen is conducted through the small apparatus, and this is 
kindled when the atmospheric air has been expelled, it burns 
green on account of containing methyl boric ether, B(OCH 8 ), , 
and the flame gives the characteristic boric acid spectrum, 
Trhen it is examined with the spectroscope (see 10, KOSEN- 
SLADT). If the escaping gas is led through a little potassium 
hydroxide free from silicic acid, this is treated in a platinum 
dish with hydrofluoric acid, and evaporated to dryness on the 
water-bath, potassium borofluoride, KF.BF,, is formed, which 
remains undissolved upon treating the residue with 1 part of 
potassium acetate in 4 parts of water. 

8. If a substance containing boric acid, reduced to a fine 
powder, is mixed, with addition of a drop of water, with 3 parts 
of a flux composed of 4& parts of potassium disulphate and 1 
part of finely pulverized calcium fluoride, free from boric acid, 
and the paste is exposed on the loop of a platinum wire in the 
outer mantle of the BUNSEN gas flame, or at the apex of the inner 
-flame of the blowpipe, boron fluoride, BF 15 escapes, which 
imparts a green tint to the flame, though only for an instant 
-(TURNER). With readily decomposed compounds, the reaction 
may be obtained by simply moistening the sample with hydro- 
fluosilieic acid, and holding it in the flame. The delicacy of the 



175,] OJXALIC ACID. 837 

test may be increased by mixing the substance intimately with 
silicic acid and fluor-spar, and heating it with concentrated sul- 
phuric acid in a test-tube, with the addition of a fragment of 
marble, and conducting the escaping gases by means of a glasa 
tube bent at a light angle and provided with a platinum blow- 
pipe tip, into a non-luminous BUNSEX flame (!VAMMEKER). 

9. If a dry substance containing boric acid is heated with a 
half or an equal volume of anuuoniwn silicojluoride* in a glass 
tube closed at one end, at last to redness, a sublimate of AMMO- 
NIUM BOEOFLUOBIDB is obtained, which, when brought into a 
colorless flame, colors the latter green, and when dissolved in 
water gives the reaction, with turmeric-paper, mentioned in 5. 
If the substance to be tested contains a free acid, this is to bo 
slightly more than neutralized with sodium carbonate (STOLBA). 

10. When placed in the flame of the spectrum aj>paratu8 t 
boric acid or borates, fused with sodium carbonate on the loop 
of a platinum wire, give (even with very small amounts of bone 
acid) a spectrum of four well-marked lines of equal width, equidis- 
tant from each other. Bj is brilliant yellowish-green (coinciding 
with Ba y) ; B a is brilliant light green (coinciding with Ba ft) ; 1 
is pale bluish-green (nearly coinciding with the blue barium line) ; 
B 4 is blue, very pale, close to Sr tf (SIMMLER). Also, if a finely 
pulverized substance containing boric acid is rubbed up with 
glycerine to a thickish paste, and is brought into the flame of a 
BUNSEN burner with the loop of a platinum wire, a green flame 
is obtained which is very well adapted for spectroscopic testing 
(M. W. ILEB). 

11. In relation to the microchemical detection of boric aci<! 4 
see HAUSHOFEB, p. 30; BEHBENS, Zeitschr. f. analyt Ohein., 30> 
159. 

175. 
o. OXALIC ACID, 11,0,0,. 

1. QXAZJO ACID is a white powder, while the CRYSTALLIZED 
ACID, CyO^ + 2H,O, forms colorless, rhombic prisms. Both dis- 
solve readily in water and in alcohol. By heating rapidly in open 

* To be obtained by carefully neutralizing hydrufluosilieic acid with 
ammoniu, and evaporating the filtrate in n platinum difih. 



338 DEPOBTMENT OF BODIES WITH REAGENTS. [ 178, 

vessels, part of the acid undergoes decomposition, while another 
portion volatilizes unaltered. The fumes are very irritating, and 
provoke coughing. If the acid is heated in a test-tube, some of 
it sublimes unaltered. 

2. The OXALATES all undergo decomposition at a red heat, 
the acid decomposing into carbon monoxide and carbon dioxide. 
The oxalates of the alkali metals, and of barium, strontium, and 
calcium, are converted into carbonates in this process (if pure, 
and if the heating takes place slowly, almost without separation 
of charcoal). Magnesium oxalate is converted into magnesia 
even by a very gentle red heat. The other metallic oxalates 
leave either the pure metal or an oxide behind, according to the 
reducibility of the metallic oxide. The alkali-metal oxalates and 
some others are soluble in water. 

3. Barium chloride produces in neutral solutions of alkali 
oxalates, a white precipitate of BARIUM OXALATE, BaC a O 4 .HaO, 
which dissolves very sparingly in water, more readily in water 
<iontaining ammonium chloride, acetic acid, or oxalic acid, and 
freely in nitric acid and in hydrochloric acid. Ammonia precipi- 
tates it unaltered from the latter solutions. 

4. Sibver nitrate produces in aqueous solutions of oxalic acid 
and of alkali oxalates, a white precipitate of SILVER OXAT.ATE, 
Ag a C a which is very slightly soluble in water, difficultly 
soluble in dilute nitric acid, and readily soluble in concentrated, 
hot nitric acid and also in ammonia. 

5. Lime-water and all the soluble calcium salts, including 
wlutim of calcium sid/phote^ produce in even highly dilute 
aqueous solutions of oxalic acid, or of oxalates of the alkalies, 
white, finely pulverulent precipitates of OALOIUM OXALATE, 
CaO a 4 .H 9 0, and sometimes OaO a 4 .3H,0, which dissolve 
readily in hydrochloric acid and in nitric acid, but are nearly 
insoluble in oxalic acid and in acetic acid, and practically insoluble 
in water. The presence of ammonium salts does not interfere in 
any way with the formation of these precipitates. Addition of 
ammonia considerably promotes the precipitation of free oxalic 
acid by calcium salts. In highly dilute solutions, the precipitate 
is formed only after some time, but more quickly by heating. 

6* If oxalic acid or an oxalate, in the dry state, is heated 
with an excess of concentrated wtphwrie acid, the latter removes 



176.J HYDROFLUORIC AOID. 

the water necessary for the existence of the oxalic acid, and it is 
decomposed into OARBOX MONOXIDE and CAEBON DIOXIDE, the two 
gases escaping with effervescence : H t C 4 4 = CO + CO, + H,O. 
If the quantity operated upon is not too minute, the carbon 
monoxide may be kindled, and burns with a blue flame. Should 
the sulphuric acid acquire a dark color in the reaction, this is a 
proof that the oxalic acid contained some organic substance as 
an admixture. 

7. If oxalic acid or an oxalate is mixed with finely pulverized 
manganese dioxide (which must be free from carbonates), and 
a little water and a few drops of sulphuric acid are added, a lively 
effervescence ensues, caused by escaping CARBON DIOXIDE: H a C,O 4 
+ MnO a + H 9 SO 4 = 2CO 9 + 2H fl O + i!nS0 4 . Free oxalic 
acid gives this reaction without the addition of sulphuric acid, 
but with less delicacy. 

8. If a small quantity of a solution of oxalic acid is added 
to a solution of ferrous plwsphate in phosphoric acid, the liquid 
assumes a DARK WINE-YELLOW coloration. The delicacy of the 
reaction is heightened by gentle warming (GUNN). 

9. If oxalates of alkali-earth metals are boiled with a con- 
centrated solution of sodium carbonate^ and filtered, sodium 
oxalate is obtained in the filtrate, while the precipitate contains 
the base as carbonate. With oxalates of heavy metals, this 
operation is not always sure to attain the desired object, as many 
of these oxalates (e.g., nickel oxalate) will partially dissolve in 
the alkaline fluid, with formation of double salts. Metals of 
this kind should therefore be separated as sulphides. 

10. In relation to the detection of oxalic acid or calcium 
oxalate by means of the microscope, compare 0. BISCHOFF, 
Zeitschr. f. analyt. Chem., 22, 633; HAUSHOFER, p. 81. 

176. 
d. HTDROFLUOBIO Aou>, HP, 

1. Anhydrous HTDEOFLTTOKIO ACID is a colorless, corrosive 
liquid, which fumes in the air, boils at 19 .4, and is readily dis- 
solved by water. Aqueous hydrofluoric acid is distinguished 
from all other acids by the property of dissolving silicic oxide, 



840 DEPORTMENT OF BODIES WITH BEAGENTS. [ 176. 

and also of dissolving or decomposing the silicates which are 
insoluble in hydrochloric acid. Hydrofluosilicic acid and water 
are formed in the process of dissolving silicic acid : SiO s + 6HP 
= H,SiF fl + 2H a O. With metallic oxides and hydroxides, hydro- 
fluoric acid forms metallic fluorides and water. 

2. The normal FLDTOEIDBS of the alkali metals are soluble in 
water (lithium fluoride is very difficultly soluble), and the solutions 
have an alkaline reaction. The fluorides of the alkali-earth metals 
are either insoluble or very difficultly soluble in water. Alumin- 
ium fluoride is not soluble. Many of the fluorides of the heavy 
metals are very sparingly soluble in water, as the fluorides of 
copper, lead, and zinc, while others dissolve in water without 
difficulty, as nickelous and cobaltous fluorides, silver fluoride, 
antimony fluoride, and stannous fluoride. Many of the fluorides 
insoluble or difficultly soluble in water dissolve in hydrofluoric 
acid, while others do not. Most of the normal fluorides bear 
ignition in a crucible without suffering decomposition. 

3. JSarium cJdoride precipitates aqueous solutions of hydro- 
fluoric acid, but much more completely solutions of fluorides- 
of the alkali metals. The bulky, white precipitate of BARIUM 
FLUORIDE, BaF a , is almost absolutely insoluble in water, but dis- 
solves in large quantities of hydrochloric acid or nitric acid, from 
which solutions, ammonia fails to precipitate it, or throws it 
down only very incompletely, owing to the dissolving action of 
the ammonium salts. 

4. Calcium chloride produces in aqueous solutions of hydro- 
fluoric acid or of fluorides, a gelatinous precipitate of OALOITTM 
FLTTORIDE, CaF a , which is so transparent as at first to induce 
the belief that the fluid has remained perfectly clear. Addition 
of ammonia promotes the complete separation of the precipitate. 
The latter is practically insoluble in water, and only very 
slightly soluble in hydrochloric acid and nitric acid in the cold ; 
but it dissolves somewhat more readily upon boiling with hydro- 
chloric acid. Ammonia produces no precipitate in the solution, 
or only a very trifling one, as the ammonium salt formed retains. 
it in solution. Calcium fluoride is scarcely more soluble in 
hydrofluoric acid than in water. It is insoluble in alkaline 
fluids. 

5. If a finely pulverized fluoride, whether soluble or insol- 



176.] HYDROFLUORIC ACID. 341 

uble in water, is treated in a platinum crucible with ju*t 
enough concentrated sulphuric acid to make it into a thin paste 
(not with more), the crucible covered \\ith the convex face of a 
watch-glass of hard glass coated with beeswax in which lines 
have been traced with a pointed piece of wood, the hollow of the 
glass filled with water, and the crucible gently heated for the 
space of half an hour or an hour, the exposed lines, upon the 
removal of the wax, will be found more or less deeply ETCHED 
into the glass. (The coating is made by heating the glass 
cautiously, putting a small piece of wax upon the convex face, 
and spreading the wax equally as it melts. It is removed 
by heating the glass gently, and wiping with a cloth.) If the 
quantity of hydrofluoric acid disengaged by the sulphuric acid 
was very minute, the etching is often invisible upon the removal 
of the wax ; but in such cases, it will appear when the glasb 
is breathed upon. This appearance of the etched lines is 
owing to the unequal capacity of condensing water which the 
etched and the untouched parts of the plate respectively possess. 
The impressions which thus appear upon breathing on the glass 
may, however, owe their origin to other causes; therefore, 
though their non-appearance may be held as a proof of the 
absence of fluorine, their appearance is not a positive proof of 
the presence of that element. At all events, they ought to be con- 
sidered of value only where they can be developed again after the 
glass has been properly washed with water, dried, and wiped.* 

This reaction fails if there is too much silicic oxide present, 
or if the substance is not decomposed by sulphuric acid. In 
such cases, one of the two following methods is resorted to, ac- 
cording to circumstances: 

6. If a substance containing fluorine, which is decomposable 
by concentrated sulphuric acid, is heated in a finely pulverized 

* J. NICKI&S states that etchings on glass may be obtained with all kinds 
of sulphuric acid, and, in fact, with all acids suited to effect evolution of 
hydrofluoric acid. I have tried watch-glasses of Bohemian glass with sul- 
phuric and other acids, but could get no etchings in confirmation of this 
statement. Still, proper caution demands that before using the sulphuric acid, 
it should first be positively ascertained that its fumes will not etch glass 
Should the sulphuric acid contain hydrofluoric acid, the latter may be easily 
removed by diluting with an equal volume of water, and evaporating in a 
platinum dish to the original strength. 



842 DEPORTMENT OF BODIES TVTTH EBAGBNTS. [ 176. 

condition with that acid (directly in case it is rich in silicic acid, 
but with the addition of finely divided silicic oxide if it contains 
little or none of the latter substance), SILICON FLUOBTDB GAS is 
evolved, which forms thick, white fumes in moist air, and sepa- 
rates silicic acid when brought in contact with water or ammo- 
nia. If the gas is led into water through a bent tube moistened 
inside, the latter at once has its transparency impaired, owing 
to the separation of silicic acid. If the quantity operated upon 
is rather considerable, silicic acid separates in the water, and the 
fluid is rendered acid by hydroflnosilicic susid (compare 32). 
This process is best applied for the detection of small quantities 
of fluorine as follows: Heat the substance with concentrated 
sulphuric acid to about 160 in a small flask closed with a cork 
witL double perforation, bearing two tubes, one of which reaches 
to the bottom .of the flask, while the other terminates immedi- 
ately under the cork. Conduct through the longer tube a slow 
stream of dry air into the flask, and conduct this, upon its issu- 
ing through the other tube, into a small U-shaped tube enlarged 
to a small bulb at the bend and containing a few drops of water. 
The other end of the IT-tube is connected with an aspirator. The 
silicon fluoride which escapes with the air gives a separation of 
silicic acid where it comes in contact with the water ; and with 
the described arrangement of the apparatus, even very small 
amounts may be distinctly recognized. For more difficultly 
decomposable substances, potassium disulphate is used instead of 
sulphuric acid, and the mixture, to which some marble is added 
(to insure a continuous slight evolution of gas), is heated to 
fusion, and kept in that state for some time in a tube of diffi- 
cultly fusible glass, which is closed at one end, and provided 
with a gas delivery-tube at the other end. The silicon fluoride 
evolved in the first operation described above may also be con- 
ducted in a very slow stream into a test-tube which contains 
about .3 g of aniline dissolved in 15 cc of ether and 15 cc of 
alcohol. If fluorine is present, there is formed a white, glisten- 
ing sediment of aniline silicofluoride. If this is suspended in 
the liquid, and a few drops of a moderately concentrated solu- 
tion of sodium hydroxide in absolute alcohol are added, sodium 
rilicofluoride gradually settles to the bottom of the tube (W. 
KKOP). 



176.] HYDROFLUORIC AOID. 343 

7. If silicates which are not decomposable by sulphuric 
acid are to be tested for fluorine, it is first necessary to decom- 
pose them. This is accomplished by fusing them with 4 parts 
of sodium and potassium carbonates. The mass is then extracted 
with water, the liquid is filtered, concentrated by evapora- 
tion, cooled, transferred to a platinum vessel, hydrochloric 
acid added to feebly acid reaction, and the fluid allowed to 
stand until the carbon dioxide has escaped. It is then super- 
saturated with ammonia, heated, filtered into a bottle, calcium 
chloride added to the still hot fluid, the bottle is closed, and 
allowed to stand. If a precipitate separates after some rime, it 
is collected on a filter, dried, and examined by the method de- 
scribed in 5 or 6 (H. HOSE). The foregoing method may be 
also used for other substances containing fluorides (e.g., phos- 
phates containing calcium fluoride), if silica is added to them; 
but without this addition, calcium fluoride is only very incom- 
pletely decomposed by fusion with alkali carbonates. 

8. Minute quantities of fluorides in minerals, slags, etc., 
may also be readily detected by means of the llowpipe. Bend 
a piece of platinum foil, and in- 
sert it in a glass tube, as shown 

in Fig. 43 ; introduce the finely 
triturated substance mixed with 
sodium metaphosphate which has been fused upon charcoal and 
powdered, and let the blowpipe flame play upon it so that the 
products of combustion may pass into the tube. A fluoride 
treated in this way yields hydrofluoric acid gas, which betrays 
its presence by its pungent odor, the dimming of the glass tube 
(which becomes perceptible only after cleaning and drying), antf 
the yellow tint which the acid air issuing from the tube imparts 
to a moist strip of Brazil-wood paper* (BBEZBLIUS, SIOTHSON). 
When silicates containing metallic fluorides are treated in this 
manner, gaseous silicon fluoride is formed, which also colors 
yellow a moist strip of Brazil- wood paper inserted in the tube, 
find causes silicic acid to be deposited within the tube. After 
washing and drying the tube, it appears here and there dimmed. 
A small quantity of a fluoride present in a mineral containing 

Prepared by moistening stripe of fine printing-paper with a decoction of 
Brazil-wood. 




844 DEPORTMENT OF BODIES WITH REAGENTS. [ 177. 

water may generally be detected by heating the substance by 
itbelf in a glass tube sealed at one end, and inserting a slip of 
Brazil-wood paper in the tube ; under these circumstances, the 
paper will usually turn yellow (BEKZELIUS). 

9. Concerning the microchemical detection of fluorine, see 
IJArsuoFEB, p. 50; BEHRESS, Zeitschr. f. analyt. Chem., 
30, 17U. 



177, 

and Remarks. The barium compounds of 
the acids of the third division of the first group are dis- 
solved by hydrochloric acid, apparently without decomposition ; 
and alkalies therefore reprecipitate them unaltered by neutralizing 
the hydrochloric acid. Tho barium compounds of the acids of 
the ilrst division show, however, the same deportment; and these 
uci<l&, therefore* if present, must be removed before any conclu- 
sion regarding the presence of phosphoric acid, boric acid, oxalic 
acid, or hydrofluoric acid, can be drawn from the reprecipita- 
tiou of a barium salt by alkalies. But leaving this point 
out of the question, no great value ib to be placed on this 
reaction, not even w> fur as the simple detection of these acids is 
concerned, and far less as regards their separation from 
other acids, since ammonia fails to reprecipitate from hydro- 
chloric acid solutions their barium salts (more particularly 
barium liorate and barium fluoride), if the solution contains 
any considerable proportion of free acid or of an ammonium 
salt, lime <w!t? is very well characterized by the color- 
ation which it imparts, either directly, or as boron fluoride 
or Wic ether to the alcohol flame, the hydrogen flame, or 
the noii-luiuinniib pis flame, and also by its action on turmeric- 
paper. The latter reaction is more particularly suited for the 
detection of very minute traces. It is to be observed, however, 
that this reaction does not take place in the presence of nitrous 
acid. If oxides of the heavy metals are present, either a subli- 
mate of ammonium borofluoride is first obtained according to 
174, 9, or the metals interfering with the reaction are first 
removed by hydrogen sulphide or ammonium sulphide. Before- 
proceeding to concentrate dilute solutions of boric acid, the latter 



177.] RECAPITULATION AND REMARKS. 343 

must be combined with an alkali, otherwise a large portion of 
the boric acid will volatilize with the aqueous vapors. Small 
quantities of boric acid may also be safely and easily detected 
by the spectroscope. 

The detection of phosphoric acid in compounds soluble in 
water is not difficult, the reaction with magnesium sulphate, 
etc., being well adapted for the purpose. The detection of phos- 
phoric acid in compounds insoluble in water cannot be effected 
by means of magnesium solution. Ferric chloride ( 172, 9) is 
well suited for the detection of phosphoric acid in its salts with 
the alkali-earth metals, and more particularly for the separation 
of the acid from these metals. The nitric acid solution of am- 
monium molybdate is more especially adapted to effect the detec- 
tion of phosphoric acid in presence of aluminium and iron, and in 
general for the detection of small amounts of phosphoric acid. 
It must be again stated that both these reactions demand the 
strictest attention to the directions given. If present in com- 
bination with oxides of the fourth, fifth, or sixth group, phos- 
phoric acid may be separated by the method given 172, 11, 
or it may be simply isolated or combined with ammonium by 
precipitating the bases with hydrogen sulphide or ammonium 
sulphide. 

Oxalic acid may always be easily detected in aqueous solu- 
tions of oxalates of the alkalies by solution of calcium sulphate. 
The formation of a finely pulverulent precipitate, insoluble in 
acetic acid , leaves hardly a doubt as to its presence, as raceuiic acid, 
which occurs very rarely, alone gives the same reaction. In 
case of doubt, the calcium oxalate may be readily distinguished 
from the racemate, by simple ignition with exclusion of air, as 
the decomposed racernate leaves a considerable proportion of 
charcoal behind, and, moreover, the racemate dissolves in cold 
solution of potassium or sodium hydroxide, in which calcium 
oxalate is insoluble. The deportment of the oxalates with sul- 
phuric acid, or with manganese dioxide and sulphuric acid, 
also affords sufficient means to confirm the results of other tests. 
In insoluble salts, the oxalic acid is detected most safely by 
-decomposing them by boiling with solution of sodium carbonate, 
or by hydrogen sulphide or ammonium sulphide ( 175, 9). 
Attention should also be called here to the fact that there are 



346 DEPORTMENT OF BODIES WITH BKAGEWTB. [ 17R 

certain soluble oxalates which are not precipitated by calcium 
salts, more particularly chromic and ferric oxalates. Their non- 
precipitation is due to the fact that these salts form soluble 
double salts with calcium oxalate. 

Hydrofluoric acid is readily detected in salts decomposable 
by sulphuric acid; only it must be borne in mind that too 
large a proportion of sulphuric acid impedes the free evolution of 
hydrofluoric gas, and thus impairs the delicacy of the reaction j 
also that the glass cannot be distinctly etched if, instead of hydro* 
fluoric acid, silicon fluoride alone is evolved. Therefore, in 
the case of compounds abounding in silica, the safer way is to 
try, besides, the reaction given in 176, 5, as well as the one given 
in 6. In silicates which are not decomposed by sulphuric acid, 
the presence of fluorine is often overlooked, because the analyst 
omits to examine the compound carefully by the method given, 
in 176, 7. 



178. 

PHOSPHOROUS Aoro, E,P0 3 . (Phosphorous Anhydride, PA-> 

PHOSPHOROUS OXIDE, PaO, is a white powder, which admits of sublima- 
tion, and burns when heated in the air. With a small proportion of water, 
it forms a thickish fluid, which by long standing yields crystals. Heat 
decomposes phosphorous acid into phosphoric acid and hydrogen phos- 
phide gas which does not take fire spontaneously. It dissolves freely in. 
water, and is poisonous. Of the salts, those with alkali bases are readily 
soluble in water, all the others being sparingly soluble, and dissolving in 
dilute acids. All the salts are decomposed by ignition into phosphates, 
which are left behind, and hydrogen, or a mixture of hydrogen and 
hydrogen phosphide, which escapes. With stiver nitrate, separation of 
metallic silver takes place, more especially upon addition of ammonia and 
application of heat ; and with mercurous nitrate, under the same circum- 
stances, there is a separation of metallic mercury. From mercuric chloride 
in excess, phosphorous acid throws down mercurous chloride after some 
time, but more rapidly upon heating. Barium chloride and calcium chloride 
produce in not too dilute solutions of phosphorous acid, upon addition of 
ammonia, white precipitates soluble in acetic acid. A mixture of magne- 
sium sulphate, ammonium chloride, and ammonia, precipitates only rather 
concentrated solutions. Lead acetate throws down white lead phosphite, 
insoluble in acetic acid. By heating to boiling with sulphurous acid in. 
excess, phosphoric acid is formed, attended by separation of sulphur.. 



179.] CARBONIC AOHX 347 

In contact with zittc and dilute sulphuric arid, phosphorous acid gives a 
mixture of hydrogen with hydrogen phosphide, which accordingly fumes 
in the air, burns with an emerald-green color, and precipitates silver and 
silver phosphide from solution of silver nitrate. Nitric acid interferes 
with the formation of hydrogen phosphide. If this is present only in small 
quantity, a little ferrous chloride is first added, and finally, after some 
time, the zinc is added. The gas containing hydrogen phosphide may bt! 
allowed to act upon pure filter-paper soaked with silver nitrate solution, or 
upon parchment-paper moistened with this solution, instead of using the 
silver nitrate solution directly (H. EAGER). If the amount of pho^hroiis 
acid is minute, the silver paper is blackened only after some ho ,IN It 
should be remembered that blackening of the paper is also caused by 
hydrogen sulphide and hydrogen arsenide. 



Fawrih Division of the First Growp of Inorganic Adds. 

179. 
a. CAEBONIO Aoii> 3 H a OO t . (Carbon Dioxide, CO V ) 

1. CARBON is a solid, tasteless, and odorless body, and only the 
very highest degrees of heat can effect its fusion and volatiliza- 
tion (DESPRETZ). All carbon is combustible, and yields carbon 
dioxide when burnt with a sufficient supply of oxygen or atmos- 
pheric air- In the diamond, carbon is crystallized, transparent, 
pellucid, exceedingly hard, difficultly combustible ; while in the 
form of graphite, it is opaque, grayish-black, soft, greasy to the 
touch, difficultly combustible, and stains the fingers ; and as char- 
coal, produced by the decomposition of organic matter, it is 
black, opaque, non-crystalline, sometimes dense, shining, and 
difficultly combustible, but often porous, dull, and readily com- 
bustible. 

2. CARBON DIOXIDE, CARBONIC ANHYDRIDE, or CARBONIC 
AOID, OO a , at the common temperature and common atmos- 
pheric pressure, is a colorless gas of far higher specific gravity 
than atmospheric air, so that it may be poured from one vessel 
into another. It has a faint odor, a sourish taste, and reddens 
moist litmus-paper; but the red tint disappears again upon 
drying. Carbon dioxide is readily absorbed by solution of 
potassium hydroxide, forming a carbonate; and it dissolves 
rather copiously in water* 



348 DEPORTMENT OF BODIES WITH REAGENTS. [ 179, 

3. The AQUEOUS SOLUTION OF CAEBONIO AOID has a feebly acid 
and pungent taste. It transiently imparts a red tint to litmus- 
paper, and colors solution of litmus wine-red ; but it loses carbon 
dioxide when shaken with air in a half-filled bottle, and more 
completely still upon application of heat. Some of the OABBO- 
NATES lose carbon dioxide by ignition ; and all of them are white or 
colorless in cases where their metals usually give colorless salts. 
Of the normal carbonates, only those with alkali bases are soluble 
in water. The solutions manifest a very strong alkaline reaction. 
The acid carbonates of the alkali and alkali- earth metaLs as well 
as those of some other metals dissolve in water. 

4. The carbonates are decomposed by all free acids soluble in 
water, with the exception of hydrocyanic acid. Most of them 
are decomposed by acids even in the cold, but several (magnesite, 
for instance) require heat. The decomposition is attended with 
EFFERVESCENCE, carbon dioxide being disengaged as a colorless 
and scarcely odorous gas, which transiently imparts a reddish 
tint to moist litmus-paper. It is necessary to apply the decom- 
posing acid in excess, especially when operating upon carbonates 
with alkali bases, since the formation of acid carbonates will 
frequently prevent effervescence if too little of the decomposing 
acid is added. Substances which it is intended to test for car- 
bonic acid In this way should first be heated with a little water, 
to prevent any mistake which might arise from the escape of 
;air bubbles upon treating the dry substances with the acid. 
Where there is reason to apprehend loss of carbonic acid upon 
boiling with water, lime-water should be used instead of pure 
water. If it is wished to prove that the escaping gas is really 
carbon dioxide, pass it into lime-water or baryta-water, or 
dip a glass rod in baryta-water and hold it inside the test-tnbe 
near the fluid. If the gas is carbon dioxide, the lime- or 
barytar-water becomes turbid (see 5).* 

5. Solutions of calcium <md barvum hydroxides (lime- and 
baryta-water) brought into contact with carbonic acid, or with 
-soluble carbonates, produce white precipitates of normal OALOIUH 

* The delicacy of the reaction maybe increased by the use of the apparatus 
described by O. ROSSLER (Ber. der. deutsch. chem. Gesellsch., 1887, p. 2680). 
although I prefer to use the apparatus described in 5 when it is desired to de- 
tect very small amounts of carbonic acfct. 



179.] OABBOKIO ACID. 349 

CARBONATE, CaCO, , or BARIUM CARBONATE, BaCO 3 . In testing 
for free carbonic acid, the reagents ought always to be added in 
excess, as the acid carbonates of the alkali earths are soluble in 
water. The precipitates when separated from the liquids dissolve 
in acids with effervescence, and the resulting solutions, after the 
complete expulsion of the carbon dioxide by boiling, give no 
precipitates with ammonia. For the detection of exceedingly 
minute traces of carbonic acid, the apparatus shown in Fig. 4i is 
recommended, which scarcely needs a detailed description. The 




FIG. 41 

tube a contains soda-lime. The substance to be tested is placed 
in rather large amount in 5, together with a little water, while 
o is empty at first. By suction applied at d by means of a jet- 
pump or an aspirator, the apparatus is now filled with air free 
from carbonic acid, then a little lime-water or baryta- water is 
placed in 0, and a little hydrochloric acid is allowed to flow in 
through the funnel-tube, while a slow current of air freed from 
carbonic acid is allowed to flow through the apparatus, and 5 is 
gently warmed. Since lime-water dissolves a veiy small amount 
of calcium carbonate, it is advisable to saturate this by long 
digestion therewith (WELTER, BBKTHOLLBT). 

6. In solutions of normal alkali carbonates, calcium chloride 
and fiarium chloride immediately produce precipitates of 

Oirrtf CABBQNATE Or of BABIUM CARBONATE; but in dilute 

tions of acid carbonates, these precipitates are formed only upon 



850 DEPORTMENT OF BODIES WITH REAGENTS. [ 180* 

ebullition ; while with aqueous carbonic acid, these reagents give 
no precipitate. 

7. In aqueous solutions of normal and acid carbonates of 
the alkalies and alkali-eartlis, even when very dilute, an aqueous 
solution of lead chloride produces a milky, white precipitate 
of LEAD CARBONATE (EL SoHULZE). Free carbonic acid does not 
interfere with nor prevent the reaction. Acetic acid dissolves 
the precipitate (difference from lead sulphate). 

8. For the detection of free carbonic acid in the presence of 
acid carbonates, a solution of 1 part of rosolic acid in 500 parts 
of 80 per cent alcohol, which has been treated with barium hy- 
droxide solution until it begins to show a red coloration, may 
be used. For example, in testing a well-water, if there is added 
about .5 cc of the rosolic acid solution to 50 cc of the water, 
there is obtained, if the water contains free carbonic acid, a 
colorless, or at the most a faint yellowish, liquid ; but if it con- 
tains no free carbonic acid, but only acid carbonates, the liquid 
becomes red (M. v. PETTENKOFER). 

9. The detection of free carbonic acid, or that which is com- 
bined with normal carbonates to form acid carbonates, in the 
presence of normal carbonates, may be accomplished by use of 
the fact that NESSLER'S ammonia reaction ( 97) does not take 
place when free carbonic acid or acid carbonates are present 
(compare SALZER, Zeitschr. f. analyt. Ohem., 20, 227.) 

10. In relation to the microchemical detection of carbonic 
acid, see HAUSHOFEE, p. 66; BEHRENS, Zeitschr. f. analyt. 
Ohem., 30, 158. 



180. 
1. SILICIC Aon), H 4 Si0 4 , HjSiO, , etc. (Anhydride, SiO 9 .) 

1. SILICIC OXIDE or SILICA is colorless or white, and in the com- 
mon blowpipe flame it is unalterable and infusible. It fuses in 
the flame of the oxyhydrogen blowpipe, and is volatile at a very 
high temperature (E. CRAMER, H. MOISSABT). It is met with in 
both the crystalline and amorphous states. It is insoluble in water 
and acids (with the exception of hydrofluoric acid, which dis- 
solves the amorphous variety easily, but the crystalline varieties 



180.] SILICIC ACID. 351 

with more difficulty). Hydrated silicic acid dissolves in acids, 
but only at the moment of its liberation. Amorphous silicic 
oxide and hydrated silicic acid dissolve in hot, aqueous solutions 
of potassium and sodium hydroxides and their carbonates; but 
crystallized silica is insoluble or nearly so in thef-e liquids. If 
any one of them is fused with excess of a caustic alkali or alkali 
carbonate, a basic alkali silicate is obtained, which is soluble in 
water. Aqueous ammonia dissolves gelatinous silicic acid rather 
readily, the dry hydrate or the amorphous anhydride more 
difficultly, and crystallized silica very little. The SILICATES 
with alkali bases are the only ones soluble in water. 

2. The solutions of the alkali silicates are decomposed by 
all acids. If a large proportion of hydrochloric acid is added 
at once, even to concentrated solutions of alkali silicates, the 
liberated silicic acid remains in solution ; but if the hydrocliloric 
acid is added gradually, drop by drop, while the fluid is stirred, 
the greater part of the silicic acid separates in a gelatinous form. 
The more dilute the fluid, the more silicic acid remains in solu- 
tion, and in highly dilute solutions, no precipitate is formed. 
If the solution of an alkali silicate, mixed with hydrochloric or 
nitric acid in excess, is evaporated to dryness, silicic acid sepa- 
rates as the acid escapes. Upon treating the residue with hydro- 
chloric acid and water, silicic anhydride or, if it has been dried 
at only 100, hydrated silicic acid remains as an insoluble, white 
powder. In not too dilute solutions of alkali silicates, am- 
monium chloride produces precipitates of silicic acid (containing 
alkali), and heating promotes the separation. 

3. Some of the silicates insoluble in water are decomposed 
by hydrochloric or nitric acid, while others are attacked scarcely 
or not at all by these acids, even upon boiling. In the decom- 
position of the former, the greater portion of the silicic acid 
separates, usually in the gelatinous, more rarely in the pulveru- 
lent, form. To effect the complete separation of the silicic acid, 
the hydrochloric acid solution, with the precipitated silicic acid 
suspended in it, is evaporated to dryness, the residue is heated 
with stirring, at a uniform temperature, somewhat above the 
boiling-point of water until acid vapors no longer escape, then 
it is moistened with hydrochloric acid, heated with water, and 
the fluid containing the bases filtered from the residuary, insoluble 



352 DEPOimiKXT OF BODIES WITH REAGENTS. [ 180- 

silicic acid. Of the silicates not decomposed by hydrochloric 
acid, many <0.^., kaolin) are completely decomposed by heating 
with a mixture of S parts of strong sulphuric acid and 3 parts of 
water, the silicic acid being separated in the pulverulent form ; 
many others are acted upon to some extent by this reagent. 
Silicates not decomposable by boiling with hydrochloric or sul- 
phuric acid in the open air (at the ordinary atmospheric pres- 
sure) may generally be completely decomposed by heating, in a 
state of line powder, with the acids, in strong, sealed glass tubes 
at aOO-210 in an air- or paraffin-bath. 

4. If any silicate, reduced to a tine powder, is fused with 
i parts of $odiuw> and potassium carbonates until no more car- 
bon dioxide escapes, and the mass is then boiled with water, the 
greater part of the .silicic acid dissolves as alkali-metal silicate, 
while alkali-earth and earth metals (with the exception of 
aluminium, which passes more or less completely into the 
solution) and heavy metals are left undissolved as carbonates or 
oxides. If the fused mass is softened with water, then, with- 
out previous filtration, hydrochloric or nitric acid added to 
strongly acid reaction, and the fluid evaporated as directed in 
8, the silicic acid is left undissolved, while the bases are in solu- 
tion. If a fusion is made with 4 parts of larium hydroxide, the 
mass is digested with water with the addition of hydrochloric or 
nitric acid, and the acid solution is treated according to 3, silicic 
acid is separated as before. The bases, especially the alkalies, 
may then be found in the tiltrate. [If an insoluble silicate con- 
taining alkali metals is mixed in the state of powder with 8 times 
its weight of precipitated calcium carbonate and its own weight 
of ammonium chloride* and the mixture is heated to redness 
iu a covered platinum crucible for half an hour, too high a heat 
being avoided, a somewhat sintered mass is obtained, which, on 
being digested in hot water, falls to powder, and yields a solu- 
tion containing, besides calcium chloride and hydroxide, all the 
alkalies of the silicate in the form of chlorides (J. LAWBBNOB 
SMITH).] 

5. If hydrofluoric acid^ in concentrated aqueous solution or 
in the gaseous state, is made to act upon silicic oxide, silicon 
fluoride gas escapes : Si0 9 + *HF = SiF 4 -f 2H.O. The dilute 
acid dissolves silica to hydrofluoailicic acid : SiO, + 6HF = 



180.] SILICIC ACID. 353 



, + 2H a O. If this solution is evaporated to dryness, 
and if the silicic and hydrofluoric acids were pure, and the 
ktter was in excess, no residue is left. Hydrofluoric acid acting 
upon silicates gives rise to the formation of silicofluorides : CaSiO 
+ 6HF = CaSiF 6 -f 3H a O. By heating with sulphuric acid, 
these are changed to sulphates, with evolution of hydrofluoric 
acid and silicon fluoride gases. If the powdered silicate is 
mixed with 3 parts of ammonium fluoride, or 5 parts of calcium 
fluoride in powder, the mixture made into paste with concen- 
trated sulphuric acid, and heat is applied until no more fumes 
escape, the whole of the silicic acid present volatilizes as silicon 
fluoride. The bases are found in the residue as sulphates, 
mixed, if calcium fluoride was used, with calcium sulphate. 
All the experiments described in 5 should be performed in 
platinwni vessels, and the evaporations must be made under a 
good hood) or better still in the open awr. 

6. On mixing 1 part of finely powdered silica, or a silicate, 
with 2 parts of powdered cryolite or fluor-spar (free from silica), 
and 4 or 5 parts of concentrated sulphuric acid, heating the mix- 
ture moderately in a platinum crucible, but not allowing it to 
spurt, and then holding close over the surface the loop of a stout 
platinum wire which has been freshly ignited, and now contains 
a drop of water, a pellicle of silicic acid will soon form on the 
latter from decomposition of the escaping silicon fluoride (BAB- 
FOED). 

7. If silicic oxide or a silicate is fused with a small propor- 
tion of sodwwn carbonate in the loop of a platinum wire, FROTH* 
ING is observed in the bead, owing to the evolution of carbon 
dioxide. The bead obtained with pure silicic acid, or silicic 

A ide, is always clear when hot; and with silicates rich in 
silicic acid (as the feldspathic rocks), the bead is also clear; 
otherwise it is opaque. The clearness of the cold bead depends 
upon the proportion between silicic acid, soda, and other bases. 

8. Sodvum meta/phosphate in a state of fusion nearly fails 
to dissolve silicic oxide. If, therefore, silicic acid or a 
silicate (best in 'small fragments) is fused with sodium meta- 
phosphate on a platinum wire, the bases are dissolved, while 
generally the greater part of the silicic oxide separates and floats 
about in a clear bead as a more or less translucent mass, exhibit- 



854 DEPORTMENT OF BODIES WITH EEAGENTS. [ 181. 

ing the shape of the fragment of substance used, and forming the 
so-called SILICA SKELETON. 

9. In regard to the microchemical detection of. silicic acid, 
see HAUSHOFEB, p. 120 ; BEHRENS, Zeitschr. 1 analyt. Chem., 
30, 157. 



181. 

Recapitulation and Remarks. Carbon dioxide or free car- 
Ionic acid is readily known by the reaction with lime- or baryta* 
water ; while the carbonates are easily detected by the evolution of 
a scarcely odorous gas when they are treated with acids. Many 
Carbonates (s.y., magnesite) are decomposed by acids only upon 
heating, When operating upon compounds which evolve other 
gases besides carbon dioxide, the gas should be tested with lime- 
water or baryta-water, fiitkle acid, both in the free state and 
in silicates, may usually be readily detected by the reaction with 
sodium metaphosphate. In the form in which it is always 
obtained in analyses, it differs from all other bodies by its 
insolubility in acids (except hydrofluoric acid) and in fusing 
potassium disulphate, and its solubility in boiling solutions of 
alkalies and alkali carbonates ; and from many bodies (especially 
from alumina and titanic oxide), by completely volatilizing upon 
repeated evaporation in a platinum dish, with hydrofluoric acid 
(or ammonium fluoride) and sulphuric acid. 

Second Group of Lwrganic Acids. 

ACIDS WHICH ARK PRECIPITATED BY SlLVEE KlTRATE, BUT NOT BY 

BARIUM CHLORIDE : Hydrochloric Acid, Hydrolromic Acid, 
Jf yd r unfit* Acid, Hydrocyanic Acid, Hydroferro- and Hy- 
drqfi'?rwyant<* Acfd^ Hydrowlphocyanic Acid, Hydrosul- 
pJmfir Arid (Xitrous Acid, Hypochlorous Acid, Chlorous 
Acid, Hypopliosphorous Acid). 

The silver compounds, corresponding to the halogen, and 
wlplnr adds of this group, are insoluble in dilute nitric acid. 
These acids react with metallic oxides and hydroxides, the 
metals combining with the chlorine, bromine, iodine, cyanogen, 
or sulphur, etc., while the oxygen of the metallic oxide, or the 



182.] HYDBOOHLOBIC ACID, 355 

hydroxyl of the hydroxide, forms water with the hydrogen of 
the acid. 

182. 

a. HYDEOCHLOEIC Aero, HOI. 

1. CHLOBINE is a heavy, yellowish-green gas of a disagreea- 
ble and suffocating odor, which has a most injurious action upon 
the respiratory organs. It destroys many vegetable colors (lit- 
mus, indigo-blue, etc.), is not inflammable, and supports the 
combustion of a few bodies only. Minutely divided antimony, 
tin, etc., spontaneously ignite in it, and are converted into 
chlorides. It dissolves rather freely in water ; and the CHLOKIXE- 
WATEE formed has a faint yellowish-green color, smells strongly 
of the gas, bleaches vegetable colors, is decomposed by the 
action of light ( 30), and loses its odor when shaken with mer- 
cury, the latter being partly converted into rnercurous chloride. 
Small quantities of free chlorine may be readily detected in a 
liquid by adding it to a dilute solution of indigo having only a 
faint blue color, which is decolorized by the action of the free 
chlorine, or also, in the absence of nitrous acid, by the blue 
color imparted to a mixture of starch paste and potassium iodide 
(see 184, 9). 

2. HYDEOOHLOBIO ACID, at the common temperature and 
common atmospheric pressure, is a colorless gas, which forms 
dense fumes in moist air, is suffocating and very irritating:, and 
dissolves in water with exceeding facility. The concentrated 
aqueous solution (fuming hydrochloric acid) loses a large portion 
of its gas upon heating. 

3. The normal METALLIC CHLOEIDES are readily soluble in 
water, with the exception of lead, silver, cuprous, and mer- 
curous chlorides, and most of them are white or colorless. 
Many chlorides volatilize at a high temperature, without suffer- 
ing decomposition ; while others are decomposed upon ignition, 
and some axe fixed at a moderate red heat. 

i. Even in highly dilute solutions of free hydrochloric acid 
or of almost all metallic chlorides, silver nitrate produces a white 
precipitate of SILVER CHLOEIDE, AgCl, which npon exposure to 
light becomes first violet, then black. It is insoluble in dilute 



856 DEPORTMENT OF BODIES WITH REAGENTS. [ 182. 

nitric acid, but dissolves readily IB ammonia as well as in potas- 
sium cyanide solution, and also in a boiling solution of ammonium 
*' sesqui" -carbonate * (H. EAGER). [Placed in contact with 
metallic zinc and water slightly acidulated with sulphuric acid, 
silver chloride is decomposed, soluble zinc chloride and metallic 
silver being formed.] Silver chloride fuses without decomposi- 
tion (compare 135, Y). From a solution of green chromium 
chloride, chlorine is incompletely precipitated by means of 
silver nitrate (PELIGOT), and it is not precipitated from a 
solution of molybdenous oxycliloride in sulphuric acid (BLOM- 
BTRAND). From a solution of auric chloride, even in the pres- 
ence of nitric acid, silver nitrate produces an ochre-yellow 
precipitate, containing gold, silver, and chlorine. 

5. In solutions containing free hydrochloric acid or metallic 
chlorides, mercurous nitrate and lead acetate produce precipi- 
tates Of MEBCUROUS CHLORIDE, Hg 9 Cl a , and LEAD CHLORIDE, 

PbCl,. For the properties of these precipitates, see 136, 6, 
and 137, 7. Lead acetate precipitates lead auric chloride 
from a solution of hydrochlorauric acid. 

6. If hydrochloric acid is heated with manganese dioxide 
or lead dioxide^ or a chloride with mwngtmese dioxide or lead 
dioxide and rather concentrated sulphuric add, CHLORINE is 
evolved, which may be readily recognized by its odor, its yel- 
Wish-green color, and its bleaching action upon vegetable 
colors. The best way of testing the latter is to expose to the 
gas a moist strip of litmus-paper, or of paper colored with solu- 
tion of indigo. When chlorides are heated with manganese or 
lead dioxide and acetic acid, no chlorine is evolved. 

7. If a metallic chloride is triturated with half its weight 
or somewhat more of potassium dichromate^ the dry mixture 
treated with concentrated sulphuric acid in a tubulated retort, 
and a gentle heat applied, the deep brownish-red gas of CHROMIC 
OXYOHLORIDE, CrOaOlj (OHLOROOHROMIO ACID), is evolved, which 

condenses into a fluid of the same color, and passes into the 

f * * 

receiver. If this distillate is mixed with ammonia in excess, a 
yellow-colored liquid is produced from the formation of ammo- 

* To prepare this, dissolve 1 part of the transparent ammonium carbonate 
of commerce in 9 parts of water of ordinary temperature, and add, for each. 
10 cc of the liquid, 5 drops of ammonia-water of .06 sp. gr. 



183.] HTDROBROMIC ACID. 357 



nium chromate : CrO a Cl a +4XH<On = 2XH 4 Cl-|-(XE 4 ) s Cr0 4 + 
2H S 0. Upon addition of an acid, the color of the solution changes 
to a reddish-yellow, owing to the formation of acid ammonium 
chromate. 

8. Chlorine is detected in the metallic chlorides insoluble in 
water and nitric acid by fusing them with 8^!u//t-j^otu^!u?/i 
carbonate, and treating the mass with water, which diVulves 
the sodium and potassium chlorides formed in the process, to- 
gether with the excess of the sodium and pota<&ium carbonates. 

9. If cupmc oxide is dissolved in a bead of wtilivm meta- 
phosphate on a platinum wire in the outer blowpipe flame, in suf- 
ficient quantity to make the mass nearly opaque, a truce of a 
substance containing chlorine added to it while still in fusion, ami 
the bead then exposed to the reducing flame, a fine BLUE-COLORIID 
flame, inclining to PURPLE, will be seen encircling it a& lonjr as 
chlorine is present (BEEZELIUS). 

10. In relation to the microscopic detection of chlorine, see 
HAUSHOFER, p. 47; BEHRESS, Zeitsclir. f. analyt. Chern., 30, 
170; A. PERCY SMITH, Pharmac. Centralhalle, 1886, p. 63$. 



183. 

5. HYDBOBROMIO Aoro, HBr. 

1. BROMINE is a heavy, brownish-red liquid of a very disa- 
greeable, chlorine-like odor ; it boils at 63, and volatilizes rapidly 
even at the common temperature. The vapor is brownish-red. 
Bromine bleaches vegetable colors like chlorine, is rather sol- 
uble in water, dissolves still more readily in alcohol, and 
very freely in ether, carbon disulphide, and chloroform. The 
solutions are yellowish-red. Ether, carbon disulphide, or chloro- 
form, when shaken with an aqueous solution of bromine, extract 
the latter from it. 

2. HYDROBROMIC ACID GAS, its AQUEOUS SOLUTION, and the 
METALLIC BROMIDES, in their general deportment, show a great 
analogy to the corresponding chlorides. 

3. In aqueons solutions of hydrobromic acid or of bro- 
mides, siUer nitrate produces a yellowish-white precipitate of 
SILVER BROMIDE, AgBr, wliich becomes gray upon exposure to 



358 DEPORTMENT OF BODIES WITH REAGENTS. [ 183. 

light. This precipitate is insoluble in dilute nitric acid, and almost 
insoluble in a boiling solution of ammonium "sesqui" -carbon, 
ate (H. HAGER). Ainmouia-water dissolves silver bromide, but 
much more difficultly than silver chloride. It dissolves with 
facility in potassium cyanide. [With metallic zinc and water 
acidulated with sulphuric acid, it yields soluble zinc bromide and 
metallic biker.] 

4. lu neutral solution of metallic bromides, $alla<Lioub 
nitrate, but not palladiou& chloride, produces a reddish-brown 
precipitate of PALLAIHOUS BROMIDE, PdBr a . In concentrated 
solutions, this precipitate is formed immediately ; but in dilute 
solutions, it makes its appearance only after standing some time. 
5* Sltrit ticfd decomposes hydrobroniic acid and the bro- 
mides, with the exception of bilver bromide, upon the application 
of heat, and liberates the bromine by oxidizing the hydrogen or 
the metal. In the case of a solution, the liberated bromine colors 
it yellow or yellowish-red. With bromides in the solid state or 
in concentrated solution, brownish-red (if diluted, brownish- 
yellow) vaporb of bromine escape at the same time, which, if 
evolved iu Mifficient quantity, condense in the cold part of the 
test-tube t< * wnall drops. In the cold, nitric acid, even when red and 
fuming, fails to liberate the bromine in very dilute solutions of 
bromides, nor is it liberated by solution of nitrous acid in con- 
centrated sulphuric acid, nor by hydrochloric acid and potassium 
nitrite. 

t>. C7Jarine, in the gaseous state or in aqueous solution, 
immediately liberates bromine in solutions of its compounds, 
the fluid a&iuuing a yellowiah-red tint if the quantity of bro- 
mine present id not too minute. A large excess of chlorine must 
l>e avoided, since this causes the formation of bromine chlo- 
ride, which destroys the color wholly or nearly so. This reac- 
tion is made much more delicate by the addition of a fluid which 
dib>olves bromine and does not mix with water, such as carbon 
dixulphide or c?dorofwm. Mix the neutral or feebly acid 
solution in a test-tube with a little of one of these fluids, sufficient 
to form a large drop at the bottom, then add dilute chlorine- 
water drop by drop, and shake the tube. With appreciable 
quantities of bromine (e.g. , 1 part in 1000 parts of water), the 
ilrop at the bottom acquires a reddish-yellow tint; but with very 



8 IN}.] HYDKOBROMIC ACID. 359 

minute quantities (1 part of bromine in 30,000 parts of water), 
a pale yellow tint, which, however, is still distinctly discernible.* 
Ether, which was previously used for the purpose, is far leas 
well adapted for this reaction. A large excess of chlorine- water 
must be avoided in this experiment also, and it must always be 
ascertained first whether the chlorine-water, mixed with a large 
quantity of water and some carbon disulpbide or chloroform, arid 
shaken, will leave these solvents quite uncolored. If not, the 
reagent is not suited for the purpose. If the solution of 
bromine in carbon disulphide or chloroform (or ether) is mixed 
with some solution of potassium hydroxide, the mixture shaken, 
and heat applied, the yellow color disappears, and the solution 
now contains potassium bromide and bromate. By evaporation 
and ignition, the potassium bromate is converted into potassium 
bromide, and the ignited mass may then be further tested as 
directed in 7. 

7. If bromides are heated with manganese or Uad dioxide 
and concentrated or dilute sulphuric aoid^ BROWNISH-BED VAPOKS 
OF BROMINE are evolved. In the presence of chlorides, it is 
necessary to operate with dilute solutions so that no bromine 
chloride can be formed. When heated with manganese dioxide 
and acetic acid, bromides give off no bromine, but they do 
evolve bromine when heated with lead dioxide and acetic acid 
(YORTMASFN). If the bromine is present only in very minute 
quantity, the color of the escaping vapor is not visible ; but if 
the mixture is heated in a small retort, and the vapors are trans- 
mitted through a long gloss condenser, the color of the bromine 
may generally be seen by looking lengthwise through the tube. 
The first drops of the distillate are also colored yellow, and 
these together with the first vapors should be received in a test- 
tube containing some starch moistened with water; since, 

S. If moistened starch is brought into contact with free 
bromine, more especially in the form of vapor, YELLOW BBOMIZBD 
STABCH is formed. The coloration is not always instantaneous. 
The reaction is rendered most delicate by sealing the test-tube 

* In solutions of hydrobromides of the alkaloids, the reaction does not take 
place. The alkaloids are therefore to be first removed by means of sodium 
hydroxide or carbonate solution, etc. (A. WBLLER, Zeitscfar. f. analyt. Chem. f 
26, 740). 



360 DEPORTMENT OF BODIES WITH REAGENTS. [ 183. 

which contains the moistened starch and the first drops of the 
distillate from 7, and then cautiously inverting it, so as totalise 
the moirf starch to occupy the upper part of the tube, while the 
fluid is at the bottom. The presence of even the slightest 
trace of bromine will now, in the course of from twelve to 
twenty-four hours, impart a yellow tint to the starch, which, 
however, after tome time will again disappear. The reaction 
may be called forth in a simpler manner, with ahno&t the same 
degree of delicacy, by gently heating the fluid containing free 
bromine, or aKo the original mixture of bromide, manganese 
dioxide, and sulphuric acid, in a very small beaker covered 
with a watcli-jrlasa having a <trip of paper attached to the lower 
ride, moistened with starch paste and sprinkled with starch 
powder. 

D. If concentrated mlpJi uric acid is poured over a mixture of a 
bromide with iMtumuiu Jirft ruinate, aud heat is then applied, a 
brownish-red gas i& evolved, exactly as in the case of chlorides. 
But this gat (ioiihiPtp of pure BROMINE, and therefore the fluid pass- 
ing over does not turn yellow, but becomes colorless upon super- 
Hfttnnitiun with ammonia. Bromine may also be expelled 
from Polutioiirf by heating with potassium chromate and sulphuric 
acid. 

10. If a solution of hydrobromic acid or an alkali-metal 
bromide is mixed with a little gold chloride solution, a straw 
or dark orange color is produced from the formation of GOLD 
BROMIDK. If iodine is present, it must be removed before the 
solution of gold is added (BiLL). 

11. In order to detect bromine in them, the metallic 
bromides which are insoluble in water and nitric acid are treated 
in the name way as the corresponding chlorides, 

12. If a substance containing bromine is added to a sodium 
wetopJiMfJiate lead saturated with cupric (mde, and the bead 
ib then ignited in the inner blowpipe flame, the flame is colored 
BLUE, inclining to GREEN, more particularly at the edges 



13. In relation to the microscopic detection of bromine, see 
HEESS, Zeitschr. f. analyt. Chem., 30, 170; A. PBEOT 
SMITH, Pharmac. Centralhalle, 1886, p. 638. 



S 184.] HTDBIODIO ACID. 361 

184. 
0. HTDEIODIC ACID, HI. 

1. IODINE is a soft solid body, with a peculiar, disagreeable 
odor. It generally occurs in the form of black, shining, crystalline 
scales. It fuses at 114, boils above 200, giving iodine vapor, 
which has a beautiful violet-blue color, and condenses upon 
cooling to a black sublimate. It is very sparingly soluble in 
water, but readily in alcohol, ether, carbon disulphide, and 
chloroform, as well as in aqueous solution of potassium iodide. 
The aqueous solution is light brown, the alcoholic, ethereal, 
and potassium iodide solutions are deep red-brown, while those 
in carbon disulphide and chloroform are violet-red. Iodine 
destroys vegetable colors, only slowly and imperfectly. It stains 
the skin brown, and with starch forms a compound of a most 
intense, dark blue color. This always results when iodine vapor 
or a solution containing free iodine is brought into contact with 
starch, best in the form of starch paste. The color of iodized 
starch is destroyed by alkalies, by chlorine and bromine, and by 
sulphurous acid and other reducing agents. 

2. HYDBIODIO ACID GAS resembles hydrochloric and hydro- 
bromic acid gases, and dissolves copiously in water. The colorless 
solution of hydriodic acid turns speedily to a reddish-brown in 
contact with the air, water and a solution of iodine in hydri- 
odic acid being formed. 

3. The IODIDES also correspond in many respects with the 
chlorides. Of the iodides of the heavy metals, however, many 
more are insoluble in water than is the case with the correspond- 
ing chlorides. Many iodides have characteristic colors, e.g., 
lead iodide, mercurous iodide, and mercuric iodide. 

4. In aqueous solutions of hydriodic acid and of iodides, 
silver nitrate produces yellowish-white precipitates of SILVER 
IODIDE, Agl, which blacken on exposure to light. Silver iodide 
is insoluble in dilute nitric acid, scarcely soluble in ammonia- 
water containing 5 per cent of ammonia, and not soluble in a 
boiling solution of ammonium " sesqui "-carbonate (EL HAGEE). 
It dissolves readily in potassium cyanide [and with zinc and dilute 
sulphuric acid, reacts like silver chloride and bromide]. 



862 DEPORTMENT OF BODIES WITH BEAGENTS. [ 184. 

5. Even in very dilute solutions of hydriodic acid or metallic 
iodides, palladioits chloride and palladious nitrate produce a 
brownish-bluck precipitate of PALLADIOUS IODIDE, Pdl fl , which 
dissolves to a triding extent in saline solutions (sodium chloride, 
magnesium chloride, etc.), but is insoluble or nearly so in dilute, 
cold hydrochloric and nitric acids. 

6. From neutral aqueous solutions of the iodides, a solution 
of 1 part of cupric sulphate and 2 parts of ferrwts sulphate 
throws down CUPKOUS IODIDE, Ou 9 I 9 , in the form of a dirty 
white precipitate. The addition of ammonia promotes the 
complete precipitation of the iodine. Chlorides and bromides 
are not precipitated by this reagent. Instead of using the 
above mixture of sulphates, cupric sulphate alone may be added, 
and afterwards enough sulphurous acid or acid sodium sulphite 
to remove the brown color produced by separated iodine. 

7. Pure nitric acid, free from nitrous acid, decomposes 
hydriodic acid or iodides, only when acting upon them in its 
concentrated form, particularly when aided by the application 
of heat. But nitrous acid and nitrogen peroxide decompose 
hydriodic acid and iodides with the greatest facility, even in the 
moat dilute solutions. Colorless solutions of iodides therefore 
acquire immediately a brownish-red color upon addition of some 
red fuming nitric acid, or of a mixture of this with concentrated 
Milphuric acid, or better still, upon addition of a solution of 
nitrous acid in concentrated sulphuric acid, or of potassium 
nitrite and some sulphuric or hydrochloric acid. From more 
concentrated solutions, the iodine separates in the form of black 
scales, while nitrogen oxides and iodine vapor escape.* 

S. Art the blue coloration of iodized starch remains visible 
in much more highly dilute solutions than the yellow color of 
solution of iodine in water, the delicacy of fche reaction just 
demilwi (7) is considerably heightened by first mixing the fluid 
to be tested for iodine with some thin, tolerably clear starch 
ywtff, then adding a few drops of dilute sulphuric acid, to make 
the fluid strongly acid, and finally one of the reagents given in 
7. Of the solution of nitrous acid in concentrated sulphuric 

* From cyanogen iodide, iodine is not separated by oxidizing agents; but 
It Is let free by reducing agents iE. v. METER, Zeitschr. f . analyt Ghem., 27, 



184] HTDBIODIO ACID. 363 

acid, a single drop on a glass rod suffices to produce the reaction 
most distinctly, and I can, therefore, recommend thi* reagent 
most highly, as does FR. J. OTTO, who iirbt proposed its u&e. 
Eed fuming nitric acid must be added in somewhat larger 
quantity to call forth the reaction in its highest intensity ; there- 
fore, this reagent is not well adapted to detect very minute 
quantities of iodine. The reaction with potassium nitrite ako is 
very delicate. The fluid to be tested is mixed with dilute sulphuric 
acid or with hydrochloric acid to distinctly acid reaction, and a 
drop or two of a concentrated solution of potassium nitrite is 
then added in the presence of a little starch paste. lu cases 
where the quantity of iodine present is very minute, the fluid 
turns reddish, instead of blue. An excess of the fluid contain- 
ing nitrous acid does not materially impair the delicacy of the 
reaction. As iodized starch becomes colorless in hot water, 
the fluids must of necessity be cold, aud the colder they are the 
more delicate the reaction. To attain the highest degree of 
delicacy, cool the fluid with ice, let the starch deposit, and place 
the test-tube upon white paper to observe the reaction (compare 
ulso " Eecapitulation and Kemarks" below, 188). 

9. Chlorine gas and chlorine-water decompose compounds of 
iodine also, setting the iodine free ; but if the chlorine is applied 
in excess, the liberated iodine combines with it to iodine chloride. 
A dilute solution of a metallic iodide, mixed with starch paste, 
acquires at once, therefore, upon addition of a little chlorine- 
water, a blue tint, but becomes colorless again upon addition 
of more chlorine-water. As it is difficult not to exceed the 
proper limit, especially where the quantity of iodine present 
is only small, chlorine- water is not well adapted for the detection 
of minute quantities of iodine. 

10. If a solution containing hydriodic acid or an iodide, 
acidified if necessary, is mixed with chloroform or wrlvn 
disulphide, so as to leave a large drop imdissolved, and one of 
the agents by which iodine is liberated (a drop of a solution of 
nitrous acid in sulphuric acid, hydrochloric acid and potassium 
nitrite, chlorine-water, etc.) is added, the mixture vigorously 
shaken, and then allowed to frtand at rest, the chloroform or the 
carbon disulphide, colored violet-red by the iodine dissolved in 
it, subsides to the bottom- This reaction, also, is exceedingly 



364 DEPORTMENT OJT BODIES WITH REAGENTS. [ 186. 

delicate. If a solution containing free iodine is shaken with 
^tfoUum oil) benzol, or ether, the first two are colored almost 
red, and the ether more reddish-brown or yellow. (Iodine colors 
ether innch more intensely than an equal amount of bromine.) 

11. If metallic iodides are heated with concentrated m*2- 
phuric acid, or with manganese or lead dioxide and dilute sub* 
j/fitiric acid or even acetic acid, or with dilute sulphuric acid 
and potassium dichromate, or vifh ferric chloride or ferric 
wljpkatt, iodine separates, and may be recognized by the color 
of its vapor, or in the case of very minute quantities, by its 
action upon a strip of paper coated with starch paste. 

12. Upon fusion with sodium carbonate, the iodides which 
are insoluble in water and nitric acid comport themselves in the 
same manner as tlic corresponding chlorides. 

13. A wlium */iety/}toy>?iate lead, saturated with ouprio 
wide, when charged with a substance containing iodine, and 
ignited in tlie inner blowpipe flame, imparts an intense GREEK 
color to the flame. 

14. In regard to the microscopic detection of iodine, see 
EAUSHOFEB, p. 52 ; BEHBEOT, Zeitschr. f. analyt. Ohem., 30, 
171; DEKIOES, Ohem. Centralbl., 1894, 1, p. 104. 

185. 
d. HYDROCYANIC ACID, HON. 

1. OYAJTOGEN, O^N,, is a colorless gas of a peculiar, pene- 
trating odor. It burns with a crimson flame, is rather soluble in 
water, and has a specific gravity of 1.8. 

2. HTDBOOTAKIO ACID (prussio acid) is a colorless, volatile, 
inflammable liquid, the stupefying odor of which distantly re- 
sembles that of bitter almonds. It is miscible with water in all 
proportions, and in the pure state, it speedily suffers decompo- 
sition. It is extremely poisonous, and the aqueous solution does 
not redden litmus-paper. 

3. The CYANIDES of the alkali and alkali-earth metals are 
soluble in water, and the solutions smell of hydrocyanic acid. They 
are readily decomposed by acids, even by carbonic acid. At 
SO to 80, mercuric cyanide, and at 100, finely divided cyanides, 



185.] HTDEOOTAKIO AOID. 365 

suspended in water and insoluble in it, are decomposed by car- 
bonic acid (EL HILGEB and K. TAMBA). When ignited with 
exclusion of air, potassium and sodium cyanides fuse without 
decomposition ; but when fused with oxides of lead, copper, anti- 
mony, tin, and many other oxides, they reduce these, and are 
converted into cyanates. Upon fusion with almost every metal- 
lic sulphide, a metallic sulphocyanide is produced. Only a few of 
the cyanides of heavy metals are soluble in water ; but all of them 
are decomposed by ignition, the cyanides of the noble metals 
being converted into cyanogen gas and metal or metallic para- 
cyanide, and the cyanides of the other heavy metals, into nitrogen 
gas and metallic carbides. Many of the cyanides of heavy 
metals are not decomposed by dilute oxygen acids, and only with 
difficulty by concentrated nitric acid. By heating and evapora- 
tion with concentrated sulphuric acid, all cyanides are decom- 
posed ; while hydrochloric acid decomposes a few, and hydro- 
gen sulphide decomposes many. 

1. The CYANIDES have a great tendency to combine with each 
other ; hence most of the cyanides of the heavy metals dissolve 
in potassium cyanide. The resulting compounds are either : 

a. Double salts, e.g.^ potassium nickel cyanide, 2KCN. 
Ni(CN) 9 . From solutions of such double salts, acids precipitate 
the metallic cyanide, by decomposing the potassium cyanide 
which was combined with it. Or, 

J. Compounds which behave like simple halogen salts, in 
which a metal (e.g., potassium) is combined with a compound 
radical consisting of cyanogen and another (metal iron, cobalt, 
manganese, chromium). The ferro- and the ferricyanides of 
potassium, K 4 Fe(ON) and K,Fe(CX)., are compounds of this 
kind. From solutions of such compounds, dilute acids do 
not separate metallic cyanides in the cold. If the potassium 
is replaced by hydrogen, corresponding hydrogen acids are 
formed, which must not be confounded with hydrocyanic acid. 

The reactions of hydrocyanic acid and the simple cyanides 
will first be considered ; then, in an appendix to this paragraph, 
those of hydroferro- and hydrofenicyanic acid and also of 
hydrosnlphocyanic acid. 

5. Sifoer nitrate produces in solutions of free hydrocyanic 
acid and of cyanides of the alkali metals, white precipitates of 



366 DEPORTMENT OF BODIES WITH REAGENTS. [ 185. 

SILTEE CYANIDE, AgCN, which are readily soluble in potassium 
cyanide, dissolve with some difficulty in ammonia, and are 
insoluble in dilute nitric acid. These precipitates are decomposed 
by ignition, leaving metallic silver with some silver paraeyanide. 
When free hydrocyanic acid is present, the delicacy of this reac- 
tion is increased by first adding ammonia in excess, then silver 
nitrate, and finally acidifying with nitric acid. 

6. If a solution si ferrous sulphate and a drop of ferric 
chloride solution are added to a solution of free hydrocyanic 
acid, no alteration takes place ; but if a few drops of a solution 
of potassium or sodiwn hydroxide are now added, until the 
liquid just reacts alkaline, a bluish-green precipitate forms, 
which consists of a mixture of Prussian blue (compare 127, 6) 
and ferrous-ferric hydroxide. Upon now acidifying with hydro- 
chloric acid, the ferrous-ferric hydroxide dissolves, while the 
PRUSSIAN BLUE remains undissolved. If only a very minute 
quantity of hydrocyanic acid is present, the fluid simply appears 
green after the addition of the hydrochloric acid, and it is only 
after long standing that a trifling blue precipitate separates from 
it. The same final reaction is observed when a mixture of 
ferrous and ferric salt is mixed with the solution of an alkali- 
metal cyanide, and hydrochloric acid is then added. 

7. If a liquid containing a little hydrocyanic acid Dr alkali- 
metal cyanide is mixed with sufficient yellow ammonium sulphide 
to impart a yellowish tint to the fluid, after the addition 
of a drop of weak potassium or sodium hydroxide solution 
when free hydrocyanic acid was present, and the mixture is 
warmed in a porcelain dish upon the water-bath until it has 
become colorless and the excess of ammonium sulphide is 
decomposed or volatilized, and finally evaporated to dryness, 
the residue now contains ammonium sulphocyanide. This is dis- 
solved in a little water, made acid with 2 or 3 drops of hydro- 
chloric acid, allowed to stand a few minutes, and then a little 
ferric chloride is added. A blood-red coloration shows the 
presence of the sulphocyanogen which has been formed. Should 
a violet color appear, or should the resulting red color disap- 
pear quickly, some more ferric chloride must be added to call 
forth the reaction (LEEBIG, ALMEN). This reaction is exceeding- 
ly delicate. The following equation expresses the transformation 



185*] HYDROCYANIC ACID. 367 

of a cyanide into a sulphocyanide : (2s H 4 ), S. + 4KCN" = 4KCNS 
+ (NH 4 ),S. If an acetate is present, the reaction takes place only 
upon addition of more hydrochloric acid. To discover the 
cyanogen in insoluble compounds by converting it into ferric sul- 
phocyanide, proceed as follows : Fuse some sodium thiosulphate in 
the loop of a platinum wire in an alcohol flame, until the water 
of crystallization has escaped and the mass swells up, introduce 
a small portion of the substance, heat for a little time, removing 
it from the flame as soon as the sulphur begins to burn, and then 
dip the mass into a few drops of ferric chloride mixed with water 
and a little hydrochloric acid. A permanent, blood-red color 
will be produced if cyanogen was present. If the substance is 
heated too long, the reaction fails, as the sodium sulphocyanide 
formed is then destroyed. This method is well suited to dis- 
tinguish silver chloride, bromide, or iodide from cyanide (A. 
FBOHDE). 

8. If, to a liquid containing hydrocyanic acid or a metallic 
cyanide, a few drops of a solution of potassium nitrite are 
added, then from 2 to 4 drops of feme cfdoride solution, and 
enough dilute sulphuric acid so that the brown color of the 
ferric salt formed at first just changes into light yellow, the 
liquid is then heated to incipient boiling, cooled, some ammonia 
added to precipitate the iron which is in excess, the precipi- 
tate filtered off, and one or two drops of hydrogen sulphide 
water are added to the filtrate (which should still contain free 
ammonia), the solution takes on a violet color from the action of 
the sulphide upon the potassium nitroprusside which has been 
formed (G. VOETBIAIOT). 

9. On mi-ring a moderately concentrated solution of an 
alkali-metal cyanide with a tittle picric add solution (1 part of 
picric acid to 250 parts of water) and boiling, the fluid appears 
dark red from formation of alkali-metal picrocyaminate (isopur- 
purate), the coloration increasing in intensity by standing. If 
the solution of the cyanide is very dilute, no more picric acid 
must be added than is just sufficient to color the fluid yellow. 
After boiling, the red coloration often does not make its appear- 
ance till the fluid has cooled and stood for some time (C. D. 
BBATJCT). The reaction is not as delicate as those described in 6, 
7, and 8, but it may be used for the detection of an alkali-metal 



388 DEPORTMENT OF BODIES WITH REAGENTS. [ 186. 

cyanide in the presence of potassium ferrocyanide, which does 
not give potassium picrocyaminate when treated in the same 
way. 

10, On soalring filter-paper vn&\ freshly prepared, alcoholic 
tincture of guaiacum containing 3 or 4 per cent of the resin, 
allowing the alcohol to evaporate, moistening the paper with 
solution of copper sulphate containing J per cent of the salt, 
and then exposing it to air in which a trace of hydrocyanic 
acid is present, it becomes blue from liberation of active 
oxygen : 3CuO + 4HCX = Cu a (CN) a . Cu (CN) a + 2H 9 O + O 
(PAGESSTECHER, SCHONBEIN). The reaction is exceedingly deli- 
cate, but it is not conclusive for hydrocyanic acid without con- 
firmation, because the guaiacum-copper paper is also made blue 
by air containing ammonia, nitrous acid, ozone, bromine, iodine, 
and hypochlorous acid. It is still less conclusive when it is 
produced in solutions, for a mixture of guaiacum tincture with 
very dilute copper sulphate solution is turned blue, not only by 
hydrocyanic acid and cyanides, but also by soluble lower 
chlorides, bromides, iodides, fluorides, etc. 

11, If a very dilute solution of iodised starch is mixed with 
a trace of hydrocyanic acid, or, after addition of dilute sulphuric 
acid, with a trace of an alkali-metal cyanide, the blue color dis- 
appears immediately or after a short time, the iodine and the 
hydrocyanic acid being transformed into cyanogen iodide and 
hydriodic acid (SOHONBEIN). This is a very delicate reaction, 
but cannot be relied upon without further tests, as many other 
substances decolorize iodized starch. 

12, None of the above methods will serve to effect the 
detection of cyanogen in mercuric cyanide. To detect cyanogen 
in that compound, its solution is mixed with hydrogen sulphide, 
when mercuric sulphide precipitates, and the solution contains 
free hydrocyanic acid. In solid mercuric cyanide, the cyanogen 
is most readily detected by heating in a glass tube (com- 
pare 3). Upon heating a solution of mercuric cyanide with 
hydrochloric acid, with sodium chloride and oxalic acid, or with 
sodium chloride and dilute sulphuric acid, in a distilling apparatus, 
a large part of the cyanogen is obtained in the distillate as hydrogen 
cyanide. In the presence of small amounts, it is best to distil with 
tartaric acid and a little hydrogen sulphide 



186.] APPENDIX TO HYDROCYANIC ACID. 369 

13. Regarding the microscopic detection of hydrogen 
cyanide, sue BEHBENS, Zeitsehr. f. analyt. Chem., 30, 166.* 



Appendix to Hydrocyanic Add. 

186. 

a. Hydroferrocyanic acid^ H 4 Fe(CX) e . Hydroferrocyanic 
acid is colorless, crystalline, and readily soluble in water. Its 
solution has a strong acid reaction. Some of the ferry ocyanides, 
as those containing alkali and alkali-earth metals, are soluble iu 
water, but the greater number of them are insoluble in that liquid. 
All f errocyanides are decomposed by ignition ; and where they 
are not quite anhydrous, hydrocyanic acid, carbonic acid, and am- 
monia escape ; otherwise, nitrogen and occasionally cyanogen. In 
aqueous solutions of hydroferrocyanic acid or f errocyanides, ferric 
chloride produces a blue precipitate of FEHRIC FEBEOCYANIDB 
(Prussian blue, compare 127, 6); n&AMjpricwJj&atei a brown- 
ish-red precipitate of OUPRIC FERROCYANIDE (compare 140, 9). 
Silver nitrate gives a white precipitate of SILTER FEBROCYANIDE, 
Ag 4 Fe(CN) t , which is insoluble in nitric acid and in ammonia 
(upon short action in the cold), but dissolves in potassium 
cyanide. Upon boiling with aqueous ammonia, silver ferro- 
cyanide yields ferrous oxide, while the solution contains silver 
cyanide and ammonium cyanide (WEITH). If a not too dilute 
solution of an alkali-metal ferrocyanide is mixed with hydro- 
chloric acid) and some ether is poured on the top of the mixture 
HYDROFEREOOYANIO ACID separates in the crystalline form wher* 
the two fluids meet. Alkali-metal ferrocyanides are not decom- 
posed by carbonic acid in aqueous solution in the cold (differ- 
ence from the cyanides), but they are decomposed at from 72 to 
7i (AUTHENREETH). Prussian blue and cupric ferrocyamde sus- 
pended in water, however, do not decompose with carbonic acid 
below 100. Upon lotting with water, soluble ferrocyanides, 
as well as those which are insoluble but finely divided, are de- 

* Concerning the detection of cyanogen in flames, compare 0. LUDBKING, 
Zeitschr. f. analyt. Chem., 29, 842. 



37U DEPORTMENT OF BODIES WITH REAGENTS. L 

composed, even without the aid of carbonic acid, with the formation 
of hydrogen cyanide (A. HILGER and K. TAMBA). Solutions of 
metallic ferrocyaiiides which are made alkaline with sodinm 
carbonate give no prussic acid when distilled in a stream of 
wrlto/iie acid, nor is any hydrogen cyanide obtained by the 
distillation of a ferrocyanide with lujdrvyen sodium carbonate 
(JACSBUEMIN). Upon warming, f errocyauides in acidified solutions 
aru converted by hydrogen peroxide into ferricyanogen com- 
pounds (\\ T ELTZIN). Insoluble ferrocyanides are decomposed 
by boiling with eolation of sodium hydroxide^ sodium ferro- 
cyauide being formed, and the metals separating as hydroxides, 
unle&s they are boluble in sodium hydroxide. Upon heating 
amtuvniaeal silver xohtiion with ferrocyanogen compounds (e.g., 
Prussian blue), ferric oxide separates. The solution then gives 
a precipitate of silver cyanide upon acidifying it with nitric 
acid (WEITU). If ferrocyanides are heated with a mixture of 3 
parts concentrated sulphuric acid and 1 part water till the free 
acid is expelled, they are decomposed, and the cyanogen is 
driven off in the form of hydrocyanic acid, while the metals 
remain behind as sulphates. On projecting metallic ferrocya- 
nides into fusing potassium nitrate, the cyanogen is converted 
into carbon dioxide and nitrogen, and the metals are converted 
into oxides, which remain in the crucible. 

1. Hydrqferricyunic acid, H e Fe a (GX) 19 . Hydroferricyanic 
acid and many of the ferrieyanides are soluble in water; and all 
ferricyanideK are decomposed by ignition similarly to the ferro- 
cyanides. In the aqueous solutions of hydroferricyanic acid and 
its salts, ferric chloride produces no blue precipitate ( 127, 7), 
\miferrou8 sulphate produces a blue precipitate of FERROUS FER- 
RICVAMPE (compare 126, 8). Cupric sulphate gives a yellow- 
islj-jLrreen precipitate of CUPRIC FERRICYAOTDE, Cu s Fe a (0]Sr) ia , 
which is insoluble in hydrochloric acid; and stiver nitrate 
yieMp an orange-colored precipitate of SILVER FERRIOYANEDE, 
Ajr.Fe/CXX, , which is insoluble in nitric acid, but dissolves 
readily in ammonia and in potassium cyanide. The aqueous 
solutions of alkali-metal femcyanides behave like the corre- 
sponding ferrocyanogen compounds, when they are boiled with 
water, or when carbonic acid or hydrogen sodium carbonate acts 
upon them. Hydrogen snljphide decomposes the alkali-metal 



186.] APPENDIX TO HYDROCYANIC ACID. 371 

terricyanides, with separation of sulphur and the formation of 
alkali-metal ferrocyanides and hydroferrocyanic acid. Free 
hydroferricyanic acid suffers a similar decomposition, and con- 
sequently, also, a solution of potassium ferricyanide to which 
hydrochloric acid is added. Ferricyanides in alkaline solution 
are reduced by hydrogen peroxide to ferrocyanogen compounds, 
with evolution of oxygen (WELTZIEN). The insoluble ferricya- 
nides are decomposed by boiling in solution of sodium hydroxide. 
In the fluid filtered off from the .separated metallic oxide?, either 
sodium ferricyanide alone is found, or a mixture of &odium 
ferro- with ferricyanide- The ferricyanogen compounds are 
decomposed by aitimoniacal silver solution like the ferrocyauogen 
compounds, and nitric acid precipitates silver cyanide from the 
ainmoniacal filtrate. By heating with a mixture of 3 parta con- 
centrated sulphuric acid and 1 part water, and also by fusing 
Txifa potassium nitrate, the ferricyanides are decomposed like 
the ferrocyanides. 

c. Hydrosulphocyanic (or thiocyanic) acid^ HCXS. This 
forms a colorless, oily liquid, which solidifies in crystals at 12. S, 
and, according to ABTUS, boils at 85. It has a penetrating odor 
similar to acetic acid, and dissolves in water ab well as in alcohol, 
forming liquids with an acid reaction. It acts as a poison, and 
gradually decomposes into hydrogen cyanide and yellow, crys- 
talline perthiocyanic acid, H fl C a !N,iv By the action of much 
concentrated hydrochloric acid upon a concentrated aqueous solu- 
tion of hydrosnlphocyanic acid (or also potassium sulphocyanide), 
this decomposition completes itself rapidly. Hydro&ulphocy- 
anic acid forms sulphocyanides (thiocyanates) with bases. Most 
of these are soluble in water, and their neutral aqueous solutions 
are not, or are scarcely, decomposed by boiling. Upon boiling 
with alkali-metal acid carbonates, ammonium carbonate is formed, 
but no hydrogen cyanide. By distilling with dilute sulphuric 
acid, phosphoric acid, or tartaric acid, a part of the sulpho- 
cyanogen is obtained in the distillate as dilute hydrosulphocyanic 
acid, but the rest is decomposed. Upon heating with dilute nitric 
acid, a violent decomposition takes place, accompanied by the 
liberation of nitric oxide and carbonic acid, and the formation 
of sulphuric acid. When ignited with access of air, all metallic 
sulphocyanides are decomposed, and yield, according to the 



372 DEPOK1MENT OF BODIES WITH KEAGETSTS. [ 187. 

nature of the liases, sulplmr dioxide, sulphates, and cyanates, or 
nitrogen, cyanogen, carbon dibiilphide, and metallic sulphides. 

Solutions of hydrobnlpLocyanic acid or of metallic sulpho- 
cvanides are colored blood-red by/*/Wc chloride solution acidi- 
fied with hydrochloric acid (g 127, 8). In concentrated solu- 
tions of alkali-metal sulphocyauides, copper mlpAat* produces a 
velvet-black precipitate of CCPKIO SULPHOCTASIDE, Cu(CNS) 9 , 
while, if the solutions are dilute, only an emerald -green color- 
ation ib produced. Copper sulphate solution mixed with an 
excess of sulphurous acid throws down, even from very dilute 
solutions, pale, reddish-white CUPEOUS SULPHOCYANIDE ( 140, 
10). Stiver nitrate produces a white, curdy precipitate of 
SILVER 8CLPHOCTANIDE, AgCXS, insoluble in dilute nitric acid, 
but soluble in ammonia. Mereuroua nitrate produces, according 
to the proportions and the concentration, a gray or white pre- 
cipitate. The latter is aiERcrRous SULPHOOYANIDE, Hg a (CNS) a . 
With metallic zinc^ hydrosulphocyanic acid or the acidified solu- 
tion of a sulphocyanide gives HYDROGEN SULPHIDE. 



8187. 
. HYDROSULPHURIC ACID (HYDROGEN SULPHIDE), HJS. 

1. SULPHUR is usually a solid, brittle, friable, tasteless body, 
insoluble in water. It occasionally occurs in the form of 
yellow or brownish crystals, or crystalline masses of the same 
colors, and sometimes as a yellow, yellowish-white, or grayish- 
white powder. It melts at 118; and upon the application 
of a stronger heat, it is converted into a brownish-yellow vapor, 
which in cold air condenses to a yellow powder, and on the sides 
of the vessel to drops. Heated in the air, it burns with bluish 
Uame to sulphur dioxide, which betrays its presence at once by 
5t sufft mating odor. Concentrated nitric acid, bromine in hy- 
drochloric acid, nitro-hydrochloric acid, and a mixture of potas- 
sium chlorate and hydrochloric acid dissolve sulphur gradually, 
with the aid of a moderate heat, and convert it into sulphuric 
acid. In boiling solution of sodium hydroxide, sulphur dissolves 
to a yellow fluid, which contains sodium sulphide and sodium 
thiosulphate. It is insoluble in cold aqueous ammonia, but in warm 



187.] HYDEOSULPHURIC ACID. 373 

ammonia, it dissolves to a small extent. Carbon disnlphide* ben- 
zol, and petroleum-ether dissolve the ordinary variety of sulphur 
with ease, but there is a kind which is insoluble in the^e solvents. 
A hydrogen flame when brought into contact with sulphur (but 
also with sulphides or sulphates; shows a line blue inner flame. 

2. HTDBOSULPHURIC ACID, or IIYDKOOLX SULPHIDE, at the com- 
mon temperature and under common atmospheric pressure, is a 
colorless, poisonous, inflammable gas, soluble in water, and readily 
recognized by its odor of rotten eg^s. . It transiently imparts a 
red tint to moist litmus-paper. AVhen it i& kindled, it burns 
with a blue flame to water and bulphur dioxide. Hydrogen 
sulphide water, the properties of which have been already 
given in 33, is decomposed by chlorine, bromine, iodine, ferric 
chloride, permanganic acid, chromic acid, nitroub acid, and other 
oxidizing agents, with the separation of sulphur. 

3. Of the SULPHIDES, only those of alkali and alkali-earth 
metals are soluble in water. These, as well as the sulphides of 
iron, manganese, and zinc, are decomposed by dilute mineral 
acids, with evolution of hydrogen sulphide gas, which may be 
readily detected by its smell, and by its action upon solution of 
lead (see 4). The decomposition of polysulphides is also attended 
with separation of sulphur in a finely divided state, and the 
white precipitate may be readily distinguished from other pre- 
cipitates by its solubility in benzol or petroleum-ether. Part of 
the sulphides of the metals of the fifth and sixth groups are de- 
composed by concentrated and boiling hydrochloric acid, with 
evolution of hydrogen sulphide, while others are not dissolved 
by hydrochloric acid, but by concentrated and boiling nitric 
acid. The compounds of sulphur, with mercury, gold, and 
platinum, resist, more or less, the action of both acids, but 
dissolve in nitro-hydrochloric acid. Upon the solution of sul- 
phides in nitric acid and in nitro-hydrochloric acid, sulphuric 
acid is formed, and in most cases sulphur is also separated. 
Many metallic sulphides, more especially those of a higher degree 
of sulphuration, give a sublimate of sulphur when heated in a 
tube closed at one end. All sulphides are decomposed by fusion 
with potassium nitrate and sodium carbonate; and on extract- 
ing the fusion with water, the sulphur is found in solution as 
sodium or potassium sulphate. 



374 DEPORTMENT OF BODIES WITH REAGENTS. [187. 

-i. If hydrogen sulphide, in the gaseous state or in solution, 
is brought into contact with ulcer nitrate or lead acetate, black 
precipitates of SILVER SULPHIDE or LEAD SULPHIDE are formed. 
In cases therefore, where the odor fails to afford sufficient proof 
of the presence of hydrogen sulphide, these reagents will remove 
all doubt. If the hydrogen sulphide is present in the gaseous 
form, the air suspected to contain it is tested by placing in it a 
small strip of paper moistened with solution of lead acetate and a 
little ammonia. If the gas is present, the paper becomes covered 
with a brownish-black, shining iilrn of lead sulphide. To detect 
a trace of an alkali-inetal sulphide in presence of a free alkali or an 
alkali carlxmate, the best way is to mix the fluid with a solution 
of lead hydroxide in sodium hydroxide, which is prepared by 
mmiiK solution of lead acetate with sodium hydroxide solution 
until the precipitate which forms at first is redissolved. 

ft. If a fluid containing hydrogen sulphide or an alkali-metal 
sulphide is mixed with solution of sodium hydroxide, then with 
wllvm mtroprwside, Xa,Fe(XO; (ON) 6 .2H S O, it acquires a 
tine reddish-violet tint. The reaction is very delicate ; but that 
with bolution of lead hydroxide in sodium hydroxide is still more 
sensitive. 

t). Exceedingly minute traces of hydrogen sulphide in aque- 
ous *olution may be detected by adding -fa of the volume of 
f niuiiifr hydrochloric acid and some small fragments of the sul- 
phuric acid salt of para-amido-diniethyl aniline,* and also, as 
soon as the latter has dissolved, one or two drops of a dilute fer- 
ric chloride solution. In the presence of hydrogen sulphide, the 
liquid takes on a pure blue color in consequence of the formation 

Of METHYLENE BLUE (H. CABO, E. FlSOHEE). 

7. If metallic sulphides aro exposed to the oxidizing flame 
of the llowpipe, the sulphur burns with a blue flame, emitting 
at the name time the well-known odor of SULPHUR DIOXIDE. 
If n sulphide is heated in a glass tube open at both ends, 
in the upper part of which a strip of moist, blue litmus-paper 
is inserted, and the tube is held in a slanting position during 
the oj>e ration, the escaping sulphur dioxide reddens the litmus- 



* Concerning the preparation of this reagent, see Zeftschr. f. analyt Chemu, 
33, 226. 



188.] RECAPITULATION AND REMARKS. 375 

8. If a finely pulverized metallic sulphide is boiled in a 
porcelain dish with solution of potassium hydroxide, and the 
mixture heated to incipient fusion of the caubtic pjta&h, or if the 
substance to be tested is fused in a platinum spoon with caustic 
potash, and the mass is in either case dissolved in a little water, 
a piece of bright silver (a polished coin) put into the solution, 
and the fluid is warmed, a brownish-black film of SILVER SUL- 
PHIDE forms on the metal. This film may be removed after- 
wards by rubbing the metal with leather and quicklime (v. 
KOBELL). 

9. If the powder of a sulphide which is decomposed by 
hydrochloric acid with difficulty or not at all, is mixed in a 
small cylinder or in a wide-necked flask, with an equal volume 
of finely divided iron free from sulphur (ferrum alcoholisatum), 
and some moderately dilute hydrochloric acid (1 volume of con- 
centrated acid to 1 volume of water) is poured over the mix- 
ture, in a layer a few millimeters tliiek, HYDBOGEK SCLPHID* 
escapes along with the hydrogen. This may be easily detected 
by placing a strip of paper moistened with solution of lead 
acetate and dried again, under the cork, so that the bottom ia 
covered by it, the ends of the strip projecting on both sides, and 
then loosely inserting the cork into the mouth of the flask, 
Kealgar, orpiment, and molybdenite do not show this reaction 
(T. KOBELL). 

10. In relation to the microscopic detection of sulphur, set 
HAUSHOFBB, p. 115; BEHRENS, Zeitschr. t analyt. Chencu 
30, 166; F. Emon, Hid., 32, 163. 

188. 

Recapitulation and Remarto.Wo*t of the acids of the 
first group are also precipitated by silver nitrate, but the precip- 
itates cannot well be confounded with the silver compounds of 
the acids of the second group, since the former are soluble in 
dilute nitrfc acid, while the latter are insoluble in that acid. 
The presence of hydrogen sulphide interferes more or less with 
the tests for the other acids of the second group. This acid 
must therefore, if present, be removed before the testing for 
the other acids can be proceeded with. The removal of 



376 DEPORTMENT OF BODIES WITH KEAGENTS. [ 188. 

hvdrosulphuric acid, when present in the free state and when 
cyanogen compounds are not also present, may be effected by 
simple* ebullition. In other cases, it is best accomplished by the 
addition of a solution of zinc sulphate which has been treated 
with an excess of sodium or potassium hydroxide, and filtering 
off the zinc sulphide [or by the addition of cadmium sul- 
phate solution to neutral, acid, or alkaline liquids, and filtering 
oil the cadmium sulphide, which filters better than zinc sul- 
phide], Mixtures of insoluble metallic sulphides with insolu- 
ble chlorine, bromine, or iodine compounds may be prepared 
for analysis by fusing with sodium carbonate and potassium 
nitrate- "When the mass is treated with carbonic acid water, 
heated, and filtered, the filtrate contains the sulphur as sulphate, 
virile the chlorine, bromine, and iodine are combined with the 
alkali xiietaU The two latter may, however, be present partly 
as alkali liromate and iodate, but if the solution is acidified 
with dilute sulphuric acid and sulphurous acid is added in slight 
excete, it then contains only hydrochloric, hydrobromic, and 
hydriodic acids. 

Hvdrocyanic acid can be recognized, even in the presence 
of hydrochloric, hydrobromic, and hydriodic acids, by the re- 
action with ferrous-ferric solution, which is as delicate as it is 
characteristic. In the presence of alkali-metal ferro- and ferri- 
evanidcs as well as sulphocyanides, a metallic cyanide may be 
detected by subjecting the liquid to distillation with the addi- 
tion of hydrogen sodium carbonate. The cyanogen of cyanides 
in then found as hydrocyanic acid in the distillate. Ferrocyan- 
ogen and f erricyanogen may also be removed by careful precipi- 
tation by ferric or ferrous sulphate, respectively, and the cyano- 
gen may be detected in the filtrate according to 185, 6. The 
separation of ferrocyanogen from ferricyanogen, cyanogen, 
sulphocyanogen, chlorine, and bromine (but not from iodine), 
may be accomplished by treating the freshly precipitated silver 
compounds with aqueous ammonia, since silver ferrocyanide is 
insoluble in this liquid, while the other silver compounds dissolve 
in it. Silver ferroeyanide and also silver ferricyanide may be 
identified by the blue coloration which they show when they are 
moistened with sodium chloride solution and ferric chloride or 
ferrous sulphate solution, respectively. 



188.] BECAPITULATION AND BEMABKS. 877 

Hydriodic acid may be readily detected in the presence of 
hydrogen chloride and bromide, with starch or carbon disulphide, 
upon the addition of a liquid containing nitrous acid. These 
iodine reactions may, however, be interfered with or prevented 
by the presence of cyanogen compounds, and, moreover, the 
detection of chlorine and bromine in the presence of iodine or 
cyanogen compounds is more or less difficult. Any cyanogen 
present must, therefore, be removed or rendered harmless before 
testing for iodine, and, furthermore, both cyanogen and iodine, 
if necessary, must be removed or rendered harmless before 
testing for bromine and chlorine. The removal of cyanogen, as 
well as ferrocyanogen, ferricyanogen, and sulphocyanogen, is 
accomplished by igniting all the silver compounds. Silver 
cyanide, ferrocyanide, ferricyanide, and sulphocyanide are de- 
composed (the latter with formation of silver sulphide), while 
silver chloride, bromide, and iodide suffer no decomposition. 
If, therefore, the ignited residue is fused with sodium and potas- 
sium carbonates, and the mass is boiled with water, sodium or 
potassium chloride, bromide, and iodide are obtained in solution. 
The fused silver compounds are also readily decomposed by 
metallic zinc. For this purpose, they are covered with water, a 
little dilute sulphuric acid is added and a fragment of zinc, the 
whole is allowed to stand for some time, and the resulting zinc 
chloride, bromide, and iodide solution is filtered from the sepa- 
rated metallic silver. If sulphocyanogen was present, hydrogen 
sulphide appears in this reduction, and this must be removed in 
the first place by boiling. 

The separation of iodine from chlorine and bromine is ef- 
fected by treating the silver compounds with ammonia, but more 
accurately by precipitating the iodine as cuprous iodide ( 184, 
6, first method). From bromine alone, iodine is separated most 
accurately by palladious chloride, which only precipitates the 
iodine ; while from chlorine, it is separated by palladious nitrate, 
or, after the addition of a sufficient amount of ammonium sulphate, 
by means of thaUous sulphate (P. JAKNASOH and K* ASCHOFF). 

Bromine in presence of iodine and chlorine may be identified 
by the following simple operation: Mix the liquid with a few 
drops of dilute sulphuric acid, then with some starch paste, and 



378 DEPORTMENT OF BODIES WITH REAGENTS. [ 188. 

add a little red fuming nitric acid or, better still, a solution of ni- 
trous acid in sulphuric acid, whereupon the iodine reaction shows 
itself immediately. Add now chlorine- water drop by drop until 
that reaction has disappeared; then add some more chlorine- water 
to set the bromine also free, which may then be separated and 
identified by means of chloroform or carbon disulphide. Or, the 
iodine after being liberated in a highly dilute fluid may be also 
taken up with chloroform or carbon disulphide, the aqueous fluid 
may then be filtered through a wet filter, and the bromine de- 
tected in the filtrate by means of chloroform or carbon disulphide 
and chlorine- water. For the latter process, the following may be 
substituted: Directly after the liberation of the iodine, cau- 
tiously add chlorine-water, when the violet-red coloration of 
the chloroform or carbon disulphide will gradually fade away, 
and give place to the brownish-yellow color indicative of bromine. 
For the detection of chlorine, iodine, and bromine, in tho 
presence of each other, the fresh precipitate of silver chloride, 
bromide, and iodide, washed by decantation, is heated from two 
to three minutes to boiling with 80 to 100 parts by weight of an 
aqueous solution of ammonium sesqui-carbonate (see 182,4, 
foot-note), it is allowed to stand a short time, the liquid is 
decanted, and the boiling with the ammonium carbonate is 
repeated with more of that solution. The solution contains the 
silver chloride (together with a trace of silver bromide). If the 
residual silver iodide and bromide is treated with 5 per 
cent ammonia- water (.9783 sp. gr.), the silver bromide dis- 
solves (with traces of silver iodide), while almost the whole 
amount of the silver iodide remains behind (H. HAGEB). The 
precipitates thrown down by nitric acid from the ammoniacal 
solutions and the silver iodide remaining undissolved may then be 
fused with sodium carbonate, the fusions treated with water, and 
the filtrates, each of which now contains a halogen in an almost 
pure condition, may be subjected to further tests. For the 
detection of chlorine, the solution is neutralized with sulphuric 
acid (the reaction may be still somewhat alkaline, but must not 
be acid), it is evaporated to dryness, the residue is melted 
together with potassium dichromate, and the resulting mass is 
treated acording to 182, 7. [The moist silver salts may be de- 
composed also very readily by agitating them with a little dilute 



188.] BEOAPITULATION AND BEMABES. 379 

sulphuric acid and metallic zinc until they have become thoroughly 
black from their conversion into metallic silver. The filtrates 
may be directly subjected to further tests for iodine and bro- 
mine, but before evaporating the solution, sufficient sodium 
carbonate solution should be added to it to produce a per- 
manent precipitate of basic zinc carbonate.] 

The following method for the detection of small amounts of 
chlorine in the presence of iodine and bromine is similar in prin- 
ciple : Treat the completely washed silver precipitate for a few 
minutes in the cold with four or five volumes of a 10 to 15 
per cent solution of ammonium sesqui-carbonate, allow it to 
settle, filter, and add potassium bromide to the filtrate. The 
formation of a precipitate shows the presence of silver which has 
gone into solution as silver chloride, and consequently the pres- 
ence of chlorine. If iodates or cyanides were present, it would 
have been necessary to destroy them in the first place (L. L. DE 
KONINCK). 

Chlorine may also be detected in the presence of bromine and 
iodine in the following way : Heat the solution, in which the 
halogens are presumed to be combined with alkali or alkali-earth 
metals, with lead dioxide and acetic acid, until the liquid is color- 
less after settling, and has no longer the slightest odor of iodine 
or bromine. In this operation, the bromine escapes with a part 
of the iodine, while the rest of the latter remains as lead iodate 
with the lead dioxide added in excess. Filter, wash the precipitate 
with hot water, and precipitate the chlorine from the filtrate with 
silver solution (G. VOBTMANN). 

After a great amount of experience, it is possible to detect 
chlorine, bromine, and iodine in the presence of ea*h other 
by spectrum analysis, according to AL. MITSOHERLIOH (compare 
Zeitschr. f. analyt. Ohem., 4, 153). 

As regards the starch reaction, it should be noted that 
many salts (alum, alkali sulphates, magnesium sulphate, etc.) 
its delicacy; and also, in regard to this and the 



carbon disulphide reaction, that many organic substances may 
entirely prevent their appearance, e.g., albuminoids (Pucnor), 
resorcin, orcin, phloroglncin (ELABIWETZ), and especially tannin. 
The fact should also T>e mentioned that when nitrous acid 
is naed for the liberation of iodine in the presence of sul- 



380 DEPOBTMENT OP BODIES WITH REAGENTS. [ 

phocyanides, mistakes may occur (NADLEB), because the fluid then 
assumes a reddish color, even in the absence of iodine, from the 
formation of psendo-sulphocyanogen. Upon shaking with car- 
bon disulphide, the greater part of the colored substance is taken 
up by this solvent. 

As far as the agents for setting iodine free are concerned, 
many others have been proposed besides those mentioned above, 
e.g., iodicacid, or an alkali-metal iodate and hydrochloric acid 
(v. LIEBH*), ferric chloride and sulphuric acid, platinic chloride 
with the addition of some hydrochloric acid (HEMPEL), potassium 
permanganate or chromic acid in slightly acidified solution, etc. 
In respect to these agents, it should be observed that iodic acid 
must be used with the greatest caution ; in the first place, because 
in presence of reducing substances, iodine is set free from the 
reagent, and in the second place, an excess of iodic acid will at 
once put an end to the reaction. Ferric chloride, with addition 
of sulphuric acid, will not act immediately upon very dilute 
solutions ; but after a time, the reaction will make its appearance, 
revealing the presence of even the minutest trace of iodine ; and 
the delicacy of the reaction is not materially impaired by an excess 
of the reagent. Ferric chloride may be used with advantage 
when iodine is to be liberated in the gaseous state, which should 
be done, for example, in the presence of organic substances 
which prevent the iodized starch reaction, and when, sulphocya- 
nides are present. For this purpose, the liquid is heated nearly 
to boiling, and the escaping fumes are allowed to act on paper 
smeared with fresh starch paste. If a solution of ferric sulphate 
is used instead of ferric chloride, the residue may be used after* 
wards for testing for bromine and chlorine. If this is heated 
after the addition of potassium permanganate, the bromine escapes 
and is conveniently collected in some chloroform (HABT), so that 
the residue now remaining, after reduction of the potassium 
permanganate by alcohol, may be tested for chlorine by means 
of silver solution. Where potassium permanganate is used for 
the liberation of iodine, if the reaction of starch solution with 
iodine is used, a conclusion concerning it ought not to be made 
until from six to twelve hours have elapsed, because a liquid colored 
with a little iodized starch may also appear reddish, and there- 
fore may be confused witl the coloration produced by perman- 



189-] NITROUS ACID. 381 

ganic add alone. The modus opewndi may of course be 
modified in various ways to increase the delicacy of the starch 
reaction, and interesting particulars upon this point may be found 
in the papers of MOEIX* and HEirpEL.f 

For the distinction of the polysulphides of the alkali and 
alkali-earth metals from their normal sulphides, the following 
reaction will serve, in addition to the one given in 1*7, 3: 
Heat pure 96 per cent alcohol in a tiask to boiling, with the 
addition of some pieces of glass in order to regulate this, and, 
after the alcohol vapor has expelled the air. add the liquid tu be 
tested drop by drop. If this contains a polysulphide, the liquid 
transiently assumes a sky-blue color, which changes into a per- 
manent greenish-blue (J. C. GILL).;]; 

1S. 

Rarer Acids of the Second Group. 
1. NITROUS Aoro, HNO 9 . (Citron* AnJtytlride, X,0 t .) 

NITROUS ANHYDRIDE forms a brownish-red gas at the ordinary temper- 
ature. In contact with water, it decomposes, mostly at least, into nitric acid, 
which dissolves, and nitric oxide, which partly escapes if the amount of water 
is not very large : 8N,0 + H S = SHNOs + 3N 9 O a . The nitrites are decom- 
posed by ignition, and most of them are soluble in water. If the salts or 
their concentrated solutions are treated with dilate sulphuric acid, nitrous 
anhydnde is not evolved, but nitric oxide is, while at the same time nitric 

* Joura f. prakt. Chem., 78, 1. 

f Annal. d. Chem. u. Phann., 107, 102. 

| Concerning further reactions for the detection of small amounts of 
hydrogen sulphide, compare CURTUAN, Zeitschr f. analyt. Chem., 25, 561; 
ITALMB, Chem. Ceutralhl,, 1891, II, 498. In relation to the detection of 
small amounts of a chloride in the presence of much iodide, compare DIET- 
ZELL, Zeitschr f. analyt. Chem., 8, 453; small amounts of bromine in piesence 
of chlorine, BEBGLUND, ibid,, 24, 184; small amounts of chlorine or bromine 
beside much iodine, BOHLIG, ibid., 9, 315; small amounts of iodine in bromine 
and bromides, JORIBSEN, &id., 19, 358; of chlorine, biomlne, and iodine in 
presence of each other, DECHAN, ibid., 28, 705; JOKES, Pbarmac. Centralhalle, 
1884, p. 188; MACNAIR, ibid,, 1898, p. 519; EAGER, Chem. Centralbl., 1885, 
p. 815; F. KBBLBB, fMd-, 1893* I, 355 , of chlorine, bromine, iodine, cyano- 
gen, forro- and ferricyanogen, also of chloric, broraic, and Jodie acids, as well 
as hydrogen sulphide in mixtures of all of them, LOHGI, Zeitschr. 1 analyt 
Chem., 23, 70; WELLS and VULTE, Pharmac. Centralhalle, 1890, p. 118. 



382 DKPOIIT3H3OT OF BODIES WITH KEAGE3TS. [g 189. 

aei<l is formed. Very dilute solutions OL nitrites (e.g., such as contain 
.000 q MF less of nitrous acid per liter), when acidified with dilute sulphuric 
or acetic acid, and dibtilled, give, on the other hand, a distillate which 
COL tin na aimost the whole amount of the nitrous acid originally present, 
ami. in fact, the first 10 or 20 cc which go over contain the greater 
part of it. This gives a means of obtaining the nitrous acid in a small 
volume of liquid, and at the same time of separating it from subbtances 
which might prevent its detection. It is self-evident that this method is 
not applicable when substances which decompose nitrous acid (e.g., hydro- 
gn sulphide) are present In solutions of alkali nitrites, silver nitrate 
produces a white precipitate, which dissolves in a very large proportion of 
water, especially upon application of heat. Ferrous sulphate produces in 
neutral solutions a faint brownish-yellow coloration, but upon the addition 
of acetic acid, a deep blackish-brown coloration results, due to the solution 
of nitric oxide in the ferrous sulphate solution (difference from nitric acid). 
Hydrogen sulphide gives at once in solutions containing free nitrous acid, 
and srradunlly in solutions of normal alkali-metal nitrites, a white precipi- 
tate of separated sulphur, Pyrogallic acid imparts a brown color to even 
very dilute solutions of nitrites acidified with sulphuric acid (SCHONBEIN). 
On addition ol^tassium cyanide solution to an alkaline nitrite, then of 
some neutral solution of wlalt chloride and a little acetic acid, the fluid 
becomes orange-rose colored from the formation of potassium cobalt nitro- 
cyanide (C. D. BRATJN). But a far mo^ delicate reagent for nitrous acid is 
solution of potassium iodide or zi?ic iodide * mixed with starch paste, 
especially upon addition of sulphuric acid (PRICE, SCHON*BEIN). Water con- 
taining one hundred-thousandth part of potassium nitrite, together with 
free sulphuric acid, is colored distinctly blue by this reagent in a few 
seconds, and a few minutes suffice to produce the same effect m water 
containing one millionth part of potassium nitrite. This reaction is trust- 
worthy, only where no other substance is present that might exercise a 
decomposing action upon potassium iodide, such as iodic acid, ferric 
salts, etc. In order to exclude the detrimental action of such sub- 
stances, and to increase the delicacy of the reaction, about 300 cc of 
the water to be tested are distilled, with the addition of a little acetic acid, 
aud the first drops going over are collected in a solution of an iodide and 
stprch paste acidified with sulphuric acid. If a liquid containing nitrons 
acid is mixed with a colorless solution of nietadiamidobemol (metapheny- 
lene diamine) in an excess of dilute sulphuric acid,t there is produced, 

* A stable zinc iodide solution may be obtained according to the following 
directions- 5 g of starch and 20 g of zinc chloride are boiled with about 100 
cc of distilled water, the evaporated water being replaced, until the crusts of 
starch are almost completely dissolved ; then 2 g of dry zinc iodide are added, 
the solution ia diluted tol liter, and filtered. The solution should be preserved 
fn well-closed bottles la the dark. 

| The solution is decolorized with animal charcoal, and is then stable for 
mouths in closed bottles, 



189.] XITBOUS ACID. 383 

even in exceedingly dilute solutions, a characteristic yellow coloration (P. 
GKIESS). If a bolution of shlphamlic awl m acetic acid, mi^d with a col- 
orless solution of napfithylamuie in acetic acid;* la added to a liquid 
containing nitrous acid, and it ia heated to 7o or 8U~, there is produced m 
concentrated solutions a red coloration, which rapidly change^ to yellow, 
while in dilute solutions a permanent ro&e-red culor i* produced fP. GKIES&, 
L. ILOSVAT, LuxfrEj. On adding Indigo soffit ion in uaier til. the latter 
has lost its transparency from the depth of color, then hydroculonc acid, 
and afterwards a solution of alkrth-infta? pofyuifjjfmfe with i-tsrniiff, rill 
the blue color just vanishes, filtering and adding to the clear filtrate a 
solution of the merest trace of nitrous acid, a most distinct, bluzsu cuiora- 
tion will at once 1x3 produced. This reaction ia to be recommended m the 
presence of other reducing bodies which interfere with the action of nitrous 
acid upon an acidified solution of starch audpota>smm iodide (*SCHONBEIN;. 
But it must not be overlooked that other oxidizing substances reproduce 
the blue color. Ou mixing a solution of nitrous acid (for instance, a 
solution of potassium nitrite acidified with acetic acid) with potatunuin 
sulphocyanide, the fluid is not colored, but on the addition of nitric acid, 
hydrochloric acid, or sulphuric acid, a dark- red color makes its appearance, 
which vanishes on addition of alcohol, or after heating for a bhort time 
(difference from ferric sulphocyauide). The coloring substance is mostly 
taken up by shaking with carbon disulplude. The following reac- 
tion is * especially adapted for the detection of nitrous acid in concen- 
trated sulphuric acid: A trace of resorcin is added to 1 cc of the acid, and 
it is then diluted with 5 cc of water and shaken. The slightest trace of 
nitrous acid maybe thus detected by a yellow coloration ( WILSON). Ma*, 
sium permanganate does not act upon neutral solutions of nitrites, but 
upon the addition of a dilute acid, decoloration takes place, and in the 
presence of an excess of permanganic acid, all the nitrons acid is con- 
verted into nitric acid. Hydrogen peroxide also rapidly oxidizes nitrous 
acid in acid solution to nitric acid (WILFBATH, ScuoNE).f Concerning the 

* .5 g of sulphanilic acid is dissolved in 150 cc of acetic acid; .1 g of solid 
naphJhylamine is boiled with 20 cc of water, the colorless solution is poured 
off from the bluish-violet residue and mixed with 130 cc of acetic acid Tha 
two solutions are mixed, decolorized, Sf necessary, by shaking with zinc dust, 
and the reagent is preserved in well-closed bottles. 

f Other means of detecting minute, or exceedingly minute, amounts of 
Dftrous acid are diamidobenzoic acid, P. GteESfl, Zeitschr. f. analyt. Chem. f 
ID, 92; diphenylamine, E KOPP, ibid., 11, 461; carbolic acid and mercur- 
ous nitrate, P 0. PLUGGE, ibid., 14, 131; fnchsine, A JORIRSEK, ibid., 21, 
210; para-amidobenzolazodimethyl aniline, MELDOLA, Bcr. d. deutwh, ch<*m, 
Gesellsch., 17, 266; Zeitschr. f. analyt Chem., 24, 9S; calHc acid, PAVT, 
Zeitschr. f analyt. Chem., 23, 72; antipyrine. CURTMAX, ibid, 29, 194; 
Bulpbanilic acid and phenol, P F. FRANKLAKD, ibid , 30, 713; potassium 
ferrocyamde and acetic acid, SCHEFFER. DEVENTKK, Ber. d. deatsch. cliem. 
Gesellsch , 1893, p. 589. Many reactions of nitrous acid may be confused 



884 DEPORTMEOT OF BODIES WITH REAGEOTS. [ 190. 

microscopic detection of nitrous acid, see BEHBENS, Zeitschr. f. analyt. 
Chem., 30, 165. 



190. 
2. HYPOCHLOBOUS ACID, HC1O. (ffflwAlowus Oxide, 01,0.) 



HYPOCHLOROUS OXIDE, C1 3 0, at the common temperature, is a deep 
yellow gas of a disagreeable, irritating odor, similar to that of chlorine. 
It explodes upon heating, decomposing into chlorine and oxygen. It dis- 
solves in water, aud the dilute aqueous solution bears distillation. The 
hypocltloriteb usually occur mixed with metallic chlorides, as is the case, 
for instance, in chloride of lime, eau de Jacette, etc. The solutions of 
hypochlontcd undergo alteration by boiling, the hypochlorite being re- 
solved into chloride and chlorate, attended in the case of concentrated, but 
not in that of dilute solutions, with evolution of oxygen. If a solution of 
chloride of lime is mixed with hydrochloric acid or sulphuric acid in 
excess, chlorine is disengaged, while hypochlorous acid is set free by passing 
carbonic acid into it. Silccr nitrate throws down silver chloride from a 
solution of chloride of lime which has been so far neutralized with 
nitric acid that it does not yet give an odor of chlorine. The silver hypo- 
chlorite which is transiently formed, decomposes very soon into silver 
chloride and chlorate: 3AgC10 = AgCIO, + SAgCl. Lead nitrate pro- 
ducts a precipitate which from its original white color changes gradually 
to orange-red, and ultimately, owing to formation of lead dioxide, to brown. 
Manganese salts give brownibh- black precipitates of hydrated manganese 
dioxide. Free hypochlorous acid, acting upon mercury, produces yel- 
lowish-brown mercuric oxychloride (while chlorine gives mercurous chlo- 
ridei. If so little hypochlorous acid is present, with much chlorine, that 
the color of the precipitate cannot be certainly recognized after the shak- 
ing, the precipitate resulting after long shaking is treated with hydro- 
chloric add (which dissolves the oxycubride, but leaves the mercurous 
chloride unchungd), this is filtered, and hypochlorous acid is recognized 
by the presence of mercuric chloride in the filtrate. Hypochlorites may be 
detected even more easily than the free acid by shaking their solutions 
with mercury, because in their presence mercuric oxide is formed, yellow 
In color and gradually becoming red, which adheres to the surface of 

with those of ot&ne and hydrogen peroxide, and in relation to those by which 
they may be dhtingutehed (since this subject does not admit of being suf. 
tictently explained in a concise manner), I will refer to the treatises of EM. 
BCHONE, Ber. d. deutsch. chem. Gesellsch., 7, 1693; 11, 482, 561, 874, 1028; 
Zeitschr. f. nnalyt. Chem,, 18, 133; and above all, to the one most recently 
published, &&, 33, 187, in which the work of other investigators upon this 
abject is referred to and discussed. 



191, 192.] HTPOPHOSPHOEOUS ACID. 385 

the glass upon shaking. Chlorous and chloric acids, when they are com- 
bined with bases, do not attack mercury (\VOLTERSJ. Solution of potas- 
sium permanganate is not decolorized. Solutions of litmus and indigo 
are decolorized somewhat by alkaline solution* of hypoehlorites, but 
far more rapidly and completely upon addition of au acid. If a solution 
of arsenious oxide in hydrochloric acid is colored blue with solution of 
indigo, and a solution of chloride of lime J added, with active stirring 
the decoloration will take place only after the whole of the arsenious oxide 
has been converted to arsenic acid. 



191. 

3. CHLOBOUS Aon>, HC10,, (Chlorous Oxide, C^O,.) 

CHLOROUS OXIDE, ClaOa , is a yellowish-green gas of a j>cculiar and very 
disagreeable odor. It explodes at 57, and is thereby converted into chlo- 
rine and oxygen. It is soluble in water, and the solution has an intensely 
yellow color, even when highly dilute. Most of the chlorites are holuble 
in water, and the solutions readily suffer decomposition, the chlorite^ being 
resolved into chlorides and chlorates. Silver nitrate precipitates white 
silver chlorite, which is soluble in much water. A solution of potassium 
permanganate is immediately decomposed by free chlorous acid, and a 
brown precipitate separates after some time. Tincture of Htmm and 
solution of indige are instantly decolorized, even if mixed with arsenious 
acid in excess. If a slightly acidified, dilute solution of a ferrous salt id 
mixed with a dilute solution of chlorous acid, the fluid transiently acquires 
an amethyst tint, and not until after the lapse of a few seconds, assumes 
the yellowish coloration of ferric salts (LENSSEN). 

192. 
4. HYPOPHOSPHOBOUS ACID, B^PO,. 

The concentrated solution of hypophospborous acid is of a syrupy con- 
sistence, and resembles that of phosphorous acid (see 178), with which it 
also has this in common, that it is resolved by heating, with exclusion of air, 
into phosphoric acid and hydrogen phosphide gas which is not spontaneously 
inflammable. Almost all hypophos-phites are soluble in water ; and by igni- 
tion, all of them are resolved into phosphates, and hydrogen phosphide 
which in most cases is spontaneously inflammable, and a portion of which 
decomposes into phosphorus and hydrogen. Barium, chloride* calcium 
chloride, and lead acetate fail to precipitate solutions of hypophoaphites 
(difference from phosphorous acid). Silrer nitrate gives at first with 
hypophosphites a white precipitate of silver hypophoephite, which turns 
black even at the common temperature, but more rapidly on heating, the 



DEPORTMENT OF BODIES WITH REAGENTS. [ 193. 

change of color heing attended with separation of metallic silver. From 
excess of me? cnric chloride* hypophosphorous acid precipitates mercurous 
chloride slowly in the cold, but more rapidly on heating. If the nitric acid 
solution of ammonium molybdate ( 55) is mixed with a liquid contain- 
ing hypophosphorous acid, and a few drops of aqueous sulphurous acid 
are added, upon warming gently, a blue precipitate or a fine blue colora- 
fi.m h produced. Hydrogen sulphide, thiosulphates, chlorates, as well as 
-tannous chloride, prevent the appearance of this very delicate reaction 
(MlLLARDI. A solution of copper sulphate gives with hypophosphorous 
acid, and also with its salts, upon heating, a reddish-brown precipitate of 
cuprous hydride, CuH ( WCRTZ). When brought together with zinc and 
dilute sulphuric awl, hypophosphorous acid gives hydrogen containing 
hydrogen phosphide (compare phosphorous acid, 178). 

Third Group of Inorganic Adda. 

ACIDS WHICH ARE NOT PRECIPITATED BY BARIUM SALTS NOB BY 

SILVER SALTS: Nitric Acid, Chloric Acid (Perchloric 
Acid). 

193. 
a. XITRTC ACTD, HNO,. (Nitric Anhydride^ N,O.O 

1. XITRIO ANHYDRIDE crystallizes in six-sided prisms. It 
fuses at 29.5, and boils at about 45 (DEVILLE). NITRIC ACID, 
HXO iS is a colorless (red when it contains nitrogen peroxide), 
exceedingly corrosive fluid, which emits fumes in the air, exer- 
ciscs a rapidly destructive action upon organic substances, and 
colors many nitrogenous matters intensely yellow. It boils at 
86, and has a specific gravity of 1.522. 

2. The NOBMAL SALTS of iritric acid, with few exceptions 
(cinchonainiiie, ABNACD and FADE), are soluble in water, but 
some of the l>aic nitrates are insoluble. All nitrates undergo 
decomposition at an intense red heat. Nitrates of the alkali 
metals at first yield oxygen, and change to nitrites ; but after- 
wards they yield oxygen and nitrogen. Some others yield oxy- 
gen and nitrogen peroxide, while many (containing water) give 
off nitric acid. 

3. If a nitrate is thrown upon red-hot charcoal, or if char- 
coal or some organic substance, paper for instance, is brought 



193.] NITRIC ACID. 387 

into contact with a nitrate in fusion, DEFLAGRATION takes place, 
i.e., the charcoal burns at the expense of the oxygen of the 
nitric acid, with vivid scintillation. 

4. If a mixture of a nitrate with potassium cyanide in 
powder is heated on platinum foil, a vivid DEFLAGRATION en- 
sues, attended with distinct ignition and detonation. Very 
small quantities only should be used fur this experiment. 

5. If a nitrate is mixed with copper filings, and the mixture 
heated in a test-tube with concentrated sulphuric acid, the air 
in the tube acquires a yellowish-red tint, owing to the nitric 
oxide gas which is liberated upon the oxidation of the copper 
by the nitric acid, combining with the oxygeu of the air to 
form nitrogen peroxide. The coloration may be observed 
most distinctly by looking lengthwise through the tube. 

6. If the solution of a nitrate is mixed with an equal vol. 
ume of concentrated sulphuric acid, free from nitric and nitrous 
acids, the mixture allowed to cool, and a concentrated solution 
of ferrous sulphate then cautiously added to it, so that the 
fluids do not mix, the junction shows ut first a purple, after- 
wards a brown color, or, in cases where only a very minute 
quantity of nitric acid is present, a reddish color. On mixing 
the fluids a little, the brown zone becomes wider. The nitric 
acid is decomposed by the ferrous salt, three fifths of the oxy- 
gen of nitric anhydride oxidizing a part of the ferrous sulphate 
to ferric sulphate, while the nitric oxide, NX), thus formed, 
combines with more of the ferrous sulphate to form a peculiar 
compound which dissolves in water with a brownish-black 
color. Considerable amounts of chlorides interfere with the 
delicacy of the reaction. A similar reaction is observed in 
presence of selenious acid ; but on mixing the fluid and letting 
it stand, red selenium separates (WrrrsTOCK). 

7. If a little hydrochloric acid is boiled in a test-tube, one 
or two drops of very dilute solution of indigo in sulphuric acid 
are added, and the mixture is again boiled, the liquid remains 
blue (if the hydrochloric acid was free from chlorine). If a 
nitrate, either solid or dissolved, is now added to the faintly 
light blue solution and it is again boiled, the liquid is decolor- 
ized on account of the destruction of the indigo. The addi- 
tion of sodium chloride increases the delicacy of this (in its 
simple form) very delicate reaction. It must be borne in 



388 DEPORTMENT OF BODIES WITH BEAGENT8. [ 193. 

mind, however, that several other oxidizing agents, especially 
free chlorine, also cause decoloration of solution of indigo. 

8. If a little brucine is dissolved in a porcelain dish or upon 
a watch-glass, iu pure concentrated sulphuric acid,* and a drop 
of a fluid containing nitric acid added to the edge of the solu- 
tion, the latter immediately acquires a magnificent red color 
at the place of contact. This reaction is extraordinarily deli- 
cate. The bright red color soon passes into reddish-yellow. 
Chloric acid gives a similar reaction. 

9. If 1 part of phenol (carbolic add) is dissolved in 4 parts 
of concentrated sulphuric acid, and 2 parts of water are 
added, and a drop or two of this fluid added to a solid 
nitrate (e.g. 9 to the residue obtained by evaporating a small 
amount of well-water containing nitrates), a reddish-brown 
color is produced, from the formation of a nitro-compound of 
phenol On addition of a drop or two of strong ammonia, 
this color turns yellow, sometimes passing through a green 
shade. This is a very delicate reaction (H. SPBENGEL). It 
may also be carried out by adding one or two drops of the 
liquid to be tested to some pure concentrated sulphuric acid, 
then adding a crystal of phenol and warming a little ; and also 
by acidifying the liquid to be tested for nitric acid strongly 
with hydrochloric acid, adding a little phenol, and heating to 
about 80 or 90. In the presence of nitric acid, a dark colora- 
tion always takes place, which is generally red or brown, but 
under certain conditions is green (EL HAGER). 

10. If a little pure concentrated sulphuric acid is poured , 
over a few crystals of diphenylamine, a little water is added, 
and the resulting solution is mixed with more concentrated 
sulphuric acid, an excellent reagent for nitric acid is ob- 
tained, which is best adapted for the detection of very small 
quantities when it contains only 1 mg of diphenylamine in 
10 oc. If only about .5 cc of this solution are placed upon a 
watch-glass or the inverted cover of a porcelain crucible, and 
a drop of the liquid to be tested for nitric acid is allowed to 

* In consequence of containing a small quantity of oxides of nitrogen, 
the common, pure concentrated sulphuric acid of commerce usually gives, 
with brucine alone, a rose-red coloration. But such an acid may be easily 
purified by diluting it with water to a specific gravity of 1.4, and heating it to 
boiling for a long time, beet in a platinum dish, 



193.] NITRIC ACID. 389 

fall into the middle of the reagent, there is formed, to the 
extent to which the liquids mix, a ring of a magnificent blue 
color (E. KOPP). This very delicate reaction may also be 
carried out by adding a few drops of the sulphuric acid salt 
of diphenylamine to the liquid to be tested for nitric acid, 
then adding pure concentrated sulphuric acid in such a man- 
ner that two layers are formed. The blue colorations gradu- 
ally change to green, and finally disappear. The interpretation 
of the reactions requires caution, since many other substances 
also give a blue coloration, e.g> 9 nitrous, chloric, hypochlorous, 
bromic, iodic, vanadic, chromic, permanganic, and molybdic 
acids, and also ferric salts, hydrogen peroxide, and barium 
peroxide (LAAB). 

11. If a few drops of sulphate of paratcHuidine solution are 
added to the solution of a nitrate, and then an equal volume of 
concentrated sulphuric acid, with the precaution that the 
liquids do not mix, there appears at once at the surface 
of contact of the two liquids a red zone, the color of 
which slowly changes to dark yellow.* The reaction is 
not as delicate as those given by brucine or diphenyla* 
mine, but, on the other hand, it is adapted for the de- 
tection of nitric acid in the presence of small quantities 
of nitrous acid, since the latter produces at first a yel- 
lowish or yellowish-brown coloration, which changes to red 
only after some time (LoNGij. Chloric acid and other oxidiz- 
ing agents yield similar colorations. 

12. Very minute quantities of nitric acid may be detected, 
also, by first reducing the nitric acid to nitrous acid, which 
may be effected both in the wet and in the dry way ; in the 
former, by heating the solution of the nitric acid or of the 
nitrate for some time with finely divided zinc, best with zinc 
amalgam, and then filtering (SCHoNBEiN) ; in the dry way, by 
fusing the substance with sodium carbonate at a moderate 
heat, extracting the mass, after cooling, with water, and filter- 
ing. Upon adding either of the filtrates to a solution of 

*The reaction may be also produced with & sulphuric acid solution of an 
aniline oil which contains aniline and paratolnidine. C. D. BRA.UN recom- 
mended such a solution as early as 1867 (Zeitschr. f. analyt, Chem,, 6, 72). 
The manner of carrying out the operation, as recommended by him, varied 
somewhat from that given by LOHGX. 



390 DEPORTMENT OF BODIES WITH REAGENTS. [ 194. 

potassium iodide mixed with starch paste%and pure dilute 
sulphuric acid, the fluid acquires a blue color from iodized 
starch (compare g 189). 

13. If a nitrate is brought into a solution of potassium 
hydroxide, and some aluminium or some zinc and iron filings 
are added, ammonia is set free upon gentle heating, and this 
may Le readily detected by 96, 3 or 4. Of course, nitrous 
acid gives the same reaction. 

14 In relation to the microscopic detection of nitrates, see 
EAUSHOFER, p. 115 ; BEHBEKS, Zeitschr. f. analyt. Chem., 30, 
165. 



194- 
6. CHLOBIO ACID, HC10,. 

1. CHLOBIC ACID, in its most highly concentrated solution, 
Is a colorless or slightly yellowish fluid, having a faint odor 
resembling that of nitric acid. It first reddens litmus, then 
bleaches it. Dilute chloric acid is colorless and odorless. 

2. All CHLORATES are soluble in water. When they are 
heated to redness, either the whole of the oxygen escapes 
and metallic chlorides remain, or chlorine and the oxygen of 
the chloric anhydride are evolved, while oxides remain behind 
(chlorates of the earth metals). 

3. Heated with charcoal or some organic substance, the 
chlorates DEFLAGRATE, and with far greater violence than the 
nitrates. 

4. If a mixture of a chlorate with potassium cyanide is heat- 
ed ou platinum foil, DEFLAGRATION takes place, attended with 
strong detonation and ignition, even though the chlorate is 
present only in minute quantity. This experiment should be 
made with very small quantities and urith great caution t 

5. If the solution of a chlorate is colored light blue with a 
sulphuric acid solution of indigo, a little dilute sulphuric acid 
added, and a solution of sodium sulphite dropped cautiously 
into the blue fluid, the color of the indigo disappears im- 
mediately. The cause of this equally characteristic and deli- 
cate reaction is, that the sulphurous acid deprives the chloric 



194.] CHLOTUC ACID. 391 

acid of its oxygen, thus setting chlorine or a lower oxide of 
it free, which then decolorizes the indigo. An excess of 
sulphurous acid is evidently to be avoided, because otherwise 
hydrochloric and sulphuric acids are produced. 

6. If chlorates are treated with moderately dilute hydro- 
chloric acid, the constituents of the two acids transpose, 
especially upon heating, forming water, chlorine, and chlorine 
peroxide, 010 2 . In this process, the test-tube in which the 
experiment ;s made becomes filled with a greenish-yellow 
gas of a vt^ f disagreeable odor, resembling that of chlorine, 
while the hydrochloric acid acquires a greenish-yellow color. 
If the hydrochloric acid is colored blue with indigo solu- 
tion, the presence of very minute quantities of chlorates will 
suffice to destroy the indigo color at once. 

7. If a little chlorate is added to a few drops of concen- 
trated sulphuric add in a watch-glass, the liberated chloric acid 
breaks up into perchloric acid and chlorine peroxide : 3HC10, 
= H010 4 + 201O 9 + H a O. Chlorine peroxide imparts an 
intensely yellow tint to the sulphuric acid, and betrays its 
presence also by its characteristic and very disagreeable odor. 
The application of heat must be avoided in this experiment, 
and the quantities operated upon should be very small, since 
otherwise the decomposition may take place with such violence 
as to cause a dangerous explosion, for the greenish-yellow 
chlorine peroxide explodes at as low a temperature as 60. 

8. If a drop of an aqueous solution of the sulphuric acid 
salt of aniline is added to the solution of a chlorate iu con- 
centrated sulphuric acid, prepared as in 7, a deep blue color- 
ation of the liquid is produced, which is increased by adding? 
a few drops of water. This is a very delicate reaction, which 
nitric acid does not give (ViTALi), 

9. Towards solutions of brudnt (LtJOK), diphenylamine, 
paratcluidine, and also phend in concentrated sulphuric acid, 
chloric acid behaves like nitric acid, or at least so similarly 
that the two acids cannot be certainly distinguished by these 
reagents. On the other hand, chloric acid may be distin- 
guished from nitric acid according to 8, as well as by phend 
in hydrochloric acid solution (compare 193, 9), since chloric 
acid produces in such a solution, according to circumstances, 
an orange-red turbidity or a transient yellow coloration. 



802 DEPORTMENT OF BODIES WITH REAGEXTS. [ 195. 

10. If a dilute, aqueous solution of an alkali-metal chlorate 
is boiled with the copper-zinc dement* of GLADSTONE and TBIBE, 
complete reduction to alkali-metal chloride takes place, with 
separation of zinc oxide (THOBPE and ECCLES). In solutions 
acidified by sulphuric acid, the chloric acid set free is con- 
verted into hydrochloric acid by the nascent hydrogen pro- 
duced when zinc is added. 



195. ' 

Jlecapitidation and Remarks. Of the reactions which have 
been given to effect the detection of nitric acid, those with 
ferrous sulphate and sulphuric acid, with copper filings and sul- 
phuric acid, and also those based upon the reduction to nitrites 
or to ammonia, give the most positive results. With regard to 
deflagration with charcoal, detonation with potassium cyanide, 
decoloration of solution of indigo, and the delicate reactions 
with brucine, diphenylamine, and paratoluidine, it has been 
shown that these reactions give no certain distinction, and are 
consequently decisive only where no chloric acid is present. 
The presence of free nitric acid in a fluid may be detected by 
evaporating it to dryness in a porcelain dish on the water-bath, 
having first 'thrown in a few white quill-cuttings. A yellow 
coloration of the latter shows the presence of nitric acid 
(RuNGE). The best way to ascertain whether or not OHLOEIO 
ACID is present (in the absence of other oxygen compounds of 
chlorine) is to ignite the substance, with addition of sodium 
carbonate, dissolve the mass, and test the solution with silver 
nitrate. If a chlorate was present, this is converted into a 
chloride upon ignition, and silver nitrate produces a precipi- 
tate of silver chloride. However, the process is thus simple 
oiily if no chloride is present with the chlorate. In presence 
of a chloride, the chlorine of the latter must be removed by 
adding silver nitrate to the solution as long'as a precipitate 
continues to form, and filtering; after addition of pure 
sodium carbonate, the filtrate is then evaporated and ignited. 

* The copper-zinc element is obtained by treating thin sheet-zinc "with 1 
per cent copper sulphate Holution, whereupon the zinc becomes black from 
precipitated copper. After washing and drying, the element is ready for use. 



196.] PERCHLORIC ACID. 393 

It is generally unnecessary, however, to pursue this circuitous 
way, since the reactions with concentrated sulphuric acid, 
with indigo and sulphurous acid, as well as with the sulphuric 
acid salt of aniline, are sufficiently marked and characteristic 
to afford positive proof of the presence of chloric acid, even in 
presence of nitrates. The best way of detecting nitric acid in 
presence of a large proportion of chloric acid is to mix the sub- 
stance with sodium carbonate in excess, evaporate if necessary, 
ignite the residue moderately, but sufficiently long to convert 
the chlorate into chloride, and then test the residue for nitric 
acid, or for nitrous acid. If it is desired to detect nitric acid in 
the presence of nitrous acid, pure urea is added to the aqueous 
solution, and the liquid is slowly added to a solution of urea 
in dilute sulphuric acid. The decomposition of the nitrous 
acid then takes place at once, with the evolution of nitrogen 
and carbonic acid. If potassium iodide and dilute starch 
paste are added as soon as the reaction is finished, the liquid 
remains colorless. If a little finely divided zinc is now added, 
the blue coloration which appears (193, 12) shows the presence 
of nitric acid 



196. 
PEBOHLOBIC Acn>, HC1O 4 . 

The anhydride of perchloric acid is unknown. PERCHLORIC ACID forms 
a colorless, corrosive liquid, which gives dense fumes in the air, and 
decomposes with violent explosion after some time when kept, but at once 
when dropped upon charcoal, wood, or paper. The hydrate, HU10*.HtO, 
crystallizes m needles. The acid and the crystals dissolve in water with 

* In regard to the detection of nitric acid in the presence of nitrous acid, 
see also Loiroi, Zeitschr. f. analyt Chem., 23, 352 ; concerning the detection 
of nitric acid in solutions containing iodides, bromides, chlorates, bromates, 
iodates, etc., see LOSGI, 0?& v 23, 149; and in relation to the detection of 
chloric acid beside hydrochloric, hydrobromic, bydriodic, hydrocyanic, 
hydroferrocyanicand hydroferricyanic acids, and also bromic and iodic acids, 
see LONGI, iWtf., 23, 70. In regard to further means of detecting small 
quantities of nitric aci3, see BREAL, Chem, Centralbh, 1888, p. 864 ; LINDO, 
fct, 1888, p. 1442 ; ROSENFBLD, Zeitschr. 1 analyt Chem., 29, 661 ; v. 
UDRAJTSZEY, i&jS., 29, 78B ; and in relation to the detection of chloric acid 
In presence of nitric add, see B&HAL, Chem. Centralbl., 1886, p. 134. 



39-4 UEPOUTHKNT OF BODIES WITH REAGENTS. [ 197. 

the production of much heat. By distillation, the dilute solution gives 
first water, then dilute acid, and finally concentrated acid. All perchlo- 
rates are soluble in water, most of them freely. They are all decomposed 
by ignition, those with alkali bases leaving chlorides behind, with disen- 
gagement of oxygen. In not too dilute solutions, potassium salts produce 
a white, crystalline precipitate of potassium perchlorate, ZC1O 4 , which is 
sparingly soluble in water, but insoluble in alcohol. Barium salts and silver 
salts are not precipitated. Concentrated sulphuric acid fails to decompose 
perchloric acid in the cold, and decomposes it with difficulty on heating 
/difference from chloric acid). Hydrochloric acid, nitric acid, and sulphur- 
ous acid fail to decompose aqueous solutions of perchloric acid or perchlo- 
ratea ; and therefore solution of indigo, previously added to it, is not decolor- 
ized {difference from all other acids of chlorine). Alkali-metal perchlorates 
are not reduced by the copper-zinc element ( 194, 10, difference from 
chloric acid). 



II. ORGANIC ACIDS, 
First Group. 

The acids of the first group are decomposed partially 
or entirely by ignition ; * also by boiling with concentrated 
nitric acid.f Their normal calcium salts are insoluble or 
difficultly soluble in water. The solutions of their normal 
alkali-metal salts are not precipitated nor colored by ferric 
chloride : OXALIC ACID, TABTABIC ACTO (racemic acid), OITBIO 

ACID, MALIC ACID* 

197. 
a. OXALIC ACID, E 9 C,0 4 . 

The reactions of this acid have already been given in 
175. 

6. TABTABIC ACID, H,,C 4 H 4 O t . 

1. TABTABIO ACID forms colorless crystals of an agreeable, 
acid taste, which are stable in the air, and soluble in water 

* Oxalic add, when cautiously heated, partially sublimes unaltered, 
f The decomposition of oxalic add by boiling nitric add into carbon di. 
oxide and water is slow* 



197.] TAliTAKIC ACID* 395 

and in alcohol. It is but slightly soluble in ether (.4 : 100, 
according to E. BOUBGOIN). Heated to 100 5 , tartaric acid loses 
no water ; heated to 170, it fuses ; while at a higher tempera- 
ture, it becomes carbonized, emitting during the process a 
very peculiar and highly characteristic odor, which resembles 
that of burnt sugar. Aqueous solution of the commonly 
occurring tartaric acid, as also of almost all tartrates, turns 
the plane of polarization of light towards the right. There 
is, however, a left-rotating or hevo-tartaric acid, which, in 
its crystalline form, differs somewhat from the ordinary or 
dextro-tartaric acid, but otherwise both show the same re- 
actions. 

2. The TARTRATES of the alkali metals are soluble in 
water, as are some others, for example, aluminium and ferric 
tartrates. Evaporated on the water-bath to a syrupy consist- 
ence, the solution of ferric tartrate deposits a pulverulent 
basic salt. Those tartrates which are insoluble in water 
dissolve in hydrochloric or nitric acid, ilauy tartrates 
which are insoluble or difficultly soluble by themselves form 
with alkali- metal tartrates double salts, soluble in water. 
When heated to redness, the tartrates suffer decomposition, 
charcoal separates, and the same peculiar odor is emitted as 
attends the carbonization of the free acid. 

3. If to a solution of tartaric acid, or to that of an alkali 
tartrate, solution of an alumininm or a ferric salt is added in 
not too large proportion, and then ammonia or potassium 
hydroxide, no precipitation of aluminium or ferric hydroxide 
takes place, since the double tartrates formed are not decom- 
posed by alkalies. Tartaric acid also prevents the precipita- 
tion of several other hydroxides by alkalies (as do citric acid, 
malic acid, etc.). 

4. Free tartaric acid produces with potassium salts best 
with the acetate a sparingly soluble precipitate of HYDROGEN 
POTASSIUM TABTBATE, HKC 4 H 4 O. The same precipitate is 
formed when potassium acetate and free acetic acid are 
added to the solution of the normal tartrate. Hydrogen 
potassium tartrate dissolves readily in alkalies and mineral 
acids ; but tartaric and acetic acids do not increase its solu- 
bility in water. The separation of the hydrogen potassium 
tartrate precipitate is greatly promoted by shaking, or by 



300 DEPORTMENT OF BODIEb WITH REAGENTS. [ 197. 

rubbing the sides of the vessel with a glass rod. In order 
that the reaction may be delicate, the tartaric acid solution 
should be very concentrated. The addition of an equal 
volume of alcohol heightens the delicacy of the reaction. In 
the presence of boric acid, the reaction appears only -when 
potassium fluoride is used instead of potassium acetate, since 
this forms potassium borofluoride, and prevents the produc- 
tion of the very soluble compound containing boric acid, tar- 
taric acid, and potassium (BABFOED). 

5. From solutions of normal tartrates, calcium chloride 
added in excess * throws down a white precipitate of CALCIUM: 
TARTBATE, Ga0 4 H 4 O i .4H 1 0. Presence of ammonium salts re- 
tards the formation of this precipitate for a more or less con- 
siderable space of time. Agitation of the fluid or friction on 
the sides of the vessel promotes the separation of the pre- 
cipitate. The precipitate is crystalline, or invariably becomes 
so after some time ; and dissolves to a clear fluid in a cold, 
not too dilute solution of potassium or sodium hydroxide 
which is pretty free from carbonate. But upon boiling the 
solution, the dissolved calcium tartrate separates again in the 
form of a gelatinous precipitate, which redissolves upon 
cooling. 

6. Lime-water added in excess * produces in solutions of 
normal tartrates and also in a solution of free tartaric acid, if 
added to alkaline reaction white precipitates which, while 
flocculent at first, assume afterwards a crystalline form. As 
long as they remain flocculent, they are readily dissolved by 
tartaric acid as well as by solution of ammonium chloride. 
From these solutions, the calcium tartrate separates again, 
after the lapse of several hours, in the form of small crystals 
deposited upon the sides of the vessel. 

7. Solution of calcium sulphate added in excess * fails to 
produce a precipitate in a solution of tartaric acid ; but in 
solutions of normal tartrates of the alkali metals, it produces 
a trifling precipitate after some time. 

* Potassium or sodium tartrate dissolves calcium tartrate (as well as 
certain other salts insoluble la water, such as calcium phosphate, barium 
sulphate, etc.). Hence the alkali tartrate must be fully decomposed by the 
reagent before the reactions depending upon the separation of calcium tar- 
trate can take place. 



197.] TARTARIC ACID. &)7 

8. If solution of ammonia is poured upon even a very 
minute quantity of calcium tartrate, a small fragment of crys- 
tallized silver nitrate is added, and the mixture is slowly and 
gradually heated, the sides of the test-tube are covered with 
a bright coating of metallic silver. If, instead of a crystal, 
solution of silver nitrate is used, or heat is applied more 
rapidly, the reduced silver will separate in a pulverulent 
form (ARTHUR CASSELMANSJ. 

9. Lead acetate produces white precipitates in solutions 
of tartaric acid and its salts. The washed precipitate, 
PbG 4 H 4 O , dissolves readily in nitric acid, and in ammonia 
free from carbonic acid. 

10. Silver nitrate does not give a precipitate with free tar- 
taric acid ; but in solutions of normal tartrutes, it produces a 
white precipitate of SILVER TARTIIATE, Ag 3 C 4 H 4 O fl , which dis- 
solves readily in nitric acid and in ammonia. Upon boiling, it 
turns black, owing to reduced silver. 

11. If there is added to a solution of free tartaric acid, or 
to that of an alkali-metal tartrate, a small quantity of ferrous 
chloride ox ferrous sulphate, then one or two drops of hydrogen 
peroxide or some small particles of ttotlinm peroxide, and 
finally an excess of sodium or potassium hydroxide solution, 
a beautiful violet coloration appears. The reaction is not 
very delicate, but it permits tartaric acid to be distinguished 
from citric, malic, and succinic acids (FusTON). 

12. If tartaric acid or a tartrate is heated in a test-tube, 
with concentrated sulphuric acid, upon the water-bath, a 
browning of the sulphuric acid occurs almost simultaneously 
with the evolution of gas (difference from citric acid), 

13. If a saturated solution of potassium, dichromate is 
poured over a crystal of tartaric acid at the ordinary tem- 
perature, carbonic acid is given off, and the zone surrounding 
the tartaric acid crystal is colored purplish-violet to black 
(means of detecting tartaric acid in citric acid, for this is col- 
ored coffee-brown, and, in fact, very slowly, CAILLETET). This 
reaction may be carried out with an aqueous solution of tar- 
taric acid. This is mixed with dilute sulphuric acid, one or 
two drops of a solution of potassium chromate are added, 
and it is heated for some time, whereupon the yellow color 
changes to the blue-violet of a chromic salt solution 



DEPORTMENT OF BODIES WITH REAGENTS. [ 198. 

14. If a weakly acid solution of ammonium molyHate is 
mixed with some tartaric acid, one or two drops of hydrogen 
peroxide, or a trace of sodium peroxide (but not more) are 
added, and it is gently warmed (60), tlie original wine-yellow 
color changes through green to blue (CBISMEB). 

15. If there are added to some solid tartaric acid or to a 
tartrate a few drops of a solution of resorcin in concentrated 
sulphuric acid (about 1 : 100), and the mixture is warmed 
until sulphuric acid vapors just begin to escape, the liquid 
assumes a beautiful wine-red color. This reaction permits 
the detection of even the minutest quantities of tartaric acid 
(E. MOHLERJ. 

1C. Concerning the microscopic detection of tartaric acid, 
see HAUSHOFEB, p. 85. 



198. 

c. CITMC ACID, H.C.H.O,. 

1. Crystallized CITRIC ACID, obtained by the cooling of 
its solution, has the formula C 6 H 8 0,.H a O. It forms pel- 
lucid, colorless, and inodorous crystals of an agreeable, 
strongly acid taste, which dissolve readily in water and in 
alcohol, more difficultly in ether (2.26 : 100), and effloresce 
slowly in the air. When pulverized and heated gradually to 55, 
the acid loses its water of crystallization (SALZEB); when subject- 
ed to the action of a stronger heat, it fuses at first, and after- 
wards carbonizes, with evolution of pungent acid fumes, the 
odor of which may be readily distinguished from that emitted 
by tartaric acid upon carbonization. The aqueous solution 
of citric acid is optically inactive. By heating with moder- 
ately dilute nitric acid, in addition to nitro-compounds, oxalic 
and mesaconic acids are formed. 

2. The CITBATES with alkali bases, whether normal or acid, 
are readily soluble in water, and therefore, solution of citric 
acid is not precipitated by potassium acetate. Various citrates 
containing weak bases, such as ferric citrate, are also 
freely soluble in water. Evaporated on the water-bath 



198.] CITRIC ACID. 899 

to a syrupy consistence, the solution of ferric citrate deposits 
no solid salt. Citrates, like tartrates, and for the same reason, 
prevent the precipitation of aluminium and ferric hydroxides, 
etc., by alkalies. 

3. Calcium chloride fails to produce a precipitate in solu- 
tion of free citric acid, even upon boiling ; but a precipitate of 
NORMAL CALCIUM CITEATE, Ca 3 (C e H 6 7 j a .4H a O, form sim mediately 
upon saturating with potassium or sodium hydroxide, the 
somewhat concentrated solution of citric acid mixed with 
calcium chloride in equivalent amount or in slight excess.* 
The precipitate is insoluble in potassium or sodium hydrox- 
ide, readily soluble in alkali citrates, and rather more difficultly 
so in calcium chloride. It also dissolves freely in solution 
of ammonium chloride, and upon boiling this solution, if it is 
not prepared with too much ammonium chloride, normal cal- 
cium citrate separates again in the form of a white, crystalline 
precipitate, which, however, is now no longer soluble in am- 
monium chloride. If a solution of citric acid mixed with 
calcium chloride, as described above, is saturated with 
ammonia, or if ammonium chloride, calcium chloride, and 
ammonia are added to the solution of an alkali citrate, a 
precipitate will form in the cold only after many hours' stand- 
ing or upon the addition of alcohol ; but upon boiling the 
clear fluid, normal calcium citrate of the properties just stated 
will suddenly precipitate. By heating calcium citrate with 
ammonia and silver nitrate, the latter salt is not reduced, or 
only to a trifling extent 

4. Lime-water added in excess* produces no precipitate in 
cold solutions of citric acid or of citrates. But upon boiling 
some time with a tolerable excess of hot-prepared lime-water, 
a white precipitate of CALCIUM CITRATE is formed, the greater 
portion of which redissolves upon cooling. 

5. Barium acetate added in excess to a solution of an alkali 
citrate, whether hot or cold, produces an amorphous precip- 

* Alkali citrates dissolve calcium citrate, and are effective solvents for many 
compounds insoluble in water (barium sulphate, calcium phosphate, calcium 
oxalate, etc.). Hence sufficient calcium chloride or hydroxide must be added, 
so that the alkali citrate is fully decomposed by the reagent, in order that the 
reactions in 3 and 4, depending upon the separation of calcium citrate, may 
succeed. 



400 DEPOBTMENT OP BODIES WITH BEAOENTS. [ 198. 

itate of the formula Ba/O.HAVTE.O. Barium hydroxide 
solution added in excess to citric acid produces the same pre- 
cipitate. This does not make its appearance in dilute solu- 
tions, because it is not insoluble in water, but if such solutions 
are heated, a precipitate separates, which is first amorphous, 
and soon changes to microscopic needles of the formula 
Ba,(C B H.O,) a .5H a O. On heating this or the amorphous salt with 
excess of barium acetate for two hours on the water-bath, an- 
other yery characteristic salt is formed. The latter consists 
of well-formed clinorhombic prisms, and has the formula 
Ba,< C f H s 7 ) fl .3iH a O. If the solution is very dilute, the salt does 
not form till after evaporation. This is an infallible reaction 
Eor citric acid (H. KAMIEBER). 

6. Lead acetate added in excess to a solution of citric acid 
produces a white, amorphous precipitate of LEAD OTTBATE, 
which after washing is readily boluble in ammonia free from 
carbonate. By digestion for several hours with water or 
acetic acid on the water-bath, the precipitate becomes crys- 
talline, and then has the formula Pb s (O a H O T ) 9 .3H 3 O. The 
microscope does not reveal the presence - of well-formed 

crystals. 

7. In solutions of normal citrates of the alkali metals, silver 
nitrate produces a white, flocculent precipitate of SILVER 
CITKATE, Ag 9 C.H t 7 . On boiling a rather large quantity of 
this precipitate with only a little water, a gradual decompo- 
sition sets in, with separation of silver. 

8. Upon heating citric acid or a citrate with concentrated 
sulphuric acid upon the water-bath, carbon monoxide escapes 
at first, then carbonic acid and acetone also, the sulphuric 
acid retaining its natural color. Upon continued boiling, how- 
ever, the solution acquires a dark color, and sulphurous acid 
is evolved. 

9. If citric acid (e.g., .01 g) with excess of ammonia solution 
(3 cc) is introduced into a strong glass tube closed at one end, 
the tube is sealed in such a manner that only a small amount 
of free space is left above the liquid, and heated for six hours 
at 110 or 120, and the liquid is then allowed to stand ex- 
posed to the air in a porcelain dish, an intensely blue or green 
product is obtained (difference from oxalic, tartaric, and malic 
acids, and means of detecting small amounts of citric acid in 



199.] MALIC ACID. 401 

the presence of these acids, SARASDISAEI, SABANIN and 
LASEOWSKY). This coloration characteristic for citric aci<l is 
also obtained when the acid is heated with a little thick 
glycerine (about .7 parts), at as low a temperature as possible, 
until the mass begins to puff up, the residue is dissolved in 
ammonia, the greater part of this is evaporated, and a little 
water and then two drops of red, fuming nitric acid which has 
been diluted with 5 parts of water, are added. Upou heating 
on the water-bath, the color, which is green at first, changes 
to blue (MANN). The reaction also appears when a minute 
amount of hydrogen peroxide is added instead of the nitric 
acid. 

10. In relation to the microscopic detection of citric acid, 
see also HAUSHOFEB, p. 75, 



199. 



d. MALIC ACID, E.C.H.O,, 

1. MALIC ACID crystallizes with difficulty, forming crystal- 
line crusts or tufts of needles, which deliquesce in the air, and 
dissolve readily in water and in alcohol. The dilute aqueous 
solution of ordinary malic acid rotates a ray of polarized 
light towards the left (there is an artificial, inactive acid, and 
also one which is dextro-rotary). Exposed to a temperature 
of 140 or 150, malic acid is slowly converted, with loss of 
water, into fumaric acid, H^HjO,. Wheu heated between 
150 and 200 in a glass tube or a retort, malic acid yields 
fumaric acid, which remains behind, while water and inaleic 
anhydride, G^HjO,, are given off. The latter then partially 
combines with water, forming inaleic acid, H,C\H B O 4 . Upon 
heating above 200, the fumario acid also volatilizes, partly 
undecomposed. The crystalline sublimates produced, which 
are deposited in the glass tube above the heated part or in 
the neck of the retort, are very characteristic for malic acid. 
By heating with nitric acid, malic acid readily yields oxalic 
acid, with evolution of carbon dioxide. 



402 DEPORTMENT OF BODIES TVITH REAGENTS. [ 199. 

2. With most bases, malic acid forms salts soluble in water. 
Hydrogen potassium malate is not difficultly soluble in water ; 
and therefore, potassium acetate fails to precipitate solutions 
of malic acid. This acid, like tartaric acid, prevents the pre- 
cipitation of ferric hydroxide, etc., by alkalies. 

3. If cddum cUoride, ammonium chloride, and ammonia in 
excess are added to a solution of malic acid or an alkali-metal 
malate, the solution remains clear, and no precipitate is 
formed (if the amount of ammonium chloride was not too 
slight) even upon protracted boiling (difference from citric 
acid). If, however, two or three volumes of alcohol are added, 
CALCIUM MALATE, CaC 4 H 4 6 .3H,0, separates in white flocks. 
If the fluid is previously heated nearly to boiling, and hot 
Alcohol is added in no greater quantity than is just necessary 
for the precipitation, the precipitate is deposited in the form 
of soft lumps, which adhere to the sides of the vessel; and on 
cooling, they harden and crumble by pressure to a crystalline 
powder (BABFOED). When heated with ammonia and silver 
nitrate, calcium malate causes no separation of silver, or 
hardly any. Calcium malate dissolves in boiling lime-water 
(difference and means of separation from calcium citrate, 
FLEISCHER). 

4. Liine-water produces no precipitate in solutions of free 
malic acid, nor in solutions of malates. The fluid remains 
perfectly clear even upon boiling, provided the lime-water was 
prepared with boiling water. 

5. Lead acetate throws down from solutions of malic acid 
and of malates, a white precipitate of LEAD MALATE, Pb0 4 H 4 O . 
3H,0. The precipitation is most complete if the fluid is 
neutralized by ammonia, as the precipitate is slightly soluble 
in free malic acid and acetic acid, and also in ammonia. If 
the liquid in which the precipitate is suspended is heated to 
boiling, a portion of the precipitate dissolves, and the 
remainder fuses to a mass resembling resin melted under 
water. Upon cooling the hot solution, the salt separates in 
needles or plates. To obtain this fusion of lead malate 
with small quantities, warm at first gently till the precipitate 
has shrunk together, then pour off the principal part 1 of 
the fluid, and heat the rest with the precipitate to boiling. 
This reaction is distinctly marked only if the lead malate is 



200.] BBOAPITUIATION AND BEMAKKS. 403 

tolerably pure; for if mixed with other lead salts or 
if, for instance, ammonia is added to alkaline reaction 
it is only imperfect or fails altogether to make its appear- 
ance. 

6. From solutions of normal malates of the alkali metals, 
stiver nitrate throws down a white precipitate of SILVER 
BIALATE, Ag,C 4 H 4 , which upon long standing or boiling turns 
a little gray. 

7. On mixing the warm solution of free malic acid with 
magnesia or magnesium carbonate, till the acid reaction is 
destroyed, filtering, evaporating, and mixing the hot solution 
with hot alcohol, magnesium malate, 3tgC 4 H 4 B , separates 
as a glutinous mass on the sides of the vessel. It becomes 
hard upon cooling. Malic acid cannot be distinguished from 
citric acid by this reaction (BARFOED). 

8. Upon heating malic acid with concentrated sulphuric 
acid on the water-bath, carbon dioxide and carbon monoxide 
are evolved at first ; then the fluid turns brown and ultimately 
black, with evolution of sulphur dioxide. 

9* In regard to the microscopic detection of malic acid, see 
HAUSHOFEB, p. 67. 



200. 

Recapitulation and Semarfa. Of the organic acids of this 
group, OXAUO ACID is characterized by the fact that gypsum 
solution causes a precipitation in solutions of the free acid, or 
of its alkali-metal salts acidified with acetic acid. TARTAJMO 
ACID is characterized by the sparing solubility of the hydrogen 
potassium salt, the solubility of the calcium salt in cold solu- 
tions of sodium and potassium hydroxides, the reaction of the 
calcium salt with ammonia and silver nitrate, and the peculiar 
odor which the acid and its salts emit upon heating. It is 
most safely detected in presence of the other acids by means 
of potassium acetate or potassium fluoride ( 197, 4). Without 
considering the reactions which are based upon the observation 
of characteristic tartaric acid salts, the reactions given in 197, 



404 DEPORTMENT OF BODIES WITH REAGENTS. [ 200. 

11, 13, 14, and 15, allow tartaric acid to be distinguished from 
citric, malic, and also suecinic acids, and permit its detection 
in their presence. Reaction 12 is also well adapted for the 
detection of tartaric acid iu the presence of citric acid, for the 
latter gives ouly a lemon-yellow and no brownish to reddish 
liquid when heated in a test-tube upon the water-bath with 
concentrated sulphuric acid (1 g with 10 cc). (E. SCHMIDT, 
PUSCH).* CITRIC ACID is usually recognized by its reaction 
with lime-water, or with calcium chloride and ammonia in 
presence of ammonium chloride ; but in this, the absence or 
the removal of oxalic and tartaric acids is always presup- 
posed, and also the employment of a sufficient quantity of lime- 
water or a properly regulated amount of calcium chloride. 
A very safe characteristic of citric acid consists in the 
microscopic appearance of its barium salt ( 198, 5), and also 
the production of the blue or green decomposition product 
mentioned in 198, 9. MALIC ACID would be sufficiently 
characterized by the deportment of lead malate when heated 
under water, were this reaction more sensitive, and not so 
easily prevented by the presence of other acids. The safest 
means of identifying malic acid is to convert it into maleic 
acid and f umaric acid by heating in a glass tube ; but this 
conversion can be effected successfully only with pure malic 
acid. Lead malate is sparingly soluble in ammonia, while the 
citrate and tartrate of lead dissolve freely in ammonia which 
is free from carbonic acid. This different deportment of the 
lead salts of the acids affords a means of distinguishing 
them. Calcium citrate and malate may be separated by 
means of boiling lime-water, which dissolves the latter and 
leaves the former behind* Malic acid may be detected also 
in the presence of citric (and succinic) acid by mixing the solu- 
tion, after acidifying it with a few drops of sulphuric acid, 
with a little potassium dichromate, and heating to boiling, 
whereupon, in the presence of malic acid, an odor of fresh 
apples is given off (PAPASOGLI and POLI). If only one of 
the four acids is present in a solution, lime-water will suf- 



* Concerning the distinction of tartaric acid from the other organic adds 
by means of liexamine cobaltic chloride, compare C. D. BRATTN, Zeitschr. 1 
analyt, Ohern., 7, 849. 



200.] KECAPITCLATTQN AND REMARKS. 405 

fice to indicate which one it is ; since malic acid is not pre- 
cipitated by this reagent, citric acid is precipitated only upon 
boiling, while tartaric acid and oxalic acid are thrown down 
in the cold, and the calcium tartrate redissolves upon addi- 
tion of ammonium chloride, while the oxalate does not. If 
the four acids together are present in a solution, the oxalic 
and tartaric acids are usually precipitated first by calcium 
chloride and ammonia, in presence of ammonium chloride. 
But it must be noted here that the calcium tartrate requires 
some time (about two hours) for a precipitation that is toleral >ly 
complete (it is separated from the oxalate by sodium hydroxide 
solution), and also that an alkali citrate when present iu any 
quantity prevents the thorough separation of oxalic acid and 
still more of tartaric acid. On cautiously adding alcohol iti 
moderate quantity to the filtrate, the calcium citrate sepa- 
rates (and with it the rest of the calcium oxalate and tartrate). 
On filtering, and mixing the filtrate with more alcohol, calcium 
malate is thrown down. From the latter, the acid is prepared by 
dissolving it in acetic acid, adding alcohol, filtering if neces- 
sary, mixing the filtrate with lead acetate, neutralizing with 
ammonia, washing the precipitate, suspending it in water, 
treating with hydrogen sulphide, filtering, and evaporating the 
filtrate to dryness* 

A better method for the detection of malic acid iu the 
presence of the three other acids consists in combining 
the acids with ammonia, concentrating strongly, neutral* 
izing the still warm fluid with ammonia (to dissolve the 
acid salts produced during the evaporation), and adding 
8 volumes of alcohol of 98 per cent. After 12 or 24 hours, the 
solution of ammonium malate is filtered from the undissolved 
oxalate, tartrate, and citrate of ammonium, the malic acid is 
precipitated with lead acetate, and the acid prepared from the 
precipitate is tested further (BARFOED). Where a small quan- 
tity of citric or malic acid is to be detected in presence of a 
large proportion of tartaric acid, the best way ia to first re. 
move the latter by potassium acetate, with addition of an 
equal volume of strong alcohol. The other acids may then 
be completely precipitated in the filtrate by excess of cal- 
cium chloride and ammonia, if the quantity of the alcohol 
is a little increased. The calcium malate may be finally 



406 DEPORTMENT OF BODIES WITH BEAGENTS. [ 201. 

separated from calcium citrate by treatment with boiling 
hot liine-water.* 



20L 

AGED, H 9 4 H 4 O . 

The formula of crystallized BACTMIO ACID is C4HO..H a O. The water 
of crystallization escapes slowly in the air, but rapidly at 100 (differ- 
ence between racemic aoid and tartaric acid). To solvents, racemic 
acid comports itself like tartaric acid. The RACEMATES also show very 
similar deportment to that of the tartrates. However, many of them 
differ from the corresponding tartrates in the amonnt of water they con- 
tain, and in form and solubility. The aqueous solution of racemic acid 
and' the racemates exercises no diverting action upon polarized light 
(difference from dextro- and lavo-tartaric acids). From the solutions of 
free racemic acid and of racemates, calcium chloride precipitates CALCIUM 
BACKDATE, CaC 4 H4O..4H a O, as a white, crystalline powder. Ammonia 
throws down the precipitate from its solution m hydrochloric acid, either 
immediately or at least very speedily (difference from tartaric acid). It 
dissolves in solution of sodium or potassium hydroxide, but is reprecipi- 
tated from this solution by boiling (difference from oxalic acid). Lime- 
water added in excess immediately produces a white precipitate insoluble 
m ammonium chloride and also in acetic acid (difference from tartario 
acid). Solution of calcium sulphate does not immediately produce a 
precipitate in a solution of racemic acid (difference from oxalic acid) ; 
but after ten or fifteen minutes, calcium racemate separates (difference 
from tartaric acid), and in solutions of normal racemates, the precipitate 
forms immediately. Vith potassium salts, racemic acid comports itself 
like tartaric acid. By letting sodium potassium racemate or sodium 
ammonium racemate crystallize, two kinds of crystals are obtained, which 
resemble each other as the image reflected by a mirror resembles the 
object reflected. One kind of crystals contains common or dextro-tartaric 
acid (which turns the plane of polarized light towards the right) ; the 
other kind contains Isevo-tartaric acid, t'<?., an acid which is the same 
in every respect as tartaric acid, with this exception only, that it turns the 
polarized light towards the left. If the two kinds of crystals are redissolved 
together, the solution shows again the reactions of the racemic acid. In 
regard to the microscopic detection of this acid, see EADSHOFEB, p. 83. 

* Concerning the separation of malic add from citric, as well as succinic 
add, see also MICKO, Zeitschr. t analyt. Ohem. 31, 465 ; and concerning the 
reparation of malic, citric, and succinic acids, see also W. KEIM, ibtiL, 30, 405. 



202.] sucoraro ACID. 407 



Second Group of Organic Acids. 

The acids of the second group sublime without alteration, 
or are decomposed only to the anhydride and water. By 
heating with nitric acid, they are either left unchanged (sue- 
cinic acid), or merely converted into nitro-acids (benzoic acid, 
salicylic acid). The calcium salts are readily soluble in 
water (benzoic acid, salicylic acid), or are difficultly soluble 
(succinic acid). The solutions of the normal alkali-metal salts 
are precipitated (succinic and benzoic acids) or very intensely 
colored (salicylic acid) by ferric chloride : SUCCDHC ACID, 

BENZOIC ACID, SALICYLIC ACID. 



202. 
a. SUCCINIC ACID, H,C 4 E 4 4 . 

1. SUCCINIC ACID forms colorless and inodorous prisms or 
tables. It is readily soluble in hot water and hot alcohol, 
more difficultly soluble in the cold liquids, and slightly solu- 
ble in ether (1.265 : 100). When heated for a considerable 
time to 140, the acid sublimes, partly undecomposed, and 
partly yielding water and the sublimed anhydride. When 
rapidly heated, the acid fuses at 180 and boils at 235, where 
upon it is mostly decomposed into water and the anhydride* 
The sublimed anhydride forms needles with a silky luster. 
When heated in the air, succinic acid burns with a blue flame 
free from soot. When pure, the acid is odorless and has a 
slight, acid taste. The officinal acid, which has an empyreu- 
matic odor, leaves a moderate carbonaceous residue upon 
volatilization. Succinic acid is not destroyed by heating 
with nitric acid, and may therefore be easily obtained in the 
pure state by boiling with that acid for half an hour, by which 
means any oil of amber present is destroyed. 

2. The SUCCINATES are decomposed at a red heat; and 
those which contain alkali or alkali-earth metals are con- 
verted into carbonates, with separation of charcoal. Many 



408 DEPORTMENT OF BODIES WITH REAGENTS. [ 202. 

of the succinates are soluble in water. Sodium succinate is 
scarcely soluble in strong alcohol, and crystallizes well both 
as normal and acid salt ; hence it may be readily obtained in 
a pure state from very impure fluids. This property may be 
utilized for the detection and separation of the acid.* On 
heating the succinates with potassium disulphate in a tube, 
the acid sublimes. It may be also obtained from the salts 
by decomposing them with sulphuric acid, and extracting 
with warm absolute alcohol, and also by repeatedly shak- 
ing the solution, strougly acidified with sulphuric acid, with 
ether, when almost all the succinic acid is obtained in the 
ethereal solution. 

3. If calcium cJJoride, ammonium chloride, and ammonia 
>n excess are added to a solution of succinic acid or of an 
alkali-metal succiuate, the liquid remains clear in the cold, 
and also upon boiling if the amount of ammonium chloride 
was not too small. But if two or three volumes of alcohol 
are added, CALCIUM SUCCINATE, CaC 4 HA .3H a O, separates 
(often only after some time) in a crystalline condition. 

4. Barium chloride produces in solutions of alkali succi- 
nates, but not in solutions of free succinic acid, usually only 
after some time, a white, crystalline precipitate of BARIUM 
SUCCINATE, Ba0 4 H 4 O 4 . Warming facilitates the separation, 
and upon the addition of alcohol, it separates quickly, even 
from dilute solutions. 

5. In a solution of a normal alkali succinate, ferric ctto- 
ride, carefully treated with very dilute ammonia until the 
solution has a dark, brownish-red color, but is still clear, 
prodnces a pale brownish-red, voluminous precipitate of 
msic FERMC SUCCINATE, 2Fe a (C 4 H 4 4 ) 1 .Pe a O,. The precipitate 
dissolves readily in mineral acids, but difficultly in cold acetic 
acid. It is decomposed by ammonia, which causes the separa- 
tion of a highly basic ferric succinate of a less bulky nature, 
while the greater part of the succinic acid goes into solution 
as ammonium succinate. Alkali tartrates prevent or interfere 
with the precipitation of the basic ferric succinate. 

6. Lead acetate, when added drop by drop to a solution of 
free succinic acid, or of an alkali succinate, produces a white 



* Compare MEIBSNER and JOLLY, Zeltschr. t. analyt. Chem., 4, 602. 



203.] BENZOIO ACID. 409 

amorphous precipitate, -which is immediately redissolyecl in 
excess of succinic acid, iii alkali succinate, and in lead acetate, 
but in a short time separates from such solutions in the crystal- 
line form. The latter precipitate consists of normal T.T;AT> sue- 
CINATE, PbC 4 H 4 O 4 , which IK barely soluble in water, even when 
boiling, as well as in succiiiic acid and lead acetate, readily 
soluble in nitric acid, and dissolves somewhat more difficultly 
in acetic acid. By ammonia it is converted into a basic salt. 

7. In regard to the microscopic detection of succinic acid, 
see HAUSHOFEB, p. 73. 



203, 
b. BENZOIC ACID, HC.H.O,. 

1. BENZOIC ACID forms white scales or needles, or simply a 
crystalline powder. It is odorless in the pure state, but 
usually has a faint aromatic odor. It fuses at 121.4 r , and boils 
at 250, volatilizing completely. TVhen heated in an open 
dish, it evaporates in considerable quantity even at 100. The 
fumes cause a peculiar, irritating sensation in the throat, and 
provoke coughing ; when cautiously cooled, they condense to 
brilliant needles; and when kindled, they burn with a luminous, 
sooty flame. The common officinal benzoic acid has the odor 
of benzoin, and leaves a small, carbonaceous residue upon 
volatilization. Benzoic acid dissolves at in 588, at 20 C in 
345, and at 100 in 17 parts of water (BoUBGOix). It u taken 
up readily by alcohol as well as by ether. Addition of water 
imparts, therefore, a milky turbidity to a saturated solution 
of the acid in alcohol. The solutions of beuzoic acid have an 
acid reaction. The acid dissolves in concentrated sulphuric 
acid to a colorless liquid, from which it is separated by 
water unchanged. 

2. Most of the BENZOATES are soluble in water, only those 
with weak bases (e.g. t ferric benzoate) being insoluble. The 
soluble benzoates have a peculiar, pungent taste. The addition 
of a strong acid to COXCESTBATED aqueous solutions of benzo- 
ates displaces the benzoic acid, which separates in the form 
of a dazzling white, sparingly soluble, crystalline powder. 



410 DEPORTMENT OF BODIES WITH REAGENTS. [ 204. 

In the same way, benzoic acid is separated from the insoluble 
benzoates by such strong acids as form soluble salts with the 
bases with which the benzoic acid is combined. 

3. Ferric cUoride, carefully mixed with very dilute am- 
monia until the solution has a dark brownish-red color, but is 
still clear, precipitates all the benzoic acid in combination 
with ferric oxide, from solutions of normal alkali benzoates. 
The voluminous, flesh-colored precipitate, BASIC FEEBIO BENZO- 
ATE, Fe s (C,H 6 O fl ) 6 .re 3 3 .15H 3 0, is decomposed (similarly to 
basic ferric succiuate) by treatment with ammonia, but it is dis- 
tinguished from the succinate by the fact that it dissolves in a 
little hydrochloric acid, with the separation of the greater 
part of the beuzoic acid. Alkali tartrates prevent or inter- 
fere with the precipitation of basic ferric benzoate. 

4. Lrml ucrfate fails to precipitate free benzoic acid, but it 
produces flocculeut precipitates in solutions of alkali benzo- 
ates. The precipitate, Pb(0 7 H s O s ),.H a O, is insoluble in 
sodium benzoate, but dissolves in an excess of the lead 
acetate, and also in acetic acid. Upon heating to boiling the 
solution in which the precipitation has taken place, the pre- 
cipitate does not dissolve, nor does it dissolve in ammonia. 

5. A mixture of alcohol, ammonia, and barium or calcium 
chloride, produces no precipitate in solutions of benzoic acid or 
of the alkali benzoates (difference from succinic acid). 

6. In relation to the microscopic detection of benzoic acid, 
see HAUSHOFEE, p. 71* 



204. 
c. SALECIUO ACID, HC,H 6 O t . 

1. SAWOYUC ACID crystallizes in colorless, odorless prisms* 
It dissolves only slightly in cold water, but more readily in hot 
water ; 1 part requires for solution 666 parts of water at 0, 
370 parts at 20, and 12.6 parts at 100 (BOUBGOIN). It dis- 
solves very abundantly in alcohol and in ether, and also in 
amyl alcohol and chloroform. It fuses at 155, and with care* 
ful heating sublimes unchanged in needles. When heated 
quickly and strongly, it is partly decomposed into carbonic 



204.] SALICYLIC ACID. 411 

acid and phenol. When an aqueous solution of salicylic acid 
is boiled, the acid volatilizes in considerable quantity. The 
aqueous solution gives a distinctly acid reaction. By the 
action of strong nitric acid upon salicylic acid, with the aid 
of heat, nitro-salicylic acids are produced. 

2. Salicylic acid forms TWO REIUES OF SALTS with bases, 
which are usually designated as SGIIMVL and BASIC SALTS. The 
solutions of the alkali salts, especially when containing ba&ic 
salts, become colored brownish by heating in the air. 3Iosi 
of the normal salicylates are easily soluble in water, but many 
of the basic salts are insoluble or slightly soluble in that liquid. 
Most of the salicylates give off phenol upon being heated. 
From sufficiently concentrated solutions, mineral acids precipi- 
tate salicylic acid as a white, crystalline precipitate. Acetic 
acid produces no precipitation. 

3. If a small amount of a very dilute ferric cJJoriflc solu- 
tion is added to an aqueous solution of salicylic acid or one 
of its salts, the liquid becomes colored intensely violet. Free 
acetic acid, lactic acid, and butyric acid interfere with the 
delicacy of this very characteristic reaction. Hydrochloric 
acid as well as ammonia destroy it. 

4. In solutions of normal alkali salicylates, lead acetate pro- 
duces a white precipitate of lead salicylate, Pb^HjOjj-HjO, 
which is soluble in an excess of lead acetate and also in acetic 
acid, but not in ammonia. When the precipitate is heated 
with the liquid from which it was formed, it dissolves, and 
separates in crystals upon cooling. 

5. Neither cddum cJdoride nor barium chloride precipitates 
solutions of alkali salicylates, not even upon the addition of 
ammonia and alcohol, 

6. If a solution of salicylic acid in methyl alcohol is mixed 
with half its volume of concentrated sulphuric acid, and 
heated, METHYL SALICTIAXE is formed, a compound with an 
aromatic odor, which is the chief constituent of oil of winter- 
green. This may be collected by distillation. "With a solu- 
tion of salicylic acid in ordinary alcohol, the analogous ethyl 
compound with a similar odor is obtained. 



A12 DEPORTMENT OF BODIES WITH BEAGENTS. [ 205. 



205. 

Jlecapitulafion and Remarks. Benzole and salicylic acids 
are especially distinguished from succinic acid, by the fact 
that the latter is far more soluble in water than the others, 
from which it follows that benzoic and salicylic acids are 
precipitated from the concentrated solutions of their salts by 
mineral acids. 

Succinic and beuzoic acids are distinguished from salicylic 
acid by the fact that they are precipitated by ferric chloride, 
while the latter is not precipitated, but causes an intense 
violet coloration of the liquid. If the basic ferric salts which 
separate are decomposed by digestion with ammonia, the 
liquid is filtered, and the filtrate is concentrated, the benzoic 
acid may be separated by the addition of acid, and the succinic 
acid may be detected as barium or calcium succinate. Suc- 
cinic acid may be also separated from salicylic acid by pre* 
cipitatioii as the calcium or barium salt. 

If it is desired to separate the three acids or one of them 
from a liquid containing other organic substances, this may 
be accomplished by repeatedly extracting the liquid with 
ether after acidifying it strongly with sulphuric acid. If the 
ether is distilled off, the acids remain behind. In con- 
nection with the detection of salicylic acid in wine, in order 
to prevent tannic acid from also going into the solution, it is 
better to shake the acidified wine (about 50 cc) with a mixture 
of equal parts of ether and petroleum-ether, to evaporate the 
separated layer of the solvent, after the addition of a little 
water, upon the water-bath, and to test the residue with ferrio 
chloride { 204 3). Instead of the mixture of ether and petro- 
leum-ether, carbon disulphide or arnyl alcohol may be used. 

Succiuic, benzoic, and salicylic acids do not prevent the 
precipitation of ferric oxide, alumina, etc., by the alkalies.* 

* In relation to a method for the separation of salicylic acid from benzoia 
acid, see also, J. SCHAAP, Zeitachr. f. analyt Chem., 32, 107. 



206.] ACETIC ACID. 413 



Third Group of Organic Acids. 

The acids of the third group may be distilled with water 
(lactic acid with difficulty). The calcium salts are readily 
soluble in water. The solutions of the normal alkali-metal 
salts are not precipitated in the cold by ferric chloride : 
ACETIC ACID, FOBMIC ACID (lactic acid, propionic acid, butyric 
add). 

206. 

a. ACETIC ACID, H0 1 H 1 S , 

1. ACETIC ACID forms transparent, crystalline scales, which 
fuse at 17 to a colorless fluid of a peculiar, pungent, and pene. 
trating odor and exceedingly acid taste. It boils at 119, and 
volatilizes completely, forming pungent vapors, which burn 
with a blue flame. It is miscible with water in all proportions. 
It is to such mixtures of the acid with water that the name of 
acetic acid is commonly applied. Acetic acid is also soluble 
in alcohol. 

2. The ACETATES undergo decomposition at a red heat. 
When thus ignited, the alkali salts and other salts with strong 
bases yield chiefly acetone, C.H.O, and carbon dioxide, the 
latter, according to the nature of the base, either remaining 
combined with the base or escaping. The acetates with weak 
bases allow a large part of the acetic acid to escape unchanged. 
The residues left upon igniting acetates are usually carbona- 
ceous. Nearly all acetates dissolve in water and in alcohol ; 
most of them are readily soluble in water, while a few only are 
difficult of solution in that liquid. If acetates are distilled 
with dilute sulphuric acid, free acetic acid is obtained in the 
distillate. 

3. If ferric chloride is added to acetic acid, and the acid is 
then nearly saturated with ammonia, or if a neutral acetate is 
mixed with ferric chloride, the fluid acquires a deep red color, 
owing to the formation of EEBBIO ACETATE. By boiling, the 
fluid becomes colorless if it contains an excess of acetate, the 



414 DEPORTMENT OF BODIES WITH REAGENTS. [ 206. 

whole of the iron precipitating as a basic acetate, in the form 
of brownish-yellow flocks. Ammonia precipitates from the 
solution of ferric acetate the whole of the iron as hydroxide. 
By addition of hydrochloric acid, a fluid which appears red 
from the presence of ferric acetate turns yellow (difference 
from ferric sulphocyanide). 

4. Neutral acetates (but not free acetic acid, if somewhat 
diluted) give with silver nitrate white, crystalline precipitates 
of SILVER ACETATE, AgC,!!^ , which are very sparingly soluble 
in cold water. They dissolve more easily in hot water, but 
upon cooling, separate again in the form of very small crystals. 
Ammonia dissolves them readily, but free acetic acid does 
not increase their solubility in water. 

o* Mercurous nitrate produces with acetic acid, and more 
readily still with acetates, white, scaly, crystalline precipitates 
of MERCUROUS ACETATE, Hg 9 (C a H s O 2 ) a , which are sparingly solu- 
ble in water and acetic acid in the cold, but dissolve without 
difficulty in an excess of the precipitant. The precipitates 
dissolve in water upon heating, but separate again in the form 
of small crystals upon cooling. In this process, the salt 
undergoes partial decomposition, and a portion of the mer- 
cury separates in the metallic state, imparting a gray color 
to the precipitate. If the mercurous acetate is boiled with 
dilute acetic acid instead of water, the quantity of the metallic 
mercury which separates is exceedingly minute. 

6. Mercuric chloride produces no precipitate of mercurous 
chloride with acetic acid or acetates upon heating. 

7. By heating acetates with concentrated sulphuric acid, 
ACETIC ACID is evolved, which may be known by its pungent 
odor. But if the acetates are heated with a mixture of about 
equal volumes of concentrated sulphuric add and alcohol, ETHYL 
ACETATE, (C.HJC.HjO,, is formed. The odor of this ether is 
highly characteristic and agreeable. It is most distinct upon 
shaking the mixture when somewhat cooled, and is much less 
liable to lead to mistakes than the pungent odor of the acid. 

8. If dilute acetic acid is heated with an excess of lead 
oxide, part of the latter dissolves as basic lead acetate* The 
fluid has an alkaline reaction, and gives no crystals on cooling. 

9. In regard to the microscopic detection of acetic acid, 
see HAUSHOFEB, p. 76* 



207.] FORMIC ACID. 415 

207. 

6. FORMO AOID, HCEO,. 

1. FORMIO AOID is a transparent and colorless, corrosive, 
slightly fuming liquid, with a characteristic and exceedingly 
penetrating odor. It crystallizes at 1 in colorless plates. 
It is miscible in all proportions with water and alcohol. It 
boils at 98.5, and distils without decomposition. The vapors 
burn with a blue flame. 

2. Upon ignition, the FORMATES, like the corresponding 
acetates, leave behind either carbonates, oxides, or metals, the 
process being attended with the separation of charcoal, and 
the escape of combustible gases, carbon dioxide, and water. 
All the compounds of formic acid with bases are soluble in 
water, and alcohol also dissolves many of them, but not all. 

3. Formic acid shows the same reaction as acetic acid with 
ferric chloride. 

4. Silver nitrate fails to precipitate free formic acid, and 
gives a precipitate with the alkali formates in concentrated 
solutions only. The white, sparingly soluble, crystalline 
precipitate of SILVER FORMATE, AgCHO,, acquires a darker tint 
very rapidly, owing to the separation of metallic silver. 
Complete reduction of the silver to the metallic state takes 
place after the lapse of some time, even in the cold ; but im- 
mediately upon applying heat to the fluid containing the pre- 
cipitate. The same separation of metallic silver occurs in 
a solution of free formic acid, and also in solutions of for- 
mates so dilute that the addition of the silver nitrate fails to 
produce a precipitate, but it does not take place in presence 
of an excess of ammonia. In this reaction, formic acid re- 
moves oxygen from the silver oxide ; carbonic acid, which es- 
capes, and water are formed, and the metal separates. 

5. Mercurous nitrate gives no precipitate with free formic 
acid ; but in solutions of alkali formates, this reagent pro- 
duces a glistening white, sparingly soluble precipitate of HER- 
O0ROUS FORMATE, Hg a (OHO a ) s , which rapidly becomes gray, 
owing to the separation of metallic mercury. Complete re- 
duction ensues, even in the cold, after the lapse of some time, 
but is immediate upon application of heat. This reduction 



416 DEPORTMENT OF BODIES WITH REAGENTS. [ 208. 

is also attended with the formation of carbon dioxide and 
water, and takes place both in fluids so highly dilute that the 
mercurous formate is retained in solution and in solutions of 
free formic acid. 

6. If formic acid or an alkali formate is heated with 
mercuric chloride, MERCUBOUS CHLORIDE precipitates before the 
liquid has reached the boiling-point. Presence of free hydro- 
chloric acid or of rather large quantities of alkali-metal chlor- 
ides prevent the reaction. 

7. If formic acid or a formate is heated with concentrated 
sulphuric acid, the formic acid is resolved, without blacken- 
ing, into water and CARBON MONOXIDE gas. The latter escapes 
with effervescence, and, if kindled, burns with a blue flame. 
The sulphuric acid removes from the formic acid the water 
necessary for its existence, and thus causes a transposition of 
its elements : OH 9 O, = H,O + 00. Upon heating formates 
with dilute sulphuric acid in a distilling apparatus, free 
formic acid is obtained in the distillate, and may usually be 
readily detected by its odor. Upon heating a formate with a 
mixture of strong sulphuric acid and alcohol, ETHYL FORMATE 
is evolved, which is characterized by its peculiar rum-like 
smell. 

8. If dilute formic acid is heated with excess of lead oxide, 
the latter partially dissolves. The fluid has an alkaline reac- 
tion, and on cooling the solution, which is concentrated by 
evaporation if necessary, T.F.AD FORMATE, Pb(CH0 9 ) a , separ- 
ates in brilliant prisms or needles. 

9. Concerning the microscopic detection of formic acid, 
see HAUSHOFER, p. 68. 

208. 

Secajpitidation and Hemarks. Acetic and formic acids are 
readily distinguished from the other organic acids by the 
fact that they can be distilled with water, and form with ferric 
oxide, soluble normal salts which dissolve in water with a 
blood-red color, and are decomposed by boiling. The two 
acids are distinguished from each other by their odor and 
that of their ethyl compounds, and by their different re- 
actions with silver salts and salts of mercury, with lead 



209.] LACTIC ACID. 417 

oxide, and with concentrated sulphuric acid. The separation 
of acetic from formic acid is effected by heating the mixture 
of the two acids with an excess of mercuric or silver oxide. 
Formic acid reduces the oxide and suffers decomposition, 
while the acetic acid dissolves the oxide and remains in solu- 
tion as an acetate. The separation may be also effected by 
boiling the free acids for ten minutes with an equal volume of 
a solution of potassium dichromate and sulphuric acid* in 
connection with an inverted condenser, by which means the 
formic acid is oxidized to water and carbonic acid, while the 
acetic acid remains unchanged, and may be obtained from the 
residue by distillation (MAONAIE). 

209. 
Barer Organic Adds of the Third Grovp. 

1. LAOTIO Aom, HC.H.O,. 

LAOTIO Aoro occurs in animal fluids, vegetable matters that have 
turned sour, etc. When as pure as possible, it is a colorless, syrupy 
liquid, which is odorless and has a pure, sharp, acid taste. When it is 
slowly heated in a retort to 130, water containing a little lactic acid dis- 
tils over, leaving a residue of lactic anhydride, which between 250 and 
300 is decomposed into carbon monoxide, carbon dioxide, lactide, and 
other products. Lactic 1 acid dissolves freely in water, alcohol, and ether. 
Upon boiling the aqueous solution, a little lactic acid volatilizes with the 
aqueous vapor. If a little lactic acid is added to a solution of phenol 
made blue with feme chloride, the blue color changes to yellow. The 
reaction is delicate (UFFELMANN), but it should be noticed that butyrio 
acid behaves in a similar manner. All the lactates are soluble in water, 
the greater part of them, however, only sparingly. They behave simi- 
larly with alcohol. Lead acetate with the addition of alcoholic am- 
monia produces a granular-sandy precipitate, which is insoluble in alcohol 
(PAiiM). The lactates are insoluble in ether. The production of some 
of the salts and the examination of their form under the microscope 
supply the means for the detection of lactic acid ; and calcium and zinc 
lactates axe the best suited for this purpose. Calcium lactate may be con- 
veniently prepared from animal or vegetable juices by the following method 
devised by SOHBEBE : Dilute the liquid, if necessary, with water, mix with 
baryta-water, and filter. Distil the filtrate with some sulphuric acid (to 
remove volatile acids), digest the residue several days with strong alcohol, 

* 12 g potassium dichromate, 100 cc water, and 30 cc concentrated sul- 
phuric add. 



418 DBPOKTMENT OP BODIES WITH REAGENTS- [ 210. 

distil the acid solution with a little milk of lime, filter, while warm, from 
the excess of lime and calcium sulphate, conduct carbon dioxide into the 
filtrate, heat once more to boiling, filter from the precipitated calcium car- 
bonate, evaporate the filtrate, warm the residue with strong alcohol, filter, 
and let the neutral filtrate stand several days to give the calcium lactate 
time to crystallize. Should the quantity of lactic acid present be insuffi- 
cient to allow the formation of crystals, evaporate the fluid to syrupy con- 
sistence, mix with strong alcohol, let the mixture stand some time, decant 
or filter the alcoholic solution into a vessel that can be closed, and add 
gradually small quantities of ether. This process will cause even traces of 
calcium lactate to separate from the fluid. For the preparation from 
urine of a lactic acid which is adapted for obtaining the characteristic salts, 
SCHULTZEN and BIESS recommend the following method : Concentrate the 
urine very much, precipitate warm with 95 per cent alcohol, and pour off 
the alcoholic solution after twenty-four hours, evaporate it to a syrup, 
acidify with dilute sulphuric acid, and extract by shaking with ether. 
Distil the ethereal solution, dissolve the residue in water, precipitate with 
basic lead acetate, filter, treat the filtrate with hydrogen sulphide, filter 
again, and drive off the acetic acid by repeated evaporation upon the water- 
bath. Under the microscope, calcium lactate appears in the form of tufts 
of needles. Two of the tufts are always joined together by their short 
stems, so that they are like two united brushes. Zinc lactate, after rapid 
separation, appears under the microscope in the form of spherical groups 
of n