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- 4 UNIVERSmfgrCALIFORNIA
1 COLLEGE of MINING
DEPARTMENTAL
LIBRARY
BEQUEST OF
SAMUELBENEDlCrCHRISTY
PROFESSOR OF
MINING AND METALLURGY
1885-1914
A
SYSTEM OF IlSrSTEUCTIOX
IN
QUALITATIVE CHEMICAL ANALYSIS.
In tJie Press,
BY THE SAME AUTHOR.
QUANTITATIVE CHEMICAL ANALYSIS.
Third Edition. Svo. cloth.
SYSTEM OF INSTRUCTION
QUALITATIVE CHEMICAL
. ANALYSIS.
BY
DR C. KEMIGIUS FRESENIUS,
PRtVY ATTLIC COUNSELLOR OF THE DUKE OF NASSAU;
DIRECTOR OF THK CHEMICAL LABORATORY AT "WIESBADEN ;
PROFESSOR OF CHEMISTRY, NATURAL PHILOSOPHY, AND TECHNOLOGY AT Till
WIESBADEN AGRICULTURAL INSTITUTE.
Jtftfj CEfoition.
EDITED BY
J. LLOYD BULLOCK, F.C.S.
LONDON:
JOHN CHURCHILL, NEW BUKLINGTON STREET.
MDCCCLIX.
f 8
EDITOR'S PREFACE
TO THE
FIFTH EDITION.
THIS Edition of Dr. Fresenius's Qualitative Chemical Analysis, though
simply professing to be a translation from the NIKTH GERMAN Edition,
is really very much in advance of that work ; it contains a large amount
of important original matter communicated by the Author during the
time it was passing through the press. Some of the sections have also
been remodelled, to adapt them to the more advanced state of scientific
instruction.
It is very gratifying to the Editor to find that, notwithstanding the
numerous and important English works on chemical analysis published
within the last few years, the valuable system of Dr. tYesenius still
enjoys the undirninished confidence of British chemists.
In conclusion, the Editor expresses a hope that the present edition
will receive the same amount of favor as the former works of the dis-
tinguished Author.
J. LLOYD BULLOCK.
3, HANOVER STREET, W.
October, 1859.
EDITOK'S PREFACE.
THIS work of Dr. Fresenius has already gone through two editions in
Germany. The abundant opportunities enjoyed by its Author of dis-
covering the wants felfc by students in entering upon the practice of che-
mical analysis, and his position in the School of Giessen, have enabled
him to devise a method of study of the highest value. That it has re-
ceived the approbation of the illustrious HEAD of that school, and the
benefit of three years' practical experience under his immediate observa-
tion, must powerfully recommend it to the English student of chemistry.
Whoever is desirous of obtaining the knowledge necessary to become a
practical chemist, will be in no small degree indebted to Dr. Fresenius
for the facilities thus afforded him. Every one who knows anything of
Giessen, will bear testimony to the rigid economy of time, and the reso-
lute adoption of every improvement in method which characterize that
school, and serve to accomplish the many chemists annually flocking
there for the completion of their studies. The Author, in his Preface to
the First Edition, tells us that he was led to compose this volume upon
perceiving that the larger works on chemical analysis, such as H. Rose's,
Duflos's, and others, although admirable in themselves, present great
difficulties to beginners, which difficulties maybe summed -up under
three heads ; 1st, Too great copiousness and detail; 2nd, The absence of
explanations of the causes of phenomena, i. e. the theory of the opera-
tions and reactions ; and 3rd, The omission altogether of many substances
viii EDITOR'S PREFACE.
of very frequent occurrence, especially in the operations of the pharma-
ceutist, such as the organic acids, &c.
In avoiding these objections to former works on chemical analysis,
Dr. Fresenius, I think, is not chargeable with having fallen into the
opposite extreme of being too concise or elementary.
The student may, perhaps, at first be disappointed in taking up this
work to find that there are no tables constructed to furnish him at a
glance with all he is desirous to know of tests and reactions, and to save
him, as he may think, trouble and time. But this has not arisen from
oversight ; the question of the advantage or disadvantage of tables to
the student has been fully considered, and the Author has decided and
the decision is borne out by the highest authorities that such tables
serve no really good purpose ; they rather, on the contrary, supply but
very superficial information, and satisfy the student before they have
really informed him. The information contained in this work, like
every other professing to teach a practical science, requires application
and perseverance to attain ; but if begun at the beginning, if the student
will carefully go over the necessary preliminary facts, the examination
of his tests, and the reaction of the simple bodies consecutively, and
make himself master of this very simple and elementary part of the
course, he will find few or no difficulties when entering upon the more
elaborate, and what might appear, without this preparation complex
and intricate processes of the Second Part, the analysis of compound
bodies. It is altogether another question whether the student should
or should not exercise himself and his memory by tabulating the results
of his experiments as he proceeds ; and to this question we reply in the
affirmative ; but it must be left to individuals to act in this according
to their own judgment, and their own feeling of its necessity.
In the Preface to the Second Edition, Dr. Fresenius tells us that his
work has met with much success, having been adopted in the Pharma-
ceutical Institution of Bonn, &c., as well as in the laboratory of Giessen ;
and that he has improved it by many corrections and additions.
IX
For my own part, I may be allowed to observe that the English
Edition was undertaken by the express desire of Professor Liebig, who
kindly recommended its being intrusted to my care. The Author has
supplied me with many corrections, and some additions, and the hope
is shared by us in common that it will facilitate the study of analytical
chemistry to the English student, and in every way serve to promote
the interests of the science.
J. LLOYD BULLOCK.
22, CONDUIT STREET,
October 1, 1843.
CONTENTS.
PART I.
INTRODUCTORY PART.
PRELIMINARY REMARKS.
Definition, objects, general principles,
utility, and importance of qualitative
chemical analysis, the conditions and
requirements for a successful study of
that science
SECTION I.
OPERATION, 1 .... "' '
1. Solution, 2
2. Crystallization, 3
3. Precipitation, 4
4. Filtration, 5 .
, ' . . 3
. 3
5
. 5
6
5. Decantation, 6
6. Evaporation, 7
7. Distillation, 8 .
8. Ignition, 9
9. Sublimation, 10
10. Fusion and Fluxing,
11. Deflagration, 12
12. The use of the blowprj
. 8
. 9
9
.',' ...,'." . 10
. 11
11 . .11
. 12
>e, 13 .12
Appendix to the First Section.
Apparatus and utensils, 14 . .16
SECTION II.
Reagents, 15 . . . .20
A. EEAGENTS IN THE HUMID WAT.
I. SIMPLE SOLVENTS . . .22
1. Water, 16 . . .22
2. Alcohol, 17 . '" *.". . , . 23
3. Ether, 18 23
II. ACIDS AND HALOGENS, 19 . .23
a. Oxygen acids.
1. Sulphuric acid, 20 . . .24
2. Nitric Acid, 21 . . .25
3. Acetic acid, 22 . . .26
4. Tartaric acid, 23 . . .27
6. Hydrogen acids and halogens.
1. Hydrochloric acid, 24 . .27
2. Chlorine, 25 . . . .28
3. Nitrohydrochloric acid, 26 .29
4. Hydrofluosilicic acid, 27 . .29
35
37
PAGE
c. Sulphur acids.
5. Hydrosulphuric acid, 28 . .30
III. BASES AND METALS, 29 .34
a. Oxygen l)ases.
a. Alkalies.
1. Potassa and soda, 30
2. Ammonia, 31 . .
/3. Alkaline earths.
1. Baryta, 32 . . .38
2. Lime, 33 . . . .39-
7. Heavy metals and their oxides.
1. Zinc, 34 . . . .40
2. Iron, 35 . . . .40
3. Copper, 36 . . .40
4. -Hydrate of teroxide of bismuth,
37 ..... 40
6. Sulphur bases.
1. Sulphide of ammonium, 38
2. Sulphide of sodium,
IV. SALTS.
39
10.
11.
12.
13.
14.
15.
16.
a. Salts of the alkalies.
Sulphate of potassa, 40
Phosphate of soda, 41
Oxalate of ammonia, 42 .
Acetate of soda, 43 .
Carbonate of soda, 44
Carbonate of ammonia, 45
Bisulphate of soda, 46
Nitrate of potassa, 47
Bichromate of potassa, 48
Antimouate of potassa, 49
Molybdate of ammonia, 50
Chloride of ammonium, 51
Cyanide of potassium, 52 .
Ferrocyanide of potassium, 53
Ferricyanide of potassium, 54
Sulphocyanide of potassium, 55
6. Salts of the alkaline earths.
Chloride of barium, 56
Nitrate of baryta, 57
Carbonate of baryta, 58 .
41
42
43
43
43
44
44
45
45
46
46
46
47
47
48
4&
49-
50
50
51
51
Xll
CONTKNTS.
4. Sulphate oflimo, . r -0
5. Hiloridi' of calcium. $ tiO
u*. Sulphato of magnesia, 55 61
PAGE
. 61
. 52
.52
r. ttifo o/ f/<c oxides of the heavy
metals.
1 . Snlphato of protoxide of iron, 62
Sosquii'hloride of iron, 08
3. Nitrate of silver. 04 .
4. Acotato of load, $ l>5 . .
5. Nitrate of suboxide of mercury
52
53
53
54
54
55
55
65
56
6. Chloride of mercury, 67 .
7. Sulphate of copper, 68 .
8. rrotoehloruie of tin, >5 09 .
9. Bichloride of platinum, 70
10. Sodio-protochloride of palladium
in..,. 56
11. Tercklorideofgold, 72 . 56
V. COLOURING MATTERS AND INDIF-
FERENT VKOKTABLK SCBSTASOKS, 73 57
1. Test papers.
a. Blue litmus paper . 57
p. Reddened litmus paper 57
7. Georgiua paper . 57
5. Turmeric paper . 58
2. Indigo solution, 74 . 58
B. REAGENTS IN TITE DRY WAY.
I. Fluxes and decomposing agents.
1. Mixture of carbonate of soda and
earb.n'.at o of pofcussa, 75 .58
. Hydrate of baryta, TO . . 60
3. Fluoride of calcium, 77 . .60
4. Nitrate of soda, 78 . . .60
II. Elotcpipe reagents.
1. Carbonate of soda, 79 . . 61
J. Cyanide of potassium, 80 . . 61
3. Biborate of soda, 81 . .62
4. Phosphate of soda and ammonia,
$$2 ..... 63
5. Nitrate of protoxide of cobalt, S3 63
6. Chloride of silver, 84 . .64
SECTION III.
ON THE DEPORTMENT OP BODIES WITH
RKAGEXTS, 85 . . . .64
A. DEPORTMENT AND PROPERTIES OF
THR METALLIC OXIDES AXD THEIR
RADICALS, 86 . . . .65
FIRST GROUP.
Potassa, soday and ammonia, 87 .66
Special inactions.
. V. :>>:-..*>>. . , 66
b. Soda, 89 ..... 67
c. Ammonia, 90 . . . .68
Recapitulation and remarks, 91 . 69
Supplement to the first group.
Lithia, 92 ..... 70
SECOND GROUP.
Baryta, ttrontia, lime, magnesia, \
Special reactions.
a. Ivirvta, 94
l>. StrJntia, 95 .
<-. Lime, 90 . .
d. Magnesia, 97 .
l\(capitnlation and remarks, 98
PAGE
93 71
71
72
73
74
70
THIRD GROUP.
Alumina, scsqirio.ridcofdtromium, 99 77
Special reactions,
a. Alumina, 100 . . . .78
6. Sesquioxide of chromium, 101 . 79
Recapitulation and remarks, 102 . 80
Supplement to tftc third group.
Titanic acid, 103 . .
SO
FOURTH GROUP.
Oxide of zinc, protoxide of inanyancttc,
protoxide of nickel, protoxide of
cobalt, protoxide of trow, scsqui-
oxide of iron, 104 '. . .81
Special reactions.
a. Oxide of zinc, 105 . . 82
b. Protoxide of inamranoso, 100 S3
e. Protoxide of nickel, 107 . 84
d. Protoxide of cobalt, 108 . 86
e. Protoxide of iron, 109 . 87
f. Sesquioxide of iron, 110 . 89
Recajiitttlation- and remarks, 111 i)0
Supplement to the fourth group.
Sesquioxide of uranium, 112 . . 92
FIFTH GROUP.
Oxide of silver, si&oxide of mercury,
oxide of mercury, oxide of lead t
teroxide of bismuth, oxide of cop-
per, oxide of cadmium, 113 . 93
First dirifionof thcjifth group : oxides
which are precipitated b;/ hydro-
chloric acid.
Special reactions.
a. Oxide of silver, 114 . * . 93
6. Suboxide of mercury, 115 . 94
c. Oxide of lead, 116 . . 95
Recapitulation and remarks, 117 . 97
Second division of thefifth group: oxides
which arc not precipitated by hy-
drochloric acid.
Special reactions.
a. Oxide of mercury, 118 . .97
b. Oxide of copper, * 119 , .98
c. Teroxide of bismuth, 120 . . 100
d. Oxide of cadmium, 121 . . 101
Recapitulation and remarks, 122 . 102
CONTKNT-i.
XU1
Supplement to thefiff,!>
Protoxide of palladium, 1 123
103
SIXTH 0BOVF.
'/<: o/yo/'/, t/inoxide of platinum,
ts.r'txifa (ff antimony, bmftxide of
tin. f,r',toxide of tin, arscnious
/>>/, ou//./ artf.ti.ic acid, 124 . 104
ivision of the sixth group.
Special reaction*.
a. Teroxideofgold,|125 . . 104
&. Binoxide of platinum, 1 126 . 105
Recapitulation and remark*, 127 . 106
Second division of the sixth group.
Special reaction*.
.. Protoxide of tin, 1 128 .
', Kinoxideoftin, 129 .
c. Teroxide of antimony, 130
d. Araeniotu acid, 131 .
. Arsenic acid, $132 . .
Recapitulation and remark*, 133
.piemen* to the tixth group.
Molybdic acid, 134 . . .125
B. DBPORTME5T OF THE ACIDS AWD THEIR
RADICALS WITH RKACtEYTS, f 135 126
Classification of acida in gronpa, 136 126
I. IKOROAJTIC ACIDS.
FIRST GROUP.
106
108
109
112
121
122
Acid* vJi.if.J'. art wt&
tralsolutionsby chloride of barium:
arsenious acid, arsenic acid, chro-
mic acid, sulphuric add, phot-
jtkoric acid, boradc acid, oxalic
o.c/W, hydrofluoric add, carbonic
acid, iiicic acid, 137 . . 127
Pint division of the first group of the
inorganic add*, 138 . . 128
a. Ar*OTioiw acid and arsenic acid . 128
6. Chromic acid .... 128
Remark*, $139 . . . .129
Supplement to the first division of the
129
129
130
130
a. Selenions acid .
b. Snlphuricacid
c. Hypoeulpliiiric acid
d. lodicacid .
Second diritionof the first group of the
inorganic acids.
Sulphoric acid, 141 . . .131
Remarks . ..... 131
Supplement to the second division of
the first group.
HydrofluoBiiicic acid, 142 . . 132
Tfiird division of the first group of the
inorganic add*.
a. Phosphoric acid, 143
Supplement, 144 .
a. Bibasic phosphoric acid
8. Monobasic phosphoric acid
o. Boracic acid, 145 .
<r. Oxalic acid, 146 .
d. Hydrofluoric acid, 147
Recapitulation and remarks,
132
IS5
135
137
IM
140
JVarTA division of the first group of the
inorganic add*.
a. Carbonic acid, 1 149 . . 142
b. Silicic acid, 1 150 . . .143
Recapitulation and remarks, 1 151 . 144
S1C09D OBOUP OF IKOROAHC ACIDS.
Add* which arepredpitated by nitrate
of silver, but not by chUridc of ba-
rium: hydrfjcldoric add, kydrr*-
bromic acid, hydriodic add,
hydrocyanic add, hydrosulphuric
add.
a. Hydrochloric acid, 152 . . 145
&, Hydrobromic acid, f 153 . . 146
c. Hydriodic acid, 1 154 . . 148
d. Hydrocyanic acid, 155 . . 150
a. Hydroferrocyanic acid
& Hydroferricyanic acid .
e. Hydrosulphuric acid, 156
Recapitulation and remarks,
151
151
152
1 157 . 153
Supplement to the second group, 115S 154
1. KHnmsaeid .... 154
2. HypocbloTous acid . . .154
THIRD 6BOITP OF THE IKOROAMIC ACH*.
^ euZ> wltdk notpredpitated by salt*
of baryta nor by salts of tUver:
nitric add, cldoric add.
a. Nitric acid, 159 . . .155
6. Chloric acid, 1 160 ... 156
Recapitulation and remark*, 161 . 157
IL OROAJTIC ACTDS.
FIRST OROCP.
^4 <rufc &e& are invariably predpitated
by ehlr/ride of caldum: oxalic
add, tartaric add, paratartaru;
or racemic add, citric add, malic
add.
a. Oxalic acid, |162 ... 158
b. Tartarie acid, 162. . . 158
e. Citric add, f 163 . . .159
d. Malie acid, 164 . . .160
Recapitulation and remarks, 165 . 161
Appendix. Baeemie or paratertaric
CONTENTS.
PAGE
SECOND GROUP OP THE ORGANIC ACIDS.
Adda which chloride of calcium fails
to precipitate wider any circum-
stances, but which arc precipitated
from neutral solutions by sesqui-
chloride of iron: succinic acid,
benzole add.
a. Succinic acid, 167 . . 162
5. Benzole acid, 168 . . .163
Recapitulation and remarks, 169 . 164
PAGE
THIRD GROUP OP THE ORGANIC ACIDS.
Adds which are not precipitated by
chloride of caldum nor by scsqui-
chloride of iron: acetic acid,
formic add.
a. Acetic acid, 170 . . .164
b. Formic acid, 171 . . . 166
Recapitulation and remarks, 172 . 167
PART II.
SYSTEMATIC COURSE OF QUALITATIVE CHEMICAL ANALYSIS.
PAGE
Preliminary remarks on the course of
qualitative analysis in general, and
the plan of this part of the present
work in particular . . .171
SECTION I.
PRACTICAL PROCESS.
I. Preliminary examination, 173 . 173
A. The body under examination is solid.
I. It is neither a pure metal nor an
alloy, 174 . . . . 174
II. The substance is a metal or an
alloy, 175 . . . .178
B. The substance under examination is
a fluid, 176 . . . . 179
II. Solution of bodies, or classification
of substances according to their
deportment with certain solvents,
177 180
A. The substance under examination is
neither a metal nor an alloy, 178 180
B. The substance under examination is
a metal or an alloy, 179 . . 182
III . Act ual cxamina tion.
SIMPLE COMPOUNDS.
A. Substances soluble in water.
Detection of the base, 180 . 183
Detection of the acid.
I. Detection of inorganic acids, 181 189
II. Detection of organic acids, 182 191
B. Substances insoluble or sparingly
soluble in water, but soluble in
hydrochloric add, nitric add,
or nitrohydrochloric add.
Detection of the base, 183 . 192
Detection of the acid.
I. Detection of inorganic acids, 184 194
II. Detection of organic acids, 185 195
C. Substances insoluble or sparingly
sohible in water, hydrochloric add,
nitric add, or nitrohydrochloric
add.
PAGE
Detection of the base and the acid,
186 .... 196
COMPLEX COMPOUNDS.
A. Substances soluble in water, and
also such as are insoluble in water,
but dissolve in hydrochloric acid,
nitric add, or nitrohydrochloric
add.
Detection of the bases . . .197
Treatment with hydrochloric acid :
detection of silver, suboxide of mer-
cury (lead), 187 . . . 197
Treatment with hydrosulphuric acid,
precipitation of the metallic oxides
of Group V., 2nd division, and of
Group VI., 188 . . .200
Treatment of the precipitate produced
by hydrosulphuric acid with sul-
phide of ammonium ; separation of
the 2nd division of Group V. from
Group VI., 189 . . . 202
Detection of the metals of Group VI.
Arsenic, antimony, tin, gold, pla-
tinum, 190 . . . . 203
Detection of the metallic oxides of
Group V., 2nd division. Oxide of
lead, teroxide of bismuth, oxide of
copper, oxide of cadmium, oxide of
mercury, 191 . . . . 206
Precipitation with sulphide of ammo-
nium, detection and separation of
the oxides of Groups III. and IV.
Alumina, sesquioxide of chromium,
oxide of zinc, protoxide of manga-
nese, protoxide of nickel, protoxide
of cobalt, proto- and sesquioxide of
iron, and also of those salts of the
alkaline earths which are precipi-
tated by ammonia from their solu-
tion in hydrochloric acid : phos-
phates, borates, oxalates, silicates,
and fluorides, 192 . . . 207
Separation and detection of the oxides
of Group II., which are precipitated
by carbonate of ammonia in pre-
CONTENTS.
PAGE
sence of chloride of ammonium,
viz., baryta, strontia, lime, 193 213
Examination for magnesia, 194 . 215
Examination for potassa and soda,
195 ..... 215
Examination for ammonia, 196 . 216
DETECTION OP THE ACIDS.
1. Af&fftMtfM soluble in water.
I. In the absence of organic acids,
7 ..... 216
II. In presence of organic acids,
198 ..... 219
2. S a balances insoluble in water, but
soliMe in hydrochloric acid,
nitric acid, or nilrohydrochloric
acid.
I. In the absence of organic acids,
199 ..... 221
II. In presence of organic acids,
200 ..... 222
B. fiubstances insoluble, or sparingly
tottMt both in water awl in
hydrochloric acid, nitric acid,
or nitrohydrockloric acid.
Detection of the bases, acids, and
non-metallic elements, 201 . 222
SECTION II.
PRACTICAL COURSE IN PARTICULAR CASES.
I. Special method of effecting the ana-
lysis of cyanides, ferrocyanides,
&c., insoluble in water, and also
of insoluble mixed substances
containing such compounds,
202 ..... 226
II. Analysis of silicates, 203 . . 227
A. Silicates decomposable by acids,
204 ..... 228
B. Silicates which are not decom-
posed by acids, 205 . . 229
C. Silicates which are partially de-
composed by acids, 206 . 231
III. Analysis of natural waters, 207 231
A. Analysis of the fresh waters
(spring- water, well-water, brook-
water, river- water, &c.), 208 232
B. Analysis of mineral waters,
209 ..... 235
1. Examination of the water
a. Operations at the spring, 210 235
I. Operations in the laboratory,
211 ..... 236
2 . Examination of the sinter deposits,
212 ..... 240
IV. Analysis of soils, 213 . .242
1. Preparation and examination of
the aqueous extract, 214 . 243
2. Preparation and examination of
the acid extract, 215 . . 245
3. Examination of the inorganic con-
stituents insoluble in water and
acids, 216 . . . . 245
PAOB
4. Examination of the organic consti-
tuents of the soil, 217 . . 246
a. Examination of the organic sub-
stances soluble in water . .246
6. Treatment with an alkaline car-
bonate 246
c. Treatment with caustic alkali 246
Y. Detection of inorganic substances in
presence of organic substances,
218 247
1. General rules for the detection of
inorganic substances in presence
of organic matters, which by
their color, consistence, &c., im-
pede the application of the re-
agents, or obscure the reactions
produced, 219 ... 247
2. Detection of inorganic poisons in
articles of food, in dead bodies,
&c., in chemico-legai cases.
220 248
I. Method for the detection of arsenic,
221 249
A. Method for the detection of undis-
solved arsenious acid, 222 . 250
B. Method for the detection of arsenic
in whatever form of combination
it may exist, which allows also a
quantitati vedeter mination of that
poison, and permits at the same
time the detection of other metal-
lic poisons which may be present,
223 251
1. Decolorization and solution . 251
2. Treatment of the solution with
hydrosulphuric acid . . 251
3. Purification of the precipitate
produced by hydrosulphuric acid 252
4. Preliminary examination for ar-
senic and other metallic poisons
of the fifth and sixth groups . 252
5. Treatment of the purified preci-
pitate produced by hydrosulphu-
ric acid in cases where arsenic
alone is assumed to be present . 253
6. Treatment of the purified preci-
pitate produced by hydrosulphu-
ric acid in cases where there is
reason to suppose that another
metal is present, perhaps with
arsenic 254
7. Reduction of the sulphide of
arsenic 255
8. Examination of the reserved
residues for other metals of the
fifth and sixth groups 256
a. Residue I. . 256
b. Residue II. . 256
c. Residue III. . 257
d. Residue IV. . 257
9. Examination of the reserved fil-
trate for metals of the third and
fourth groups . . . 257
IL Method for the detection of hydro-
cyanic acid, 224 . . . 257
XVI
CONTENTS.
Ill Method for the detection of phos-
phorus, 225 . . . 259
3. Examination of the inorganic con-
stituents of plants, animals, or
parts of the same, of manures,
&c. (analysis of ashes).
A. Preparation of the ash, 226 261
B. Examination of the ash . 261
a. Examination of the part
soluble in water . . . 262
b. Examination of the part soluble
in hydrochloric acid . .263
c. Examination of the residue in-
soluble in hydrochloric acid . 263
SECTION III.
EXPLANATORY NOTES AND ADDITIONS TO THE
SYSTEMATIC COURSE OP ANALYSIS.
I. Additional remarks to the preliminary
examination, To 173176 . 264
II. Additional remarks to the solution of
substances, &c., To 177179 265
III. Additional remarks to the actual
examination, To 180201 . 266
A. General review and explanation of
the analytical course . . 266
a. Detection of the bases . .266
b. Detection of the acids . . 269
B. Special remarks and additions to
the systematic course of analysis.
To 187 272
188 273
191 274
202 274
APPENDIX.
I. Deportment of the most important
medicinal alkaloids with reagents,
and systematic method of effect-
ing the detection of these sub-
stances, 227 . . . 276
I. Volatile alkaloids.
1. Nicotia, 228 . . . 277
2. Conia, 229 . . . 278
II. Non-volatile alkaloids.
FIRST GROUP.
Non-volatile alkaloids which are pre-
cipitated by potassa or soda from
the solution of their salts, and
redissolve readily in an excess
of the precipitant . . .279
Morphia, 230 . . . . 279
SECOND GROUP.
Non-volatile alkaloids which are pre-
cipitated by potassa from the
solution of their salts, but do
not redissolve to a, perceptible
extent in an excess of the preci-
pitant, and are precipitated by
bicarbonate of soda even from
acid solutions . , 280
PAGE
a. Narcotina, 231 . . . 280
b. Quina, 232 ... 281
c. Cinchonia, 233 . . . 282
Recapitulation and remarks, 234 283
THIRD GROUP.
Non-volatile alkaloids which arepre-
cipitated by potassa from the
solutions of their salts, and do
not redissolve to a perceptible
extent in an excess of the preci-
pitant, but are not precipitated
from acid solutions by the bicar-
bonates of the fixed alkalies . 284
a. Strychnia, 235 . - . ... . 284
6. Brucia, 236 . . . 285
c. Veratria, 237
286
Recapitulation and remarks, 238 287
Salicine, 239 ... . .288
Systematic course for the detection of
the alkaloids treated of in the
preceding paragraphs, and of
salicine, 240 . . . 288
I. Detection of the alkaloids, and of
salicine, in solutions supposed to
contain only one of these sub-
.stances, 241 . . . 288
II. Detection of the alkaloids, and of
salicine, in solutions supposed to
contain several or all of these
stances, 242 . . .289
Detection of the alkaloids, in presence
of coloring and extractive vege-
table or animal matter, 243 . 291
1. Stas's method of detecting poi-
sonous alkaloids . . . 291
2. Merck's method of detecting non-
volatile alkaloids . . .293
3. Method of effecting the detection
of strychnia in beer, by Graham
and Hofmann . . . 294
II. General plan of the order and suc-
cession in which substances
should be analyzed for practice 294
III. Arrangement of the results of the
analyses performed for practice 295
IV. Table of the more frequently occur-
ring forms and combinations of the
substances treated of in the pre-
sent work; arranged with special
regard to the class to which they
respectively belong, according to
their solubility in water, in hy-
drochloric acid, nitric acid, or
nitrohydrochloric acid . . 298
Preliminary remarks . . 1:: .?. 298
Table . . , ^;, ;v . . 300
Notes . . ..., .'>.: * . 300
V. Table of weights and measures . 303
INDEX , 305
PART I.
INTRODUCTORY,
PRELIMINARY REMARKS.
DEFINITION, GENERAL PRINCIPLES, OBJECTS, UTILITY, AND IMPORTANCE
OF QUALITATIVE CHEMICAL ANALYSIS, THE CONDITIONS AND REQUIRE-
MENTS FOR A SUCCESSFUL STUDY OF THAT SCIENCE.
CHEMISTRY is the science which treats of the various materials entering
into the structure of the earth, their composition and decomposition,
their mutual relations and deportment in general. A special branch
of this science is designated Analytical Chemistry, inasmuch as it
pursues a distinct and definite object viz., the analysis of compound
bodies, and the examination of their component elements. Analy-
tical chemistry, again, is subdivided into two branches viz., qualitative
analysis, which simply studies the nature and properties of the com-
ponent parts of bodies ; and quantitative analysis, which ascertains the
quantity of every individual element present. The office of quali-
tative analysis, therefore, is to exhibit the constituent parts of a substance
of unknown composition in forms of known composition, from which the
constitution of the body examined, and the presence of its several
component elements may be positively 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 quantity.
These different ends are, of course, attained respectively by very
different ways and means. The study of qualitative analysis must,
therefore, be pursued separately from that of quantitative analysis, and
must naturally precede it,
Having thus generally denned the meaning and scope of qualitative
analysis, we have now still to consider, in the first place, the preliminary
information required to qualify students for a successful cultivation of
this branch of science, the rank which it holds in the domain of
chemistry, the bodies that fall within the sphere of its operations, and its
utility and importance ; and, in the second place, the principal parts into
which its study is divided.
2 PRELIMINARY REMARKS.
It is, above all, absolutely indispensable for a successful pursuit of qua-
litative investigations, 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 apprehension of
chemical processes. The practical part of this science demands, more-
over, strict order, great neatness, and a certain skill in manipulation. If
the student joins to these qualifications the habit of invariably ascribing
the failures with which he may happen to meet, to some error or defect
in his operations, or, in other words, to the absence of some condition or
other indispensable to the success of the experiment and a firm reliance
on the immutability of the laws of nature cannot fail to create this habit
he possesses every requisite to render his study of analytical che-
mistry successful.
Now, although chemical analysis is based on general chemistry, and
cannot be cultivated without some previous knowledge of the latter, yet,
on the other hand, 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 I need not expatiate here on the advantages which the
physician, the pharmaceutist, the mineralogist, the rational farmer, the
manufacturer, the artisan, and many others derive from it.
This consideration would surely in itself be sufficient reason to re-
commend a thorough and diligent study of this branch of science, even it
its cultivation lacked those attractions which yet it unquestionably pos-
sesses for every one who devotes himself zealously and ardently to it.
The human mind is constantly striving for the attainment of truth ; it
delights in the solution of problems ; and where do we meet with 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. in
like manner, do chemical investigations, if the object in view is not
attained if the results do not bear the stamp of truth, of unerring
certainty. A half-knowledge is therefore, as indeed in every department
of science, but more especially here, to be considered worse than no know-
ledge at all ; and a mere superficial cultivation of chemical analysis is
consequently to be particularly guarded against.
A qualitative investigation may be made with a twofold view viz.,
either, 1st, to prove that a certain body is or is not contained in a sub-
stance, e.g. lead in wine ; or, 2ud, to ascertain all the constituents of a
chemical compound or mixture. Any substance whatever may of course
become the object of a chemical analysis.
In the present work, however, we purpose to confine ourselves to
those elements and compounds which are more generally employed in
pharmacy, in the arts and manufactures, and in agriculture.
The study of qualitative analysis is most properly divided into four
principal parts viz.,
1. CHEMICAL OPERATIONS.
2. REAGENTS AND THEIR USES.
3. DEPORTMENT OP THE VARIOUS BODIES WITH REAGENTS.
4. SYSTEMATIC COURSE OF QUALITATIVE ANALYSIS.
It will now be readily understood that the pursuit of chemical
1, 2.] OPERATIONS. 3
analysis requires practical skill and ability, as well as theoretical know-
ledge ; and that, consequently, a mere speculative study of that science
can be as little expected to lead to success as purely empirical expe-
riments. To attain the desired end, theory and practice must be com-
bined.
SECTION I.
OPERATIONS.
I-
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 investigations.
The following are the principal operations in qualitative analysis.
2.
1. SOLUTION.
The term " solution" in its widest sense, denotes the perfect union of
a body, no matter whether gaseous, liquid, or solid, with a fluid, resulting
in a homogeneous liquid. However, when the substance dissolved is
gaseous, the term " absorption" is more properly made use of; and the
solution of one fluid in another is more generally called a mixture. The
application of the term solution, in its usual and more restricted sense,
is confined to the perfect union of a solid body with a fluid.
A solution is the more readily effected the more minutely the body to
be dissolved is divided. The fluid by means of which the solution is
effected, is called the solvent. We call the solution chemical, where the
solvent enters into chemical combination with the substance dissolved ;
simj)le, where no definite combination takes place.
In a simple solution the dissolved body exists in the free state, and
retains all its original properties, except those dependent on its form and
cohesion ; it separates unaltered when the solvent is withdrawn. Com-
mon salt dissolved in water is a familiar instance of a simple solution.
The salt in this case imparts its peculiar taste to the fluid. On evapo-
rating the water, the salt is left behind in its original form. A simple
solution is called saturated when the solvent has received as much as it
can hold of the dissolved substance. But as fluids dissolve generally
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. It may be laid down as a general
rule, that elevation of temperature facilitates and accelerates simple
solution.
A chemical solution contains the dissolved substance not in the same
state nor possessed of the same properties as before ; the dissolved body
is no longer free, but intimately combined with the solvent, which latter
also has lost its original properties ; a new substance has thus been pro-
duced, and the solution manifests therefore now the properties of this
new substance. A chemical solution also may be accelerated by elevation
of temperature ; and this is indeed usually the case, since heat generally
B 2
SOLUTION.
[2-
promotes the action of bodies upon each other. But the quantity of the
dissolved body remains always the same in proportion to a given
quantity of the solvent, whatever may be the difference of temperature
the combining proportions of substances being invariable, and altogether
independent of the gradations of temperature.
The reason of this is, that in a chemical solution the solvent and the
body upon which it acts have invariably opposite properties, which they
strive mutually to neutralize. Further solution ceases as soon as this
tendency of mutual neutralization is satisfied. The solution is in this
case also said to be saturated or, more properly, neutralized, and the
point which denotes it to be so is termed the point of saturation or neu-
tralization. The substances which produce chemical solutions are, m
most cases, either acids or alkalies. With few exceptions, they have
first to be converted to the fluid state by means 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 solution of acetic
acid in water is brought into contact with oxide of lead, there ensues,
first, a chemical combination of the acid with the oxide, and then a
simple solution of the new-formed acetate of lead in the water of the
menstruum.
In pharmacy, solutions are often made in a mortar having a lip, by
triturating the body to be dissolved with the solvent added gradually in
small quantities at a time ; in chemical laboratories solutions are rarely
made in this manner, but generally by digesting or heating the substance
to be dissolved with the fluid in beaker-glasses, flasks, test-tubes, or
dishes. In the preparation of chemical solutions, the best way generally
is to mix the body to be dissolved in the first place with water (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 process greatly facilitated, and complete solution ensured, which is a
matter of some importance, as it will not seldom happen in chemical
combinations that the product formed refuses to dissolve if an excess of
the chemical solvent is present ; in which case the molecules first formed
of the new salt, being insoluble in the menstruum present, gather round
and enclose the portion still unacted on, weakening thereby or preventing
altogether further chemical action upon them. Thus, for instance,
Witherite (carbonate of baryta) dissolves readily when, after being
reduced 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 chloride of barium will indeed dissolve in water, but not in hydro-
chloric acid.
CRYSTALLIZATION and PRECIPITATION are the reverse of solution, 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 many 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, 4.] CRYSTALLIZATION. 5
3.
2. CRYSTALLIZATION.
We understand by the term crystallization, in a more general sense,
every operation, or process, whereby bodies 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
the more regular, and consequently the more perfect, the more slowly
the operation is carried on, we always connect with the term " crystal-
lization" 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 ultimate constituent particles of bodies (molecules or
atoms) ; it can only take place, therefore, if these atoms possess perfect
freedom of motion, 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 (crystal-
lization) prevail over the diminished force of cohesion such as, 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 gaseous form of a
substance must be removed. These causes are either heat alone, e.g., in
the case of fused metals ; or solvents alone, as in the case of an aqueous
solution of common salt ; or both combined, as in the case of a hot satu-
rated solution of nitrate of potassa in water. In the first case we obtain
crystals by cooling the fused mass ; in the second, by evaporating the
menstruum ; and in the third by either of these means. The most
frequently occurring case is that of crystallization by cooling hot saturated
solutions. The liquors which remain after the separation of the crystals
are called mother-waters, or mother-liquors. The term amorphous is
applied to such solid bodies as have no crystalline form.
We have recourse to crystallization generally either to obtain the
crystallized substance in a solid form, or to separate it from other sub-
stances dissolved in the same menstruum. 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 sulphate of soda and sulphate of potassa.
The process of crystallization is usually effected in dishes, or, in the case
of very small quantities, in watch-glasses.
In cases where the quantity of fluid to be operated upon is only
small, the surest way of getting well-formed crystals is to let the fluid
evaporate in the air, or, better still, under a bell-glass, with an open
vessel half-filled with concentrated sulphuric acid. Minute crystals are
examined best with a lens, or under the microscope.
4.
3. PRECIPITATION.
This operation differs from the preceding one in this much, that the
dissolved body is converted to the solid state, not slowly and gradually,
6 FILTRATION. [ 5.
but suddenly, no matter whether the substance separating is crystalline
or amorphous, whether it sinks to the bottom of the vessel, or ascends,
or remains suspended in the liquid. Precipitation is either caused by a
modification of the solvent thus sulphate of lime (gypsum) separates
immediately from its solution in water upon the addition of alcohol ; or
it ensues in consequence of the separation of an educt insoluble in the
menstruum thus when ammonia is added to a solution of sulphate of
alumina, the latter salt is decomposed, and the alumina, not being
soluble in water, precipitates. Precipitation takes place also when, by
the action of simple or double chemical affinity, new compounds are
formed which are insoluble in the menstruum ; thus oxalate of lime
precipitates upon adding oxalic acid to a solution of acetate of lime \
chromate of lead upon mixing chromate of potassa with nitrate of lead.
In decompositions of this kind, induced by simple or double affinity, one
of the new compounds remains generally in solution, and the same is
sometimes the case also with the educt ; thus in the instances just men-
tioned the sulphate of ammonia, the acetic acid, and the nitrate of
potassa, remain in solution. It may, however, happen also that both
the product and the educt, or two products, precipitate, and that nothing
remains in solution ; this is the case, for instance, when a solution of
sulphate of magnesia is mixed with water of baryta, or when a solution
of sulphate of silver is precipitated with chloride of barium.
Precipitation is resorted to for the same purposes as crystallization,
viz., either to obtain a substance in the solid form, or to separate it from
other substances dissolved in the same menstruum. But in qualitative
analysis we have recourse to this operation more particularly for the
purpose of detecting and distinguishing substances by the color, pro-
perties, 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 sub-
stance which acts as the immediate cause of the separation is termed the
precipitant. Various terms are applied to precipitates by way of par-
ticularizing them according to their different nature ; thus we distin-
guish crystalline, pulverulent, flocculent, curdy, gelatinous precipitates, &c.
The terms turbid, turbidity, 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, yet cannot be clearly distinguished. The separation
of flocculent precipitates may generally be promoted by a vigorous shake
of the vessel ; that of crystalline precipitates, by stirring the fluid and
rubbing the sides of the vessel with a glass rod ; elevation of tempera-
ture is also an effective means of promoting the separation of most pre-
cipitates. The process is therefore conducted, according to circumstances,
either in test-tubes, flasks, or beakers.
The two operations described respectively in 5 and 6, viz., filtration
and decantation, serve to effect the mechanical separation of fluids from
matter suspended therein.
5.
4. FILTRATION.
This operation consists simply in passing the fluid from which we wish
to remove the solid particles mechanically suspended therein through a
5.]
FILTRATION.
filtering apparatus, formed usually by a properly arranged piece of unsized
paper placed in a funnel ; an apparatus of this description allows the
fluid to trickle through with ease, whilst it completely retains the solid
particles. We employ smooth filters and plaited filters ; the former in
cases where the separated solid substance is to be made use of, the latter
in cases where it is simply intended to clear the solution. Smooth filters
are prepared by double-folding a circular piece of paper, with the folds
at right angles ; they must in every part fit close to the funnel. The
preparation of plaited filters is more properly a matter for ocular
demonstration than for description. In cases where the contents of the
filter require washing, the paper must not project over the rim of the
funnel. It is in most cases 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 filters must be as
free as possible from inorganic substances, especially such as are dissolved
by acids, e.g., sesquioxide of iron and lime. The common filtering paper
of commerce seldom comes up to our wants in this respect, and I would
therefore always recommend to wash it carefully with dilute hydrochloric
acid whenever it is intended for use in accurate analyses. With the
stronger sorts of paper this may be done by placing the paper cut in
circular discs, in a layer of moderate thickness, in a shallow porcelain,
dish, pouring over it a mixture of one part of hydrochloric acid or nitric
acid with about nine parts of water, and letting it digest for several hours
at a moderate heat. The fluid is then poured off, and the paper repeatedly
washed with water (finally with distilled water), until litmus paper is
no longer reddened by the washings : the water is then drained off,
and the entire layer is carefully transferred to a quire of blotting-
paper, and left there until they can be taken off singly without injury;
they are then hung up to dry on lines in
a place free from dust. With the finer
sorts of paper (Swedish paper) I prefer
washing the filters in the funnel. To this
end they are first sprinkled with a little
moderately diluted hydrochloric or nitric
acid, and then thoroughly washed with
Avater, finally with distilled water. Fil-
tering paper, to be considered good, must,
besides being pure, also let fluids pass
readily through, whilst yet completely re-
taining even the finest pulverulent preci-
pitates, such as sulphate of baryta, oxalate
of lime, &c. 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
separation of grosser particles. The funnels must be of glass or por-
celain ( 14, 10); they are usually placed on an appropriate stand, to
keep them in a fixed position. The stand shown in Fig. 1 is particularly
well adapted for the reception of the small-sized funnels used in quali-
tative analyses.
Fig. 1.
8 DECANTATION. [ 6.
6.
5. DECANTATION.
This operation is frequently resorted to instead of nitration, in cases
where the solid particles to be removed are of considerably 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 the supernatant fluid by simply inclining the vessel, or
to draw it off by means of a syphon or pipette.
In cases where nitration or decantation are resorted to for the purpose
of obtaining the solid substance, the latter has to be freed afterAvards by
repeated washing from the liquid still adhering to it. This operation is
termed washing or edulcoration. The washing of precipitates collected
on a filter is usually effected by means of a washing bottle, such as is
shown in Fig. 2.
Fig. 2.
This washing bottle consists of a flask closed with a perforated cork,
into which a small glass tube is fitted, with the outer end drawn out to
a fine point. By blowing air into the flask through this tube and, when
the air is sufficiently compressed, reversing the flask, so as to place the
inner aperture of the tube under water, a tine jet of that fluid is ex-
pelled with a certain degree of force ; this contrivance is well adapted
for washing precipitates. Fig. 3 represents a washing bottle of a dif-
ferent construction, which is used more especially to wash precipitates
with boiling water, and affords also the advantage that it enables the
operator to produce an uninterrupted jet of water. The drawing needs
no explanation ; the outer end of the tube a is drawn out to a fine point.
An India-rubber cap fitted with two tubes may be used instead of the
double-perforated cork.
There are four operations which serve to separate volatile substances
from less volatile or from fixed bodies, viz., evaporation, distillation,
ignition, and sublimation. The two former of these operations are ap-
plied exclusively to fluids, the two latter exclusively to solids.
7, 8.] EVAPORATION. 9
7.
6. EVAPORATION.
This operation is of very frequent occurrence. It serves to separate
volatile fluids from less volatile or from fixed bodies (no matter whether
solid or fluid), in cases where the residuary substance alone is of im-
portance, whilst the evaporating matter is entirely disregarded ; thus,
for instance, we have recourse to evaporation for the purpose of removing
from a saline solution part of the water, in order to bring about crystal-
lization of the salt ; we resort to this process also for the purpose of re-
moving the whole of the water of the menstruum from the solution of a
non-crystallizable substance, so as to obtain the latter in a solid form,
&c. The evaporated water is entirely disregarded in either of these
cases, the only object in view being to obtain, in the former case a more
concentrated fluid, and in the latter a dry substance. These objects are
invariably attained by converting the fluid which is to be removed to
the gaseous state. This is generally done by the application of heat ;
sometimes also by leaving the fluid for a certain time in contact with
the atmosphere, or with an enclosed volume of air constantly kept dry by
hygroscopic substances, such as concentrated sulphuric acid, chloride of
calcium, <fec. ; or, lastly, in many cases, by placing the fluid in rarefied
air, with simultaneous application of hygroscopic substances. As it is
of the utmost importance in qualitative analyses to guard against the
least contamination, and as an evaporating fluid is the more liable to
this the longer the operation lasts, the process is usually conducted, with
proper expedition, over the flame of a spirit or gas-lamp, in a separate
place free from dust and not exposed to draughts of air. If the operator
has no place of the kind, he must have recourse to the much less suitable
proceeding of covering the dish ; the best way of doing this is to place
over the dish a large glass funnel secured by a retort holder, in a manner
to leave sufficient space between the rim of the funnel and the border of
the dish ; the funnel is placed slightly aslant that the drops running
down its sides may be received in a beaker. Or the dish may also be
covered with a sheet of filter paper previously freed from inorganic sub-
stances by washing with dilute hydrochloric or nitric acid (see 5) ;
were common and unwashed filter paper used for the purpose, the sesqui-
oxide of iron, lime, &c., contained in it, would dissolve in the vapors
evolved (more especially if acid), and the solu-
tion dripping down into the evaporating fluid
would speedily contaminate it. These precau-
tions are necessary of course only in accurate
analyses. Larger quantities of fluid are eva-
porated best in glass flasks standing aslant,
covered with a cap of pure filtering paper,
over a charcoal fire or gas ; or also in retorts. Fig. 4.
Evaporating processes at 212 are conducted
in an appropriate steam apparatus, or in the water-baths shown in
Fig. 4.
7. DISTILLATION.
This operation serves to separate a volatile liquid from a less volatile
10
IGNITION.
or a fixed substance (no matter whether solid or fluid), where the object
is to recover the evaporating fluid. In order to attain this object it
necessarv to reconvert the liquid from the gaseous form in which it- eva-
porates, into the fluid state. A distilling apparatus consists consequently
always of three parts, no matter whether admitting of separation or not
These three parts are-lst, a vessel in which the liquid to be distilled is
heated, and thus converted into vapor; 2nd, an apparatus in which this
vapor is cooled again or condensed, and thus reconverted to the fluid
state and 3rd, a vessel to receive the fluid thus reproduced by the con-
densation of the vapor (the distillate). For the distillation of large
Fig. 5.
quantities we use either a metallic apparatus (a copper still with
head and condenser made of tin or pewter), or large glass retorts ;
in analytical investigations we generally employ the apparatus shown
in Fig. 5.
9.
8. IGNITION.
Ignition is, in a certain measure, for solid bodies what evaporation is
with regard to fluids ; since it serves (at least generally) to separate
volatile substances from less volatile or from fixed bodies, in cases where
the residuary substance alone is of importance. The process of ignition
always presupposes the application of a high temperature, in which it
differs from that of drying or exsiccation. The form or state which the
eliminated substance assumes on cooling whether it remains gaseous, as
in the ignition of carbonate of lime ; or assumes the liquid state, as in
the ignition of hydrate of lime ; or solidifies, as in the ignition of a
mixture containing chloride of ammonium is a matter of perfect indif-
ference as regards the name given to the operation.
The process of ignition is mostly employed, as has just been said, to
effect the elimination of a volatile body. In some instances, however,
substances are ignited simply for the purpose of modifying their state,
without any volatilization taking place ; thus the sesquioxide of chro-
10j 11.] SUBLIMATION. 11
mium is converted by ignition into its insoluble modification, <fec. In
analytical investigations substances under examination are often ignited
also, that the operator may from their deportment at a red heat draw a
conclusion as to their nature in general ; their fixity, their fusibility,
the presence or absence of organic matter, &c.
Crucibles are the vessels made use of in ignition. In operations on a
large scale Hessian or black-lead crucibles are used, heated by charcoal
or coke ; in analytical experiments small-sized crucibles or dishes are
selected, of porcelain, platinum, silver, or iron, or glass tubes sealed at
one end, according to the nature of the substances to be ignited ; these
crucibles, dishes, or tubes are heated over a Berzelius spirit-lamp or a
properly-con str acted gas-lamp.
10.
9. SUBLIMATION.
The term sublimation designates the process which serves to expand
solid bodies into vapor by the application of heat, and subsequently to
recon dense the vapor to the solid state by refrigeration ; the substance
volatilized and recondensed is called a sublimate. Sublimation is con-
sequently a distillation of solid bodies. We have recourse to this process
mostly to effect the separation of substances possessed of different degrees
of volatility. Its application is of the highest importance in analysis for
the detection of certain substances, e. g. of arsenic. The vessels used in
sublimation are of various shapes, according to the different degrees of
volatility of the substances operated upon. In sublimations for analytical
purposes we generally employ sealed glass tubes.
11.
10. FUSION AND FLUXING.
We designate by the term " fusion" the conversion of a solid substance
into the fluid form by the application of heat ; fusion is most frequently
resorted to for the purpose of effecting the combination or the decom-
position of bodies. The term " fluxing" is applied to this process in
cases where substances insoluble or difficult of solution in water and acids
are by fusion in conjunction with some other body modified or decom-
posed in such a manner, that they or the new-formed compounds will
subsequently dissolve in water or acids. Fusion and fluxing are con-
ducted either in porcelain, silver, or platinum crucibles, according to the
nature of the compound. The crucible is supported on a triangle of
moderately stout platinum wire, resting on, or attached to, the ring of
the spirit or gas-lamp. Triangles of thick iron wire, especially when
laid upon the still stouter brass ring of the lamp, carry off too much
heat to allow of the production of very high temperatures. Small quan-
tities of matter are also often fused in glass tubes sealed at one end.
Resort to fluxing is especially required for the analysis of the sul-
phates of the alkaline earths, and also for that of many silicates. The
flux most commonly used is carbonate of soda or carbonate of potassa,
or, better still, a mixture of both in equal atomic proportions (see 75).
In certain cases, hydrate of baryta is used instead of the alkaline carbo-
nates (see 76). But in either case the operation is conducted in pla-
tinum crucibles.
I have to add here a few precautionary rules for the prevention of
12 DEFLAGRATION. [ 12, 13
damage to the platinum vessels used in these operations. No substance
evolving chlorine ought to be treated in platinum vessels ; no nitrate of
potassa, caustic potassa, metals, sulphides of the metals, or cyanides of the
alkalies, should be fused in such vessels ; nor ought readily deoxidizable
metallic oxides, organic metallic salts, or phosphates to be ignited in
them in the presence of organic compounds. It is also detrimental to
platinum crucibles, and especially to their covers, to expose them directly
to an intense charcoal fire, since the action of the ash, under such circum-
stances, gives readily rise to the formation of silicide of platinum, which
renders the vessel brittle. It is always advisable to support the platinum
crucible in which a process of ignition or fusion is to be conducted, on a
triangle of platinum wire. Soiled platinum crucibles are cleaned by
fusing in them bisulphate of potassa, and boiling afterwards with water.
We have still to speak here of another operation which bears some
affinity to fusion.
12.
11. DEFLAGRATION.
We understand by the term " deflagration," in a more general sense,
every process of decomposition attended with noise or detonation (the
cause of the decomposition is a matter of perfect indifference as regards
the application of the term in this sense).
We use the same term, however, in a more restricted sense, to desig-
nate 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 chlo-
rate), and connect with it the idea of a sudden and violent combustion
attended with vivid incandescence and noise or detonation. Deflagra-
tion is resorted to either to produce the desired oxide thus tersulphide
of arsenic is deflagrated with nitrate of potassa to obtain arsenate of
potassa ; or it is applied as a means to prove the presence or absence of
a certain substance thus salts are tested for nitric or chloric acid, by
fusing them in conjunction with cyanide of potassium, and observing
whether this process will cause deflagration or not, &c.
To attain the former object, the perfectly dry mixture of the substance
under examination arid of the deflagrating agent is projected in small
portions into a red-hot crucible. Experiments of the latter description
are invariably made with very minute quantities ; the process is, in such
cases, best conducted on a piece of thin platinum foil, or in a small
spoon.
13.
12. THE USE OF THE BLOWPIPE.
This operation belongs exclusively to the province of analytical che-
mistry, and is of paramount importance in many analytical processes.
We have to examine here, 1, the apparatus ; 2, the mode of its applica-
tion ; and, 3, the results of the operation.
The blowpipe (Fig. 6) is a small instrument, usually made of brass or
German silver. It was originally used by metallurgists for the purpose
of soldering, whence it derived the name of " soldering-pipe" (Lothrohr)
by which the Germans designate it. It consists of three distinct parts j
13.]
THE USE OF THE BLOWPIPE.
13
Figs. 6, 7.
viz. 1st, a tube (a 6), fitted, for greater convenience, with a horn or ivory
mouthpiece, through which air is blown from the mouth ; 2nd, a small
cylindrical vessel (c d), into which a b is screwed air-
tight, and which serves as an air-chamber, and to
retain the moisture of the air blown into the tube ;
and, 3rd, a smaller tube (f g), also fitted into the
vessel (c d). This small tube, which forms a right
angle with the larger one, is fitted at its aperture
either simply with a finely perforated platinum
plate, or more conveniently with a finely per-
forated platinum cap (h) screwed in air-tight. The
construction of the cap is shown in Fig. 7. It is,
indeed, a little dearer than a simple plate, but it is
also much more durable. Whenever the opening of
the cap happens to be stopped up, the obstruction
may be removed by heating the cap to redness
before the blowpipe.
The proper length of the blowpipe depends upon
the distance to which the operator can see with dis-
tinctness ; it is usually from twenty to twenty-five
centimetres. The form of the mouthpieces varies.
Some chemists like them of a shape to be encircled
by the lips ; others prefer the form of a trumpet
mouthpiece, which is only pressed against the lips.
The latter require less exertion on the part of the operator, and are
accordingly generally chosen by those who have 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. The flame of a candle
(and equally so that of gas or of an oil lamp), burning under ordinary
circumstances, is seen to consist of three distinct parts, as shown in
Fig. 8, viz., 1st, a dark nucleus in the centre (a) ; 2nd, a luminous cone
surrounding this nucleus (e f g) ; and, 3rd, a feebly
luminous mantle encircling the whole flame (b c d).
The dark nucleus is formed by the gases which the
heat evolves from the wax or fat, and which cannot
burn here 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
carbides of hydrogen evolved which burns, whilst the
carbon separates in a state of intense ignition, which
imparts to the flame the luminous appearance observed
in this part. In the outer coat, the access of air is no
longer limited, and all the gases not yet burned are
consumed here. This part of the flame is the hottest \
oxidizable bodies oxidize therefore with the greatest
possible rapidity when placed in it, since all the condi-
tions of oxidation are here united, viz. high tempera-
ture, and an unlimited supply of oxygen. This
outer part of the flame is therefore called the oxidizing 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
Fig. 8.
14 THE USE OF THE BLOWPIPE. [13.
oxygen being withdrawn from them by the carbon and the still uncon-
sumed carbide of hydrogen present in this sphere. The luminous part
of the flame is therefore called the reducing flame.
Now the effect of blowing a fine current of air across a flame, is first
to alter the shape of the latter, which, from tending upward, is now
driven sideways in the direction of the blast, and 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 of the heat of the flame, and the former
a concentration of that heat within narrower limits, it is easy to under-
stand the exceedingly energetic action of the blowpipe flame. The
way of holding the blowpipe and the nature of the current, will always
depend upon the precise object in view, viz., whether the operator wants
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
tube, terminating in a flat top with a somewhat slantingly downward-
turned slit 1 centimetre long and 1 1 to 2 millimetres wide ; as with the use
of gas the operator is enabled to control and regulate not only the blow-
pipe flame, but the gas stream also. The task of keeping the blowpipe
steadily in the proper position may be greatly facilitated by firmly resting
that instrument upon some moveable metallic support, such as, for
instance, the ring of Bunseris gas lamp for supporting dishes, &c.
Fig. 9 shows the flame for reducing, Fig. 10 the flame for oxidizing.
The luminous parts are shaded.
Fig. 9.
The reducing flame is produced by keeping the jet of the blowpipe
just on the border of a tolerably strong gas flame, and driving a moderate
blast across it. The resulting mixture of the air with the gas is only im-
perfect, 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 pro-
duce the oxidizing flame, the gas is lowered, the jet of the blowpipe pushed
a little further into the flame, and the strength of the current some-
what increased. This 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
13.] THE USE OF THE BLOWPIPE. 15
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 broad wick of proper thickness may be used instead of coal-gas ; a
thick wax candle also will do. For an oxidizing flame, a small spirit-
lamp will in most cases answer the purpose.
Fig. 10.
The current is produced with the cheek muscles alone, and not with the
lungs. The way of doing this may be easily acquired by practising for
some time to breathe calmly with puffed-up cheeks, and with the blow-
pipe between the lips ; with a little patience the student will soon be
able to produce an even and uninterrupted current.
The supports on which substances are exposed to the blowpipe flame
are generally either wood, charcoal, or platinum wire or foil.
Charcoal supports are used principally in the reduction of metallic
oxides, &c., or in trying the fusibility of bodies. The substances to be
operated upon are put into small conical 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 fumes are
re-oxidized, and the oxide formed is deposited around the portion of
matter upon the support. Such deposits are called incrustations. Many
of these exhibit characteristic colors leading to the detection of the
metals. Thoroughly-burnt pieces of charcoal only should be selected
for supports in blowpipe experiments, as imperfectly-burnt pieces are apt
to spirt and throw off the matter placed on them. The charcoal of the
wood of the pine, linden, or willow is greatly preferable for supports to
that of harder and denser woods. Smooth pieces ought to be selected
for supports, as knotty pieces are apt to spirt when heated, and throw
off the matter placed on them. The most convenient way is to saw the
charcoal of well-seasoned and straight-split pinewood into parallelo-
pipedic pieces, and to blow or brush off the dust ; they may then be
handled without fear of soiling the hands. Those sides alone are used
on which the annual rings are visible as circles or segments, as on the
other sides the fused matters are apt to spread over the surface of the
charcoal (Berzeliua).
The properties which make charcoal so valuable as a material for sup-
ports in blowpipe experiments are 1st, its infusibility ; 2nd, its low
conducting power for heat, which admits of substances being heated
more strongly upon a charcoal than upon any other support ; 3rd, its
porosity, which makes it imbibe readily fusible substances, such as
16 APPARATUS AND UTENSILS. [ 14.
borax, carbonate of soda, &c., whilst infusible bodies remain on the sur-
face ; 4th, its power of reducing oxides, which greatly contributes to
effecting the reduction of oxides in the inner blowpipe flame.
We use platinum wire, and occasionally also platinum foil, in all
oxidizing processes before the blowpipe, and also when fusing substances
with fluxes, with a view to try their solubility in them, and to watch
the phenomena attending the solution, and mark the color of the bead.
The wire, which should be about the thickness of lute-strings, is cut
into lengths of 8 centimetres, and each length twisted at both ends into
a small loop (Fig. 11).
O O
Fig. 11.
When required for use, the loop is moistened with a drop of water,
then dipped into the flux, and the portion adhering exposed to the flame
of a gas- or spirit-lamp. The bead produced, which continues to adhere
to the loop, is let cool, then moistened again, a small portion of the
substance to be examined added to it, and the loop finally exposed,
according to circumstances, to the inner or to the outer blowpipe flame.
What renders the application of the blowpipe particularly useful in
chemical experiments is the great expedition with which the intended
results are attained. These results are of a twofold kind, viz., either
they afford us simply an insight into the general properties of the exa-
mined body, and enable us accordingly only to determine the class to
which it belongs, i. e., whether it is fixed, volatile, fusible, &c. ; or the
phenomena which we observe enable us at once to recognise the par-
ticular body which we have before us. We shall have occasion to de-
scribe these phenomena when treating of the deportment of the different
substances with reagents.
APPENDIX TO SECTION I.
H.
APPARATUS AND UTENSILS.
As many students of chemical analysis might find some difficulty in
the selection of the proper apparatus, &c., I append here a list of the
articles which are required for the performance of simple experiments
and investigations, together with instructions to guide the student in the
purchase or making of them.
1. A BERZELIUS SPIRIT-LAMP, with suitable stand. The part en-
closing the wick and the vessel containing the spirit of wine must be in
separate pieces, connected together by means of a narrow tube j other-
wise most inconvenient explosions are apt to occur on lighting the
lamp. The chimney must not be too narrow. The stopper on the
mouth through which the spirit of wine is poured in must not fit air-
tight. The stand must be fitted with proper brackets, and also with a
moveable brass ring to support dishes and flasks in processes of
ebullition, and a ring of moderately stout iron wire to support
APPARATUS AND UTENSILS.
17
the triangle for holding the crucibles in the processes of ignition and
fusion.
Of the various forms of lamps to be had, the one shown in Fig. I 2 is
the most suitable and elegant. Fig. 13 shows a triangle of pfatinum
Fig. 13.
Fig. 12.
Fig. 14.
wire fixed within an iron wire triangle ; this is the most suitable construc-
tion for supporting the crucible in processes of ignition. Glass vessels,
more particularly beakers, which it is in-
tended to heat over the lamp, are most
conveniently rested on a circular piece
of gauze made of fine iron wire such as is
iised in the making of sieves of medium
fineness.
2. A GLASS SPIRIT LAMP, with ground
glass cap and brass wick-holder. (Fig. 14.)
In towns lighted by gas, spirit lamps
are now almost entirely superseded by
gas larnps. Of the many gas lamps pro-
posed, Bunseris, as shown in its simplest
form in Fig. 15, is the most convenient.
a b is a foot of cast-iron measuring 7
centimetres in diameter. In the centre
of this is fixed a square brass box, c d,
which slightly slants towards the top ; the
sides of this box are 25 millimetres high
and 1 6 millimetres wide ; it has a cylin-
dric cavity 12 millimetres deep and 10
millimetres in diameter. Each side of the
box has, 4 millimetres from the upper rim, a
circular aperture of 8 millimetres diameter,
leading to the inner cavity. One of the
sides has fitted into it, about 1 millimetre Fig. 15.
18
APPARATUS AND UTENSILS.
below the circular aperture, a tube to which is attached some vulcanized
india-rubber, which serves to convey the gas to the apparatus. This tube
is turned as shown in Fig. 15 ; it has a bore of 4 millimetres diameter.
The gas conveyed into it through the india-rubber re-issues from a
tube placed in the centre of the cavity of the box. This tube, which is
4 millimetres thick at the top, thicker at the lower end, projects 3
millimetres above the rim of the box ; the gas issues from a narrow
opening which appears formed of 3 radii of a circle, two of them
forming an angle of 120 with one another. The length of each radius
is 1 millimetre, the opening | millimetre wide ; ef is a brass tube
75 millimetres long, open at both ends, and having an inner diameter of
9 millimetres ; the screw at the lower end of this tube fits in to a nut
in the upper part of the cavity of the box. With this tube screwed in,
the lamp is completed. On opening the stop-cock, the gas rushes from the
opening into the tube ef, when it mixes with the air coming in through
the circular apertures (c). When this mixture is kindled at f t it
burns with a straight, bluish flame, entirely free from soot, which may
be regulated at will by opening the stop-cock more or less ; a par-
tial opening of the cock suffices to give a flame fully answering the
purpose of the common simple spirit lamp ; whilst, with the full stream
of gas turned on, the flame, which will now rise up to 2 decimetres in
height, burning with a roaring noise, affords a most excellent substitute
for the Berzelius lamp. Flasks, &c., which it is intended to heat over
the gas lamp, are most con-
veniently supported on wire
gauze. If it is wished to use the
gas lamp for blowpipe opera-
tions, the tube g h must be in-
serted into e f ; this tube
terminates in a flattened top
slanting at an angle of 68,
to the axis, and having an
opening in it 1 centimetre .
long and 1J to 2 millimetres
wide j its insertion into e f
serves to close up the air-
apertures in the box, and
pure gas, burning with a
luminous flame, issues ac-
cordingly now from the top
of the tube. Fig. 16 shows
the apparatus complete, fixed
in the forked iron stand \
this arrangement permits the
lamp being moved backward
and forward between the
prongs of the fork, and up
and down the pillar of the
stand. The moveable ring on
the same pillar serves to sup-
port the object to be ope-
Fig. 16.
rated upon. The 6 radii round the tube of the lamp serve to support
a porcelain plate used in quantitative analyses.
APPARATUS AND UTENSILS.
19
3. A BLOWPIPE (see 13).
4. A PLATINUM CRUCIBLE which will contain about a quarter of an ounce
of water, with a cover of the form of a shallow dish ; it must not be too
deep in proportion to its breadth.
5. PLATINUM FOIL, as smooth and clean as possible, and not very thin :
length about 40 millimetres; width about 25 millimetres.
6. PLATINUM WIRE (see 13) ; three or four wires are amply sufficient.
They are kept most conveniently in a glass filled with water, most of
the beads being dissolved by that fluid when left in contact with it for
some time ; the wires may thus be always kept clean.
7. A STAND WITH TWELVE TEST TUBES 16 to 18 centimetres is about
the proper length of the tubes, from 1 to 2 centimetres the proper
width. The pegs on the
upper shelf serve for
the clean tubes, which
may thus be always kept
dry and ready for use.
The tubes must be made
of thin white glass, and
so well annealed that
they do not crack even
though boiling water be
poured into them. The
rim must be quite round,
and slightly turned over ;
it ought not to have a
lip, as this is useless, sim-
ply preventing the tube
being closely stopped Fig. 17.
with the finger, and also
shaking the contents.
8. SEVERAL BEAKER GLASSES AND SMALL RETORTS of thin, well
annealed glass.
9. SEVERAL PORCELAIN EVAPORATING DISHES, AND A VARIETY OF
SMALL PORCELAIN CRUCIBLES. Those of the royal manufacture of Berlin
are unexceptionable, both in shape and durability.
10. SEVERAL GLASS FUNNELS of various sizes. They must be inclined
at an angle of 60, and merge into the neck at a definite angle.
11. A WASHING BOTTLE of a capacity of from 300 to 400 cubic centi-
metres (see 6).
12. SEVERAL GLASS RODS AND GLASS TUBES. The latter are bent,
drawn out, &c., over a Berzelius spirit lamp ; the former are rounded at
the ends before the blowpipe.
1 3. A selection of WATCH-GLASSES.
14. A small AGATE MORTAR.
15. A pair of small STEEL or BRASS PINCERS, about four or five inches
long.
16. A WOODEN FILTERING STAND (see 5).
17. A TRIPOD of thin iron, to support the dishes, &c., which it is
intended to heat over the small spirit or gas lamp.
KE AGENTS.
[15,
SECTION II.
REAGENTS.
A VARIETY of phenomena may manifest themselves upon the decom-
position or combination of bodies. In some cases liquids change their
color, in others precipitates are formed ; sometimes effervescence takes
place, and sometimes deflagration, &c. Now, if these phenomena are very
striking, and attendant 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 precipitate 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 their application we
make a distinction between general and special reagents. By general
reagents we understand those which serve to determine the class or
group to which a substance belongs ; and by special reagents those which
serve to detect and determine 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 a valid objection to
this classification, which, in fact, 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 under examination belongs,
or to determine the latter individually.
Now whilst the usefulness of general reagents depends principally
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 upon their being sensitive. We call a reagent
characteristic, if the alteration produced 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, protochloride
of tin for mercury, because the phenomena produced by these reagents
viz., the separation of metallic copper and of globules of mercury, admit
of no mistake. We call a reagent sensitive or delicate, if its action is
distinctly perceptible, even though a very minute quantity only of the
substance tested for be present ; such is, for instance, the action of
starch upon iodine.
Very many reagents are both characteristic and delicate ; thus, for
instance, terchloride of gold for protoxide of tin ; ferrocyanide of
potassium for sesquioxide of iron and oxide of copper, &c.
I need hardly mention that, as a general rule, reagents must be che-
mically pure i.e. } they must consist purely and simply of their essential
15.] REAGENTS. 21
constituents, and must contain no admixture of foreign substances. We
must therefore make it an invariable rule to test the purity of our reagents
before we use them, no matter whether they be articles of our own pro-
duction or purchased. Although the necessity of this is fully admitted
on all hands, yet we find that in practice it is too often neglected ;
thus it is by no means uncommon to see alumina entered among the sub-
stances detected in an analysis, simply because the solution of potassa
used as one of the reagents happened to contain that earth ; or iron,
because the chloride of ammonium used was not free from that metal.
TLe directions given in this section 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 ad-
mixture.
One of the most common sources of error in qualitative analysis pro-
ceeds from missing the proper measure the right quantity in the appli-
cation of reagents. Such terms as " addition in excess" " supersaturation"
&G., often induce novices to suppose that they cannot add too much of
the reagent, and thus some will Jill a test tube with acid, simply to super-
saturate a few drops of an alkaline fluid, whereas every drop of acid
added, after the neutralization point has once 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, when added
in insufficient quantity, often produces phenomena quite different from
those which will appear if the same reagent be added in excess : e. g., a
solution of chloride of mercury yields a white precipitate, if tested with a
small quantity of hydrosulphuric acid ; but if treated with the same
reagent in excess, the precipitate is black. Experience has, however,
proved that the most common mistake beginners make, is to add the
reagents too copiously. The reason why this over-addition must impair
the accuracy of the results, is obvious ; we need simply bear in mind
that the changes effected by reagents are perceptible within certain limits
only, and that therefore they may be the more readily overlooked the
nearer we approach these limits by diluting the fluid.
No special and definite rules can be given for avoiding this source of
error ; a general rule may, however, 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 : let the student always reflect, before the addition
of a reagent, for what purpose he applies it, and what are the phenomena
he intends to produce.
We divide reagents into two classes, according to whether the state
of fluidity which is indispensable for the manifestation of the action of
reagents upon the various bodies, is brought about by the application of
heat, or by means of liquid solvents ; we have consequently, 1, Reagents
in the humid way ; and 2, -Reagents in the dry way. For greater clear-
ness we subdivide these two principal classes as follows :
A. REAGENTS IN THE HUMID WAY.
I. SIMPLE SOLVENTS.
II. ACIDS (and HALOGENS).
a. Oxygen acids.
b. Hydrogen acids and halogens.
c. Sulphur acids.
SIMPLE SOLVENTS. [ 16.
III. BASES (and METALS).
a. Oxygen bases.
b. Sulphur bases.
IV. SALTS.
a. Of the alkalies.
b. Of the alkaline earths.
c. Of the oxides of the heavy metals.
V. COLORING MATTERS AND INDIFFERENT VEGETABLE SUBSTANCES.
B. REAGENTS IN THE DRY WAY.
I. FLUXES.
II. BLOWPIPE REAGENTS.
A. REAGENTS IN THE HUMID WAY.
I. SIMPLE SOLVENTS.
Simple solvents are fluids which do not enter into chemical combina-
tion with the bodies dissolved in them j they will accordingly dissolve
any quantity of matter up to a certain limit, which is called the point
of saturation, and is in a measure dependent upon the temperature of
the solvent. The essential and characteristic properties of the dissolved
substances (taste, reaction, color, &c.) are not destroyed by the solvent.
(See 2.)
16-
1. WATER (H 0).
Preparation. Pure water is obtained by distilling spring water from
a copper still, with head and condenser made of pure tin, or from a
glass retort ; which latter apparatus, however, is less suitable for the
purpose. 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 carbonate of ammonia, the portions passing over
first must be thrown away. In the larger chemical, and in most phar-
maceutical laboratories, the distilled water required is obtained from the
steam apparatus which serves for drying, heating, boiling, &c. Kaiii
water collected in the open air may in many cases be substituted for
distilled water.
Tests. Pure distilled water must be colorless, inodorous, and taste-
less, and must leave no residue upon evaporation in a platinum vessel.
Sulphide of ammonium must not alter it (copper, lead, iron) ; its
transparency must not be in the least impaired by basic acetate of
lead (carbonic acid, carbonate of ammonia), nor, even after long standing,
by oxalate of ammonia (lime), chloride of barium (sulphates), or nitrate
of silver (metallic chlorides).
Uses. We use water* principally as a, simple solvent for a great
variety of substances ; the most convenient way of using it is with the
washing bottle (see 6, Fig. 3), by which means a large or fine stream
may be obtained. It serves also to effect the conversion of several
neutral metallic salts (more particularly terchloride of antimony and the
salts of bismuth) into soluble acid, and insoluble basic compounds.
* In analytical experiments we use only distilled water ; whenever, therefore, the term
" water" occurs in the present work, distilled water is meant.
1719.] ALCOHOL. 23
17.
2. ALCOHOL (C 4 H 6 O 2 = Ae 0, H 0).
Preparation. Two sorts of alcohol are used in chemical analyses :
viz., 1st, spirit of wine of 0'83 or 0'84 spec. gr. = 91 to 88 per cent, by
volume (spiritus vini rectificatissimus of the shops) ; and 2nd, absolute
alcohol. The latter may be prepared by distilling the former from fused
chloride of calcium, or by adding to it perfectly dry potassa, or anhydrous
sulphate of copper, shaking the mixture, decanting the fluid, and re-
distilling it.
Tests. Pure alcohol must completely volatilize, and ought not to leave
the least smell of fusel oil, when rubbed between the hands ; nor should
it redden litmus paper. When kindled, it must burn with a faint
bluish, barely perceptible flame.
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 chloride of stron-
tium from chloride o$ barium ; (b] to precipitate from aqueous solutions
many substances which are insoluble in dilute alcohol, e.g., gypsum, malate
of lime ; (c) to produce various kinds of ether, e.g., acetic ether, which is
characterized by its peculiar and agreeable smell ; (d) to reduce, mostly
with the co-operation of an acid, certain peroxides and metallic acids, e.g.,
binoxide of lead, chromic acid, &c. ; (e) to detect certain substances which
impart a characteristic tint to its flame, especially boracic acid, strontia,
potassa, soda, and lithia.
18-
3. ETHER (C 4 H 5 = Ae 0).
Ether finds but very limited application in the analysis of inorganic
bodies. It serves, indeed, almost exclusively to detect and isolate
bromine, and for this purpose the officinal ether of commerce is suffi-
ciently pure and strong.
II. ACIDS AND HALOGENS.
19.
The acids at least those of more strongly pronounced character are
soluble in water. The solutions taste acid, and redden litmus paper.
Acids are divided into oxygen acids, sulphur acids, and hydrogen acids.
The oxygen acids produced generally by the combination of a non-
metallic element with oxygen, combine with water in definite propor-
tions to hydrated acids. It is with these hydrates that we have
usually to do in analytical processes ; they are commonly designated by
the name of " free acids," as the accession of the water does not destroy
the acid properties. In the action of hydrated acids upon oxides of
metals, the oxide takes the place of the water of hydration, and an
oxygen salt is formed (H O, S O 3 + K O = K O, S O 3 + H O). Where
these salts are the product of the combination of an acid with a strong
base, their reaction (supposing the combining acid also to be a strong
acid) is neutral ; the salts formed with weaker bases, for instance, with
the oxide of a heavy metal, generally show acid reaction, but are never-
theless called neutral salts, if the oxygen of the base bear the same pro-
portion to that of the acid in which it is found in the distinctly neutral
24 SULPHURIC ACID. [ 20.
salts of the same acid, or, in other terms, if it corresponds with the satu-
ration capacity of the acid. Sulphate of potassa (K O, S O 3 ) has a neutral
reaction, whilst the reaction of sulphate of copper (Cu O, S O 3 ) is acid ;
yet the latter is nevertheless called neutral sulphate of copper, because
the oxygen of the oxide of copper in it bears a proportion of 1 : 3
to that of the sulphuric acid, which is the same proportion as the
oxygen of the potassa bears to that of the sulphuric acid in the con-
fessedly neutral sulphate of potassa.
The hydrogen acids are formed by the combination of the salt radicals
with hydrogen. Most of these possess the characteristic properties of
acids in a high degree. They neutralize oxygen bases with formation of
haloid salts and water, H Cl and Na O = Na Cl and H O = 3 H 01 and
Fe 2 O 3 = Fe 2 C1 3 and 3 H O. The haloid salts produced by the action of
powerful hydrogen acids upon strong bases, have a neutral reaction ;
whilst the solution of these haloid salts show acid reactions, which have
been produced by the action of powerful hydrogen acid upon weak
bases (such as the oxides of the heavy metals).
The sulphur acids are more frequently the result of the combination
of metallic than of non-metallic elements with sulphur ; they combine
with sulphur bases to sulphur salts, H S + K S - K S, H S, - Sb S 5 +
3 Na S = 3 Na S, Sb S 6 . The sulphur acids being weak acids, the
soluble sulphur salts have all of them alkaline reaction.
a. OXYGEN ACIDS.
20.
1. SULPHURIC ACID (H 0, S 0,).
TTT * **/
We use
a. Concentrated sulphuric acid of commerce, generally known in
Germany as English sulphuric acid.
b. Concentrated pure sulphuric acid.
To be prepared as follows : heat sulphuric acid of commerce in a
porcelain dish to about 230 F., and add, whilst stirring, small por-
tions of dry oxalic acid (Lowe), or of dry sulphate of ammonia (Pelouze),
until a portion of the acid taken out and cooled no longer turns red
when solution of sulphate of protoxide of iron is poured upon it -a sign
that every trace of hyponitric acid and nitric acid is gone. Add now (in
the open air) pure dry chloride of sodium (about J per cent.) in small
portions, with frequent stirring, and heat until the hydrochloric acid is
completely expelled. All the arsenic originally present in the sulphuric
acid is carried off with the fumes of the hydrochloric acid (Lowe,
A. Buchner). The acid so purified is fit for nearly all the purposes of
chemical analysis ; if it is wished, however, to free it also from non-volatile
substances, it may be distilled from a luted non-tubulated retort resting
on a reversed crucible cover, and heated directly over charcoal. The
lowest part of the retort, where the sulphate of lead, &c., is deposited,
being thus in some measure protected by the interposed cover from
the direct action of the fire, gets less strongly heated than the sides,
which prevents the inconvenient and dangerous bumping of the liquid in
the retort (compare GrahamOtto, ii. 1, p. 275). The neck of the
retort must reach so far into the receiver that the acid distillino- over
drops directly into the body. Refrigeration of the receiver by means of
21.] NITEIC ACID. 25
water is unnecessary and even dangerous. To prevent the flask coming
into direct contact with the hot neck of the retort, some asbestos in
long fibres is wrapt round that part of the neck where such contact
might be apprehended.
c. Dilute sulphuric acid. This is prepared by adding to 5 parts of water
in a leaden, or porcelain dish, gradually, and whilst stirring, 1 part of
concentrated sulphuric acid. The sulphate of lead which separates is
allowed to subside, and the clear fluid finally decanted from the precipitate.
Tests. Pure sulphuric acid must be colorless when colorless solution
of sulphate of protoxide of iron is poured upon it in a test tube, no red
tint must mark the line of contact of the two fluids (nitric acid, hypo-
nitric acid) ; when diluted with twenty parts of water, it must not im-
part a blue tint to a solution of iodide of potassium mixed with starch
paste (hyponitric acid).
When 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 four or
five parts of spirit of wine (oxide of lead, sesquioxide of iron, lime).
The presence of small quantities of lead is detected most easily by adding
some hydrochloric acid to the sulphuric acid in a test tube. If the
point of contact is marked by turbidity (chloride of lead), lead is present.
(LowenthaL).
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 of phosphoric, boracic, hydrochloric,
nitric, and acetic acids. It serves also for the liberation of iodine from
metallic iodides. In this latter process it oxidizes the metal at the ex-
pense of its own oxygen, and is accordingly reduced to the state of sul-
phurous acid. Several substances which cannot exist in an anhydrous
state (e. g., oxalic acid), are decomposed when brought into contact with
concentrated sulphuric acid ; this decomposition is owing to the great
affinity which sulphuric acid possesses for water. The nature of the de-
composed body may in such cases be inferred from the liberated products
of the decomposition. Sulphuric acid is also frequently used for the
evolution of certain gases, more particularly of hydrogen, and hydro-
sulphuric acid. It serves also as a special reagent for the detection and
precipitation of baryta, strontia, and lead. What kind of sulphuric
acid is to be used, whether the pure, or the purified acid, or the ordinary
acid of commerce, whether concentrated or dilute, depends upon what the
circumstances in each case may require. It will, however, be found
that the necessary directions on this point are generally given in the
present work.
21.
2. NITEIC ACID (H O, N 5 ).
Preparation. a. Heat crude nitric acid of commerce, as free as pos-
sible from chlorine, and of a specific gravity of at least 1'31*, in a glass
retort, to boiling, with addition of some nitrate of potassa : let the dis-
tillate run into a receiver kept cool, and try from time to time whether
it still continues to precipitate or trouble solution of nitrate of silver.
* A weaker acid will not suit.
26 ACETIC ACID. [ 22.
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 of the diluted acid is 1 -2.
b. Dilute crude nitric acid of commerce of about 1 '38 specific gravity,
with two-fifths of its weight of water ; add solution of nitrate of silver as
long as a precipitate of chloride of silver continues to form ; let the pre-
cipitate subside, decant the perfectly clear supernatant acid into a tubu-
lated retort ; add some nitrate of potassa, free from chlorine, and distil
until only a small quantity remains, taking care to attend to the proper
cooling of the fumes distilling 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. Additions of solution of nitrate of
silver, or of nitrate of baryta, must not cause the slightest turbidity
in it. It is advisable to dilute the acid with water before adding
the reagents, as otherwise nitrates will precipitate.
Uses. Nitric acid serves as a chemical solvent for metals, oxides,
sulphides, oxygen salts, &c. With metals, and sulphides of metals, the
acid oxidizes the metal present first, at the expense of part of its own
oxygen, and then dissolves the oxide, forming a nitrate. Most oxides
are dissolved by nitric acid at once as nitrates ; and so are also most of
the insoluble salts with weaker acids, the latter being expelled in the pro-
cess by the nitric acid. Nitric acid dissolves also salts with soluble, non-
volatile acids, as e. g. phosphate of lime, with which it forms nitrate of
lime and acid phosphate of lime. Nitric acid is used also as an oxidizing
agent: for instance, to convert protoxide of iron into sesquioxide,
protoxide of tin into binoxide, &c.
22.
3. ACETIC ACID (H O, C 4 H 3 3 = H 0, A).
A highly concentrated acetic acid is not required in qualitative
analytical processes ; the common acetic acid of commerce, which contains
25 per cent, of anhydrous acid, and has a specific gravity of 1'04,
answers the purpose.
Tests. Pure acetic acid must leave no residue upon evaporation, and
after saturation with carbonate of soda emit no empyreumatic odor.
Hydrosulphuric acid, solution of nitrate of silver, and solution of nitrate
of baryta must not impair the transparency of the dilute acid, nor must
sulphide of ammonium, after neutralization of the acid by oxide of
ammonium. Solution of indigo must not lose its color, when heated
with the acid.
Tf the acid is not pure, add some acetate of soda and redistil from a
glass retort, not quite to dryness ; if it contains sulphurous acid (in
which case hydrosulphuric acid will produce a white turbidity in it),
digest it first with some binoxide of lead or finely pulverized binoxide
of manganese, and then distil with acetate of soda,
Uses. Acetic acid possesses a greater solvent power for some sub-
stances than for others ; it is used, therefore, to distinguish the former
from the latter ; thus it serves, for instance, to distinguish oxalate of
lime from phosphate of lime. Acetic acid is occasionally used also to
acidulate fluids where it is wished to avoid the employment of mineral
acids.
23, 24.] TARTAKIC ACID. 27
23.
4. TARTAKIC ACID (2 H O, C s H 4 10 , - 2 H 0, T).
The tartaric acid of commerce is sufficiently pure for the purposes of
chemical analysis. It is kept best in powder, as its solution suffers de-
composition after a time, a white film forming upon its surface. For
use, it is dissolved in a little water with the aid of heat.
Uses. The addition of tartaric acid to solutions of sesquioxide of iron,
protoxide of manganese, and various other oxides of metals, prevents the
usual precipitation of these metals by an alkali ; this non-precipitation
is owing to the formation of double tartrates, which are not decomposed
by alkalies.
Tartaric acid may therefore be employed to effect the separation of
these metals from others, the precipitation of which it does not prevent.
Tartaric acid forms a difficultly soluble salt with potassa, but not so
with soda; it is, therefore, one of our best reagents to distinguish between
the two alkalies.
b. HYDKOGEN ACIDS AND HALOGENS.
24.
1. HYDROCHLORIC ACID (H 01).
Preparation. Pour a cooled mixture of seven parts of concentrated sul-
phuric acid and two parts of water over four parts of chloride of sodium 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 double limbed tube, into a flask containing six parts of water, and
take care to keep this vessel constantly cool. To prevent the gas from
receding, the tube ought only to dip about one line 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. If you wish to ensure the absolute purity of the acid, and its
perfect freedom from every trace of arsenic and chlorine, you must take
care to free the sulphuric acid, intended to be used in the process, from
arsenic and the oxygen compounds of nitrogen, according to the direc-
tions of 20. A pure acid may also be prepared cheaply from the crude
hydrochloric acid of commerce, by diluting the latter to a specific gravity
of 1-12, and distilling the fluid, with addition of some . chloride of
sodium. If the crude acid contains chlorine, this should be removed first
by the cautious addition of solution of sulphurous acid, before proceed-
ing to the distillation ; if, on the other hand, it contains sulphurous
acid, this is removed in the same way by the cautious addition of some
chlorine water.
Tests. Hydrochloric acid intended for the purposes of chemical
analysis must be perfectly colorless, and leave no residue upon evapo-
ration. It must not impart a blue tint to a solution of iodide of potas-
sium mixed with starch paste (chlorine), nor discolor a fluid made
faintly blue with iodide of starch (sulphurous acid). Chloride of barium v
ought not to produce a precipitate in the highly diluted acid (sulphuric
acid). Hydrosulphtiric acid must leave it unaltered. Sulphocyanide of
potassium must not impart the least red tint to the diluted acid.
28 CHLORINE AND CHLORINE WATER. [25.
tfses. Hydrochloric acid serves as a solvent for a great many sub-
stances. It dissolves many metals and sulphides of metals, forming chlo-
rides, with evolution of hydrogen or of hydrosulphuric acid. It dissolves
lower and higher oxides in the form of chlorides, the solution being, in
the case of the higher oxides, mostly attended with liberation of chlorine.
Salts with insoluble or volatile acids are also converted by hydrochloric
acid into chlorides, with separation of the original acid ; thus carbonate
of lime is converted into chloride of calcium, with liberation of carbonic
acid. Hydrochloric acid dissolves salts with non-volatile and soluble
acids, apparently without decomposing them (e. g., phosphate of lime) ;
but the fact is that, in cases of this kind, a metallic chloride and a soluble
acid salt of the acid of the dissolved compound are formed ; thus, for
instance, in the case of phosphate of lime, chloride of calcium and acid
phosphate of lime are formed. With salts of acids forming no soluble
acid compound with the base present, hydrochloric acid forms metallic
chlorides, the liberated acids remaining free in solution (borate of lime).
Hydrochloric acid is also applied as a special reagent for the detection
and separation of oxide of silver, suboxide of mercury, and lead (see
below) ; and likewise for the detection of free ammonia, with which it
produces in the air dense white fumes of chloride of ammonium.
25.
2. CHLORINE (Cl) AND CHLORINE WATER.
Preparation. Mix 18 parts of finely ground common salt with 15
parts of finely pulverized good bin oxide of manganese ; put the mixture
in a flask, pour a completely cooled mixture of 45 parts of concentrated
sulphuric acid and 21 parts of water upon it, and shake the flask : a uni-
form and continuous evolution of chlorine gas will soon begin, which,
when slackening, may be easily increased again by the application of
a gentle heat. This method of Wiggers is excellent, and can be highly
recommended. 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. The chlorine water
must be kept in a cellar, and carefully protected from the action of
light ; since, if this precaution is neglected, it speedily suffers complete
decomposition, being 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 from the influence of light by a case of
pasteboard. Chlorine water which has lost its strong peculiar odor is
unfit for use.
Uses. Chlorine has a greater affinity than iodine and bromine for
metals and for hydrogen. Chlorine water is therefore an efficient agent
to effect the expulsion of iodine and bromine from their compounds.
Chlorine serves, moreover, to convert sulphurous acid into sulphuric
acid, protoxide of iron into sesquioxide, &c. ; and also to effect the de-
struction of organic substances, in presence of water, as it withdraws
hydrogen from the latter, enabling thus the liberated oxygen to combine
with the vegetable matters and to effect their decomposition. For this
latter purpose it is most advisable to evolve the chlorine in the fluid
which contains the organic substances ; this is effected by adding hydro-
chloric acid to the fluid, heating the mixture to boiling, and then adding
chlorate of potassa. This gives rise to the formation of chloride of potas-
26, 27.] KITKO-HYDROCHLORIC ACID. 29
slum, water, free chlorine, and bichlorate of chlorous acid, which acts in
a similar manner to chlorine.
26.
3. NITRO-HYDROCHLORIC ACID. Aqua regia.
Preparation. Mix one part of pure nitric acid with from three to
four parts of pure hydrochloric acid.
Nitric acid and hydrochloric acid decompose each other, the decom-
position resulting, in most cases, as Guy-Lussac has shown, in the
formation of two compounds which are gaseous at the ordinary tem-
perature, N O 2 C1 2 and N O 2 Cl, and of free chlorine and water. If
one equivalent of N 5 is used to three equivalents of Cl H, it may be
assumed that only chloro-hyponitric acid (N" O 2 Cl,), chlorine and water,
are formed (N 0, + 3 H Cl = N O 2 C1 2 + 01 + 3 H O).
This decomposition occurs as soon as the fluid is saturated with the
gas ; but it recommences the instant this state of saturation is disturbed
by the application of heat or by decomposition of the acid. The pre-
sence of the free chlorine, and also, but in a very subordinate degree,
that of the acids named, makes aqua regia our most powerful solvent for
metals (with the exception of those which form insoluble compounds
with chlorine). Nitro-hyclrochloric acid serves principally to effect the
solution of gold and platinum, which metals are insoluble both in
hydrochloric and in nitric acid ; and also to decompose various metallic
sulphides, e. y., cinnabar, pyrites, &c.
27.
4. HYDROFLUOSILICIC ACID (II F, S I F 2 ).
Preparation. Take quartz sand, wash off every particle of dust, and dry
thoroughly. Mix one part of the dry sand intimately with one part of
perfectly dry fluor spar in powder ; pour six parts of concentrated sul-
phuric acid over the mixture in a strong glass flask or in a mineral
water bottle dry inside, and mix carefully by shaking the vessel. As the
mixture swells up, when getting warm, it must at first fill the vessel only
to one-third. The mouth of the flask or bottle must be closed with a
perforated cork, or a cap of india-rubber, into which one end of a some-
what wide glass tube, twice bent at a right angle, is fitted air-tight ; the
other limb reaching to the bottom of a tall flat-bottomed glass jar with
just sufficient mercury to allow the end of the tube to dip into it to the ex-
tent of several lines ; the mercury in the jar is covered with four parts of
water. Promote the disengagement of fluosilicic gas, which commences
even in the cold, by exposing the flask or bottle to a moderate heat in
the sand-bath. Towards the end of the process a pretty strong heat
should be applied. Every gas bubble ascending through the mercury
produces in the water a precipitate of hydrated silicic acid. The
rationale of this process is that, of every three equivalents of fluoride of
silicon (Si F1 ), one equivalent decomposes with two equivalents of water
into silicic acid (Si O 2 ), which separates, and hydrofluoric acid, which
combines with the two undecomposed equivalents of fluoride of silicon,
forming hydrofluosilicic acid.
[3 Si F 2 + 2 H O - 2 (H F, S I F 2 ) + Si OJ.
The precipitated hydrate of silicic acid renders the liquid gelatinous, and
it is for this reason that the aperture of the exit tube must be placed
30
HYDllOSULPHUHIC ACID.
K 28-
under mercury, since it would speedily be choked if this precaution were
neglected. The same end may be attained also by attaching a funnel to
the exit tube, by means of vulcanized india-rubber, and letting the funnel
alone dip into the water. It sometimes happens in the course, and
especially towards the end of the operation, that the gas forms complete
channels of silica in the gelatinous liquid, through which it gains the
surface without undergoing decomposition, if the liquid is not occa-
sionally stirred. When the evolution of gas has completely ceased,
throw the gelatinous paste upon a linen cloth, squeeze the fluid through,
and filter it afterwards. Keep the filtrate for use.
Tests. Hydrofluosilicic acid, mixed with two parts of water, must
produce no precipitate in solutions of salts ofstrontia.
Uses. Bases decompose with hydrofluosilicic acid, forming water and
metallic silicofluorides. Many of these are insoluble, whilst others are
soluble ; the latter may therefore by means of this reagent be distin-
guished from the former. In the course of analysis, hydrofluosilicic acid
is applied simply for the detection of baryta.
c. SULPHUR ACIDS.
28.
5. HYDROSULPHURIC ACID (Sulphuretted Hydrogen) (H S).
Preparation. Hydrosulphuric acid gas is evolved best from sulphide
of iron, which is broken into small lumps, and then treated with dilute
sulphuric acid. Fused sulphide of iron may be procured so cheaply in
commerce that it is hardly worth while to take the trouble of preparing
it expressly. However, if you wish to prepare it yourself, this may be
done by heating iron turnings or nails, from 1 to 1J inch long, in a
Hessian crucible to a white heat, and then adding 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 out on sand, or into an old
Hessian crucible. Or make a
hole in the bottom of the cruci-
ble in which you fuse the mass,
when the sulphide of iron will, as
fast as it forms, run through the
hole in the bottom of the cru-
cible, and may thus be easily
received in a coal-shovel placed in
the ash-pit. Or, introduce an
intimate mixture of thirty parts
of iron filings and twenty-one
parts of flowers of sulphur, gra-
dually and in small portions at a
time, into a red-hot crucible,
awaiting always the incandescence
Fi g- 18. of the portion last introduced,
before proceeding to the addition
)f a fresh one. When you have thus put the whole mixture into the
crucible, cover the latter closely, and expose it to a more intense heat,
sufficient to make the sulphide of iron fuse more or less.
28.]
HYDROSULPHURTC A.CID.
31
The evolution of the gas is effected in the apparatus illustrated
by Fig. 18.
Pour water over the sulphide of iron in a, add concentrated sulphuric
acid, and shake the mixture ; the evolved gas is washed in c. When a
sufficient quantity of gas is evolved, pour the fluid from, off the still un-
decomposed sulphide of iron, wash the bottle repeatedly with water, fill
it with that fluid, and keep it for next operation. If you neglect this,
the apparatus will speedily become incrusted with crystals of sulphate
of protoxide of iron, which is apt to interfere injuriously with subsequent
processes of evolution of gas.
For larger laboratories, or for chemists, having to operate often and
largely with hydrosulphuric acid, I can recommend the lead apparatus
designed by myself, which I have now for several years employed
with the most satisfactory results in my own laboratory* (see Figs. 19
and 20).
abed and efg h (Fig. 20) are two cylindrical leaden vessels, soldered
with pure lead. They are both of the same size (in my own apparatus 33
centimetres high, and 30 centimetres in diameter), i is a false bottom
of lead, perforated like a sieve, placed from 4 to 5 centimetres above the
actual bottom of the vessel, and resting on leaden feet, which support it
on the sides as well as also more particularly in the middle. The
numerous holes in the sieve-like bottom have a diameter of 1 \ milli-
* The apparatus is made by Mr, Stumpf, of Wiesbaden, mechanist, and fully answers
all reasonable demands, both as. regards workmanship and price.
HYDHOSULPHUFdC ACID.
[ 28.
metres; k shows the opening through which the sulphide of iron is
introduced into the vessel. In my apparatus this aperture has a
diameter of 7 centimetres, and is closed
by putting a greased leather ring on its
broad smooth rim, and pressing down
upon this by means of three winged
screws, the broad rim of the smooth-
turned cover. I shows the opening
through which the solution of sulphate
of protoxide of iron is drawn off ; it will
be seen by the drawing that the bottom
of the vessel (g h) slants towards the
part where this opening is placed. The
aperture has a diameter of 3 centi-
metres ; it is closed by means of a
smooth- turned broad and thick leaden
cap, fitting on the smooth-turned
broad rini, and pressed down upon it
with a winged screw. The semi-ellip-
tical bar in which the female screw
is set, is moveable, and hinged to the
sides of I in a manner to admit of its
being bent out of reach of the liquid on
drawing off the latter. The construc-
tion of the filling tube, m, may be learned
from the drawing, and equally so that
of the tube d h, which is intended to
convey the acid from the upper to the
lower vessel, and vice versa. It will be
seen from the drawing that this tube reaches down into the slanting and
deepened part of the bottom g h, without, however, actually touching
the latter. The tube c e is closed at the top, and has, therefore, no
communication with the upper vessel, being simply intended to let off
the gas evolved in efg h] to which end it is connected laterally by a
branch tube, with the tube o ; this latter tube is fitted with a stop-cock (?i).
The tube q is closed at both ends, and serves simply as an additional
support for the upper vessel. The tubes in my apparatus have an inner
diameter of 10 millimetres.
The process of filling is conducted as follows : put 3 '3 kilogrammes* of
fused sulphide of iron, broken in lumps, through the mouth k, upon the
perforated bottom i \ screw the covers properly down upon k arid I, shut
the cock n, and pour through the funnel of in first 7 litres of water,
then 1 litre of concentrated sulphuric acid, and then again 7 litres of
water. The air in abed escapes in this operation through p, even when
the latter tube is already connected with the flasks r, s, t.
If the cock n is now opened, and one of the cocks u, the acid will (low
through the tube dl into efgh j and through o air will escape at first,
followed by the hydrosulphuric acid evolved in efg h. As is seen in
the figure, the tube o rises only to a certain elevation, when it makes a
bend, running on thence in a horizontal direction. As many cocks, u u,
are added as is thought desirable ; these cocks are common brass gas stop-
Fig. 20.
The quantities here given are calculated for an apparatus of the dimensions stated.
28.]
HYDROSULPHURIC ACID.
33
cocks, close-fitting and well ground in. They are connected with a small
washing bottle ; a double-bent tube conveys the gas from the latter,
with the co-operation of a straight tube connected with it by means of
vulcanized india-rubber, into the fluid which it is intended to operate
on ; this arrangement greatly facilitates the cleansing of the straight tube
dipping into the fluid. Upon now opening one of the cocks, u, the cock
n being of course also open, you will at once obtain a current of gas of
any strength desired, which will keep on for days in a continuous and
steady stream. If all the cocks M, are shut, the gas evolved in efg h
forces the acid back to the upper vessel through the tube li 'd, and the
evolution ceases.
The cessation of the evolution of gas is not instantaneous, however,
as the sulphide of iron in efgh remains still moistened with acid ;
moreover, small particles of the sulphides will always crumble off, and
dropping through the sieve, come into contact with the rest of the acid
covering the bottom, g h. Now the gas which still continues to be
evolved in efg h, being no longer able to escape through o, forces the
fluid up h d, and passing through the acid in a b c d, makes its way out
through p. To save this gas and keep it from poisoning the air, the flasks
r, s, t, are connected with/), r contains cotton, and serves the purpose of a
washing bottle ;* s and t contain solution of ammonia ; but the two flasks
together should contain no more than either of them can conveniently
hold ; since, as the pressure of the gas increases or relaxes, the fluid is
forced from s to t, or
back from t to s. It will
be readily understood
that sulphide of ammo-
nium is formed in these
flasks.
The evolution of gas
ceases completely when
all the acid is consumed,
but there remains still the
one half of the sulphide
of iron, as the quantity
used is calculated for
double the amount of
acid. The solution of sul-
phate of protoxide of
iron is therefore drawn
off, and 1 litre of acid
and 14 of water a^ain
poured in as directed.
This apparatus is now
made also of much less
dimensions to adapt it
for smaller laboratories.
Kipp has devised a glass
apparatus constructed
upon the same principle.
T* .! ~1_ _ _ T* ^ .
Fig. 21.
It is shown in Fig. 21. The drawing fully explains its construction
and application.
Juld
**
34 BASES AND METALS. [ 29.
Sulphuretted hydrogen water (solution of hydrosulphuric acid) is pre-
pared 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 completely saturated with the gas, which may be readily
ascertained by closing the mouth of the flask with the thumb, and
shaking it a little : if, upon this, a pressure is felt from within, tending
to push the thumb off the aperture of the flask, the operation may be
considered at an end ; but if, on the contrary, the thumb feels sucked
into the mouth of the flask, this is a sure sign that the water is still
capable of absorbing more gas.
Sulphuretted hydrogen water must be kept in well-closed vessels,
otherwise it will soon suffer complete decomposition, the hydrogen being
oxidized to water, and a small portion of the sulphur to sulphuric acid,
the rest of the sulphur separating. The best way of preserving it un-
altered for a very long time is to pour the freshly-prepared solution
immediately into small phials, and to place the latter, carefully corked,
in an inverted position, into bottles filled with water.
Tests. Pure sulphuretted hydrogen water must be perfectly clear,
and strongly emit the peculiar odor of the gas ; when treated with
sesquichloride of iron, it must yield a copious precipitate of sulphur.
Addition of ammonia must not impart a blackish appearance to it. It
must leave no residue upon evaporation on platinum.
Uses. Hydrosulphuric acid has a strong tendency to undergo decom-
position with metallic oxides, forming water and metallic sulphides ; and
the latter being mostly insoluble in water, are usually precipitated in
the process. The conditions under which the precipitation of certain
sulphides ensues differ materially ; by altering or modifying these con-
ditions, we may therefore divide the whole of the precipitable metals
into groups, as will be found explained below. Hydrosulphuric acid
is therefore an invaluable agent to effect the separation of metals into
principal groups. Some of the precipitated sulphides exhibit a charac-
teristic color indicative of the individual metals which they respectively
contain. Hydrosulphuric acid serves thus more particularly for the
special detection of tin, antimony, arsenic, cadmium, manganese, and
zinc. For more ample information upon this point, I refer to the third
section. The great facility with which hydrosulphuric acid is decom-
posed, renders this substance also a useful reducing agent for many com-
pounds ; thus it serves, for instance, to reduce salts of sesquioxide of iron
to salts of protoxide, chromic acid to the state of sesquioxide of chro-
mium, &c. In these processes of reduction, the sulphur separates in
the form of a fine white powder. Whether the hydrosulphuric acid had
better be applied in the gaseous form, or in aqueous solution, depends
always upon the special circumstances of the case.
III. BASES AND METALS.
29.
Bases are divided into oxygen bases and sulphur bases. The former
result from the combination of metals or of compound radicals of similar
character with oxygen, the latter from the combination of the same
bodies with sulphur.
The oxygen bases are classified into alkalies, alkaline earths, earths
proper, and oxides of the heavy metals. The alkalies are readily soluble
30.] POTASSA AND SODA. 35
in water ; the alkaline earths dissolve with greater difficulty in that
menstruum ; and magnesia, the last member of the class, is only very
sparingly soluble in it. The earths proper, and the oxides of the heavy
metals are insoluble in water, or nearly so. The solutions of the alkalies
and alkaline earths are caustic when sufficiently concentrated ; they
have an alkaline taste, change the yellow color of turmeric paper to
brown, and restore the blue tint of reddened litmus paper ; they saturate
acids completely, so that even the salts which they form with strong
acids do not change vegetable colors, whilst those with weak acids
generally have an alkaline reaction. The earths proper and the oxides
of the heavy metals combine likewise with acids to form salts, but, as a
rule, they do not entirely take away the acid reaction of the latter.
The sulphur bases resulting from the combination of the metals of the
alkalies and alkaline earths with sulphur, are soluble in water. The
solutions have a strong alkaline reaction. The other sulphur bases do
not dissolve in water. All sulphur bases form with sulphur acids
sulphur salts.
a. OXYGEN BASES,
a. ALKALIES.
30.
1. POTASSA (K 0) AND SODA (Na 0).
The preparation of perfectly pure potassa or soda is a difficult opera-
tion. It is advisable, therefore, to prepare, besides perfectly pure caustic
alkali, also some which is not quite pure, and some which, being free
from certain impurities, may in many cases be safely substituted for the
pure substance.
a. Common solution of soda.
Preparation. Put into a clean cast-iron pan provided with a lid, 5
parts of crystallized carbonate of soda of commerce and 20 parts of water,
heat to boiling, and add, in small portions at a time, thick milk of lime
prepared by pouring 4 parts of warm water upon 1^ parts of quicklime,
and letting the mixture stand in a covered vessel until the lime is
reduced to a uniform pulpy mass. Keep the liquid in the pan boiling
whilst adding the milk of lime, and for a quarter of an hour longer,
then filter off a small portion, and try whether the filtrate still
causes effervescence in hydrochloric acid . If this is the case, the boiling
must be continued, and, if necessary, some more milk of lime added to
the fluid. When the solution is perfectly free from carbonic acid, cover
the pan, allow the fluid to cool a little, and then draw off the clear solu-
tion from the residuary sediment, by means of a syphon filled with water,
and transfer it to a glass flask. Boil the residue a second and a third
time with water, and draw off the fluid in the same way. Cover the
flask close with a glass plate, and allow the lime suspended in the fluid
to subside completely. Scour the iron pan clean, pour the clear solu-
tion back into it, and evaporate it to 11 or 12 parts. The solution
so prepared contains from 9 to 10 per cent, of soda. It must be clear,
colorless, and as free as possible from carbonic acid ; sulphide of ammo-
nium must not impart a black color to it. Traces of silicic acid,
alumina, and phosphoric acid, are usually found in a solution of soda
D 2
36 POTASS A AND SODA. [ 30.
prepared in this manner ; on which account it is unfit for use in accu-
rate experiments.
Solution of soda is kept best in bottles closed with ground glass caps.
In default of capped bottles, common ones with ground stoppers may
be used ; but in that case, the neck must be wiped perfectly dry and
clean inside, and a slip of writing paper rolled round the stopper ; since,
if these precautions are neglected, it will be found impossible, after a
time, to remove the stopper, particularly if the bottle is only rarely
opened.
b. Hydrate of potassa purified with alcohol.
Preparation. Dissolve some sticks of caustic potassa of commerce in
rectified spirit of wine in a stoppered bottle, by digestion and shaking ;
let the fluid stand, decant or filter if necessary, and evaporate the clear
fluid in a covered silver dish over the spirit-lamp, until no more aqueous
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 caustic potassa
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 some of it
in water.
The hydrate of potassa so prepared is sufficiently pure for most pur-
poses j it contains, indeed, a minute trace of alumina, but is usually free
from phosphoric acid, sulphuric acid, and silicic acid. The solution must
remain clear upon addition of sulphide of ammonium ; hydrochloric acid
must only produce a barely perceptible effervescence in it. The solution,
acidified with hydrochloric acid, must, upon evaporation to dry ness, leave
a residue which dissolves in water to a clear fluid ; when boiled with
molybdate of ammonia, it must exhibit no yellow colour ; when treated
with ammonia, it ought not to deposit slight flakes of alumina imme-
diately ; but only after standing several hours in a warm place.
c. Hydrate of potassa prepared with baryta.
Preparation. Dissolve pure crystals of baryta ( 32) by heating with
water, and add to the solution pure sulphate of potassa, 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 sul-
phate (16 parts of crystals of baryta require 9 parts of sulphate of
potassa). Let the turbid fluid clear, decant, and evaporate in a silver
dish as in b. The hydrate of potassa so prepared is perfectly pure,
except that it contains a trifling admixture of sulphate of potassa, which
is left behind upon dissolving the hydrate in a little water. This hydrate
is but rarely required, its use being in fact exclusively confined to the
detection of minute traces of alumina.
Uses. The great affinity which the fixed alkalies possess for acids
renders these substances powerful agents to effect the decomposition of
the salts of most bases, and consequently the precipitation of those bases
which are insoluble in water. Many of the so precipitated oxides redis-
solve in an excess of the precipitant, as, for instance, alumina, sesqui-
oxide of chromium, and oxide of lead ; whilst others remain undissolved,
e. g., sesquioxide of iron, teroxide of bismuth, &c. The fixed alkalies
serve therefore also as a means to separate the former from the latter.
Potassa and soda dissolve also many salts (e. g., chromate of lead), sul-
phur compounds, &c., and serve thus to separate and distinguish them
from other substances. Many of the oxides precipitated by the action
31.] AMMONIA OXIDE OF AMMONIUM. 37
of potassa or soda exhibit a peculiar color, or possess other charac-
teristic properties that may serve to lead to the detection of the individual
metal which they respectively contain ; such are, for instance, the pre-
cipitate of protoxide of manganese, hydrate of protoxide of iron, sub-
oxide of mercury, &c. The fixed alkalies expel ammonia from its salts,
and enable us thus to detect that body by its smell, its reaction on vege-
table colors, &c.
31.
2. AMMONIA Oxide of Ammonium (N H 4 0).
Preparation. The apparatus illustrated by Fig. 18 (28) may also
serve for the preparation of solution of ammonia, with this modification
however, that no funnel tube being required in the process, the cork
upon the flask a has only one perforation for the reception of the tube
which serves to conduct the evolved ammonia into the washing bottle.
Introduce into a 4 parts of chloride of ammonium in pieces about the
size of a pea, and dry hydrate of lime prepared from 5 parts of lime ;
mix by shaking the flask, and add cautiously a sufficient quantity of
water to make the powder into lumps. Put a small quantity of water
only into the washing bottle (which should be rather capacious); but
have 10 parts of water in the flask which is intended for the final recep-
tion of the washed gas. Set the flask a now in a sand bath, connect
it with the rest of the apparatus, place the flask d in a vessel of cold
'water, and apply heat. The evolution of gas speedily commences. Con-
tinue to heat until no more bubbles appear. Open the cork of the flask a,
to prevent the receding of the fluid. The solution of ammonia con-
tained in the washing bottle is impure, but that contained in the
receiver d is perfectly pure; dilute it with water until the specific
gravity is about O96 = 10 per cent, of ammonia. Keep the fluid in
bottles closed with ground stoppers. This is the best way of preparing
solution of ammonia in small quantities. That prepared on a large
scale in cast-iron vessels is of course cheaper.
Tests. Solution of ammonia must be colorless, and ought not to
leave the least residue when evaporated on a watch-glass, nor should it
cause the slightest turbidity in lime water (carbonic acid). When super-
saturated with nitric acid, neither solution of nitrate of baryta, nor of
nitrate of silver, must render it turbid, nor must sulphuretted hydrogen
impart to it tha slightest color.
Uses. Solution of ammonia, although formed by conducting ammo-
niacal gas (N H g ) into water, and letting that gas escape upon exposure
to the air, and much quicker when heated, is conveniently regarded as a
solution of oxide of ammonium (N H 4 0) in water, the equivalent of
water (H O) existing with N H 3 being assumed to form with the
latter N H 4 O. Solution of ammonia is accordingly regarded as corre-
sponding to the solution of potassa and soda, which greatly serves to
facilitate the explanation of many chemical transformations into which
the ammoniacal compounds enter, the oxygen salts resulting from the
neutralization of oxygen acids by solution of ammonia being also assumed
to contain oxide of ammonium N H 4 O, instead of N H 3 . In the pre-
sent edition, therefore, ammonia signifies oxide of ammonium (N H 4 O),
and corresponds to the oxides of potassium and sodium, or potassa and
soda. Ammonia is one of the most frequently used reagents. It is
especially applied for the saturation of acid fluids, and also to effect the
38 BARYTA. [ 32.
precipitation of a great many metallic oxides and earths ; many of these
precipitates redissolve in an excess of ammonia, as, for instance, the
oxides of zinc, cadmium, silver, copper, &c., whilst others are insoluble
in free ammonia. This reagent may serve, therefore, 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 individual metal which they respec-
tively contain.
Many of the oxides 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 formation of a salt
of ammonia. Compare 51, choride of ammonium.
/3. ALKALINE EARTHS.
32.
1. BARYTA (Ba 0).
Preparation. a. From sulphate of baryta. Mix together 6 parts
of finely pulverized sulphate of baryta, 1 part of powdered charcoal,
and 1J part of flour ; or 8 parts of sulphate of baryta, 2 parts of char-
coal, and 1 part of common resin. Put the mixture in a crucible, and
expose it in a wind furnace to a long-continued red heat ; or put the
mixture in an earthen pot, lute the lid on with clay, and expose the
pot to the heat of a brick-kiln. Boil the crude sulphide of barium
obtained by this process for some time with water, and, when the
crystallization point is attained, filter off hot : let the filtrate cool in a
well-covered vessel. Pour off the mother liquor, which, together with
the residue left from the boiling of the sulphide of barium, may be used
for the preparation of chloride of barium ; boil the crystals with just
sufficient water to dissolve them ; keep boiling (taking care to replace
the evaporated water) ; add finely triturated and sifted copper scales in
small portions at a time, until a filtered sample of the fluid gives a
pure white precipitate when mixed with a little acetate of lead.
Filter boiling. As solution of baryta eagerly absorbs carbonic acid
from the air, great care must be taken to exclude the air in the pro-
cesses of filtration and crystallization. To effect this it is necessary
to place the beaker intended to receive the filtrate on a flat dish or
flat iron pot containing a little milk of lime, invert a bell-glass over it
with an opening in the top, insert the funnel through this, filter,
then remove the funnel, close the opening in the top of the bell-glass
with an india-rubber cap, and let the fluid thus protected from access of
air stand for several days in a cool place. After this decant the fluid
(baryta water), let the crystals (Ba O, H O + 8 aq.) drain in a well-
covered funnel, dry them quickly between sheets of blotting-paper, and
keep them in well -stoppered bottles. For use dissolve 1 part in 20
parts of water, and filter. The baryta water so obtained is preferable
to that decanted from the crystals.
b. From nitrate of baryta. Project a mixture of 8 parts of finely
pulverized nitrate of baryta and 3 parts of clean iron filings, a spoonful
at a time, but not in too quick succession, into a ret-hot Hessian, or,
better still, into a red-hot iron crucible. When the mass has left off
33.] LIME. 39
frothing, and become pasty and in the end friable, take it out with an
iron spatula, let it cool, and when cool powder it. Boil the crucible
now for half an hour with 64 parts of water in an iron pot, take the
crucible out, put the powdered mass into the boiling fluid, add 16 parts
more of water, boil another half hour, filter, and proceed with the
filtrate as in a ( Wittstein).
c. From Witherite. Mix intimately 100 parts of finely pulverized
Witherite, 10 parts of powdered charcoal, and 5 parts of resin; or 100
parts of Witherite and 15 parts of finely powdered caking coal. Put
the mixture in a pot or crucible, lute on the lid with clay, and expose
to the heat of a brick-kiln. Triturate the mass, and boil the powder
with water ; filter, and proceed with the filtrate as in a. The undis-
solved residue, which consists of undecomposed Witherite and coal, may
be used in the preparation of chloride of barium. This is a most
excellent method, both as regards cheapness and purity of product.
Tests. Solution of baryta, or baryta water, must, after precipitation of
the baryta by sulphuric acid, give a filtrate remaining clear when mixed
with spirit of wine, and leaving no fixed residue upon evaporation in a
platinum crucible.
Uses. Caustic baryta, being a strong base, precipitates the earths and
metallic oxides insoluble in water from the solutions of their salts. In
the course of analysis we use it simply to precipitate magnesia. Baryta
water may also be used to precipitate those acids which form insoluble
compounds with this base ; it is applied with this view to effect the detec-
tion of carbonic acid, the removal of sulphuric acid, phosphoric acid, &c.
33.
2. LIME (Ca 0).
We use
a. Hydrate of lime.
b. Lime water.
The former is obtained by slacking pure calcined lime in lumps, in a
porcelain dish, with half its weight of water. Hydrate of lime must be
kept in a well-stoppered bottle.
To prepare lime water, digest hydrate of 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-stop-
pered flask.
Tests. Lime water must impart a strongly-marked brown tint to
turmeric paper, and give a considerable precipitate with carbonate of
soda. It speedily loses these properties upon exposure to air, and is
thereby rendered totally unfit for analytical purposes.
Uses. Lime forms with many acids insoluble, with others soluble
salts. Lime water may therefore serve to distinguish the former acids,
which it precipitates from their solutions, from the latter, which it will ot
course fail to precipitate. 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 condi-
tions. We use lime water in analysis principally to effect the detection
of carbonic acid, and also to distinguish between citric acid and tartaric
acid. Hydrate of lime is chiefly used to liberate ammonia from the
salts of ammonia.
40 ZINC, IRON, COPPER. [ 34 37.
7 . HEAVY" METALS AND THEIR OXIDES.
34.
1. ZINC (Zn).
Select zinc of good quality and, above all, perfectly free from arsenic.
The method described 131, 10 will serve to detect the presence of the
slightest trace of this substance. Fuse the metal, and pour the fused
mass in a thin unbroken stream into a large vessel with water. Should
the zinc contain arsenic, put the granulated metal into a Hessian crucible,
in alternate layers, with i part of nitrate of potassa, heat the crucible
gradually until the reaction sets in, and the metal ultimately fuses ;
granulate now again (Meillet).
Uses. Zinc serves in qualitative analysis for the evolution of hydrogen,
and also of arsenetted and antimonetted hydrogen gases (compare 130
and 131); it is occasionally used also to precipitate some metals from
their solutions; in which process the zinc simply displaces the other
metal (Cu 0, S 3 + Zn = Zn 0, S 3 + Cu).
35.
2. IRON (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, <kc., will
serve for this purpose.
36.
3. COPPER (Cu).
We use copper exclusively to effect the reduction of mercury, which
precipitates upon it as a white coating shining with silvery lustre when
rubbed. A copper coin scoured with fine sand, or in fact any clean sur-
face of copper, may be employed for this purpose.
37.
4. HYDRATE OF TEROXIDE OF BISMUTH (Bi0 3 ,HO).*
Preparation. Dissolve bismuth, freed from arsenic by fusion with
hepar sulphuris or nitrate of potassa, in dilute nitric acid ; dilute the
solution as much as is practicable without producing a permanent preci-
pitate ; 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, and dry the white precipitate, and keep it for use.
Tests. Hydrosulphuric acid must throw down from a solution of
this reagent in dilute nitric acid, a precipitate insoluble in ammonia and
sulphide of ammonium ; and, accordingly, the fluid filtered off from the
precipitate treated with ammonia must remain perfectly clear upon addi-
tion of hydrochloric acid, whilst in that filtered off from the precipitate
* The basic nitrate of teroxide of bismuth of commerce, if perfectly free from arsenic
and antimony, may also be used instead of the hydrate of teroxide.
38.] SULPHIDE OF AMMONIUM. 41
treated with sulphide of ammonium, that acid must only produce a pure
white turbidity (sulphur).
Uses. Teroxide of bismuth, when boiled with alkaline solutions of
metallic sulphides, decomposes with the latter, giving rise to the forma-
tion of metallic oxides and sulphide of bismuth. It is better adapted
to effect decompositions of this kind than oxide of copper, since it enables
the operator to judge immediately upon the addition of a fresh portion
whether the decomposition is complete or not. It has still another ad-
vantage over oxide of copper, viz., it does not, like the latter, dissolve
in the alkaline fluid in presence of organic substances ; nor does it act
as a reducing agent upon reducible oxygen compounds. We use it
principally to convert tersulphide and pentasulphide of arsenic into
arsenious and arsenic acids, for which purpose oxide of copper is alto-
gether inapplicable, since it converts the arsenious acid immediately
into arsenic acid, being itself reduced to the state of suboxide.
b. SULPHUR BASES.
4
38.
1. SULPHIDE OF AMMONIUM (NH 4 S).
We use in analysis
a. Colorless proto-sulphide of ammonium.
b. Yellow bi-, ter-, &c., sulphide of ammonium.
Preparation. Transmit hydrosulphuric acid gas through 3 parts
of solution of oxide of ammonium until no further absorption takes
place ; then add 2 parts more of the same solution of oxide of ammo-
nium. The action of hydrosulphuric acid upon oxide of ammonium gives
rise to the formation, first, of N H 4 , S (N H 4 O and H S = N H 4 S and
H O), then of N H 4 S, H S ; upon addition of the same quantity of solu-
tion of ammonia as has been saturated, the oxide of ammonium decom-
poses with the double sulphide of ammonium and hydrogen, or, as it is
commonly called, the hydrosulphate of sulphide of ammonium, and
simple or proto-sulphide of ammonium is formed (N H 4 S, H S + N H 4
O = 2 (N H 4 S) + H O. The rule, however, is to add only two-thirds of
the quantity of solution of ammonia, as it is better the preparation
should contain a little hydrosulphate of sulphide of ammonium, than that
free ammonia should be present. To employ, as has usually been the
case hitherto, hydrosulphate of sulphide of ammonium instead of the
simple proto-sulphide, is unnecessary, and simply tends to increase the
smell of sulphuretted hydrogen in the laboratory, as the preparation
allows that gas to escape when in contact with metallic sulphur acids.
Sulphide of ammonium should be kept in small well-stoppered bottles.
It is colourless 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 bisulphide of ammonium, which is attended also
with formation of ammonia and water :
Continued action of the oxygen of the air upon the sulphide of ammo-
nium tends at first to the formation of still higher sulphides ; but after-
wards the fluid deposits sulphur, and, in the end, there remains
42 SULPHIDE OF SODIUM. [ 39.
nothing in solution but pure ammonia, the whole of the sulphur having
separated.
The sulphide of ammonium, which has turned yellow by exposure to
the air, may be used for all purposes requiring the employment of yellow
sulphide of ammonium : the yellow sulphide may also be expeditiously
prepared by digesting the proto-sulphide with some sulphur. All kinds
of yellow sulphide of ammonium deposit sulphur, and look turbid and
milky on being mixed with acids.
Tests. Sulphide of ammonium must strongly emit the odor peculiar
to it ; with acids it must evolve abundance of sulphuretted hydregen ; the
evolution of gas may be attended by the separation of a pure white de-
posit, but no other precipitate must be formed. Upon evaporation and
exposure to a red heat on a platinum dish, it must leave no residue. It
must not precipitate, nor even render turbid, solution of magnesia or
solution of lime (carbonate of ammonia or free ammonia).
Uses. Sulphide of ammonium is one of the most frequently employed
reagents. It serves (a) to effect the precipitation of those metals which
t hydrosulphuric acid fails to throw down from acid solutions, e. g. of iron,
cobalt, &c. (N H 4 S + Fe O, S O 8 = Fe S + N H 4 O, S 0,), (b) to separate
the metallic sulphides thrown down from acid solutions by hydrosul-
phuric acid, as it dissolves some of them to sulphur salts, as, for instance,
the sulphides of arsenic and antimony, &c. (N H 4 S, As S 8 , &c.), whilst
leaving others undissolved for instance, sulphide of lead, sulphide of
cadmium, &c. The sulphide of ammonium used for this purpose must
contain an excess of sulphur, if the metallic sulphides to be dissolved
will dissolve only as higher sulphides, as, for instance, Sn S, which
dissolves with ease only as Sn S 2 .
From solutions of salts of alumina and sesquioxide of chromium,
sulphide of ammonium precipitates hydrates of these oxides, with escape
of sulphuretted hydrogen, as the sulphur compounds corresponding to
these oxides cannot form in the humid way. [A1 2 O 3 , 3 S O 3 + 3 N H 4 S =
A1 2 3 , 3 H + 3 (N H 4 0, S O 8 ) ]. Salts insoluble in water are thrown
down by sulphide of ammonium unaltered from their solutions in
acids; thus, for instance, phosphate of lime is precipitated unaltered
from its solution in hydrochloric acid.
39.
2. SULPHIDE OF SODIUM (Na S).
Preparation. Same as sulphide of ammonium, except that solution
of soda is substituted for solution of ammonia. Keep the fluid ob-
tained in well-stoppered bottles. If required to contain some higher
sulphide of sodium, digest it with powdered sulphur.
Uses. Sulphide of sodium is substituted for sulphide of ammonium
to effect the separation of sulphide of copper from sulphur compounds
soluble in alkaline sulphides, e. g., from proto-sulphide of tin, as sulphide
of copper is not quite insoluble in sulphide of ammonium.
IV. SALTS.
Of the many salts employed as reagents, those of potassa, soda, and
ammonia are used principally on account of their acids; salts of
soda may, therefore, often be substituted for the corresponding potassa
40 42.] SULPHATE OF POTASSA. 43
salts, &c. Thus it is almost always a matter of perfect indifference
whether we use carbonate of soda or carbonate of potassa, ferrocyauide
of potassium or ferrocyanide of sodium, &c. I have, accordingly, here
classified the salts of the alkalies by their acids. With the salts of the
alkaline earths and those of the oxides of the heavy metals the case is
different ; these are not used for their acid, but for their base ; we may,
therefore, often substitute for one salt of a base another similar one,
as e.g., nitrate or acetate of baryta for chloride of barium, &c. For
this reason I have classified the salts of the alkaline earths and of the
heavy metals by their bases.
a. SALTS OF THE ALKALIES.
40.
1. SULPHATE OF POTASSA (K 0, S 3 ).
Preparation. Purify sulphate of potassa of commerce by recrystal-
lization, and dissolve 1 part of the pure salt in 12 parts of water.
Uses. Sulphate of potassa serves to detect and separate baryta and
strontia. It is in many cases used in preference 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.
41.
2. PHOSPHATE OF SODA (2 Na 0, H 0, P O 6 + 24 aq.).
Preparation. Purify phosphate of soda of commerce by recrystalli-
zation, and dissolve one part of the pure salt in 10 parts of water for
use.
Tests. Solution of phosphate of soda must not become turbid when
heated with ammonia. The precipitates which solution of nitrate of
baryta and solution of nitrate of silver produce in it, must completely,
and without effervescence, redissolve upon addition of dilute nitric
acid.
Uses. Phosphate of soda precipitates the alkaline earths, and all
metallic oxides, by double affinity. It serves, in the course of analysis,
after the separation of the oxides of the heavy metals, as a test for
alkaline earths in general ; and, after the separation of baryta, strontia,
and lime, as a special test for the detection of magnesia ; for which latter
purpose it is used in conjunction with ammonia, the magnesia preci-
pitating, under these circumstances, as basic phosphate of magnesia and
ammonia.
42.
3. OXALATE OF AMMONIA (N H 4 O, C 2 0, + aq., or N H 4 O,"O + aq.).
Preparation. Dissolve commercial oxalic acid in 20 parts of water,
add caustic ammonia, or carbonate of ammonia, until the fluid begins
to manifest a slight alkaline reaction ; let it stand at rest for 12 hours,
filter, and evaporate to crystallization. Purify by recrystallization. Dis-
solve 1 part of the pure salt in 24 parts of water for use.
Tests. The solution of oxalate of ammonia must not be precipi-
tated nor rendered turbid by hydrosulphuric acid, nor by sulphide of
ammonium.
s?. Oxalic acid forms with lime, strontia, baryta, oxide of lead,
44 ACETATE OF SODA. [ 43, 44.
and other metallic oxides, insoluble or very difficultly soluble com-
pounds ; oxalate of ammonia produces, therefore, in the aqueous solutions
of the salts of these bases precipitates of the corresponding oxalates. In
analysis it serves principally for the detection of lime.
43.
4. ACETATE OF SODA (Na 0, C 4 H 3 O 3 + 6 aq., or Na 0, A + 6 aq.).
Preparation. Dissolve crystallized carbonate of soda in a little water,
add to the solution acetic acid to slight excess, evaporate to crystal-
lization, and purify the salt by recrystallization. For use dissolve 1
part of the salt in 10 parts of water.
Tests. Acetate of soda when boiled with a solution of molybdate of
ammonia mixed with hydrochloric acid must not impart a yellow color
to it.
Uses. The stronger acids in the free state decompose acetate of soda,
combining with the base, and setting the acetic acid free. In the course
of analysis, acetate of soda is used principally to precipitate phosphate of
sesquioxide of iron (which is insoluble in acetic acid) from its solution in
hydrochloric acid.
44.
5. CARBONATE or SODA (NaO, C0 2 + lOaq.).
Preparation. Take bicarbonate of soda of commerce, put the powder
into a funnel stopped loosely with some cotton, make the surface even,
cover it with a disc of difficultly permeable paper with turned-up
edges, and wash by pouring small quantities of water on the paper disc,
until the filtrate, when acidified with nitric acid, is not rendered turbid
by solution of nitrate of silver, nor by solution of chloride of barium.
Let the salt dry, and then convert it by gentle ignition into the simple
carbonate. This is effected best in a crucible or dish of silver or plati-
num ; but it may be done also in a perfectly clean vessel of cast iron, or,
on a small scale, in a porcelain dish. Pure carbonate of soda may be
obtained also by repeated recrystallization of carbonate of soda of com-
merce. For use, dissolve 1 part of the anhydrous salt or 2 -7 parts of
the crystallized salt in 5 parts of water.
Tests. Carbonate of soda intended for analytical purposes must be
perfectly white. Its solution, when supersaturated with nitric acid, must
not be rendered turbid by chloride of barium nor by nitrate of silver ;
nor must addition of sulphocyanide of potassium impart a red, or boiling
with molybdate of ammonia a yellow tint to it ; the residue which
remains upon evaporating its solution to dryness, after previous super-
saturation with hydrochloric acid, must leave no residue (silicic acid)
when redissolved in water.
Uses. With the exception of the alkalies, carbonate of soda precipi-
tates the whole of the bases, most of them as carbonates, but some also
as hydrated oxides. Those bases which are soluble in water as bicar-
bonates require boiling for their complete precipitation from acid solu-
tions. Many of the precipitates produced by the action of carbonate of
soda exhibit a characteristic color, which' may lead to the detection of
the individual metals which they respectively contain. Solution of car-
bonate of soda serves, moreover, for the decomposition of many insoluble
salts of the alkaline earths or of the metals, more particularly of those
45, 46.] CAEBONATE OF AMMONIA. 45
with organic acids. Upon boiling with carbonate of soda, these salts are
converted into insoluble carbonates, whilst the acids combine with the
soda, and are thus obtained in solution in the form of salts of soda.
Carbonate of soda is often used also to saturate free acids.
45.
6. CARBONATE OF AMMONIA (N H 4 0, C 2 ).
Preparation. We use for the purposes of chemical analysis purified
sesquicarbonate of ammonia, entirely free from any smell of animal oil,
such as is prepared on a large sale from chloride of ammonium and car-
bonate of lime by sublimation. The outer and the inner surface of the
mass are carefully scraped. One part of the salt is dissolved by digestion
with 4 parts of water, to which one part of solution of caustic am-
monia has been added.
Tests. Pure carbonate of ammonia must completely volatilize.
Neither solution of nitrate of baryta nor nitrate of silver, nor sul-
phuretted hydrogen, must color or precipitate it, after supersaturatioii
with nitric acid.
Uses. Carbonate of ammonia precipitates, like carbonate of soda,
most metallic oxides and earths ; it is generally employed in preference
to the latter reagent, because it introduces no non-volatile body into
the solution. Complete precipitation of many of the oxides takes place
only on boiling. Several of the precipitates redissolve again in an
excess of the precipitant. In like manner, carbonate of ammonia dissolves
many hydrated oxides, and thus enables us to distinguish and separate
them from others which are insoluble in this reagent.
Carbonate of ammonia, like caustic ammonia, and for the same reason,
fails to precipitate from acid solutions many -oxides which it precipitates
from neutral solutions. (Compare 51.) We use carbonate of ammonia
in chemical analysis principally to effect the precipitation of baryta,
strontia, and lime, and the separation of these substances from magnesia,
as the latter is not precipitated by this reagent in the presence of salts
of ammonia.
46.
7. BISULPHITE OF SODA (Na 0, 2 S 2 ).
Preparation. Heat 5 parts of copper shreds with 20 parts of con-
centrated sulphuric acid in a flask, and conduct the sulphurous acid
gas evolved, first through a washing bottle containing some water, then
into a flask containing 4 parts of purified bicarbonate of soda ( 44),
or 7 parts of crystallized carbonate of soda, and from 20 to 30 parts
of water, and which is not much more than half full ; continue the
transmission of the gas until the evolution of carbonic acid ceases.
Keep the solution, which smells strongly of sulphurous acid, in a* well-
stoppered bottle.
Tests. Sulphite of soda, when evaporated to dryness with pure sul-
phuric acid, must leave a residue,* the aqueous solution of which is not
altered by hydrosulphuric acid, nor coloured yellow by boiling with a
solution of molybdate of ammonia mixed with hydrochloric acid.
Uses. Sulphurous acid has a great tendency to pass to the state of
* The evaporation is attended with copious evolution of sulphurous acid.
46 NITRITE OF POTASSA. [ 47 49.
sulphuric acid by absorbing oxygen. It is therefore one of our most
powerful reducing agents. Sulphite of soda, which has the advantage of
being less readily decomposed than sulphurous acid, acts in an analogous
manner as a reducing agent upon acids and higher oxides. We employ
it principally to reduce arsenic acid to arsenious acid, chromic acid to
sesquioxide of chromium, and sesquioxide of iron to protoxide.
47-
8. NITRITE OF POTASSA (K O, N 3 ).
Preparation. Fuse 1 part of nitrate of potassa in an iron pan, then
add 2 parts of lead, and keep stirring the mixture with an iron rod.
The lead oxidizes in a great measure even at a dull red heat, changing
to a yellow powder ; to oxidize the last remaining particles of the metal,
increase the heat to visible redness ; in this process the mixture generally
takes fire ; this, however, is entirely without danger, at least when no
more than a quarter of a pound of nitrate of potassa has been used. Let
the mass cool, and then treat it with cold water to dissolve out the
soluble part ; filter this solution, arid conduct carbonic acid into the
filtrate. This serves to precipitate nearly the whole of the oxide of
lead that has passed into the solution ; a little hydrosulphuric acid will
remove the remainder. Filter again, and evaporate the filtrate to
dryness, stirring the mass towards the end of the operation ; heat the
dry residue to fusion, to destroy any hyposulphite of potassa that may
have been formed. Dissolve 1 part of the fused mass in 2 parts of water
for use (Aug. Stromeyer).
Tests. Nitrite of potassa must, upon addition of dilute sulphuric acid,
copiously evolve nitric oxide gas.
Uses. Nitrite of potassa is an excellent means to effect the detection
and separation of cobalt ; in the solutions of which metal ifc produces a
precipitate of nitrite of potassa and sesquioxide of cobalt. It serves also
in presence of free acid to liberate iodine from its compounds.
48.
9. BICHROMATE OF POTASSA (K 0, 2 Or 3 ).
Preparation. Purify the salt of commerce by recrystallization, and
dissolve 1 part of the pure salt in 10 parts of water for use.
Uses. Chromate of potassa decomposes most of the soluble salts of
metallic oxides, by double affinity. Most of the precipitated chromates
are very difficultly soluble, and many of them exhibit characteristic
colors which lead readily to the detection of the particular metal which
they respectively contain. We use bichromate of potassa principally as
a test for lead.
49.
10. ANTIMONATE OF POTASSA (K O, Sb 5 + 5 aq.).
Preparation. Deflagrate in a Hessian crucible 1 part of antimony
with 4 parts of nitrate of potassa, and extract the soluble part of the
mass with cold water; boil the residue from 2 to 3 hours with 12
parts of water, taking care to replace the evaporating water ; this
serves to convert the insoluble antimonate of potassa into the soluble
50, 51.] MOLYBDATE OF AMMONIA. 47
salt. Filter the solution from the small amount of binantimonate which
still remains undissolved, and keep for use.
Uses. Antimonic acid forms with soda a very difficultly soluble
salt. Antimonate of potassa affords us, therefore, a means of detecting
the presence of soda. For certain conditions and precautions to be
observed in its application, I refer to 89.
50.
11. MOLYBDATE OF AMMONIA (NH 4 O.Mo0 8 ).
Preparation. Triturate sulphide of molybdenum with an equal bulk
of coarse quartz sand washed with hydrochloric acid, until the mass
is reduced to a moderately fine powder (JBrunner) ; heat the powder
to feeble redness, until the mass has acquired a lemon-yellow color
(which after cooling turns whitish). With small quantities, this ope-
ration may be conducted in a flat platinum dish, with large quantities,
in a muffle properly protected from the ashes ; take care to stir
the mixture repeatedly during the operation. After cooling, digest
the impure molybdic acid produced with solution of ammonia, and let
the solution stand at rest for some time in a beaker covered with
filtering paper ; a yellowish precipitate containing sesquioxide of iron
will usually subside. Filter, and keep the perfectly colorless fluid for
use. It is sufficiently concentrated if it contains 5 per cent, of molybdic
acid. Keep the residuary sulphide of molybdenum for the next operation.
Tests. Solution of molybdate of ammonia mixed with nitric acid or
hydrochloric acid until the precipitate of molybdic acid which forms at
first is reclissolved, must remain colourless upon boiling. If it acquires
a yellow tint, the reagent contains phosphoric acid, and is unfit for use
(supposing always, of course, that the hydrochloric or nitric acid was
perfectly pure).
Uses. Molybdic acid forms with phosphoric acid and ammonia a
peculiar compound which, in presence of an excess of molybdic acid, is
very difficultly soluble in water and acids. The hot solution of this
compound has an intensely yellow color. Molybdate of ammonia
affords therefore an excellent means to detect minute quantities of phos-
phoric acid.
51.
12. CHLORIDE OF AMMONIUM (NH 4 , Cl).
Preparation. Select sublimed white sal ammoniac of commerce. If
it contains iron, it must be purified. For that purpose, add to the solution
some sulphide of ammonium, let the precipitate which forms subside, and
filter ; add hydrochloric acid to the filtrate until the latter manifests a
feebly acid reaction ; boil the mixture some time, saturate with ammonia,
filter, if necessary, and crystallize. For use, dissolve 1 part of the salt
in 8 parts of water.
Tests. Solution of chloride of ammonium must upon evaporation
on a platinum knife leave a residue which volatilizes completely upon
continued application of heat. Sulphide of ammonium must leave it
unaltered. Its reaction must be perfectly neutral.
Uses. Chloride of ammonium serves principally to retain in solution
certain oxides (e. g., protoxide of manganese, magnesia) or salts (e. g.,
48 CYANIDE OF POTASSIUM. [ 52.
tartrate of lime), upon the precipitation of other oxides or salts by
ammonia or some other reagent. This application of chloride of ammo-
nium is based upon the tendency of the ammonia salts to form double
compounds with other salts. Chloride of ammonium serves also to dis-
tinguish between precipitates possessed of similar properties ; for instance,
to distinguish the basic phosphate of magnesia and ammonia, which is
insoluble in chloride of ammonium, from other precipitates of magnesia.
It is used also to precipitate from their solutions in potassa various sub-
stances which are soluble in that alkali, but insoluble in ammonia ; e. g.,
alumina, sesquioxide of chromium, &c. In this process the elements of the
chloride of ammonium transpose with those of the potassa, and chloride
of potassium, water, and ammonia are formed. Chloride of ammonium
is applied also as a special reagent to effect the precipitation of platinum
as ammonio-bichloride of platinum.
52.
13. CYANIDE OF POTASSIUM (K Cy).
Preparation. Heat ferrocyanide of potassium of commerce (perfectly
free from sulphate of potassa) gently, with stirring, until the crystalli-
zation water is completely expelled ; triturate the anhydrous mass, and
mix 8 parts of the dry powder with 3 parts of perfectly dry car-
bonate of potassa ; fuse the mixture in a covered Hessian or, better
still, in a covered iron crucible until the mass is in a faint glow, and
appears clear, and a sample of it, taken out with an iron spatula, looks
perfectly white. Remove the crucible now from the fire, tap it gently,
and let it cool a little until the evolution of gas has ceased ; pour the
fused cyanide of potassium into a heated crucible-shaped vessel of
clean scoured iron or silver, or into a moderately hot Hessian crucible,
with proper care, to prevent the running out of any of the minute par-
ticles of iron which have separated in the process of fusion and have sub-
sided to the bottom of the crucible. Let the mass now slowly cool in a
somewhat warm place. The cyanide of potassium so prepared is exceed-
ingly well adapted for analytical purposes, although it contains car-
bonate and cyanate of potassa ; which latter is upon solution in water
transformed into carbonate of ammonia and carbonate of potassa
(K 0, C 2 N + 4 H = K 0, C O 2 + N H 4 O, C O 2 ). The proper
formula for the cyanide of potassium is therefore* 5 K Cy + K O,
Cy O + x K 0, C 2 . Keep it in the solid form in a well-stoppered
bottle, and for use dissolve 1 part in 4 parts of distilled water, without
application of heat.
Tests. Cyanide of potassium must be of a milk-white color, and
quite free from particles of iron or charcoal. It must completely dis-
solve in water to a clear fluid. It must contain neither silicic acid nor
sulphide of potassium ; the precipitate which salts of lead produce in its
solution must accordingly be of a white color, and the residue which
its solution leaves upon evaporation, after previous supersaturation
with hydrochloric acid, must completely dissolve in water to a clear
fluid.
Uses. Cyanide of potassium prepared in the manner described produces
in the solutions of most of the salts with metallic oxides, precipitates of
cyanides of metals or of oxides or carbonates, which are insoluble in
water. The precipitated cyanides are soluble in cyanide of potassium,
and may therefore be separated from the oxides or carbonates which are
53, 54.] FEREOCYANIDE OF POTASSIUM. 49
insoluble in cyanide of potassium, by further addition of the reagent.
Some of the metallic cyanides redissolve in the cyanide of potassium,
even in presence of free hydrocyanic acid and upon boiling, invariably
as double cyanides ; whilst others combine with cyanogen, forming new
radicals, which remain in solution in combination with the potassium.
The most common compounds of this nature are cobalticyanide of potas-
sium, and ferro- and ferricyanide of potassium. These differ from the
double cyanides of the other descriptions particularly in this, that
dilute acids fail to precipitate the metallic cyanides which they contain.
Cyanide of potassium may accordingly serve also 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
cyanide of potassium. In the course of analysis, this reagent serves
to effect the separation of cobalt from nickel, and also of copper from
cadmium.
53.
14. FERROCYANIDE OF POTASSIUM (2 K, C 6 N g Fe + 3 aq. = 2 K,
Cfy + 3 aq.).
Preparation. The ferrocyanide of potassium is found in commerce
sufficiently pure for the purposes of chemical analysis. 1 part of the
salt is dissolved in 12 parts of water for use.
Uses. Ferrocyanogen forms with most metals compounds insoluble
in water, and which frequently exhibit highly characteristic colors.
These ferrocyanides are formed when ferrocyanide of potassium is
brought into contact with soluble salts of metallic oxides, with chlorides,
&c., the potassium changing places with the metals. Ferrocyanide of
copper and ferrosesquicyanide of iron exhibit the most characteristic
colors of all ; ferrocyanide of potassium serves therefore particularly as
a test for oxide of copper and sesquioxide of iron.
54.
15. FERRICYANIDE OF POTASSIUM (3 K, C 12 N 6 Fe 2 = 3K Cfdy).
Preparation. Conduct chlorine gas slowly into a solution of 1 part
of ferrocyanide of potassium in 10 parts of water, with frequent stirring,
until the solution exhibits a fine deep red colour by transmitted light
(the light of a candle answers best), and a portion of the fluid produces
no longer a blue precipitate, in a solution of sesquichloride of iron, but
imparts a brownish tint to it ; evaporate the fluid now in a dish to ^ of
its weight, and crystallize. The mother liquor will upon further
evaporation yield a second crop of crystals equally fit for use as the first.
Dissolve the whole of the crystals obtained in 3 parts of water, filter, if
necessary ; evaporate the solution briskly to half its volume, and crystal-
lize again. Dissolve 1 part of the crystals, which are of a splendid red
color, in 10 parts of water for use. The solution, as already remarked,
must produce neither a blue precipitate nor a blue color in a solution of
sesquichloride of iron.
Uses. Ferricyanide of potassium decomposes with solutions of
metallic oxides in the same manner as ferrocyanide of potassium. Of
the metallic ferricyanides, the ferriprotocyanide of iron is more par-
ticularly characterized by its color, and we apply ferricyanide of potas-
sium therefore principally as a test for protoxide of iron.
50 SULPHOCYANIDE OF POTASSIUM. [ 55, 56.
55.
16. SULPHOCYANIDE OF POTASSIUM (K, C 2 N S 2 or K, Cy S 2 ).
Preparation. Mix together 46 parts of anhydrous ferrocyanide of
potassium, 17 parts of carbonate of potassa, and 32 parts of sulphur ;
introduce the mixture into an iron pan provided with a lid, and fuse at a
gentle heat ; 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 ; increase the temperature now,
towards the end of the operation, to dull redness, in order to decompose
the hyposulphite of potassa which has been formed in this process.
Bemove the half refrigerated and still soft mass from the pan, pulverize it,
and boil with alcohol. Let the alcoholic solution cool, when part of
the sulphocyanide of potassium will separate in colorless crystals ; to
obtain the remainder, distil the alcohol from the mother-liquor. Dissolve
1 part of the salt in 10 parts of water for use.
Uses. Sulphocyanide of potassium serves for the detection of sesqui-
oxide of iron ; it is for that substance at once the most characteristic
and delicate test.
b. SALTS OF THE ALKALINE EARTHS.
56.
1. SULPHATE OF BARYTA, CHLORIDE OF BARIUM (Ba Cl + 2 aq.)
Preparation. a. From heavy spar. Triturate crude sulphide of barium
( 32), boil about of the powder with 4 times the quantity of
water, and add hydrochloric acid until all effervescence of sulphuretted
hydrogen has ceased, and the fluid manifests a feeble acid reaction ; add
now the remaining y 1 ^ part of the sulphide of barium, boil for some
time longer, then filter, and let the alkaline fluid crystallize. Dry the
crystals, redissolve them in water, and crystallize again.
b. From Wither ite. Pour 10 parts of water upon 1 part of Witherite,
and gradually add crude hydrochloric acid until the Witherite is almost
completely dissolved. Add now a little more finely pulverized Witherite,
and heat, with frequent stirring, until the fluid has entirely or very
nearly lost its acid reaction; add some baryta water or solution of sul-
phide of barium, as long as a precipitate forms ; filter, evaporate to crys-
tallization ; dry the crystals, redissolve them in water, and crystallize
again. For use, dissolve 1 part of the chloride of barium obtained in
10 parts of water.
Tests. Pure chloride of barium must not alter vegetable colors ; its
solution must not be colored or precipitated by hydrosulphuric acid,
nor by sulphide of ammonium. Pure sulphuric acid must precipitate
every fixed particle from it, so that the fluid filtered from the precipi-
tate formed upon the addition of that reagent leaves not the slightest
residue when evaporated on platinum foil.
Uses. Baryta forms with many acids soluble,- with others insoluble
compounds. This property of baryta affords us, therefore, a means of
distinguishing the former acids which are not precipitated by chloride of
barium from the latter, in the solution of the salts of which this reagent
57 59.] NITRATE OF BARYTA. 51
produces a precipitate. The precipitated salts of baryta severally show
with other bodies (acids) a different deportment. By subjecting these
salts to the action of such bodies, we are therefore enabled to subdivide
the group of precipitable acids, and even to detect certain individual
acids. This makes chloride of barium one of our most important re-
agents to distinguish between certain groups of acids, and more especially
also for the detection of sulphuric acid.
57.
2. NITRATE OF BARYTA (Ba 0, N 5 ).
Preparation. Pour 12 parts of water upon 1 part of carbonate of
baryta, no matter whether Witherite or precipitated by carbonate of soda
from solution of sulphide of barium, gradually add dilute nitric acid
free from chlorine, and proceed exactly as directed in the preparation of
chloride of barium from Witherite. For use, dissolve 1 part of the salt
in 15 parts of water.
Tests, Solution of nitrate of baryta must not be made turbid by
solution of nitrate of silver. Other tests the same as for chloride of
barium.
Uses. Nitrate of baryta is used instead of chloride of barium in
cases where it is necessary to avoid the presence of a metallic chloride in
the fluid.
58.
3. CARBONATE OF BARYTA (Ba 0, C 2 ).
Preparation. Dissolve crystallized chloride of barium in water, heat
to boiling, and add a solution of carbonate of ammonia mixed with some
caustic ammonia, or of pure carbonate of soda, as long as a precipitate
forms ; let it 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 nitrate of silver. 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. Pure sulphuric acid must precipitate every fixed particle from
a solution of carbonate of baryta in hydrochloric acid (compare caustic
baryta).
Uses. Carbonate of baryta completely decomposes the solutions of
many metallic oxides, e. g., sesquioxide of iron, alumina \ precipitating
from them the whole of the oxide as hydrate and basic salt, whilst some
other metallic salts are not precipitated by it. It serves therefore to
separate the former from the latter, and is an excellent means to effect
the separation of sesquioxide of iron and alumina from protoxide of
manganese, oxide of zinc, &c., and also from lime and magnesia.
59.
4. SULPHATE OF LIME (Ca 0, S O a , crystallized Ca O, S 3 + 2 aq.).
Preparation. Digest and shake powdered crystallized gypsum for
some time with water ; let the undissolved portion subside, decant, and
keep the clear fluid for use.
R'2
52 CHLORIDE OF CALCIUM. [ 60 62.
Uses, Sulphate of lime being a difficultly soluble salt, is a convenient
agent in cases where it is wished to apply a solution of a lime salt or of
a sulphate of a definite degree of dilution . As dilute solution of a lime
salt, it is used for the detection of oxalic acid ; whilst as dilute solution
of a sulphate it affords an excellent means of distinguishing between
baryta, strontia, and lime.
60.
5. CHLORIDE OP CALCIUM (Ca Cl, crystallized Ca Cl + 6 aq.).
Preparation. Dilute 1 part of crude hydrochloric acid with 6 parts
of water, and add to the fluid marble or chalk until the last portion
added remains undissolved ; add some hydrate of lime, and let the mix-
ture stand for several days in 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.
Tests. Solution of chloride of calcium must be perfectly neutral, and
neither be colored nor precipitated by sulphide of ammonium ; nor
ought it to evolve ammonia when mixed with hydrate of potassa or
hydrate of lime.
Uses. Chloride of calcium is, in its action and application, analogous
to chloride of barium. For, as the latter reagent is used to divide the
inorganic acids into groups, so chloride of calcium serves in the same
manner to effect the separation of the organic acids into groups, since it
precipitates some of them, whilst it forms soluble compounds with others.
And, as is the case with the baryta precipitates, the different conditions
under which the various insoluble lime salts are thrown down, enable us
to subdivide the group of precipitable acids, and even to detect certain
individual acids.
61.
6. SULPHATE OF MAGNESIA (Mg 0, S , crystallized Mg 0, S 0.,
H O + 6 aq.).
Preparation. Dissolve 1 part of sulphate of magnesia of commerce
in 10 parts of water; if the salt is not perfectly pure, subject it to re-
crystallization.
Uses. Sulphate of magnesia serves almost exclusively for the detec-
tion of phosphoric acid, which it precipitates from aqueous solutions of
phosphates in presence of ammonia and chloride of ammonium, in the
form of a double salt (basic phosphate of magnesia and ammonia), which
is nearly insoluble, and has highly characteristic properties. Sulphate
of magnesia is, moreover, employed to test the purity of sulphide of
ammonium (see 38).
c. SALTS OF THE OXIDES OF THE HEAVY METALS.
62.
1. SULPHATE OF PROTOXIDE OF IRON (Fe 0, S , crystallized Fe 0,
S0 3 , H0 + 6aq.).
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 concentrated solution, add a few drops of
63, 64.] SESQUICHLORIDE OP IRON. 53
dilute sulphuric acid to the filtrate, and allow it to cool. Wash the
crystals with water very slightly acidulated with sulphuric acid, dry, and
keep for use. The sulphate of protoxide of iron may also be prepared
from the solution of sulphide of iron in dilute sulphuric acid, which is
obtained in the process of evolving hydrosulphuric acid.
Uses. Sulphate of protoxide of iron has a great disposition to absorb
oxygen, and to be converted into the sulphate of the sesquioxide. It
acts therefore as a powerful reducing agent. We employ it principally
for the reduction of nitric acid, from which it separates nitric oxide by
withdrawing three, atoms of oxygen from it. The decomposition of the
nitric acid being attended, in this case, with the formation of a very
peculiar brownish-black compound of nitric oxide with an undecom-
posed portion of the salt of the protoxide of iron : this reaction affords
a particularly characteristic and delicate test for the detection of nitric
acid. Sulphate of protoxide of iron serves, also, for the detection of
hydroferricyanic acid, with which it produces a kind of Prussian blue,
and also to effect the precipitation of metallic gold from solutions of the
salts of that metal.
63.
2. SESQUICHLORIDE OF IRON (Fe a C1 3 ).
Preparation. Heat in a flask a mixture of 10 parts of water and 1
part of pure hydrochloric acid with small iron nails until no further
evolution of hydrogen is observed, even after adding the nails in excess ;
filter the solution into another flask, and conduct into it chlorine gas,
with frequent shaking, until the fluid no longer produces a blue precipi-
tate in solution of ferricyanide of potassium. Heat until the excess of
chlorine is expelled. Dilute until the fluid is twenty times the weight of
the iron dissolved, and keep the dilute fluid for use.
Tests. Solution of sesquichloride of iron must not contain an excess
of acid ; this may be readily ascertained by stirring a sample of it with a
glass rod dipped in ammonia, when the absence of any excess of acid will
be proved by the formation of a precipitate, which shaking the vessel
and agitating the fluid^ fail to redissolve. Ferricyanide of potassium
must not impart a blue color to it.
Uses. Sesquichloride of iron serves to subdivide the group of organic
acids which chloride of calcium fails to precipitate ; as it produces pre-
cipitates in solutions of benzoates and succinates, but not in solutions
of acetates and formates. The aqueous solutions of the neutral acetate
and formate of sesquioxide of iron exhibit an intensely red color ; ses-
quichloride of iron is therefore a useful agent for detecting acetic acid
and formic acid. Sesquichloride of iron is exceedingly well adapted to
effect the decomposition of phosphates of the alkaline earths (see 143).
It serves also for the detection of hydroferrocyanic acid, with which it
produces Prussian blue.
64.
3. NITRATE OF SILVER (Ag 0, N 6 ).
Preparation. Dissolve pure silver in pure nitric acid, evaporate the
solution to dryness, and dissolve 1 part of the salt in 20 parts of water.
Tests. Solution of nitrate of silver must be completely precipitated by
54 ACETATE OF LEAD. [ 65, 66.
dilute hydrochloric acid, so that the fluid filtered from the precipitated
chloride of silver leaves no residue when evaporated on a watch-glass, and
is neither precipitated nor colored by hydrosulphuric acid.
Uses. Oxide of silver forms with many acids soluble, with others
insoluble compounds. Nitrate of silver may therefore serve, like
chloride of barium, to effect the separation and arrangement of acids
into groups.
Most of the insoluble compounds of silver dissolve in dilute nitric
acid ; chloride, bromide, iodide, and cyanide of silver, &c., are insoluble
in that menstruum. Nitrate of silver is therefore a most excellent agent
to distinguish and separate from all other acids, the hydracids corre-
sponding to the last enumerated four compounds of silver. Many of the
insoluble salts of silver exhibit a peculiar color (chromate of silver,
arsenate of silver), or manifest a characteristic deportment with other
reagents, or upon the application of heat (formate of silver) ; nitrate of
silver is therefore an important agent for the positive detection of
certain acids.
65.
4. ACETATE OF LEAD (Pb 0, A^ crystallized Pb 0, A7+ 3 aq.).
The best acetate of lead of commerce is sufficiently pure for the pur-
pose of chemical analysis ; for use, dissolve 1 part of the salt in 10 parts
of water.
Uses. Oxide of lead forms with a great many acids compounds in-
soluble in water, which are marked either by peculiarity of color or
characteristic deportment. The acetate of lead, therefore, produces pre-
cipitates in the solutions of these acids, or of their salts, and essentially
contributes to the detection of several of them. Thus, chromate of lead,
for instance, is characterized by its yellow colour, phosphate of lead by
its peculiar deportment before the blowpipe, and malate of lead by its
ready fusibility.
66.
5. NITRATE OF SUBOXIDE OF MEECURY (Hg 2 O, N Oo> crystallized
Hg 2 0,N0 6 + 2
Preparation. Pour 1 part of pure nitric acid on 1 part of 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 one-sixteenth
part of nitric acid, by trituration, in a mortar. Filter the solution, and
keep the filtrate in a bottle, with metallic mercury covering the bottom
of the vessel.
Uses. Nitrate of suboxide of mercury acts in an analogous manner
to the corresponding salt of silver. In the first place, it precipitates
many acids, especially the hydracids ; 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, at the expense of the oxygen of the sub-
oxide of mercury, is attended with the highly characteristic separation of
metallic mercury.
67 69.] CHLORIDE OF MERCURY. 55
67.
6. CHLOKIDE OF MERCURY (Hg Cl).
The chloride of mercury of commerce is sufficiently pure for the pur-
pose of chemical analysis. For use, dissolve 1 part of the salt in 16
parts of water.
Uses. Chloride of mercury gives with several acids, e. g., with hydri-
odic acid, peculiarly colored precipitates, and may accordingly be used
for the detection of these acids. It is an important agent for the detec-
tion of tin, when that metal is in solution in the state of protochlo-
ride ; if only the smallest quantity of that compound is present, the
addition of chloride of mercury in excess to the solution is followed by
separation of subchloride of mercury insoluble in water. In a similar
manner chloride of mercury serves also for the detection of formic acid.
68.
7. SULPHATE OF COPPER (Cu 0, S 8 , crystallized Cu 0, S 8 , H + 4 aq.).
Preparation. This reagent may be obtained in a state of great purity
from the residue remaining in the retort in the process of preparing
bisulphite of soda ( 46), by treating that residue with water, apply-
ing heat, filtering, crystallizing, and purifying the salt by recrystal-
lization. For use, dissolve 1 part of the pure crystals in 10 parts of
water.
Tests. Pure sulphate of copper must be completely precipitated from
its solutions by hydrosulphuric acid ; ammonia and sulphide of ammo-
nium must accordingly leave the nitrate unaltered.
Uses. Sulphate of copper is employed in qualitative analysis to effect
the precipitation of hydriodic acid in the form of subioclide of copper.
For this purpose it is necessary to mix the solution of 1 part of sulphate
of copper with 2^ parts of sulphate of protoxide of iron, otherwise half of
the iodine will separate in the free state. The protoxide of iron changes, in
this process, to sesquioxide, at the expense of the oxygen of the oxide of
copper, which latter is thus reduced to the state of suboxide. Sulphate
of copper is used also for the detection of arsenious and arsenic acid ;
it serves, likewise, as a test for the soluble ferrocyanides.
69.
8. PROTOCHLORIDE OF TIN (Sn 01, crystallized Sn Cl + 2 aq.).
Preparation. Reduce English tin to powder by means of a file, or
fuse it in a small porcelain dish, remove from the fire, and triturate the
fused liquid mass with a pestle until it has passed again to the solid
state ; boil the powder for some time with concentrated hydrochloric acid
in a flask (taking care always to have an excess of tin) until no more
hydrogen gas is evolved ; dilute the solution with 4 times the quantity
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 protochloride will soon change to bichloride, which will, of course,
render the reagent totally unfit for the purpose for which it is intended.
Tests. Solution of protochloride of tin, when added to a solution of
56 BICHLORIDE OF PLATINUM. [ 70 72.
chloride of mercury, must immediately produce a white precipitate of sub-
chloride of mercury ; when treated with hydrosulphuric acid, it must
give a dark brown precipitate ; it must not be precipitated nor rendered
turbid by sulphuric acid.
Uses. The great tendency of protochloride of tin to absorb oxygen,
and thus to form binoxide, or rather bichloride as the binoxide, in the
moment of its formation, decomposes with the free hydrochloric acid pre-
sent makes this substance one of our most powerful reducing agents.
We employ it in the course of analysis as a test for mercury, and also to
effect the detection of gold, for which latter purpose it is previously
mixed with some nitric acid, without heat.
^7 f\
70.
9. BICHLORIDE OF PLATINUM (Pt C1 2 , crystallized Pt Cl a + 10 aq.).
Preparation. Treat platinum filings purified by boiling with nitric
acid, with concentrated hydrochloric acid and some nitric acid, in a
narrow-necked flask, and apply a very gentle heat, adding occasionally
fresh portions of nitric acid, until the platinum is completely dissolved.
Evaporate the solution to dryness on the water-bath, with addition of
hydrochloric acid, and dissolve the residue in 1 parts of water for use.
Tests. Bichloride of platinum must, upon evaporation to dryness in
the water-bath, leave a residue which dissolves completely in spirit of wine.
Uses. Bichloride of platinum forms very sparingly soluble double
salts with chloride of potassium and chloride of ammonium, but not so
with chloride of sodium ; it serves, therefore, to detect ammonia and
potassa, and is, indeed, almost our most delicate reagent for the latter
substance.
71.
10. SODIO-PROTOCHLORIDE OF PALLADIUM (NaCl, PdCl).
Dissolve 5 parts of palladium in nitrohydrochloric acid (comp. 70),
add 6 parts of pure chloride of sodium, evaporate in the water-bath to
dryness, and dissolve 1 part of the residuary double salt in 12 parts of
water for use. The brownish solution forms an excellent means of
detecting and separating iodine.
72.
11. TERCHLORIDE OF GOLD (AuCl 2 ).
Preparation. Take fine shreds of gold, which may be alloyed with
silver or copper, treat them in a flask with nitrohydrochloric acid
in excess, and apply a gentle heat until no more of the metal dissolves.
If the gold was alloyed with copper, which is known by the brownish-red
precipitate produced by ferrocyanide of potassium in a portion of the
solution diluted with water, mix it with solution of sulphate of pro-
toxide of iron in excess ; this will reduce the terchloride to metallic
gold, which will separate in the form of a fine brownish-black powder ;
wash the powder in a small flask, and redissolve it in nitrohydrochloric
acid ; evaporate the solution to dryuess 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 to dryness,
and dissolve in water for use.
73.] TEST PAPERS. 57
Uses. Terchloride of gold has a great tendency to yield up its
chlorine ; it therefore readily converts protochlorides into higher
chlorides, protoxides, with the co-operation of water, into higher oxides.
These peroxidations 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 protoxide of tin,
in the solu-tions of which it produces a purple color or a purple pre-
cipitate.
Y. COLORING MATTERS AND INDIFFERENT VEGETABLE
SUBSTANCES.
73.
1. TEST PAPERS.
a. BLUE LITMUS PAPER.
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 the 1 part, by re-
peatedly stirring with a glass rod dipped in very dilute sulphuric acid,
until the colour 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 fine
unsized paper through it ; suspend these slips over threads and leave
them to dry. The color of litmus paper must be perfectly uniform, and
neither too light nor too dark.
Uses. Litmus paper serves to detect the presence of free acid in
fluids, as acids change its blue color to red. It must be borne in mind,
however, that the soluble neutral salts of most of the heavy metallic
oxides produce the same effect.
j3. REDDENED LITMUS PAPER.
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. Steep slips of paper in the solution, and dry them as in a.
The dried slips must look distinctly red.
Uses. Pure alkalies and alkaline earths, and also the sulphides of
their metals, restore the blue color of reddened litmus paper ; alkaline
carbonates and the soluble salts of several other weak acids, especially of
boracic acid, possess the same property. This reagent serves therefore
for the detection of these bodies in general.*
y. GEORGIKA. PAPER (Dahlia Paper).
Preparation. Boil the violet-colored petals of Georgina purpurea
(purple dahlia) in water, or digest them with spirit of wine, and steep
slips of paper in the tincture obtained. The latter should be neither
more nor less concentrated than is necessary to make the paper, after
drying, appear of a fine and light violet blue color. Should the color
too much incline to red, this may be remedied by adding a very little
ammonia to the tincture.
* Mr. A. S. Taylor has suggested that a very delicate test paper for detecting alkalies
may be prepared by steeping slips of paper in an acid infusion of rose petals.
53 TURMERIC PAPEE. [ 74, 75.
Uses. Georgina paper is reddened by acids, whilst alkalies impart a
beautiful green tint to it. It is therefore an extremely convenient sub-
stitute both for the blue and the reddened litmus paper. This reagent, if
properly prepared, is a most delicate test both for acids and alkalies.
Concentrated solutions of caustic alkalies turn Georgina paper yellow, by
destroying the coloring matter.
8. TURMERIC PAPER,
Preparation. Digest and heat 1 part of bruised turmeric root with
6 parts of weak spirit of wine, filter the tincture obtained, and steep
slips of fine paper in the filtrate. The dried slips must exhibit a fine
yellow tint.
Uses. Turmeric paper serves, like reddened litmus paper and dahlia
paper, for the detection of free alkalies, &c., as they change its yellow color
to brown. It is not quite so delicate a test as the other reagent papers ;
but the change of color which it produces is highly characteristic, and
is very distinctly perceptible in many colored fluids ; we cannot well
dispense, therefore, with this paper. When testing with turmeric paper,
it is to be borne in mind that, besides the substances enumerated in /3,
several other bodies (boracic acid, for instance) possess the property of
turning its yellow color to brown -red. It affords an excellent means
for the detection of the latter substance.
All test papers are cut into slips, which are kept in small well-
closed boxes, or in bottles covered with black paper, as continued action
of light destroys the color.
74.
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 con-
tains 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 ; it is therefore advisable, when dissolving
larger quantities of the substance, 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.
Uses. Indigo is decomposed by boiling with nitric acid, yellow-
colored oxidation products being formed. It serves, therefore, for the
detection of nitric acid. Solution of indigo is also well adapted to
effect the detection of chloric acid and of free chlorine.
B. REAGENTS IN THE DRY WAY.
I. FLUXES AND DECOMPOSING AGENTS.
75.
1. MIXTURE OF CARBONATE OF SODA AND CARBONATE OF POTASSA
(NaO,C0 2 + KO,C0 2 ).
Preparation. Digest 10 parts of purified bitartrate of potassa in
powder with 10 parts of water and 1 part of hydrochloric acid for
75.] CARBONATE OF SODA AND POTASSA. 59
several hours on the water-bath, with frequent stirring ; put the mass
into a funnel with a small filter inserted into the pointed end ; let it
drain ; cover with a disc of rather difficultly permeable filtering paper with
upturned edges, and wash by repeatedly pouring upon this small quantities
of cold water ; continue this washing process until the fiuid running off
is no longer rendered turbid by solution of nitrate of silver, after addition
of nitric acid. Dry the bitartrate of potassa freed in this manner from
lime (and phosphoric acid). It is now necessary to prepare pure
nitrate of potassa. To effect this, dissolve nitrate of potassa of commerce
in half its weight of boiling water, filter the solution into a porcelain or
stoneware dish, using a hot funnel, and stir it well with a wooden or
porcelain spatula until cold. Transfer the crystalline powder to a
funnel loosely stopped with cotton, let it drain, press down tight, make
it even at the top, and cover with a double disc of difficultly permeable
filtering paper with upturned edges, and pour upon this at proper
intervals small portions of water, until the washings are no longer made
turbid by solution of nitrate of silver. Empty now the contents of the
funnel into a porcelain dish, dry in this vessel, and reduce the mass to a
fine powder by trituration. Mix now 2 parts of the pure bitartrate
of potassa with 1 part of the pure nitrate of potassa ; put the perfectly
dry mixture in small portions at a time into a clean- scoured cast-iron
pot heated to gentle redness ; when the mixture has deflagrated, heat
strongly, until a sample taken from the edges gives with water a per-
fectly colorless solution. Triturate the charred mass with water, filter,
wash slightly, and evaporate the filtrate in a porcelain or, better still,
in a silver dish, until the fluid is covered with a persistent pellicle.
Let the mixture now cool, with constant stirring ; put the crystals of car-
bonate of potassa on a funnel, let them well drain, wash slightly, dry
thoroughly in a silver or porcelain dish, and keep the crystals in a well-
stoppered bottle. The mother-liquor leaves, upon evaporation, a salt
which, though containing traces of alumina and silicic acid, may still be
turned to account for many purposes.
Mix 13 parts of the pure carbonate of potassa prepared in the
manner just now described, with 10 parts of pure anhydrous carbonate
of soda, and keep the mixture in a well-stoppered bottle. The mixture
of carbonate of potassa and carbonate of soda may also be prepared by
deflagrating 20 parts of pure bitartrate of potassa with 9 parts of
pure nitrate of soda, treating with water, and evaporating the solution
to dryness.
Tests. The purity of the mixed salt is tested as directed 44 (car-
bonate of soda).
Uses. If silicic acid or silicates are fused with about 4 parts (con-
sequently with an excess) of carbonate of potassa or soda, carbonic acid
escapes with effervescence, and a basic alkaline silicate is formed, which,
being soluble in water, may be readily separated from such metallic
oxides as it may contain in admixture ; from this basic alkaline silicate,
hydrochloric acid separates the silicic acid as hydrate. If a fixed
alkaline carbonate is fused together with sulphate of baryta, strontia, or
lime, there are formed carbonates of the alkaline earths and sulphate of
the alkali, in which new compounds both the base and the acid of the
originally insoluble salt may now be readily detected. However, we do
not employ carbonate of potassa separately, nor carbonate of soda, to
effect the decomposition of the insoluble silicates and sulphates ; but we
60 HYDRATE OP BARYTA. [ 76 78.
apply for this purpose the above-described mixture of both, because this
mixture requires a far lower degree of heat for fusion than either of its
two components, and thus enables us to conduct the operation over a
Berzelius lamp, or over a simple gas lamp. The fusion with alkaline
carbonates is invariably effected in a platinum crucible, provided no
reducible metallic oxides be present.
76.
2. HYDEATE OF BARYTA (Ba 0, H 0).
Preparation. The crystals of baryta prepared in the manner directed
32, are heated gently in a silver or platinum dish, until the water
of crystallization is completely expelled. The residuary white mass is
pulverized, and kept for use in a well-closed bottle.
Uses. Hydrate of baryta fuses at a gentle red heat without losing
its water. Upon fusing silicates together with about 4 parts of hy-
drate of baryta, a basic silicate of baryta is formed, and the oxides are
liberated. If the fused mass is treated with hydrochloric acid, the solu-
tion evaporated to dryness, and the residue digested with hydrochloric
acid, the silicic acid is left behind, and the oxides are obtained in solu-
tion in the form of chlorides. We use hydrate of baryta as a flux when
we wish to test silicates for alkalies. This reagent is preferable as a
flux to the carbonate or nitrate of baryta, since it does not require a very
high temperature for its fusion, as is the case with the carbonate, nor
does it cause any spirting in the fusing mass, arising from disengage-
ment of gas, as is the case with the nitrate. The operation is conducted
in silver or platinum crucibles.
77.
3. FLUORIDE OF CALCIUM (Ca Fl).
Take fluor-spar as pure as can be procured, and more particularly free
from alkalies, reduce to fine powder, and keep this for use.
Uses. Fluoride of calcium applied in conjunction with sulphuric acid,
serves to effect the decomposition of silicates insoluble in acids, and more
especially to detect the alkalies which they contain. Compare Section
III. Silicic acid, 150.
78.
4. NITRATE OF SODA (Na 0, N0 6 ).
Preparation. Neutralize pure nitric acid with pure carbonate of soda
exactly, and evaporate to crystallization. Dry the crystals thoroughly,
triturate, and keep the powder for use.
Tests. A solution of nitrate of soda must not be made turbid by
solution of nitrate of silver or nitrate of baryta, nor precipitated by
carbonate of soda.
Uses. Nitrate of soda serves as a very powerful oxidizing agent, by
yielding oxygen to combustible substances when heated with them. We
use this reagent principally to convert several metallic sulphides, and
more particularly the sulphides of tin, antimony, and arsenic, into oxides
and acids; and also to effect the rapid and complete combustion of
organic substances ; for the latter purpose, however, nitrate of ammonia
79j 80.] CARBONATE OF SODA. 61
is in many cases preferable ; this latter reagent is prepared by saturating
nitric acid with carbonate of ammonia.
II. BLOWPIPE REAGENTS.
79.
1. CARBONATE OF SODA (Na 0, C 2 ).
Preparation. See 44.
Uses. Carbonate of soda serves, in the first place, to promote the
reduction of oxidized substances in the inner flame of the blowpipe. In
fusing it brings the oxides into the most intimate contact with the char-
coal support, and enables the flame to embrace every part of the substance
under examination. It co-operates in this process also chemically by the
transposition of its constituents (according to R. Wagner, in consequence
of the formation of cyanide of sodium). If the quantity operated upon
was very minute, the reduced metal is often found in the pores of the
charcoal. In such cases, the parts surrounding the little cavity which
contained the sample are dug out with a knife, and triturated in a small
mortar ; the charcoal is then washed off from the metallic particles,
which now become visible either in the form of powder or as small flat
spangles, according to the nature of the particular metal or metals
present.
Carbonate of soda serves, in the second place, as a solvent. Platinum
wire is the most convenient support for testing the solubility of substances
in fusing carbonate of soda. A few only of the bases dissolve in fusing
carbonate of soda, but acids dissolve in it with facility. Carbonate of
soda is, moreover, applied as a decomposing agent and flux, and more par-
ticularly to effect the decomposition of the insoluble sulphates, with which
it exchanges acids, the newly formed sulphate of soda being reduced at the
same time to sulphide of sodium ; and to effect the decomposition of sulphide
of arsenic, with which it forms a double sulphide of arsenic and sodium,
and arsenite or arsenate of soda, thus converting it to a state which
permits its subsequent reduction by hydrogen. Finally, carbonate of
soda is the most sensitive reagent in the dry way for the detection of
manganese, since when fused in the outer flame of the blowpipe together
with a substance containing manganese, it produces a green opaque bead,
owing to the formation of manganate of soda.
80.
2. CYANIDE OF POTASSIUM (K Cy).
Preparation. See 52.
Uses. Cyanide of potassium is an exceedingly powerful reducing agent
in the dry way ; indeed it excels in its action almost all other reagents of
the same class, and separates the metals not only from most oxygen com-
pounds, but also from sulphur compounds : this reduction is attended in
the former case with formation of cyanate of potassa, by the absorption
of oxygen, and in the latter case with formation of sulphocyanide of
potassium. By means of this reagent we may effect the reduction of
metals from their compounds with the greatest possible facility ; thus we
may, for instance, produce metallic antimony from antimonious acid or
from sulphide of antimony, metallic iron from sesquioxide of iron, &c.
62 BIBORATE OF SODA. [ 81.
The readiness with which cyanide of potassium enters into fusion facili-
tates the reduction of the metals greatly ; the process may usually be
conducted even in a porcelain crucible over a spirit lamp. Cyanide of
potassium is a most valuable and important agent to effect the reduction
of arsenites and arsenates, and more particularly of tersulphide of arsenic
(see 131). Cyanide of potassium is equally important as a blowpipe
reagent. Its action is exceedingly energetic ; substances like binoxide
of tin, bisulphide of tin, &c., the reduction of which by means of car-
bonate of soda requires a tolerably strong flame, are reduced by cyanide
of potassium with the greatest facility. In blowpipe experiments we in-
variably use a mixture of equal parts of carbonate of soda and cyanide
of potassium ; the admixture of carbonate of soda is intended here to
check in some measure the excessive fusibility of the cyanide of potas-
sium. This mixture of cyanide of potassium with carbonate of soda,
besides being a far more powerful reducing agent than the simple car-
bonate of soda, has, moreover, this great advantage over the latter, 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.
si.
3. BIBOKATE OF SODA (Sorax) (Na 0, 2 B O 3 , crystallized +10 aq.).
The purity of commercial borax may be tested by adding to its solu-
tion carbonate of soda, or after previous addition of nitric acid, solu-
tion of nitrate of baryta or of nitrate of silver. 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 crys-
tallized borax is exposed to a gentle heat, in a platinum crucible, until
it ceases to swell ; when cool, it is pulverized and kept for use.
Uses. Boracic acid manifests a great affinity for oxides when brought
into contact with them in a state of fusion. This affinity enables it, in.
the first place, to combine directly with oxides ; secondly, to expel
weaker acids from their salts ; and, thirdly, to predispose metals, sul-
phides, and haloid compounds to oxidize in the outer flame of the blow-
pipe, that it may combine with the oxides. Most of the thus produced
borates fuse readily, even without the aid of a flux, but far more so in
conjunction with borate of soda ; the latter salt acts in this operation
either as a mere flux, or by the formation of double salts. Now, in the
biborate of soda we have both free boracic acid and borate of soda ; the
union of these two substances renders it one of our most important blow-
pipe reagents. In the process of fluxing with borax, we usually select
platinum wire 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 colourless bead of fused borax is thus produced. A small portion of
the substance under examination is then attached to the bead, by bring-
ing the latter into contact with it, either whilst still hot or having
previously moistened it. The bead with the sample of the substance
intended for analysis adhering to it, is now exposed to the blowpipe flame,
and the phenomena to the manifestation of which this process gives rise
are carefully observed and examined. The following points ought to be
more particularly watched: (1) Whether or not the sample under
examination dissolves to a transparent bead, and whether or not the bead
retains its transparency on cooling ; (2) whether the bead exhibits a dis-
82, S3.] PHOSPHATE OF SODA AND AMMONIA. 63
tinct color, which in many cases at once clearly indicates the individual
metal which the analysed compound contains, 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. Phenomena of the
latter kind arise from the ensuing reduction of higher to lower oxides,
or even to the metallic state, and are for some substances particularly
characteristic.
82.
4. PHOSPHATE OF SODA AND AMMONIA (Microcosmic Salt)
(Na O, N H 4 O, H O, P 5 , crystallized + 8 aq.).
Preparation. Heat to boiling 6 parts of phosphate of soda and 1
part of pure chloride of ammonium with 2 parts of water, and let the
solution cool. Free the crystals produced of the double phosphate of
soda and ammonia by recrystallization from the chloride of sodium which
adheres to them. Dry the purified crystals, and pulverize them for use.
Uses. When phosphate of soda and ammonia is subjected to the
action of heat, the ammonia escapes with the water of crystallization,
and readily fusible metaphosphate of soda is left behind. The action of
microcosmic salt is quite analogous to that of biborate of soda. We
prefer it, however, in some cases, to borax as a solvent or flux, the beads
which it forms with many substances being more beautifully and dis-
tinctly colored than those of borax. Platinum wire is also used for a
support in the process of fluxing with microcosmic salt ; the loop of the
wire must be made small and narrow, otherwise the bead will not adhere
to it. The operation is conducted as directed in the preceding para-
graph.
83.
5. NITRATE OP PROTOXIDE OF COBALT (Co 0, N 5 , crystallized + 5 aq.).
Preparation. Fuse in a Hessian crucible 3 parts of bisulphate of
potassa, and add to the fused mass, in small portions at a time, 1 part of
well roasted cobalt ore (the purest zaffre you can procure) reduced to
fine powder. The mass thickens, and acquires a pasty consistence.
Heat now more strongly, until it has become more fluid again, and
continue to apply heat until the excess of sulphuric acid is completely
expelled, and the mass accordingly no longer emits white fumes.
Remove the fused mass now from the crucible with an iron spoon
or spatula, let it cool, and reduce it to powder ; boil this with water
until the undissolved portion presents a soft mass ; then filter the
rose-red solution, which is free from arsenic and nickel, and mostly also
from iron, and remove the copper, &c., from the filtrate by means of
hydrosulphuric acid. Filter again, and evaporate the filtrate, with
addition of some chlorine water, until it is much concentrated. Mix
the concentrated filtrate now with a hot saturated solution of binoxalate
of potassa, and let the mixture stand at a gentle heat until the fluid
appears colorless. Wash the precipitated oxalate of protoxide of cobalt
thoroughly, dry, and heat to redness in a covered platinum or porcelain
crucible. This decomposes the oxalate into water and carbonic acid, which
escapes, and metallic cobalt, which is left behind. Dissolve a portion of
the latter in nitric acid, taking care to avoid a large excess of the
solvent ; evaporate the solution in the water-bath to dryness, and dis-
solve 1 part of the residue in 10 parts of water for use.
64 CHLORIDE OP SILVER. [ 84, 85.
Tests. Solution of nitrate of protoxide of cobalt must be free from
other metals, and especially also from salts of the alkalies ; when pre-
cipitated with sulphide of ammonium and filtered, the filtrate must,
upon evaporation on platinum, leave no fixed residue.
jj ses , Protoxide of cobalt forms, upon ignition with certain infusible
bodies, peculiarly colored compounds, and may accordingly serve for the
detection of these bodies (oxide of zinc, alumina, and magnesia ; see
Section III.).
84.
6. CHLOEIDE OF SILVER (Ag Cl).
Preparation. Precipitate solution of nitrate of silver with hydro-
chloric acid ; wash the precipitate, mix it with water to a thick pulp,
and keep in a small bottle for use.
Uses. Chloride of silver has lately been recommended by Gericke as
a means of making the colorations more distinct and lasting which
certain bodies, upon exposure to the inner blowpipe flame, impart to the
outer flame. I can from my own experience confirm the results arrived
at by Gericke. The action of the chloride of silver is owing to the cir-
cumstance that this compound loses its chlorine only gradually upon
exposure to heat, and gives rise accordingly for a certain time to the
formation of metallic chlorides, which it is well known impart more
distinct colorations to flame than any other class of salts. As platinum
wire would speedily be rendered unfit for use by the reduced silver, thin
iron wire is employed ; every operation requires a new loop.
SECTION III.
ON THE DEPORTMENT OF BODIES WITH REAGENTS.
85.
I STATED in my introductory remarks that the operations and experi-
ments of qualitative analysis have for their object the conversion of the
unknown constituents of any given compound into forms of which we
know the deportment, relations, and properties, and which will accord-
ingly permit us to draw correct inferences regarding the several con-
stituents of which the analysed 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, no matter whether of a positive or
negative nature. But as a question does not render us any the wiser if
we do not know the language in which the answer is returned, so, in
like manner, will analytical investigations 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 our reagents upon the substance
examined.
Before we can therefore proceed to enter upon the practical investiga-
86.] METALLIC OXIDES AND THEIR RADICALS. 65
tions of analytical chemistry, it is indispensable that we should really
possess the most perfect knowledge of the deportment, relations, and
properties of the new forms into which we intend to convert the sub-
stances we wish to analyse. Now, this perfect knowledge consists,
in the first place, in a clear conception and comprehension of the condi-
tions necessary for the formation of the new compounds and the
manifestation of the various reactions; and, in the second place,
in a distinct impression of the color, form, and physical properties
which characterize the new compound. This section of the work
demands therefore not only the most careful and attentive study, but
requires moreover that the student should examine and verify by actual
experiment every fact asserted in it.
The method usually adopted in elementary works on chemistry is to
treat of the various substances and their deportment with reagents in-
dividually and separately, and to point out their characteristic reactions.
I have, however, in the present work, deemed it more judicious and
better adapted to its elementary character, to arrange those substances
which are in many respects analogous into groups, and thus, by com-
paring their analogies with their differences, to place the latter in the
clearest possible light.
A. DEPORTMENT AND PROPERTIES OF THE METALLIC OXIDES AND
OF THEIR RADICALS.
86.
Before proceeding to the special study of the several metallic oxides,
I give here a general view of the whole of them, classified in groups
showing which oxides belong to each group. The grounds upon which
the classification has been arranged will appear from the special con-
sideration of the several groups.
First group
Potassa, soda, ammonia (lithia).
Second group
Baryta, strontia, lime, magnesia.
Third group
Alumina, sesquioxide of chromium (glucina, thorina, noria, yttria,
terbia, erbia, zirconia earths ; oxides of cerium, lanthanium, didymium ;
oxide of titanium and titanic acid ; tantalic acid, niobic acid).
Fourth group s * ;
Oxides of zinc, manganese, nickel, cobalt, iron (uranium).
Fifth group
Oxides of silver, mercury, lead, bismuth, copper, cadmium (palladium,
rhodium, osmium, ruthenium).
Sixth group
Oxides and acids of antimony, tin, arsenic, gold, platinum (iridium,
molybdenum, tellurium, tungsten, vanadium).
Of these metallic oxides only those printed in italics are found exten-
sively and in large quantities in that portion of the earth's crust which
is accessible to our investigations ; these, therefore, are most important
to chemistry, arts and manufactures, agriculture, pharmacy, &c. &c. ;
and these therefore we shall dwell upon at greater length. The more
important among the remainder are more briefly considered in sup-
plementary paragraphs; and the less important ones are altogether
i. F
66 POTASSA, SODA, AMMONIA. [ 87, 88.
omitted. The deportment of the metals I have given only in the case
of tiiose that are more frequently met with in analytical operations in
the metallic state.
87.
FIRST GROUP.
POTASSA, SODA, AMMONIA.
Properties of the group. The alkalies are readily soluble in water, as
well in the pure or caustic state as in the form of sulphides, carbonates,
and phosphates. Accordingly they do not precipitate one another in
the pure state, nor as carbonates or phosphates, nor are they precipitated
by hydrosulphuric acid under any condition whatever. Tbe solutions of
the pure alkalies, as well as of their sulphides and carbonates, restore the
blue color of reddened litmus-paper, and impart an intensely brown tint
to turmeric paper.
Special Reactions.
88.
a. POTASSA (K 0).
1. Potassa and its hydrate and salts are not volatile at a faint red-
heat. Potassa and its hydrate deliquesce in the air ; the oily liquids
formed do not solidify by absorption of carbonic acid.
2. Nearly the whole of the salts of potassa are readily soluble in water.
They are colorless, if the constituent acid is so. The neutral salts of
potassa with strong acids do not alter vegetable colors. Carbonate of
potassa crystallizes with difficulty, and deliquesces in the air. Sulphate
of potassa is anhydrous, and suffers no alteration in the air.
3. Bichloride of platinum produces in the neutral and acid solutions
of the salts of potassa a yellow, crystalline, heavy precipitate of BICHLO-
RIDE OP PLATINUM AND CHLORIDE OF POTASSIUM (potassio-Uchloride of
platinum) (K 01, Pt C1 2 ). In concentrated solutions this precipitate
separates immediately upon the addition of the reagent : in dilute solu-
tions it forms only after some time, often after a considerable time.
Yery dilute solutions are not precipitated by the reagent. The preci-
pitate consists of octahedrons discernible under the microscope. Alka-
line solutions must be acidified with hydrochloric acid before the bi-
chloride of platinum is added. The precipitate is difficultly soluble in
water ; the presence of free acids does not greatly increase its solubility ;
it is insoluble in alcohol. Bichloride of platinum is therefore a par-
ticularly delicate test for salts of potassa dissolved in spirit of wine.
The best method of applying this reagent is to evaporate the aqueous
solution of the potassa salt with bichloride of platinum nearly to dryness
on the water-bath, and to pour a little water on the residue, or, better
still, some spirit of wine, provided no substances insoluble in that
menstruum be present : the potassio-bichloride of platinum is left un-
dissolved. Care must be taken not to confound this double salt with
ammonio-bichloride of platinum, which greatly resembles it (see 90, 4).
4. Tartaric acid produces in neutral or alkaline* solutions of salts of
potassa a white, quickly subsiding, granular crystalline precipitate of
* In the case of alkaline solutions, the reagent must be added until the fluid shows a
strongly acid reaction.
89.] SODA. 67
BITABTRATE OF POTASSA (K 0, H 0, C H 4 OJ. In concentrated solu-
tions this precipitate separates immediately ; in dilute solutions often
only after the lapse of some time. Yigorous shaking or stirring of the
fluid promotes its formation considerably. Very dilute solutions are not
precipitated by this reagent. Free alkalies and free mineral acids dis-
solve the precipitate ; it is difficultly soluble in cold, but pretty readily
soluble in hot water. In the case of acid solutions, the free acid must, if
practicable, first be expelled by evaporation and ignition, or the solution
must be neutralized with soda or carbonate of soda, before we can pro-
ceed to test for potassa with tartaric acid.
5. If a salt of potassa, more particularly chloride of potassium, is held
on a platinum wire in the apex of the inner blowpipe flame, the outer
flame acquires a VIOLET color. The tint which phosphate and borate
of potassa impart to the outer blowpipe flame is scarcely perceptible.
Presence of a salt of soda completely obscures the reaction. Decre-
pitating salts are pulverized and made to adhere to the wire with water.
Addition of chloride of silver promotes the reaction in the case of nitrate,
carbonate, &c., of potassa ( 84).
6. If a salt of potassa (more particularly chloride of potassium) is
heated with a small quantity of water, alcohol (burning with colorless
flame) added, heated, and then kindled, the flame appears VIOLET. The
presence of soda obscures this reaction,
89.
6. SODA (NaO).
1. Soda and its hydrate and salts present in general the same deport-
ment and properties as potassa and its corresponding compounds. The
oily fluid which soda forms by deliquescing in the air, resolidifies speedily
by absorption of carbonic acid. Carbonate of soda crystallizes readily ;
the tabular crystals (Na 0, C O 2 + 10 aq.) effloresce rapidly when ex-
posed to the air. The same applies to the prismatic crystals of sulphate
of soda (Na 0, S O 3 + 10 aq.).
2. Antimonate of potassa produces in neutral or feebly alkaline solu-
tions of salts of soda a white, crystalline precipitate of METANTIMONATE
OF SODA (Na O, Sb O 6 + 7 aq.). Yigorous shaking of the mixture pro-
motes its formation. If the fluid, after the addition of the reagent, be
stirred with a glass rod, moving the latter along the sides of the
vessel, the lines described will, even in very dilute solutions, speedily
become visible, since the precipitate forms first on the parts rubbed
by the rod. If the precipitate separates slowly, it consists of well-
formed microscopic quadrilateral octahedrons. The presence of neutral
salts of potassa interferes only slightly with the formation of the preci-
pitate ; but carbonate of potassa, when present in larger proportion,
wholly prevents its separation from more dilute solutions. In cases,
therefore, where the solution under examination contains this salt, it is
necessary to precede the application of the antimonate of potassa by
addition of hydrochloric or acetic acid until the reaction of the solution
remains only feebly alkaline. Acid solutions must first be neutralized
with potassa, since otherwise the reagent would suffer decomposition,
and hydrated antimonic acid or acid antimonate of potassa be precipi-
tated from it.
3. Salts of soda (more particularly chloride of sodium), when exposed
F 2
68 AMMONIA. [ 90.
on a platinum wire to the inner blowpipe flame, color the outer flame
INTENSELY YELLOW. This reaction remains clearly perceptible, even if
the soda contains a considerable admixture of potassa. Chloride of silver
promotes the reaction in the case of some, but not of all salts of soda.
4. If a salt of soda (more particularly chloride of sodium) is heated
with a small quantity of water, alcohol added, and the latter heated
and then kindled, the flame appears strongly YELLOW. The presence of
a salt of potassa does not impair the distinctness of this reaction.
5. Bichloride of platinum produces no precipitate in solutions of
salts of soda ; tartaric acid only when a highly concentrated solution of
soda or carbonate of soda is mixed with a saturated solution of tartaric
acid in excess. The bulky precipitate of BITARTRATE OF SODA which in
that case separates, consists of small needles and columns, and requires
only 12 parts of cold water for its solution ; it is not likely, therefore,
to be confounded with the granular crystalline precipitate of bitartrate
of potassa.
90.
c. AMMONIA (NH 4 0).
1. Anhydrous ammonia (N H~ 3 ) is gaseous at the common temperature ;
but we have most frequently to deal with it 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 it as oxide of ammonium (N H 4 0)
(see 31).
2. All the salts of ammonia are volatile at a high temperature, either
with or without decomposition. Most of them are readily soluble in
water. The solutions are colorless. The neutral compounds of ammonia
with strong acids do not alter vegetable colors.
3. If salts of ammonia are triturated together with hydrate of lime,
best with the addition of a few drops of water, or are, either in a solid
form or in solution, heated with solution of potassa or of soda, the
ammonia is liberated in the gaseous state, and betrays itself ( 1 ) by its
characteristic odor ; (2) by its reaction on moistened test-papers ; and
(3) by giving rise to the formation of white fames, 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 fumes
arise from the formation of solid ammoniacal salts produced by the con-
tact of the gases in the air. Hydrochloric acid is the most delicate test
in this respect ; acetic acid, however, admits less readily of a mistake.
In cases where the quantity of ammonia present is only very small, the
best way of testing the alkaline reaction of the fumes is to cover a
small beaker containing the mixture with a watch-glass, having a
slip of moistened turmeric or reddened litmus-paper attached to the
convex side, to place it on a hot slab, and observe, after a few minutes,
whether the test-paper has changed color.
4. Bichloride of platinum shows the same deportment with salts of
ammonia as with salts of potassa ; the yellow precipitate of BICHLORIDE
OF PLATINUM AND CHLORIDE OF AMMONIUM (N H 4 Cl, Pt C1 2 ) is. however,
of a somewhat lighter color than potassio-bichloride of platinum. It
consists, like the corresponding potassium compound, of octahedrons, dis-
cernible under the microscope.
5. Tartaric acid added in excess to a solution of ammonia or carbonate
91.] RECAPITULATION. 69
of ammonia, produces a white crystalline precipitate of BITARTRATE OF
AMMONIA (N H 4 H O, C 8 H 4 10 ). In concentrated solutions this preci-
pitate forms immediately ; in dilute solutions only after some time.
The solutions of other ammoniacal salts (chloride of ammonium, nitrate
of ammonia, &c.) are not precipitated by this reagent, even when highly
concentrated ; or a trifling precipitate only separates after long stand-
ing. Bitartrate of ammonia comports itself with solvents like the corre-
sponding salt of potassa; however, it is some what "more readily soluble
in water and acids than the latter.
6. If a solution of potassio-iodide of mercury* containing much
caustic potassa, is mixed with a fluid containing ammonia or an ammo-
niacal salt, a reddish-brown precipitate of hydrated TETRAHYDRARGYRO-
IODIDE OF AMMONIUM (N HgJ + 2 H 0) : 4 (Hg I, K I) + 3 K O + N H 3 =
(N Hg 4 1+ 2HO) + 7K1 + HO, separates immediately or upon ap-
plication of a gentle heat. This precipitate redissolves in presence of an
excess of ammoniacal salts ; but reprecipitates upon further addition of
potassa ; it is soluble also in solution of iodide of potassium, but the less
so the more free potassa happens to be present. When a considerable
excess of potassa exists, therefore, the precipitate is insoluble in iodide of
potassium. Presence of chlorides of the alkali metals, or of salts of
potassa and soda, does not interfere with the reaction ; but cyanides and
sulphides of the alkali metals prevent it. This reaction was first pointed
out by Nessler; it is not required for ordinary analyses, but is ex-
tremely valuable in cases where the presence of minute traces of
ammoniacal salts are to be detected. I have found it to give distinct
indications of the presence of ammonia in solutions of '00001 gramme of
chloride of ammonium in 1 cubic centimetre of water.
91.
Recapitulation and remarks. The salts of potassa and soda are not
volatile at a moderate red heat, whilst the salts of ammonia volatilize
readily ; the latter may therefore be easily separated from the former by
ignition. The expulsion of ammonia from its compounds, by hydrate of
lime, affords the surest means of ascertaining the presence of this sub-
stance. Salts of potassa can be detected positively only after the removal
of the ammoniacal salts which may be present, since both classes of salts
manifest the same or a similar deportment with bichloride of platinum
and tartaric acid. After the removal of the ammonia, the potassa is
clearly and positively characterized by either of these two reagents. The
most simple way of detecting the potassa in the two difficulty-soluble
compounds that have come under our consideration here viz., the
potassio-bichloride of platinum and bitartrate of potassa is to decompose
these salts by ignition ; the former, thereupon, yields the potassa in the
form of chloride of potassium, the latter in the form of carbonate of
potassa. With respect to soda, the yellow tint which its salts impart to
the blowpipe flame and to the flame of alcohol, is a safe and mostly in
itself sufficient proof of its presence, provided always no other bodies be
present besides salts of fixed alkalies. In form of chlorides, T ^th part
of soda may by this means be detected in presence of potassa. Anti-
* To prepare this reagent, digest at a gentle heat 2 grammes of iodide of potassium,
and 3 grammes of iodide of mercury, in 5 cub. cent, of water ; add 20 cub. cent, of
water, let the mixture stand for some time, then filter ; add to the filtrate 30 cub.
cent, of pure concentrated solution of potassa (1 : 4) ; and, should a precipitate form, let
this settle ; decant, and use the clear decanted fluid.
70 LITHIA. [ 92.
monateof potassa also gives decisive results when no other bases besides soda
or potassa are present, and especially if these latter are present as chlorides
or nitrates. Even from very dilute solutions of salts of soda, antimonate
of potassa added in excess will, after twelve hours' standing, throw down
antimonate of soda, the crystals of which may always be readily and
distinctly recognised under the microscope by their form quadrilateral
octahedrons.
92.
SUPPLEMENT TO THE FIRST GROUP.
LITHIA (Li 0).
Lithia dissolves with difficulty in water ; it does not attract moisture
from the air. Most of its salts are soluble in water ; some of them are
deliquescent (chloride of lithium). Carbonate of lithia is difficultly
soluble, particularly in cold water. Phosphate of soda produces, in not over
dilute solutions of salts of lithia, upon boiling, a heavy white crystalline
precipitate of basic phosphate of lithia (3 Li O, P 5 4 aq.). From very
dilute solutions of lithia the same basic phosphate is obtained by adding
phosphate of soda and one or two drops of solution of soda to the solu-
tion, evaporating the mixed fluid to clryness, and treating the residue
with water. The basic phosphate of lithia obtained is sparingly soluble
in water, and still less so in ammoniated water ; it dissolves much more
readily in water containing salts of ammonium. It is immediately dis-
solved by acids ; addition of ammonia produces no precipitate in some-
what dilute acid solutions in the cold, but upon boiling, a precipitate
separates. The basic phosphate of lithia fuses before the blowpipe, and
gives upon fusion with carbonate of soda on the platinum wire a clear
bead ; when fused upon charcoal, it is absorbed by the pores of the latter
body (another difference between it and the phosphate of the alkaline
earths). Tartaric acid and bichloride of platinum fail to precipitate even
concentrated solutions of salts of lithia ; but in a solution of chloride of
potassium containing chloride of lithium, bichloride of platinum readily
produces a precipitate containing lithia (Jenzsch). If a salt of lithia
(more particularly chloride of lithium) is exposed on a platinum wire to
the inner blowpipe flame, the outer flame shows a strong CARMINE tint.
Presence of salts of soda (but not of salts of potassa) conceals this reaction.
Addition of chloride of silver promotes it in the case of some, but not of
all salts of lithia. If spirit of wine is poured over a salt of lithia (more
particularly chloride of lithium), and then kindled, the flame appears of
a CARMINE colour ; presence of salts of soda conceals this reaction.
To detect lithia in presence of potassa and soda, convert the bases into
dry chlorides ; treat them, after addition of a drop of hydrochloric acid,
with a mixture of absolute alcohol and anhydrous ether ; filter, distil, and
treat the residue remaining after distillation again with the said mixture,
after previous addition of a drop of hydrochloric acid ; filter, concentrate
the filtrate by evaporation, and then set fire to the concentrated fluid.
A carmine-coloured flame indicates the presence of lithia. The residue
remaining after evaporation of the alcohol must dissolve in water to a
clear fluid ; the solution must not be precipitated by carbonate of am-
monia (lime, strontia), and must give the above-mentioned reaction with
phosphate of soda. This method is based upon the insolubility of chloride
93, 94.] BARYTA. 71
of potassium, and chloride of sodium in absolute alcohol and ether, in
which chloride of lithium readily dissolves.
93.
SECOND GROUP.
BARYTA, STRONTIA, LIME, MAGNESIA.
Properties of the group. The alkaline earths are soluble in water in
the pure (caustic) state and as sulphides. Magnesia, however, dissolves
but very sparingly in water. The solutions manifest alkaline reaction ;
the alkaline reaction of magnesia is most clearly apparent when that
earth is laid upon moistened test-paper. The neutral carbonates and
phosphates of the alkaline earths are insoluble in water. The solutions
of the salts of the alkaline earths are therefore precipitated by alkaline
carbonates and phosphates, whilst hydrosulphuric acid fails to precipi-
tate them under any condition. This deportment distinguishes the oxides
of the second group from those of the first. The alkaline earths and their
salts are non-volatile and colorless ; their solutions are not precipitated
by sulphide of ammonium, nor by carbonate of baryta.
Special Reactions.
94.
a. BARYTA (Ba 0).
1. Caustic baryta is pretty readily soluble in hot water, but rather
difficultly so in cold water ; it dissolves easily in dilute hydrochloric or
nitric acid. Hydrate of baryta does not lose its water upon ignition.
2. Most of the salts of baryta are insoluble in water. The soluble
salts do not affect vegetable colors, and are decomposed upon ignition,
with the exception of chloride of barium. The insoluble salts dissolve
in dilute hydrochloric acid, except the sulphate of baryta. Nitrate of
baryta and chloride of barium are insoluble in alcohol, and do not deli-
quesce in the air. Concentrated solutions of baryta are precipitated by
hydrochloric or nitric acid added in large proportions, as chloride of
barium and nitrate of baryta are not soluble in the aqueous solutions of
the said acids.
3. Ammonia (free from carbonic acid) produces no precipitate in the
aqueous solutions of salts of baryta ; potassa or soda (free from carbonic
acid) only in highly concentrated solutions. Water redissolves the
bulky precipitate of CRYSTALS OF BARYTA (Ba 0, H + 8 aq.) produced
by potassa or soda.
4. Alkaline carbonates throw down from solutions of baryta CARBONATE
OF BARYTA (Ba O, C 2 ) in the form of a white precipitate. When car-
bonate of ammonia is used as the precipitant, or if the solution was
previously acid, complete precipitation takes place only upon heating the
fluid. In chloride of ammonium the precipitate is soluble to a trifling
yet clearly perceptible extent ; in very dilute solutions of baryta, therefore,
which contain much chloride of ammonium, carbonate of ammonia pro-
duces no precipitate.
5. Sulphuric acid and all the soluble sulphates, also solution of sul-
phate of lime, produce even in very dilute solutions of baryta, a
72 STRONTIA. [95.
heavy, finely pulverulent, white precipitate of SULPHATE OF BARYTA
(Ba O, S 3 ), which is insoluble or very difficultly soluble in dilute
acids, alkalies, and salts of ammonia. As a rule, this precipitate is
formed immediately upon the addition of the reagent ; from highly
dilute solutions, however, especially when strongly acid, it separates
only after some time. Sulphate of baryta is completely decomposed
by fusion with carbonates of the alkalies less readily and less com-
pletely by boiling with solution of carbonate of soda and carbonate
of potassa. The decomposition leads to the formation of sulphates
of the alkalies, which are soluble in water, and carbonate of baryta,
which is insoluble in that fluid. Digestion with solution of carbonate
of ammonia in the cold fails to effect the decomposition of sulphate of
baryta, as also boiling with a solution of 1 part of carbonate and 3 parts
of sulphate of potassa (H. Rose).
6. Hydrofluosilicic acid throws down from solutions of baryta SILICO-
FLUORIDE OF BARIUM (Ba Fl + Si F1J, in form of a colorless, crystalline,
quickly subsiding precipitate. In dilute solutions this precipitate is
formed only after the lapse of some time ; it is perceptibly soluble in
hydrochloric and nitric acids. Addition of an equal volume of alcohol
hastens the precipitation and makes it so complete that the filtrate
remains clear upon addition of sulphuric acid.
7. Phosphate of soda produces in neutral or alkaline solutions of baryta
a white precipitate of PHOSPHATE OF BARYTA (2 Ba 0, H O, P 6 ), which
is soluble in free acids. Addition of ammonia only slightly increases the
quantity of this precipitate ; chloride of ammonium dissolves it to a
clearly perceptible extent.
8. Oxalate of ammonia produces in moderately dilute solutions of baryta
a white, pulverulent precipitate of OXALATE OF BARYTA (Ba O, O + aq.),
which is soluble in hydrochloric and nitric acids. When recently
thrown down, this precipitate dissolves also in oxalic and acetic
acicte; but the solutions speedily deposit binoxalate of baryta (Ba
O, O + H O,0 + 2 aq.) in the form of a crystalline powder.
9. Salts of baryta in powder, when heated with dilute spirit of wine,
impart to the flame a YELLOWISH colour, which, however, is not very
characteristic.
10. Salts of baryta, particularly chloride of barium, when exposed on
a platinum wire to the inner blowpipe flame, color the outer flame YEL-
LOWISH-GREEN. With chloride of barium and nitrate and acetate of
baryta this reaction is the most distinct, but it is also shown by carbonate
and sulphate of baryta. The presence of salts of lime and strontia does
not prevent the reaction ; addition of chloride of silver considerably
heightens its intensity.
95.
6. STRONTIA (Sr 0).
1. Strontia and its hydrate and salts manifest nearly the same general
deportment and properties as baryta and its corresponding compounds.
Hydrate of strontia is more difficulty soluble in water than hydrate of
baryta. Chloride of strontium dissolves in absolute alcohol, and deli-
quesces m moist air. Nitrate of strontia is insoluble in absolute
alcohol, and does not deliquesce in the air.
2. The salts of strontia manifest with ammonia and potassa, and also
96.] LIME. 73
with the alkaline carbonates and with phosphate of soda, nearly the same
deportment as the salts of baryta. Carbonate of strontia dissolves some-
what more difficultly in chloride of ammonium than is the case with car-
bonate of baryta.
3. Sulphuric acid and sulphates precipitate from solutions of strontia
SULPHATE OF STRONTIA (Sr 0, S OJ, in form of a white powder, which
is insoluble in dilute acids and alkalies. Application of heat greatly
promotes the precipitation. Sulphate of strontia is far more soluble in
water than sulphate of baryta ; owing to this readier solubility, the pre-
cipitated sulphate of strontia separates from rather dilute solutions in
general only after the lapse of some time ; and this is invariably the
case (even in concentrated solutions) if solution of sulphate of lime is used
as precipitant. In boiling hydrochloric acid sulphate of strontia dissolves
perceptibly, a solution of the kind showing, after dilution with water, a
distinct turbidity upon the addition of a drop of solution of chloride of
barium. Sulphate of strontia is readily and completely decomposed by
fusion with carbonates of the alkalies, and by boiling with their solutions ;
it is decomposed also when long digested in the cold with solution of
carbonate of ammonia, or boiled with a solution of 1 part of carbonate of
potassa and 3 parts of sulphate of potassa (difference from sulphate of
baryta).
4. Hydrojluosilicic acid fails to produce a precipitate even in concen-
trated solutions of strontia ; even upon addition of an equal volume of
alcohol no precipitation takes place, except in very highly concentrated
solutions.
5. Oxalate of ammonia precipitates even from rather dilute solutions,
OXALATE OF STRONTIA (2 S 2 O, O +5 aq.), in form of a white powder,
which dissolves readily in hydrochloric and nitric acid, and percep-
tibly in salts of ammonia, but is only sparingly soluble in oxalic and
acetic acid.
6. If salts of strontia soluble in water or alcohol are heated with
dilute spirit of wine, and then kindled, the flame appears of an in-
tense CARMINE color, more particularly upon stirring the alcoholic
mixture.
7. Chloride of strontium when exposed on platinum wire to the
inner blowpipe Jlame, imparts an intense RED color to the outer flame.
With carbonate and sulphate of strontia the coloration is less intense ;
addition of chloride of silver, however, makes the reaction with these
two salts also lasting and distinct. Presence of baryta prevents this
reaction of strontia.
96.
c. LIME (Ca 0).
1. Lime and its hydrate and salts present, in their general deportment
and properties, a great similarity to baryta and strontia and their cor-
responding compounds. Hydrate of lime is far more difficultly soluble
in water than the hydrates of baryta and strontia ; it dissolves, besides,
more sparingly in hot than in cold water. Hydrate of lime loses its water
upon ignition. Chloride of calcium and nitrate of lime are soluble in
absolute alcohol, and deliquesce in the air.
2. Ammonia, potassa, alkaline carbonates, and phosphate of soda, pre-
sent nearly the same deportment with salts of lime as with salts of
74 MAGNESIA. [97.
baryta. Recently precipitated carbonate of lime (Ca 0, C 2 ) is bulky
and amorphous after a time, and immediately upon application of heat,
it falls down and assumes a crystalline form. When recently precipitated,
it dissolves pretty readily in solution of chloride of ammonium ; but the
solution speedily becomes turbid, and deposits the greater part of the
dissolved salt in form of crystals.
3. Sulphuric acid and sulphate of soda produce immediately in very
concentrated solutions of lime white precipitates of SULPHATE OF LIME
(Ca 0, S O 3 , H O 4- aq.), which redissolve completely in a large propor-
tion of water, and are still far more soluble in acids. In less concen-
trated solutions the precipitates are formed only after the lapse of some
time ; and no precipitation whatever takes place in dilute solutions.
Solution of sulphate of lime of course cannot produce a precipitate in
salts of lime ; but even a cold saturated solution of sulphate of potassa,
mixed with 3 parts of water, produces a precipitate only after standing
from twelve to twenty -four hours. In solutions of lime which are so
very dilute that sulphuric acid has no apparent action on them, a preci-
pitate will immediately form upon addition of alcohol. When fused
with carbonates of the alkalies, or boiled or digested with their solu-
tions, sulphate of lime comports itself the same as sulphate of strontia.
4. Hydrofluosilicic acid does not precipitate salts of lime.
5. Oxalate of ammonia produces even in very dilute solutions of lime
a white pulverulent precipitate of OXALATE OF LIME. The composition
of this precipitate, when thrown down hot or from concentrated solu-
tions, is Ca O, C 2 O 3 + aq. ; whilst when thrown down cold from dilute
solutions, it consists of a mixture of Ca O, C 3 4- aq. with Ca O, C 2 O 3
+ 3 aq. In very dilute solutions the precipitate forms only after some
time. It is readily soluble in hydrochloric and nitric acids, but dis-
solves to a trifling extent only in acetic and oxalic acids.
6. Soluble salts of lime, when heated with dilute spirit of wine, im-
part to the flame of the latter a YELLOWISH-KED color, which is often con-
founded with that communicated to the flame of alcohol by salts of
strontia.
7. Chloride of calcium, when exposed on a platinum wire to the inner
blowpipe flame, imparts a RED colour to the outer flame. With the other
salts of lime this reaction is less intense ; with phosphate and borate of
lime it fails altogether. Chloride of silver, as a rule, heightens the in-
tensity of the color. Presence of baryta prevents this reaction of lime.
97.
d. MAGNESIA (Mg 0).
1. Magnesia and its hydrate are white powders of far greater bulk
than. the other alkaline earths and their hydrates. Magnesia and hydrate
of magnesia are nearly insoluble both in cold and hot water. Hydrate
of magnesia loses its water upon ignition.
2. Some of the salts of magnesia are soluble in water, others are in-
soluble in that fluid. The soluble salts of magnesia have a nauseous
bitter taste ; in the neutral state they do not alter vegetable colors ;
with the exception of sulphate of magnesia, they undergo decomposition
when ignited, and the greater part of them even upon simple evapora-
tion of their solutions. Nearly all the salts of magnesia which are in-
soluble in water dissolve in hydrochloric acid.
97.] MAGNESIA. 75
3. Ammonia throws down from the solutions of neutral salts of mag-
nesia part of the magnesia as hydrate (Mg O, H O), in form of a white,
bulky precipitate. The rest of the magnesia remains in solution as a
double salt, viz., in combination with the ammoniacal salt which forms
upon the decomposition of the salt of magnesia; these double salts
are not decomposed by ammonia. It is owing to this tendency of
salts of magnesia to form such double salts with ammoniacal
compounds, that ammonia fails to precipitate them in presence of
ammoniacal salts in sufficient proportion, or, what is the same, that
ammonia produces no precipitate in solutions of magnesia containing a
sufficient quantity of free acid ; and that precipitates produced by am-
monia in neutral solutions of magnesia are redissolved upon the addition
of chloride of ammonium.
4. Potassa, soda, and caustic baryta throws down from solution of
magnesia HYDRATE OF MAGNESIA. The separation of this precipitate is
greatly promoted by boiling the mixture. Chloride of ammonium and
other similar salts of ammonia redissolve the precipitated hydrate of mag-
nesia if the precipitant has not been added greatly in excess. If the
salts of ammonia are added in sufficient quantity to the solution of mag-
nesia 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 potassa, the precipitate will of course
make its appearance, since this process causes the decomposition of the
ammoniacal salt, removing thus the agent which retains the hydrate of
magnesia in solution.
5. Carbonate of potassa and carbonate of soda produce in neutral solu-
tions of magnesia a white precipitate of BASIC CARBONATE OF MAGNESIA
3 (Mg O, C 2 , + aq.) + Mg O, H O. One fourth of the carbonic acid
of the decomposed alkaline carbonate is liberated in the process, and
combines with a portion of the carbonate of magnesia to bicarbonate,
which remains in solution. This carbonic acid escapes upon ebullition ;
application of heat therefore promotes the separation and increases the
quantity of the precipitate, Chloride of ammonium and other similar
salts of ammonia prevent this precipitation also, and redissolve the pre-
cipitates already formed.
6. Carbonate of ammonia does not precipitate solutions of magnesia
in the cold (at least never immediately, nor even after a short time) ;
upon boiling, it precipitates them only incompletely. Addition of
chloride of ammonium and other similar salts of ammonia, in sufficient
quantity, entirely prevents the formation of a precipitate.
7. Phosphate of soda precipitates from solutions of magnesia, if they
are not too dilute, PHOSPHATE OF MAGNESIA (2 Mg O, H 0, P 5 ) as a
white powder. The separation of the precipitate is greatly promoted by
ebullition. But if the addition of the precipitant is preceded by that of
chloride of ammonium and ammonia, a white crystalline precipitate of
BASIC PHOSPHATE OF MAGNESIA AND AMMONIA (2 Mg O, N H 4 O, P O g
+ 12aq.) will separate, even from very dilute solutions of magnesia; its
separation may be greatly promoted and accelerated by vigorous stirring
with a glass rod : even 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 side of the vessel will after the lapse
of some time appear distinctly as white streaks. Water and solutions of
salts of ammonia dissolve the precipitate but very slightly ; but it is
76 RECAPITULATION. [ 98.
readily soluble in acids, even in acetic acid. In water containing ammo-
nia it may be considered insoluble.
8. Oxalate of ammonia produces no precipitate in highly dilute solu-
tions of magnesia ; in less dilute solutions no precipitate is formed at
first, but after some time crystalline crusts of various oxalates of
ammonia and magnesia make their appearance. In highly concentrated
solutions oxalate of ammonia very speedily produces precipitates of
oxalate of magnesia (Mg 0, O + 2 aq.), which contain small quantities of
the above-named double salts. Chloride of ammonium, especially in
presence of free ammonia, interferes with the formation of these preci-
pitates ; but, as a rule, it does not absolutely prevent it.
9. Sulphuric acid and hydrofluosilicic acid do not precipitate salts of
magnesia.
1 0. If magnesia, or a salt of magnesia, is moistened with water, heated
to redness on a charcoal support, then moistened with 1 drop of solution
of nitrate of protoxide of cobalt, and again heated at first to gentle red-
ness, ultimately to intense redness, in the oxidation flame, a pinkish
mass is obtained, the color of which becomes distinctly apparent only upon
cooling, but is never very intense. Alkalies, alkaline earths, and heavy
metallic oxides prevent the reaction.
98-
Recapitulation and remarks. The difficult solubility of the hydrate
of magnesia, the ready solubility of the sulphate, and the disposition of
salts of magnesia to form double salts with ammoniacal compounds, are
the three principal points in which magnesia differs from the other
alkaline earths. To detect magnesia we always first remove the baryta,
strontia, and lime, if these bodies happen to be present. In cases re-
quiring no very high degree of accuracy, and where the quantity of salts
of ammonia present in the solution is inconsiderable, this removal may
be effected by means of carbonate of ammonia and ammonia ; but the
separation is never perfect, owing to the solvent action which salts of
ammonia exercise more especially upon carbonate of baryta and lime j
indeed, minute traces of baryta and lime can rarely be precipitated in
this manner. Baryta is separated the most completely by sulphuric
acid or a sulphate ; lime, by oxalate of ammonia in presence of ammonia
and some chloride of ammonium j strontia, in the same manner as lime, or
by ammonia and carbonate of ammonia in presence of chloride of ammo-
nium. After the removal of the other alkaline earths, the magnesia may
be readily detected in the filtrate by phosphate of soda in conjunction with
ammonia. The detection of baryta is an easy task under any circum-
stances ; since the precipitate of sulphate of baryta which separates from
baryta solutions immediately upon the addition of sulphate of lime, and
the reaction of baryta with hydrofluosilicic are indubitable proofs of the
presence of this earth. Strontia may likewise be readily detected by its
deportment with solution of sulphate of lime, provided of course no
baryta be present. If baryta is present, the detection of the strontia
may be effected by converting the two earths into dry chlorides, and
digesting the latter with absolute alcohol ; the greater part of the
chloride of barium is left undissolved, whilst the chloride of strontium,
dissolves ; if the alcohol is now heated, and then ignited, the carmine
tint of the flame will indicate the presence of strontia. However, the
results obtained in this way can only be considered satisfactory if the
99.] ALUMINA, SESQUIOXIDE OF CHROMIUM. 77
quantity of the strontia is not too minute, and if there is not much lime
present ; since in the latter case the yellowish-red flame of the lime will
mask the carmine flame of the strontia. In cases of this kind strontia is
detected best by the following process. Mix the solution containing baryta,
strontia, and lime with hydrofluosilicic acid and a volume of alcohol
equal to that of the fluid present ; let the mixture stand several hours ;
filter off the silicofluori.de of barium, and mix the filtrate with sulphuric
acid ; filter the precipitate formed, wash, arid convert the sulphates into
carbonates by boiling with solution of carbonate of soda ; wash the car-
bonates, dissolve them in a small quantity of hydrochloric acid, and test
the solution for strontia with solution of sulphate of lime. The preci-
pitate of sulphate of strontia thus obtained may then be tested before
the blowpipe, with addition of chloride of silver. For the detection of
lime we invariably select oxalate of ammonia. Before applying this test,
however, baryta and strontia must be removed, as they are equally pre-
cipitated by it. This removal is effected best by adding to the solution
sulphate of potassa in excess, and boiling the mixture for some time.
If there is much lime present, a portion of the latter earth precipi-
tates with the baryta and strontia; this is, however, a matter of
indifference, since there remains always a sufficient amount of lime in
solution to permit the positive and indubitable detection of this substance
in the filtrate by oxalate of ammonia ; to prevent precipitation of traces
of oxalate of strontia, the filtrate must be diluted with J volume of water.
The best way of effecting the detection of the alkaline earths, when in
the form of phosphates, is to decompose these latter by means of sesqui-
chloride of iron with the addition of acetate of soda ( 143). The
oxalates of the alkaline earths are converted into carbonates by ignition,
preparatory to the detection of the individual earths which they contain.
Sulphate of baryta and sulphate of strontia are fused with alkaline car-
bonates, to effect the detection of the baryta and strontia (compare
141). To separate sulphate of baryta from sulphate of strontia and
sulphate of lime, digest the finely triturated substance with solution of
carbonate of ammonia for twelve hours in the cold, or boil it ten minutes
with a solution of 3 parts of sulphate and 1 part of carbonate of potassa ;
sulphate of strontia and sulphate of lime are decomposed in both cases,
whilst sulphate of baryta remains unaltered. Filter, wash thoroughly
with hot water, and test the washed residue with dilute hydrochloric acid,
which will dissolve the carbonate of strontia and carbonate of lime
formed, leaving the sulphate of baryta undissolved (H. Rose).
99.
THIRD GROUP.
ALUMINA, SESQUIOXIDE OF CHROMIUM.
Properties of the group. Alumina and sesquioxide of chromium are
insoluble in water, both in the pure state arid as hydrates. They form
no neutral salts with carbonic acid. Their sulphides cannot be produced
in the humid way. Hydrosulphuric acid therefore fails to precipitate
solutions of alumina and sesquioxide of chromium ; sulphide of ammonium
precipitates the hydrated oxides from these solutions. This deportment
with sulphide of ammonium distinguishes the oxides of the third from
those of the two preceding groups.
78 ALUMINA. [ 100.
Special Reactions.
100.
a. ALUMINA (A1 2 3 ).
1. Alumina is non-volatile and colorless ; the hydrate is also colorless.
Alumina dissolves in acids (particularly when dilute) slowly and with very
great dimculty ; in fusing bisulphate of potassa it dissolves readily to a
mass soluble in water. The hydrate in an amorphous state, and recently
precipitated, is readily soluble in acids ; but after being left some time in
the fluid from which it was precipitated, its solubility decreases, and in the
crystallized state it dissolves with very great dimculty in acids. After pre-
vious ignition with alkalies, which leads to the formation of aluminates
of the alkalies, alumina is readily dissolved by acids.
2. The salts of alumina are colorless, and most of them are non-
volatile : some of them are soluble, others insoluble. The soluble
salts have a sweetish, astringent taste, redden litmus-paper, and lose
their acids upon ignition. The insoluble salts are dissolved by hydro-
chloric acid, with the exception of certain native compounds of alumina ;
the compounds of alumina which are insoluble in hydrochloric acid are
decomposed and made soluble by ignition with carbonate of soda and
potassa, or bisulphate of potassa.
3. Potassa and soda throw down from solutions of alumina a bulky
precipitate of HYDRATE OF ALUMINA (A1 2 3 , 3 H 0), which contains
alkali, and generally also an admixture of basic salt ; this precipitate re-
disfcolves readily and completely in an excess of the precipitant, but from
this solution it is reprecipitated by addition of chloride of ammonium,
even in the cold, but more completely upon application of heat (com-
pare 51). The presence of salts of ammonia does not prevent the
precipitation by potassa or soda.
4. Ammonia also produces in solutions of alumina a precipitate of
HYDRATE OF ALUMINA, containing ammonia and an admixture of basic
salt ; this precipitate also redissolves in a very considerable excess of the
precipitant, but with difficulty only, which is the greater the larger the
quantity of salts of ammonia contained in the solution. It is this deport-
ment which accounts for the complete precipitation of hydrate of alumina
from solution in potassa, by an excess of chloride of ammonium.
5. If the solution of a salt of alumina is digested with finely pulverized
carbonate of baryta, the greater part of the acid of the alumina salt
combines with the baryta, the liberated carbonic acid escapes, and the
alumina precipitates completely as HYDRATE mixed with BASIC SALT OF
ALUMINA ; even digestion in the cold suffices to produce this reaction.
6. If alumina or one of its compounds is ignited upon charcoal before
the blowpipe, and afterwards moistened with a solution of nitrate of
protoxide of cobalt, and then again strongly ignited, an unfused mass of
a deep SKY-BLUE color is produced, which consists of a compound of the
two oxides. The blue color becomes distinct only upon cooling. By
candlelight it appears violet. This reaction is decisive only in the case
of infusible or difficultly fusible compounds of alumina pretty free from
other oxides, as solution of cobalt imparts a blue tint to readily fusible
salts, even though no alumina be present.
101.] SESQUIOXIDE OF CHROMIUM. 79
101.
b. SESQUIOXIDE OF CHROMIUM (Cr 2 3 ).
1. Sesquioxide of chromium is a green, its hydrate a bluish gray- green
powder. The hydrate dissolves readily in acids } the non-ignited sesqui-
oxide dissolves more difficultly, and the ignited sesquioxide is almost
altogether insoluble.
2. The salts of sesquioxide of chromium have a green or violet color.
Many of them are soluble in water. Most of them dissolve in hydro-
chloric acid. The solutions usually exhibit a fine green color. Many
double salts of sesquioxide of chromium, e.g., sulphate of sesqui-
oxide of chromium and potassa (chrome alum), have a deep violet
color, and give with cold water bluish-violet solutions which, however,
acquire a green tint when even moderately heated. The salts of sesqui-
oxide of chromium with volatile acids are decomposed upon ignition, the
acids being expelled. The salts of sesquioxide of chromium which are
soluble in water redden litmus.
3. Potassa and soda produce in solutions of salts of sesquioxide of
chromium a bluish-green precipitate of HYDRATE OF SESQUIOXIDE OF
CHROMIUM, which dissolves readily and completely in an excess of the
precipitant, imparting to the fluid generally an emerald-green tint, but
in cases where the solution originally precipitated was bluish-violet, a
violet color. Upon long -continued ebullition of this solution, the whole
of the hydrated sesquioxide separates again, and the supernatant fluid
appears perfectly colorless. The same reprecipitation takes place if
chloride of ammonium is added to the alkaline solution, and the mixture
heated. If the alkaline solution of sesquioxide of chromium is gently
heated with binoxide of lead, the sesquioxide of chromium is con-
verted into chromic acid, and the alkaline fluid now holds chromate
of lead in solution ; upon supersaturation with acetic acid, chromate of
lead separates in form of a yellow precipitate.
4. Ammonia also produces in solutions of salts of sesquioxide of chro-
mium a precipitate of HYDRATE OF SESQUIOXIDE OF CHROMIUM : this precipi-
tate contains more or less water, according as the ammonia has been added
gradually or suddenly, and appears, therefore, sometimes grayish-green,
sometimes grayish-blue. A small portion of it redissolves in an excess of
the precipitant in the cold, imparting to the fluid a peach-blossom red
tint j but if, after the addition of ammonia in excess, heat is applied to
the mixture, the precipitation is complete.
5. Carbonate of baryta precipitates from solutions of sesquioxide of
chromium the whole of the sesquioxide as a GREENISH HYDRATE mixed
with BASIC SALT. The precipitation takes place in the cold, but is com-
plete only after long-continued digestion.
6. The fusion of sesquioxide of chromium or of any of its compounds
with nitrate of soda and some carbonate of soda gives rise to the formation
of yellow CHROMATE OF SODA, part of the oxygen of the nitric acid sepa-
rating from the nitrate of soda, and converting the sesquioxide of chro-
mium into chromic acid, which then combines with the soda. For
the reactions of chromic acid, see 138.
7. Phosphate of soda and ammonia dissolves sesquioxide of chromium
and its salts, both in the oxidizing and reducing flame of the blowpipe,
to clear beads of a faint YELLOWISH- GREEN tint, which upon cooling
80 TITANIC ACID. [ 102, 103.
changes to EMERALD-GREEN. The sesquioxide of chromium and its salts
show a similar deportment with biborate of soda.
102.
Recapitulation and remarks. The solubility of hydrate of alumina in
solutions of potassa and soda, and its reprecipitation from the alkaline
solutions by chloride of ammonium, afford a safe means of detecting
alumina only in the absence of sesquioxide of chromium. If the latter
is present therefore, which is seen either from the color of the solution,
or by the reaction with phosphate of soda and ammonia, it must be
removed before we can proceed to test for alumina. The separation of
sesquioxide of chromium from alumina is effected the most completely
by fusing 1 part of the mixed oxides together with 2 parts of carbonate
and 2 parts of nitrate of soda, which may be done in a platinum crucible.
The yellow mass obtained is boiled with water; by this process the
whole of the chromium is dissolved as chromate of soda, and part of the
alumina as aluminate of soda, the rest of the alumina remaining undis-
solved. If the solution is acidified with nitric acid, it acquires a reddish
tint ; if ammonia is then added to feebly alkaline reaction, the dissolved
portion of the alumina separates.
The precipitation of sesquioxide of chromium, effected by boiling its solu-
tion in solution of potassa or soda, is also sufficiently reliable if the ebullition
is continued a sufficient length of time ; still it is often liable to mislead in
cases where only little sesquioxide of chromium is present, or where the
solution contains organic matter, even though in small proportion only.
The deportment of a solution of sesquioxide of chromium with solution
of potassa or soda is completely changed by the presence of certain other
metallic oxides, especially oxide of zinc, oxide of lead, sesquioxide of
iron ; in presence of these oxides, and according to the greater or less
relative proportion in which they happen to be present, sesquioxide of
chromium does not dissolve, or dissolves only incompletely in an excess
of solution of potassa. This circumstance should never be lost sight of
in the analysis of compounds containing sesquioxide of chromium.
Lastly, it must be borne in mind, also, that alkalies produce no precipi-
tates in the solutions of alumina if non-volatile organic substances are
present, such as sugar, tartaric acid, &c. ; whilst the precipitation of sesqui-
oxide of chromium is less seriously interfered with by the presence of
such bodies.
103.
SUPPLEMENT TO THE THIRD GROUP.
TITANIC ACID (Ti0 2 ).
From among the other oxides enumerated in 86 as belonging to the
third group, we have selected titanic acid as deserving of special
notice, since this substance is met with more frequently than the
others in analytical investigations, more especially also in the analysis of
the slag adhering to the bottom of blast furnaces in which iron ore is
reduced, which slag is often found to contain small copper-coloured cubes,
consisting of a combination of cyanide of titanium with nitride of
titanium ( Wohler).
Titanium burns in the air with considerable brilliancy to titanic acid
104.] ZINC, MANGANESE, NICKEL, COBALT, IRON. 81
(TiO 2 ). Besides the acid, another oxide of titanium is known, the
sesquioxide (Ti 2 O 3 ). According to the different mode of its prepa-
ration, titanic acid appears sometimes as a white powder, which, when
heated, transiently acquires a yellow tint, sometimes in the form of small
lumps of a reddish-brown color. It is infusible, and insoluble in
water and acid, with the exception of concentrated sulphuric acid.
With bisulphate of potassa it fuses into a mass, which dissolves
in a large proportion of cold water to a clear fluid. Fusion of
titanic acid with carbonate of soda gives rise to the formation of
titanate of soda, which is by addition of water converted into soda
and bititanate of soda ; the latter salt is insoluble in water, but soluble
in hydrochloric acid. The hydrate of titanic acid is white ; it dissolves,
both in the moist state and when dried without the aid of heat, in
dilute acids, especially hydrochloric and sulphuric acids. Solutions of
titanic acid in hydrochloric or sulphuric acid, but more especially the
latter, when subjected in a highly dilute state to long-continued ebulli-
tion, deposit titanic acid as a white powder, insoluble in dilute acids.
The precipitate thus formed in hydrochloric acid cannot be separated
by nitration, unless an acid or chloride of ammonium is added, as it
will pass through the filter with the washing water. Solution of
potassa throws down from solutions of titanic acid in hydrochloric
or sulphuric acid, hydrate of titanic acid in form of a bulky , white
precipitate, which is insoluble in an excess of the precipitant ; am-
monia, sulphide of ammonium, carbonates of the alkalies, and car-
bonate of baryta act in the same way. The precipitate, if thrown
down without application of heat, and washed with cold water,
is soluble in hydrochloric acid and dilute sulphuric acid ; presence
of tartaric acid prevents its formation. Ferrocyanide of potassium pro-
duces in acid solutions of titanic acid a dark brown precipitate ;
infusion of galls a brownish precipitate, which speedily turns orange-
red. Metallic zinc produces, in consequence of the ensuing reduction
of titanic acid to sesquioxide of titanium, at first a blue coloration
of the solution, afterwards a blue precipitate of hydrate of sesquioxide
of titanium. Phosphate of soda and ammonia readily dissolves titanic
acid in the outer flame of the blowpipe to a clear bead of a yellowish
color whilst hot, but colorless when cold. If this bead is exposed to the
reducing flame, it acquires a yellow tint, which turns to red when the
bead is half cold, and to violet when quite cold.
104.
FOURTH GROUP.
OXIDE OF ZINC, PROTOXIDE OF MANGANESE, PROTOXIDE OF NICKEL,
PROTOXIDE OF COBALT, PROTOXIDE OF IRON, SESQUIOXIDE OF
IRON.
Properties of the group. The solutions of the oxides of the fourth
group, when containing a stronger free acid, are not precipitated by
hydrosulphuric acid ; neutral solutions also are not, or only very incom-
pletely, precipitated by that reagent ', but alkaline solutions are com-
pletely precipitated by hydrosulphuric acid ; and other solutions also if
a sulphide of an alkali metal is used as the precipitant, instead of
hydrosulphuric acid. The precipitated metallic sulphides corresponding
82 OXIDE OF ZINC. [ 105.
to the respective oxides are insoluble in water; some of them are
readily soluble in dilute acids ; others (sulphide of nickel and sulphide
of cobalt) dissolve only with very great difficulty in these menstrua.
Some of them are insoluble in sulphides of the alkali metals ; others are
sparingly soluble in them, under certain circumstances.
Special Reactions.
.^' 105.
a. OXIDE or ZINC (Zn 0).
1. Metallic zinc is bluish- white and very bright ; when exposed to the
air, a thin coating of basic carbonate of zinc forms on its surface. It is
of medium hardness, ductile at a temperature of between 212 and
302 Fah., and under ordinary circumstances 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 support with oxide. Zinc dissolves in hydrochloric and
sulphuric acids, with evolution of hydrogen gas ; in dilute nitric acid,
with evolution of nitrous oxide ; in more concentrated nitric acid, with
evolution of nitric oxide.
2. The oxide of zinc and its hydrate are white powders, which dis-
solve readily in hydrochloric, nitric, and sulphuric acids. The oxide
of zinc acquires a lemon-yellow tint when heated, but it reassumes
its original white color upon cooling. When ignited before the blow-
pipe, it shines with considerable brilliancy.
3. The compounds of oxide of zinc are colorless ; part of them are
soluble in water, the rest in acids. The neutral salts of zinc which are
soluble in water redden litmus-paper, and are readily decomposed by
heat, with the exception of sulphate of zinc, which can bear a dull red
heat, without undergoing decomposition. Chloride of zinc is volatile at
a red heat.
4. Hydrosulphuric acid precipitates from neutral solutions of salts of
zinc a portion of the metal as white hydrated SULPHIDE of ZINC (Zn S).
In acid solutions this reagent fails altogether to produce a precipitate if
the free acid present is one of the stronger acids ; but from a solution
of oxide of zinc in acetic acid, it throws down the whole of the zinc,
even if the acid is present in excess.
5. Sulphide of ammonium throws down from neutral, and hydrosid-
phuric acid from alkaline solutions of salts of zinc, the whole of the
metal as hydrated SULPHIDE OF ZINC, in form of a white precipitate.
This precipitate is not reclissolved by an excess of sulphide of ammonium,
iior by potassa or ammonia ; but it dissolves readily in hydrochloric acid,
nitric acid, and dilute sulphuric acid.
6. Potassa and soda throw down from solutions of salts of zinc
HYDRATED OXIDE OF ZINC (Zn O, H O), in form of a white, gelatinous
precipitate, 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 oxide of zinc separates as a white precipitate. Chloride of
ammonium does not precipitate alkaline solutions of oxide of zinc. If a
solution of oxide of zinc in solution of potassa or soda is mixed with a
solution of sesquioxide of chromium also in solution of potassa or soda,
106.] PROTOXIDE OF MANGANESE. 83
a green precipitate is formed, consisting of a compound of sesquioxide of
chromium with oxide of zinc (Zu 0, Cr 2 3 ). A solution of caustic
soda or potassa therefore can never contain both oxides together in
solution (Chancel}.
7. Ammonia also produces in solutions of oxide of zinc, if they do not
contain a large excess of free acid, a precipitate of , HYDRATED OXIDE OF
ZINC, which readily dissolves in an excess of the precipitant. The con-
centrated solution turns turbid when mixed with water. On boiling
the concentrated solution, part of the oxide of zinc separates imme-
diately ; on boiling the dilute solution, all the oxide of zinc precipitates.
8. Carbonate of soda produces in solutions of salts of zinc a precipitate
of BASIC CARBONATE OF ZINC (3 [Zn O, H 0] 4 2 [Zn O, C 2 + 4 aq.),
which is insoluble in an excess of the precipitant. Presence of salts
of ammonia in great excess prevents the formation of this precipitate.
9. Carbonate of ammonia also produces in solutions of salts of zinc
the same precipitate of BASIC CARBONATE OF ZINC as carbonate of soda ;
but this precipitate redissolves upon further addition of the precipitant.
On boiling the dilute solution, oxide of zinc precipitates.
10. Carbonate of baryta fails to precipitate solutions of oxide of zinc
in the cold.
11. If a mixture of oxide of zinc, or one of its salts, with carbonate
of soda is exposed to the reducing flame of the blowpipe, the charcoal
support becomes covered with a slight coating of OXIDE OF ZINC, which
presents a yellow color whilst 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.
12. If oxide of zinc or one of the salts of zinc is moistened with
solution of nitrate of protoxide of cobalt, and then heated before the
blowpipe, an unfused mass is obtained, of a beautiful GREEN color : this
mass is a compound of oxide of zinc with protoxide of cobalt. If there-
fore in the experiment described in 1 1 the charcoal is moistened, around
the little cavity, with solution of nitrate of protoxide of cobalt, the
coating appears green when cold.
106.
b. PROTOXIDE OF MANGANESE (Mn 0).
1. Metallic manganese has a whitish-gray color and but little lustre ;
it is brittle, and fuses with very great difficulty ; it oxidizes slowly in cold
water, rapidly in boiling water, and dissolves readily in acids. The
solutions contain protoxide,
2. Protoxide of manganese is grayish-green ; the hydrated protoxide
is white. Both the protoxide and its hydrate absorb oxygen from the
air, and are converted into the brown sesquioxide. They are readily
soluble in hydrochloric, nitric, and sulphuric acids.
3. The salts of protoxide of manganese are colorless or pale red ;
part of them are soluble in water, the rest in acids. The salts soluble
in water are readily decomposed by a red heat, with the exception of the
sulphate. The solutions do not alter vegetable colors.
4. Hydrosulphuric acid does not precipitate acid solutions of salts of
protoxide of manganese ; neutral solutions also it fails to precipitate, or
precipitates them only very imperfectly.
G 2
84 PEOTOXIDE OF NICKEL. [ 107.
5. Sulphide of ammonium throws down from neutral, and hydrosul-
phuric acid from alkaline solutions of salts of protoxide of manganese,
the whole of the metal as hydrated SULPHIDE OF MANGANESE (Mn S), in
form of a light flesh-colored* precipitate, which acquires a dark-brown
color in the air; this precipitate is insoluble in yellow sulphide of
ammonium and in alkalies, soluble to a very trifling extent in color-
less sulphide of ammonium, but readily soluble in hydrochloric and
nitric acids. From very dilute solutions the precipitate separates only
after standing some time in a warm place. ~v '
6. Potassa, soda, and ammonia produce whitish precipitates of HY-
DRATE OF PROTOXIDE OF MANGANESE (Mn O, H O), which upon exposure
to the air speedily acquire a brownish and finally a deep blackish-brown
color, owing to the conversion of the hydrated protoxide into hydrated
sesquioxide, by the absorption of oxygen from the air. Ammonia and
carbonate of ammonia do not redissolve this precipitate ; but presence
of chloride of ammonium prevents the precipitation by ammonia alto-
gether, and that by potassa partly. Of already formed precipitates
solution of chloride of ammonium redissolves only those parts which
have not yet undergone peroxidation. The solution of the hydrated
protoxide of manganese in chloride of ammonium is owing to the dis-
position of the salts of protoxide of manganese to form double salts with
salts of ammonia. The ammoniacal solutions of the double salts turn
brown in the air, and deposit dark-brown hydrate of sesquioxide of
manganese (Otto).
7. If a few drops of a fluid containing protoxide of manganese, and
free from chlorine, are sprinkled on binoxide of lead, or red-lead, nitric
acid free from chlorine added, the mixture boiled and allowed to
settle, the fluid is of a purple red color from the formation of perman-
ganic acid.
8. Carbonate of baryta does not precipitate protoxide of manganese
from its solutions, upon digestion in the cold.
9. If any compound of manganese, in a state of minute division, is
fused with carbonate of soda on a platinum wire in the outer flame of
the blowpipe, MANGANATE OF SODA (Na O, Mn O 3 ) is formed, which
makes the fused mass appear GREEN while hot, and of a BLUISH-GREEN
tint after cooling, the bead at the same time becoming turbid. This
reaction enables us to detect the smallest quantities of manganese. The
delicacy of the test may be still further increased by the addition of a
minute quantity of nitrate of potassa to the carbonate of soda.
10. Borax and phosphate of soda and ammonia dissolve manganese
compounds in the outer flame of the blowpipe to clear VIOLET-RED beads,
which upon cooling acquire an AMETHYST-RED tint : they lose their
color in the inner flame, owing to a reduction of the sesquioxide to
protoxide. The bead which borax forms with manganese compounds
appears black when containing a considerable portion of sesquioxide
of manganese, but that formed by phosphate of soda and ammonia
never loses its transparency. But the latter loses its color in the inner
flame of the blowpipe far more readily than the former.
107.
c. PROTOXIDE OF NICKEL (Ni O).
1. Metallic nickel in the fused state is silvery white, inclining to gray ;
* If the quantity of the precipitate is only trifling, the color appears yellowish-white.
107.] PROTOXIDE OF NICKEL. 85
it is bright, hard, malleable, ductile, difficultly fusible ; it does not oxidize
in the air at common temperatures, but it oxidizes slowly upon ignition ;
it is attracted by the magnet, and may itself become magnetic. It slowly
dissolves in hydrochloric acid and dilute sulphuric acid upon the applica-
tion of heat, the solution being attended with evolution of hydrogen gas.
It dissolves readily in nitric acid.
2. Protoxide of nickel is a gray, its hydrate a green powder. Both
the protoxide and its hydrate are unalterable in the air, and readily
soluble in hydrochloric, nitric, and sulphuric acids.
3. Most of the salts of protoxide of nickel are yellow in the anhydrous,
green in the hydrated state ; their solutions are of a light green color.
The soluble neutral salts slightly redden litmus paper, and are decom-
posed at a red heat.
4. Hydrosulphuric acid does not precipitate acid solutions of salts of
nickel ; it fails also to precipitate neutral solutions of salts of nickel with
the stronger acids, or it precipitates them only very imperfectly.
5. Sulphide of ammonium produces in neutral, and hydrosulphuric acid
in alkaline solutions of salts of protoxide of nickel, a black precipitate of
hydrated SULPHIDE OF NICKEL (Ni S), which is not altogether insoluble
in sulphide of ammonium, especially if containing free ammonia ; the
fluid from which the precipitate has been thrown down exhibits
therefore usually a brownish color. Sulphide of nickel dissolves with
great difficulty in hydrochloric acid, but readily in nitrohydrochloric
acid upon application of heat.
6. Potassa and soda produce a light green precipitate of HYDRATE OF
PROTOXIDE OF NICKEL (Ni O, H 0), which is insoluble in an excess of the
precipitants, and unalterable in the air. Carbonate of ammonia dis-
solves this precipitate, when filtered and washed, to a greenish-blue fluid,
from which potassa or soda reprecipitates the nickel as an apple-green
hydrate of protoxide of nickel.
7. Ammonia added in small quantity to solutions of protoxide of
nickel produces in them a trifling greenish turbidity ; upon further
addition of the reagent this redissolves readily to a blue fluid containing
a compound of protoxide of nickel and ammonia. Potassa and soda
precipitate from this solution hydrate of protoxide of nickel. Solutions
containing salts of ammonia or free acid are not rendered turbid by
ammonia.
8. Cyanide of potassium produces a yellowish-green precipitate of
CYANIDE OF NICKEL (Ni Cy), which redissolves readily in an excess of
the precipitant as a double cyanide of nickel arid potassium (Ni Cy +
K Cy) ; the solution is brownish-yellow. If sulphuric acid or hydro-
chloric acid is added to this solution, the cyanide of potassium is decom-
posed, and the cyanide of nickel reprecipitated ; the latter substance is
very difficultly soluble in an excess of these acids in the cold, but more
readily upon boiling.
9. Carbonate of baryta does not precipitate protoxide of nickel from its
solutions, upon digestion in the cold.
10. Nitrite of potassa, used in conjunction with acetic acid, fails to
precipitate even concentrated solutions of nickel.
11. Borax &nd phosfihate of soda and ammonia dissolve compounds of
protoxide of nickel in the outer flame of the blowpipe to clear beads ; the
bead produced with borax is violet whilst hot, reddish-brown when cold ;
the bead produced with the phosphate of soda and ammonia is reddish,
inclining to brown whilst hot, but turns yellow or reddish-yellow upon cool-
86 PROTOXIDE OF COBALT. [ 108.
ing. The bead which phosphate of soda and ammonia forms with salts
of protoxide of nickel remains unaltered in the inner flame of the blow-
pipe, but that formed with borax turns gray and turbid from reduced
metallic nickel. Upon continued exposure to the blowpipe flame the
particles of nickel unite, but without fusing to a grain, and the bead
becomes colorless.
108.
d. PROTOXIDE OF COBALT (Co 0).
1. Metallic cobalt is reddish-gray, slightly lustrous, pretty hard, slightly
malleable, ductile, and difficultly fusible ; it does not oxidize in the air at
the common temperature, and oxidizes only slowly at a red heat ; with
acids it comports itself like nickel.
2. Protoxide of cobalt is an olive-green, its hydrate a pale red powder.
Both dissolve readily in hydrochloric, nitric, and sulphuric acids.
3. The salts of protoxide of cobalt, containing water of crystallization,
are red, the anhydrous salts mostly blue. The moderately concentrated
solutions appear of a light red color, which they retain even though
considerably diluted. The soluble neutral salts redden litmus paper
slightly, and are decomposed at a red heat ; sulphate of protoxide of
cobalt alone can bear a moderate red heat without suffering decomposi-
tion. When a solution of chloride of cobalt is evaporated, the light red
color changes towards the end of the operation to blue; addition of
water restores the red color.
4. Hydrosulphuric acid does not precipitate acid solutions of cobalt ;
it also fails to precipitate neutral solutions of salts of protoxide of cobalt
with the stronger acids, or it precipitates them only very imperfectly.
5. Sulphide of ammonium precipitates from neutral, and hydrosulphuric
acid from alkaline solutions of salts of protoxide of cobalt, the whole of
the metal as black hydrated SULPHIDE OF COBALT (Co S). This substance
is insoluble in alkalies and sulphide of ammonium, very difficultly soluble
in hydrochloric acid, but readily so in nitrohydrochloric acid upon appli-
cation of heat.
6. Potassa and soda produce in solutions of cobalt BLUE precipitates of
basic salts of cobalt, which turn GREEN upon exposure to the air, owing
to the absorption of oxygen ; upon boiling, they are converted into pale
red hydrate of protoxide of cobalt, which contains alkali, and generally
appears rather discolored from an admixture of sesquioxide formed in
the process. These precipitates are insoluble in solutions of potassa and
soda ; but neutral carbonate of ammonia dissolves them completely to
intensely violet-red fluids, in which a somewhat larger proportion of
potassa or soda produces a blue precipitate, the fluid still retaining its
violet color.
7. Ammonia produces the same precipitate as potassa, but this redis-
solves in an excess of the ammonia to a reddish-brown fluid, from which
solution of potassa or soda throws down part of the cobalt as a blue
basic salt. Ammonia fails to precipitate solutions of protoxide of cobalt
containing salts of ammonia or free acid.
8. Addition of cyanide of potassium to a solution of cobalt gives rise
to the formation of a brownish-white precipitate of PROTOCYANIDE OF
COBALT (Co Cy), which dissolves readily as a double cyanide of cobalt
and potassium in an. excess of solution of cyanide of potassium. Acids
precipitate from this solution cyanide of cobalt. But if the solution is
109.] PROTOXIDE OF IRON. 87
boiled with cyanide of potassium in excess, in presence of free hydrocyanic
acid (liberated by addition of one or two drops of hydrochloric acid), a
double compound of sesquicyanide of cobalt and cyanide of potassium
(K 3 , Co 2 Cy 6 = K 3 Ckdy) is formed, in the solution of which acids pro-
duce no precipitate.
9. Carbonate of baryta does not precipitate solution of protoxide of
cobalt in the cold.
10. If nitrite of potassa is added in not too small proportion to a
solution of protoxide of cobalt, then acetic acid to strongly acid reaction,
and the mixture put in a moderately warm place, all the cobalt separates,
from concentrated solutions immediately or very soon, from dilute solu-
tions after some time, as NITRITE OF SESQUIOXIDE OF COBALT AND POTASSA
(Co 2 O 3 , 3 K O, 5 K 3 , 2 H O), in form of a crystalline precipitate of a
beautiful yellow color. The mode in which this precipitate forms may
be seen from the following equation : 2 (Co O, S 3 ) + 6 (K O, N O 3 ) +
A = K 0, A + 2 K 0, S O 3 + Co, O 3 , 3 K O, 5 N O 3 + N 2 . The pre-
cipitate is only sparingly soluble in pure water, and altogether insoluble
in saline solutions and in alcohol. When boiled with water, it dissolves,
though not copiously, to a red fluid, which remains clear upon cooling,
and from which alkalies throw down hydrate of protoxide of cobalt
(Fischer, Aug. Stromeyer). This excellent reaction enables us to dis-
tinguish nickel from cobalt. It is always necessary to concentrate the
solution of protoxide of cobalt to a considerable extent before adding the
nitrite of potassa.
11. Borax dissolves compounds of cobalt both in the inner and outer
flame of the blowpipe, giving clear beads of a magnificent BLUE color,
which appear violet by candle-light, and almost black if the cobalt is
present in considerable proportion. This test is as delicate as it is cha-
racteristic. Phosphate of soda and ammonia manifests with salts of
cobalt before the blowpipe an analogous but less delicate reaction.
109.
e. PROTOXIDE OF IRON (FeO).
1. Metallic iron 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 difficult to fuse, and is attracted by the
magnet. In contact with air and moisture a coating of rust (hydrate of
sesquioxide of iron) forms on its surface ; upon ignition in the air, a
coating of black protosesquioxide. Hydrochloric acid and dilute sulphuric
acid dissolve iron, with evolution of hydrogen gas ; if the iron contains
carbon, the hydrogen is mixed with carbide of hydrogen. The solu-
tions contain protoxide. Dilute nitric acid dissolves iron in the cold
to nitrate of protoxide, with evolution of nitrous oxide ; at a high tem-
perature, to nitrate of sesquioxide, with evolution of nitric oxide ; if
the iron contains carbon, some carbonic acid is also evolved, and there
is left undissolved a brown substance resembling humus, which is soluble
in alkalies.
2. Protoxide of iron is a black powder ; its hydrate is a white
powder, which in the moist state absorbs oxygen and speedily acquires a
grayish-green, and ultimately a brownish-red color. Both the protoxide
and its hydrate are readily dissolved by hydrochloric, sulphuric, and
nitric acids.
88 PROTOXIDE OF IRON. [ 109.
3. The salts of protoxide of iron have in the anhydrous state a white,
in the hydrated state a greenish color ; their solutions appear colored
only when concentrated. Exposed to the air, they absorb oxygen and
are converted into salts of the protosesquioxide. The soluble neutral
salts redden litmus paper, and are decomposed at a red heat.
4. Acid solutions of salts of protoxide of iron are not precipitated by
hydrosulphuric add; neutral solutions of salts of protoxide of iron with
weak acids are precipitated by this reagent at the most but very in-
completely ; the precipitates are of a black color.
5. Sulphide of ammonium precipitates from neutral, and hydrosul-
phuric acid from alkaline solutions of salts of protoxide of iron, the
whole of the metal as black hydrated PROTOSULPHIDE OF IRON (Fe S),
which is insoluble in alkalies and sulphides of the alkali metals, but
dissolves readily in hydrochloric and nitric acids : this black precipi-
tate turns reddish-brown in the air by oxidation. To highly dilute
solutions of protoxide of iron, addition of sulphide of ammonium imparts
a green color, and it is only after some time that the protosulphide of
iron separates as a black precipitate.
6. Potassa and ammonia produce a precipitate of HYDRATE OF PROT-
OXIDE OF IRON (FeO, HO), which in 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. Pre-
sence of salts of ammonia prevents the precipitation by potassa partly,
and that by ammonia altogether. If alkaline solutions of protoxide of
iron thus obtained by the agency of salts of ammonia are exposed to the
air, hydrate of sesquioxide of iron precipitates.
7. Ferrocyanide of potassium produces in solutions of protoxide of
iron a bluish-white precipitate of FERROCYANIDE OF POTASSIUM AND IRON
(K, Fe 3 , Cfy 2 ), which, by absorption of oxygen from the air, speedily
acquires a blue color. Nitric acid or chlorine converts it immediately
into Prussian blue, 3 (K, Fe 3 , Cfy 2 ) + 4 01 = 3 K 01 + Fe Cl + 2 (Fe 4 Cfyj.
8. ferricyanide of potassium produces a magnificently blue precipitate
of FERRICYANIDE OF IRON (Fe g Cfdy). This precipitate does not differ in
color from Prussian blue. It is insoluble in hydrochloric acid, but is
readily decomposed by potassa. In highly dilute solutions of salts of
protoxide of iron the reagent produces simply a deep blue-green
coloration.
9. Sulphocyanide of potassium does not alter solutions of protoxide
of iron free from sesquioxide.
10. Carbonate of baryta does not precipitate solutions of protoxide of
iron in the cold.
11. Borax dissolves salts of protoxide of iron in the oxidizing flame,
giving beads varying in color from YELLOW to DARK RED ; when cold,
the beads vary from colorless to dark yellow. In the inner flame the
beads change to bottle-green, owing to the reduction of the newly-formed
sesquioxide to protosesquioxide. Phosphate of soda and ammonia mani-
fests a similar deportment with the salts of protoxide of iron ; the beads
produced with this reagent lose their color upon cooling still more com-
pletely than is the case with those produced with borax ; the signs of
the ensuing reduction in the reducing flame are also less marked.
110.] SEsquioxiDE or IKON. 89
HO.
/ SESQUIOXIDE OF IRON (Fe a 3 ).
1. The native crystallized sesquioxide of iron is steel-gray ; the
native as well as the artificially prepared sesquioxide of iron gives upon
trituration a brownish-red powder ; the color of hydrate of sesquioxide
of iron is more inclined to reddish-brown. Both the sesquioxide and
its hydrate dissolve in hydrochloric, nitric, and sulphuric acids; the
hydrate dissolves readily in these acids, but the anhydrous sesquioxide
dissolves with greater difficulty, and completely only after long exposure
to heat.
2. The neutral anhydrous salts of sesquioxide of iron are nearly white ;
the basic salts are yellow or reddish-brown. The color of the solution is
brownish-yellow, and becomes reddish-yellow upon the application of heat.
The soluble neutral salts redden litmus paper, and are decomposed by heat.
3. Hydrosulphuric acid produces in neutral and acid solutions of salts
of sesquioxide of iron a milky white turbidity, proceeding from separated
SULPHUR. This reaction is caused by a mutual decomposition of the
sesquioxide of iron and the hydrosulphuric acid, in which the former is
deprived of one-third of its oxygen, and thus reduced to the state of
protoxide ; the oxygen forms water with the hydrogen of the hydro-
sulphuric acid, and the liberated sulphur separates. Solution of hydro-
sulphuric acid, rapidly added to neutral solutions, imparts to the fluid
a transitory blackening. In solution of neutral acetate of sesquioxide
of iron it produces a permanent precipitate of sulphide of iron.
4. Sulphide of ammonium precipitates from neutral, and hydrosulphuric
acid from alkaline solutions of salts of sesquioxide of iron, the whole of
the metal as black hydrated PROTOSULPHIDE OF IRON (FeS).. This pre-
cipitation is preceded by the reduction of the sesquioxide to protoxide. In
very dilute solutions the reagent produces only a blackish-green colora-
tion. The minutely divided protosulphide of iron subsides in such cases
only after long standing. Protosulphide of iron, as already stated
( 109, 5), is insoluble in alkalies and alkaline sulphides, but dissolves
readily in hydrochloric and nitric acids.
5. Potassa and ammonia produce bulky reddish-brown precipitates of
HYDRATE OF SESQUIOXIDE OF IRON (F 2 O 3 , H 0), which are insoluble in
an excess of the precipitant as well as in salts of ammonia. In presence
of sesquioxide of chromium, an excess of solution of potassa or ammonia
will dissolve, part of the sesquioxide of iron along with the sesquioxide
of chromium. Generally, however, a portion of both oxides remains undis-
solved ; and, moreover, the dissolved oxides speedily separate again from
the solution.
6. Ferrocyanide of potassium produces even in highly dilute solutions
a magnificently blue precipitate of FERROCYANIDE OF IRON, or Prussian
blue (Fe 4 Cfy 3 ), which is insoluble in hydrochloric acid, but is decom-
posed by potassa, with separation of hydrate of sesquioxide of iron.
7. Ferricyanide of potassium deepens the color of solutions of salts of
sesquioxide of iron to reddish-brown ; but it fails to produce a precipitate.
8. Sulphocyanide of potassium imparts to neutral or slightly acid solu-
tions of salts of sesquioxide of iron a most intense blood-red color,
arising from the formation of a soluble SULPHOCYANIDE OF IRON. Addi-
tion of acetate of soda destroys this color, hydrochloric acid restores it
90 RECAPITULATION AND REMARKS. [ 111.
again. This test is the most delicate of all ; it will indicate the presence
of sesquioxide of iron even in fluids which are so highly dilute that every
other reagent fails to produce the slightest visible alteration. The red
coloration may in such cases be detected most distinctly by resting
the test-tube upon a sheet of white paper, and looking through it from
the top.
9. Carbonate of baryta precipitates even in the cold all the iron as a
basic salt mixed with hydrate of sesquioxide.
10. The reactions before the Uovjpipe are the same as with the prot-
oxide.
111.
Recapitulation and remarks. On observing the behavior of the
oxides of the fourth group with solution of potassa, it would appear that
the separation of the oxide of zinc, which is soluble in an excess of this
reagent, might be readily effected by its means ; however, in the actual
experiment, we find that in the presence of sesquioxide of iron, protoxide
of cobalt, &c., some of the oxide of zinc precipitates with these oxides ;
and if only a small quantity of oxide of zinc is present, it frequently
occurs that no trace of this metal can be detected in the alkaline
filtrate.
Again, from the behavior of the different oxides with chloride of
ammonium and an excess of ammonia, one would conclude that the sepa-
ration of sesquioxide of iron from the protoxides of cobalt, nickel, and
manganese, and from oxide of zinc, might be readily effected by these
agents. But this method also applied to the mixed oxides, is inaccurate,
since greater or smaller portions of the other oxides will always preci-
pitate with the sesquioxide of iron ; and it may therefore happen that,
in this process, small quantities of cobalt, manganese, <fec., altogether
escape detection.
It is far safer therefore to separate the other oxides of the fourth
group from sesquioxide of iron by carbonate of baryta, as in that case the
iron is precipitated free from oxide of zinc and protoxides of manganese
and nickel, and mixed only with a very trifling quantity of protoxide of
cobalt.
Protoxide of manganese may conveniently be separated from the
protoxides of cobalt and nickel and from oxide of zinc, by treating the pre-
cipitated sulphides with moderately dilute acetic acid, which dissolves the
sulphide of manganese, leaving the other sulphides unacted on. If the
acetic acid solution is now mixed with solution of potassa, the least trace
of a precipitate will be sufficient to recognise the manganese before the
blowpipe with carbonate of soda.
If the sulphides left undissolved by acetic acid are now treated with
very dilute hydrochloric acid, the sulphide of zinc dissolves, leaving
almost the whole of the sulphides of cobalt and nickel behind. If the
fluid is then boiled, to expel the hydrosulphuric acid, and afterwards
treated with solution of potassa or soda in excess, the zinc is sure to be
detected in the filtrate by hydrosulphuric acid.
Cobalt may mostly be readily and safely detected in presence of nickel
by the reaction with borax in the inner flame of the blowpipe. The
detection of nickel in presence of cobalt is a less easy task, which may,
however, be effected with great accuracy by three different methods. The
first method is 1$ add to the solution containing the two metals nitrate of
111.] RECAPITULATION AND EEMA11KS. 91
potassa in not too small proportion, then acetic acid to strongly acid
reaction, and to let the mixture stand for at least several hours in a
moderately warm place, when the cobalt will separate as nitrate of sesqui-
oxide of cobalt and potassa ; the nickel may then be readily precipitated
from the nitrate by soda or sulphide of ammonium. The second method is
to saturate with chlorine the very dilute solution of the two metals in
hydrochloric acid, having the acid slightly in excess ; add carbonate of
baryta in excess, and let the fluid stand twenty-four hours. The cobalt is
entirely precipitated in this process as black sesquioxide, whilst the
nickel remains in solution, and may, after the removal of the baryta by
sulphuric acid, be thrown down with solution of soda. The third method
is based upon the application of cyanide of potassium. Both cyanide of
nickel and cyanide of cobalt dissolve in cyanide of potassium ; but cyanide
of nickel is precipitated from this solution by acids, whilst cyanide of
cobalt is not precipitated if the solution contains free hydrocyanic acid,
and has been exposed to the action of heat.* This reaction, i. e. } the
formation of a precipitate upon adding hydrochloric acid or dilute sul-
phuric acid to the solution of the two cyanides in cyanide of potassium,
prepared under the conditions stated, ^indicates the presence of nickel.
Whether the precipitate be cyanide of nickel or cobalticyanide of nickel,
is quite immaterial as far as the detection of nickel is concerned : all we
have to bear in mind is simply this, that no precipitate will form if
cobalt alone is present in the solution, since cobalticyanide of potassium
is not decomposed by hydrochloric acid. In order to get at the compo-
sition of the various precipitates which are formed by hydrochloric acid
in solutions of the mixed cyanides of nickel and cobalt, and to com-
prehend the general process of their formation, we have to assume and
consider three special and distinct cases, differing from one an other in the
relative proportions of nickel and cobalt which the solutions under ex-
amination respectively contain.
1, JSTi Co :: 3 eq. : 2 eq.
2, Ni Co :: 3 eq. : 2 eq. +x
3, Ni Co :: 3 eq. + x : 2 eq.
The solution will accordingly, in the first case, contain one eq. of cobal-
ticyanide of potassium (K 8 , Co 2 Cy 6 ) and 3 eq. of double cyanide of
nickel and potassium 3 (Ni Cy, K Cy) ; now upon the addition of
hydrochloric acid in excess to this solution, the double cyanide of nickel
and potassium suffers decomposition, and the potassium of the cobalti-
cyanide of potassium transposes with the nickel of the cyanide of
nickel : the products of this process of double decomposition and transpo-
sition are chloride of potassium, hydrocyanic acid, and cobalticyanide of
nickel (Ni 3 , Co 2 Cy 6 ), which latter separates in the form of a dirty-green
precipitate containing the whole of the nickel and cobalt present in the
solution. In the second case we obtain equally a precipitate of cobalti-
cyanide of nickel ; but this precipitate, though containing the whole of
the nickel, does not contain all the cobalt of the solution, since the excess
of cobalticyanide of potassium is not decomposed. In the third case,
lastly, we obtain a precipitate of cobalticyanide of nickel; which contains
* In this process the double cyanide of cobalt and potassium (K Cy, Co Cy), which forms
at first, is converted by the aid of the free hydrocyanic acid and the excess of cyanide of
potassium, into cobalticyanide of potassium (K 3 , Co 8 Cy 6 ) : 2 (Co Cy, K Cy) + K Cy +
HCy =(K,, Co 8 Cy a )+H.
92 SESQUIOXIDE OF URANIUM. [ 112.
the whole of the cobalt and a portion of the nickel, mixed with insoluble
cyanide of nickel, which contains the rest of the nickel. The cobalti-
cyanide of nickel has been formed here in the same manner as in the
first case, whilst the cyanide of nickel owes its formation to the decom-
position of the excess of the double cyanide of nickel and potassium.
Hence it is evident that the presence of nickel is indispensable to the
formation of a precipitate, and consequently that the production of a
precipitate is the most positive proof of the presence of this metal.
Protoxide and sesquioxide of iron may be detected in presence of each
other, by testing for the former with ferricyanide of potassium, for the
latter with ferrocyanide of potassium or, better still, with sulphocyanide
of potassium.
In conclusion, it is necessary to mention that alkalies fail to preci-
pitate the oxides of the fourth group in presence of non-volatile organic
substances (such as sugar, tartaric acid, &c.). We have already seen
that the same applies to alumina.
112.
SUPPLEMENT TO THE FOURTH GROUP.
SESQUIOXIDE OF URANIUM (U 2 O 3 ).
Sesquioxide of uranium is brick-red, the hydrate is of a yellow color.
Upon ignition both are con verted into the dark blackish-green protosesqui-
oxide. The solutions of sesquioxide of uranium in acids are yellow ; hydro-
sulphuric acid does not alter them ; sulphide of ammonium throws
down after neutralization of the free acid, a dark brown precipitate of
SULPHIDE OF URANIUM, which subsides slowly, and is readily soluble
in acids, even in acetic acid, but does not dissolve in an excess of the
precipitant. Ammonia, potassa, and soda produce yellow precipitates of
sesquioxide of uranium and alkali, insoluble in excess of the precipitants.
Carbonate of ammonia produces a yellow precipitate of carbonate of ses-
quioxide of uranium and ammonia, which dissolves readily in an excess
of the precipitant. Potassa and soda throw down from the solution the
whole of the sesquioxide of uranium. Carbonate of baryta completely
precipitates solutions of sesquioxide of uranium, even in the cold. Ferro-
cyauide of potassium produces a reddish-brown precipitate : this is a very
delicate test for uranium. Borax and phosphate of soda and ammonia
give with sesquioxide of uranium in the inner flame of the blowpipe
green beads, in the^outer flame yellow beads, which upon cooling acquire
a yellowish-green tint.
To separate sesquioxide of uranium from the other oxides of the fourth
group, and from alumina, precipitate first with carbonate of baryta,
which throws down the sesquioxide of iron, the sesquioxide of uranium,
and the alumina, leaving the other oxides in solution. Dissolve the
precipitate in hydrochloric acid, remove the baryta from the solution by
means of sulphuric acid, filter, and add ammonia to the filtrate until a
precipitate begins to form ; add now a suflftcient quantity of carbonate
of ammonia, which has previously been once boiled, to destroy any
bicarbonate of ammonia it may contain. Dilute with water and
filter off the precipitate, which contains the whole of the sesquioxide
of iron and alumina, the filtrate containing all the sesquioxide of
uranium.
113, 114.] OXIDE OF SILVER. 93
H3.
FIFTH GROUP.
OXIDE OF SILVER, SUBOXIDE OF MERCURY, OXIDE OF MERCURY,
OXIDE OF LEAD, TEROXIDE OF BISMUTH, OXIDE OF COPPER, OXIDE
OF CADMIUM.
Properties of the group. The sulphides corresponding to the oxides of
this group are insoluble both in dilute acids and in alkaline sulphides.*
The solutions of these oxides are therefore completely precipitated by
hydrosulphuric acid, 110 matter whether their reaction be neutral, alka-
line, or acid.
For the sake of greater clearness and simplicity, we divide the oxides
of this group into two divisions, and distinguish,
1. OXIDES PRECIPITABLE BY HYDROCHLORIC ACID, viz. : oxide of silver,
suboxide of mercury, oxide of lead.
2. OXIDES NOT PRECIPITABLE BY HYDROCHLORIC ACID, viz. : oxide of
mercury, oxide of copper, teroxide of bismuth, oxide of cadmium.
Lead must be considered in both divisions, since the sparing solubility
of its chloride might lead to confounding its oxide with suboxide of
mercury and oxide of silver, without affording us, on the other hand,
any means of effecting its perfect separation from the oxides of the second
division.
FIRST DIVISION OF THE FIFTH GROUP : OXIDES WHICH ARE PRECIPITATED
BY HYDROCHLORIC ACID.
Special Reactions.
H4.
a. OXIDE OF SILVER (Ag 0).
1. Metallic silver is white, very lustrous, moderately hard, highly
malleable, ductile, rather difficultly fusible. It is not oxidized by ignition
in the air. Nitric acid dissolves silver readily ; the metal is insoluble in
dilute sulphuric acid and in hydrochloric acid.
2. Oxide of silver is a grayish-brown powder ; it 'is not altogether inso-
luble in water, and dissolves readily in dilute nitric acid. It forms no
hydrate. It is decomposed by heat into metallic silver and oxygen gas.
3. The salts of oxide of silver are non- volatile and colorless ; most of
them acquire a black tint upon exposure to light. The soluble neutral
salts do not alter vegetable colors, and are decomposed at a red heat.
4. Hydrosulphuric acid and sulphide of ammonium precipitate from
solutions of salts of silver black SULPHIDE OF SILVER (Ag S), which is
insoluble in dilute acids, alkalies, alkaline sulphides, and cyanide of
potassium. Boiling nitric acid decomposes and dissolves this precipitate
readily, with separation of sulphur.
5. Potassa and soda precipitate from solutions of salts of silver the
oxide of this metal in the form of a LIGHT BROWN POWDER, which is in-
soluble in an excess of the precipitant, but dissolves readily in am-
monia.
* Consult, however, the paragraphs on oxide of copper and suboxide and oxide of mer-
cury, as the latter remark applies only partially to them.
94 SUBOXIDE OF MERCURY. [ 115.
6. Ammonia, when added in very small quantity to neutral solu-
tions of oxide of silver, throws down the oxide as a brown precipitate,
which readily redissolves in an excess of ammonia. Acid solutions of
silver are not precipitated.
7. Hydrochloric acid and soluble metallic chlorides produce in solutions
of salts of silver a white, curdy precipitate of CHLORIDE OF SILVER
(A<* Cl). In very dilute solutions these reagents impart simply a bluish -
white opalescent appearance to the fluid. By the action of light
chloride of silver first acquires a violet tint, and ultimately turns black ;
it is insoluble in nitric acid, but dissolves readily in ammonia as am-
monio-chloride of silver, from which double compound the chloride of
silver is again separated by acids. Concentrated hydrochloric acid and
concentrated solutions of chlorides of the alkali metals dissolve some
chloride of silver, more particularly upon application of heat j but the
dissolved chloride separates again upon dilution. Upon exposure to heat,
chloride of silver fuses without decomposition, giving upon cooling a
transparent horny mass.
8. If compounds of silver, mixed with carbonate of soda, are exposed on
a charcoal support to the inner flame of the blowpipe, WHITE, BRILLIANT,
DUCTILE METALLIC GLOBULES are obtained, unattended with incrustation
of the charcoal .
115.
b. SUBOXIDE OF MERCURY (Hg 2 O).
1. Metallic mercury is grayish- white, lustrous, fluid at the common tem-
perature ; it solidifies at - 40, and boils at 680 Fah. It is insoluble in
hydrochloric acid ; in dilute cold nitric acid it dissolves to nitrate of sub-
oxide, in more concentrated hot nitric acid to nitrate of oxide of mercury.
'2. Suboxide of mercury is a black powder which is readily soluble in
nitric acid, and is decomposed by the action of heat, the mercury vola-
tilizing in the metallic state. It forms no hydrate.
3. The salts of suboxide of mercury volatilize upon ignition ; most
of them suffer decomposition in this process. Subchloride and sub-
bromide of mercury volatilize unaltered. Most of the salts of suboxide
of mercury are colorless. The soluble salts in the neutral state redden,
litmus paper. Nitrate of suboxide of mercury is decomposed by addi-
tion of much water into an insoluble basic and soluble acid salt.
4. Hydrosulphuric acid and sulphide of ammonium produce black
precipitates of SUBSULPHIDE OF MERCURY (Hg 2 S), which are insoluble in
dilute acids, sulphide of ammonium, and cyanide of potassium. Proto-
sulphide of sodium dissolves this subsulphide to sulphide, with separation
of metallic mercury. Bisulphide of sodium dissolves the subsulphide to
sulphide, without separation of metallic mercury. Subsulphide of mer-
cury is readily decomposed arid dissolved by nitrohydrochloric acid, but
not by boiling concentrated nitric acids.
5. Potassa and ammonia produce in solutions of salts of suboxide of
mercury black precipitates, which are insoluble in an excess of the
precipitants. The precipitates produced by potassa consist of SUB-
OXIDE OF MERCURY ; whilst those produced by ammonia consist of a
BASIC DOUBLE SALT OF SUBOXIDE OF MERCURY AND AMMONIA, e.g.
(NH s ,N0 5 + 2H gj p).
6 . Hydrochloric acid and soluble metallic chlorides precipitate from
solutions of salts of suboxide of mercury SUBCHLORIDE OF MERCURY
116.] OXIDE OF LEAD. 95
(Hg a Cl), as a fine powder of dazzling whiteness. Cold hydrochloric
acid and cold nitric acid fail to dissolve this precipitate ; it dissolves,
however, although very difficultly and slowly, upon long protracted boil-
ing with these acids, being resolved by hydrochloric acid into chloride
of mercury and metallic mercury, which separates ; and converted by
nitric acid into chloride of mercury and nitrate of oxide of mercury.
Nitrohydrochloric acid and chlorine water dissolve the subchloride of
mercury readily, converting it into chloride. Ammonia and potassa
decompose the subchloride of mercury, and separate black suboxide
from it.
7 . If a drop of a neutral or slightly acid solution of suboxide of mer-
cury 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, &c., appear WHITE arid LUSTROUS like silver. The application of a
gentle heat to the copper causes the metallic mercury precipitated on its
surface to volatilize, and thus removes the silvering.
8. Protochloride of tin produces in solutions of suboxide of mercury a
gray precipitate of METALLIC MERCURY, which may be united into glo-
bules by boiling the metallic deposit, after decanting the fluid, with
hydrochloric acid.
9. If an intimate mixture of an anhydrous compound of mercury
with anhydrous carbonate of soda is, introduced into a drawn-out glass
tube, and covered with a layer of carbonate of soda, and the tube is then
heated before the blowpipe, the mercurial compound invariably under-
goes decomposition, and metallic mercury separates, forming a coat of
gray sublimate above the heated part of the tube. The minute particles
of mercury may be united into larger globules by rubbing this coating
with a glass rod.
H6.
c. OXIDE OF LEAD (PbO).
1. Metallic lead is bluish-gray; its surface recently cut exhibits a
metallic lustre ; it is soft, malleable, readily fusible. Fused upon charcoal
before the blowpipe, it forms a coating of yellow oxide on the charcoal.
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 particularly on heating.
2. Oxide of lead is a yellow or reddish-yellow powder,* which upon
exposure to a red heat fuses to a vitreous mass. Hydrated oxide of lead
is white. Both the oxide and its hydrate dissolve readily in nitric and
acetic acids.
3. The salts of oxide of lead are non- volatile ; most of them are
colorless ; the neutral soluble salts redden litmus paper, and are de-
composed at a red heat.
4. Hydrosufyhuric acid and sulphide of ammonium produce in solu-
tions of salts of lead black precipitates of SULPHIDE OF LEAD (Pb S), which
are insoluble in cold dilute acids, in alkalies, alkaline sulphides, and
cyanide of potassium. Sulphide of lead is decomposed by boiling con-
centrated nitric acid ; the whole of the lead is first converted into nitrate
of lead, and the greater part of the sulphur separates, whilst another
portion is converted into sulphuric acid. The sulphuric acid thus
While hot, the oxide of lead appears red.
96 OXIDE OF LEAD. [ 116.
formed decomposes a portion of the nitrate of lead, and forms with the
liberated oxide sulphate of lead, which precipitates as a white powder ; the
deposit in the solution consists therefore of a mixture of sulphate of lead
and sulphur. In solutions of salts of lead containing an excess of a concen-
trated mineral acid, hydrosulphuric acid produces a precipitate only
after the addition of water or after neutralization of the free acid by
an alkali. If a solution of lead is precipitated by hydrosulphuric acid,
in presence of a large quantity of free hydrochloric acid, a red precipi-
tate is formed, consisting of chloride and sulphide of lead, which, how-
ever, is converted by an excess of hydrosulphuric acid into black sulphide
of lead.
5. Potassa and ammonia throw down BASIC SALTS OF LEAD in the
form of white precipitates, which are insoluble in ammonia, and diffi-
cultly soluble in potassa. In solutions of acetate of lead ammonia does not
immediately produce a precipitate, owing to the formation of a soluble
triacetate of lead.
6. Carbonate of soda throws down from solutions of salts of lead a
white precipitate of BASIC CARBONATE OF LEAD [e. g. 5 (Pb 0, C O 2 ) +
Pb O, H 0], which is insoluble in an excess of the precipitant and also
in cyanide of potassium.
7. Hydrochloric acid and soluble chlorides produce in concentrated
solutions of salts of lead heavy, white precipitates of CHLORIDE OF LEAD
(Pb 01), which are soluble in a large amount of water, especially upon
application of heat. This chloride of lead is converted by ammonia
into basic chloride of lead (Pb Cl, 3 Pb + H O), which is also a white
powder, but almost absolutely insoluble in water. In dilute nitric
and hydrochloric acids, chloride of lead is more difficultly soluble than
in water.
8. Sulphuric acid and sulphates produce in solutions of salts of lead
white precipitates of SULPHATE OF LEAD (PbO, SO 3 ), which are nearly
insoluble in water and dilute acids. From dilute solutions, especially
from such as contain much free acid, the sulphate of lead precipitates
only after some, frequently after a long time. It is advisable under all cir-
cumstances to add a considerable excess of dilute sulphuric acid, since
sulphate of lead is more insoluble in this menstruum than in water. The
separation of small quantities of sulphate of lead is best effected by eva-
porating, after the addition of the sulphuric acid, as far as practicable
on the water-bath, and then treating the residue with water. Sulphate
of lead is slightly soluble in concentrated nitric acid ; it dissolves with
difficulty in boiling concentrated hydrochloric acid, but more readily in
solution of potassa. It dissolves also pretty readily in the solutions
of some of the salts of ammonia, particularly in solution of acetate
of ammonia \ dilute sulphuric acid precipitates it again from these
solutions.
9. Chromate of potassa produces in solutions of salt of lead a yellow
precipitate of CHROMATE OF LEAD (Pb 0, Or O 3 ), which is readily soluble
in potassa, but difficultly so in dilute nitric acid.
10. If a mixture of a compound of lead with carbonate of soda is ex-
posed on a charcoal support to the reducing flame, of the blowpipe, soft,
malleable METALLIC GLOBULES OF LEAD are readily produced, the charcoal
becoming covered at the same time with a slight yellow incrustation of
OXIDE OF LEAD.
117, 118.] OXIDE OF MERCURY. 97
H7.
Recapitulation and remarks. The metallic oxides of the first division
of the fifth group are most distinctly characterized in their corresponding
chlorides j since the different respective deportment of these chlorides
with water and ammonia affords us a simple means both of detecting
them and effecting their separation from one another. For if the pre-
cipitate containing the three metallic chlorides is boiled with a some-
what large quantity of water, or boiling water is repeatedly poured over
it on the filter, the chloride of lead dissolves, whilst the chloride of silver
and the subciiloride of mercury remain undissolved. If these two
chlorides are then treated with ammonia, the subchloride of mercury is
converted into a black basic salt, insoluble in an excess of the ammonia ;
whilst the chloride of silver dissolves readily in that agent, and precipi-
tates from this solution again upon addition of nitric acid. When
operating upon small quantities, it is advisable first to expel the greater
part of the ammonia by heat. In the aqueous solution of chloride of
lead the metal may be readily detected by sulphuric acid.
SECOND DIVISION OF THE FIFTH GROUP I OXIDES WHICH ARE NOT
PRECIPITATED BY HYDROCHLORIC ACID.
Special Reactions.
H8.
a. OXIDE OF MERCURY (Hg 0).
1. Oxide of mercury is generally crystalline, and has a bright red
color, which upon reduction to powder changes to a pale yellowish-red ;
the oxide precipitated from solutions of the nitrate of the oxide, or from
solutions of the chloride, forms a yellow powder. Upon exposure to
heat it transiently acquires a deeper tint j at a dull red heat it is
resolved into metallic mercury and oxygen. Both the crystalline and
non-crystalline oxide dissolve readily in hydrochloric and nitric acids.
2. The salts of oxide of mercury volatilize upon ignition ; they suffer
decomposition in this process ; chloride, bromide, and iodide of mercury
volatilize unaltered. Most of the salts of oxide of mercury are color-
less. The soluble neutral salts redden litmus paper. The nitrate and
sulphate of oxide of mercury are decomposed by water added in large
quantity, into soluble acid and insoluble basic salts.
3. Addition of a very small quantity of hydrosulphuric acid or sul-
phide of ammonium produces in solutions of oxide of mercury, after
shaking, a perfectly white precipitate. Addition of a somewhat larger
quantity of these reagents causes the precipitate to acquire a yellow,
orange, or brownish-red color, according to the less or greater proportion
added ; an excess of the precipitant produces a purely black precipitate
of SULPHIDE OF MERCURY (Hg S). This progressive variation of color
from white to black, which depends on the proportion of the hydrosulphuric
acid or sulphide of ammonium added, distinguishes the oxide of mercury
from all other bodies. The white precipitate which forms at first con-
sists of a double compound of sulphide of mercury with the still unde-
composed portion of the salt of oxide of mercury (in a solution of
chloride of mercury, for instance, Hg 01 + 2 Hg S) ; the gradually in-
I. H
98 OXIDE OF COPPER. [ 119.
creasing admixture of black sulphide causes the precipitate to pass
through the several gradations of color above mentioned. Sul-
phide of mercury is not dissolved by sulphide of ammonium, nor by
potassa or cyanide of potassium ; it is altogether insoluble in hydro-
chloric acid and in nitric acid, even upon boiling. It dissolves com-
pletely in sulphide of potassium, and is readily decomposed and dissolved
by nitrohydrochloric acid.
4. Potassa, added in small quantity, produces in neutral or slightly
acid solutions of oxide of mercury a reddish-brown precipitate, which
acquires a yellow tint if the reagent is added in excess. The reddish-
brown precipitate is a BASIC SALT ; the yellow precipitate consists of
OXIDE OF MEKCURY. 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 incomplete. In presence
of salts of ammonia, potassa produces in solutions of salts of oxide of
mercury, instead of reddish-brown or yellow, white precipitates. The
precipitate thrown down by potassa from a solution of chloride of mer-
cury containing an excess of chloride of ammonium is of analogous
composition to the precipitate produced by ammonia (see 5).
5. Ammonia produces in solutions of salts of oxide of mercury white
precipitates quite analogous to those produced by potassa in presence of
chloride of ammonium ; thus, for instance, ammonia precipitates from
solutions of chloride of mercury a double compound of chloride of mer-
cury and amide of mercury (Hg 01 + Hg N HJ.
6. Protochloride of tin, added in small quantity to salts of oxide of
mercury, reduces the oxide to suboxide, thus giving rise to the formation
of a white precipitate of SUBCHLORIDE OF MERCURY (Hg 2 Cl) ; but if
added in excess, this reagent deprives the mercury completely of the
oxygen and acid, or of the salt-radical, and throws it down in the metallic
state, the same as in the case of the suboxide of mercury. The pre-
cipitate, which was white at first, acquires therefore now a gray tint, and
may be readily united into globules of metallic mercury by boiling
with hydrochloric acid.
7. The salts of oxide of mercury present the same deportment as the
salts of the suboxide, both with metallic copper and when heated toge-
ther with carbonate of soda in a glass tube before the blowpipe.
H9.
b. OXIDE OF COPPER (Cu 0).
1. Metallic copper has a peculiar red color, and a strong lustre ; it is
moderately hard, malleable, ductile, rather difficultly fusible ; in contact
with water and air it becomes covered with a green crust of basic car-
bonate of oxide of copper ; upon ignition in the air it becomes coated
over with black oxide. In hydrochloric acid and dilute sulphuric acid
it is insoluble or nearly so, even upon boiling. Nitric acid dissolves
the metal readily. Concentrated sulphuric acid converts it into sulphate
of oxide of copper, with evolution of sulphurous acid.
2. Suboxide of copper is red, its hydrate yellow; both change to
oxide upon ignition in the air. On treating the suboxide with dilute
sulphuric acid, metallic copper separates, whilst sulphate of oxide of
copper dissolves ; on treating suboxide of copper with hydrochloric acid,
119.] OXIDE OP COPPER. 99
white subchloride of copper is formed, which dissolves in an excess of
the acid, but is reprecipitated from this solution by water.
3. Oxide of copper is a black, fixed powder ; its hydrate (Cu 0, H 0)
is of a light blue color. Both the oxide of copper and its hydrate
dissolve readily in hydrochloric, sulphuric, and nitric acids.
4. Most of the neutral salts of oxide of copper are soluble in water ;
the soluble salts redden litmus, and 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; the hydrated salts are usually of a blue, or green color, which
their solutions continue to exhibit even when much diluted.
5. Hydrosulpliuric acid and sulphide of ammonium produce in alka-
line, neutral, arid acid solutions of salts of oxide of copper, brownish-
black precipitates of SULPHIDE OF COPPER (Cu S). This sulphide is
insoluble in dilute acids and caustic alkalies. Hot solutions of sulphide
of potassium and sulphide of sodium fail also to dissolve it or dissolve
it only to a very trifling extent ; but it is a little more soluble in sul-
phide of ammonium. The latter reagent is therefore not adapted to
effect the perfect separation of sulphide of copper from other metallic
sulphides. Sulphide of copper is readily decomposed and dissolved by
boiling concentrated nitric acid ; it dissolves completely in solution of
cyanide of potassium. In solutions of salts of copper which contain an
excess of a concentrated mineral acid, hyclrosulphuric acid produces a
precipitate only after the addition of water.
6. Potassa or soda produces in solutions of salts of oxide of copper a
light blue, bulky precipitate of HYDRATE OF OXIDE OF COPPER (Cu O,
H O). If the solution is highly concentrated, and the potassa added in
excess, the precipitate turns 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 in which it is suspended (and
which must, if necessary, be diluted for the purpose). In this process
the (Cu 0, H 0) hydrated oxide is converted into the (3 Cu O, H 0)
hydrated oxide.
7. Carbonate of soda produces in solutions of salts of oxide of copper a
greenish-blue precipitate of HYDRATED BASIC CARBONATE OF COPPER
(Cu O, C O 2 4- Cu O, H O), which upon boiling changes to brownish-black
oxide of copper, and dissolves in ammonia to an azure-blue, and in cyanide
of potassium to a brownish fluid.
8. Ammonia added in small quantity to solutions of salts of oxide of
copper produces a greenish-blue precipitate, consisting of a BASIC SALT OF
COPPER. This precipitate redissolves readily upon further addition of
ammonia, giving a perfectly clear solution of a magnificent azure-blue,
which owes its color to the formation of a BASIC DOUBLE SALT OF AMMONIO-
OXIDE OF COPPER. Thus, for instance, in a solution of sulphate of oxide of
copper, ammonia produces a precipitate of N H 3 , Cu O + N H 4 0, S O 3 .
The blue color ceases to be perceptible only in very dilute solutions.
Potassa produces in such blue solutions in the cold, after the lapse of
some time, a precipitate of blue hydrate of oxide of copper ; but upon
boiling the fluid this reagent precipitates the whole of the copper as black
oxide. Carbonate of ammonia presents the same deportment with salts
of copper as pure ammonia.
9. Ferrocyanide of potassium produces even in moderately dilute solu-
tions a reddish-brown precipitate of FERROCYANIDE OF COPPER (Cu 2 , Cfy)
H 2
100 TEROXIDE OF BISMUTH. [ 120.
which is insoluble in dilute acids, but suffers decomposition when acted
upon by potassa. In very highly dilute solutions the reagent produces
only a reddish coloration of the fluid.
10. Metallic iron when brought into contact with concentrated solu-
tions of salts of copper is almost immediately covered with a COPPERY-RED
COATING OP METALLIC COPPER ; very dilute solutions produce this coat-
ing only after some time. Presence of a little free acid accelerates the
reaction.
If a fluid containing copper and a little free hydrochloric acid is poured
into a small platinum dish (the lid of a platinum crucible), and a small
piece of zinc is introduced, the bright platinum surface speedily becomes
covered with a COATING OF COPPER ; even with very dilute solutions
this coating is clearly discernible.
11. If a mixture of a compound of copper with carbonate of soda is
exposed on a charcoal support to the reducing flame of the blowpipe,
METALLIC COPPER is obtained, without simultaneous incrustation of the
charcoal. The best method of freeing this copper from the particles of
charcoal, is to triturate the fused mass in a small mortar with water, and
to wash off the charcoal powder ; when the coppery-red metallic particles
will be left behind.
12. Copper, its alloys, and other compounds, when exposed to the
inner blowpipe flame, impart an EMERALD GREEN tint to the outer flame.
Addition of chloride of silver considerably heightens the delicacy of the
reaction.
13. Borax and phosphate of soda and ammonia readily dissolve oxide
of copper in the outer blowpipe flame. The beads are green while hot,
blue when cold. In the inner flame the bead produced with borax ap-
pears colorless, that produced with phosphate of soda and ammonia turns
dark green ; both acquire a brownish-red tint upon cooling.
120.
c. TEROXIDE OF BISMUTH (Bi 3 ).
1. Bismuth has a reddish tin-white color and moderate metallic
lustre ; it is of medium hardness, brittle, readily fusible ; when fused
upon a charcoal support, it forms a coating of yellow teroxide on the
surface of the charcoal. It dissolves readily in nitric acid, but is
nearly insoluble in hydrochloric acid, and altogether so in dilute sul-
phuric acid. Concentrated sulphuric acid converts it into sulphate of
teroxide of bismuth, with evolution of sulphurous acid.
2. The teroxide of bismuth is a yellow powder; when heated, it tran-
siently acquires a deeper tint ; it fuses at a red heat. Hydrate of ter-
oxide of bismuth is white. Both the teroxide and its hydrate dissolve
readily in hydrochloric, sulphuric, and nitric acids.
3. The salts of bismuth are non-volatile, with the exception of a few
(terchloride of bismuth). Most of them are decomposed at a red heat.
They are colorless ; some of them are soluble in water, whilst others are
insoluble in this menstruum. The soluble salts, in the neutral state,
redden litmus paper, and are decomposed into soluble acid and insoluble
basic salts when treated with a large amount of water.
4. Hydrosulphuric ac^and sulphide of ammonium produce in neutral
and acid solutions of salts of bismuth black precipitates of TERSULPHIDE
OF BISMUTH (Bi S 3 ), which are insoluble in dilute acids, alkalies, alkaline
121.] OXIDE OP CADMIUM. 101
sulphides, and cyanide of potassium, but are readily decomposed and
dissolved by boiling concentrated nitric acid. In solutions of salts of
bismuth which contain a considerable excess of hydrochloric or nitric
acid, hydrosulphuric acid produces a precipitate only after the addition
of water.
5. Potassa and ammonia throw down from solutions of salts of bis-
muth HYDRATE OF TEROXIDE OF BISMUTH as a white precipitate, which is
insoluble in an excess of the precipitant.
6. Carbonate of soda throws down from solutions of salts of bismuth
BASIC CARBONATE OF BISMUTH (Bi O 3 , C O 2 ) as a white bulky precipitate,
which is insoluble in an excess of the precipitant, and equally so in
cyanide of potassium.
7. Chromate of potassa precipitates from solutions of salts of bismuth
CHROMATE OF BISMUTH as a yellow powder. This substance differs from
chromate of lead in being soluble in dilute nitric acid and insoluble in
potassa.
8. The reaction which characterizes the teroxide of bismuth more par-
ticularly, is the decomposition of its neutral salts by water into soluble
acid and insoluble basic salts. The addition of a large amount of water
to solutions of salts of bismuth causes the immediate formation of a
dazzling white precipitate, provided there be not too much free acid pre-
sent. This reaction is the most sensitive with terchloride of bismuth, as
the basic chloride of bismuth (Bi C1 3 , 2 Bi O 3 ) is nearly insoluble in
water. If water fails to produce a precipitate in nitric acid solutions of
bismuth, owing to the presence of too much free acid, the excess of the
acid must be removed by evaporation, before the water is added. From
the basic salts of antimony which are formed under analogous circum-
stances, the precipitated basic salts of bismuth may be readily distin-
guished by their insolubility in tartaric acid.
9. If a mixture of a compound of bismuth with carbonate of soda is
exposed on a charcoal support to the reducing flame of the blowpipe,
brittle GLOBULES OF BISMUTH are obtained, which fly into pieces under
the stroke of a hammer. The charcoal becomes covered at the same
time with a slight yellow incrustation of TEROXIDE OF BISMUTH.
121.
d. OXIDE OF CADMIUM (Cd 0).
1. Metallic cadmium has a tin- white colour; it is lustrous, not very hard,
malleable, ductile; it fuses at a temperature below red heat, and volatilizes
at a temperature somewhat above the boiling point of mercury. Heated
on charcoal before the blowpipe, it takes fire and burns, emitting brown
fumes of oxide of cadmium, which form a coating on the charcoal.
Hydrochloric acid and dilute sulphuric acid dissolve it, with evolution of
hydrogen ; but nitric acid dissolves it most readily.
2. Oxide of cadmium is a yellowish-brown, fixed powder ; its hydrate
is white. Both the oxide and its hydrate dissolve readily in hydro-
chloric, nitric, and sulphuric acids.
3. The salts of oxide of cadmium are colorless or white ; some of
them are soluble in water. The soluble salts, in the neutral state, redden
litmus paper, and are decomposed at a red heat.
4. Hydrosulphuric acid and sulphide of ammonium produce in alkaline,
neutral, and acid solutions of salts of cadmium, bright yellow precipitates
102 RECAPITULATION AND REMARKS. [ 122.
of SULPHIDE OF CADMIUM (Cd S), which are insoluble in dilute acids,
alkalies, alkaline sulphides, and cyanide of potassium. They are readily
decomposed and dissolved by boiling concentrated nitric acid. In solu-
tions of salts of cadmium which contain a considerable excess of acid,
hydrosulphuric acid produces a precipitate only after dilution with
water.
5. Potassa produces in solutions of salts of cadmium a white precipitate
of HYDRATE OF OXIDE OF CADMIUM (Cd O, H O), which is insoluble in
an excess of the precipitant.
6. Ammonia likewise precipitates from solutions of salts of cadmium
white HYDRATE OF OXIDE OF CADMIUM, which, however, redissolves
readily to a colorless fluid in an excess of the precipitant.
7. Carbonate ofpotassa and carbonate of ammonia produce white pre-
cipitates of CARBONATE OF CADMIUM (Cd O, C O 2 ), which are insoluble
in an excess of the precipitants. The presence of salts of ammonia does
not prevent the formation of these precipitates. The precipitated car-
bonate of cadmium dissolves readily in solution of cyanide of potassium.
From dilute solutions the precipitate separates only after some time.
8. If a mixture of a compound of cadmium with carbonate of soda, is
exposed on a charcoal support to the reducing flame of the blowpipe, the
charcoal becomes covered with a reddish-brown coating of OXIDE OF
CADMIUM, owing to the volatilization of the reduced metal and its sub-
sequent re-oxidation in passing through the oxidizing flame. The coating
is seen most distinctly after cooling.
122.
Recapitulation and remarks. The perfect separation of the metallic
oxides of the second division of the fifth group from suboxide of mercury
and oxide of silver may, as already stated, be effected by means of hydro-
chloric acid ; but this agent fails to separate them completely from oxide
of lead. The oxide of mercury is distinguished from the other oxides of
this division by the insolubility of the corresponding sulphide in boiling
nitric acid. This property affords a convenient means for its separation.
Moreover, the reactions with protochloride of tin or with metallic copper,
as well as those in the dry way, will, after the previous removal of the
suboxide, always readily indicate the presence of oxide of mercury.
From the still remaining oxides the oxide of lead is separated by addi-
tion of a sufficient quantity of dilute sulphuric acid ; the separation is
the most complete if the fluid, after the addition of the sulphuric acid,
is evaporated on the water-bath, and the residue diluted with water.
Teroxide of bismuth may be separated from oxide of copper and oxide of
cadmium by addition of ammonia in excess, as the latter two oxides are
soluble in an excess of this agent. If the filtered precipitate is dissolved
in one or two drops of hydrochloric acid on a watchglass, and water
added, the appearance of a milky turbidity is a confirmation of the
presence of teroxide of bismuth. The presence of a notable quantity of
oxide of copper is revealed by the blue color of the amnioniacal solution ;
smaller quantities are detected by evaporating the ammoniacal solution
nearly to dryness, adding a little acetic acid, and then ferrocyanide of
potassium. The separation of oxide of copper from oxide of cadmium
may be effected by means of carbonate of ammonia ; however, by that
method minute quantities of cadmium might readily escape detection.
123.] PROTOXIDE OF PALLADIUM. 103
The separation by means of cyanide of potassium is safer. The process
is very simple, being as follows : precipitate the solution with hydro-
sulphuric acid, let the precipitate settle, wash it slightly by decantation,
and treat it with some cyanide of potassium, when the sulphide of copper
will dissolve, the yellow sulphide of cadmium remaining undissolved.
123.
SUPPLEMENT TO THE FIFTH GROUP.
PROTOXIDE OF PALLADIUM (Pd 0).
Palladium greatly resembles platinum ; its color is somewhat darker.
It fuses with great difficulty ; when heated in the air to dull redness, it
becomes covered with a blue coating ; but, upon more intense ignition,
it recovers its light color and metallic lustre. It is difficultly soluble
in pure nitric acid, but dissolves somewhat more readily in nitric acid,
containing nitrous acid ; it dissolves very sparingly in boiling con-
centrated sulphuric acid, but readily in nitro-hydrochloric acid. It
combines with 1 and 2 eq. of oxygen to form protoxide and binoxide. The
latter, when heated with dilute hydrochloric acid, evolves chlorine, and
gives solution of protochloride of palladium. Protoxide of palladium is
black, its hydrate dark brown ; both are, upon intense ignition, resolved
into oxygen and metallic palladium. The salts of protoxide of palla-
dium are mostly soluble in water ; they are brown, or reddish- brown ; their
solutions, when concentrated, are reddish-brown ; when dilute, yellow.
Water precipitates from a solution of nitrate of protoxide of palladium
containing a slight excess of acid, a brown-colored basic salt. The
oxygen salts, as well as the protochloride, are decomposed upon ignition,
leaving metallic palladium behind. Hydrosulphuric acid and sulphide of
ammonium throw down from acid or neutral solutions of salts of pro-
toxide of palladium, black protosulphide of palladium, which dissolves
neither in sulphide of ammonium nor in boiling hydrochloric acid, and
with difficulty in boiling nitric acid, but readily in nitro-hydrochloric
acid. From the solution of the protochloride potassa precipitates a
brown basic salt, soluble in an excess of the precipitant, ammonia,
flesh-colored ammonio-protochloride of palladium (Pd 01, N H 3 ), cy-
anide of mercury, yellowish- white gelatinous protocyanide of palladium,
soluble in hydrochloric acid, and in ammonia. Protochloride of tin pro-
duces, in absence of free hydrochloric acid, a brownish-black precipitate ;
in presence of free hydrochloric acid, a red-colored solution, which speedily
turns brown, and ultimately green, and, upon addition of water,
brownish-red. Sulphate of protoxide of iron produces a deposit of pal-
ladium on the sides of the glass. Iodide of potassium precipitates black
protiodide of palladium. Chloride of potassium precipitates from highly
concentrated solutions of protoxide of palladium, potassio-protochloride of
palladium (K 01, Pd Cl), in form of golden-yellow needles, which dissolve
readily in water giving a dark red fluid, but are insoluble in absolute
alcohol.
104 TEKOXIDE OF GOLD. [ 124, 125.
124.
SIXTH GROUP.
TEROXIDE OF GOLD, BINOXIDE OF PLATINUM, TEROXLDE OF ANTIMONY,
BINOXIDE OF TIN, PROTOXIDE OF TIN, ARSENIOUS ACID AND ARSENIC
ACID.*
Properties of the group. The sulphides corresponding to the oxides of
the sixth group are insoluble in dilute acids. These combine with alka-
line sulphides forming soluble sulphur salts, in which they perform the
part of the acid. Hydrosulphuric acid precipitates these oxides there-
fore, like those of the fifth group, completely from acidified solutions.
The precipitated sulphides differ, however, from those of the fifth group
in this, that they dissolve in sulphide of ammonium, sulphide of
potassium, &c., and are reprecipitated from these solutions on the addi-
tion of acids.
We divide the oxides of this group into two classes, and distinguish,
1. OXIDES WHOSE CORRESPONDING SULPHIDES ARE INSOLUBLE IN
HYDROCHLORIC ACID AND IN NITRIC ACID, and are reduced to the metallic
state upon fusion in conjunction with nitrate and carbonate of soda : viz.,
teroxide of gold and binoxide of platinum,
2. OXIDES WHOSE CORRESPONDING SULPHIDES ARE SOLUBLE IN BOILING
HYDROCHLORIC ACID OR NITRIC ACID, and are upon fusion with nitrate and
carbonate of soda converted into oxides or acids, which combine with the
soda : viz., Teroxide of antimony, protoxide and binoxide of tin,
arsenious and arsenic acids.
FIRST DIVISION.
Special Reactions.
125.
a. TEROXIDE OF GOLD (Au 3 ).
1. Metallic gold has a reddish yellow color, and a high metallic lustre :
it is rather soft, exceedingly malleable, ductile, difficultly fusible ; it
does not oxidize upon ignition in the air, and is insoluble in hydro-
chloric, nitric, and sulphuric acids ; but it dissolves in fluids containing or
evolving chlorine, e. y. in nitro-hydrochloric acid. The solution contains
terchloride of gold.
2. Teroxide of gold is a blackish-brown, its hydrate a chesnut-browii
powder. Both are reduced by light and heat, and dissolve readily in
hydrochloric acid, but not in dilute oxygen acids. Concentrated nitric
and sulphuric acids dissolve a little teroxide of gold ; water reprecipitates
it from these solutions.
3. Salts of gold with oxygen acids are nearly unknown. The haloid
salts of gold are yellow, and their solutions continue to exhibit this color
up to a high degree of dilution. The whole of them are readily decom-
* I have placed the two acids of arsenic with the metallic oxides, since the deportment
of the sulphides of arsenic might readily lead to their being confounded with some of the
oxides of the sixth group, and because in the systematic course of analysis the sulphide
of arsenic is invariably obtained in the same precipitate with the sulphide of antimony,
the sulphide of tin, &c.
126.] BINOXIDE OF PLATINUM. 105
posed upon ignition. Neutral solution of terchloride of gold reddens
litmus paper.
4. Hydrosulphuric acid precipitates from neutral and acid solutions of
gold the whole of the metal as black TERSULPHIDE OF GOLD (Au S 3 ),
which is insoluble in either of the acids, partly soluble in potassa, and
perfectly so in sulphuretted alkaline sulphides and in nitro-hydro-
chloric acid. From boiling solutions hydrosulphuric acid throws down
metallic gold.
5. Sulphide of ammonium produces the same precipitate. This re-
dissolves in an excess of the precipitant only if the latter contains ail
excess of sulphur.
6. Ammonia produces, but only in tolerably concentrated solutions of
gold, reddish-yellow precipitates of AURATE OF AMMONIA (fulminating
gold). The more acid the solution and the greater the excess of
ammonia added, the more gold remains in solution.
7. Protochloride of tin containing an admixture of bichloride produces
even in extremely dilute solutions of gold, a purple-red precipitate (or
coloration at least), which sometimes inclines rather to violet or to
brownish-red. This precipitate, which has received the name of PURPLE OF
CASSIUS, is insoluble in hydrochloric acid. It is assumed to be a hydrated
compound of binoxide of tin and protoxide of gold with protoxide and
binoxide of tin (Au O, Sn O 2 + Sn O, Sn O 2 + 4 H 0).
8. Salts of protoxide of iron reduce the teroxide of gold, when added
to its solutions, and precipitate metallic gold in form of a most minutely
divided brown powder, which shows metallic lustre when pressed with
the blade of a knife, or when rubbed. The fluid in which the precipitate is
suspended appears of a blackish-blue color by transmitted light.
126.
I. BINOXIDE OF PLATINUM (Pt 2 ).
1. Metallic platinum has a light steel-gray color; it is very lustrous,
moderately hard, very malleable and ductile, difficultly fusible ; it does
not oxidize upon ignition in the air, and is insoluble in hydrochloric,
nitric, and sulphuric acids. It dissolves in nitro-hydrochloric acid,
especially upon heating. The solution contains bichloride of platinum.
2. Binoxide of platinum is a blackish-brown, its hydrate a reddish-brown
powder. Both are reduced by heat ; they are both readily soluble in
hydrochloric acid, and difficultly soluble in oxygen acids.
3. The salts of binoxide of platinum are decomposed at a red heat.
They are yellow ; bichloride of platinum is reddish-brown, its solution
reddish-yellow, which tint it retains up to a high degree of dilution. The
solution reddens litmus paper. Exposure to a very low red heat converts
bichloride of platinum to protochloride ; application of a stronger red
heat reduces it to the metallic state. Solution of bichloride of platinum,
containing protochloride, has a deep dark brown color.
4. Hydrosulphuric acid throws down from acid and neutral solutions
(but not from alkaline solutions, or, at all events, not completely)
after the lapse of some time a blackish-brown precipitate of BISULPHIDE
OF PLATINUM (Pt S,). If the solution is heated after the addition of the
hydrosulphuric acid the precipitate forms immediately. It dissolves
in a great excess of alkaline sulphides, more particularly of the higher
degrees of sulphuration. Bisulphide of platinum is insoluble in
106 PROTOXIDE OF TIN. [ 127, 128.
hydrochloric acid and in nitric acid ; but it dissolves in nitrohydro-
chloric acid.
5. Sulphide of ammonium produces the same precipitate; this redis-
solves completely in a large excess of the precipitant, if the latter contains
an excess of sulphur. Acids reprecipitate the bisulphide of platinum
unaltered from this solution.
6. Potassa and ammonia produce in not too highly dilute solutions of
salts of platinum, mixed with some hydrochloric acid, yellow crystalline
precipitates of POTASSIO- and AMMONIO-BICHLORIDE OF PLATINUM, which
are insoluble in acids, but dissolve in an excess of the precipitants upon
application of heat. From dilute solutions these precipitates are
obtained by evaporating the fluid mixed with potassa or ammonia (or
chloride of potassium or chloride of ammonium), but remaining still acid,
on the water-bath to dry ness, and treating the residue with dilute spirit
of wine until the alkaline chlorides are dissolved. Upon ignition,
ammonio-bichloride of platinum leaves spongy platinum behind.
Potassio-bichloride leaves platinum and chloride of potassium.
7. Protochloride of tin imparts to solutions of salts of binoxide of
platinum which contain much free hydrochloric acid an INTENSELY DARK
BROWNISH-RED COLOR, owing to a reduction of the binoxide or bichloride of
platinum to protoxide or simple chloride. But the reagent produces no
precipitate in such solutions.
8. Sulphate of protoxide of iron does not precipitate solution of
bichloride of platinum.
127.
Recapitulation and remarks. The reactions of gold and platinum
enable us, at least partially, to detect these two metals in the presence
of many other oxides, and also when platinum and gold are present in
the same solution. In the latter case the solution is either evaporated to
dryness with chloride of ammonium, and the residue treated with spirit
of wine, in order to obtain the gold in solution, and the platinum in the
residue ; or the gold is precipitated with protochloride of iron, and the
fluid filtered off after standing sometime. The presence of the platinum
in the filtrate may then be proved by means of chloride of ammonium,
after previous evaporation and addition of spirit of wine. The latter
method is applicable only in cases where both metals are in solution as
chlorides.
SECOND DIVISION OF THE SIXTH GROUP.
Special Reactions.
128.
a. PROTOXIDE OF TIN (Sn O).
1. Tin has a light gray- white color and a high metallic lustre ; it is
soft and malleable ; when bent, it produces a crackling sound. When
heated in the air, it absorbs oxygen, and is converted into grayish- white
binoxide ; heated on charcoal before the blowpipe, it forms a white coat-
ing on the support. Concentrated hydrochloric acid dissolves tin to
protochloride, with evolution of hydrogen gas ; nitrohydrochloric acid
dissolves it, according to circumstances, to bichloride or to a mixture of
proto- and bichloride. Tin dissolves with difficulty in dilute sulphuric
acid ; concentrated sulphuric acid converts it, with the aid of heat, into
sulphate of binoxide; moderately concentrated nitric acid oxidizes it
128.] PROTOXIDE OF TIN. 107
readily, particularly with the aid of heat ; the white binoxide formed
does not redissolve in an excess of the acid.
2. Protoxide of tin is a black or grayish-black powder; its hydrate is
white. Protoxide of tin is reduced by fusion with cyanide of potassium.
It is readily soluble in hydrochloric acid. Nitric acid converts it into
binoxide of tin, which is insoluble in an excess of the acid.
3. The salts of protoxide of tin are colorless, and are decomposed by
heat. The soluble salts, in the neutral state, redden litmus paper. The
salts of protoxide of tin rapidly absorb oxygen from the air, and are
partially or entirely converted into salts of biuoxide ; hence a solution
of protochloride of tin becomes speedily turbid (from ensuing separation of
oxybichloride of tin), if the glass is often opened and there is only little
free acid present ; hence it is only quite recently prepared protochloride
of tin which will completely dissolve in water free from air, &c.
4. Hydro sulphuric acid throws down from neutral and acid solutions
of salts of protoxide of tin a dark brown precipitate of hydrated PROTO-
SULPHIDE OF TIN (Sn S), which is insoluble, or nearly so, in protosul-
phide of ammonium, but dissolves readily in the higher yellow sulphide.
Acids precipitate from this solution yellow bisulphide of tin, mixed with
sulphur. Protosulphide of tin dissolves also in solution of soda or
potassa. Acids precipitate from these solutions brown protosulphide.
Boiling hydrochloric acid dissolves it, with evolution of hydrogen ; boil-
ing nitric acid converts it into insoluble binoxide of tin. Alkaline solu-
tions of protosalts of tin are not, or at least only imperfectly, preci-
pitated by hydrosulphuric acid.
5. Sulphide of ammonium produces the same precipitate of hydrated
PROTOSULPHIDE OF TIN.
6. Potassa, ammonia, carbonate of potassa, and carbonate of ammonia
produce in solutions of salts of protoxide of tin a white, bulky precipitate
of HYDRATE OF PROTOXIDE OF TIN (Sn O, H O), which redissolves readily
in an excess of potassa, but is insoluble in an excess of the other three
precipitants. If the solution of hydrate of protoxide of tin in potassa is
briskly evaporated, a compound of binoxide of tin and potassa is formed,
which remains in solution, whilst metallic tin precipitates ; but, upon
evaporating slowly, crystalline anhydrous protoxide of tin separates.
7. Ter chloride of gold produces in solutions of protochloride or
protoxide of tin, upon addition of some nitric acid (without application
of heat), a precipitate or coloration of PURPLE OF CASSIUS. (Compare
125, 7.)
8. Solution of chloride of mercury, added in excess, produces in solu-
tions of protochloride or protoxide of tin a white precipitate of SUB-
CHLORIDE OF MERCURY, owing to the protosalt of tin withdrawing from
the chloride of mercury half of its chlorine.
9. If a fluid containing protoxide or protochloride of tin is added to a
mixture of ferricyanide of potassium and sesquichloride of iron, a preci-
pitate of Prussian blue separates immediately, owing to the reduc-
tion of the ferricyanide. This reaction, which was first pointed out by
Lowenthal, is extremely delicate, but it can be held to be decisive only
in cases where no other reducing agent is present.
10. If compounds of protoxide of tin, mixed with carbonate of soda
and some borax, or, better still, with a mixture of equal parts of car-
bonate of soda and cyanide of potassium, are exposed on a charcoal
support to the inner blowpipe flame, malleable grains of METALLIC TIN are
obtained. The best way of making quite sure of the real nature of these
108 BIN OXIDE OF TIN. [ 129.
grains, is to triturate them and the surrounding parts of charcoal with
water in a small mortar, pressing heavily upon the mass ; then to wash
the charcoal off 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 bin oxide.
129.
b. BINOXIDE OF TIN (Sn 2 ).
1. Binoxide of tin is a powder varying in color from white to straw-
yellow, and which upon heating transiently assumes a brown tint. It
forms two different series of salts with acids, bases, and water. The
hydrate precipitated by alkalies from solution of bichloride of tin dis-
solves readily in hydrochloric acid ; whilst that formed by the action of
nitric acid upon tin hydrate of metastannic acid remains undissolved.
But if it is boiled for some time with hydrochloric acid, it takes up acid ;
if the excess of the acid is then poured off, and water added, a clear
solution is obtained. Upon boiling this solution, hydrate of metastannic
acid separates from it ; whilst from a solution of bichloride, largely diluted
with water, common hydrate of binoxide separates upon boiling.
2. The salts of binoxide of tin are colorless ; they are decomposed at
a red heat. The soluble salts of binoxide of tin, in the neutral state,
redden litmus paper. Bichloride of tin is a volatile liquid, strongly
fuming in the air.
3. Hydrosulphuric acid throws down from all acid and neutral solu-
tions of salts of binoxide of tin, particularly upon heating, a white floc-
culent precipitate, if the solution of the binoxide is in excess ; a faintly
yellow precipitate, if the hydrosulphuric acid is in excess. The former
(the white precipitate) may safely be assumed, in the case of a solution
of bichloride of tin, to consist of a mixture of bichloride and bisulphide
of tin (however, it has not as yet been analysed) ; the latter (the yellow
precipitate) consists of hydrated BISULPHIDE OF TIN (Sn S 2 ). Alkaline
solutions are not precipitated by hydrosulphuric acid. The bisulphide
of tin dissolves readily in potassa, alkaline sulphides, and concentrated
boiling hydrochloric acid. It dissolves with some difficulty in pure am-
monia, and is altogether insoluble in carbonate of ammonia. Nitric acid
converts it into insoluble binoxide of tin. It is insoluble in a heated
solution of acid sulphite of potassa and sulphurous acid. Upon defla-
grating bisulphide of tin with nitrate and carbonate of soda, sulphate of
soda and binoxide of tin are obtained. If a solution of bisulphide of tin
in potassa is boiled with teroxide of bismuth, tersulphide of bismuth and
binoxide of tin are formed, which latter substance remains dissolved in
the potassa solution.
4. Sulphide of ammonium produces the same precipitate of hydrated
BISULPHIDE ,OF TIN ; the precipitate redissolves readily in an excess of
the precipitant. From this solution acids reprecipitate the bisulphide of
tin unaltered.
5. Potassa and ammonia, carbonate of soda and carbonate of am-
monia, produce in solutions of salts of binoxide of tin white precipitates
which, according to the nature of the solutions, consist of hydrate of
binoxide of tin, or of hydrate of metastaunic acid. Both dissolve readily
in an excess of potassa.
6. Sulphate of soda, nitrate of ammonia (in fact, most neutral salts),
when added in excess, throw down from solutions of both modifications
130.] TEROXIDE OF ANTIMONY. 109
of binoxide of tin, provided they are not too acid, the whole of the tin as
HYDRATED BINOXIDE Or HYDRATED METASTANNIC ACID.
7. Metallic zinc precipitates from solutions of bichloride or of salts of
binoxide of tin, in the absence of free acid, white, gelatinous hydrate of
binoxide ; but in presence of a sufficient quantity of free hydrochloric
acid, 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 between tin and antimony).
8. The compounds of the binoxide of tin manifest the same deport-
ment before the blowpipe as those of the protoxide. Binoxide of tin
is also readily reduced when fused with cyanide of potassium in a glass
tube.
130.
c. TEROXIDE OF ANTIMONY (Sb 3 ).
1. Metallic antimony has a bluish tin- white color and is very lustrous ;
it is hard, brittle, readily fusible. When heated on charcoal before
the blowpipe, it emits thick white fumes of teroxide of antimony, which
form a coating on the charcoal j this combustion continues for some time,
even after the removal of the metal from the name ; it is the most dis-
tinctly visible if a current of air is directed with the blowpipe directly
upon the sample on the charcoal. But if the sample on the support is
kept steady, that the fumes may ascend straight, the metallic grain
becomes surrounded with a net of brilliant crystals of teroxide of
antimony. Nitric acid oxidizes antimony readily : the dilute acid
converting it almost entirely into teroxide, the more concentrated
acid into antimonic acid ; both are nearly insoluble in nitric acid ; still
in the acid fluid filtered from the precipitate there are always found
traces of antimony. Hydrochloric acid, even boiling, does not attack
antimony. In nitrohydrochloric acid the metal dissolves readily. The
solution contains terchloride of antimony (Sb C1 3 ), or pentachloride of
antimony (Sb C1 5 ), according to the degree of concentration of the acid
and the duration of the action.
2. According to the different modes of its preparation, teroxide of
antimony occurs either in the form of white, brilliant crystalline needles,
or as a grayish-white powder. It fuses at a moderate red heat ; when ex-
posed to a higher temperature, it volatilizes without decomposition. It is
almost insoluble in nitric acid, but dissolves readily in hydrochloric and
tartaric acids. Teroxide of antimony is easily reduced to the metallic
state by fusion with cyanide of potassium.
3. Antimonic acid (Sb 5 ) is pale yellow ; its hydrates are white.
Both the acid and its hydrates redden litmus paper ; they are slightly
soluble in water, and insoluble in nitric acid, but dissolve pretty readily
in hot concentrated hydrochloric acid : the solution contains pentachlo-
ride of antimony (Sb C1 5 ), and turns turbid upon addition of water.
Upon ignition, antimonic acid loses oxygen, and is converted into anti-
monate of teroxide of antimony (Sb O 3 , Sb O.). Of the antimonates the
potassa and ammonia salts alone are soluble in water : acids precipitate
hydrate of antimonic acid from the solutions, chloride of sodium throws
down from them antimonate of soda ( 89, 2).
4. Part of the salts of teroxide of antimony are decomposed upon
ignition ; the haloid salts volatilize readily and unaltered. The soluble
neutral salts of antimony redden litmus paper. When treated with
110 TEROXIDE OF ANTIMONY. [ 130.
a large amount of water, they are decomposed into insoluble basic
and soluble acid salts. Thus, for instance, water throws down from
solutions of terchloride of antimony in hydrochloric acid, a white bulky
precipitate of basic terchloride of antimony (powder of Algaroth)
Sb C1 3 , 5 Sb O 3 , which after some time 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 by this property that the basic terchloride of antimony
is distinguished from the basic salts of bismuth formed under similar
circumstances.
5. Hydrosulphuric acid precipitates from acid solutions of teroxide of
antimony the whole of the metal as orange-red TERSULPHIDE OF ANTI-
mony (Sb S 3 ). In alkaline solutions this reagent fails to produce a pre-
cipitate or, at least, it precipitates them only imperfectly ; neutral solu-
tions also are only imperfectly thrown down by it. The tersulphide of
antimony produced is readily dissolved by potassa and by alkaline sul-
phides, especially if the latter contain an excess of sulphur ; it is but
sparingly soluble in ammonia, and if it contains no free sulphur nor
pentasulphide of antimony almost insoluble in bicarbonate of ammonia.
It is insoluble in dilute acids. Concentrated boiling hydrochloric acid
dissolves it, with evolution of hydrosulphuric acid gas. It is not dis-
solved by heating with an aqueous solution of acid sulphite of potassa
and sulphurous acid. When heated in the air, it is converted into a
mixture of antimonate of teroxide of antimony with tersulphide of
antimony. When deflagrated with nitrate of soda, it gives sulphate
and antimonate of soda. If a potassa solution of tersulphide of antimony
is boiled with teroxide of bismuth, tersulphide of bismuth precipitates,
and teroxide of antimony dissolved in potassa remains in the solution.
On fusing tersulphide of antimony with cyanide of potassium, metallic
antimony and sulphocyanide of potassium are produced. If the operation
is conducted in a small tube expanded into a bulb at the lower end, or
in a stream of carbonic acid gas (see 131, 12), no sublimate of antimony
is produced. But if a mixture of tersulphide of antimony with car-
bonate of soda or with cyanide of potassium and carbonate of soda,
is heated in a glass tube in a stream of hydrogen gas (compare 131,
4), a mirror of antimony is deposited on the inner surface of the tube,
immediately behind the spot occupied by the mixture.
From a solution of antimonic acid in hydrochloric acid, sulphuretted
hydrogen throws down pentasulphide of antimony (Sb S 5 ), which dissolves
readily when heated with solution of soda or ammonia, and equally so in
concentrated boiling hydrochloric acid, with evolution of hydrosulphuric
acid gas and separation of sulphur.
6. Sulphide of ammonium produces in solutions of teroxide of an-
timony an orange-red precipitate of TERSULPHIDE OF ANTIMONY, which
readily redissolves in an excess of the precipitant if the latter contains
an excess of sulphur. Acids throw down from this solution penta-
sulphide of antimony (Sb S 5 ). However, the orange color appears in
that case usually of a lighter tint, owing to an admixture of free sulphur.
7. Potassa, ammonia, carbonate of potassa, and carbonate of ammonia
throw down from solutions of terchloride of antimony, and also of simple
salts of teroxide of antimony but not, or at least not immediately, from
solutions of tartar emetic or analogous compounds a white, bulky pre-
cipitate of TEROXIDE OF ANTIMONY, which redissolves pretty readily
in an excess of potassa, but requires the application of heat for its
130.] TEROXIDE OF ANTIMONY. 11]
re-solution in carbonate of potassa, and is alogether insoluble in
ammonia.
8. Metallic zinc precipitates from all solutions of teroxide of antimony,
if they contain no free nitric acid, METALLIC ANTIMONY as a black powder.
If a few drops of a solution of antimony, containing some free hydro-
chloric acid, are poured into a platinum dish (the inside of a platinum
crucible cover), and a small piece of zinc introduced, hydrogen 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 :
these new reactions I can therefore recommend as being delicate and
characteristic. Cold hydrochloric acid fails to remove the stain, which,
however, may be immediately removed by warm nitric acid.
9. If a solution of teroxide of antimony in solution of potassa or
soda is mixed with solution of nitrate of silver, a deep black precipitate
of SUBOXIDE OF SILVER forms with the grayish-brown precipitate
of oxide of silver. Upon now adding ammonia in excess, the oxide is
redissolved, whilst the suboxide is left undissolved (H. Rose). The fol-
lowing equation will explain the formation of the suboxide of silver in
this process : K O, Sb 3 + 4 Ag = K O, Sb O 5 + 2 Ag 2 O. This ex-
ceedingly delicate reaction affords us an excellent means of detecting
teroxide of antimony in presence of antimonic acid.
10. If a solution of teroxide of antimony is introduced into a flask in
which hydrogen gas is being evolved from pure zinc arid dilute sulphuric
acid, the zinc oxidizes not only at the expense of the oxygen of the water,
but also at the expense of that of the teroxide of antimony, and the
antimony separates accordingly in the metallic state ; but a portion of
the metal combines in the moment of its separation with the liberated
hydrogen of the water, forming ANTIMONETTED HYDROGEN GAS (Sb H 3 ).
If this operation is conducted in a gas-evolution flask, connected by
means of a perforated cork with the limb of a bent tube of which the
other limb ends in a finely drawn-out point, pinched off at the top,* and
the hydrogen passing through the fine aperture of the tube is ignited after
the atmospheric air is completely expelled, the flame appears of a bluish-
green tint, which is imparted to it by the antimony separating in a state
of intense ignition upon the combustion of the antimonetted hydrogen ;
white fumes of teroxide of antimony rise from the flame, which con-
dense readily upon cold substances, forming spots on them which are
not dissolved by water. But if a cold body, a porcelain dish, for in-
stance, is now depressed upon the flame, METALLIC ANTIMONY is deposited
upon the surface of the plate, in a state of the most minute division,
forming a deep black and almost lustreless 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 lustre is formed within the tube on both sides of the
heated part.
As the acids of arsenic give under the same circumstances similar spots
of metallic arsenic, it is always necessary to examine the spots produced, in
order to ascertain whether they really consist of antimony or contain any
of that metal. With spots deposited on a porcelain dish the object in
view is most readily attained by treating them with a solution of chloride
of soda (a compound of hypochlorite of soda with chloride of sodium, pre-
* In accurate experiments it is advisable to use Marsh's apparatus. ( 131, 10).
112 AUSENIOUS ACID. [ 131.
pared by mixing a solution of chloride of lime with carbonate of soda
in excess, and filtering) ; which will immediately dissolve arsenical spots,
leaving the spots proceeding 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 whilst the current of hydrogen gas still continues to pass through
the tube : if the mirror volatilizes only at a higher temperature, and the
hydrogen gas then issuing from the tube does not smell of garlic j 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 glo-
bules distinctly discernible through a magnifying glass, the presence of
antimony may be considered certain. Or, better still, the metals may be
identified by conducting through the tube a very slow stream of dry hydro-
sulphuric acid gas, and heating the mirror, by means of a spirit-lamp,
proceeding from the outer to the inner border, and accordingly in an
opposite direction to that of the gaseous current. The antimonial
mirror is by this means converted into tersulphide of antimony, which
appears of a more or less reddish-yellow color, and almost black when in
thick layers. If a feeble stream of dry hydrochloric acid gas is now
transmitted through the glass tube, the tersulphide of antimony, if
present in thin layers only, disappears immediately ; if the incrustation
is somewhat thicker, it takes a short time to dissipate it. The reason
for this is, that the tersulphide of antimony decomposes readily with
hydrochloric acid, and the terchloride of antimony formed is exceedingly
volatile in a stream of hydrochloric acid gas. If the gaseous current is
now conducted into some water, the presence of antimony in the latter
fluid may readily be proved by means of hydrosulphuric acid. By this
combination of reactions, antimony may be distinguished with positive
certainty from all other metals.
11. If a mixture of a compound of antimony with carbonate of soda
and cyanide of potassium is exposed on a charcoal support to the reducing
flame of the blowpipe, brittle globules of METALLIC ANTIMONY are pro-
duced, which may be readily recognised by the peculiar appearances
attendant upon their oxidation (compare 130, 1).
131.
d. ARSENIOUS ACID (As 3 ).
1. Metallic arsenic has a blackish-gray color and high metallic lustre,
which it retains in dry air, but loses in moist air, becoming covered with
suboxide; the metallic arsenic of commerce looks therefore rather dull,
the planes of crystallization appearing bronze-colored and feebly shining.
Arsenic is not very hard, but very brittle : at a dull red heat it volatilizes
without fusion. The fumes have a most characteristic odor of garlic,
which proceeds from the suboxide of arsenic formed. Heated with
free access of air, arsenic burns at an intense heat with a bluish
flame emitting white fumes of arsenious acid, 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 recondenses above the heated
spot as a lustrous black sublimate (arsenical mirror) ; a very thin coating
of the sublimate appears of a brownish-black color. In contact with air
and water arsenic oxidizes slowly to arsenious acid. Weak nitric acid
converts it, with the aid of heat, into arsenious acid, which dissolves only
131.] ARSENIOUS ACID. 113
sparingly in an excess of the acid ; strong nitric acid converts it partially
into arsenic acid. It is insoluble in hydrochloric acid and dilute sul-
phuric acid ; concentrated boiling sulphuric acid oxidizes it to arsenious
acid, with evolution of sulphurous acid.
2. Arsenious acid generally presents the appearance either of a trans-
parent vitreous or of a white porcelain-like mass. Triturated, it gives a
heavy, white, gritty powder. When heated, it volatilizes in white in-
odorous 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 ; it comports itself
in this respect like a fatty substance. It is difficultly soluble in cold,
but more readily in hot water. It is copiously dissolved by hydrochloric
acid, as well as by solution of soda and potassa. Upon boiling with
nitrohydrochloric acid it dissolves to arsenic acid. It is highly
poisonous.
3. The arsenites are mostly decomposed upon ignition either into
arseuates and metallic arsenic, which volatilizes, or into arsenious acid
and the base with which it was combined. Of the arsenites those only
with alkaline bases are soluble in water. The insoluble arsenites are
dissolved, or at least decomposed, by hydrochloric acid. Terchloride of
arsenic is a colorless, volatile liquid, fuming in the air, which allows
the addition of a little water, but is decomposed by a larger amount into
arsenious acid, which partly separates, and hydrochloric acid, which
retains the rest of the arsenious acid in solution.
4. Hydrosulpliuric acid precipitates solutions of arsenious acid and
of neutral arsenites slowly and imperfectly, except a free acid be pre-
sent, in which case the precipitation is immediate and perfect. Alka-
line solutions are not precipitated. The precipitates are of a bright
yellow color ; they consist of TEKSULPHIDE OP ARSENIC (As SJ, and are
readily and completely dissolved by pure alkalies, alkaline carbonates and
bicarbonates, and also by alkaline sulphides ; but they are nearly inso-
luble in hydrochloric acid, even when concentrated and boiling. Boiling
nitric acid decomposes and dissolves them readily. The deflagration of
tersulphide of arsenic with carbonate of soda and nitrate of soda gives rise
to the formation of arsenate and sulphate of soda. If a solution of ter-
sulphide of arsenic in potassa is boiled with hydrated carbonate or basic
nitrate of teroxide of bismuth, tersulphide of bismuth and arsenite of
potassa are produced.
If recently precipitated tersulphide of arsenic is digested with sul-
phurous acid and acid sulphite of potassa, the precipitate is dissolved ;
upon heating the solution to boiling, the fluid turns turbid, owing to the
separation of sulphur, which upon continued boiling is for the greater part
redissolved. The fluid contains, after expulsion of the sulphurous acid,
arsenite and hyposulphite of potassa (2 As S 3 + 8 K 0, 8 2 = 2 K O,
As O 3 + 6 K 0, S 2 O a + S 8 + 7 S O a ). Tersulphide of antimony and bi-
sulphide of tin do not show this reaction, as I have already stated
( 129, 3 and 130, 5) (Bunsen).
If a mixture of tersulphide of arsenic with from 3 to 4 parts of car-
bonate of soda is made into a paste with some water, and this spread over
small glass splinters, and after being well dried, rapidly heated to red-
ness in a glass tube through which dry hydrogen gas is transmitted,
a large portion of the arsenic present is reduced to the metallic state and
expelled, if the temperature applied is sufficiently high. Part of the
i. i
114 ARSENIOUS ACTD. [ 131.
reduced arsenic forms a metallic mirror on the inner surface of the
tube, the remainder is carried away suspended in the hydrogen gas ; the
minute particles of arsenic impart a bluish tint to the flame when the
gas is kindled, and form stains of arsenic upon the surface of a porcelain
dish depressed upon the flame. The fusion of the mixture of tersulphide
of arsenic with carbonate of soda first gives rise to the formation of a
double tersulphide of arsenic and sulphide of sodium, and of arsenite of
soda (2 As S 3 + 4 Na O, C O 2 = 3 Na S, As S 3 + Na O, As O 3 + 4 C O 2 ).
Upon heating these products the arsenite of soda is resolved into arsenic
and arsenate of soda (5 As O 3 = 2 As + 3 AsO g ), and the tersulphide of
arsenic and sulphide of sodium into arsenic and pentasulphide of arsenic
and sulphide of sodium (5 As O 3 2 As + 3 As 5 ) ; and by the action of
the hydrogen the arsenate of soda is also converted into hydrate of soda,
arsenic, and water. With the exception, therefore, of that portion of the
arsenic which constitutes a component part of the double pentasulphide of
arsenic and sulphide of sodium formed in the process, a sulphur salt which
is not decomposed by hydrogen, all the arsenic is expelled (H. RQse).
This method of reduction gives indeed very accurate results, but it
does not enable us to distinguish arsenic from antimony with a sufficient
degree of certainty, nor to detect the one in presence of the other.
(Compare 130, 5.)
The operation is conducted in the apparatus illustrated by
Fig. 22.
a is the evolution flask, b a tube containing chloride of calcium, c the
tube in which, at the point d, the glass splinter with the mixture of
tersulphide of arsenic and carbonate of soda is placed ; this tube is made
of difficultly fusible glass free from lead. When the apparatus is com-
pletely filled with pure hydrogen gas, d is exposed to a gentle heat at
first, in order to expel all the moisture which may still be present, and
then suddenly to a very intense heat,* to prevent the sublimation of
undecomposed tersulphide of arsenic. The metallic mirror is deposited
near the point e. Another method of effecting the reduction of ter-
sulphide of arsenic to the metallic state, and which combines with the
very highest degree of delicacy the advantage of precluding the possi-
bility of confounding arsenic with antimony, will be found described in
number 12.
5. Sulphide of ammonium also causes the formation of TERSULPHIDE
OF ARSENIC. In neutral and alkaline solutions, however, the tersulphide
* The flame of the blowpipe answers the purpose best.
131.] ARSENTOUS ACID. 115
formed does not precipitate, but remains dissolved as a double sulphide
of arsenic and ammonium (tersulphide of arsenic and sulphide of ammo-
nium). From this solution it precipitates immediately upon the addition
of a free acid.
6. Nitrate of silver leaves aqueous solutions of arsenious acid perfectly
bright, or at least produces only a trifling yellowish-white turbidity
in them ; but if a little ammonia is added, a yellow precipitate of
ARSENITE OP SILVER (3 Ag 0, As O g ) separates. The same precipitate
forms, of course, immediately upon the addition of nitrate of silver to the
solution of a neutral arsenite. The precipitate dissolves readily in nitric
acid as well as in ammonia, and is not insoluble in nitrate of ammonia ;
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, as it
remains dissolved in the nitrate of ammonia formed.
7. Sulphate of copper produces under the same circumstances as the
nitrate of silver a yellowish-green precipitate of ARSENITE OF COPPER.
8. If to a solution of arsenious acid in an excess of concentrated solution
of soda or potassa, or to the solution of an alkaline arsenite mixed with
caustic potassa or soda a few drops of a dilute solution of sulphate of copper
are added, a clear, blue fluid is obtained, which upon boiling deposits a red
precipitate of SUBOXIDE OF COPPER, leaving arsenate of potassa in solu-
tion. This reaction is exceedingly delicate, provided not too much of the
solution of sulphate of copper be used. Even should the red precipitate
of suboxide of copper be so exceedingly minute as to escape detection
by transmitted light, yet it will always be discernible with great dis-
tinctness upon looking in at the top of the test tube. Of course this
reaction, although really of great importance in certain instances, as a
confirmatory proof of the presence of arsenious acid, and more particu-
larly also as a means of distinguishing that acid from arsenic acid, is
yet entirely inapplicable for the direct detection of arsenic, since grape
sugar and other organic substances also produce suboxide of copper from
salts of oxide of copper in the same manner.
9. If a solution of arsenious acid mixed with hydrochloric acid is
heated with a clean slip of copper, an IRON-GRAY film of metallic arsenic
is deposited on the copper, even in highly dilute solutions ; when this
film increases in thickness, it peels off in black scales. If the coated
copper slip is heated with solution of ammonia, the film peels off from the
copper, and separates in form of minute spangles (Reinsch). Let it be
observed that these are not pure arsenic, but always contain copper, and
will accordingly never completely volatilize. Upon heating them in a
tube containing air, arsenious acid sublimes.
10. If an acid or neutral solution of arsenious acid or any of its com-
pounds is mixed with zinc, water, and sulphuric acid, ARSENETTED
HYDROGEN (As H S ) is formed, in the same manner as compounds of
antimony give under analogous circumstances antimonetted hydrogen.
(Compare 130, 10 ) This reaction affords us a most delicate test for the
detection of even the most minute quantities of arsenic.
The operation is conducted in the apparatus illustrated by Fig. 23, or
in one of similar construction.* a is the evolution flask; b a bulb in-
tended to receive the water carried along with the gaseous current ; c a
* I willingly adopt the very convenient form of Marsh's apparatus recommended by
Otto in his excellent Manual of Chemistry.
i 2
116
ARSENIOUS ACID.
[ 181.
tube filled with cotton and small lumps of chloride of calcium to remove
water. This tube is connected with b and d by vulcanized india-rubber ;
d should have an inner diameter of 7 millimetres (see Fig. 24), and must
Fig. 24.
Fig. 23.
be made of difiicultly fusible glass free from lead. In experiments
requiring great accuracy the tube should be drawn out as shown in
Fig. 23. The operation is now commenced by evolving in a a mode-
rate and uniform current of hydrogen gas, from pure granulated
zinc and concentrated sulphuric acid diluted with 3 parts of
water. When the evolution of hydrogen has proceeded for
some time, so that it may safely be concluded the air has
been completely expelled from the apparatus, the gas is kindled
at the open end of the tube d. It is advisable to wrap a piece
of cloth round the flask before kindling the gas, to guard against
accidents in case of an explosion. It is now absolutely necessary first to
ascertain whether the zinc and the sulphuric acid are quite free from
any admixture of arsenic. This is done by depressing a porcelain
dish horizontally upon the flame to make it spread over the surface :
if the hydrogen contains arsenetted hydrogen, brownish or brownish-
black stains of arsenic will appear on the porcelain ; the non-appearance
of such stains may be considered as a proof of the freedom of the zinc and
sulphuric acid from arsenic. In very accurate experiments, however, addi-
tional evidence is required to ensure the positive certainty of the purity
of the reagents employed for this purpose the part of the tube d, shown
in Fig. 23, is heated to redness with a Berzelius or gas-lamp, and kept
some time in a state of ignition : if no arsenical coating makes its
appearance in the narrowed part of the tube, the reagents employed may
be pronounced free from arsenic, and the operation proceeded with, by
pouring the fluid to be tested for arsenic through the funnel tube into the
131.] ARSENIOUS ACID. 117
flask, and afterwards some water to rinse the tube. Only a very little of
the fluid ought to be poured in at first, as 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 contains arsenic, there is immediately evolved,
with the hydrogen, arsenetted hydrogen, which at once imparts a bluish
tint ^ to the flame of the kindled gas, owing to the combustion of the
particles of arsenic separating from the arsenetted hydrogen* in pass-
ing through the flame. At the same time white fumes of arsenious
acid arise, which condense upon cold objects. If a porcelain plate is now
depressed upon the flame, the separated and not yet reoxidized arsenic
condenses upon the plate in black stains, the same way as antimony.
(See 130, 10.) The stains formed by arsenic incline, however, more to
a blackish-brown tint, and show a bright metallic lustre : whilst the anti-
monial stains are of a deep black color and but feebly lustrous. The
arsenical stains may be distinguished moreover from the antimonial
stains by solution of chloride of soda (compare 130, 10), which will at
once dissolve arsenical spots, leaving antimonial spots unaffected, or
removing them only after a considerable time.
If the heat of a Berzelius, or gas-lamp, is now applied to the part of
the tube d, shown in Fig. 23, a brilliant arsenical mirror makes its
appearance in the narrowed portion of the tube behind the heated part ;
this mirror is of a darker and less silvery white hue than that produced
by antimony under similar circumstances ; from which it is, moreover,
distinguished by the facility with which it may be dissipated in a current
of hydrogen gas without previous fusion, and by the characteristic odor
of garlic emitted by the escaping (imkindled) gas. If the gas is kindled
whilst the mirror in the tube is being heated, the flame will, even with
a very weak current of gas, 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 antimony. Now, 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 the long tube through which the arsenetted hydrogen passes to
redness in several parts, to produce distinct metallic mirrors ; then
transmit through the tube a very weak stream of dry hydrosulphuric
acid gas, and heat the metallic mirrors with a common spirit-lamp,
proceeding from the outer towards the inner border. If arsenic alone
is present, yellow tersulphide of arsenic is formed inside the tube ;
if antimony alone is present, an orange-red or black tersulphide
of antimony is produced ; and if the mirror consisted of both metals, the
two sulphides appear side by side, the sulphide of arsenic as the more
volatile lying invariably before the sulphide of antimony. It you now
transmit through the tube containing the sulphide of arsenic, sulphide of
antimony, or both sulphides together, dry hydrochloric gas, without
applying heat, no alteration will take place if sulphide of arsenic alone is
present, even though the gas be transmitted through the tube for a con-
siderable time. If sulphide of antimony alone is present, this will
118 ARSENIOUS ACID. [ 131.
entirely disappear, as already stated, and if both sulphides are present,
the sulphide of antimony will immediately volatilize, whilst the yellow
sulphide of arsenic will remain. If a small quantity of ammonia is now
drawn into the tube, the sulphide of arsenic is dissolved, and may thus
be readily distinguished from sulphur which perhaps may have separated.
My personal experience has convinced me of the infallibility of these
combined tests for the detection of arsenic.
Marsh was the first who suggested the method of detecting arsenic by
the production of arsenetted hydrogen.
11. If a small lump of arsenious acid (a) be introduced into the pointed
end of a drawn-out glass tube (Fig. 25) and a fagment of very re-
cently burnt charcoal (6) pushed down the tube to within a short
distance of the arsenious acid, and the flame of a spirit-lamp applied, first
to the piece of charcoal, then to the arsenious acid, a MIRROR OF ME-
TALLIC ARSENIC will form at c, owing to the reduction of the arsenious
acid vapor by the red-hot charcoal. If the tube be now cut between 6
and c, and then heated in an inclined position, with the cut end c turned
upwards, the metallic mirror will volatilize, emitting the characteristic
odor of garlic. This is both the simplest and safest way of detecting
pure arsenious acid.
Fig. 25.
12. If arsenites, or arsenious acid, or tersulphide of arsenic are fused
together with a mixture of equal parts of dry carbonate of soda and cya-
nide of potassium, the whole of the arsenic is reduced to the metallic
state, and so is the base also, if easily reducible ; the eliminated oxygen
converts part of the cyanide of potassium into cyanate of potassa. In
the reduction of tersulphide of arsenic, sulphocyanide of potassium is
formed. The operation is conducted as follows : introduce the perfectly
dry arsenical compound into the bulb of a small bulb-tube (Fig. 26), and
cover it with six times the quantity of a perfectly dry mixture of equal
parts of carbonate of soda and cyanide of potassium. The whole quantity
must not much more than half-fill the bulb, otherwise the fusing cyanide
of potassium is likely to ascend into the tube. Heat the bulb now
gently with a gas or spirit-lamp ; should some water still escape upon
gently heating the mixture, wipe the inside of the i\^Q perfectly dry with a
131.]
ARSENIOUS ACID.
119
twisted slip of paper. It is of the highest importance for the success
of the experiment to bestow great care upon the expulsion of the
water, drying the mixture, and wiping the tube clean and dry. Apply
now a strong heat to the bulb, to effect the reduction of the arsenical
compound, and continue this for awhile, as the arsenic often requires
Fig. 26.
some time for its complete sublimation. The mirror, which is deposited
at b, is of exceeding purity. It is obtained from all arsenites whose
bases remain either altogether untouched, or are reduced to such metallic
arsenides as lose their arsenic partly or totally upon the simple applica-
tion of heat. This method deserves to be particularly recommended on
account of its simplicity and neatness, as well as for the accuracy of
the results attainable by it, even in cases where only very minute
quantities of arsenic are present. It is more especially adapted for the
direct production of arsenic from tersulphide of arsenic, and is in this
respect superior in simplicity and accuracy to all other methods hitherto
suggested. The delicacy of the reaction may be very much heightened
by heating the mixture in a stream of dry carbonic acid gas. A series
of experiments made by Dr. V. Babo and myself has shown that the
most accurate and satisfactory results are obtained in the following
manner :
Figs. 27 and 28 show the apparatus in which the process is con
ducted.
Fig. 27.
A is a capacious flask intended for the evolution of carbonic acid ; it
is half-filled with water and lumps of solid limestone or marble (not
120 ARSENIOUS ACID. [ 131.
chalk, as this would not give a constant stream of gas). is a smaller
flask containing concentrated sulphuric acid. The flask A is closed with a
double-perforated cork, into the one aperture of which is inserted a
funnel-tube (a), which reaches nearly to the bottom of the flask ; into
the other perforation is fitted a tube (6), which serves to conduct the
evolved gas into the sulphuric acid in B, where it is thoroughly freed
from moisture. The tube c conducts the dried gas into the reduction-
tube C, of which Fig. 28 gives a representation on the scale of one-third
of the actual length. The tubes which I employ for the purpose in my
own experiments, have an inner diameter of eight millimetres.
Fig. 28.
When the apparatus is fully prepared for use, triturate the per-
fectly dry sulphide of arsenic, or arsenite in a slightly heated mortar with
about twelve parts of a well-dried mixture consisting of three parts of
carbonate of soda and one part of cyanide of potassium. Put the powder
upon a narrow slip of card-paper bent into the shape of a gutter, and
push this into the reduction-tube down to e ; turn the tube now half-
way round its axis, which will cause the mixture to drop into the tube
between e and d, every other part remaining perfectly clean. Connect
the tube now with the gas-evolution apparatus, and evolve a moderate
stream of carbonic acid, by pouring some hydrochloric acid into the
flask A. Heat the tube G in its whole length very gently with a
spirit-lamp, until the mixture in it is quite dry; when every trace of
water is expelled, and the gas -stream has become so slow that the single
bubbles pass through the sulphuric acid in B at intervals of one second,
heat the reduction-tube to redness at c, by means of a spirit or gas-lamp ;
when c is red-hot, apply the flame of a second gas or larger spirit-lamp
to the mixture, proceeding from d to e, until the whole of the arsenic is
expelled. The far greater portion of the volatilized arsenic recondenses
at A, whilst a small portion only escapes through C, imparting to the
surrounding air the peculiar odor of garlic. Advance the flame of the
second lamp slowly and gradually up to c, by which means the whole of
the arsenic which may have condensed in the wide part of the tube
is driven to h. When you have effected this, close the tube at the
point i by fusion, and apply heat, proceeding from i towards h, by which
means the extent of the mirror is narrowed, whilst its beauty and lustre
are correspondingly increased. In this manner perfectly distinct mirrors
of arsenic may be produced from as little as the g-J-^th part of a grain
of tersulphide of arsenic. No mirrors are obtained by this process
from tersulphide of antimony, nor from any other compound of antimony.
13. If arsenious acid or one of its compounds is exposed on a charcoal
support to the reducing flame of the blowpipe, a highly characteristic
garlic odor is emitted, more especially if some carbonate of soda is added
to the examined sample. This odor has its origin in the reduction and
re-oxidation of the arsenic, and enables us to detect very minute quanti-
ties. This test, however, like all others that are based upon the mere in-
dications of the sense of smell, cannot be implicitly relied on.
132.] ARSENIC ACID. 121
132.
e. ARSENIC ACID (As 6 ).
1. Arsenic acid is a transparent or white mass, which gradually deli-
quesces in the air, and dissolves slowly in water. It fuses at a gentle
red heat without suffering decomposition ; but at a higher temperature
it is resolved into oxygen, and arsenious acid, which volatilizes. It is
highly poisonous.
2. Most of the arsenates are insoluble in water. Of the so-called
neutral arsenates those with alkaline bases alone are soluble in water.
Most of the neutral and basic arsenates can bear a strong red heat with-
out suffering decomposition. The acid arsenates lose their excess of acid
upon ignition, the free acid being resolved into arsenious acid and
oxygen.
3. Hydrosulphuric acid fails to precipitate alkaline and neutral solu-
tions of arsenates ; but in acidified solutions it produces a yellow precipi-
tate of PENTASULPHIDE OF ARSENIC (As S fi ). This precipitate never forms
instantaneously, and in dilute solutions frequently only after the lapse of
a considerable time (twenty-four hours, for instance). Heat promotes
its separation. The pentasulphide of arsenic manifests the same deport-
ment as the tersulphide with the various solvents and decomposing agents
mentioned in the preceding paragraph. If a solution of arsenic acid, or
of an arsenate, is mixed with sulphurous acid, or with sulphite of soda
and some hydrochloric acid, the sulphurous acid is converted into sul-
phuric acid, and the arsenic acid reduced to arsenious acid ; applica-
tion of heat promotes the change. If hydrosulphuric acid is now added,
the whole of the arsenic is thrown down as tersulphide.
4. Sulphide of ammonium converts the arsenic acid in neutral and
alkaline solutions of arsenates into pentasulphide of arsenic, which re-
mains in solution as amrnonio-pentasulphide of arsenic (pentasulphide of
arsenic and sulphide of ammonium). Upon the addition of an acid to
the solution, this double sulphide is decomposed, and pentasulphide of
arsenic precipitates. The separation of this precipitate proceeds more
rapidly than is the case when acid solutions of arsenates are precipitated
with hydrosulphuric acid. It is promoted by heat.
5. Nitrate of silver produces under the circumstances stated 131, 6,
a highly characteristic reddish-brown precipitate of ARSENATE OF SILVER
(3 Ag O, As 5 ), which is readily soluble in dilute nitric acid and in
ammonia, and dissolves also slightly in nitrate of ammonia. Accord-
ingly, if a little of the precipitate is dissolved in a large proportion of
nitric acid, neutralization with ammonia often fails to reproduce the
precipitate.
6. /Sulphate of copper produces under the circumstances stated 131,
7, a greenish-blue precipitate of ARSENATE OF COPPER (2 Cu 0, H O,
As O.).
7. With zinc in presence of sulphuric acid, with copper, with cyanide
of potassium, and before the blowpipe, the compounds of arsenic acid
comport themselves in the same way as those of arsenious acid. If the
reduction of arsenic acid by zinc is effected in a platinum dish, the pla-
tinum does not turn black, as is the case in the reduction of antimony by
zinc ( 130, 8).
8. If a solution of arsenic acid, or of an arsenate soluble in water, is
122 RECAPITULATION AND REMARKS. [ 133.
added to a clear mixture of sulphate of magnesia, cJdoride of ammonium,
and a sufficient quantity of ammonia, a crystalline precipitate of ARSE-
NATE OF AMMONIA AND MAGNESIA (2 Mg O, 1ST H 4 O, As O g + 12 aq.)
separates ; from concentrated solutions immediately, from dilute solutions
after some time.
133.
Recapitulation and remarks. I have again made the separation
and positive identification of the oxides belonging to the second divi-
sion of the sixth group the object of a most careful study, and my
endeavors have been crowned with complete success. I will here
describe first the different ways best adapted to effect the detection or
separation of tin, antimony, and arsenic, when present together in the
same compound or mixture, and afterwards the most reliable means
of distinguishing between the several oxides of each of the three
metals.
1. If you have a mixture of sulphide of tin, sulphide of antimony,
and sulphide of arsenic, triturate 1 part of it, together with 1 part of dry
carbonate of soda, and 1 part of nitrate of soda, and transfer the mixed
powder gradually to a small porcelain crucible containing 2 parts of
nitrate of soda kept in a state of fusion at a not over-strong heat ; oxi-
dation of the sulphides ensues, attended with slight deflagration. The
fused mass contains binoxide of tin, arsenate and antimonate of soda,
with sulphate, carbonate, nitrate, and nitrite of soda. You must take
care not to raise the heat to such a degree, nor continue the fusion so
long, as to lead to a reduction of the nitrite of soda to the caustic
state. Treat the fused mass, poured out upon a piece of porcelain, with
cold water until it is completely softened ; then filter the fluid off" from
the undissolved residue, which contains the binoxide of tin and antimo-
nate of soda nearly unacted on. Mix the filtrate, which contains the
arsenate of soda and the other salts, with nitric acid to distinctly acid re-
action, then with a sufficient proportion of solution of nitrate of silver ; a
precipitate of chloride of silver forms (if the reagents employed or the
precipitated sulphides contained a chlorine compound) and some nitrite
of silver. Filter, and carefully add to the filtrate dilute solution of am-
monia, whereupon the characteristic reddish-brown precipitate of arsenate
of oxide of silver will make its appearance, first in the uppermost stratum
of the fluid where the solution of ammonia comes first into contact with it,
but subsequently, upon complete neutralization of the free acid, in every
part of the fluid.
Wash now the filter containing the residuary binoxide of tin and anti-
monate of soda once with water, then three times with a mixture of
equal parts of water and spirit of wine, dry, incinerate,* and put
the ash into a tube of difficultly fusible glass, sealed at one end, mea-
suring some eight or ten centimetres in length, and having an inner
diameter of from five to seven millimetres ; add to the ash in the tube
four times the quantity of cyanide of potassium, and heat over a Berzelius
or gas- lamp, t This effects the reduction of the binoxide of tin and
* With small quantities of substance this may be done most conveniently by twisting
the little filter together, inserting it into a spiral coil of platinum wire, and holding this
in the outer mantle of a flame.
f Had not the nitrate of soda been removed by washing, as directed, this part of the
process would be attended with an explosion.
133.] RECAPITULATION AND REMARKS. 123
antimonic acid, and a fused mass is produced which appears gray from
the minutely divided reduced metals in it. If the tube is now dipped
whilst still red-hot into a test-tube filled with cold water, the part con-
taining the fused mass will crack off, arid the broken fragments sink to
the bottom of the water. Upon application of heat, the fused mass will
readily dissolve, leaving the metals behind, which may now by repeated
boiling with water and decantation be freed from the last traces of other
matters still adhering to them. Heat the residuary metallic mass with
hydrochloric acid just to the boiling point, when the tin or a portion of it
will dissolve to protochloride, with evolution of hydrogen gas ; by means
of chloride of mercury or a mixture of ferricyanide of potassium and ses-
quichloride of iron you may now easily, and with positive certainty, detect
the protochloride of tin in the solution, even though only a minute trace
of the metal be present. Upon heating the residue remaining in the
tube repeatedly with hydrochloric acid, the whole, or nearly the whole
of the tin present is dissolved out, and the black-colored antimony alone
is left undissolved. Upon heating this residue with hydrochloric acid,
with addition of one or two drops of nitric acid, it dissolves, and if you
now add to the solution hydrosulphuric acid, an orange-colored pre-
cipitate of tersulphide of antimony is obtained. If only slight traces of
antimony are present, the color of this precipitate is not very distinct,
owing to imperfect separation from the tin. Let, therefore, the precipi-
tate of the impure tersulphide of antimony settle, decant the clear fluid,
dissolve the precipitate in a little boiling hydrochloric acid, concentrate
the solution somewhat, and then test in the lid of a platinum crucible
with zinc, which will at once remove all doubt, showing even the minutest
trace of antimony.
2. Instead of incinerating the filter with the binoxide of tin and anti-
monate of soda, you may also dissolve the precipitate on it in a little hot
hydrochloric acid, wash the filter with water, concentrate the fluid some-
what, and test with zinc in a small platinum dish, when the antimony
will at once reveal its presence by staining the platinum brownish-black ;
to detect the tin, wait until the little slip of zinc is almost entirely dissolved,
then decant the fluid, heat the residue with some hydrochloric acid, and
test the solution for protochloride of tin as in 1.
3. If the quantity of binoxide of tin and antimonate of soda is some-
what larger, the two bodies may be separated also by boiling with con-
centrated solution of soda, which dissolves the binoxide of tin, leaving
the antimonate of soda unaffected. It is advisable to add, after the
process of boiling, some spirit of wine, say about ^ by volume of the
entire fluid, to guard against the antimonate of soda being dissolved ;
for the same reason the precipitate must be washed with equal volumes
of water and spirit of wine. If the alkaline solution is now evaporated
to drive off the spirit of wine, hydrochloric acid then added, and lastly,
hydrosulphuric acid, the tin is precipitated as sulphide ; the antimony-
may in like manner be precipitated from the solution of the anti-
niouate of soda in hydrochloric acid.
4. If the mixed sulphides are treated with fuming hydrochloric acid,
the sulphide of antimony and sulphide of tin dissolve, whilst the sulphide
of arsenic is left nearly altogether undissolved. If the residuary sulphide
of arsenic is treated with ammonia, and the solution obtained evaporated,
after adding to it a very little carbonate of soda, an arsenical mirror
may readily be produced from the residue with cyanide of potassium and
124 RECAPITULATION AND REMARKS. [ 133.
carbonate of soda in a stream of carbonic acid gas. The solution, which
contains the tin and antimony, may be treated as directed in 2. Or, if
there is a considerable excess of antimony, the solution may be mixed
with sesquicarbonate of ammonia in excess, and boiled. A considerable
proportion of the antimony present dissolves in this process, whilst bin-
oxide of tin mixed with a small quantity of teroxide of antimony remains
undissolved. The presence of the tin may now be the more readily
proved by the method given in 1 (Bloxani).
5. If sulphide of antimony, sulphide of tin, and sulphide of arsenic
are dissolved in sulphide of potassium, a large excess of a concentrated
solution of sulphurous acid added, the mixture digested for some time
in the water- bath, then boiled until all sulphurous acid is expelled, and
filtered, the filtrate contains all the arsenic as arsenious acid (which may
be precipitated from it by hydrosulphuric acid), whilst tersulphide of
antimony and bisulphide of tin are left behind undissolved (Bunsen}.
After dissolving the residue in hydrochloric acid, the antimony and tin
may be detected as directed in 2.
6. In the analysis of alloys, binoxide of tin and teroxide of antimony
are often obtained together as a residue insoluble in nitric acid. If the
quantities are considerable, the teroxide of antimony may be extracted
with tartaric acid, and the solution tested for it with hydrosulphuric
acid ; the binoxide of tin may be reduced with cyanide of potassium.
For minute quantities I recommend the method described in 1. An
absolute separation of the two oxides may be effected by fusing them
with hydrate of soda in a silver crucible, treating the mass with water,
and adding one-third (by volume) of spirit of wine. The binoxide of
tin is by this means obtained in solution as a compound of binoxide of
tin and soda, whilst the antimonate of soda is left undissolved (H. Rose).
7. For the most accurate way of separating antimony and arsenic, and
distinguishing between the two metals, viz., by treating with hydro-
sulphuric acid the mirror produced by Marsh's method, and sepa-
rating the resulting sulphides by means of hydrochloric acid gas, I refer
to 131, 10. Antimony and arsenic may, however, when mixed toge-
ther in form of hydrides, be separated also in the following way :
Conduct the gases mixed with an excess of hydrogen, first through a
tube containing glass splinters moistened with solution of acetate of
lead, to retain the hydrochloric and hydrosulphuric gas, then in a slow
stream into a solution of nitrate of silver. All the antimony in the gas
falls down as black antimonide of silver, whilst the arsenic remains in
solution as arsenious acid, and may, after precipitation of the excess of
silver by hydrochloric acid, be readily detected in the fluid.
Protoxide and binoxide of tin may be detected and identified in presence
of each other, by testing one portion of the solution containing both
oxides for the protoxide with chloride of mercury, terchloride of gold or
a mixture of ferricyanide of potassium and sesquichloride of iron, and
another portion for the binoxide, by pouring it into a concentrated
solution of soda.
Teroxide of antimony in presence of antimonic acid may be identified
by the reaction described in 130, 9. Antimonic acid in presence of
teroxide of antimony, by heating the teroxide suspected to contain an
admixture of the acid, but without any other admixture, with hydro-
chloric acid free from chlorine, and iodide of potassium free from iodate
of potassa. If antimonic acid is present, iodine will separate, which, in
131'.] MOLYBDIC ACID. 125
the case of larger quantities of acid, may be known from the brown
color exhibited by the fluid, in the case of only slight traces of acid,
after addition of a few drops of bisulphide of carbon (see 154, 10).
(Bunsen.}
Arsenious acid and arsenic acid in the same solution may be distin-
guished by means of nitrate of silver. If the precipitate contains little
arsenate and much arsenite of silver, it is necessary, in order to iden-
tify the former, to add cautiously and drop by drop most highly dilute
nitric acid, which dissolves the yellow arsenite of silver first.
A still safer way to detect small quantities of arsenic acid in presence
of arsenious acid, is to precipitate the solution which contains the two
acids, with a mixture of sulphate of magnesia, chloride of ammonium,
and ammonia. The precipitate formed may be further examined by dis-
solving it in a very small quantity of nitric acid, mixing the solution
with nitrite of silver, and then very cautiously adding dilute ammonia,
which will lead to the formation of a precipitate of brownish-red arsenate
of silver, if arsenic acid is present. A rsenious acid in presence of arsenic
acid may also be identified by the reduction of oxide of copper effected
by its agency. To distinguish between the ter- and the pentasulphide
of arsenic, boil the potassia solution of the sulphide of arsenic under
examination with hydrate of teroxide of bismuth, filter off from the ter-
sulphide of bismuth formed, and test the filtrate for arsenious and
arsenic acids. If silver is to be used as the reagent to distinguish
between the two acids in the filtrate, the sulphide of arsenic may also be
dissolved in ammonia, the solution mixed with nitrate of silver, the
fluid filtered off from the sulphide of silver formed, and the filtrate cau-
tiously tested with dilute nitric acid, to see whether a yellow or a brown
precipitate or a mixture of both is produced.
134.
SUPPLEMENT TO THE SIXTH GROUP.
MOLYBDIC ACID (MoO s ).
Molybdenum is silvery- white, the protoxide of the metal (Mo 0)
is black, the binoxide (Mo O 2 ) dark brown. The metal and the two
oxides, when heated in the air, oxidize to molybdic acid (Mo 3 ).
Molybdic acid is a white, porous mass, which in water separates as
fine scales ; it fuses at a red-heat ; in close vessels it volatilizes only at a
very high temperature, in the air easily at a red-heat, subliming to
transparent lamina and needles. The non-ignited acid dissolves in
acids. The solutions are colorless ; in contact with zinc or tin they
first turn blue, then green, and ultimately black, with separation of
protoxide of molybdenum ; when digested with copper, they acquire a
red tint, in consequence of ensuing reduction of the acid to binoxide.
Ferrocyanide of potassium produces a reddish-brown precipitate, infusion
of galls a green precipitate. Hydrosulphuric acid, when added in small
proportion, imparts a blue tint to solutions of molybdic acid ; when
added in larger proportion, it produces a brownish-black precipitate ; the
fluid over the latter at first appears green, but after standing some time,
and upon application of heat, it deposits an additional portion of brownish-
black tersulphide of molybdenum (Mo S s ). The precipitated tersulphide
126 DEPORTMENT OF THE ACIDS WITH REAGENTS. [ 135, 136.
of molybdenum dissolves in sulphides of the alkali metals ; acids re-
precipitate from the sulphur salts the sulphur acid (Mo S 8 ). When
roasted at a red-heat in the air or heated with nitric acid, sulphide of
molybdenum is converted into molybdic acid.
Molybdic acid dissolves readily in solutions of pure alkalies and car-
bonates of the alkalies ; from rather concentrated solutions, sulphuric,
nitric, and hydrochloric acids throw down molybdic acid, which redis-
solves upon further addition of the precipitant. The solutions of
molybdates of the alkalies are colored yellow by hydrosulphuric acid,
and give afterwards, upon addition of acids, a brownish-black preci-
pitate. For the deportment of molybdic acid with phosphoric acid and
ammonia, see 143, 11.
B. DEPORTMENT OF THE ACIDS AND THEIR RADICALS WITH
EEAGENTS.
135.
The reagents which serve for the detection of the acids are divided,
like those used for the detection of the bases, into GENERAL REAGENTS,
i. <?., such as indicate the GROUP to which the acid under examination
belongs .; and SPECIAL REAGENTS, i.e., such as serve to effect the detection
and identification of the INDIVIDUAL ACIDS. The groups into which we
classify the various acids can scarcely be defined and limited with the
same degree of precision as those into which the bases are divided.
The two principal groups into which acids are divided are those of
INORGANIC and ORGANIC ACIDS. We base this division upon those cha-
racteristics by which, irrespectively of theoretical considerations, the
ends of analysis are most easily attained. We select therefore here, as
the characteristic mark to guide us in the classification into organic arid
inorganic acids, the deportment which the various acids manifest at a
high temperature, and call organic those acids of which the salts (par-
ticularly those which have an alkali or an alkaline earth for base) are
decomposed upon ignition, the decomposition being attended with sepa-
ration of carbon.
By selecting this deportment at a high temperature as the distinctive
characteristic of organic acids, we are enabled to determine at once by a
most simple preliminary experiment the class to which an acid belongs.
The salts of organic acids with alkalies or alkaline earths are converted
into carbonates when heated to redness.
Before proceeding to the special study of the several acids considered
in this work, I give here, the same as I have done with the bases, a
general view of the whole of them classified in groups.
136.
CLASSIFICATION OF ACIDS IN GROUPS.
I. INORGANIC ACIDS.
FIRST GROUP :
Division a. Arsenious acid, arsenic acid, chromic acid (selenious acid,
sulphurous and hyposulphurous acids, iodic acid).
Division b. Sulphuric acid (hydrofluosilicic acid).
Division c. Phosphoric acid, boracic acid, oxalic acid, hydrofluoric
acid.
137.] INORGANIC ACIDS. 127
Division d. Carbonic acid, silicic acid.
SECOND GROUP :
Chlorine and hydrochloric acid, bromine and hydrobromic acid, iodine
and hydriodic acid, cyanogen and hydrocyanic acid, together
with hydroferro- and hydroferricyanic acids, sulphur and
hydros ulphuric acid (nitrous acid and hypochlorous acid).
THIRD GROUP I
Nitric acid, chloric acid.
II. ORGANIC ACIDS.
FIRST GROUP :
Oxalic acid, tartaric acid, citric acid, malic acid (racemic acid).
SECOND GROUP :
Succinic acid, benzoic acid.
THIRD GROUP :
Acetic acid, formic acid.
I. INORGANIC ACIDS.
137.
First Group.
ACIDS WHICH ARE PRECIPITATED FROM NEUTRAL SOLUTIONS BY
CHLORIDE OF BARIUM.
This group is again subdivided into four divisions, viz. :
1. Acids which are decomposed in acid solution by hydrosulphuric acid,
and to which attention has therefore been directed already in the
testing for bases, viz., ARSENIOUS ACID, ARSENIC ACID, and CHROMIC
ACID. (In a supplement, page 129, I give selenious acid, sulphurous
acid, and hyposulphurous acid, the latter because it is decomposed
and detected by the mere addition of hydrochloric acid to the solution
of one of its sjilts ; and also iodic acid.)
2. Acids which are not decomposed in acid solution by hydrosulphuric
acid, and the baryta compounds of which are insoluble in hydrochloric
acid. Of the acids claiming our attention here, SULPHURIC ACID alone
belongs to this class. (In a supplement, page 132, I give hydro-
fluosilic acid.)
3. Acids which are not decomposed in an acid solution by hydrosulphuric
acid, and the baryta compounds of which dissolve in hydrochloric
acid, apparently WITHOUT DECOMPOSITION, inasmuch as the acids cannot
be completely separated from the hydrochloric acid solution by heating
or evaporation; these are PHOSPHORIC ACID, BORACIC ACID, OXALIC
ACID, and HYDROFLUORIC ACID. (Oxalic acid belongs more properly to
the organic group. We consider it, however, here with the acids of
the inorganic class, as the property of its salts to be decomposed upon
ignition without actual carbonization may lead to its being overlooked
as an organic acid.)
4. Acids which are not decomposed in acid solution by hydrosulphuric
acid, and the baryta salts of which are soluble in hydrochloric acid,
WITH DECOMPOSITION (separation of the acid) : CARBONIC ACID, SILICIC
ACID.
128 CHROMIC ACID. [ 138.
First Division of the First Group of the Inorganic A cids.
138.
a. ARSENIOUS ACID and ARSENIC ACID are, as we have seen above, de-
composed by hydrosulphuric acid, and are precipitated by that reagent
respectively as ter- and pentasulphide of arsenic. As this would lead to
confounding them rather with the metallic oxides than with other acids,
it has been deemed more judicious to class these two acids with the
oxides of the sixth group. (See 131 and 132.)
b. CHROMIC ACID (Or O 3 ).
1. Chromic acid presents the appearance of a scarlet-red crystalline
mass, or of distinct acicular crystals. Upon ignition it is resolved into
sesquioxide of chromium and oxygen. It deliquesces rapidly upon
exposure to the air. It dissolves in water, imparting to the fluid a deep
reddish-brown tint, which remains still visible in very dilute solutions.
2. The chromates are all red or yellow, and for the most part insoluble
in water. Part of them are decomposed upon ignition ; those with
alkaline bases are fixed, and soluble in water ; the solutions of the
neutral alkaline chromates are yellow, those of the alkaline bichromates
are red. These tints are still visible in highly dilute solutions. The
yellow color of the solution of a neutral salt changes to red on the addi-
tion of a mineral acid, owing to the formation of an acid chromate.
3. Hydrosulphuric acid reduces chromic acid readily when present in
the solution in the free state, more difficultly when present in form of a
chromate ; sesquioxide of chromium, water, and sulphuric acid are
formed in this process, and sulphur precipitates. Heat promotes this
decomposition. If no free acid is present, a greenish-gray precipitate is
produced, consisting of a mixture of hydrated sesquioxide of chromium
and sulphur. But if free acid is present, the precipitate is far less con-
siderable, and consists of pure sulphur. In the latter case, the salt of
sesquioxide of chromium formed imparts a green tint to the fluid,
which may lead to the erroneous impression that the precipitate itself is
green.
4. Chromic acid may also be reduced to sesquioxide of chromium by
means of many other substances, and more particularly by sulphurous acid,
or by heating with hydrochloric acid, especially upon the addition of
alcohol (in which case chloride of ethyle and aldehyde are evolved) ; also
by metallic zinc, or by heating with tartaric acid, oxalic acid, &c. All
these reactions are clearly characterized by the change of the red or
yellow color of the solution to the green tint of the salt of sesquioxide of
chromium.
5. Chloride of barium produces a yellowish-white precipitate of CHRO-
MATE OF BARYTA (Ba O, Cr O 3 ), which is soluble in dilute hydrochloric
acid and nitric acid.
6. Nitrate of silver produces a dark purple-red precipitate of CHRO-
MATE OF SILVER (Ag O, Cr O g ), which is soluble in nitric acid and in
ammonia ; in acid solutions it produces a precipitate of BICHROMATE OF
SILVER (Ag 0, 2 Cr O 8 ).
7. Acetate of lead produces a yellow precipitate of CHROMATE OF LEAD
(Pb 0, Cr 3 ), which is soluble in potassa, but only difficultly soluble in
139, 140.] SELENIOUS ACID. 129
dilute nitric acid. Upon heating with alkalies, the yellow neutral salt
is converted into basic red chromate of lead (2 Pb O, Cr O ).
8. If insoluble chromates are fused together with carbonate of soda
and nitrate of soda, and the fused mass is treated with water, the fluid
produced appears YELLOW from the alkaline chromate which it holds in
solution ; upon the addition of an acid the yellow color changes to
red. The oxides remain behind either in the pure state or as carbonates,
if they are not soluble in the caustic soda formed from the nitrate.
139.
Remarks. When testing for bases, we always find the chromic acid as
sesquioxide of chromium, since hydrosulphuric acid reduces it to that
state. The characteristic color of the solution frequently renders the
application of any further test unnecessary. The reactions with salts of
silver and salts of lead afford positive and confirmatory proof of the
presence of chromic acid in aqueous solutions. Acid solutions are boiled
with carbonate of soda in excess, and filtered ; the filtrate is acidified
with acetic acid, and acetate of lead then added to it. If there is reason
to suppose that chromic acid is present in a solution, metallic oxides
being also present, it is preferable to effect the reduction of the chromic
acid by means of hydrochloric acid and alcohol, or by sulphurous acid,
instead of reducing it by hydrosulphuric acid.
140.
Supplement to the First Division of the First Group.
a. Selenious acid (Se O 2 ). Sublimed anhydrous selenious acid appears
in form of white four-sided needles, its hydrate in form of crystals re-
sembling those of nitrate of potassa. Both the acid and its hydrate dis-
solve readily in water to a strongly acid fluid. Of the neutral salts only
those with the alkalies are soluble in water. All selenites dissolve
readily in nitric acid, with the exception of the selenites of lead and
silver, which dissolve with difficulty. Hydrochloric acid, even when
boiling, fails to decompose selenites; sulphuric acid decomposes them
readily with the aid of heat. Hydrosulphuric acid produces in solutions
of selenious acid or of selenites (in presence of free hydrochloric acid) a
yellow precipitate of SULPHIDE OF SELENIUM, which, upon heating, turns
reddish-yellow, and is soluble in sulphide of ammonium. Chloride of
barium produces (after neutralization of the free acid, should any be
present) a white precipitate of selenite of baryta, which is soluble in
hydrochloric acid and in nitric acid. Protochloride of tin produces a
red precipitate of SELENIUM, which turns gray at a high temperature ;
sulphurous acid produces the same precipitate. When exposed on a
charcoal support to the reducing flame, the selenites evolve selenium,
exhaling at the same time a characteristic odor of decaying horse-
radish.
b. Sulphurous acid (SO 2 ) is a colorless, uninflammable gas, which
exhales the stifling odor of burning sulphur. It dissolves copiously in
water. The solution has the odor of the gas, reddens litmus paper, and
bleaches Brazil-wood paper. It absorbs oxygen from the air, and is
L K
130 HYPOSULPHUROUS ACID. [ 140.
thereby converted into sulphuric acid. The salts of sulphurous acid are
colorless. Of the neutral sulphites those with alkaline base only are
readily soluble in water ; many of the sulphites insoluble or difficultly
soluble in water dissolve in an aqueous solution of sulphurous acid, but
fall down again upon boiling. All the sulphites evolve sulphurous acid
when treated with sulphuric acid or hydrochloric acid. Chlorine water
dissolves most sulphites to sulphates. Chloride of barium precipitates
neutral sulphites, but not free sulphurous acid. The precipitate dissolves
in hydrochloric acid. Hydrosulphuric acid decomposes free sulphurous
acid, water being formed and free sulphur eliminated, which latter
separates from the fluid. If a trace of sulphurous acid or of a sulphite
is introduced into a flask in which hydrogen is being evolved from zinc
and hydrochloric acid, hydrosulphuric acid is immediately evolved along
with the hydrogen, and the gas now produces a black coloration or a
black precipitate in a solution of acetate of lead to which has been
added a sufficient quantity of solution of soda to redissolve the precipi-
tate which forms at first. Sulphurous acid is a powerful reducing
agent ; it reduces chromic acid, permanganic acid, chloride of mercury
(to subchloride), decolorizes iodide of starch, produces a blue precipitate
in a mixture of ferricyanide of potassium and sesquichloride of iron, &c.
"With a hydrochloric acid solution of protocliloride, of tin, a brown pre-
cipitate of PROTOSULPHIDE OF TIN is formed after some time.
c. Hyposulphurous acid (S 2 O 2 ). This acid does not exist in the free
state. Its salts are generally soluble in water. The solutions of most
hyposulphites may be boiled without suffering decomposition ; hypo-
sulphite of lime is resolved upon boiling into sulphite of lime and
sulphur. If hydrochloric acid or sulphuric acid is added to the solution
of a hyposulphite, the fluid remains at first clear and inodorous, but after
a short time the shorter the more concentrated the solution it becomes
more and more turbid, owing to the separation of sulphur, and exhales
the odor of sulphurous acid. Application of heat promotes this decom-
position. Nitrate of silver produces a white precipitate of HYPOSULPHITE
OP SILVER, which is soluble in an excess of the hyposulphite ; after a
little while (upon heating almost immediately) the precipitate turns
black, being decomposed into sulphide of silver and sulphuric acid.
Hyposulphite of soda dissolves chloride of silver ; upon the addition of
an acid the solution remains clear at first, but shortly, and upon boiling,
immediately, sulphide of silver separates. Chloride of barium produces
a white precipitate, which is soluble in much water, more especially
hot water, and is decomposed by hydrochloric acid.
d. lodic acid (I O 5 ). lodic acid crystallizes in white, six-sided tables ;
at a moderate heat it is resolved into iodine vapor and oxygen ; it is
readily soluble in water. The salts are decomposed upon ignition, being
resolved either into oxygen and a metallic iodide, or into iodine, oxygen,
and metallic oxide ; the iodates with an alkaline base alone dissolve readily
in water. Chloride of barium throws down from solution of iodates of
the alkalies a white precipitate of IODATE OF BARYTA, which is soluble in
nitric acid ; nitrate of silver, a white, granular-crystalline precipitate of
IODATE OF SILVER, which dissolves readily in ammonia, but only sparingly
in nitric acid. Hydrosulphuric acid throws down from solutions of
iodic acid and iodates IODINE, which then dissolves in hydriodic acid ; if
an excess of hydrosulphuric acid is added, the fluid loses its color, and
sulphur separates, the iodine being converted into hydriodic acid. Sul-
141.] SULPHURIC ACID. 131
phurous acid throws down IODINE, which upon addition of an excess of
the acid is converted into hydriodic acid.
Second Division of the First Group of the Inorganic Acids.
141.
SULPHURIC ACID (S O 3 ).
1. Anhydrous sulphuric acid is a white, feathery-crystalline mass,
which emits strong fumes upon exposure to the air ; hydrated sulphuric
acid forms an oily liquid, colorless and transparent like water. Both the
anhydrous and hydrated 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 anhydrous
acid, with a hissing noise.
2. Most of the sulphates are soluble in water ; the insoluble sulphates
are generally white ; the soluble sulphates, in the crystalline state, are for
the most part colorless. The sulphates of the alkalies and alkaline earths
are not decomposed upon ignition.
3. Chloride of barium produces even in exceedingly dilute solutions of
sulphuric acid and of the sulphates a finely-pulverulent, heavy, white
precipitate of SULPHATE OF BARYTA (Ba 0, S O 3 ), which is insoluble in
hydrochloric acid and in nitric acid. From very dilute solutions the
precipitate separates only after standing some time. In presence of the
citrate of an alkali, the precipitate forms only after addition of hydro-
chloric acid (Spiller).
4. Acetate of lead produces a heavy, white precipitate of SULPHATE OF
LEAD (Pb 0, S O 3 ) which is sparingly soluble in dilute nitric acid, but
dissolves completely in hot concentrated hydrochloric acid.
5. The salts of sulphuric acid with the alkaline earths which are inso-
luble in water and acids are converted into CARBONATES, by fusion with
alkaline carbonates. But the sulphate of lead is reduced to the state of
PURE OXIDE when treated in this manner. Both the conversion of the
former into carbonates, and the reduction of the latter to the state of
oxide, are attended with the formation of an alkaline sulphate. The
sulphates of the alkaline earths and sulphate of lead, are also resolved
into insoluble carbonates and soluble alkaline sulphate when boiled with
concentrated solutions of carbonates of the alkalies.
6. Upon fusing sulphates with carbonate of soda on charcoal in the
inner flame of the blowpipe, the sulphuric acid is reduced, and sulphide
of sodium formed, which may be readily recognised by the odor of hydro-
sulphuric acid emitted upon moistening the sample and the part of the
charcoal into which the fused mass has penetrated, and adding some acid.
If the fused mass is transferred to a clean silver plate, or a polished
silver coin, and then moistened with water and some acid, a black stain
of sulphide of silver is immediately formed.
Remarks. The characteristic and exceedingly delicate reaction of sul-
phuric acid with salts of baryta 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 sulphate of baryta, precipitates of chloride of
barium, and particularly of nitrate of baryta, which are formed upon
K 2
132 HYDROFLUOSILICIC ACID. [ 142, 143.
mixing aqueous solutions of these salts with fluids containing a large
proportion of free hydrochloric acid or free nitric acid. It is very easy
to distinguish these precipitates from sulphate of baryta, since they re-
dissolve immediately upon diluting the acid fluid with water. To detect
free sulphuric acid in presence of a sulphate, the fluid under examina-
tion is mixed with a very little cane-sugar, and the mixture evaporated
to dryness in a porcelain dish at 212 Fah. If free sulphuric acid was
present, a black residue remains, or, in the case of most minute quantities,
a blackish-green residue. Other free acids do not decompose cane-sugar
in this way (Runge).
142.
Supplement to the Second Division of the First Group.
HYDROFLUOSILICIC ACID (HF, Si F 2 ).
Hydrofluosilicic acid is a very acid fluid ; when evaporated on
platinum, it volatilizes completely as fluoride of silicon and hydro-
fluoric acid. When evaporated on glass, it etches the latter. With
bases it forms water and silico-fluorides of the metals, which are most of
them soluble in water, redden litmus paper, and are resolved upon
ignition into metallic fluorides and fluoride of silicon.
Chloride of barium forms a crystalline precipitate with hydrofluo-
silicic acid ( 94, 6). Chloride of strontium and acetate of lead form no
precipitates with this acid ; salts of potassa precipitate transparent
GELATINOUS siLico-FLUORiDE OF POTASSIUM ; ammonia in excess preci-
pitates HYDRATED SILICIC ACID, with formation of fluoride of ammonium.
When metallic silico-fluorides are heated with concentrated sulphuric
acid in a platinum vessel covered with glass, the glass is ETCHED
( 147, 5).
Third Division of the First Group of the Inorganic Acids.
143.
a. PHOSPHORIC ACID (P0 5 ).
1. Phosphorus is a colorless, transparent, solid body, of 2'089 specific
gravity j it has a waxy appearance. Taken internally, it acts as a virulent
poison. It fuses at 113, and boils at 554 Fah. By the influence of
light, phosphorus kept under water turns first yellow, then red, and is
finally covered with a white crust. If phosphorus is exposed to the air,
at the common temperature, it exhales a garlic odor, shines in the dark,
and emits fumes of phosphorous acid, into which substance it is gradually
entirely converted. Phosphorus very readily takes fire spontaneously,
and burns with a luminous flame, being converted into phosphoric acid,
which is dissipated for the most part in white fumes through the sur-
rounding air. Nitric acid and nitrohydrochloric acid dissolve phosphorus
pretty readily upon heating. The solutions contain at first, besides phos-
phoric acid, also phosphorous acid. Hydrochloric acid does not dissolve
phosphorus j if phosphorus is boiled with solution of soda or potassa, or
with milk of lime, hypophosphites and phosphates are formed, whilst
spontaneously inflammable phosphuretted hydrogen gas escapes. If a
trace of phosphorus is put into a hydrogen gas-evolution apparatus sup-
plied with pure zinc and pure dilute sulphuric acid, phosphide of
hydrogen is evolved with the hydrogen, and the gas burns now with
143.] PHOSPHOllIC ACID. 133
a conical, emerald-green flame, surrounded by an outer hardly visible
pale blue mantle. The color does not lose in intensity upon trans-
mitting the gaseous mixture over hydrate of potassa or caustic lime,
which should always be done, in order to remove any hydrosulphuric
acid that may be evolved along with the other two gases. If the gas is
not kindled, it shines in the dark. If it is received under water, it will
form white fumes when it comes in contact with the air (Dusart). For
the deportment of phosphoric acid upon boiling with dilute sulphuric
acid in a distilling apparatus, see 225.
2. Anhydrous phosphoric acid is a white, snowlike mass, which
rapidly deliquesces in the air, and dissolves in water with a hissing
noise. It forms with water and bases three different series of com-
pounds : viz., with three equivalents of water or base, hydrate of com-
mon phosphoric acid or common phosphates ; with two equivalents of
water or base, hydrate of pyrophosphoric acid or pyrophosphates ; with
one equivalent of water or base, hydrate of metaphosphoric acid or
metaphosphates.
The phosphates which we generally meet with in nature and in
analytical investigations belong, as a rule, to the tribasic series ; we
therefore make them alone the object of a fuller study in this place,
devoting a supplemental paragraph to a briefer consideration of mono-
basic and bibasic phosphoric acids, and their salts.
3. The hydrate of common phosphoric acid (3 H O, P O 5 ) forms color-
less and pellucid crystals, which deliquesce rapidly in the air to a syrupy
non-caustic liquid. The action of heat changes it into hydrated pyro- or
metaphosphoric acid, according as either one or two equivalents of
water are expelled. Heated in an open platinum dish, the hydrate of
common phosphoric acid, if pure, volatilizes completely, though with
difficulty, in white fumes.
4. The action of heat fails to decompose the tribasic phosphates with
fixed bases, but converts them into pyrophosphates, if they contain one
equivalent of basic water or ammonia, and into metaphosphates, if^they
contain two equivalents. The tribasic phosphates with alkaline base
alone are soluble in water, in the neutral state. The solutions manifest
an alkaline reaction. If pyi'o- or metaphosphates are fused with car-
bonate of soda, the fused mass contains the phosphoric acid invariably in
the tribasic state.
5. Chloride of barium produces in aqueous solutions of the neutral or
basic phosphates, but not in solution of the hydrate, a white precipi-
tate of PHOSPHATE OF BARYTA [2 Ba 0, H O, P O g ; or 3 Ba O, P OJ,*
which is soluble in hydrochloric acid and in nitric acid, but difficultly
soluble in chloride of ammonium.
6. Solution of sulphate of lime produces in neutral or alkaline solutions
of phosphates, but not in solutions of the hydrate, a white precipitate of
PHOSPHATE OF LIME (2 Ca O, H 0, P O 5 or 3 Ca O, P 6 ) which dissolves
readilv in acids, even in acetic acid, but with difficulty in chloride of
ammonium.
7. tiulphate of magnesia produces in concentrated neutral solutions of
phosphates a white precipitate of PHOSPHATE OF MAGNESIA (2 Mg O,
H 0, P O 5 + 14 aq.), which often separates only after some time ; upon
* Precipitates of the former composition are produced in solutions containing an alkaline
phosphate with two equivalents of a fixed base or ammonia ; whilst precipitates of the
latter composition are formed in solutions which contain an alkaline phosphate with
three equivalents of a fixed base or ammonia.
134 PHOSPHOEIC ACID. [ 143.
boiling, however, a precipitate of basic salt (3 Mg 0, P 5 + 5 aq.) is thrown
down immediately. The latter precipitate forms also upon addition of sul-
phate of magnesia to the solution of a basic alkaline phosphate. But if
sulphate of magnesia, mixed with a sufficient quantity of chloride of
ammonium to leave the solution clear upon addition of ammonia, is
added to a solution of free phosphoric acid or of an alkaline phosphate,
and ammonia in excess is then added, a white, crystalline, and quickly
subsiding precipitate of BASIC PHOSPHATE OF MAGNESIA AND AMMONIA
(2 Mg O, N H 4 O, P O. 4- 12 aq.) is formed, even in highly dilute solutions.
This precipitate is insoluble in ammonia and most sparingly soluble in
chloride of ammonium, but dissolves readily in acids, even in acetic
acid. It makes its appearance often only after the lapse of some time ;
stirring promotes its separation (see 97, 7).
8. Nitrate of silver throws down from solutions of neutral and basic
alkaline phosphates a light-yellow precipitate of PHOSPHATE OF SILVER
(3 Ag O, P 5 ), which is readily soluble in nitric acid and in aramonia.
If the solution contained a basic phosphate, the fluid in which the preci-
pitate is suspended manifests a neutral reaction ; whilst the reaction is
acid if the solution contained a neutral phosphate. The acid reaction in
the latter case arises from the circumstance that the nitric acid receives
for the 3 equivalents of oxide of silver which it yields to the
phosphoric acid, only 2 eq. of alkali and 1 eq. of water ; and as the
latter does not neutralize the acid properties of the nitric acid, the solu-
tion becomes acid.
9. Acetate of lead produces in neutral and alkaline solutions of phos-
phates a white precipitate of PHOSPHATE OF LEAD (3 Pb O, P O 6 ), which
is readily soluble in nitric acid, but nearly insoluble in acetic acid. It
fuses before the blowpipe ; the cold beads exhibit brilliant facets.
10. If to a solution containing phosphoric acid and the least possible
excess of hydrochloric or nitric acid, a tolerably large amount of acetate
of soda is added, and then a drop of sesquichloride of iron, a yellowish-
white, flocculent-gelatinotis precipitate of PHOSPHATE OF SESQUIOXIDE OF
IRON (Fe 2 O 3 , P O 6 + 4 aq.) is formed. An excess of sesquichloride of iron
must be avoided, as acetate of sesquioxide of iron (of red color) would
thereby be formed, in which the precipitate is not insoluble. This
reaction is of importance, as it enables us to detect the phosphoric acid
in phosphates of the alkaline earths j to effect the complete separation
of the phosphoric acid from the alkaline earths, a sufficient quantity of
sesquichloride of iron is added to impart a reddish color to the solution,
which is then boiled (whereby the whole of the sesquioxide of iron is
thrown down, partly as phosphate, partly as basic acetate), and filtered
hot. The filtrate contains the alkaline earths as chlorides. If you wish
to detect, by means of this reaction, phosphoric acid in presence of a
large proportion of sesquioxide of iron, boil the hydrochloric acid solu-
tion with sulphite of soda until the sesquichloride is reduced to proto-
chloride, which reduction is indicated by the decoloration of the solu-
tion j add carbonate of soda until the fluid is nearly neutral, then acetate
of soda, and finally one drop of sesquichloride of iron. The reason for
this proceeding is, that acetate of protoxide of iron does not dissolve
phosphate of sesquioxide of iron.
11. If some molybdate of ammonia is mixed in a test-tube with
hydrochloric acid or nitric acid in sufficient quantity to redissolve the
precipitate which first forms, and a little of a fluid containing phos-
144.] BIBASIC PHOSPHORIC ACID. 135
phoric acid is then added, the fluid acquires a yellow color, and after
some time a yellow precipitate separates, which, in presence of molybdic
acid in excess, is insoluble in acids, and contains MOLYBDIC ACID, AM-
MONIA, AND A LITTLE PHOSPHORIC ACID. Application of heat greatly
promotes the reaction. This reaction is so delicate, that the phosphoric
acid may be detected by its means in almost all salts and most minerals
containing it. As the yellow compound is decomposed by free phos-
phoric acid, an excess of the fluid containing the phosphoric acid must
be carefully avoided. The yellow precipitate may, when it has subsided,
be perceived even in dark-colored fluids (Svanberg and Slruve). By washing
it with a solution of molybdate of ammonia, supersaturated with hydro-
chloric acid, dissolving in ammonia, and adding a mixture of sulphate of
magnesia, chloride of ammonium, and ammonia, phosphate of magnesia
and ammonia is produced.
12. If a finely powdered substance containing phosphoric acid (or also
a metallic phosphide) is intimately mixed with 5 parts of a flux con-
sisting of 3 parts of carbonate of soda, 1 part of nitrate of potassa, and
1 part of silicic acid, the mixture fused in a platinum spoon or crucible,
the fused mass boiled with water, the solution obtained decanted, car-
bonate of ammonia added to it, the fluid boiled again, and the silicic
acid which is thereby precipitated filtered off, the filtrate now holds in
solution alkaline phosphate, and may accordingly be tested for phos-
phoric acid as directed in 11, or in some other way.
13. White of egg is not precipitated by solution of hydrate of tribasic
phosphoric acid, nor by solutions of tribasic phosphates, mixed with
acetic acid.
Supplement.
a. Bibasic phosphoric acid. The solution of the hydrate 2 H 0, P 6
is converted by boiling into solution of the hydrate 3 H 0, P O 6 . The
solutions of the salts bear heating without suffering decomposition ; but
upon boiling with a strong acid, the phosphoric acid is converted into the
tribasic state. If the salts are fused with carbonate of soda in excess,
tribasic phosphates are produced. Of the neutral pyrophosphates only
those with alkaline bases are soluble in water ; the acid salts (e. g.,
Na 0, H O, P O 5 ) are by ignition converted into metaphosphates
(Na O, P O 6 ). Chloride of barium fails to precipitate the free acid ;
from solutions of the salts it precipitates PYROPHOSPHATE OP BARYTA
(2 Ba O, P O.). Nitrate of silver throws down from a solution of the
hydrate, especially upon addition of an alkali, a white, earthy-looking pre-
cipitate of PYROPHOSPHATE OF SILVER (2 Ag O, P O 5 ), which is soluble in
nitric acid and in ammonia. Sulphate of magnesia precipitates PYROPHOS-
PHATE OF MAGNESIA (2 Mg 0. P OJ. The precipitate dissolves in an excess
of the phosphate, as well as in an excess of the sulphate of magnesia.
Ammonia fails to precipitate it from these solutions. Upon boiling
the solution, it separates again. White of egg is not precipitated by
solution of the hydrate, nor by solutions of the salts, mixed with acetic
acid. Molybdate of ammonia, with addition of hydrochloric acid, fails
to produce a precipitate.
/3. Monobasic phosphoric acid. Five sorts of monobasic phosphates
are known, and the hydrates also of most of these have been produced.
136 BORACIC ACID. [ 145.
The several reactions by which to distinguish between these I will not
enter upon here, and confine myself to the simple observation that the
monobasic phosphoric acids differ from the bibasic and tribasic phos-
phoric acids in this, that the solutions of the hydrates of the monobasic
acids precipitate white of egg at once, and the solutions of their salts,
after addition of acetic acid. Those hydrates and salts which are pre-
cipitated by nitrate of silver produce with that reagent a white precipi-
tate. A mixture of sulphate of magnesia, chloride of ammonium, and am-
monia fails to precipitate the monobasic phosphoric acids and their salts,
or produces precipitates soluble in chloride of ammonium. All mono-
basic phosphates yield upon fusion with carbonate of soda tribasic phos-
phate of soda.
H5.
b. BORACIC ACID (B 8 ).
1. Boracic acid, in the anhydrous state, is a colorless, fixed glass, fusible
at a red heat ; hydrate of boracic acid (3 H 0, 2 B O 3 .) is a porous, white
mass ; in the crystalline state (3 H 0, 2 B O 8 + 3 aq.), it presents small
scaly laminae. It is soluble in water and in spirit of wine ; upon evapo-
rating the solutions, a large proportion of boracic acid 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 borates are not decomposed upon ignition ;
those with alkaline bases alone are readily soluble in water. The solu-
tions are colorless, and all of them, even those of the acid salts, manifest
alkaline reaction.
2. Chloride of barium produces in solutions of borates, if not too highly
dilute, a white precipitate of BORATE OF BARYTA, which is soluble in
acids and ammoniacal salts. The formula of this precipitate, when
thrown down from solutions of neutral borates, is Ba O, B 3 + aq. ;
when thrown down from solutions of acid borates, 3 Ba O, 5 B O 3 + 6 aq.
(H. Rose).
3. Nitrate of silver produces in concentrated solutions of neutral
borates of the alkalies a white precipitate, inclining slightly to yellow
from admixture of free oxide of silver (Ag O, B O 3 -f H O) ; in con-
centrated solutions of acid borates, a white precipitate of 3 Ag O, 4 B 3 .
Dilute solutions of borates give with nitrate of silver a grayish-brown
precipitate of oxide of silver (H. Rose). All these precipitates dissolve
in nitric acid and in ammonia.
4. If sulphuric acid or hydrochloric acid is added to highly concen-
trated, hot prepared solutions of alkaline borates, the BORACIC ACID
separates upon cooling, in the form of shining crystalline scales.
5. If alcohol is poured over free boracic acid or a borate with addi-
tion, in the latter case, of a sufficient quantity of concentrated sulphuric
acid to liberate the boracic acid and the alcohol is kindled, the flame
appears of a very distinct YELLOWISH-GREEN color, especially upon stirring
the mixture ; this tint is imparted to the flame by the ignited boracic
acid which volatilizes with the alcohol. The delicacy of this reaction
may be considerably heightened by heating the dish which contains the
alcoholic mixture, kindling the alcohol, allowing it to burn for a short
time, then extinguishing the flame, and afterwards rekindling it. At the
first flickering of the flame its borders will now appear green, even though
146.] OXALIC ACID. 137
the quantity of the boracic acid be so minute that it fails to produce a
perceptible coloring of the flame, when treated in the usual manner. As
salts of copper also impart a green tint to the flame of alcohol, the copper
which might be present must first be removed by means of hydrosul-
phuric acid. Presence of metallic chlorides also may lead to mistakes,
as the chloride of ethyle formed in that case colors the borders of the
flame greenish.
6. If the solution of a borate 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 212 Fah., the dipped
half shows a brown-red tint (H. Rose).
This reaction is very delicate ; care must be taken not to confound
the characteristic brownish-red coloration with the blackish-brown color
which turmeric paper acquires when moistened with rather concentrated
hydrochloric acid, and then dried.
7. If a substance containing boracic acid is reduced to a fine powder,
this, with addition of a drop of water, mixed with a flux composed of
4J parts of bisulphate of potassa and 1 part of finely pulverized fluoride
of calcium, free from boracic acid, and the paste exposed on the loop of a
platinum wire to the inner flame of the blowpipe, fluoride of boron
escapes, which imparts to the flame though only for a few instants a
yellow-green tint (Turner).
U6.
c. OXALIC ACID (C 2 3 = O).
1. The hydrate of oxalic acid (H 0, C 2 O 3 ) is a white powder ; the
crystallized acid (H O, C 2 O 3 4- 2 aq.) forms colorless rhombic prisms.
Both dissolve readily in water and in spirit of wine. When heated
rapidly in open vessels, part of the hydrated acid undergoes decomposi-
tion, whilst another portion volatilizes unaltered. The fumes of the
volatilizing acid are very irritating and provoke coughing. If the
hydrate is heated in a test-tube, the greater part of it sublimes un-
altered.
2. The whole of the oxalates undergo decomposition at a red heat, the
oxalic acid being converted into carbonic acid and carbonic oxide. Those
with an alkali or an alkaline earth for base are in this process converted
into carbonates (if pure, almost without separation of charcoal) ; those
with a metallic base leave either the pure metal or the oxide behind,
according to the greater or less degree of reducibility of the metallic
oxide. The alkaline oxalates, and also some of the oxalates with metallic
bases, are soluble in water.
3. Chloride of barium produces in neutral solutions of oxalates a white
precipitate of OXALATE OF BARYTA (Ba O, O + aq.), which is soluble in
nitric acid and in hydrochloric acid, but dissolves more sparingly in am-
moniacal salts than borate of baryta.
4. Nitrate of silver produces in neutral solutions of oxalates a white
precipitate of OXALATE OF SILVER (Ag 0, O), which is soluble in nitric
acid and in ammonia.
5. Lime-water and all the soluble salts of lime, and consequently also
solution of sulphate of lime) produce in even highly dilute solutions of
free oxalic acid or of oxalates, white, finely pulverulent precipitates of
138 HYDHOFLTJORIC ACID. [ 147.
OXALATE OF LIME (Ca 0, O), whicli dissolve readily in hydrochloric acid
and in nitric acid, but are nearly insoluble in oxalic acid and in acetic
acid. The presence of salts of ammonia does not interfere with the for-
mation of these precipitates. Addition of ammonia considerably pro-
motes the precipitation of the free oxalic acid by salts of lime. In highly
dilute solutions the precipitate is only formed after some time.
6. If hydrated oxalic acid (or an oxalate), in the dry state, is heated
with an excess of concentrated sulphuric acid, the latter withdraws from
the oxalic acid its constitutional water, and thus causes its decomposition
into CARBONIC ACID and CARBONIC OXIDE (C 2 O 3 = C O + C O 3 ), the two
gases escaping with effervescence. If the quantity operated upon is not
too minute, the escaping carbonic oxide gas may be kiodled ; it burns
with a blue flame. Should the sulphuric acid acquire a dark color in this
reaction, this is a proof that the oxalic acid contained some organic
substance in admixture.
7. If oxalic acid or an oxalate is mixed with some finely pulverized
birioxide of manganese (which must be free from carbonates), a little
water added and a few drops of sulphuric acid, a lively effervescence
ensues, caused by the escaping carbonic acid (Mn 2 + C O + S O
= Mn O, S 3 + 2 C O 2 ).
' 8. If oxalate of lime or any other insoluble oxalate is boiled with a
concentrated solution of carbonate of soda, and the fluid filtered, the
oxalic acid is obtained in the filtrate in combiDation with soda, whilst
the precipitate contains the base as oxide or as carbonate.
U7.
d. HYDROFLUORIC ACID (H F).
1. Hydrofluoric acid is a colorless, highly volatile fluid of pungent
odor ; it emits fumes when exposed to the air, and is miscible with water
in all proportions. Hydrofluoric acid is distinguished from all other
acids by the exclusive property it possesses of dissolving crystallized
silicic acid, and also the silicates which are insoluble in hydrochloric
acid. Fluoride of silicon and water are formed in the process of solution
(2 H F + Si O 2 = Si F 2 + 2 H O). Hydrofluoric acid decomposes
with metallic oxides in the same manner, metallic fluorides and water
being formed.
2. The fluorides of the alkali metals are soluble in water ; the solutions
have an alkaline reaction. The fluorides of the metals of the alkaline
earths are either altogether insoluble in water, or they dissolve in that
menstruum only with very great difficulty. Fluoride of aluminium is
readily soluble. Most of the fluorides corresponding to the oxides of the
heavy metals are very difficultly soluble in water, for instance, fluorides of
copper, lead, and zinc ; many other of the fluorides of the heavy metals
dissolve in water without difficulty, as, for instance, the sesquifluoride of
iron, protofluoride of tin, fluoride of mercury, &c. Many of the fluorides
insoluble or difficultly soluble in water dissolve in free hydrofluoric acid,
others do not. Most of the fluorides bear ignition in a crucible with-
out suffering decomposition.
3. Chloride of barium precipitates free hydrofluoric acid incompletely,
but upon addition of ammonia a copious, white precipitate of FLUORIDE
OF BARIUM (Ba F) forms immediately, which is soluble in hydrochloric
acid ; and not insoluble in chloride of ammonium.
147.] HYDROFLUORIC ACID. 139
4. Chloride of calcium produces in aqueous solutions of hydrofluoric
acid or of fluorides a gelatinous precipitate of FLUORIDE OP CALCIUM
(Ca F), which is so transparent, as at first to induce the belief that the
fluid has remained perfectly bright. Addition of ammonia promotes the
complete separation of the precipitate. The precipitated fluoride of
calcium is very slightly soluble in hydrochloric acid and nitric acid in the
cold ; it dissolves somewhat more largely upon boiling with hydrochloric
acid. Ammonia produces no precipitate in the solution, or only a very
trifling one, as the salt of ammonia formed retains it in solution. It is
scarcely more soluble in free hydrofluoric acid than in water. It is in-
soluble in alkaline fluids.
5. If a finely pulverized fluoride, no matter whether soluble or in-
soluble, is treated in a platinum crucible with concentrated sulphuric acid,
the crucible covered with the convex face of a watch-glass coated
with bees-wax, which has been removed again in some places by tracing
lines in it with a pointed instrument,* 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 will, upon the removal of the
wax, be found etched into the glass. 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 ; it will, however, in such cases
reappear when the plate is breathed upon. This reappearance 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.
This reaction (5) fails if there is too much silicic acid present, or if the
body under examination is not decomposed by sulphuric acid. In such
cases the one or the other of the two following methods is resorted to,
according to circumstances.
6. If we have to deal with a fluoride decomposable by sulphuric acid,
but mixed with a large proportion of silicic acid, the fluorine in it may
be detected by heating the mixture in a test-tube with concentrated
sulphuric acid, as FLUOSILICIC GAS is evolved in this process, which forms
dense white fumes in moist air. If the gas is conducted into water,
through a bent tube moistened inside, the latter has its transparency
more or less impaired, by the separation of silicic acid. If the quantity
operated upon is rather considerable, hydrate of silicic acid separates in
the water, and the fluid is rendered acid by hydrofluosilicic acid.
The following process answers best for the detection of smaller quan-
tities of fluorine. Add to the substance under examination some lumps
of marble (to ensure a continuous slight evolution of gas), boil the mix-
ture in a flask with concentrated sulphuric acid, conduct the gases
evolved into solution of ammonia, heat, filter, evaporate in a platinum
crucible to dryness, and examine the residue by the method described in
5. In the case of more difficultly decomposable substances bisulphate of
potassa is used instead of sulphuric acid, and the mixture, to which some
marble is likewise added, heated to fusion, and kept in that state for
some time.
7. Compounds not decomposable by sulphuric acid must first be fused
* The coating with wax may be readily effected by heating the glass cautiously, putting
a small piece of wax upon the convex face, and spreading the fused mass equally over it.
The instrument used for tracing the exposed lines should not be too hard; a pointed
piece of wood answers best. The removal of the wax coating is effected by heating, tn
glass gently, and wiping the wax off with a cloth.
140 RECAPITULATION AND REMARKS. [ 148.
with four parts of carbonate of soda and potassa. The fused mass is
treated with water, the solution filtered, the filtrate concentrated by evapo-
ration, allowed to cool, transferred to a platinum or silver vessel, hydro-
chloric acid added to feebly acid reaction, and the fluid allowed to stand
until the carbonic acid has escaped. It is then supersaturated with am-
monia, heated, filtered into a bottle, chloride of calcium added to the still
hot fluid, the bottle closed, and allowed to stand at rest. If a precipitate
separates after some time, it is collected on a filter, dried, and examined
by the method described in 5. (H. Rose.)
8. Minute quantities of metallic fluorides in minerals, slags, &c., may
also be readily detected by means of the blowpipe. To this end, bend a
piece of platinum foil, gutter-shape, then insert it in a glass tube as
shown in Fig. 29, introduce the finely
triturated substance mixed with pow-
dered phosphate of soda and ammonia
29. fused on charcoal, and let the blowpipe
flame play upon it in a manner to make
the product of combustion pass into the tube. If fluorides of metals are
present, hydrofluoric acid gas is evolved, which betrays its presence by
its pungent odor, the dimming of the glass tube, and the yellow tint
which the acid air issuing from the tube imparts to a moist slip
of Brazil-wood paper* (JBerzelius, Smitlison). When silicates containing
metallic fluorides are treated in this manner, gaseous fluoride of silicon
is formed, which also colors yellow a moist slip of Brazil-wood paper
inserted in the tube, and leads to silicic acid being deposited within the
tube. After washing and drying the tube, the latter appears here and
there dimmed. In the case of minerals containing water, presence of
even a small proportion of metallic fluorides will, upon heating, even
without addition of phosphate of soda and ammonia, usually suffice to
color yellow a moistened slip of Brazil-wood paper inserted in the tube
(Berzelius).
148.
Recapitulation and remarks. The baryta compounds of the acids of
the third division are dissolved by hydrochloric acid, apparently without
undergoing decomposition ; alkalies therefore reprecipitate them un-
altered, by neutralizing the hydrochloric acid. The baryta compounds
of arsenious acid, arsenic acid, and chromic acid show, however, the
(same deportment ; these acids must, therefore, if present, be removed
before any conclusion regarding the presence of phosphoric acid, boracic
acid, oxalic acid, or hydrofluoric acid, can be drawn from the reprecipi-
tation of a salt of baryta by alkalies. But even leaving this point alto-
gether out of the question, no great value is to be placed on this reaction,
not even so far as the simple detection of these acids is concerned, and
far less still as regards their separation from other acids, since ammonia
fails to reprecipitate from hydrochloric acid solutions the salts of baryta
in question, and more particularly the borate of baryta and the fluoride
of barium, if the solution contains any considerable proportion of free
acid or of an ammoniacal salt. Boracic acid may be invariably detected
by the characteristic tint which it communicates to the flame of alcohol,
provided care be taken to concentrate the solution sufficiently before
* Prepared by moistening slips of fine printing- paper with decoction of Brazil-wood.
148.] RECAPITULATION AND REMARKS. 141
adding the alcohol, and in the case of borates, to mix the solution with
a sufficient amount of concentrated sulphuric acid. Solutions of free
boracic acid must be combined with an alkali before evaporating, otherwise
a large portion of the acid will volatilize along with the aqueous vapors.
Minute traces of boracic acid are more safely detected by the method
given 145, 6.
The detection of phosplwric acid in compounds soluble in water is not
difficult ; the reaction with sulphate of magnesia is the best adapted to
effect the purpose. The detection of phosphoric acid in insoluble com-
pounds is somewhat more difficult ; but even here we have now some
excellent tests, in the reaction with sesquichloride of iron and acetate of
soda, and more particularly still in that with inolybdate of ammonia.
With regard to the former of these two tests, I repeat here once more,
that a sensitive reaction is not to be expected in a fluid colored red by
acetate of sesquioxide of iron, as the latter (as well as acetate of alumina)
dissolves phosphate of sesquioxide of iron ; the directions given in 143,
10, must therefore be strictly attended to. As regards the reaction with
molybdate of ammonia, I must not omit to remark that, on account of
its extraordinary sensitiveness, the greatest possible care and caution
must be observed in the application of the test ; not but we may almost
always or, at all events, in most cases (as arsenic acid shows the same
deportment) assume the yellow color of the solution or the forma-
tion of the yellow precipitate to indicate the presence of phosphoric acid ;
but that the reagent used may contain a trace of phosphoric acid, very
slight perhaps, yet sufficient to be brought to light by this most delicate
test ; the purity of the reagents used in the process must therefore
always be ascertained with the greatest care, otherwise it may happen
that the presence of phosphoric acid is erroneously assumed in a substance
simply because one or other of the reagents employed contained a trace
of that acid. It must also be borne in mind that the reaction is manifest
only in presence of an excess of molybdic acid. If this point is lost sight
of, the phosphoric acid may be readily overlooked in the very cases
where it is present in the largest proportion. Oxalic acid may always
be easily detected in aqueous solutions by solution of sulphate of lime.
The formation of a finely pulverulent precipitate, insoluble in acetic acid,
leaves hardly a doubt on the point, as racemic acid alone, which occurs
so very rarely, gives the same reaction. In case of doubt, the oxalate of
lime may be readily distinguished from the paratartrate, or racemate, by
simple ignition, with exclusion of the air, as the decomposed paratartrate
leaves a considerable proportion of charcoal behind ; the paratartrate dis-
solves moreover in cold solution of potassa or soda, in which oxalate of
lime is insoluble. The deportment of the oxalates with sulphuric acid,
or with binoxide of manganese and sulphuric acid, affords also sufficient
means to confirm the results of other tests. In insoluble salts the oxalic
acid is detected most safely by decomposing the insoluble compound by
boiling with solution of carbonate of soda. I must finally also call atten-
tion here to the fact that there are certain soluble oxalates which are not
precipitated by salts of lime ; these are more particularly oxalate of
sesquioxide of chromium, and oxalate of sesquioxide of iron. Their non-
precipitation is owing to the circumstance that these salts form soluble
double salts with oxalate of lime. In salts decomposable by sulphuric
acid, the hydrofluoric acid is readily detected ; only, it must be borne in
mind that the glass cannot be distinctly etched, if, instead of hydrofluoric
142 CARBONIC ACID. [ 149.
gas, fluosilicic gas alone is evolved ; and therefore, in the case of com-
pounds abounding in silica, the safer way is to try, besides the reaction
given 147, 5, also the one given in 147, 6. In silicates which are
not decomposed by sulphuric acid, the presence of fluorine is often over-
looked, because the analyst omits to examine the compound carefully by
the method given 147, 7.
Fourth Division of the First Group of the Inorganic Acids.
149.
a. CARBONIC ACID (C 2 ).
1. Carbon is a solid, tasteless, and inodorous body. The very highest
degrees of heat alone can effect its fusion and volatilization (Despretz).
Carbon is combustible, and yields carbonic acid when burnt with a suffi-
cient supply of oxygen or atmospheric air. In the diamond the carbon
is crystallized, transparent, exceedingly hard, difficultly combustible ; in
the form of graphite, it is opaque, blackish-gray, soft, greasy to the touch,
difficultly combustible, and stains the fingers ; as charcoal, produced by
the decomposition (destructive distillation) of organic matters, it is black,
opaque, noncrystalline often dense, shining, difficultly combustible
often porous, dull, readily combustible.
2. Carbonic acid, at the common temperature and common atmospheric
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 is almost
inodorous, has a sourish taste, and reddens moist litmus-paper ; but the
red tint disappears again upon drying. Carbonic acid is readily absorbed
by solution of potassa ; it dissolves pretty copiously in water.
3. The aqueous solution of carbonic acid has a feebly acid, pungent
taste ; it transiently imparts a red tint to litmus-paper, and colors solution
of litmus wine-red j it loses its carbonic acid upon the application of heat,
and also when shaken with air in a half-filled bottle. Part of the car-
bonates lose their carbonic acid upoa ignition ; those with colorless
oxides are white or colorless. Of the neutral carbonates, only those with
alkaline bases are soluble in water. The solutions manifest a very strong
alkaline reaction. Besides the carbonates with alkaline bases, those also
with an alkaline earth for base, and some of those with a metallic base,
dissolve as acid or bicarbonates.
4. The carbonates are decomposed by all free acids soluble in water,
with the exception of hydrocyanic acid and hydrosulphuric acid. The
decomposition of the carbonates by acids is attended with EFFERVES-
CENCE, the carbonic acid being disengaged as a colorless and almost
inodorous gas, which transiently imparts a reddish tint to litmus-paper.
It is necessary to apply the decomposing acid in excess, especially when
operating upon carbonates with alkaline bases, since the formation of
bicarbonates will frequently prevent effervescence, if too little of the
decomposing acid be added. Substances which it is intended to test for
carbonic acid by this method, should first be drenched with water, to
prevent any mistake which might arise from the escape of air-bubbles
upon treating the dry substances with the acid. If it is wished to deter-
mine by a direct experiment whether the disengaged gas is really car-
bonic acid or not, this may be readily accomplished by dipping the end
of a glass rod in baryta-water, and inserting the rod into the test-tube,
150.] SILICIC ACID. 143
bringing the moistened end near the surface of the fluid in the tube,
when ensuing turbidity of the baryta-water on the glass rod will prove
that the evolved gas is really carbonic acid, since
0. Lime-water and baryta-water, when brought into contact with
carbonic acid or with soluble carbonates, produce white precipitates of
neutral CARBONATE OF LIME (Ca 0, C 2 ), or neutral CARBONATE OP
BARYTA (Ba 0, C 2 ). When testing for free carbonic acid, the reagents
ought always to be added in excess, as the acid carbonates of the alka-
line earths are soluble in water. The precipitated carbonates of lime
and baryta dissolve in acids, with effervescence, and are not reprecipitated
from such solutions by ammonia, after the complete expulsion of the car-
bonic acid by ebullition.
6. Chloride of calcium and chloride of 'barium immediately produce in
solutions of neutral alkaline carbonates, precipitates of CARBONATE OF
LIME or of CARBONATE OF BARYTA ; in dilute solutions of bicarbonates
these precipitates are formed only upon ebullition ; with free carbonic
acid these reagents give no precipitate.
150.
b. SILICIC ACID (Si 2 ).
1. Silicic acid is colorless or white, even in the hottest blowpipe flame
unalterable and infusible. It fuses in the flame of the oxy hydrogen
blowpipe. It is met with in two modifications (more correctly speaking,
in the crystalline and in the amorphous state). It is insoluble in water
arid acids, with the exception of hydrofluoric acid ; whilst its hydrate is
soluble in acids, but only at the moment of its separation. The amor-
phous silicic acid and the hydrate dissolve in hot aqueous solutions of
caustic alkalies and of tixed alkaline carbonates ; but the crystallized
acid is insoluble or nearly so in these fluids. If either of the .two is
fused with pure alkalies or alkaline carbonates, a basic silicate of the
alkali is obtained, which is soluble in water, and from which acids again
separate hyd rated silicic acid. The silicates with alkaline bases alone
are soluble in water.
2. The solutions of the alkaline silicates are decomposed by all acids.
If a large proportion of hydrochloric acid is added at once to even con-
centrated solutions of alkaline silicates, the separated silicic acid remains
in solution ; but if the hydrochloric acid is added gradually drop by
drop, whilst stirring the fluid, the greater part of the silicic acid sepa-
rates as gelatinous hydrate. The more dilute the fluid, the more silicic
acid remains in solution, and in highly dilute solutions no precipitate is
formed. But if the solution of an alkaline silicate, mixed with hydro-
chloric or nitric acid in excess, is evaporated to dryness, silicic acid
separates in proportion as the acid escapes ; upon treating the residue
with hydrochloric acid and water, the silicic acid remains in the free
state (or, if the temperature in the process of drying was restricted ^ to
212, as hydrate, H 0, 4 Si O 2 ), as an insoluble white powder. Chloride
of ammonium produces in rather concentrated solutions of alkaline sili-
cates precipitates of hydrate of silicic acid.
3. Part of the silicates insoluble in water are decomposed by hydro-
chloric acid or nitric acid, part of them are not affected by these acids,
not even upon boiling. In the decomposition of the former, the greater
144 RECAPITULATION AND REMARKS. [ 151.
portion of the silicic acid separates usually as gelatinous, more rarely as
pulverulent hydrate. To effect the complete separation of the silicic
acid, the hydrochloric acid solution, with the precipitated hydrate of
silicic acid suspended in it, is evaporated to dryness, the residue heated at
a temperature above the boiling point of water until no more acid fumes
escape, then moistened with hydrochloric acid, heated with water, and
the fluid containing the bases filtered from the residuary insoluble
silicic acid.
4. Of the silicates not decomposed by hydrochloric acid, many, e. g.,
kaolin, are completely decomposed by heating with hydrated sulphuric
acid, the decomposition being attended with separation of silicic acid in
the pulverulent form ; many others are acted upon to some extent by
this reagent.
5. If any silicate, reduced to a fine powder, is fused with 4 parts of
carbonate of potassa and soda until the evolution of carbonic acid has
ceased, and the fused mass is then boiled with water, the greater por-
tion of the silicic acid dissolves as alkaline silicate, whilst the alkaline
earths, the earths proper, and the heavy metallic oxides are left un dis-
solved. If the fused mass is treated with water, then, without previous
filtration, hydrochloric or nitric acid added to strongly acid reaction,
and the fluid treated as directed in 3, the silicic acid is left undis-
solved, whilst the bases are dissolved. If the powdered silicate is fused
with 4 parts of hydrate of baryta, the fused mass digested with water,
with addition of hydrochloric or nitric acid, and the acid solution treated
as directed in 3, the silicic acid separates, and the bases, especially the
alkalies, are found in the filtrate.
6. If hydrofluoric acid, in aqueous solution or in the gaseous state, is
made to act upon finely pulverized silicates, fluosilicic gas escapes, and the
bases are converted into silicofluorides, which upon heating with hydrated
sulphuric acid change to sulphates, with evolution of fluosilicic gas. If
the powdered silicate is mixed with 5 parts of fluoride of calcium in
powder, the mixture made into a paste with hydrated sulphuric acid,
and heat applied (best in the open air), until no more fumes escape, the
whole of the silicic acid present volatilizes as fluosilicic gas. The bases
present are found in the residue as sulphates, mixed with sulphate
of lime.
7. If silicic acid or a silicate is fused with carbonate of soda on the
loop of a platinum wire, a frothing is observed in the fusing bead, owing
to the disengagement of carbonic acid. If the proper proportion of car-
bonate of soda is not exceeded, the bead of silicate of soda formed in
the process will remain transparent on cooling.
8. Phosphate of soda and ammonia, in a state of fusion, fails nearly
altogether to dissolve silicic acid. If therefore silicic acid or a silicate is
fused, in small fragments, with phosphate of soda and ammonia on a pla-
tinum wire, the bases are dissolved, whilst the silicic acid separates and
floats about in the clear bead, as a more or less transparent mass, exhi-
biting the shape of the fragment used in the experiment.
151.
Recapitulation and remarks. Free carbonic acid is readily known by
its deportment with lime-water ; the carbonates are easily detected by
the evolution of a nearly inodorous gas, which takes place when they
152.] HYDROCHLORIC ACID. 145
are treated with acids. When operating upon compounds which,
besides carbonic acid, evolve other gases, the disengaged gas is to be
tested with lime-water or baryta-water. Silicic acid, both in the free
state and in silicates, may usually be readily detected by the reaction
with phosphate of soda and ammonia. It differs moreover from all other
bodies in the form in which it is always obtained in analyses, by its
insolubility in acids (except hydrofluoric acid), and its solubility in
boiling solutions of pure alkalies and alkaline carbonates.
SECOND GROUP OF THE INORGANIC ACIDS.
ACIDS WHICH ARE PRECIPITATED BY NlTRATE OF SlLVER, BUT NOT BY
CHLORIDE OF BARIUM : Hydrochloric Acid, Hydrobromic Acid, Hy-
driodic Acid, Hydrocyanic Acid, Hydroferro- and Hydroferricyanic
Acid, Hydrosulphuric Acid.
152.
The silver compounds corresponding to the acids of this group are in-
soluble in dilute nitric acid. The acids of this group decompose with
metallic oxides, the metals combining with the chlorine, bromine,
cyanogen, iodine, or sulphur, whilst the oxygen of the metallic oxide
forms water with the hydrogen of the hydracid.
a. HYDROCHLORIC ACID (H Cl).
1. Chlorine is a heavy, yellowish-green gas of a disagreeable, suffo-
cating odor, and which has a most injurious action upon the respiratory
organs; it destroys vegetable colors (litmus, indigo-blue, &c.); it is in-
combustible, and supports the combustion of few bodies only. Minutely-
divided antimony, tin, &c., spontaneously ignite in it, being converted
into chlorides. It dissolves pretty largely in water j the chlorine water
formed has a faint yellowish-green color, smells strongly of the gas,
bleaches vegetable colors, is decomposed by the action of light ( 25),
and loses its odor when shaken with mercury ; in this process the latter
is converted into a mixture of subchloride and metallic mercury. Small
quantities of chlorine may be readily detected in a fluid, by adding the
latter to a solution of pure protoxide of iron, mixed with sulphocyanide
of potassium : the solution is at once colored red by the action of the free
chlorine ; or, in the absence of nitric acid, by adding the fluid to a dilute
solution of iodide of potassium, mixed with starch-paste. (See 154, 9.)
2. Hydrochloric acid, at the common temperature and common atmo-
spheric pressure, is a colorless gas, which forms dense fumes in the air,
is suffocating and very irritant, and dissolves in water with exceeding
facility. The more concentrated solution (fuming hydrochloric acid)
loses a large portion of its gas upon heating.
3. The neutral metallic chlorides are readily soluble in water, with
the exception of chloride of lead, chloride of silver, and subchloride of
mercury ; most of the chlorides are white or colorless. Many of them
volatilize at a high temperature, without suffering decomposition ; others
are decomposed upon ignition, and many of them are fixed.
4. Nitrate of silver produces in even highly dilute solutions of free
hydrochloric acid or of metallic chlorides white precipitates of CHLORIDE
OF SILVER (Ag Cl), which upon exposure to light change first to violet,
then to black ; they are insoluble in nitric acid, but dissolve readily in
i. L
146 HYDROBROMIC ACID. [ 153.
ammonia, as well as in cyanide of potassium, and fuse without decompo-
sition, when heated. (Compare 114, 7).
5. Nitrate of suboxide of mercury and acetate of lead produce in solu-
tions containing free hydrochloric acid or metallic chlorides precipitates
of SUBCHLORIDE OF MERCURY (Hg a 01) and CHLORIDE OF LEAD (Pb Cl).
For the properties of these precipitates see 115, 6, and 116, 7.
6. If hydrochloric acid is heated with binoxide of manganese, or a
chloride with binoxide of manganese and sulphuric acid, chlorine gas is
evolved, which may be readily recognised by its odor and YELLOWISH-
GREEN color.
7. If a metallic chloride is triturated together with ckromate of
potassa, the mixture treated with concentrated sulphuric acid, in a tubu-
lated retort, and a gentle heat applied, a deep brownish-red gas is copiously
evolved (BICHROMATE OF TERCHLORIDE OF CHROMIUM, Cr C1 3 , 2 Cr O 8 ),
which condenses into a fluid of the same color, and passes over into the
receiver. If this chromate of terchloride of chromium is mixed with
ammonia in excess, a yellow-colored liquid is produced ; the yellow tint
is imparted to the fluid by the chromate of ammonia which forms in
this process; upon the addition of an acid, the color of the solution
changes to a reddish-yellow, owing to the formation of acid chromate of
ammonia.
8. In the metallic chlorides insoluble in water and nitric acid, the
chlorine is detected by fusing them with carbonate of soda and potassa,
and treating the fused mass with water, which will dissolve, besides the
excess of the alkaline carbonate, the chloride of the alkali metal formed
in the process of fusion.
9. If in a bead of phosphate of soda and ammonia on a platinum wire,
oxide of copper be dissolved in the outer blowpipe flame in sufficient
quantity to make the mass nearly opaque, a trace of a substance contain-
ing chlorine added to it while still in fusion, and the bead then exposed
to the reducing flame, a fine BLUE-COLORED flame, inclining to PURPLE,
will be seen encircling it so long as chlorine is present (Berzelius).
153.
b. HYDROBROMIC ACID (H Br).
1. Bromine is a heavy, reddish -brown fluid, of a very disagreeable chlo-
rine-like odor ; it boils at 11 6'6 F., and volatilizes rapidly even at the
common temperature. The vapor of bromine is brownish-red. Bromine
bleaches vegetable colors like chlorine ; it is rather difficultly soluble in
water, but dissolves more easily in alcohol, and very readily in ether.
The solutions are yellowish-red.
2. Hydrobromic acid gas, its aqueous solution, and the metallic
bromides offer in their general deportment a great analogy to the cor-
responding chlorides.
3. Nitrate of silti& produces in aqueous solutions of hydrobromic acid
or of bromides a yellowish-white precipitate of BROMIDE OF SILVER
(Ag Br), which changes to violet upon exposure to light ; this preci-
pitate is insoluble in nitric acid, and somewhat difficultly soluble in
ammonia, but dissolves with facility in cyanide of potassium.
4. Nitrate of protoxide of palladium, but not protochloride of palla-
dium, produces in neutral solutions of metallic bromides a reddish-brown
153.] HYDllOBROMIC ACID. 147
precipitate of PROTOBROMIDE OF PALLADIUM (Pd Br). In concentrated
solutions this precipitate is formed immediately, in dilute solutions it
makes its appearance only after standing some time.
5. Nitric acid decomposes hydrobromic acid and the bromides, with
the exception of bromide of silver and bromide of mercury, upon the
application of heat, and liberates the bromine, by oxidizing the hydrogen
or the metal. The liberated bromine colors the solution yellowish-red.
When operating upon bromides in the solid state, brownish-red (if diluted,
yellowish-red) vapors of bromine gas escape, emitting the odor of bromine ;
these vapors, when evolved in sufficient quantity, condense in the cold
part of the test-tube to small drops. In the cold, even red fuming
nitric acid fails to liberate the bromine contained in rather dilute
solutions of metallic bromides.
6. Chlorine, in the gaseous state or in solution, immediately liberates
bromine in the solutions of its compounds; the fluid assuming a yellowish-
red tint, if the quantity of the bromine present is not too minute. If a
solution of this kind is shaken together with some ether, it loses its
yellow color, the whole of the bromine present dissolving in the ether,
which appears now distinctly yellow, even though but a very minute
quantity of bromine be present. If the ethereal solution of bromine is
mixed with some solution of potassa, and the mixture shaken, the yellow
tint disappears again, and the solution now contains bromide of potas-
sium and bromate of potassa. Upon evaporation and subsequent igni-
tion of the residue, the bromate of potassa is converted into bromide of
potassium, and the ignited mass may then be further tested as directed
in 7. A large excess of chlorine must be avoided in this experiment,
as chlorine water of a certain degree of concentration, when shaken with
ether, always imparts a faint yellow tint to it.
7. Tf bromides are heated with binoxide of manganese and concentrated
sulphuric acid, BROWNISH-RED VAPORS OF BROMINE are evolved. If the
bromine is present only in very minute quantity, the color of these
vapors is not visible. The experiment should, in that case, be con-
ducted in a small retort, and the evolved vapors transmitted through a
long glass condenser, and finally received into small test-tubes, contain-
ing some starch moistened with water ; ^ince
8. If moistened starch is brought into contact with free bromine, no
matter whether in solution or in the gaseous state, YELLOW BROMIDE OF
STARCH is formed. The coloration is not always instantaneous. The re-
action is rendered most delicate by hermetically sealing the test-tube
which contains the moistened starch and the fluid under examination,
and then inverting it, so as to cause the moist starch to occupy the
upper part of the tube whilst the fluid occupies 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 some time, will again disappear.
9. If sulphuric acid is poured over a mixture of a bromide with chro-
mate of potassa, and heat is then applied, a brownish-red gas is evolved,
exactly as in the case of chlorides. But this gas consists of pure BRO-
MINE, and therefore the fluid passing over does not turn yellow, but
becomes colorless, upon supersaturation with ammonia.
10. In the metallic bromides which are insoluble in water and nitric
acid, the bromine is detected in the same way as the chlorine in the
corresponding chlorides.
L 2
148 HYDRIODIC ACID. [ 154.
11. A. phosphate of soda and ammonia bead saturated with oxide of
copper, mixed with a substance containing bromine, and then ignited in
the inner blowpipe flame, colors the flame BLUE, inclining to GREEN, more
particularly at the edges (Berzelius).
154.
c. HYDRIODIC ACID (H I).
1. Iodine is a solid, soft body, of a peculiarly disagreeable odor. It
is generally seen in the form of black, shining, crystalline scales. It fuses
at a gentle heat ; at a somewhat higher temperature, it is converted into
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 and ether ; the aqueous solution is of a light-
brown, the alcoholic and ethereal solutions are a deep red-brown color.
Iodine destroys vegetable colors only slowly and imperfectly ; it stains the
skin brown ; with starch it forms a compound of an intensely deep blue
color. This compound is formed invariably when iodine vapor or a
solution containing free iodine comes in contact with starch, best with
starch-paste. It is decomposed by alkalies, and also by chlorine and
bromine.
2. Hydriodic acid gas resembles hydrochloric and hydrobromic acid
gas ; it dissolves copiously in water. The colorless hydrated hydriodic
acid turns speedily to a reddish-brown when in contact with the air,
owing to the formation of water, and a solution of iodine in hydriodic
acid.
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 corresponding chlorides. Many iodides
have characteristic colors.
4. Nitrate of silver produces in aqueous solutions of hydriodic acid and
of iodides yellowish-white precipitates of IODIDE OF SILVER (Ag I), which
blacken on exposure to light ; these precipitates are insoluble in dilute
nitric acid, and very sparingly soluble in ammonia, but dissolve readily in
cyanide of potassium.
o. Protochloride of palladium and nitrate of protoxide of palladium
produce even in very dilute solutions of hydriodic acid or metallic iodides
a brownish-black precipitate of PROTIODIDE OF PALLADIUM, which dissolves
to a trifling extent in saline solutions (solution of chloride of sodium,
chloride of magnesium, (fee.), but is insoluble or nearly so in dilute cold
hydrochloric and nitric acids.
6. A solution of 1 part of sulphate of oxide of copper and 2ty parts of
sulphate of protoxide of iron throws down from neutral aqueous solu-
tions of the iodides SUBIODIDE OF COPPER (Cu 2 I), in the form of a dirty-
white precipitate. The addition of ammonia promotes the complete
precipitation of the iodine. Chlorides and bromides are not precipi-
tated by this reagent.
7. Pure nitric acid, free from nitrous acid, decomposes hydriodic acid
or iodides only when acting upon them in its concentrated form, particu-
larly when aided by the application of heat. But nitrous acid and hypo-
nitric acid decompose hydriodic acid and iodides with the greatest
facility even in the most dilute solutions. Colorless solutions of iodides
f154] HYDRIODIC ACID. 149
therefore acquire immediately a brownish-red color, upon addition of some
red-fuming nitric acid, or a mixture of this with concentrated sulphuric
acid or, better still, a solution of hyponitric acid in hydrated sul-
phuric acid or nitrite of potassa and some sulphuric or hydrochloric
acid. From more concentrated solutions the iodine separates under
these circumstances in the form of small black plates or scales, whilst
nitric oxide gas and iodine vapors escape.
8. As the blue coloration of iodide of starch remains still visible in
much more highly dilute solutions than the yellow color of solutions of
iodine in water, the delicacy of the reaction just now described (7) is
considerably heightened by mixing the fluid to be tested for iodine first
with some thin, clear starch-paste, then adding one or two drops of
dilute sulphuric acid, to make the fluid acid, and adding finally one or
the other of the reagents given in 7. Of the solution of hyponitric acid
in sulphuric acid a single drop on a glass rod suffices to produce the reac-
tion most distinctly. I can therefore strongly recommend this reagent,
which was first proposed by Otto. Red fuming nitric acid must be added
in somewhat larger quantity, to call forth the reaction in its highest in-
tensity ; this reagent therefore is not well adapted to detect very minute
quantities of iodine. The reaction with nitrite of potassa also 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 nitrite of potassa is then added. In cases
where the quantity of iodine present is very minute, the fluid turns
reddish, instead of blue. An excess of the fluid containing nitrous acid
or hyponitric acid does not materially impair the delicacy of the reac-
tion. As iodide of starch dissolves in hot water to a colorless liquid,
the fluids must of necessity be cold ; the colder they are, the more deli-
cate the reaction.
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 colorless chloride of iodine. A dilute
solution of a metallic iodide, mixed with starch-paste, acquires therefore
upon addition of a little chlorine water at once a blue tint, but becomes
colorless again upon addition of more chlorine water. As it is therefore
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 in which iodine has been set free by nitrous acid,
chlorine, &c., is mixed with ether, and the mixture shaken, the ether
dissolves the liberated iodine, and acquires thereby a reddish-brown or
yellow color. The color imparted to the ether by iodine is much more
intense than that imparted to that fluid by an equal quantity of bromine.
If the solution is mixed with some chloroform or bisulphide of^ carbon,
and the mixture shaken, leaving a few drops of the reagent undissolved,
thpse will subside to the bottom of the fluid, exhibiting a lighter or darker
xed color. This reaction also is very delicate.
11. If metallic iodides are heated with concentrated sulphuric acid ,
or with sulphuric acid and binoxide of manganese, or with sulphuric acid
and chromate of potassa, iodine separates, which may be known by the
color of its vapor and, in the case of very minute quantities, also by its
action upon a slip of paper coated with starch-paste.
12. Tne iodides which are insoluble in water and nitric acid comport
150 HYDROCYANIC ACID. [ 155.
themselves upon fusion with carbonate of soda and potassa in the same
manner as the corresponding chlorides.
13. A phosphate of soda and ammonia bead, saturated with oxide of
copper, when mixed with a substance containing iodine, and ignited
in the inner blowpipe flame, impairs an intense GREEN color to the
flame.
155.
d. HYDROCYANIC ACID (H Cy).
1. Cyanogen is a colorless gas of a peculiar, penetrating odor ; it burns
with a crimson flame, and is pretty soluble in water.
2. Hydrocyanic acid is a colorless, volatile, inflammable liquid, the
odor of which resembles that of bitter almonds ; it is miscible with
water in all proportions ; in the pure state it speedily suffers decom-
position. It is extremely poisonous.
3. The cyanides with alkalies and alkaline earths are soluble in water ;
the solutions smell of hydrocyanic acid. They are readily decomposed
by acids, even by carbonic acid ; but ignition fails to decompose them,
if the access of air is precluded. When fused with oxides of lead,
copper, antimony, tin, &c., the cyanides reduce these oxides, and are
converted into cyanates. Only a few of the cyanides with heavy metals
are soluble in water ; all of them are decomposed upon ignition, the
cyanides of the noble metals being converted into cyanogen gas and
metal, the cyanides of the other heavy metals into nitrogen gas and
metallic carbides. Many of the cyanides with heavy metals are not
decomposed by dilute oxygen acids, and only with difficulty by concen-
trated nitric acid. But hydrochloric acid and hydrosulphuric acid de-
compose most of them readily and completely.
4. The cyanides have a great tendency to combine with each other ;
hence most of the cyanides of the heavy metals dissolve in cyanide of
potassium. The resulting compounds are either :
a. True double salts, compounds of the second class, e.g., K Cy + Ni Cy.
From solutions of such double salts, acids, by decomposing the cyanide
of potassium, precipitate the metallic cyanide which was combined with
it. Or they are :
b. Simple haloid salts, compounds of the first class, in which a
metal, e. (/., potassium, is combined with a compound radical consisting
of cyanogen and another metal (iron, cobalt, manganese, chromium).
Compounds of this kind are the ferro- and ferricyaiiide of potassium,
K 2 Cy, Fe or K 2 Cfy, and K g Cy 6 Fe 2 or K 3 Cfdy, cobalticyanide of potas-
sium, K 3 Cy 6 Co 2 , &c. From solutions of compounds of this nature dilute
acids do not separate metallic cyanides in the cold. If the potassium is
replaced by hydrogen, peculiar hydracids are formed, which must not be
confounded with hydrocyanic acid.
We will now first consider the reaction of hydrocyanic acid and the
simple cyanides, then, in an appendix to this paragraph, those of hydro-
ferro- and hydroferricyauic acid.
5. Nitrate of silver produces in solutions of free hydrocyanic acid and
of cyanides of the alkali metals white precipitates of CYANIDE OF SILVER
(Ag Cy), which are readily soluble in cyanide of potassium, dissolve with
some difficulty in ammonia, and are insoluble in nitric acid j these pre-
155.] HYDROCYANIC ACID. 151
cipitates are decomposed upon ignition, leaving metallic silver with some
paracyanide of silver.
6. If solution of sulphate of protoxide of iron which has been for some
time in contact with the air is added to a solution of free hydrocyanic
acid, no alteration takes place ; but if solution ofpotassa or soda is now
added, a bluish -green precipitate forms, which consists of a mixture of
Prussian-blue (Fe 4 Cfy 3 ), and hydrate of protosesquioxide of iron. Upon
now adding hydrochloric acid (best after previous application of heat),
the hydrate of protosesquioxide of iron dissolves, whilst the PRUSSIAN-
BLUE remains undissolved. If only a very minute quantity of hydro-
cyanic 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 reactions are observed
when sulphate of protoxide of iron is added to the solution of an alkaline
cyanide.
7. If a liquid containing a small quantity of hydrocyanic acid or
cyanide of potassium is mixed with a small quantity (one or two drops)
of yellow sulphide of ammonium and a trace of ammonia, and the mix-
ture warmed in a porcelain dish until it has become colorless, sulpho-
cyanide of ammonium is formed, arid the fluid, after being acidified with
hydrochloric acid, acquires a blood-red tint upon addition of sesqui-
chloride of iron (Liebig). This reaction is exceedingly delicate. The
following formula expresses the transformation of hydrocyanic acid into
sulphocyanide of ammonium : N H 4 , S 6 + 2 (N H 4 , O) + 2 H Oy =
2 (N Hj Cy S a ) + N H 4 , S + 2 H O. If an acetate is present, the re-
action takes place only upon addition of more hydrochloric acid.
8. Neither of the above methods will serve to effect the detection of
cyanogen in cyanide of mercury. To detect cyanogen in that com-
pound, the solution is mixed with hydrosulphuric acid : sulphide of mer-
cury precipitates, and the solution contains free hydrocyanic acid. In
solid cyanide of mercury the cyanogen is most readily detected by heat-
ing in a glass tube. Compare 3.
Appendix.
a. Hydroferrocyanic acid (2 H Cfy). Hydroferrocyanic acid is solu-
ble in water. In solutions of this acid or of soluble ferrocyanides, ses-
quichloride of iron produces a blue precipitate of FERROCYANIDE OF IRON
(Fe 4 Cfy,) ; sulphate of oxide of copper, a brownish-red precipitate of
FERROCYANIDE OF COPPER (Cu a Cfy) ; nitrate of silver, a white precipi-
tate of FERROCYANIDE OF SILVER (Ag a Cfy), which is insoluble in nitric
acid and in ammonia, but dissolves in cyanide of potassium. Insoluble
ferrocyanides of metals are decomposed by boiling with solution of soda,
ferrocyanide of sodium being formed and the oxides thrown down. When
heated with 3 parts of sulphate and 1 part of nitrate of ammonia, they
yield sulphates of the metals contained in them, the whole of the cyanogen
volatilizing in form of cyanide of ammonium and the products of its
decomposition (Bolley).
b. Hydroferricyanic acid. In the aqueous solutions of hydrofern-
cyanic acid and its salts, sesquichloride of iron produces no blue precipitate;
but sulphate of protoxide of iron produces a blue precipitate of PROTO-
FERRICYANIDE OF IRON (3 Fe, Cfdy) ; sulphate of copper, a yellowish-green
precipitate of FERRICYANIDE OF COPPER (3 Cu, Cfdy), which is insoluble
150 HYDROCYANIC ACID. [ 155.
themselves upon fusion with carbonate of soda and potassa in the same
manner as the corresponding chlorides.
13. A phosphate of soda and ammonia bead, saturated with oxide of
copper, when mixed with a substance containing iodine, and ignited
in the inner blowpipe flame, imparts an intense GREEN color to the
flame.
155.
d. HYDROCYANIC ACID (H Cy).
1. Cyanogen is a colorless gas of a peculiar, penetrating odor ; it burns
with a crimson flame, and is pretty soluble in water.
2. Hydrocyanic acid is a colorless, volatile, inflammable liquid, the
odor of which resembles that of bitter almonds ; it is miscible with
water in all proportions ; in the pure state it speedily suffers decom-
position. It is extremely poisonous.
3. The cyanides with alkalies and alkaline earths are soluble in water ;
the solutions smell of hydrocyanic acid. They are readily decomposed
by acids, even by carbonic acid ; but ignition fails to decompose them,
if the access of air is precluded. When fused with oxides of lead,
copper, antimony, tin, &c., the cyanides reduce these oxides, and are
converted into cyanates. Only a few of the cyanides with heavy metals
are soluble in water ; all of them are decomposed upon ignition, the
cyanides of the noble metals being converted into cyanogen gas and
metal, the cyanides of the other heavy metals into nitrogen gas and
metallic carbides. Many of the cyanides with heavy metals are not
decomposed by dilute oxygen acids, and only with difficulty by concen-
trated nitric acid. But hydrochloric acid and hydrosulphuric acid de-
compose most of them readily and completely.
4. The cyanides have a great tendency to combine with each other ;
hence most of the cyanides of the heavy metals dissolve in cyanide of
potassium. The resulting compounds are either :
a. True double salts, compounds of the second class, e.g., K Cy + Ni Cy.
From solutions of such double salts, acids, by decomposing the cyanide
of potassium, precipitate the metallic cyanide which was combined with
it. Or they are :
b. {Simple haloid salts, compounds of the first class, in which a
metal, e. y., potassium, is combined with a compound radical consisting
of cyanogen and another metal (iron, cobalt, manganese, chromium).
Compounds of this kind are the ferro- and ferricyaiiide of potassium,
K 2 Cy 3 Fe or K 2 Cfy, and K 8 Cy 6 Fe 2 or K 3 Cfdy, cobalticyanide of potas-
sium, K 3 Cy 6 Co a , &c. From solutions of compounds of this nature dilute
acids do not separate metallic cyanides in the cold. If the potassium is
replaced by hydrogen, peculiar hydracids are formed, which must not be
confounded with hydrocyanic acid.
We will now first consider the reaction of hydrocyanic acid and the
simple cyanides, then, in an appendix to this paragraph, those of hydro-
ferro- and hydroferricyanic acid.
5. Nitrate of silver produces in solutions of free hydrocyanic acid and
of cyanides of the alkali metals white precipitates of CYANIDE OF SILVER
(Ag Cy), which are readily soluble in cyanide of potassium, dissolve with
some difficulty in ammonia, and are insoluble in nitric acid j these pre-
155.] HYDROCYANIC ACID. 151
cipitates are decomposed upon ignition, leaving metallic silver with some
paracyanide of silver.
6. If solution of sulphate of protoxide of iron which has been for some
time in contact with the air is added to a solution of free hydrocyanic
acid, no alteration takes place ; but if solution ofpotassa or soda is now
added, a bluish -green precipitate forms, which consists of a mixture of
Prussian-blue (Fe 4 Cfy 3 ), and hydrate of protosesquioxide of iron. Upon
now adding hydrochloric acid (best after previous application of heat),
the hydrate of protosesquioxide of iron dissolves, whilst the PRUSSIAN-
BLUE remains undissolved. If only a very minute quantity of hydro-
cyanic acid is present, the fluid simply appears green alter the addition
of the hydrochloric acid, and it is only after long standing that a trifling
blue precipitate separates from it. The same reactions are observed
when sulphate of protoxide of iron is added to the solution of an alkaline
cyanide.
7. If a liquid containing a small quantity of hydrocyanic acid or
cyanide of potassium is mixed with a small quantity (one or two drops)
of yellow sulphide of ammonium and a trace of ammonia, and the mix-
ture warmed in a porcelain dish until it has become colorless, sulpho-
cyanide of ammonium is formed, arid the fluid, after being acidified with
hydrochloric acid, acquires a blood-red tint upon addition of sesqui-
chloride of iron (Liebig). This reaction is exceedingly delicate. The
following formula expresses the transformation of hydrocyanic acid into
sulphocyanide of ammonium : N H 4 , S 6 + 2 (N H 4 , O) + 2 H Cy =
2 (N Hj Cy S 2 ) + N H 4 , S + 2 H 0. If an acetate is present, the re-
action takes place only upon addition of more hydrochloric acid.
8. Neither of the above methods will serve to effect the detection of
cyanogen in cyanide of mercury. To detect cyanogen in that com-
pound, the solution is mixed with hydrosulphuric acid : sulphide of mer-
cury precipitates, and the solution contains free hydrocyanic acid. In
solid cyanide of mercury the cyanogen is most readily detected by heat-
ing in a glass tube. Compare 3.
Appendix.
a. Hydroferrocyanic acid (2 H Cfy). Hydroferrocyanic acid is solu-
ble in water. In solutions of this acid or of soluble ferrocyanides, ses-
quichloride of iron produces a blue precipitate of FERROCYANIDE OF IRON
(Fe 4 Cfy ) ; sulphate of oxide of copper, a brownish-red precipitate of
FERROCYANIDE OF COPPER (Cu a Cfy) ; nitrate of silver, a white precipi-
tate of FERROCYANIDE OF SILVER (Ag a Cfy), which is insoluble in nitric
acid and in ammonia, but dissolves in cyanide of potassium. Insoluble
ferrocyanides of metals are decomposed by boiling with solution of soda,
ferrocyanide of sodium being formed and the oxides thrown down. When
heated with 3 parts of sulphate and 1 part of nitrate of ammonia, they
yield sulphates of the metals contained in them, the whole of the cyanogen
volatilizing in form of cyanide of ammonium arid the products of its
decomposition (Bolley\ .
b. Hydroferricyanic acid. In the aqueous solutions of hydrofern-
cyanic acid and its salts, sesquichloride of iron produces no blue precipitate ;
but sulphate of protoxide of iron produces a blue precipitate of PROTO-
FERRICYANIDE OF IRON (3 Fe, Cfdy) ; sulphate of copper, a yellowish-green
precipitate of FERRICYANIDE OF COPPER (3 Cu, Cfdy), which is insoluble
152 HYDROSULPHURIC ACID. [ 156.
in hydrochloric acid ; nitrate of silver, an orange -colored precipitate of
FERRICYANIDE OF SILVER (3 Ag, Cfdy), which is insoluble in nitric acid,
but dissolves readily in ammonia and in cyanide of potassium. The in-
soluble ferri cyanides of metals are decomposed by boiling with solution
of soda, the metallic oxides being thrown down ; in the fluid filtered off
from them, either ferrocyanide of sodium alone is found, or a mixture of
ferro- with ferricyanide of sodium. By heating with sulphate and nitrate
of ammonia the ferricyanides are decomposed the same as the ferrocyanides.
156.
e. HYDROSULPHURIC ACID (H S).
Sulphuretted Hydrogen.
1. Sulphur is a solid, brittle, friable, tasteless body, insoluble in water.
It occurs occasionally in the form of yellow or brownish crystals, or
crystalline masses of a yellow or brownish color, and occasionally in that
of a yellow or yellowish- white or grayish- white powder. It melts at a mo-
derate heat ; upon the application of a stronger heat it is converted into
brownish-yellow vapors, which, in cold air, condense to a yellow powder,
and on the sides of the vessel, to drops. Heated in the air, it burns
with bluish flame to sulphurous acid, which betrays its presence in the
air at once by its suffocating odor. Concentrated nitric acid, nitrohydro-
chloric acid, and a mixture of chlorate of potassa and hydrochloric acid
dissolve sulphur gradually, with the aid of a moderate heat, and 'con vert
it into sulphuric acid ; in boiling solution of soda sulphur dissolves to a
yellow fluid, which contains sulphide of sodium and hyposulphite of
soda ; in ammonia sulphur is insoluble.
2. Hydrosulphuric acid, at the common temperature and under
common atmospheric pressure, is a colorless, inflammable gas, soluble in
water, and which may be readily recognised by its characteristic smell of
rotten eggs ; it transiently imparts a red tint to litmus paper.
3. Of the sulphides only those with alkalies and alkaline earths are
soluble in water. These, and the sulphides of iron, manganese, and zinc,
are decomposed by dilute mineral acids, with evolution of hydrosulphuric
acid gas, which may be readily detected by its peculiar smell, and by its
action upon solution of lead (see 4). The decomposition of higher sul-
phides is attended also with separation of sulphur in a finely-divided
state ; the white precipitate may be readily distinguished from similar
precipitates by its deportment on heating. Part of the sulphides of the
metals of the fifth and sixth groups are decomposed by concentrated and
boiling hydrochloric acid, with evolution of hydrosulphuric acid gas,
whilst others are not dissolved by hydrochloric acid, but by concen-
trated and boiling nitric acid. The compounds of sulphur with mer-
cury resist the action of both acids, but dissolve readily in nitrohydro-
chloric acid. Upon the solution of sulphides in nitric acid, and in
nitrohydrochloric acid, sulphuric acid is formed, and the process of
solution is moreover attended, in most cases, with separation of sulphur,
which is readily recognised by its color and by its deportment upon
heating. Many metallic sulphides, more especially of a higher degree
of sulphuration, give a sublimate of sulphur when heated in a test-tube.
4. If hydrosulphuric acid, in the gaseous state or in solution, is brought
into contact with nitrate of silver or acetate of lead, black precipitates of
157.] RECAPITULATION AND REMARKS. 153
SULPHIDE OF SILVER or SULPHIDE OF LEAD are formed (see 114 and
116). In cases therefore where the odor of the gas fails to afford suffi-
cient proof of the presence of hydrosulphuric acid, these reagents will
remove all doubt. If the hydrosulphuric acid is present in the gaseous
form, the air suspected to contain it is tested by placing in it a small
slip of paper moistened with solution of neutral acetate of lead and a
little ammonia ; if the gas is present, the slip becomes covered with a
thin, brownish-black, shining film of sulphide of lead. To detect a trace
of an alkaline sulphide in presence of a free alkali or an alkaline car-
bonate, the best way is to mix the fluid with a solution of oxide of lead
in solution of soda, which is prepared by mixing solution of acetate of
lead with solution of soda until the precipitate which forms at first is
redissolved.
5. If a fluid containing hydrosulphuric acid or an alkaline sulphide is
mixed with solution of soda, then with nitroprusside of sodium* it ac-
quires a fine reddish-violet tint. The reaction is very delicate ; but that
with solution of oxide of lead in solution of soda is still more sensitive.
6. If metallic sulphides are exposed to the oxidizing flame of the
blowpipe, the sulphur burns with a blue flame, emitting at the same time
the well-known odor of sulphurous acid. If a metallic sulphide is heated
in a glass tube open at both ends, in the upper part of which a slip of
blue litmus paper is inserted, and the tube is held in a slanting position
during the operation, the escaping sulphurous acid reddens the litmus
paper.
7. If a finely-pulverized metallic sulphide is boiled in a porcelain dish
with solution of potassa, and the mixture heated to incipient fusion of
the hydrate of potassa, or if the test specimen is fused in a platinum
spoon with hydrate of potassa, 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 warmed, a brownish-black film of sulphide of silver
forms on the metal. This film may be removed afterwards by rubbing
the metal with leather and quicklime (v. Kobell).
157.
Recapitulation and remarks. Most of the acids of the first group are
also precipitated by nitrate of silver, but the precipitates cannot well be
confounded with the silver compounds of the acids of the second group,
since the former are soluble in dilute nitric acid, whilst the latter are
insoluble in that menstruum. The presence of hydrosulphuric acid
interferes more or less with the testing for the other acids of the second
group ; this acid must therefore, if present, be removed first before the
testing for the other acids can be proceeded with. The removal of the
hydrosulphuric acid, when present in the free state, may be effected by-
simple ebullition ; and when present in the form of an alkaline sulphide,
by the addition of a metallic salt, such as will not precipitate any of the
other acids, or at least will not precipitate them from acid solutions.
Hydriodic and hydrocyanic acids may be detected, even in presence of
hydrochloric or hydrobromic acid, by the equally characteristic arid deli-
cate reactions with starch (with addition of a fluid containing nitrous
acid), and with solution of protosesquioxide of iron. But the detection
* Nitroprusside of sodium being a reagent which can very well be dispensed with, I
have omitted giving it a place among the reagents.
154 NITROUS ACID. [ 158.
of chlorine and bromine is more or less difficult in presence of iodine and
cyanogen. These latter must therefore, if present, be removed first
before the proper tests for chlorine and bromine can be applied. The
separation of the cyanogen may be readily effected by converting the
whole of the radicals present into salts of silver, and igniting the mixed
compound produced : the cyanide of silver is decomposed in this pro-
cess, whilst the chloride, bromide, and iodide of silver remain unaltered.
Upon fusing the ignited residue with carbonate of soda and potassa,
and boiling the fused mass with water, chloride, bromide, and iodide of
the alkali metals are obtained in solution.
Bromine in presence of iodine and chlorine may, according to experi-
ments recently made by me, be identified by the following simple opera-
tion : Mix the fluid with a few drops of dilute sulphuric acid, then with
some starch-paste, and add a little red fuming nitric acid or, better still,
a solution of hyponitric acid in sulphuric acid, whereupon the iodine
reaction will show itself immediately. Add now chlorine water drop by
drop until that reaction has disappeared ; and then add some more chlo-
rine water to set the bromine also free, which may then be separated
and identified by means of ether. Or the liberated iodine may also
be removed first by means of ether, chloroform, or bisulphide of
carbon, and the fluid then tested for bromine, by means of chlorine water
and ether. The iodine may be separated from the chlorine and bro-
mine, by treating the mixed silver compound with ammonia, but more
accurately by precipitating the iodine as protiodide of copper. From
bromine the iodine is separated most accurately by protochloride of
palladium, which only precipitates the iodine ; from chlorine it is sepa-
rated by nitrate of protoxide of palladium. Metallic chlorides are
detected in presence of metallic bromides by the reaction with chromate
of potassa and sulphuric acid.
158.
Supplement to the Second Group of the Inorganic Acids.
1. Nitrous acid (N 3 ). Nitrous acid, in the free state, at the common
temperature, is a brownish-red gas. In contact with water it is converted
into nitric acid, which dissolves, and nitric oxide gas, which remains
nndissolved (3 N O 3 N O 5 + 2 N OJ. The nitrites are decomposed by
ignition ; many of them are soluble in water. When nitrites or concen-
trated solutions of nitrites are treated with dilute sulphuric acid, it is
not nitrous acid gas which is evolved, but nitric oxide gas, attended with
formation of nitric acid. In solutions of nitrites of the alkalies nitrate
of silver produces a white precipitate, which dissolves in a very large
proportion of water, especially upon application of heat ; sulphate of
protoxide of iron, upon addition of a small quantity of acid, produces
a dark blackish-brown coloration, which is due to nitric oxide gas
in the solution of the sulphate of protoxide of iron. Hydrosulphuric
acid produces in neutral as well as in acid solutions copious precipitates
of sulphur, attended with formation of nitrate of ammonia. Solution
of iodide of potassium, mixed with starch-paste, is immediately colored
blue by nitrites, upon addition of hydrochloric acid. For the deport-
ment of nitrites with solutions of cobalt, see 108, 10.
2. Hypochlorous acid (Gl 0). Hypochlorous acid, at the common
159.] NITRIC ACID. 155
temperature, is a deep yellowish-green gas of a disagreeable, irritating odor,
similar to that of chlorine. It dissolves in water ; the dilute solution
bears distillation. The hypochlorites are usually found in combination
with metallic chlorides, as is the case, for instance, in chloride of lime,
eau deJavelle, &c. The solutions of hypochlorites undergo alteration by
boiling, the hypochlorite being resolved into chloride of the metal and
chlorate of the oxide, attended, in the case of concentrated, but not in
that of dilute solutions, with evolution of oxygen. If a solution of
chloride of lime, &c., is mixed with hydrochloric acid or sulphuric acid,
chlorine is disengaged, whilst addition of a little nitric acid leads to the
liberation of hypochlorous acid. Nitrate of silver throws down from
solution of chloride of lime chloride of silver ; nitrate of lead produces
a precipitate which from its original white changes gradually to orange-
red, and ultimately, owing to formation of binoxide, to brown ; salts of
protoxide of manganese give brown- black precipitates of hydrate of
binoxide of manganese, &c. Solutions of litmus and indigo are decolorized
even by the alkaline solutions of hypochlorites, but still more rapidly
and completely upon addition of an acid.
THIRD GROUP OF THE INORGANIC ACIDS.
ACIDS WHICH ARE NOT PRECIPITATED BY SALTS OF BARYTA NOR BY
SALTS OF SILVER : Nitric Acid, Chloric Acid.
159.
a. NITRIC ACID (N 6 ).
1. Anhydrous nitric acid crystallizes in six-sided prisms.^ It fuses at
85-2 F., and boils at about 1 1 3 F. (Deville). The pure hydrate is a color-
less, exceedingly corrosive fluid, which emits fumes in the air, exercises a
rapidly destructive action upon organic substances, and colors nitrogenous
matter intensely yellow. Hydrate of nitric acid containing nitrous acid
has a red color.
2. All the neutral salts of nitric acid are soluble in water ; only some
of the basic nitrates are insoluble in this menstruum. All nitrates with-
out exception undergo decomposition at an intense red heat. Those with
alkaline bases yield at first oxygen, and change to nitrites, which are then
further resolved into oxygen and nitrogen ; the others yield oxygen
and nitrous or hyponitric acid.
3. If a nitrate is thrown upon red-hot charcoal, or if charcoal or some
organic substance, paper for instance, is brought 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, the combustion being at-
tended with vivid scintillation.
4. If a mixture of a nitrate with cyanide of potassium in powder is
heated on a platinum plate, a vivid DEFLAGRATION will ensue, attended
with distinct ignition and detonation. Even very minute quantities of
nitrates may be detected by this reaction.
5. If the solution of a nitrate is mixed with an equal volume of concen-
trated sulphuric acid, free from nitric and hyponitric acid, the mixture
allowed to cool, and a concentrated solution of sulphate of protoxide of iron
then cautiously added to it so that the fluids do not mix, the stratum,
where the two fluids are in immediate contact, shows a brown or, in cases
156] CHLOllIC ACID. [ 160.
where only a very minute quantity of nitric acid is present, a reddish
color. In this process the nitric acid is decomposed by the protoxide of
iron, three-fifths of its oxygen combining with the protoxide and con-
verting a portion of it into sesquioxide, whilst the remaining nitric oxide
combines with the remaining portion of the protoxide of iron, and forms
with it a peculiar compound, which dissolves in water, imparting a
brownish-black color to the fluid.
6. If to the solution of a nitrate some sulphuric acid is added, and as
much solution of indigo in sulphuric acid as will impart a faint light-
blue tint to the fluid, and the mixture is heated to boiling, the blue color
changes to a faint yellowish tint, or the fluid becomes colorless. This
change of color is owing to the oxidation of the indigo at the expense of
the oxygen of the nitric acid which is liberated by the sulphuric acid.
It must be borne in mind, however, that several other substances also
cause decoloration of solution of indigo free chlorine more particularly
produces this effect.
7. 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 ac-
quires 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
oxygen of the air to nitrous acid. The coloration may be observed most
distinctly by looking lengthways through the tube.
8. If a little brucia is dissolved in concentrated sulphuric acid, and
a little of a fluid containing nitric acid added to the solution, the latter
immediately acquires a magnificent red color. This reaction is exceed-
ingly characteristic.
9. Very minute quantities of nitric acid may be detected also, by
fusing the substance under examination with carbonate of soda and
potassa at a moderate heat, extracting the mass, after cooling, with water,
filtering, adding the filtrate to a solution of iodide of potassium mixed
with starch-paste, and then adding hydrochloric acid. In making the
experiment, the operator has to ascertain whether the solution of iodide
of potassium mixes with the hydrochloric acid without being colored
blue by it, since this blue coloration would indicate the presence of
iodic acid in the iodide of potassium, or of free chlorine in the hydro-
chloric acid.
160.
b. CHLORIC ACID (Cl 5 ).
1. Chloric acid, in its most highly concentrated solution, is a yellow,
oily fluid ; its odor resembles that of nitric acid. It first reddens litmus
and then bleaches it. Dilute chloric acid is colorless and inodorous.
2. All chlorates are soluble in water. When chlorates are heated to
redness, the whole of their oxygen escapes and metallic chlorides
remain.
3. Heated with charcoal or some organic substance, the chlorates
DEFLAGRATE, and this with far greater violence than the nitrates.
4. If a mixture of a chlorate with cyanide of potassium is heated on
platinum foil, DEFLAGRATION takes place, attended with strong detona-
tion and ignition, even though the chlorate be present only in very small
quantity. This experiment should be made with very minute quantities
only.
161.] RECAPITULATION AND REMARKS. 157
5. Free chloric acid oxidizes and decolorizes indigo in the same manner
as nitric acid ; consequently if the solution of a chlorate is mixed with
sulphuric acid and solution of indigo, and the mixture heated, the same
reaction is observed as with nitric acid (see 159, 6).
6. If the solution of a chlorate is colored light-blue with solution
of indigo in sulphuric acid, a little dilute sulphuric acid added, and a
solution of sulphite of soda dropped cautiously into the blue fluid, the
color of the indigo disappears immediately. The cause of this equally
characteristic and delicate reaction is, that the sulphurous acid de-
prives the chloric acid of its oxygen, thus setting free chlorine or a
lower oxide of it, which then decolorizes the indigo.
7. When chlorates are treated with hydrochloric acid, the constituents
of the two acids transpose, forming water, chlorine, and chloro-
chloric acid (2 Cl O 5 , 01 O 8 ). Application of heat promotes the reaction.
The test-tube in which the experiment is made becomes filled in this
process with a greenish-yellow gas of a very disagreeable odor resembling
that of chlorine ; the hydrochloric acid acquires a greenish-yellow color.
8. Concentrated sulphuric acid, poured over a chlorate, converts two-
thirds of the metallic oxide into a sulphate and the remaining one-third
into perchlorate ; this conversion is attended, moreover, with liberation
of chlorochloric acid, which imparts an intensely yellow tint to the
sulphuric acid, and betrays its presence also by its odor and the green-
ish color of the evolved gas. [3 (K O, 01 O 5 ) 4- 4 S O 3 = (K O, 2 S O 3 ) +
K O, 01 O 7 + (01 5 , 01 0,)]. The application of heat must be avoided
in this experiment, and the quantities operated upon should be very
small, since otherwise the decomposition might take place with such
violence as to cause an explosion.
161.
Recapitulation and remarks. Of the reactions which have been sug-
gested to effect the detection of nitric acid, those with sulphate of prot-
oxide of iron and sulphuric acid, with copper filings and sulphuric acid,
with brucia, and also those based upon the reduction of the nitrates to
nitrites, give the most positive results ; with regard to deflagration with
charcoal, detonation with cyanide of potassium, and decoloration of solu-
tion of indigo, we have seen that these reactions belong equally to
chlorates as to nitrates, and are consequently decisive only when no
chloric acid is present. The presence of free nitric acid in a fluid may
be detected by evaporating the fluid, in a porcelain dish on the water-
bath, to dryness, having first thrown in a few quill-cuttings : yellow-
coloration of these indicates the presence of nitric acid (Runge).
The best way to ascertain whether chloric acid is present or not, is
to ignite the sample under examination, dissolve the mass, and test
the solution with nitrate of silver. If a chlorate is present, this is
converted into a chloride upon ignition, and nitrate of silver will now
precipitate chloride of silver from the solution. However, the process is
thus simple only if no chloride is present along with the chlorate. But
in presence of a chloride, the latter must be removed first by adding
nitrate of silver to the solution as long as a precipitate continues to form,
and filtering the fluid from the precipitate ; the filtrate is then, after
addition of pure carbonate of soda, evaporated to dryness, and the residue
ignited. It is, however, generally unnecessary to pursue this circuitous
158 OXALIC ACID. [ 162.
way, since the reactions with concentrated sulphuric acid, and with indigo
and sulphurous acid, are sufficiently marked and characteristic to afford
positive proof of the presence of chloric acid.
II. ORGANIC ACIDS.
First Group.
ACIDS WHICH ARE INVARIABLY PRECIPITATED BY CHLORIDE OF CAL-
CIUM : Oxalic Acid, Tartar ic Acid (Paratartaric or Eacemic Acid),
Citric Acid, Malic Acid.
162.
a. OXALIC ACID.
For the reactions of oxalic acid I refer to 146.
b. TARTARIC ACID (2 H 0, C s H 4 10 ).
1. The hydrate of tartaric acid forms colorless crystals of an agreeable
acid taste, which are persistent in the air, and soluble in water and in
spirit of wine. Tartaric acid when heated fuses at first, and afterwards
becomes carbonized, emitting during the process a very peculiar and
highly characteristic odor, which resembles that of burnt sugar.
2. The tartrates with alkaline base are soluble in water, and so are
those with the metallic oxides of the third and fourth groups ; those of
the tartrates which are insoluble in water dissolve in hydrochloric or
nitric acid. The tartrates suffer decomposition when heated to redness;
charcoal separates, and the same peculiar odor is emitted as attends the
carbonization of free tartaric acid.
3. If to a solution of tartaric acid, or to that of a tartrate, solution of
sesquioxide of iron, protoxide of manganese or alumina is added, and then
ammonia or potassa, no precipitation of sesquioxide of iron, protoxide of
manganese or alumina will ensue, since the double tartrates formed are
not decomposed by alkalies. Tartaric acid prevents also the precipitation
of several other oxides by alkalies.
4. Free tartaric acid produces with salts of potassa, and more particu-
larly with the acetate, a difficultly soluble precipitate of BITAHTKATE OF
POTASSA. A similar precipitate is formed when acetate of potassa and
free acetic acid are added to the solution of a neutral tartrate. The
acid tartrate of potassa dissolves readily in alkalies and mineral acids ;
tartaric acid and acetic acid do not increase its solubility in water. The
separation of the bitartrate of potassa precipitate is greatly promoted by
shaking, or by rubbing the sides of the vessel with a glass rod.
5. Chloride of calcium throws down from solutions of neutral tar-
trates a white precipitate of TARTRATE OF LIME (2 Ca O, C 8 H 4 10 + 8 aq.).
Presence of ammoriiacal salts retards the formation of this precipitate
for a more or less considerable 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 it invariably assumes a
crystalline form after some time ; it dissolves in a cold not over
dilute solution of potassa or soda, pretty free from carbonic acid, to a
clear fluid. But upon boiling this solution, the dissolved tartrate of
lime separates again in the form of a gelatinous precipitate, which redis-
solves upon cooling.
163.] CITRIC ACID. 159
6. Lime-water produces in solutions of neutral tartrates and also in
a solution of free tartaric acid, if added to alkaline reaction white pre-
cipitates which, flocculerit at first, assume afterwards a crystalline form ;
bo long as they remain fiocculent, they are readily dissolved by tartaric
acid as well as by solution of chloride of ammonium. From these solu-
tions the tartrate of lime separates again, after the lapse of several
hours, in the form of small crystals deposited upon the sides of the vessel.
7. Solution of sulphate of lime fails to produce a precipitate in a solu-
tion of tartaric acid ; in solutions of neutral tartrates it produces a
trifling precipitate after the lapse of some time.
8. If solution of ammonia is poured upon even a very minute quantity
of tartrate of lime, a small fragment of crystallized nitrate of silver
added, and the mixture slowly and gradually heated, the sides of the
test-tube are covered with a bright coating of metallic silver. If in-
stead of a crystal, solution of nitrate of silver be used, or heat be applied
more rapidly, the reduced silver will separate in pulverulent form
(Arthur Casselmann).
9. Acetate of lead produces white precipitates in solutions of tartaric
acid and its salts. The precipitate (2 Pb 0, C 8 H 4 10 ) dissolves readily
in nitric acid and in ammonia.
10. Nitrate of silver does not precipitate free tartaric acid ; but in
solutions of neutral tartrates it produces a white precipitate of TARTRATE
OF SILVER (2 Ag 0, C 8 H 4 O 10 ), which dissolves readily in nitric acid and
in ammonia ; upon boiling it turns black, owing to ensuing reduction of
the silver to the metallic state.
1 1 . Upon heating hydrated tartaric acid, or a tartrate, with hydrate
of sulphuric acid, the sulphuric acid acquires a brown color almost simul-
taneously with the evolution of gas.
163.
c. CITRIC ACID (3 H O, C 12 H 5 O u ).
1. Crystallized citric acid, obtained by the cooling of its solution, has
the formula, 3 H O, C 12 H 5 O n + 2 aq. It crystallizes in pellucid, color-
less, and inodorous crystals of an agreeable acid taste, which dissolve
readily in water and in spirit of wine. Heated to 212 F., the crystal-
lized acid loses its water of crystallization ; when subjected to the action
of a stronger heat, it fuses at first, and afterwards carbonizes, with
evolution of pungent acid fumes, the odor of which may be readily dis-
tinguished from that emitted by tartaric acid upon carbonization.
2. The citrates with alkaline base are readily soluble in water, as well
in the neutral as in the acid state ; the same applies to the compounds
of citric acid with such of the metallic oxides as are weak bases, sesqui-
oxide of iron, for instance. Citrates, like tartrates, and for the same
reason, prevent the precipitation of sesquioxide of iron, protoxide of
manganese, alumina, &c., by alkalies.
3. Chloride of calcium fails to produce a precipitate in solution of free
citric acid, even upon boiling ; but a precipitate of NEUTRAL CITRATE OP
LIME (3 Ca O, C 12 H 5 O u + 4 aq.) forms immediately upon saturating with
potassa or soda the concentrated solution of citric acid, mixed with
chloride of calcium in excess. The precipitate is insoluble in potassn,
but it dissolves readily in solution of chloride of ammonium ; upon boil-
160 MALIC ACID. [ 164.
ing this chloride of ammonium solution, neutral citrate of lime of the
same composition separates again in the form of a white crystalline pre-
cipitate, which, however, is now no longer soluble in chloride of ammo-
nium. Jf a solution of citric acid mixed with chloride of calcium is
saturated with ammonia, a precipitate will form in the cold only after
many hours' standing; but upon boiling the clear fluid, neutral citrate of
lime of the properties just stated will suddenly precipitate. When
citrate of lime is heated with ammonia and nitrate of silver, no re-
duction of the latter salt ensues.
4. Lime-water produces no precipitate in cold solutions of citric acid
or of citrates. But upon heating the solution to boiling, with a tolerable
excess of hot prepared lime-water, a white precipitate of CITRATE OP
LIME is formed, of which the greater portion redissolves upon cooling.
5. Acetate of lead, when added in excess to a solution of citric acid,
produces a white precipitate of CITRATE OF LEAD (3 Pb 0, C 12 H 5 O n ),
which, after washing, dissolves readily in ammonia.
6. Nitrate of silver produces in solutions of neutral citrates of the
alkalies a white, flocculent precipitate of CITRATE OF SILVER (3 AgO,
C 12 H 6 O n ), which does not become black on boiling.
7. Upon heating citric acid or citrates with concentrated sulphuric
acid, carbonic oxide and carbonic acid escape at first, the sulphuric acid
retaining its natural color; upon continued ebullition, however, the
solution acquires a dark color, and sulphurous acid is evolved.
164.
d. MALIC ACID (2 H 0, C 8 H 4 8 ),
1. Hydrate of malic acid crystallizes with great difficulty, forming
crystalline crusts, which deliquesce in the air, and dissolve readily in
water and in alcohol. Exposed to a temperature of 356 F., malic acid is
resolved into MAL^IC ACID (2 H O, C 8 H 2 O 6 ) and FUMARIC ACID (2 H O,
C 8 H 2 O 6 ), which latter is upon continued application of heat also con-
verted into the former. This deportment of malic acid is highly
characteristic. If the experiment is made in a small spoon, pungent
acid vapors of mataic acid are evolved with frothing effervescence. If
the experiment is made in a small tube, these fumes condense to
crystals in the colder part of the tube.
2. Malic acid forms with most bases salts soluble in water. The acid
malate of potassa is not very difficultly soluble in water. Malic acid
prevents, like tartaric acid, the precipitation of sesquioxide of iron, &c., by
alkalies.
3. Chloride of calcium fails to produce a precipitate in solutions of
free malic acid. Even after saturation with potassa or soda no preci-
pitate is formed. But upon boiling, a precipitate of MALATE OF LIME
(2 Ca O, C 8 H 4 O 8 + 6 aq.) separates from concentrated solutions. If the
precipitate is dissolved in a very little hydrochloric acid, ammonia added
to the solution, and the fluid boiled, the malate of lime separates again ;
but if it is dissolved in a somewhat larger quantity of hydrochloric acid,
it will not reprecipitate, after addition of ammonia in excess, even upon
continued boiling. Alcohol precipitates it immediately from a solution
of the kind. Malate of lime, when heated with ammonia and nitrate of
silver, fails to affect the reduction of the latter to the metallic state.
165.] RECAPITULATION AND REMARKS. 16.1
4. Lime-water produces no precipitate, either in solutions of free malic
acid or in solutions of malates.
5. Acetate of lead throws down from solutions of malic acid and of
malates a white precipitate of MALATE OF LEAD (2 Pb O, C 8 H 4 O 8 + 6 aq.).
The precipitation is the 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 fluid in which the precipitate
is suspended is heated to boiling, a portion of the precipitate dissolves,
the remainder fuses to a mass resembling resin melted under water.
This reaction is distinctly marked only when the malate of lead is
tolerably pure; if mixed with other salts of lead if, for instance,
ammonia is added to alkaline reaction, it is only imperfect or fails
altogether to make its appearance.
6. Nitrate of silver throws down from solutions of neutral malates of
the alkalies a white precipitate of MALATE OF SILVER, which upon boiling
turns a little gray.
7. Upon heating malic acid with concentrated sulphuric acid, carbonic
acid and carbonic oxide gas are evolved at first ; the fluid then turns
brown and ultimately black, with evolution of sulphurous acid.
165.
Recapitulation and remarks. Of the organic acids of this group,
oxalic acid is characterized by the precipitation of its lime-salt from its
solution in hydrochloric acid by ammonia, and also by acetate of soda, as
well as by the immediate precipitation of the free acid by solution of
sulphate of lime. Tartaric acid is characterized by the difficult solu-
bility of the acid potassa salt, the solubility of the lime salt in cold
solution of soda and of potassa, the deportment of the lime salt with
ammonia and nitrate of silver, and the peculiar odor which the acid and
its salts emit upon heating. Citric acid is most strongly characterized
by its deportment with lime-water, or with chloride of calcium and
ammonia in presence of chloride of ammonium. Malic acid would be
sufficiently characterized by the deportment of malate of lead 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 malseic acid by heating in a glass tube ;
but this conversion can be effected successfully only with pure hydrate
of malic acid. Malate of lead is difficultly soluble in ammonia, whilst
citrate of lead dissolves readily in that agent ; this different deport-
ment of the lead salts of the two acids affords also a means of dis-
tinguishing between them. If only one of the four acids is present in a
solution, lime-water will suffice to indicate which of the four is present ;
since malic acid is not precipitated by this reagent, citric acid only upon
boiling, tartaric acid and oxalic acid already in the cold ; and the tartrate
of lime redissolves upon addition of chloride of ammonium, whilst the
oxalate does not. If the four acids together are present in a solution,
the oxalic acid and tartaric acid are precipitated first by chloride of
calcium and ammonia, in presence of chloride of ammonium (the tartrate
of lime separates under these circumstances completely only after some
time it is separated from the oxalate by treating with solution of soda) ;
the citrate of lime is then thrown down by boiling, and the malate finally
by means of spirit of wine. The precipitate produced by spirit of wine
I. M
162 RACEMIC ACID. [ 166, 167.
must never be taken positively for malate of lime, without further proof,
since the sulphate and other salts of lime are also precipitated by that
agent under the same circumstances. Positive conviction can only be
attained by the production of hydrate of malic acid from the lime-salt.
To effect this, the precipitate is dissolved in acetic acid, spirit of wine
added, and the fluid filtered, if necessary. The filtrate is precipitated
with acetate of lead, the fluid neutralized with ammonia, the precipitate
washed, stirred in water, decomposed by hydrosulphuric acid, and the
filtrate evaporated to dryness.
166.
Appendix : RACEMIC ACID, OR PARATARTARIC ACID (2 H O, C 8 H 4 O 10 ).
The formula of crystallized racemic acid is 2 H O, C 8 H 4 O 10 + 2 aq.
The crystallization water escapes slowly in the air, but rapidly at 212 F.
(difference between racemic acid and tartaric acid). To solvents the racemic
acid comports itself like the tartaric acid. The racemates also show very
similar deportment to that of the tartrates. However, many of them differ
in the amount of water they contain, in form and solubility from the
corresponding tartrates. Chloride of calcium precipitates from the solu-
tions of free racemic acid and of racemates RACEMATE OF LIME (2 Ca O,
C 8 H 4 10 + 8 aq.), as a white crystalline powder. Ammonia throws the
precipitate down from its solution in hydrochloric acid, either imme-
diately or at least very speedily (difference between racemic acid and
tartaric acid). It dissolves in solution of soda and potassa, but is repreci-
pitated from this solution by boiling (difference between racemic acid and
oxalic acid). Lime-water added in excess, produces immediately a white
precipitate insoluble in chloride of ammonium (difference between
racemic acid and tartaric acid). Solution of sulphate of lime does not
immediately produce a precipitate in a solution of racemic acid (diffe-
rence between racemic acid and oxalic acid) ; however, after ten or
fifteen minutes racemate of lime separates (difference between racemic
acid and tartaric acid) ; in solutions of neutral racemates the precipitate
forms immediately. With salts of j^otassa racemic acid comports itself
like tartaric acid.
SECOND GROUP OF THE ORGANIC ACIDS.
ACIDS WHICH CHLORIDE OF CALCIUM FAILS TO PRECIPITATE UNDER
ANY CIRCUMSTANCES, BUT WHICH ARE PRECIPITATED . FROM NEUTRAL
SOLUTIONS BY SESQUICHLORIDE OF IRON : Succlnlc Acid, Benzole
Add.
'167.
a. SUCCINIC ACID (2 H O, C 8 H 4 6 ).
1. Hydrate of Succinic acid forms colorless and inodorous prisms or
tables of slightly acid taste, which are readily soluble in water, alcohol,
and ether, difficultly soluble in nitric acid, and volatilize when ex-
posed to the action of heat, leaving only a little charcoal behind. The
officinal acid has an empyreumatic odor, and leaves a somewhat larger
carbonaceous residue upon volatilization. Succiuic acid is riot 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 the
oil of amber, if present, will be destroyed. By sublimation crystalline
168.] BENZOIC ACID. 163
needles of silky lustre are obtained ; the hydrate loses water in this
process, so that by repeated sublimation anhydrous acid is ultimately
obtained. Heated in the air, succinic acid burns with a blue flame, free
from soot.
2. ^The succinates are decomposed at a red heat ; those which have an
alkali or alkaline earth for base, are converted into carbonates in this
process, the change being attended with separation of charcoal. Most of
the succinates are soluble in water.
3. Sesquichloride of iron produces in solutions of neutral succinates of
the alkalies a brownish pale red, bulky precipitate of SUCCINATE OF SES-
QUIOXIDE OF IRON (F 2 O g , C g H 4 O G ) ; one-third of the succinic acid is
liberated in this reaction, and retains part of the precipitate in solution,
if the fluid is filtered off hot. The precipitate dissolves readily in mineral
acids ; ammonia decomposes it, causing the separation of a less bulky
precipitate of a highly basic succinate of sesquioxide of iron, and com-
bining with the greater portion of the acid to succinate of ammonia,
which dissolves.
4. Acetate of lead gives with succinic acid a white precipitate of
neutral SUCCINATE OF LEAD (2 Pb O, C 8 H 4 O 6 ), which is very sparingly
soluble in water, acetic acid, and succinic acid, but dissolves readily in
solution of acetate of lead and in nitric acid. Treated with ammonia,
the neutral succinate of lead is converted into a basic salt (6 Pb O
C,H 4 0,)._
5. A mixture of alcohol, ammonia, and solution of chloride of barium
produces in solutions of free succinic acid and of succinates a white pre-
cipitate Of SUCCINATE OF BARYTA (2 Ba 0, C g H 4 O fi ).
6. Nitrate of suboxide of mercury and nitrate of silver also precipitate
the succinates ; the precipitates, however, are not possessed of any
characteristic properties.
168.
b. BENZOIC ACID (H 0, C 14 H 6 3 ).
1. Pure hydrate of benzoic acid forms inodorous white scales or
needles, or simply a crystalline powder. When heated, it fuses, and
afterwards volatilizes completely. The fumes of benzoic acid cause a
peculiar irritating sensation in the throat, and provoke coughing ; when
cautiously cooled, they condense to brilliant needles, when kindled, they
burn with a luminous sooty flame. The common officinal hydrate of
benzoic acid has the odor of benzoin, and leaves a small carbonaceous
residue upon volatilization. Hydrate of benzoic acid is very sparingly
soluble in cold water, but it dissolves pretty readily in hot water and in
alcohol. Addition of water, therefore, imparts a milky turbidity to a
saturated solution of benzoic acid in alcohol.
2. Most of the benzoates are soluble in water ; only those with weak
bases, e. g., sesquioxide of iron, are insoluble. The soluble benzoates have
a peculiar, pungent taste. The addition of a strong acid to aqueous
solutions of benzoates displaces the benzoic acid, which separates as
hydrate in the form of a dazzling white, sparingly soluble powder. Ben-
zoic acid is expelled in the same way from the insoluble benzoates, by
such strong acids as form soluble salts with the bases with which the
benzoic acid is combined.
M 2
164 RECAPITULATION AND REMARKS. [ 169, 170.
3. Sesquichloride of iron precipitates solutions of free benzoic acid
incompletely ; solutions of neutral benzoates of the alkalies completely.
The precipitate of BENZOATE OF SESQUIOXIDE OF IRON (2 Fe 2 O 3 ,
3 [C 14 H 5 3 ] + 15 aq.), is bulky, flesh-colored, insoluble in water. It is
decomposed by ammonia jn the same manner as succinate of sesquioxide
of iron, from which salt it differs in this, that it dissolves in a little
hydrochloric acid, with separation of the greater portion of the ben-
zoic acid.
4. Acetate of lead fails to precipitate free benzoic acid and benzoate of
ammonia, at least immediately ; but it produces white, flocculent preci-
pitates in solutions of benzoates with a fixed alkaline base.
5. A mixture of alcohol, ammonia, and solution of chloride of barium
produces NO precipitate in solutions of free benzoic acid or of the alkaline
benzoates.
169.
Recapitulation and remarks. Succinic and benzoic acids are distin-
guished from all other acids by the facility with which they may be
sublimed, and by their deportment with sesquichloride of iron. They
are distinguished from one another by the different color of their salts
with sesquioxide of iron, and also by their different deportment with
chloride of barium and alcohol ; but principally by their different degrees
of solubility, succinic acid being readily soluble in water, whilst benzoic
acid is very difficult of solution. Succinic acid is seldom perfectly pure,
and may therefore often be detected by the odor of oil of amber which
it emits.
The detection of the two acids, when present in the same solution
with other acids, may be effected as follows : precipitate with sesqui-
chloride of iron, warm the washed precipitate with ammonia, filter,
concentrate the solution, divide it into two parts, and mix one part with
hydrochloric acid, the other with chloride of barium and alcohol.
Succinic acid and benzoic acid do not prevent the precipitation of ses-
quioxide of iron, alumina, &c., by alkalies.
THIRD GROUP OF THE ORGANIC ACIDS.
ACIDS WHICH ARE NOT PRECIPITATED BY CHLORIDE OF CALCIUM NOR
BY SESQUICHLORIDE OF IRON : Acetic Acid, Formic Acid.
170.
a. ACETIC ACID (H O, C 4 H 3 O 3 ).
1. The hydrate of acetic acid forms transparent crystalline scales,
which fuse at 62*6 F. to a colorless fluid of a peculiar pungent and pene-
trating odor, and exceedingly acid taste. When exposed to the action of
heat, it volatilizes completely, forming pungent inflammable 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
170.] ACETIC ACID. 165
acid is commonly applied. The hydrate of acetic acid is also soluble
in alcohol.
2. The acetates undergo decomposition at a red heat ; among the pro-
ducts of this decomposition we generally find hydrate of acetic acid, and
almost invariably acetone (C 6 H ? O a ). The acetates of the alkalies and
alkaline earths are converted into carbonates in this process ; of the
acetates with metallic bases many leave the metal behind in the pure
state, others in the form of oxide. Most of the residues which the
acetates leave upon ignition are carbonaceous. Nearly all acetates dis-
solve in water and in alcohol ; most of them are readily soluble in water,
a few only are difficult of solution in that menstruum. If acetates are
distilled with dilute sulphuric acid, the free acetic acid is obtained in the
distillate.
3. If sesquiclikride of iron is added to acetic acid, and the acid is then
nearly saturated with ammonia, or if a neutral acetate is mixed with
sesquichloride of iron, the fluid acquires a deep dark red color, owing to
the formation of ACETATE OF SESQUIOXIDE OF IRON. Upon boiling, the
fluid becomes colorless if it contains an excess of acetate, the whole of
the sesquioxide of iron precipitating as a basic acetate, in the form
of brown-yellow flakes. Ammonia precipitates from it the whole of
the sesquioxide of iron as hydrate. CJpon addition of hydrochloric acid,
a fluid which appears red from the presence of acetate of sesquioxide of
iron turns yellow (difference from sulphocyanide of iron).
4. Neutral acetates (but not free acetic acid) give with nitrate of
silver white, crystalline precipitates of ACETATE OF SILVER (Ag O, C 4 H 3 3 ),
which are very sparingly soluble in cold water. They dissolve more
easily in hot water, but separate again upon cooling, in the form of very
fine crystals. Ammonia dissolves them readily; free acetic acid does
not increase their solubility in water.
5. Nitrate of suboxide of mercury produces in solutions of acetic acid,
and more readily still in solutions of acetates, white, scaly crystalline
precipitates of ACETATE OF SUBOXIDE OF MERCURY (Hg 2 6, C 4 H 3 O 8 ),
which are sparingly soluble in water and acetic acid in the cold, but dis-
solve without difficulty in an excess of the precipitant. The precipitates
dissolve in water upon heating, but separate again upon cooling, in the
form of small crystals ; in this process the salt undergoes partial decom-
position : a portion of the mercury separates in the metallic state, and
imparts a gray color to the precipitate. If the acetate of suboxide of
mercury is boiled with dilute acetic acid instead of water, the quantity
of the metallic mercury which separates is exceedingly minute.
6. When acetates are heated with concentrated sulphuric acid, HYDRATE
OF 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 acid and alcohol, ACETIC ETHER (C 4 H 6 0, C 4 H 3 3 )
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
free acetic acid.
7. If acetates are distilled with dilute sulphuric acid, and the distillate
is digested with an excess of oxide of lead, part of the latter dissolves
as basic acetate of lead, which maybe readily recognised by its alkaline
reaction.
166 FORMIC ACID. [ 171.
171.
b. FORMIC ACID (H 0, C 2 H O a ).
1. The hydrate of formic acid is a transparent, colorless, slightly
fuming liquid, of a characteristic and exceedingly penetrating odor. When
cooled to below 32 F., it crystallizes in colorless plates. It is miscible in all
proportions with water and with alcohol. When exposed to the action
of heat, it volatilizes completely ; the vapors are inflammable and burn
with a blue flame.
2. The formates, like the corresponding acetates, leave upon ignition
either carbonates, oxides, or metals behind, the process being attended
with separation of charcoal, and escape of carbide of hydrogen, carbonic
acid, and water. All the compounds of formic acid with bases are
soluble in water ; alcohol likewise dissolves some of them.
3. Formic acid presents the same deportment with sesquichloride of
iron as acetic acid.
4. Nitrate of silver fails to precipitate free formic acid, and decom-
poses the alkaline formates only in concentrated solutions. The white,,
sparingly soluble, crystalline precipitate of FORMATE OF SILVER (Ag O,
C 2 H O 3 ) acquires very rapidly a darker tint, owing to the separation of
metallic silver. Complete reduction of the oxide of silver to the me-
tallic state takes place, even in the cold, after the lapse of some time ;
but immediately, upon applying heat to the fluid containing the preci-
pitated formate of silver. The same reduction of the oxide of silver to
the metallic state takes place in a solution of free formic acid, and also
in solutions of formates so dilate that the addition of the nitrate of silver
failed to produce a precipitate in them. But it does not take place in
presence of an excess of ammonia. The rationale of this reduction is
as follows : the formic acid, which may be looked upon as a compound
of carbonic oxide with water, deprives the oxide of silver of its oxygen,
thus causing the formation of carbonic acid, which escapes, and of water,,
whilst the reduced silver separates in the metallic state.
5. Nitrate of suboxide of mercury gives no precipitate with free formic-
acid ; but in concentrated solutions of alkaline formates this reagent
produces a white, sparingly soluble precipitate of FORMATE OF SUBOXIDE
OF MERCURY (Hg O, C 2 H O g ), which rapidly becomes gray, owing to the
separation of metallic mercury. Complete reduction ensues, even in the
cold, after the lapse of some time, but is immediate upon application of
heat. This reduction is also attended with the formation of carbonic
acid and water, and takes place, the same as with the oxide of silver,
both in solutions of free formic acid and in fluids so highly dilute that
the formate of suboxide of mercury is retained in solution.
6. If formic acid or an alkaline formate is heated with chloride of
mercury to from 140 to 158 F., SUBCHLORIDE OF MERCURY precipitates.
If the mixture is heated to 212 F., metallic mercury separates along
with the subchloride.
7. If formic acid or a formate is heated with concentrated sulphuric
acid, the formic acid is resolved into water and carbonic oxide gas, which
latter escapes with effervescence, and if kindled, burns with a blue flame.
The fluid does not turn black in this process. The rationale of the
decomposition of the formic acid is this : the sulphuric acid withdraws
from the formic acid the water or the oxide necessary for the existence-
172.] RECAPITULATION AND REMARKS. 167
of the latter acid, and thus occasions a transposition of its elements
(C 2 H O 3 = 2 C O + H O). Upon heating formates with dilute sulphuric
acid in a distilling apparatus, free formic acid is obtained in the distil-
late, and may mostly be readily detected by its odor. Upon heating a
formate with a mixture of sulphuric acid and alcohol, formic ether is
evolved, which is characterized by its peculiar arrack-like smell.
8. If dilute formic acid is heated with oxide of lead, the latter dis-
solves. On cooling the solution, which, if necessary, is concentrated by
evaporation, the FORMATE OF LEAD (Pb O, C 2 H O 3 ) separates in brilliant
prisms or needles.
172.
Recapitulation and remarks. Acetic acid and formic acid may be dis-
tilled over with water, and form with sesquioxide of iron soluble neutral
salts which dissolve in water, imparting to the fluid a blood-red color,
and are decomposed upon boiling. These reactions distinguish the two
acids of the third group from the other organic acids. From each other
the two acids are distinguished by the odor of their hydrates and ethyle
compounds, and by their different deportment with salts of silver and
salts of mercury, oxide of lead, and concentrated sulphuric acid. The
separation of acetic acid from formic acid is effected by heating the
mixture of the two acids with an excess of oxide of mercury or oxide of
silver. Formic acid reduces the oxides, and suffers decomposition, being
resolved into carbonic oxide and water ; whilst the acetic acid combines
with the oxides, forming acetates, which remain in solution.
PART II.
SYSTEMATIC COURSE
OF
QUALITATIVE CHEMICAL ANALYSIS.
PART II.
PRELIMINARY REMARKS
ON THE
COURSE OF QUALITATIVE ANALYSIS IN GENERAL AND ON THE PLAN OP
THIS PART OF THE PRESENT WORK IN PARTICULAR.
THE knowledge of reagents and of the deportment of other bodies
with them enables us to ascertain at once whether a compound of which
the physical properties permit an inference as to its nature, is in reality
what we suspect it to be. Thus, for instance, a few simple reactions
suffice to show whether a body which appears to be calcareous spar, is
really carbonate of lime, and that another, which we hold to be gypsum,
is actually sulphate of lime. This knowledge usually suffices also to
ascertain whether a certain body is present or not in a compound ; for
instance, whether or not a white powder contains subchloride of mer-
cury. But if our design is to ascertain the chemical nature of a sub-
stance entirely unknown to us if we wish to discover all the consti-
tuents of a mixture or chemical compound if we intend to prove that,
besides certain bodies which we have detected in a mixture or compound,
no other substance can possibly be present if consequently a complete
qualitative analysis is our object, the mere knowledge of the reagents,
and of the reactions of other bodies with them, will not suffice for the
attainment of this end ; this requires the additional knowledge of a
systematic and progressive course of analysis, in other words, the know-
ledge of the order and succession in which solvents, and general and
special reagents, should be applied, both to effect the speedy and certain
detection of every component element of a compound or mixture, and to
prove with certainty the absence of all other substances. If we do not
possess the knowledge of this systematic course, or if, in the hope of
attaining our object more rapidly, we adhere to no method whatever in
our investigations and experiments, analyzing becomes (at least in the
hands of a novice) mere guess work, and the results obtained are no
longer the fruits of scientific calculation, but mere matters of accident,
which sometimes may prove lucky hits, and at, others total failures.
Every analytical investigation must therefore be based upon a definite
method. But it is not by any means necessary that this method should
be the same in all cases. Practice, reflection, and a due attention to
circumstances will, on the contrary, generally lead to the adoption of
different methods for different cases. However, all analytical methods
agree in this, that the substances present or supposed to be present in a
172 PRELIMINARY REMARKS.
compound or mixture, are in the first place classed into certain groups,
which are then again subdivided, until the individual detection of the
various substances present is finally accomplished. The diversity of
analytical methods depends partly on the order and succession in which
reagents are applied, and partly on their selection.
Before we can venture upon inventing methods of our own for indi-
vidual cases, we must first 'make ourselves thoroughly conversant with
a certain definite course, or system, of chemical analysis in general.
This system must have passed through the ordeal of experience, and
must be adapted to every imaginable case, so that afterwards, when we
have acquired some practice in analysis, we may be able to determine
which modification of the general method will in certain given cases
most readily and rapidly lead to the attainment of the object in view.
The exposition of such a systematic course, adapted to all cases, tested
by experience, and combining simplicity with the greatest possible
security, is the object of the First Section of the second part of this work.
The elements arid compounds comprised in it are the same which we
have studied in Part I., with the exception of those given in that part
simply by way of appendix.
The First Section of the Second Part consists of PRACTICAL INSTRUC-
TIONS IN ANALYSIS, wherein I have laid down a systematic course which,
with due care and attention, will, by progressive steps, lead speedily
and safely to the attainment of the end in view.
The subdivisions of this practical course are, 1, Preliminary examina-
tions ; 2, Solution ; 3, Actual examination.
The third subdivision (the actual examination) is again subdivided
into, (1) Examination of compounds in which but one base and one acid
are assumed to be present ; and, (2) Examination of mixtures or com-
pounds in which all the substances treated of in the present work are
assumed to be present. With respect to the latter section, I have to
remark that where the preliminary examination has not clearly demon-
strated the absence of certain groups of substances, the student cannot
safely disregard any of the paragraphs to which reference is made in
consequence of the reactions observed. In cases where the intention is
simply to test a compound or mixture for certain substances, and not to
ascertain all its constituents, it will be easy to select the particular num-
bers which ought to be attended to.
As the construction of a universally applicable systematic course of
analysis requires due regard to, and provision for, every contingency
that may possibly arise, it is self-evident that, though in the system here
laid down the various bodies comprised in it have been assumed to be
mixed up together in every conceivable way, it was absolutely indis-
pensable to proceed throughout upon the supposition that no foreign
organic matters whatever were present, since the presence of such matters
would of course tend to prevent or obscure many reactions, and variously
modify others.
Although the general analytical course laid down here is devised and
arranged in a manner to suit all possible contingencies, with a very few
exceptions, still there are special cases in which it may be advisable to
modify it. A preliminary treatment of the substance is also sometimes
necessary, before the actual analysis can be proceeded with ; the pre-
sence of coloring, slimy, organic matters more especially requires certain
preliminary operations.
173.] PRELIMINARY EXAMINATION. 173
The Second Section of this Part will be found to contain a detailed
description of the special methods employed to effect the analysis of a
few important compounds and mixtures which chemists are frequently
called upon to examine. Some of these methods show how the analy-
tical processes become simplified as the number of substances decreases
to which regard must be had in the analysis.
In conclusion, as an intelligent and successful pursuit of analysis is
possible only with an accurate knowledge of the principles whereon the
detection and separation of bodies depend, since this knowledge alone
can furnish the student with a guide to the selection of the proper re-
agents, and the order in which they ought to be applied, I have given in
the Third Section of the Second Part an explanation and elucidation of
the general analytical process, with numerous additions to the practical
operations. As this third section may properly be regarded as the key
to the first and second sections, I strongly recommend students to make
themselves early and thoroughly acquainted with it. I have devoted a
special section to this theoretical explanation of the process, as I think
it will be understood better in a connected form, than it would have
been by explanatory additions to several paragraphs, which, moreover,
might have materially interfered with the plainness and perspicuity of
the plan of the practical process.
SECTION I.
PRACTICAL PROCESS FOR THE ANALYSIS OF COMPOUNDS
AND MIXTURES IN GENERAL.
I. PRELIMINAKY EXAMINATION.*
173.
1. EXAMINE, in the first place, the physical properties color, It
shape, hardness, gravity, odor, &c. of the substance intended for
analysis, since these will often enable you in some measure to
infer its nature. Before proceeding to the application of any che-
mical process, you must always consider how much of the substance
to be analyzed you have at command, since it is necessary, at this
early period of the examination, to calculate the quantity which may
safely be used in the preliminary investigation. A reasonable eco-
nomy is in all cases advisable, even though you may possess the sub-
stance in large quantities ; but, under all circumstances, let it be a
fixed rule, never to use at once the whole of what you possess of
a substance, but always to keep a portion of it for unforeseen con-
tingencies, and for confirmatory experiments.
* Consult also the observations and additions in the Third Section,
t These marginal numbers are simply intended to facilitate reference.
174 PRELIMINARY EXAMINATION. [ 174
A. THE BODY UNDER EXAMINATION is SOLID.
I. IT IS NEITHER A PURE METAL NOR AN ALLOY.
1. The substance is fit for examination if in powder or in minute 2
crystals ; but if in larger crystals or in solid pieces, it is necessary
in the first place to reduce a portion of it to powder if practicable.
Bodies of the softer kind may be triturated in a porcelain mortar ;
those of a harder nature must first be broken into small pieces in a
steel mortar, or upon a steel anvil, and the pieces then be triturated
in an agate mortar.
2. Put some of the powder into a glass tube, sealed at one end, 3
about six centimetres long and five millimetres wide, and heat first
gently over the spirit or gas-lamp, then intensely in the blowpipe
flame. The reactions resulting may lead to many positive or pro-
bable conclusions regarding the nature of the substance. The fol-
lowing are the most important of these reactions, to which particular
attention ought to be paid ; it often occurs that several of them are
observed in the case of one and the same substance.
a. THE SUBSTANCE REMAINS UNALTERED : absence of organic 4
matters, salts containing water of crystallization, readily fusible
matters, and volatile bodies.
b. THE SUBSTANCE DOES NOT FUSE AT A MODERATE HEAT, BUT 5
SIMPLY CHANGES COLOR. From white to yellow, turning white
again on cooling, indicates OXIDE OF ZINC ; from white to yellowish-
brown, turning to a dirty light yellow on cooling, indicates
BINOXIDE OF TIN ; if the color changes from white to brownish-
red, turning to yellow on cooling, and the body is fusible at a red
heat, this indicates the presence of OXIDE OF LEAD j if the color
changes from white to orange-yellow, or a deeper and more red-
dish tint, up to reddish-brown, turning pale yellow on cooling,
and the body fuses at an intense red heat, this indicates the pre-
sence of TEROXIDE OF BISMUTH j if the color changes from red
to black, turning red again on cooling, this indicates the presence
Of SESQUIOXIDE OF IRON, &C.
C. THE SUBSTANCE FUSES WITHOUT EXPULSION OF AQUEOUS 6
VAPOR. If on intense heating, gas (oxygen) is evolved, and a
small fragment of .charcoal thrown in is energetically consumed,
NITRATES or CHLORATES may be assumed to be present.
d. AQUEOUS VAPORS ARE EXPELLED, WHICH CONDENSE IN THE 7
COLDER PART OF THE TUBE : this indicates the presence either (a) of
SUBSTANCES CONTAINING WATER OF CRYSTALLIZATION, ill which
case they will generally readily fuse, and re-solidify after expul-
sion of the water; many of these swell considerably whilst
yielding up their water, e. g. (borax, alum) ; or (/3) of decompos-
able HYDRATES, in which case the bodies often will not fuse ; or
(y) of anhydrous salts, holding water mechanically enclosed be-
tween their lamellae in which case the bodies will decrepitate ;
or (c>) of bodies with moisture externally adhering to them.
174.] PRELIMINARY EXAMINATION. 175
Test the reaction of the condensed fluid in the tube: if
it is alkaline, ammonia may be assumed to be present; if
acid, a volatile acid (sulphuric acid, sulphurous acid, hydro-
fluoric acid, hydrochloric, hydrobromic, or hydriodic acids, nitric
acid, &c.).
e. GASES OR FUMES ESCAPE. Observe whether they have a 8
color, smell, acid or alkaline reaction, whether they are inflam-
mable, &c.
aa. OXYGEN. The disengagement of this gas indicates the
presence of peroxides, chlorates, nitrates, <fec. A glimmering
slip of wood is relighted in the gaseous current.
bb. SULPHUROUS ACID. This is often produced by the de-
composition of sulphates ; it may be known by its peculiar
odor and by its acid reaction.
cc. HYPONITRIC ACID, resulting from the decomposition of
nitrates, especially with oxides of the heavy metals ; it may
be known by the brownish-red color of the fumes.
dd. CARBONIC ACID. The evolution of carbonic acid indi-
cates the presence of carbonates decomposable by heat. The gas
evolved is colorless and tasteless, non-inflammable ; a drop of
lime-water on a watch-glass becomes turbid on exposure to the
gaseous current.
ee. CARBONIC OXIDE GAS. The escape of this gas indicates
the presence of oxalates, and, when attended with actual car-
bonization, also of formates. The gas burns with a blue
flame.
ff. CYANOGEN. The evolution of cyanogen gas denotes
the presence of cyanides decomposable by heat. The gas may
be known by its odor, and the crimson flame with which it
burns.
gg. HYDROSULPHURIC ACID GAS. The escape of hydrosul-
phuric acid gas indicates the presence of sulphides containing
water ; the gas may be readily known by its odor.
hh. AMMONIA, resulting from the decomposition of ammo-
niacal salts, or also of cyanides or nitrogenous organic matters,
in which latter cases browning or carbonization of the sub-
stance takes place, and either cyanogen or offensive em-
pyreumatic oils escape with the ammonia.
f. A SUBLIMATE FORMS. This indicates the presence of vola- 9
tile bodies : the following are those more frequently met
with :
aa. SULPHUR. Separated from mixtures or from many of
the metallic sulphides. Sublimes in reddish-brown drops
which become solid on cooling, and turn yellow, or yellowish-
brown.
bb. AMMONIA SALTS give white sublimates ; heated with
soda and a drop of water on platinum foil, they evolve
ammonia.
cc. MERCURY and compounds of mercury. METALLIC MER-
CURY forms globules ; SULPHIDE OF MERCURY is black, but
acquires a red tint when rubbed CHLORIDE OF MERCURY
fuses before volatilizing ; SUBCHLORIDE OF MERCURY sublimes
176 PRELIMINARY EXAMINATION. [174.
without previous fusion ; the sublimate, which is yellow whilst
hot, turns white on cooling. The red IODIDE OF MERCURY
gives a yellow sublimate.
dd. ARSENIC and compounds of that metal. METALLIC
ARSENIC forms the well-known arsenical mirror j ARSENIOUS
ACID forms small shining crystals ; the SULPHIDES OF ARSENIC
give sublimates which are reddish-yellow whilst hot, and turn
yellow on cooling.
ee. TEROXIDE OF ANTIMONY fuses to a yellow liquid before
subliming. The sublimate consists of brilliant needles.
ff. BENZOIC ACID and SUCCINIC ACID, which may be known
by the odor of their fumes.
, t gg. HYDUATED OXALIC ACID. White crystalline subli-
mate, thick fumes in the tube. Heating a small sample on
platinum foil with a drop of concentrated sulphuric acid gives
rise to a copious evolution of gas.
g. CARBONIZATION TAKES PLACE : organic substances. This 10
is always attended with evolution of gases (in the case of acetates
of acetone) and water, which latter has an alkaline or acid reaction.
If the residue effervesces with acids, whilst the original substance
did not show this reaction, organic acids may be assumed to be
present in combination with alkalies or alkaline earths.
3. Put a small portion of the substance on a charcoal support (in H
the cavity scooped out for the purpose), and expose to the inner
blowpipe flame.
As most of the reactions described under 2 (3 10) are also pro-
duced by this process, I will here enumerate only those which result
more particularly and exclusively from its application.
a. THE BODY FUSES, AND is ABSORBED BY THE CHARCOAL OR 12
FORMS A BEAD IN THE CAVITY : this denotes more particularly
the presence of salts of the alkalies.
b. AN INFUSIBLE WHITE RESIDUE REMAINS on the charcoal, 13
either at once or after previous melting in the water of crystal-
lization. This indicates more particularly the presence of baryta,
strontia, lime, magnesia, alumina, oxide of zinc (which appears
yellow whilst hot), and silicic acid. Among these substances,
STRONTIA, LIME, MAGNESIA, and OXIDE OF ZINC, are distinguished
by strong luminosity in the blowpipe flame. Moisten the white
residue with a drop of solution of nitrate of protoxide of cobalt,
and expose again to a strong heat. If the mass assumes a
fine blue tint, this indicates the presence of ALUMINA ; if a
reddish tint, of MAGNESIA ; if a green color, of OXIDE OF ZINC.
If SILICIC ACID is present, the mass also assumes a faint bluish
tint, which must not be confounded with that proceeding from
the presence of alumina.
C. TlIE SUBSTANCE LEAVES AN INFUSIBLE RESIDUE OF 14
ANOTHER COLOR, OR REDUCTION TO THE METALLIC STATE
TAKES PLACE, WITH OR WITHOUT INCRUSTATION OF THE CHAR-
COAL. Mix a portion of the powder with carbonate of soda,
and heat on charcoal in the reducing flame ; observe the residue
in the cavity, as well as the incrustation on the charcoal.
a. The sustained application of a strong flame produces a me- 15
tallic globule, without incrustation of the charcoal ; this indi-
174'-] PRELIMINARY EXAMINATION. 177
cates the presence of GOLD, SILVER, or COPPER. The oxides of
platinum, iron, cobalt, and nickel, are indeed also reduced, but
they yield no metallic globules.
/3. The charcoal support is coated with an incrustation, 16
either with or without simultaneous formation of a metallic
globule.
aa. The incrustation is white, at a long distance from the
test specimen, and is very readily dissipated by heat, emit- '
ting a garlic-like odor : ARSENIC.
bb.^ The incrustation is white, is nearer the test specimen
than in aa, and may be driven from one part of the support
to another : ANTIMONY. Metallic globules are generally ob-
served at the same time, which continue to evolve white
fumes long after the blowpipe jet is discontinued, and
' upon cooling become surrounded with crystals of teroxide
of antimony ; the globules are brittle.
cc. The incrustation is yellow whilst hot, but turns white
on cooling ; it is near the test specimen, and is with diffi-
culty volatilized : ZINC.
dd. The incrustation has a faint yellow tint whilst hot,
but turns white on cooling ; it surrounds the test speci-
men, and both the inner and outer flame fail to volatilize
it : TIN. The metallic globules formed at the same time
are bright, readily fusible, and malleable.
ee. The incrustation has a lemon-yellow color, turning on
cooling to sulphur-yellow ; when exposed to the reducing
flame, it leaves a bluish stain : LEAD. Readily fusible,
malleable globules are formed at the same time with the
incrustation.
ff. The incrustation is of a dark orange-yellow color
whilst hot, which changes to lemon-yellow on cooling ;
when exposed to the reducing flame, it does not leave a
bluish stain : BISMUTH. The metallic globules formed at the
same time as the incrustation are readily fusible and brittle.
gg. The incrustation is reddish-brown, in thin layers,
orange-yellow ; it volatilizes without leaving a colored
stain : CADMIUM.
4. Fuse a small portion together with a bead of microcosmic salt, 17
and expose for some time to the outer flame of the blowpipe.
a. THE SUBSTANCE DISSOLVES READILY AND RATHER LARGELY
TO A CLEAR BEAD (WHILST HOT).
a. The hot lead is colored : 18
BLUE, by candlelight inclining to violet COBALT ;
GREEN, upon cooling blue ; in the reducing flame, after
cooling, red COPPER
GREEN, particularly fine on cooling, unaltered in the re-
ducing flame CHROMIUM ;
BROWNISH-RED, on cooling light yellow or colorless ; in
the reducing flame red whilst hot, yellow whilst
cooling, then greenish IRON ;
DARK. YELLOW to REDDISH, turning lighter or altogether
colorless on cooling ; in the reducing flame unaltered
NICKEL ;
I. N
178 PRELIMINARY EXAMINATION. [ 175.
YELLOWISH-BROWN, on cooling changing to light yellow or
losing its color altogether; in the reducing flame almost
colorless (especially after contact with tin), blackish-
gray on cooling BISMUTH ;
BRIGHT YELLOWISH to OPAL, when cold rather dull j in the
reducing flame whitish-gray SILVER ;
AMETHYST-RED, especially on cooling ; colorless in the re-
ducing flame, not quite clear MANGANESE.
p. The hot bead is colorless : 19
IT REMAINS CLEAR ON COOLING I ANTIMONY, ALUMINA, ZINC,
CADMIUM, LEAD, LIME, MAGNESIA ; the latter five metals,
when added in somewhat large proportion to the
microcosmic salt, give enamel- white beads j the bead
of oxide of lead is yellowish when saturated j
IT BECOMES ENAMEL-WHITE ON COOLING, even when only
a small portion of the powder has been added to the
microcosmic salt : BARYTA, STRONTIA.
6. THE SUBSTANCE DISSOLVES SLOWLY AND ONLY IN SMALL 20
QUANTITY :
a. The bead is colorless, and remains so even after cooling ;
the undissolved portion looks semi-transparent ; upon addi-
tion of a little sesquioxide of iron, it acquires the characteristic
color of an iron bead : SILICIC ACID.
(3. The bead is colorless, and remains so after addition of
a little sesquioxide of iron : TIN.
C. THE SUBSTANCE DOES NOT DISSOLVE, BUT FLOATS (iN THE 21
METALLIC STATE) IN THE BEAD : GOLD, PLATINUM.
As the body under examination may consist of a mixture of the
most dissimilar elements, it is impossible to give well defined cases
that shall offer at the same time the advantage of general appli-
cability. If, therefore, reactions are observed in an experiment which
proceed from a combination of two or several cases, the conclu-
sions drawn from these reactions must of course be modified accord-
ingly-
II. THE SUBSTANCE is A METAL OR AN ALLOY.
1. Heat a small portion of the substance with water acidulated 22
with acetic acid.
a. HYDROGEN GAS is EVOLVED : this indicates the presence
of a light metal (possibly also of manganese in the metallic
state). The presence of alkalies and of alkaline earths must
also be had regard to in the actual examination.
b. No HYDROGEN is EVOLVED : this indicates the absence of
light metals. Alkalies and alkaline earths may be altogether
disregarded in the course of the special investigation.
2. Heat a sample of the substance on charcoal in the reducing 23
flame of the blowpipe, and watch the reactions ; for instance, whe-
ther the substance fuses, whether an incrustation is formed, or an
odor emitted, &c.
a. THE SAMPLE REMAINS UNALTERED : this is pretty conclusive
176.] PRELIMINARY EXAMINATION. 179
of the absence of antimony, zinc, lead, bismutn, cadmium, tin
mercury, and arsenic; the absence of gold, silver, and copper is
also probable ; PLATINUM, IRON, MANGANESE, NICKEL, and COBALT
are likely to be present.
b. THE SAMPLE FUSES ; NO INCRUSTATION FORMS, AND NO ODOR
is EMITTED : absence of antimony, zinc, lead, bismuth, cadmium,
and arsenic j presence of GOLD, SILVER, COPPER.
C. THE SAMPLE FUSES, AND AN INCRUSTATION IS FORMED, BUT
NO ODOR EMITTED : absence of arsenic, and presence of ANTI-
MONY, ZINC, BISMUTH, LEAD, CADMIUM (compare 174, 3, c, /3
[16]).
fit THE SUBSTANCE EMITS THE ODOR OF GARLIC ; ARSENIC IS
present. According to the nature of the other reactions which
may manifest themselves, a, b, or c must be had regard to.
3. Heat a sample of the substance before the blowpipe in a glass 24
tube sealed at one end.
a. NO SUBLIMATE IS FORMED IN THE COLDER PART OF THE
TUBE : absence of mercury.
b. A SUBLIMATE is FORMED ; presence of MERCURY, CADMIUM,
or ARSENIC. The sublimate of mercury, which consists of small
globules, cannot possibly be confounded with that of cadmium
or arsenic.
176.
B. THE SUBSTANCE UNDER EXAMINATION is A FLUID.
1. Evaporate a small portion of the fluid in a platinum dish, or in 25
a small porcelain crucible, to ascertain whether it actually contains
any matter in solution ; if a residue remains, examine this as directed
174.
2. Test with litmus paper (blue and red). 26
a. THE FLUID REDDENS BLUE LITMUS PAPER. This reaction
may be caused by a free acid or an acid salt, as well as by a
metallic salt soluble in water. To distinguish between these
two cases, pour a small quantity of the fluid into a watch-glass,
and dip into it a small glass rod, the extreme point of which
has previously been moistened with dilute solution of carbonate
of soda ; if the fluid remains clear, or if the precipitate which
may form at first, redissolves upon stirring the liquid, this
proves the presence of a free acid or of an acid salt ; but if the
fluid becomes turbid and remains so, this generally denotes the
presence of a soluble metallic salt. As a matter of course, a
solution which contains a free acid or an acid salt can no longer
be considered simply aqueous, and the subsequent examination
must accordingly be conducted with due regard to the pos-
sible presence of substances insoluble in water but soluble in
acids.
b. REDDENED LITMUS PAPER TURNS BLUE : this indicates the 27
presence of free alkalies or alkaline carbonates, free alkaline
earths, alkaline sulphides, and of a number of other salts which
show this reaction. In presence of a free alkali, a body dis-
solved in a fluid is as likely to belong to the class of sub-
stances soluble, as to that of bodies insoluble in water. For
N2
180 SOLUTION OF BODIES. [ 177, 178.
the way to settle this point, and also for further information on
the subject of alkaline solutions in general, I refer to 187,
I. 2 (104).
3. Smell the fluid or, should this fail to give satisfactory results, 28
distil, to ascertain whether the simple solvent present is water,
alcohol, ether, &c. If you find ifc is not water, evaporate the
solution to dryness, and treat the residue as directed 174.
4. If the solution is aqueous, and manifests an acid reaction, 29
dilute a portion of it largely with water. Should this impart a milky
and turbid appearance to it, the presence of ANTIMONY, BISMUTH
(possibly also of tin) may be inferred. If the precipitate disappears
upon the addition of tartaric acid, there is reason to believe it con-
sists of antimony ; if it is not redissolved by tartaric acid, but by
nitric acid, you may assume the presence of bismuth. Treat the ori-
ginal fluid either as directed 180 or as directed 187, according as
you have reason to suppose it to be the solution of a simple or a
compound (mixed) substance.
II. SOLUTION OF BODIES, OR CLASSIFICATION OF SUBSTANCES
ACCORDING TO THEIR DEPORTMENT WITH CERTAIN SOL-
VENTS.*
177.
"Water, hydrochloric or nitric acid, and aqua regla are the solvents 30
used to classify simple or compound substances, and to isolate the
component parts of mixtures. We divide the various substances
into three classes, according to their respective behavior with these
solvents.
First class. SUBSTANCES SOLUBLE IN WATER.
Second class. SUBSTANCES INSOLUBLE OR SPARINGLY SOLUBLE
IN WATER, BUT SOLUBLE IN HYDROCHLORIC ACID, NITRIC ACID, OR
AQUA REGIA.
Third class. SUBSTANCES INSOLUBLE OR DIFFICULTLY SOLUBLE
IN WATER AS WELL AS IN HYDROCHLORIC ACID, NITRIC ACID, AND
AQUA REGIA.
The solution of alloys being more appropriately effected in a dif-
ferent manner from that pursued with other bodies, I shall give a
special method for these substances (see 179).
The process of solution is conducted in the following manner.
A. THE SUBSTANCE UNDER EXAMINATION is NEITHER A METAL NOR
AN ALLOY.
178.
1. Put about a gramme (15*5 grains) of the finely pulverized sub- 31
stance under examination into a small flask or a test-tube, add from
ten to twelve times the amount of distilled water, and heat to boil-
ing over a spirit- or gas-lamp.
a. THE SUBSTANCE DISSOLVES COMPLETELY. In that case it 32
belongs to the first class ; regard must be had to what has been
* Consult the remarks in the third section.
178.] SOLUTION OF BODIES. 181
stated in 176, 2 (26), concerning the reactions with test-
papers. Treat the solution either as directed 180 or as di-
rected 187, according as either one or several acids and bases
are supposed to be present.
b. AN INSOLUBLE RESIDUE REMAINS, EVEN AFTER PROTRACTED 33
BOILING. Let the residue subside, and filter the fluid off, if
practicable in such a manner as to retain the residue in the
test-tube evaporate a few drops of the clear filtrate on pla-
tinum foil ; if nothing remains, the substance is completely
insoluble in water; in which case proceed as directed 178,
2 (34)- But if a residue remains, the substance is at least
partly soluble ; in which case boil again with water, filter, add
the filtrate to the original solution, and treat the fluid, accord-
ing to circumstances, either as directed 180, or according to
187. Wash the residue with water, and proceed as directed
178, 2 (34).
2. Treat a small portion of the residue which has been boiled with 34
water (33) with dilute hydrochloric acid. If it does not dissolve,
heat to boiling, and if this fails to effect complete solution, decant
the fluid into another test-tube, boil the residue with concentrated
hydrochloric acid, and, if it dissolves, add it to the fluid in
the other test-tube. The reactions which may manifest them-
selves in this operation, and which ought to be carefully observed
are, (a) Effervescence, which indicates the presence of carbonic acid
or hydrosulphuric acid ; (/3) Evolution of chlorine, which indicates
the presence of peroxides, chromates, &c. ; (y) Emission of the odor
of hydrocyanic acid, which indicates the presence of insoluble cya-
nides. The analysis of the latter bodies being effected in a some-
what different manner, a special paragraph will be devoted to
them (see 202).
a. THE RESIDUE is COMPLETELY DISSOLVED BY THE HYDRO- 35
CHLORIC ACID (except perhaps that sulphur separates, which
may be known by its color and light specific gravity, and may,
after boiling some time longer, be removed by filtration ; or
that gelatinous hydrate of silicic acid separates). Proceed, ac-
cording to circumstances, either as directed 183, or as directed
1 88, after "previous filtration if necessary. The body belongs to
the second class. To make quite sure of the actual nature of
the sulphur or hydrated silicic acid filtered off, examine these
residuary matters as directed 186, or as directed 201.
b. THERE is STILL A RESIDUE LEFT. In that case put aside 36
the test-tube containing the specimen which has been boiled
with the hydrochloric acid, and try to dissolve another sample of
the substance under examination, by boiling with nitric acid,
and subsequent addition of water.
a. The sample is completely dissolved, or leaves no other 37
residue but sulphur or the gelatinous hydrate of silicic acid ;
in this case also the body belongs to the second class. Use this
solution to test further for bases, and then proceed as
directed in 2, a (35).
ft. After boiling with nitric acid there is still a residue left. 38
Pass on to 3.
3. If the residue insoluble in water will not entirely dis-.39
182 SOLUTION OF BODIES. [ 179.
solve in hydrochloric acid nor n nitric acid, try to effect com-
plete solution of it by means of nitre-hydrochloric acid. To this
end mix the contents of the tube treated with nitric acid with
the contents of the tube treated with concentrated hydrochloric
acid; heat the mixture to boiling, and should this fail to effect
complete solution, decant the clear fluid off from the undissolved
residue, boil the latter for some time with concentrated nitro-
hydrochloric acid, and add the decanted solution in dilute aqua
regia as well as the solution in dilute hydrochloric acid decanted
in 178, 2 (34)- Heat the entire mixture once more to boiling,
and observe whether complete solution has now been effected, or
whether the action of the concentrated nitro-hydrochloric acid has
still left a residue. In the latter case, filter the solution if neces-
sary, after addition of some water* wash the residue with boiling
water, and proceed with the filtrate, and the washings added to it,
as directed 183, or as directed 188 ; in the former case, proceed
with the clear solution in the same way.t
4. If boiling nitrohydrochloric acid has left an undissolved re- 40
sidue, wash it thoroughly with water, and then proceed as directed
186, or as directed 201.
B. THE SUBSTANCE UNDER EXAMINATION is A METAL OR
AN ALLOY.
179.
The metals are best classed according to their respective behavior 41
with nitric acid : this gives us,
I. METALS WHICH ARE NOT ATTACKED BY NITRIC ACID : gold,
platinum.
II. METALS WHICH ARE OXIDIZED BY NITRIC ACID, BUT OF WHICH
THE OXIDES DO NOT DISSOLVE IN AN EXCESS OF THE ACID NOR IN
WATER ; antimony, tin.
III. METALS WHICH ARE OXIDIZED BY NITRIC ACID AND CONVERTED
INTO NITRATES, WHICH DISSOLVE IN AN EXCESS OF THE ACID OR IN
WATER : all other metals.
Pour nitric acid of 1'25 sp. gr. over a small portion of the metal
or alloy under examination, and apply heat.
1. COMPLETE SOLUTION TAKES PLACE, EITHER AT ONCE OR UPON 42
ADDITION OF WATER j this proves the absence of platinum,^ gold,
antimony, 1 1 and tin. Proceed, according to circumstances, either as
directed 183, or as instructed 187, III. (109).
2. A. RESIDUE IS LEFT.
a. A metallic residue. Filter, and treat the filtrate as di- 43
rected 187, III., after having examined, in the first place,
* If the fluid turns turbid upon addition of water, this indicates the presence of
bismuth or antimony ; the turbidity disappears again upon addition of hydrochloric acid.
f* If the acid solution on cooling deposits acicular crystals, the latter generally consist
of chloride of lead ; it is in that case often advisable to decant the fluid off from the
crystals, and to examine fluid and crystals separately.
_ + Alloys of silver and platinum, with the latter metal present in small proportion only,
dissolve in nitric aoid.
Very minute traces of antimony, however, are often completely dissolved by nitric
acid.
180.] ACTUAL EXAMINATION SIMPLE COMPOUNDS. 183
whether anything has really been dissolved. Wash the residue
thoroughly, dissolve in nitrohydrochloric acid, and add to a por-
tion of the solution chloride of potassium and alcohol; to
another portion, sulphate of protoxide of iron ; a yellow preci-
pitate in the first indicates the presence of PLATINUM, a black
precipitate in the second, the presence of GOLD.
b. A white, pulverulent residue ; this indicates the presence 44
of ANTIMONY and TIN. Filter, ascertain whether anything has
been dissolved, and if so treat the filtrate as directed 187, III.
"Wash the residue thoroughly, and heat it with a hot saturated
solution of bitartrate of potassa, or with a solution of tartaric
acid.
a. Complete solution ensues ; this indicates the presence of 45
oxide of ANTIMONY alone ; test the solution, with hydrosulphu-
ric acid, after addition of some hydrochloric acid.
/3. A white residue remains, even after boiling with a
fresh portion of solution of bitartrate of potassa or tartaric
acid ; this indicates the probable presence of TIN. Filter and
mix the filtrate with some hydrochloric acid, then with solu-
tion of hydrosulphuric acid. If an orange-red precipitate is
formed, TEROXIDE OF ANTIMONY is present. It is always
necessary to ascertain whether the residue consists really of
binoxide of tin : which may be known by heating it to redness,
then fusing it in a small tube with cyanide of potassium, boil-
ing the reduced metal with water, then heating with hydro-
chloric acid, and testing the solution with chloride of mercury
( 133).
III. ACTUAL EXAMINATION.
Simple Compounds.*
A. SUBSTANCES SOLUBLE IN WATER.
Detection of the Base.^
180.
1. Add some hydrochloric acid to a portion of the aqueous solu- 46
tion.
a. No PRECIPITATE is FORMED ; this is a positive proof of the
absence of silver and suboxide of mercury, and is likewise an
indication of the probable absence of lead. Pass on to 180, 2
b. A PRECIPITATE is FORMED. Divide the fluid in which 47
the precipitate is suspended into two portions, and add ammo-
nia in excess to the one.
a. The precipitate redissolves, and the fluid becomes clear ;
this shows the precipitate to have consisted of chloride of
silver, and is consequently indicative of the presence of SILVER.
* This term is used here, and wherever it happens to occur hereafter in the present
work, to designate compounds supposed to contain only one base and cid, 01
metal and one non-metallic element.
f Arsenious acid and arsenic acid are included here.
184) DETECTION OF BASES. [ 180.
To arrive at a positive conviction on this point, the original
solution must be tested with chromate of potassa, and with
hydrosulphuric acid (see 114, 4, and 138, b, 6).
j3. The precipitate turns black : this shows the precipitate 48
to have consisted of subchloride of mercury, which has now
been converted by the ammonia into suboxide of mercury ; it
is consequently indicative of the presence of SUBOXIDE OP
MERCURY. To set all doubt on this point at rest, test the ori-
ginal solution with protochloride of tin, and with metallic
copper (see 115).
y. The precipitate remains unaltered ; it consists in that 49
case of chloride of lead, which is not dissolved by ammonia ;
this reaction is accordingly indicative of the presence of LEAD.
Whether the precipitate consists really of chloride of lead or
not is conclusively ascertained : 1st, by diluting the second
portion of the fluid in which the precipitate produced by hydro-
chloric acid is suspended, with a large amount of water, and
applying heat ; the precipitate must dissolve if it consists
of chloride of lead ; and 2nd, by adding dilute sulphuric acid
to the original solution ( 116, 8).
2. Add to the fluid acidified with hydrochloric acid (1) solution 50
of hydrosulphuric acid until it smells distinctly of that gas, even after
shaking, and heat the mixture.
a. THE FLUID REMAINS CLEAR. Pass on to 3 (56), since this
is a proof that lead, bismuth, copper, cadmium, oxide of mer-
cury, gold, platinum, tin, antimony, arsenic, and sesquioxide of
iron, are not present.
b. A PRECIPITATE IS FORMED.
a. THIS PRECIPITATE is WHITE ; it consists in that case of 51
separated sulphur, and is indicative, of the presence of SESQUI-
OXIDE OF IRON ( 110, 3). However, as the separation of
sulphur may also be caused by other substances, it is indis-
pensable that you should satisfy yourself whether the sub-
stance present is really sesquioxide of iron or not. For this
purpose test the original solution with ammonia, and with
ferrocyanide of potassium ( 110, 5 and 6).
/3. THE PRECIPITATE is YELLOW ; in that case it may con- 52
sist either of sulphide of cadmium, sulphide of arsenic, or
bisulphide of tin ; it indicates accordingly the presence of
either cadmium, arsenic, or binoxide of tin. To distinguish
between them, mix a portion of the fluid wherein the pre-
cipitate is suspended with ammonia in excess, add some sul-
phide of ammonium, and heat.
aa. The precipitate does not dissolve ; it consists of CAD-
MIUM for sulphide of cadmium is insoluble in ammonia
and sulphide of ammonium. The blowpipe is resorted to
as a confirmatory test ( 121, 8).
bb. The precipitate dissolves : BINOXIDE OF TIN or
ARSENIC ; add ammonia to a small portion of the original
solution.
aa. A white precipitate is formed. BIXOXIDE OF TIN
is the substance present. Positive conviction is ob-
tained by reducing the precipitate before the blowpipe,
180.] ACTUAL EXAMINATION SIMPLE COMPOUNDS. 185
with cyanide of potassium and carbonate of soda
( 129, 8).
pp. No precipitate is formed. This indicates the pre-
sence of ARSENIC. Positive conviction may be arrived
at by the production of an arsenical mirror, which is
effected by reducing the original substance or the pre-
cipitated sulphide of arsenic, either with cyanide of
potassium and carbonate of soda, or in some other way ;
and moreover by exposing the original substance in con-
junction with carbonate of soda to the inner flame of
the blowpipe ( 131, 12 and 13). If the solution (50)
contained arsenious acid, the yellow precipitate (52)
formed immediately upon the addition of the hydrosul-
phuric acid ; if arsenic acid, it formed only upon the
application of heat, or after long standing. For further
information respecting the means of distinguishing be-
tween the two acids see 133.
y. THE PRECIPITATE is ORANGE-COLORED ; in that case it 53
consists of tersulphide of antimony, and indicates the pre-
sence of TEROXIDE OF ANTIMONY. For confirmation, the
original solution is tested with zinc in a small platinum
dish ( 130, 8).
c. THE PRECIPITATE is BROWN. It consists of protosul- 54
phide of tin, and indicates the presence of PROTOXIDE OF TIN.
To remove all doubt, test a portion of the original solution
with solution of chloride of mercury ( 128, 8).
e. THE PRECIPITATE IS BROWNISH-BLACK OR BLACK. It may 55
in that case consist of sulphide of lead, sulphide of copper,
tersulphide of bismuth, tersulphide of gold, bisulphide of
platinum, or sulphide of mercury. To distinguish between
these different sulphides, the following experiments are re-
sorted to.
aa. Add dilute sulphuric acid to a portion of the original
solution ; if a white precipitate is formed, this indicates
LEAD. To dispel all doubt, test with chromate of potassa
(116).
bb. Add solution of soda to a portion of the original
solution ; if a yellow precipitate is formed, this indicates
OXIDE OF MERCURY. The reactions with protochloride of
tin and metallic copper afford positive certainty on the
point ( 118).
The presence of oxide of mercury is usually sufficiently
indicated by the several changes of color through which the
precipitate produced by the solution of hydrosulphuric acid
in the fluid under examination is observed to pass ; this
precipitate is white at first, but changes upon the addition
of an excess of the precipitant to yellow, then to orange,
and finally to black ( 118, 3).
cc. Add ammonia in excess to a portion of the original
solution ; if a bluish precipitate is formed which redissolves
in an excess of the precipitant, imparting an azure color to
the fluid, this indicates COPPER. To remove all doubt, test
with ferrocyanide of potassium ( 119.).
186 DETECTION OF BASES. [ 180.
dd. If the precipitate produced by ammonia was white,
and excess of ammonia has failed to redissolve it, filter the
fluid off, wash the precipitate, dissolve it on a watch-glass
in 1 or 2 drops of hydrochloric acid, with addition of 2
drops of water, and then add some more water. If the
solution turns turbid and milky, this is caused by basic
terchloride of bismuth : the reaction consequently indicates
BISMUTH. The blowpipe is resorted to as a conclusive test
( 120).
ee. Add solution of sulphate of protoxide of iron to a
portion of the original solution. The formation of a fine
black precipitate is indicative of the presence of GOLD. To
remove all doubt as to the nature of the precipitate, expose
it to the flame of the blowpipe, or test the original solution
with protochloride of tin ( 125).
ff. Add chloride of potassium and alcohol to a portion of
the original solution ; the formation of a yellow crystalline
precipitate is indicative of the presence of PLATINUM.
To remove all doubt, heat the precipitate to redness
( 126).
3. Mix a small portion of the original solution with chloride of 56
ammonium, add ammonia to alkaline reaction, and then, no matter
whether the latter reagent has produced a precipitate or not, a little
sulphide of ammonium, and apply heat, if a precipitate fail to sepa-
rate in the cold.
a. No PRECIPITATE is FORMED; pass on to 180, 4 (62);
for iron, cobalt, nickel, manganese, zinc, chromium, alumina, and
silicic acid, are not present.
b. A PRECIPITATE IS FORMED.
a. The precipitate is black : protoxide of iron, nickel, or 57
cobalt. Mix a portion of the original solution with some
solution of potassa or soda.
aa. A dirty greenish- white precipitate is formed, which
soon changes to reddish-brown, upon exposure to the air :
PROTOXIDE OF IRON. To remove all doubt, test with ferri-
cyanide of potassium ( 109).
bb. A precipitate of a light greenish tint is produced,
which does not change color : NICKEL. The reaction
with ammonia, and the precipitation of the ainmoniacal
solution by potassa or soda, will afford positive certainty
on the point ( 107).
cc. A sky-blue precipitate is formed, which is discolored
upon boiling, and acquires a dark tint : COBALT. The
blowpipe is resorted to as a conclusive test ( 108).
/3. The precipitate is not black. 58
aa. If the precipitate is distinctly flesh-colored, it con-
sists of sulphide of manganese, and is consequently indicative
of the presence of PROTOXIDE OF MANGANESE. To remove
all doubt, add soda to the original solution, or try before
the blowpipe ( 106).
bb. If the precipitate is bluish-green, it consists of hy-
drated sesquioxide of chromium, and is consequently indi-
cative of the presence of SESQUIOXIDE OF CHROMIUM. To
180.] SIMPLE COMPOUNDS. 187
dispel all doubt, test the original solution with soda, and
apply the blowpipe tests ( 101).
cc. If the precipitate is white, it may consist of hydrate 59
of alumina, or hydrate of silicic acid, or sulphide of zinc,
and may accordingly point to the presence of either alu-
mina or oxide of zinc or silicic acid ; the latter, in that
case, is generally contained in the original solution as
an alkaline silicate. To distinguish between these three
bodies, add to a portion of the original solution a drop
of solution of soda, wait to see whether this produces
a precipitate, and then add some more solution of soda,
until the precipitate formed is redissolved.
aa. If solution of soda fails to produce a precipi- 60
tate, there is reason to test for SILICIC ACID. For
that purpose, evaporate a portion of the original solution
with hydrochloric acid to dryness, and treat the residue
with hydrochloric acid and water ( 150, 2), when the
silicic acid will be left undissolved. Determine the na-
ture of the alkali which has been dissolved, as directed
180, 6, b (66).
/3/3. If solution of soda produces a precipitate, which
redissolves in an excess of the precipitant, add to a por-
tion of this alkaline fluid hydrosulphuric acid ; the for-
mation of a white precipitate indicates the presence of
ZINC. The reaction with solution of nitrate of protoxide
of cobalt before the blowpipe will afford conclusive proof
( 105). If hydrosulphuric acid fails to produce a pre-
cipitate, add to the remaining portion of the alkaline
fluid chloride of ammonium, and apply heat. The for-
mation of a white precipitate indicates the presence of
ALUMINA. The reaction with solution of nitrate of prot-
oxide of cobalt before the blowpipe will afford conclusive
proof ( 100).
Note to ISO, 3, 6,/3(58).
As very slight contaminations may impair the distinctness of the
tints exhibited by the precipitates considered in 180, 3, b, (3 (58),
it is advisable, in all cases where the least impurity is suspected, to
adopt the following method for the detection of manganese, chro
mium, zinc, alumina, and silicic acid.
Add solution of soda to a portion of the original solution, first 61
in small quantity, then in excess.
aa. No precipitate is formed : SILICIC ACID may be assumed
to be present ; proceed as directed 180, 3, b, /3, aa (60)-
bb. A whitish precipitate is formed, which does not redis-
solve in an excess of the precipitant, and speedily turns black-
ish-brown upon exposure to the air : MANGANESE. The blow-
pipe is resorted to as a conclusive test ( 106).
cc. A precipitate is formed which redissolves in an excess
of the precipitant: SESQUIOXIDE OF CHROMIUM, ALUMINA,
OXIDE OF ZINC.
aa. Add hydrosulphuric acid water to a portion ot the
188 SIMPLE COMPOUNDS. [ 180.
alkaline solution. The formation of a white precipitate
indicates the presence of ZINC.
(3(3, If the original or the alkaline solution is green, and
if the precipitate produced by soda and redissolved by an
excess of the precipitant, was of a bluish color, SESQUIOXIDE
OF CHROMIUM is present. To remove all doubt, heat the
alkaline solution to boiling, or try the reaction before the
blowpipe ( 101).
yy. Add chloride of ammonium to the alkaline solution.
The formation of a white precipitate indicates the presence
of ALUMINA. The reaction with solution of nitrate of
protoxide of cobalt before the blowpipe will afford conclu-
sive proof ( 100).
4. Add to a portion of the original solution chloride of ammonium 62
and carbonate of ammonia, mixed with some caustic ammonia, and
heat gently.
a. No PRECIPITATE is FORMED : absence of baryta, strontia,
and lime. Pass on to 180, 5 (64).
b. A PRECIPITATE is FORMED : presence of baryta, strontia, 63
or lime.
Add a considerable quantity of solution of sulphate of lime to
a portion of the original solution.
a. The solution does not become turbid, not even after the
lapse of from Jive to ten minutes : LIME. To remove all doubt,
test with oxalate of ammonia ( 96).
(3. The solution becomes turbid, but only after the lapse of
some time : STRONTIA. The alcohol flame will afford conclu-
sive proof (95).
y. A precipitate is immediately formed : BARYTA. To re-
move all doubt, test with hydrofiuosilicic acid ( 94).
5. Mix that portion of the solution of 4 in which carbonate of 64
ammonia has, after previous addition of chloride of ammonium,
failed to produce a precipitate, with phosphate of soda, add some
more ammonia, and rub the sides of the vessel with a glass rod.
a. No PRECIPITATE is FORMED : absence of magnesia. Pass
on to 180, 6 (65).
b. A CRYSTALLINE PRECIPITATE IS FORMED I MAGNESIA.
6. Evaporate a drop of the original solution on perfectly clean 65
platinum foil as slowly as possible, and gently ignite the residue.
a. THERE is NO FIXED RESIDUE LEFT. Test for ammonia, by
adding to the original solution hydrate of lime, and observing
the odor and reaction of the escaping gas, and the fumes which
it forms with acetic acid ( 90).
b. THERE is A FIXED RESIDUE LEFT : potassa or soda. Add 66
bichloride of platinum to a portion of the original solution,
having first concentrated it by evaporation if dilute, and shake
the mixture.
a. No precipitate is formed, not even after the lapse often or
fifteen minutes : SODA. The blowpipe flame and alcohol flame
are selected as conclusive tests, or the reaction with anti-
monate of potassa is resorted to for the purpose ( 89).
/3. A yellow crystalline precipitate is formed: POTASSA.
181.] DETECTION OF INORGANIC ACIDS. 189
The reaction with tartaric acid, the blowpipe flame and
alcohol name are selected as conclusive tests ( 88).
Simple Compounds.
A. SUBSTANCES SOLUBLE IN WATER. DETECTION OF THE ACID.
I. Detection of Inorganic Acids.
181.
Reflect in the first place which of the inorganic acids form soluble
compounds with the detected base (compare Appendix IV.), and
bear this in mind in your subsequent operations.
1. ARSENIOUS ACID and ARSENIC ACID have already been consi- 67
dered in the preceding paragraph (detection of the base). Thes two
acids are distinguished from each other by their respective beh vior
with nitrate of silver, or with potassa and sulphate of copper (see
133).
2. The presence of CARBONIC ACID, HYDROSULPHURIC ACID, and 68
CHROMIC ACID, is also indicated already in the course of the process
pursued for the detection of the bases. The two former betray their
presence by effervescing upon the addition of hydrochloric acid ; they
may be distinguished from one another by their odor. Should addi-
tional proof be required, the presence of carbonic acid may be ascer-
tained beyond a doubt by the reaction with lime-water (see 149),
and that of hydrosulphuric acid by the reaction with solution of
acetate of lead ( 156). The presence of chromic acid is invariably
indicated by the yellow or red tint of the solution, as well as by the
transition of the red or yellow color to green, accompanied by the
separation of sulphur, upon the addition of hydrosulphuric acid water.
To remove all doubt, try the reactions with solutions of acetate of
lead and of nitrate of silver ( 138, b).
3. Add some chloride of barium to a portion of the solution, then 69
if the fluid has remained clear, and the reaction is acid ammonia
to slightly alkaline reaction.
a. THE FLUID REMAINS CLEAR. Pass on to 181, 4 (71).
The absence of sulphuric acid, phosphoric acid, and silicic acid
is certain, that of oxalic acid and boracic acid probable ; as the
baryta compounds of the two latter acids are kept in solution by
ammoniacal salts, whilst borate of baryta does not separate from
dilute solutions, even in the absence of ammoniacal salts.
b. A PRECIPITATE is FORMED. Add dilute hydrochloric acid 70
in moderate excess.
a. The precipitate dissolves : absence of sulphuric acid. Pass
on to 4 (71).
/3. The precipitate remains undissolved, even on the addition
of a large quantity of water : SULPHURIC ACID.
4. Add solution of sulphate of lime to another portiDn of the 71
solution (which, if it has an acid reaction, must first be neutralized,
or made slightly alkaline, by means of ammonia). If no sal: of
ammonia is present, add some chloride of ammonium befjre ad .ling
the solution of sulphate of lime.
190 DETECTION OF INORGANIC ACIDS. [ 181.
a. No PRECIPITATE is FORMED : absence of phosphoric acid,
silicic acid, oxalic acid, and fluorine. Pass on to 5 (73 )
b. A PRECIPITATE is FORMED. Add acetic acid in excess. 72
a. The precipitate redissolves readily : PHOSPHORIC ACID or
SILICIC ACID. The reaction with molybdic acid ( 143) will
afford conclusive proof of the presence of the former acid ; to
obtain positive certainty as to the presence of the latter,
evaporate the solution, acidified with hydrochloric acid, to
dryness, and treat the residue with hydrochloric acid.
j3. The precipitate remains nndissolved or dissolves with
difficulty : OXALIC ACID or FLUORINE. Oxalate of lime is
pulverulent, fluoride of calcium flocculent and gelatinous.
The reaction with binoxide of manganese and sulphuric acid
(146) will afford conclusive proof of the presence of oxalic
acid ; the reaction on glass (etching) of the presence of
fluorine ( 147).
5. Acidify a fresh portion of the original solution with nitric acid, 73
and add solution of nitrate of silver.
a. THE FLUID REMAINS CLEAR. This is a proof of the absence
of chlorine, bromine, iodine, ferrocyanogen, and ferricyanogen j
the absence of cyanogen (in simple cyanides) is also probable.
Of the soluble metallic cyanides, cyanide of mercury is not pre-
cipitated by nitrate of silver ; if, therefore, in the analytical
process for the detection of the bases, mercury has been found,
cyanide of mercury may be present. For the manner of de-
tecting the cyanogen in the latter, see 155, 8. Pass on to 6
(76).
b. A PRECIPITATE IS FORMED.
a. The precipitate is orange : FERRICYANOGEN ; the reaction 74
with sulphate of protoxide of iron is resorted to as a con-
firmatory test ( 155, Appendix).
j3. The precipitate is white or yellowish- white. Add ammo-
nia in excess.
act. The precipitate is not dissolved : IODINE or FERRO-
CYANOGEN. In the former case the precipitate is pale
yellow, in the latter white and gelatinous. The reaction
with starch and hyponitric acid ( 154) will afford conclu-
sive proof of the presence of iodine, the reaction with ses-
quichloride of iron of the presence of ferrocyanogen
( 155, Supplement).
/3/3. The precipitate is dissolved : CHLORINE, BROMINE, 75
or CYANOGEN. If the original substance smells of hydro-
cyanic acid, and the silver precipitate dissolves with some
difficulty in the ammonia, the precipitate may be assumed
to consist of cyanide of silver, and, consequently, to indicate
the presence of CYANOGEN. To remove all doubt on the
point, add to the original solution sulphate of protoxide of
iron, solution of soda, and hydrochloric acid ( 155). If
addition of chlorine water imparts a yellow tint to the
original solution the precipitate may be held to consist of
bromide of silver, and consequently indicates the presence
of BROMINE ; if the bromine is present only in very small
proportion, ether must be used in conjunction with
182.] DETECTION OP ORGANIC ACIDS. 191
chlorine water to make the reaction distinctly apparent
( 153). In the proved absence of both bromine and
1 cyanogen, the precipitate consists of chloride of silver, and
consequently shows the presence of CHLORINE.
6. Add to a small portion of the aqueous solution hydrochloric 76
acid, drop by drop, until a distinct acid reaction is just imparted to
the fluid, then dip in a slip of turmeric paper, take it out, and dry
it. If the dipped portion looks brownish-red, BORACIC ACID is
present. To settle all doubt on the point, add sulphuric acid and
alcohol, and set fire to the latter ( 145).
7. With regard to NITRIC ACID and CHLORIC ACID, these are 77
usually discovered already in the course of the preliminary exami-
nation (see 174, 2, c [6]). The reaction with sulphate of prot-
oxide of iron and sulphuric acid ( 159) will afford conclusive
evidence of the presence of the former, treatment of the solid salt
with concentrated sulphuric acid, of the presence of the latter acid
( 160).
Simple Compounds.
A. SUBSTANCES SOLUBLE IN WATER. DETECTION OF THE ACID.
II. Detection of Organic Acids.
182.
1. Add ammonia to a portion of the aqueous solution of the 78
compound under examination to slight alkaline reaction, then
chloride of calcium. If the solution was neutral, or only slightly
acid, add chloride of ammonium before adding the chloride of
calcium.
a. No PRECIPITATE IS FORMED, NOT EVEN AFTER SHAKING
THE FLUID NOR AFTER THE LAPSE OF A FEW MINUTES : absence
of oxalic acid and tartaric acid. Pass on to 182, 2 (80)-
b. A PRECIPITATE is FORMED. Add lime-water in excess 79
to a fresh portion of the original solution, and then add solution
of chloride of ammonium to the precipitate formed.
a. The precipitate redissolves : TARTARIC ACID. The re-
action with acetate of potassa may be resorted to as a confir-
matory test ; but a still more positive proof will be afforded
by the deportment which the precipitate produced by the
chloride of calcium, and properly washed, exhibits with solu-
tion of soda or with ammonia and nitrate of silver ( 162).
(3. The precipitate does not redissolve : OXALIC ACID. To
remove all doubt, try the reaction with concentrated sul-
phuric acid ( 146).
2. Heat the fluid of 1, a, to boiling, keep at that temperature 80
for some time, and add some more ammonia to the boiling fluid.
a. IT REMAINS CLEAR : absence of citric acid. Pass on to
182, 3 (81).
b. IT BECOMES TURBID, AND DEPOSITS A PRECIPITATE : CITRIC
ACID. To remove all doubt as to the nature of the acid, add
solution of acetate of lead in excess, wash the precipitate formed,
and see whether it dissolves readily in ammonia ( 163).
3. Mix the fluid of 2, a, with alcohol. 81
192 DETECTION OF THE BASE. [ 183,
a. IT REMAINS CLEAR: absence of malic acid. Pass on to
182, 4 (82).
b. A PRECIPITATE is FORMED i MALIC ACID. To remove all
doubt, it is invariably necessary to try the reaction with acetate
of lead, to see whether the precipitate produced by that reagent
dissolves with difficulty in ammonia, and to examine its deport-
ment when the fluid in which it is suspended is heated to boiling
( 164).
4. Neutralize a portion of the original solution completely (if not
already absolutely neutral) with ammonia or with hydrochloric 82
acid, and add solution of sesquichloride of iron.
a. A BULKY PRECIPITATE FORMS, OF A CINNAMON BROWN, OR
DIRTY YELLOW COLOR. Wash the precipitate, heat it with
ammonia, filter, concentrate the filtrate by evaporation, divide
into two parts, and add to the one some hj^drochloric acid, to
the other alcohol and chloride of barium. The formation of a
precipitate in the first portion indicates the presence of BENZOIC
ACID, a precipitate in the second denotes the presence of succi-
NIC ACID. Compare 167 and 168.
b. THE LIQUID ACQUIRES A RATHER INTENSE DEEP RED TINT, 83
AND, UPON PROTRACTED BOILING, A LIGHT REDDISH-BROWN PRECI-
PITATE SEPARATES : acetic acid or formic acid. Heat a portion
of the solid salt under examination, or, if the substance is in the
fluid state, of the residue left upon evaporating the fluid (which, if
acid, you must neutralize first with soda), with sulphuric acid
and alcohol ( 170). The characteristic odor of acetic ether
indicates the presence of ACETIC ACID.
If you do not detect acetic acid in the fluid, you may con-
clude that the substance under examination contains FORMIC
ACID : to remove all doubt, try the reactions with nitrate of
silver and chloride of mercury ( 171).
Simple Compounds.
B. SUBSTANCES INSOLUBLE OR SPARINGLY SOLUBLE IN WATER, BUT
SOLUBLE IN HYDROCHLORIC ACID, NITRIC ACID, OR NITROHYDRO-
CHLORIC ACID.
Detection of the Base.*
183.
Dilute a portion of the solution in hydrochloric acid, nitric acid, 84
or nitrohydrochloric acid with water,t and proceed exactly as directed
180, beginning at 1 (46)> i n cases where the substance is dissolved
innitricacid, and at 2 (50)>if the solution already contains hydrochloric
acid. Particular regard must be had in this to the following observa-
tions : we have seen 180, 3, b, (3, cc (59)> tna ^ if? i n cases where we
* Regard is also had here to certain salts of the alkaline earths, as this course of
examination leads directly to their detection.
f If upon the addition of water the liquid becomes white and turhid or deposits a
white precipitate, this indicates the presence of antimony or bismuth. Compare 176,
4 (29)- Heat with hydrochloric acid until the fluid has become clear again, and then
pass on to 180, 2 (50).
183.] DETECTION OF BASES. 193
have A SUBSTANCE SOLUBLE IN WATER, we obtain, in the course of the
examination, a white precipitate upon adding chloride of ammonium,
ammonia, and sulphide of ammonium, this precipitate can consist only
of sulphide of zinc, or alumina, or hydrate of silicic acid. But the case is
different if the body is INSOLUBLE IN WATER, but dissolves in hydrochlo-
ric acid ; for in that case a white precipitate produced by sulphide of
ammonium, in presence of chloride of ammonium, may consist also of
phosphates, borates, oxalates, silicates of the alkaline earths, or of
fluorides of their metals, or all their bodies are insoluble in water,
but dissolve in hydrochloric acid, and (being only very sparingly
soluble also in solution of chloride of ammonium) accordingly separate
again upon neutralization of that acid. If, therefore, a white preci-
pitate is produced upon testing an acid solution, under the circum-
stances stated, and according to the directions of 180, 3, b, (3, cc
(59) proceed as follows :
1. If the results of the preliminary examination have given you reason 85
to suspect the presence of SILICIC ACID ( 174, 4, b, a [20]), evaporate
a portion of the hydrochloric acid solution to dryness, moisten
the residue with hydrochloric acid and add water. If silicic acid is
present, it will remain undissolved. Determine the base in the solu-
tion as directed 180, 3 (56), or 4 (62).
2. Add to a portion of the original hydrochloric acid solution some
tartaric acid, and after this ammonia in excess.
a. No PERMANENT PRECIPITATE is FORMED : absence of the 86
above enumerated salts of the alkaline earths. Mix another por-
tion of the original solution with solution of soda in excess, and
add to the one half of the clear fluid chloride of ammonium, to
the other half hydrosulphuric acid. The formation of a preci-
pitate in the former indicates the presence of ALUMINA ; in the
latter, the presence of ZINC. Whether the alumina was com-
bined with PHOSPHORIC ACID, may be ascertained by testing a
portion of the original hydrochloric acid solution with molybdate
of ammonia (143).
b. A PERMANENT PRECIPITATE is FORMED : presence of a salt
of an alkaline earth.
a. If by ignition of the substance in a glass tube (in the 87
course of the preliminary examination see 174, 2) carbonic
oxide and carbonic acid have been evolved, the body turning
slightly black in the process, you may assume the presence
of an OXALATE. Heat a sample of the original substance
to slight redness, dissolve the residue with hydrochloric acid,
when ensuing effervescence will confirm the presence of oxalic
acid ; and ascertain the nature of the alkaline earth in the
solution as directed 180, 4 (62).
)3. Add to a portion of the hydrochloric acid solution ammo- 88
nia until a precipitate forms ; then acetic acid until this is re-
dissolved ; lastly, acetate of soda and a drop of solution of ses-
quichloride of iron : the formation of a white flocculent preci-
pitant indicates the presence of PHOSPHORIC ACID. Add now
some more sesquichloride of iron until the fluid has acquired a
distinct red color, boil, filter boiling, and test the filtrate, which
is now free from phosphoric acid, for the alkaline earth with
which the phosphoric acid was combined, as directed 180, 4
194? DETECTION OF INORGANIC ACIDS. [ 184.
(62)> after having previously removed, by precipitation with
ammonia, the iron which may have been dissolved.
y. Test a portion of the original substance, or of the preci- 89
pitate produced in the hydrochloric acid solution by ammonia,
with sulphuric acid for FLUORINE ( 147). After removal of
the fluorine, ascertain the nature of the alkaline earth now
in the residue, combined with sulphuric acid.
& BORACIC ACID is detected in the hydrochloric acid solution
by means of turmeric paper ( 145), and the base combined with
it, by means of solution of sulphate of lime (baryta, strontia),
sulphuric acid, and alcohol (lime), or a large proportion of
chloride of ammonium, ammonia, and phosphate of soda
(magnesia).
Simple Compounds.
B. SUBSTANCES INSOLUBLE OR SPARINGLY SOLUBLE IN WATER, BUT
SOLUBLE IN HYDROCHLORIC ACID, NITRIC ACID, OR NITRO-HYDRO-
CHLORIC ACID.
DETECTION OF THE ACID.
I. Detection of Inorganic Acids.
184.
1. CHLORIC ACID cannot be present, since all chlorates without QO 1
exception are soluble in water ; NITRIC ACID, which may be present
in form of a basic salt, must have been revealed already by ignition
of the body in a glass tube ( 174), and so must CYANOGEN ( 174, 2,
e [8]). For the analysis of the insoluble metallic CYANIDES insoluble
in water see 202. The results of the test with phosphate of soda and
ammonia will have directed attention to the presence of SILICIC
ACID ( 174, 4, b, a [20])- Evaporation of the hydrochloric acid solution
to dryness, and treatment of the residue with hydrochloric acid and
water will set all doubt at rest on the point.
2. The course of examination laid down here for the detection of 91
the bases leads likewise to that of ARSENIOUS and ARSENIC ACIDS, CAR-
BONIC ACID, HYDROSULPHURIC ACID, and CHROMIC ACID. With regard
to the latter acid, I repeat that its presence is indicated by the yellow
or red color of the compound, the evolution of chlorine which ensues
upon boiling with hydrochloric acid, and the subsequent presence of
sesquioxide of chromium in the solution. Fusion of the compound
tinder examination with carbonate of soda is, however, the most con-
clusive test for chromic acid ( 138).
3. Boil a portion of the substance with nitric acid. 92
a. If nitric oxide gas is evolved, and sulphur separates, this
is confirmative of the presence of a metallic sulphide.
b. If violet vapors escape, the compound is a metallic IODIDE.
c. If reddish-brown fumes of a chlorine-like smell are evolved,
the compound is a metallic BROMIDE, in which case the fumes
will color starch yellow ( 153).
4. Dilute a portion of the solution obtained by boiling with nitric 93
acid (3 [921) or of the nitrate of this solution, should the nitric
acid have left an undissolved residue with water, and add solution
of nitrate of silver to the fluid. The formation of a white precipitate
185.] DETECTION OF ORGANIC ACIDS. 195
which, after washing, is soluble in ammonia, and fuses without de-
composition when heated, indicates the presence of CHLORINE.
5. Boil a portion of the substance with hydrochloric acid, filter, i
necessary, dilute with water, and add chloride of barium. The for-
mation of a white precipitate, which does not redissolve even upon
addition of a large quantity of water, indicates the presence of SUL-
PHURIC ACID.
6. Test for BORACIC ACID as directed 181, 6 (76)-
7. If none of the acids enumerated from 1 to 6 are present, there 95
is reason to suspect the presence of PHOSPHORIC ACID, OXALIC ACID, or
FLUORINE, or the total absence of acids. To the presence of oxalic
acid your attention will have been called already in the course of the
preliminary examination, 174, 2, e (8). If the acids named had
been combined with an alkaline earth, or, as regards phosphoric acid,
with alumina, they would already have been detected in the course
of the examination for these bases ( 183) ; they need therefore here
be tested for, only in case the examination has revealed the presence
of some other base. To that end, precipitate the base, according to
circumstances, either with hydrosulphuric acid or with sulphide of
ammonium, and filter. If you have precipitated with sulphide of
ammonium, add to the filtrate hydrochloric acid to acid reaction,
expel in either case the hydrosulphuric acid by boiling, and filter if
necessary. Test a portion of this solution for phosphoric acid, oxalic
acid, and fluorine, as directed 181, 4 (71).
Simple Compounds.
B. SUBSTANCES INSOLUBLE OR SPARINGLY SOLUBLE IN WATER, BUT
SOLUBLE IN ACIDS.
DETECTION OF THE ACID.
II. Detection of Organic Acids.
I 185.
1. FORMIC ACID cannot be present, as all the formates are soluble 96
in water.
2. ACETIC ACID has been revealed already in the course of the
preliminary examination, by the disengagement of acetone. The re-
action with sulphuric acid and alcohol ( 170) will afford conclusive
proof. _
3. Boil a portion of the substance for some time with solution ol 97
carbonate of soda in excess, and filter hot. You have now the organic
acid in solution in combination with soda. Acidulate the solution
slightly with hydrochloric acid, expel the carbonic acid by heat, and
test as directed 182.
o 2
196 DETECTION OF THE BASE AND THE ACID. [ 186.
Simple Compounds.
C. SUBSTANCES INSOLUBLE OR SPARINGLY SOLUBLE IN WATER, HYDRO-
CHLORIC ACID, NITRIC ACID, AND NITROHYDROCHLORIC ACID.
'
DETECTION OF THE BASE AND THE ACID.
Under this head we have to consider here, SULPHATE OF BARYTA, 98
SULPHATE OF STRONTIA, SULPHATE OF LIME, FLUORIDE OF CALCIUM, SILICA,
SULPHATE OF LEAD, Compounds of LEAD with CHLORINE and BROMINE,
compounds of SILVER with CHLORINE, BROMINE, IODINE, and CYANOGEN,
and lastly, SULPHUR and CHARCOAL, as the only bodies belonging to
this class which are more frequently met with. For the simple
silicates I refer to 203, for the ferro- and ferricyanides, to 202.
The preliminary examination will have informed you whether you
need pay any regard to the possible presence of their compounds.
Sulphate of lime and chloride of lead are not altogether insoluble
in water, and sulphate of lead may be dissolved in hydrochloric acid.
However, as these compounds are so difficultly soluble that complete
solution of them is seldom effected, they are included here also among
the class of insoluble substances, to insure their detection, should
they have been overlooked in the course of the examination of the
aqueous or acid solution of the body to be analyzed.
1. Free SULPHUR must have been detected already in the course of
the preliminary examination.
2. CHARCOAL is black; it is insoluble in aqua regia ; put on
platinum foil, with the blowpipe flame playing upon the under side
of the foil, it is always consumed ; by deflagration with nitrate of
potassa it yields carbonate of potassa.
3. Pour sulphide of ammonium over a very small quantity of the 99
substance under examination.
a. It TURNS BLACK ; this indicates the presence of lead or a
salt of silver.
a. The body fused in the glass tube without decomposition
( 174, 2 [3]) : chloride of lead, bromide of lead, chloride of
silver, bromide of silver, iodide of silver. Fuse 1 part of the com-
pound with 4 parts of carbonate of soda and potassa in a small
porcelain crucible, let cool, boil the residue with water, and
test the filtrate for CHLORINE, BROMINE, and IODINE, as directed,
181, 5 (73)- Dissolve the residue, which consists either of
metallic SILVER or OXIDE OF LEAD, in nitric acid, and test
the solution as directed, 180, 1 (46)-
/3. The body evolved cyanogen, and left metallic silver behind :
CYANIDE OF SILVER.
y. The body remained unaltered : SULPHATE OF LEAD. Boil
a sample of it with solution of carbonate of soda, filter, acidu-
late the filtrate with hydrochloric acid, and test with chloride
of barium for SULPHURIC ACID ; dissolve the washed residue in
nitric acid, and test the solution with hydros ulphuric acid
and with sulphuric acid for LEAD.
I. IT REMAINS WHITE : absence of an oxide of a heavy metal. 100
187.] COMPLEX COMPOUNDS - DETECTION OF BASES. 197
a. The body fused before the blowpipe; this indicates the .
presence of FLUORIDE OF CALCIUM. Keduce a portion of the
substance to a fine powder, decompose this in a platinum
crucible with sulphuric acid, and try the reaction on glass
( 147), to prove the presence of FLUORINE ; boil the residue
with hydrochloric acid, filter, neutralize the filtrate with
ammonia, and test for LIME with oxalate of ammonia,
/3. The body did not fuse before the blowpipe. Mix a small
., - portion of the very finely pulverized substance with 4 times
the quantity of pure carbonate of soda and potassa, and fuse
the mixture in a platinum crucible, or else on platinum foil.
Boil the fused mass with water, filter, should a residue be
left, and wash the latter. Acidulate a portion of the filtrate
with hydrochloric acid, and then test with chloride of barium
for SULPHURIC ACID ; and in case you do not find that acid,
test another portion of the filtrate for SILICIC ACID, by eva-
porating the fluid acidified with hydrochloric acid.
If the SILICIC ACID was present in the pure state, the mass
resulting from the fusion of the substance with carbonate of
soda and potassa must have dissolved in water to a clear
fluid; but if silicates also happened to be present, the
bases of them are left behind undissolved, and may be further
examined.
If, on the other hand, sulphuric acid has been found, the
alkaline earth which was combined with it is found on the
filter as a carbonate. Wash this, then dissolve it in dilute
hydrochloric acid, and test the solution for BARYTA, STRONTIA,
-j-v and LIME, as directed 180, 4 (62).
Complex Compounds*
A. SUBSTANCES SOLUBLE IN WATER, AND ALSO SUCH AS ARE INSOLUBLE
IN WATER, BUT DISSOLVE IN HYDROCHLORIC ACID, NITRIC ACID,
OR NlTROHYDROCHLORIC ACID.
Detection of the Basest
187.J
(Treatment with Hydrochloric Acid : Detection of Silver, Suboxide of
Mercury [Lead].)
The systematic course for the detection of the bases is essentially 101
the same for bodies soluble in water, as for those which are soluble
only in acids. Where, in consequence of the different nature of the
original solution, deviations are rendered necessary, the fact will be
distinctly stated.
* I use this term here, and hereafter in the present work, to designate compounds in
which all the more frequently occurring bases, acids, metals, and metalloids are supposed
the explanations in the Third Section. Kegard is here had also to the pre-
sence of the acids of arsenic, and of those salts of the alkaline earths whjch dissolve m
hydrochloric acid, and separate again from that solution unaltered, upon neutralization of
the acid by ammonia.
Consult the remarks in the Third Section.
198 COMPLEX COMPOUNDS DETECTION OF BASES. [ 187.
I. SOLUTION IN WATER.
MlX THE PORTION INTENDED FOR THE DETECTION OF THE BASES
WITH SOME HYDROCHLORIC ACID.
1. THE SOLUTION HAD AN ACID OR NEUTRAL REACTION PREVIOUSLY 102
TO THE ADDITION OF THE HYDROCHLORIC ACID.
a. No PRECIPITATE is FORMED j this indicates the absence of
silver and suboxide of mercury. Pass on to 188.
b. A PRECIPITATE is FORMED. Add more hydrochloric acid
drop by drop until the precipitate ceases to increase ; then
add about six or eight drops more of hydrochloric acid,
shake the mixture, and filter.
The precipitate produced by hydrochloric acid may consist
of chloride of silver, subchloride of mercury, chloride of lead,
a basic salt of antimony, possibly also of benzoic acid. The
basic salt of antimony, however, redissolves in the excess of
hydrochloric acid ; consequently, if the instructions given have
been strictly followed, the precipitate collected upon the filter
can consist only of chloride of silver, subchloride of mercury,
or chloride of lead (possibly also of benzoic acid, which, how-
ever, is altogether disregarded here).
Wash the precipitate collected upon the filter twice with
cold water, add the washings to the filtrate, and examine the
solution as directed 188, even though the addition of the
washings to the acid nitrate should produce turbidity in the
fluid (which indicates the presence of compounds of antimony
or bismuth).
Treat the washed precipitate on the filter as follows : 103
a. Pour hot water over it upon the filter, and test the fluid
running off with sulphuric acid for LEAD. The non-forma-
tion of a precipitate upon the addition of the sulphuric acid
simply proves that the precipitate produced by hydrochloric
acid contains no lead, and does not by any means establish
the total absence of this metal, as hydrochloric acid fails to
precipitate lead from dilute solutions.
/3. Pour over the now thrice-washed precipitate upon the
filter solution of ammonia. If this changes its color to black
or gray, it is a proof of the presence of SUBOXIDE OF MER-
CURY.
y. Add to the ammoniacal fluid running off in (3 nitric
acid to strongly acid reaction. The formation of a white,
curdy precipitate indicates the presence of SILVER.* (If the
precipitate did contain lead, the ammoniacal solution gene-
rally appears turbid, owing to the separation of a basic salt
of lead. This, however, does not interfere with the testing
for silver, since the basic salt of lead redissolves upon the
addition of nitric acid.)
2. THE ORIGINAL AQUEOUS SOLUTION HAD AN ALKALINE RE-
ACTION. 104
a. THE ADDITION OF HYDROCHLORIC ACID TO STRONGLY ACID
* If the quantity of silver is only very small, the presence is indicated by opalescence
of the fluid.
187.] DETECTION OF BASES. 199
REACTION FAILS TO PRODUCE EVOLUTION OF GAS OR A PRE-
CIPITATE, OR THE PRECIPITATE WHICH FORMS AT FIRST REDIS-
SOLVES UPON FURTHER ADDITION OF HYDROCHLORIC ACID :
pass on to 188.
b. THE ADDITION OF HYDROCHLORIC ACID TO THE ORIGINAL
SOLUTION PRODUCES A PRECIPITATE WHICH DOES NOT RED1S-
SOLVE IN AN EXCESS OF THE PRECIPITANT, EVEN UPON BOILING.
a. The formation of the precipitate is attended neither with 1Q5
evolution of hydrosulphuric acid nor of hydrocyanic acid.
Filter, and treat the nitrate as directed 188.
aa. THE PRECIPITATE is WHITE. It may, in that case,
consist of a salt of lead or silver, insoluble in water and
hydrochloric acid (CHLORIDE OF LEAD, SULPHATE OF LEAD,
CHLORIDE OF SILVER, &c.). Test for the bases and acids
of these compounds as directed 201, bearing in mind
that the chloride of lead or chloride of silver which may-
be present may possibly have been formed in the pro-
cess.
bb. THE PRECIPITATE is YELLOW OR ORANGE. In that
case it may consist of SULPHIDE OF ARSENIC (and if the fluid
from which it has separated was not boiled for a long time,
or only with very dilute hydrochloric acid, also of sulphide
of antimony or bisulphide of tin), which substances were
originally dissolved in solution of ammonia, borax, phos-
phate of soda, or some other alkaline fluid, with the ex-
ception of solutions of alkaline sulphides and cyanides.
Examine the precipitate as directed 190.
/3. The formation of the precipitate is attended with evolu- 106
tion of hydro sulphuric acid gas, but not of hydrocyanic acid.*
aa. THE PRECIPITATE is OF A PURE WHITE COLOR, AND
CONSISTS OF SEPARATED SULPHUR. In that Case a SUL-
PHURETTED ALKALINE SULPHIDE is present. Boil, filter,
and pass onto 192, bearing in mind that of the substances
considered in that paragraph the heavy metals cannot be
present if the original solution was colorless.
bb. THE PRECIPITATE is COLORED. In that case you
may conclude that a METALLIC SULPHUR SALT is present,
i. e., a combination of an alkaline sulphur base with a
metallic sulphur acid. The precipitate may accordingly
Consist of TERSULPHIDE OF GOLD, BISULPHIDE OF PLA-
TINUM, BISULPHIDE OF TIN, TERSULPHIDE OF ARSENIC, Or
TERSULPHIDE OF ANTIMONY. It might, however, consist also
of SULPHIDE OF MERCURY Or of SULPHIDE OF COPPER, or
contain these substances, as the former is readily soluble
in sulphide of potassium, and the latter slightly soluble in
sulphide of ammonium. Filter, and treat the filtrate as
in aa, the preciptate as directed 189.
y. The formation of the precipitate is attended with evolu- 107
tion of hydrocyanic acid, with or without simultaneous dis-
engagement of hydrosulphuric acid. This indicates the pre-
* Should the odor of the evolved gas leave any doubt regarding the presence or absence
of hydrocyanic acid, add some chromate of potassa to a portion of the fluid, previously to
the addition of the hydrochloric acid.
200 ACTUAL EXAMINATION COMPLEX COMPOUNDS. [ 188.
sence of an ALKALINE CYANIDE, and, if the evolution of the
hydrocyanic acid is attended with that of hydrosulphuric
acid, also of an alkaline SULPHIDE. In that case the precipi-
tate may, besides the compounds enumerated in a (105) an( l
/3 (106)) contain many other substances (e. g. } sulphide of
nickel, cyanide of nickel, cyanide of silver, &c.). Boil, with
further addition of hydrochloric acid, or of nitric acid, until
the whole of the hydrocyanic acid is expelled, and treat the
solution, or, if an undissolved residue has been left, the ni-
trate, as directed 188; and the residue (if any) according
to 201.
C. THE ADDITION OF HYDROCHLORIC ACID FAILS TO PRO- 108
DUCE A PERMANENT PRECIPITATE, BUT CAUSES EVOLUTION OF
GAS.
a. The escaping gas smells of hydrosulphuric acid ; this
indicates the presence of a SIMPLE ALKALINE SULPHIDE.
Proceed as in b, /3, aa (106)-
(3. The escaping gas is inodorous; in that case it is CAR-
BONIC ACID which was combined with an alkali. Pass on to
188.
y. The escaping gas smells of hydrocyanic acid (no matter
whether hydrosulphuric acid or carbonic acid is evolved at
the same time or not). This indicates the presence of an
ALKALINE CYANIDE. Boil until the whole of the hydrocyanic
acid is expelled, and then pass on to 1 88.
II. SOLUTION IN HYDROCHLORIC ACID OR IN NITROHYDROCHLORIC
ACID.
Proceed as directed 188.
III. SOLUTION IN NITRIC ACID.
Dilute a small sample of it with water ; should this produce tur- 109
bidity or a precipitate (indicative of the presence of bismuth) add
nitric acid until the fluid is clear again, then hydrochloric acid.
1. No PRECIPITATE is FORMED. Absence of silver and sub-
oxide of mercury. Treat the principal solution as directed 188.
2. A PRECIPITATE is FORMED. Treat a larger portion of the
nitric acid solution the same way as the sample, filter, and
examine the precipitate as directed 187, I. 1, b (103), the
filtrate as directed 188.
188.*
(Treatment with Hydrosulphuric Acid, Precipitation of the Metallic
Oxides of Group V. 2nd Section, and of Group VI.)
ADD TO A small PORTION OF THE CLEAR ACID SOLUTION HYDRO-
SULPHURIC ACID WATER, UNTIL THE ODOR OF HYDROSULPHURIC ACID
IS DISTINCTLY PERCEPTIBLE AFTER SHAKING THE MIXTURE, AND
WARM GENTLY,
1. No PRECIPITATE is FORMED, even after the lapse of some HO
* Consult the remarks in the Third Section.
188.] DETECTION OF BASES.
201
time. Pass on to 192, for lead, bismuth, cadmium, copper,
mercury, gold, platinum, antimony, tin, and arsenic,* are not
present ;t the absence of sesquioxide of iron and of chromic
acid is also indicated by this negative reaction.
2. A PRECIPITATE IS FORMED.
a. The precipitate is of a pure white color, light and finely HI
pulverulent, and does not redissolve on addition of hydro-
chloric acid. It consists of separated sulphur, and indicates
the presence of SESQUIOXIDE OF IRON.* None of the other
metals enumerated in 188, 1 (HO), can be present. Treat
the principal solution as directed 192.
b. The precipitate is colored.
^ Add to the larger proportion of the acid or acidified solu- H2
tion, best in a small flask, hydrosulphuric acid water in
excess, i. e., until the fluid smells distinctly of it, and the
precipitate ceases to increase upon continued addition of the
reagent; apply a gentle heat, shake vigorously for some
time, filter, keep the filtrate (which contains the oxides pre-
sent of Groups I. IV.) for further examination, according
to the instructions of 192, and thoroughly wash the pre-
cipitate which contains the sulphides of the metals present
of Groups V. and VI.
In many cases, and more particularly when there is any
reason to suspect the presence of arsenic, it will be found
more convenient to transmit hydrosulphuric acid gas
through the solution DILUTED WITH WATER, instead of
adding hydrosulphuric acid water.
If the precipitate is yellow, it consists principally of tersul- H3
phide of arsenic, bisulphide of tin, or sulphide of cadmium ;
if orange-colored, this indicates tersulphide of antimony ; if
brown or black, one at least of the following oxides is pre-
sent : oxide of lead, teroxide of bismuth, oxide of copper,
oxide of mercury, teroxide of gold, binoxide of platinum,
protoxide of tin. However, as a yellow precipitate may
contain small admixtures of an orange-colored, a brown, or
even a black precipitate, and yet its color not be very per-
ceptibly altered thereby, it will always prove the safest way
to assume the presence of all the metals named in 188, 1
(110)> in any precipitate produced by hydrosulphuric acid,
and to proceed accordingly as the next paragraph ( 189)
directs.
* Should the preliminary examination have led you to suspect the presence of arsenic
acid, you must endeavor to obtain the most conclusive evidence of the absence of this acid ;
this may be done by allowing the fluid to stand for some time, or by heating it with sul-
phurous acid previous to the addition of the hydrosulphuric acid. (Compare 132.)
t In solutions containing much free acid, the precipitates are frequently formed only
after dilution with water.
J Sulphur will precipitate also if sulphurous acid, iodic acid, or bromic acid are pre-
sent (which substances are not included in our analytical course), and also if chromic acid,
chloric acid, or free chlorine are present. In presence of chromic acid, the separation of
the sulphur is attended with reduction of the acid to sesquioxide of chromium, in con-
sequence of which the reddish-yellow color of the solution changes to green. (Compare
138.) The white sulphur suspended in the green solution looks at first like a green pre-
cipitate, which frequently tends to mislead beginners.
202 ACTUAL EXAMINATION COMPLEX COMPOUNDS. [ 189.
189.
(Treatment of the Precipitate produced ~by Hydro sulphuric Acid with Sul-
phide of Ammonium; Separation of the 2nd Section of Group V.
from Group VI.)
INTRODUCE A SMALL PORTION OF THE PRECIPITATE PRODUCED BY 114
HYDROSULPHURIC ACID IN THE ACIDIFIED SOLUTION INTO A TEST-
TUBE,* ADD A LITTLE WATER, AND THREE OR FOUR DROPS OF YELLOW-
ISH SULPHIDE OF AMMONIUM, AND EXPOSE THE MIXTURE FOR A SHORT
TIME TO A GENTLE HEAT, t
1. THE PRECIPITATE DISSOLVES COMPLETELY IN SULPHIDE OF H5
AMMONIUM (or SULPHIDE OF SODIUM, as the case may be) : absence of
the metals of Group V. cadmium, lead, bismuth, copper, mercury.
Treat the remainder of the precipitate (of which you have digested
a portion with sulphide of ammonium) as directed 190. If the
precipitate produced by hydrosulphuric acid was so trifling that
vou have used the whole of it in treating with sulphide of ammo-
nium, precipitate the solution obtained in that process by addition
of hydrochloric acid, filter, wash the precipitate, and treat the latter
as directed 190.
2. THE PRECIPITATE IS NOT REDISSOLVED, OR AT LEAST NOT H6
COMPLETELY : presence of the metals of Group V.
Dilute with 4 or 5 parts of water, filter, and mix the filtrate
with hydrochloric acid in slight excess.
a. The fluid simply turns- milky, owing to the separation
cf sulphur. Absence of the metals of Group VI. gold,
platinum, tin, antimony, and arsenic. J Treat the rest of the
precipitate of which you have digested a portion with sul-
phide of ammonium, according to the directions of 191.
b. A colored precipitate is formed : presence of metals of H7
Group VI. by the side of those of Group V. Treat the
entire precipitate produced by hydrosulphuric acid the same
as you have treated a portion of it, i. e. } digest it with yellow
* * If there is a somewhat large precipitate, this may be readily effected by means of a
small spatula of platinum or horn ; but if you have only a very trifling precipitate, make
a hole in the bottom of the filter, insert the perforated point into the mouth of the test-
tube, rinse the precipitate into the latter by means of the washing-bottle, wait until the
precipitate has subsided, and then decant the water.
t If the solution contains copper, which is generally revealed by the color of the fluid,
and may be ascertained positively by testing with a clean iron rod (see 119, 10), use
solution of sulphide of sodium instead of sulphide of ammonium (in which sulphide of
copper is not absolutely insoluble, see 119, 5), and boil the mixture. But if the fluid,
besides copper, also contains oxide of mercury (the presence of which is generally suffi-
ciently indicated by the several changes of color exhibited by the precipitate forming
upon the addition of the hydrosulphuric acid [ 118, 3], and which, in doubtful cases,
may be detected with positive certainty by testing a portion of the original solution
acidified with hydrochloric acid, with protochloride of tin), sulphide of ammonium
must be used, although the separation of the sulphides of the antimony group from the
sulphide of copper is not fully effected in such cases ; since, were sulphide of sodium used,
the sulphide of mercury would dissolve in this reagent, and this would impede the ulterior
examination of the sulphides of the antimony group.
That this inference becomes uncertain if the precipitate produced by hydrosulphuric
acid, instead of being digested with a small quantity of sulphide of ammonium, has been
treated with a larger quantity of that reagent, is self-evident ; for the large quantity of
sulphur which separates in that case will, of course, completely conceal any slight traces
of sulphide of arsenic or bisulphide of tin which may have been thrown down.
190.] DETECTION OF BASES. 203
sulphide of ammonium, or, as the case may be, sulphide of
sodium, let it subside, pour the supernatant liquid on a
filter, digest the residue in the tube once more with yellow
sulphide of ammonium (or sulphide of sodium), and filter.
Wash the residue* (containing the sulphides of Group V.),
and treat it afterwards as directed 191. Dilute the filtrate
which contains the metals of Group VI. in the form of
sulphur salts with water, add hydrochloric acid to slightly
acid reaction, heat gently, filter the precipitate formed
which contains the sulphides of the metals of Group VI.
mixed with sulphur wash thoroughly, and proceed as
directed next paragraph ( 190).
190.
(Detection of the Metals of Group VI. : Arsenic, Antimony, Tin t
Gold, Platinum.)
If the precipitate consisting of the sulphides of Group VI. has a 118
PURE YELLOW COLOR, this indicates principally arsenic and tin; if it
is distinctly ORANGE- YELLOW, antimony is present ; if it is BROWN or
BLACK, this denotes the presence of platinum or gold.
Beyond these general indications, the color of the precipitate
affords no safe guidance. It is therefore always advisable to test
yellow precipitate also for antimony, gold, and platinum, since
minute quantities of the sulphides of these metals are completely
hid by a large quantity of bisulphide of tin or tersulphide of arsenic.
Proceed accordingly as follows :
Heat a little of the precipitate on the lid of a porcelain crucible, or
on a fragment of porcelain or glass, t
1. Complete vocalization ensues : probable presence of ARSENIC, 119
absence of the other metals of Group VI. Reduction of a
portion of the precipitate with cyanide of potassium and car-
bonate of soda ( 131, 12) will afford positive proof of the
presence or absence of arsenic. Whether that metal was pre-
sent in the form of arsenious acid or in that of arsenic acid,
may be ascertained by the method described 1 33.
2. A fixed residue is left. In that case all the metals of 120
Group VI. must be sought for. Dry the remainder of the
precipitate thoroughly upon the filter, triturate it together with
about 1 part of anhydrous carbonate of soda and 1 part of
nitrate of soda, and transfer the mixture in small portions at a
time to a little porcelain crucible, in which you have previously
* If the residue suspended in the fluid containing sulphide of ammonium, and inso-
luble therein, subsides readily, it is not transferred to the filter, but washed in the tube
by decantation. But if its subsidence proceeds slowly and with difficulty, it is transferred
to the filter, and washed there ; a hole is then made in the bottom of the filter, and the
residue rinsed into a small porcelain basin by means of a washing-bottle ; the application,
of a gentle heat will now materially aid the subsidence of. the residue, and the super-
natant water may then be decanted.
t That this preliminary examination may be omitted if the precipitate is not yellow,
and that it can give a decisive result only if the sulphur precipitate submitted to the
test has been thoroughly washed, is self-evident.
204) DETECTION OF BASES. [ 190.
heated 2 parts of nitrate of soda to fusion.* As soon as com-
plete oxidation is effected, pour the mass out on a piece of por-
celain.
After cooling, soak the fused mass (the portion still sticking
to the inside of the crucible as well as the portion poured out
on the porcelain) in cold water, filter the insoluble residue
which will remain if the mass contained antimony, tin, gold,
or platinum and well wash with a mixture of about equal
parts of water and alcohol. (The alcohol is added to prevent
the solution of the antimonate of soda. The washings are not
added to the nitrate.) The filtrate and the residue are now
examined as follows :
a. EXAMINATION OF THE FILTRATE FOR ARSENIC (which 121
must be present in it in the form of arsenate of soda).
Divide the filtrate into two portions, add highly dilute nitric
acid cautiously to the one portion to slightly acid reaction, and
apply heat.t Add to the acidified solution some nitrate of
silver (not too little), filter (in case some chloride of silver J or
nitrite of silver should have separated), pour upon the filtrate,
along the side of the tube held slanting, a layer of dilute solu-
tion of ammonia, 5 parts of water to 1 part of solution
of ammonia and let the mixture stand for some time with-
out shaking. The formation of a reddish-brown precipitate,
which appears hovering cloud-like between the two layers
(and may be seen far more readily and distinctly by re-
flected than by transmitted light), denotes the presence of
ARSENIC.
If the arsenic is present in some quantity, and the free nitric
acid of the solution is exactly saturated with ammonia, the
fluid being stirred during this process, the precipitate of arse-
nate of silver which forms imparts a brownish-red tint to the
entire fluid.
To gain more positive information respecting the presence of 122
arsenic, precipitate the second portion of the filtrate with solu-
tion of neutral acetate of lead, filter the precipitate (which con-
sists of sulphate, carbonate, and if arsenic is really present
arsenate of lead), dry between blotting paper, and then expose
on charcoal to the inner flame of the blowpipe. If arsenic
is present, a globule of metallic lead containing arsenic will
be produced, which will long continue to exhale the odor of
* Should the amount of the precipitate be so minute that this operation cannot be con-
veniently performed, cut the filter, with the dried precipitate adhering to it, into small
pieces, triturate these together with some carbonate of soda and nitrate of soda, and pro-
ject both the powder and the paper into the fusing nitrate of soda. It is preferable,
however, in such cases, to procure at once, if practicable, a sufficiently large amount of
the precipitate, as otherwise there will be but little hope of effecting the positive detec-
tion of all the metals of Group VI. Supposing all the metallic sulphides of the sixth
group to have been present, the fused mass would consist of antimonate and arsenate of
soda, binoxide of tin, metallic gold and platinum, sulphate, carbonate, nitrate, and some
nitrite of soda. Compare also 133, 1.
*f In some cases where a somewhat larger proportion of carbonate of soda had been
used, or a very strong heat applied, a trifling precipitate (hydrated binoxide of tin) may
separate upon the acidification of the filtrate with nitric acid. This may be filtered off,
and then treated in the same manner as the undissolved residue.
J Chloride of silver will separate if the reagents were not perfectly pure, and the pre-
cipitate has not been thoroughly washed.
190-] DETECTION OF BASES.
-205
garlic whenever the inner flame of the blowpipe is made to act
upon it. For further confirmation of the presence of arsenic
this substance may be exhibited in the metallic state. (Compare
131 and 132.) Whether the arsenic was present in the
form of arsenious acid or in that of arsenic acid, may be ascer-
tained by the method described, 133, at the end.
b. EXAMINATION OF THE RESIDUE FOR ANTIMONY, TIN, GOLD, 123
PLATINUM. (As the antimony, if present in the residue, must
exist as white, pulverulent antimonate of soda, the tin as white,
flocculent binoxide, the gold and platinum in the metallic state*
the appearance of the residue is in itself indicative of its nature.)
Dry the residue on the filter. If there is much of it, separate
it from the filter, and fuse it together with about 4 parts of
cyanide of potassium, either in a small porcelain crucible or in
a somewhat wide glass tube sealed at one end. If the quantity
is small, insert the filter together with the precipitate in a
platinum wire twisted into a spiral coil, and incinerate in
the outer mantle of a small spirit-lamp or gas-flame ; transfer
the residue together with the filter-ash to a narrow glass tube
sealed at one end, and fuse it in this together with 4 parts
of cyanide of potassium insert the ignited part of the tube,
whilst still red-hot, into a test-tube filled with cold water,
which will cause the part containing the fused mass to crack
off" in splinters. In either case remove the soluble salts com-
pletely by repeated warming with water and decantation, pour
hydrochloric acid over the metallic residue, heat to boiling, and
test the solution, which in case of the presence of TIN must
contain protochloride of tin, with chloride of mercury ( 128,
8). Boil the residue once more with hydrochloric acid, decant
the fluid, then dissolve the residue still remaining in hydro-
chloric acid with addition of the least possible amount of nitric
acid to effect solution, mix this with solution of hydrosulphuric
acid, and heat to incipient boiling.
If a precipitate of a distinct orange color forms, ANTIMONY is 124
present. In presence of much tin, the color is usually more or
less concealed by an admixture of bisulphide of tin (for it is not
easy to effect a complete separation of the two metals by boil-
ing with hydrochloric acid) ; the precipitate may also contain
bisulphide of platinum and metallic gold (resulting from the
reduction by heat of precipitated tersulphide of gold).
Let the precipitate, therefore, subside, wash it several times
by decantation, and finally heat it with hydrochloric acid,
to dissolve the sulphide of antimony present. If the precipitate
did contain gold or bisulphide of platinum, a black pulverulent
residue will remain. Test now in the first place the hydro-
chloric acid solution for ANTIMONY, by means of zinc and pla-
tinum ( 130, 8), then dissolve the residue, if any, in some
nitrohydrochloric acid, and test a portion of the solution for
GOLD, with protochloride of tin, another portion for the same
metal with sulphate of protoxide of iron ( 125). Evaporate
the remainder of the solution with addition of some chloride of
potassium, and add to the residue a mixture of equal parts of
alcohol and water. The formation of a yellow precipitate
indicates the presence of PLATINUM.
206 ACTUAL EXAMINATION COMPLEX COMPOUNDS. [ 191.
191.
(Defection of the Metallic Oxides of Group V. 2nd Section : Oxide of Lead.
Teroxide of Bismuth. Oxide of Copper. Oxide of Cadmium. Oxide
of Mercury.)
WASH THE PRECIPITATE WHICH HAS NOT BEEN DISSOLVED BY SUL- 125
PHIDE OF AMMONIUM, AND BOIL WITH NITRIC ACID. This operation
is performed best in a small porcelain dish ; the boiling mass must
be constantly stirred with a glass rod during the process. A great
excess of acid must be avoided.
1. THE PRECIPITATE DISSOLVES, AND THERE REMAINS FLOATING IN 126
THE FLUID ONLY THE SEPARATED, LIGHT, FLOCCULENT, YELLOW SUL-
PHUR j this indicates the absence of mercury. CADMIUM, COPPER,
LEAD, and BISMUTH may be present.
Filter the fluid from the separated- sulphur, and treat the nitrate as
follows (should there be too much nitric acid present, the greater
part of this must first be driven off by evaporation) : add to a portion
of the filtrate dilute sulphuric acid in moderate quantity, heat gently,
and let the fluid stand some time.
a. No PRECIPITATE FORMS j absence of lead. Mix the re- 127
mainder of the filtrate with ammonia in excess, and gently
heat.
a. No precipitate is formed; absence of BISMUTH. If the 128
liquid is blue, COPPER is present; very minute traces of
copper, however, might be overlooked, if the color of the
ammoniated fluid alone were consulted. To be quite safe,
and also to test for cadmium, evaporate the ammoniated solu-
tion nearly to dryness, add a little acetic acid, and, if neces-
sary, some water, and
aa. Test a small portion of the fluid for copper with 129
ferrocyanide of potassium. The formation of a reddish-
brown precipitate, or a light brownish-red turbidity, indi-
cates the presence of COPPER (in the latter case only to a
very trifling amount).
lb. Mix the remainder of the fluid with solution of 130
hydrosulphuric acid in excess. The formation of a yellow
precipitate denotes CADMIUM. If, on account of the pre-
sence of copper, the sulphide of cadmium cannot be dis-
tinctly recognised, allow the precipitate produced by the
hydrosulphuric acid to subside, decant the supernatant
fluid, and add to the precipitate solution of cyanide of
potassium until the sulphide of copper is dissolved. If a
yellow residue is left undissolved, CADMIUM is present in
the contrary case, not.
/3. A precipitate is formed. BISMUTH is present. Filter 131
the fluid, and test the filtrate for copper and cadmium, as
directed in a (128)- To test the washed precipitate more
fully for bismuth, slightly dry the filter containing it between
blotting-paper, remove the still moist precipitate with a
platinum spatula, dissolve in a watch-glass in the least
possible quantity of hydrochloric acid, and then add a
192.] DETECTION OP BASES. 207
sufficient quantity of water. The appearance of a milky
bidity confirms the presence of bismuth.
b. A PRECIPITATE is FORMED. Presence of LEAD. Treat the 132
entire fluid the same as you have treated the sample, filter off
the precipitate of sulphate of lead, and test the filtrate for
bismuth, copper, and cadmium, as directed in a (127)-* Test
the precipitate, after washing, by pouring solution of hydro-
sulphuric acid over it.
2. THE PRECIPITATE OF THE METALLIC SULPHIDES DOES NOT COM- 133
PLETELY DISSOLVE IN THE BOILING NITRIC ACID, BUT LEAVES A
RESIDUE, BESIDES THE LIGHT FLAKES OF SULPHUR THAT FLOAT IN THE
FLUID. Probable presence of OXIDE OF MERCURY (which may be
pronounced almost certain, if the precipitate is heavy and black).
Allow the precipitate to subside, filter off the fluid, which must still
be tested for CADMIUM, COPPER, LEAD, and BISMUTH ; mix a small
portion of the filtrate with a large amount of solution of hydro-
sulphuric acid, and should a precipitate form or a coloration become
visible, treat the remainder according to the directions of 191, 1
(126).
Wash the residue (which, besides sulphide of mercury, may alsa
contain sulphate of lead, formed by the action of nitric acid upon
sulphide of lead, and also binoxide of tin, as the complete separa-
tion of bisulphide of tin from many of the sulphides of the metals of
Group Y. is rather difficult), and examine one half of it for
mercury,t by dissolving it in some hydrochloric acid, with addition
of a very small proportion of nitric acid, and testing the solution
with copper, or protochloride of tin ( 118); fuse the other half
with cyanide of potassium and carbonate of soda. If you obtain
metallic grains, wash, heat with nitric acid, and test the solution
obtained with sulphuric acid for lead, the residue, which may
be left, for tin, according to the directions of 190, 2, b (123).
192.
(Precipitation with Sulphide of Ammonium, Separation and Detection of
the Oxides of Groups III. andlV. : Alumina, Sesquioxide of Chromium ;
Oxide of Zinc, Protoxide of Manganese, Protoxide of Nickel, Protoxide
of Cobalt, Proto- and Sesquioxide of Iron ; and also of those Salts of the
Alkaline Earths which are precipitated by Ammonia from their Solution
in Hydrochloric Acid; Phosphates, B orates, Oxalates, Silicates, and
Fluorides.)
PUT A small portion OF THE FLUID IN WHICH SOLUTION OF HYDRO- 134
SULPHURIC ACID HAS FAILED TO PRODUCE A PRECIPITATE ( 188, 1,
[110]), OR OF THE FLUID WHICH HAS BEEN FILTERED FROM THE PRECI-
* For another method of distinguishing cadmium, copper, lead, and bismuth from each
other, I refer to the Third Section (additions and remarks to 191) page 274. _
f If you have an aqueous solution, or a solution in very dilute hydrochloric acid, the
oxide of mercury formed was present in the original substance in that form ; but if the
solution has been prepared by boiling with concentrated hydrochloric acid, or by heating
with nitric acid, the mercury may most likely have been originally present in the form of
suboxide, and may have been converted into oxide in the process.
08 ACTUAL EXAMINATION COMPLEX COMPOUNDS. [ 192.
PITATE FORMED, in a test-tube, observe whether it is colored or not,*
boil to expel the hydrosulphuric acid which may be present, add a
few drops of nitric acid, boil, and observe again the color of the fluid ;
then cautiously add ammonia to alkaline reaction, observe whether
this produces a precipitate, and then add some sulphide of ammo-
nium, no matter whether ammonia has produced a precipitate or not.
a. NEITHER AMMONIA NOR SULPHIDE OF AMMONIUM PRO- 135
DUCES A PRECIPITATE. Pass on to 193, for iron, nickel,
cobalt, zinc, manganese, sesquioxide of chromium, alumina, are
not present, nor are phosphates, borates,t silicates, and oxalates
of the alkaline earths ; nor fluorides of the metals of the alkaline
earths.
b. SULPHIDE OF AMMONIUM PRODUCES A PRECIPITATE, AMMO- 136
NIA HAVING FAILED TO DO so ; absence of phosphates, borates,t
Silicates, and oxalates of the alkaline earths ; of the fluorides
of the metals of the alkaline earths ; and also, if no organic
matters are present, of iron, sesquioxide of chromium, and
alumina. Pass on to 192, 1 (138).
c. AMMONIA PRODUCES A PRECIPITATE before the addition of 137
sulphide of ammonium. The course of proceeding to be pur-
sued now, depends upon whether, (a) the original solution is
simply aqueous, and has a neutral reaction, or (/3) the original
solution is acid. In the former case, pass on to 192, 1
(138)> f r phosphates, borates, oxalates, and silicates of the
alkaline earths cannot be present ; nor can fluorides of the
metals of the alkaline earths. In the latter case, regard must
be had to the possible presence of all the bodies enumerated in
' 192, a (135) ; pass on to 192, 2 (150).
1. DETECTION OF THE BASES OF GROUPS III. AND IY. IF PHOS- 138
PHATES, &C., IF THE ALKALINE EARTHS ARE NOT PRESENT.
Mix the fluid mentioned at the beginning of the paragraph (134) ;
a portion of which you have submitted to a preliminary examina-
tion with some chloride of ammonium, then with ammonia, just to
alkaline reaction ; lastly, with sulphide of ammonium, until the
fluid, after being shaken, smells distinctly of that reagent ; shake the
mixture until the precipitate begins to separate in flakes, and filter.
Keep the FILTRATED which contains, or may contain, the basis of
Groups II. and I., for subsequent examination according to the
directions of 193. Wash the PRECIPITATE with water, to which
a very little sulphide of ammonia has been added, and then proceed
with it as follows :
* If the fluid is colorless, it contains no chromium. If colored, the tint will to some
extent act as a guide to the nature of the substance present ; thus a green tint, or a
violet tint turning green upon boiling, points to the presence of chromium ; a light green
tint to that of nickel ; a reddish color to that of cobalt ; the turning yellow of the fluid
upon boiling with nitric acid, to that of iron. It must, however, be always borne in mind
that these tints are perceptible only if the metallic oxides are present in larger quantity,
and also that complementary colors, such as, for instance, the green of the nickel solution
and the red of the cobalt solution will destroy each other, and that, accordingly, a solu-
tion may contain both metals and yet appear colorless.
f* Presence of much chloride of ammonium has a great tendency to prevent the precipi-
tation of borates of the alkaline earths.
If the filtrate has a brownish color, this points to the presence of nickel, sulphide of
nickel, as is well known, being "slightly soluble in sulphide of ammonium ; this, however,
involves no modification of the analytical course.
1-92.] DETECTION OF BASES.
209
a. IT is PERFECTLY WHITE ; absence of iron, cobalt, 139
nickel. You must test for all the other bases of Groups III!
and IV., as the faint tints of sesquioxide of chromium and sul-
phide of manganese are imperceptible in a large quantity
of a white precipitate. Dissolve the precipitate by heat-
ing it in a small dish with the least possible amount of hydro-
chloric acid ; boil should hydrosulphuric acid be evolved
until this gas is completely expelled, concentrate by evaporation,
neutralize with carbonate of soda, then add solution of soda in
excess, heat to boiling, and keep the mixture for some time
in a state of ebullition.
a. The precipitate formed at first dissolves completely in the 140
excess of solution of soda. Absence of manganese and chro-
mium, presence of alumina or oxide of zinc. Test a portion
of the alkaline solution with solution of hydrosulphuric acid
for ZINC ; acidify the remainder with hydrochloric acid, add
ammonia slightly in excess, and apply heat. The formation
of a white, flocculent precipitate shows the presence of
ALUMINA.
/3. The precipitate formed does not dissolve, or dissolves only 141
partially, in the excess of solution of soda. Filter and test
the FILTRATE, as in a (140), for ZINC and ALUMINA. With
the undissolved PRECIPITATE proceed as follows :
aa. If the color of the solution indicates the presence
of chromium, fuse the precipitate in the cover of a platinum
crucible, together with carbonate and nitrate of soda;
treat the fused mass with water, and filter. If the nitrate
is yellow, and, after being acidified with acetic acid, gives
with acetate of lead a yellow precipitate, CHROMIUM is
present.
bb. Test a portion of the precipitate for MANGANESE, by
means of the reaction with carbonate of soda in the outer
blowpipe flame. If chromium has been found in aa, the
residue left upon treating the fused mass with water, is
used for this purpose.
b. IT is NOT WHITE ; this points to the presence of chromium, 142
manganese, iron, cobalt, or nickel. If it is black, or inclines to
black, one of the three metals last-mentioned is present. Under
all circumstances, all the oxides of Groups III. and IY. must
be looked for.
Remove the washed precipitate from the filter with a spatula,
or by rinsing it, with the aid of a washing-bottle, into a test-
tube, through a hole made in the bottom of the filter, and
pour over it rather dilute cold hydrochloric acid in moderate
excess.
a. It dissolves completely (except perhaps a little sulphur, 143
which may separate) ; absence of cobalt and nickel, at least
of notable quantities of these two metals.
Boil until the hydrosulphuric acid is completely expelled,
filter if particles of sulphur are suspended in the fluid, con-
centrate by evaporation, neutralize with carbonate of soda,
then add solution of potassa or soda in excess, boil, filter the
fluid from the insoluble precipitate which is sure to remain,
I. P
210 ACTUAL EXAMINATION COMPLEX COMPOUNDS. [ 192.
wash the latter, and proceed first to examine the filtrate, then
the precipitate.
aa. Test a portion of the filtrate with hydrosulphuric 144
acid for zinc; acidify the remainder with hydrochloric
acid, and then test it with ammonia for ALUMINA. Com-
pare 192, 1, a, a (140).
66. Dissolve a portion of the precipitate in hydrochloric
acid, and test the solution with sulphocyanide of potas-
sium for IRON. Test other portions for chromium and
manganese, according to the directions of 192, 1, a,
ft (141).
N. B. If it is intented to make a very accurate 146
analysis, you have still to subject the remainder of
the precipitate mentioned in bb (145) to further exa-
mination, since it may contain magnesia (thrown down
with the alumina) ; or some other alkaline earths, which
may have been carried down along with the sesqui-
oxide of chromium, owing to presence of carbonate
of ammonium in the ammonia or sulphide of ammo-
nium ; and lastly, also traces of cobalt, nickel, and zinc.
Dissolve it, accordingly, in hydrochloric acid, and test
the solution for the bodies enumerated, according to the
directions of 192, 2, 6, a and /3 (155 and 156), omit-
ting, however, the addition of sesquioxide of iron, recom-
mended in 156-
(3. The precipitate is not completely dissolved, a black re-
sidue being left; this indicates the presence of cobalt and
nickel. Filter, wash the undissolved precipitate, and test
the filtrate as directed 192, 1, b, a (143) ', proceed with the
residuary precipitate as follows:
aa. Test a portion of it with borax, first in the outer, 148
then in the inner blowpipe-flame. If the bead in the oxidizing
flame is violet whilst hot, and of a pale reddish-brown when
cold, and turns in the reducing flame gray and turbid,
nickel is present ; but if the color of the bead is and re-
mains blue, in both flames, and whether hot or cold,
COBALT is present. As in the latter case the presence of
nickel cannot be distinctly recognised ; examine
66. The remainder of the precipitate by incinerating it 149
together with the filter in a coil of platinum wire, heating
the ash with some hydrochloric acid, filtering the solution,
then evaporating nearly to dryness, and adding nitrite of
potassa, and then acetic acid ( 108, 10). The formation
of a yellow precipitate confirms the presence of COBALT.
Let the fluid, with the precipitate in it, stand for some time
at a gentle heat, then filter, and test the filtrate with solu-
tion of soda for nickel.
2, DETECTION OF THE BASES OF GROUPS III. AND IY. IN CASES 150
WHERE PHOSPHATES, BORATES, OXALATES, OR SILICATES OF THE AL-
KALINE EARTHS, OR FLUORIDES OF THE METALS OF THE ALKALINE
EARTHS, MAY POSSIBLY HAVE BEEN THROWN DOWN ALONG WITH
THESE BASES, ?'.&, in cases where the original solution was acid, and
192.] DETECTION OF BASES. 211
a precipitate was produced by ammonia in the preliminary exami-
nation. See (134).
Mix the fluid mentioned in the beginning of this paragraph (134)
with some chloride of ammonium, then with ammonia just to alkaline
reaction, lastly with sulphide of ammonium, until the fluid, after being
shaken, smells distinctly of this reagent ; shake the mixture until
the precipitate begins to separate in flakes, and filter. Keep the FIL-
TRATE, which contains, or may contain, the bases of Groups II. and I.,
for subsequent examination according to the directions of 193.
Wash the precipitate with water to which a very little sulphide of
ammonium has been added, and then proceed with it as follows.
To give a clear notion of the obstacle to be overcome in this
analytical process I must remind you that it is necessary to ex-
amine the precipitate for the following bodies : Iron, nickel, cobalt
(these show their presence to a certain extent by the black or blackish
coloration of the precipitate), manganese, zinc, sesquioxide of chro-
mium (the latter generally reveals its presence by the color of the
solution), alumina ; baryta, strontia, lime, magnesia, which latter
substances may have fallen down in combination with phosphoric
acid, boracic acid, oxalic acid, silicic acid, or in form of fluorides.
Besides these bodies, free silicic acid may also be contained in the
precipitate as hydrate.
As the original substance must, under all circumstances, be 151
afterwards examined for all acids that might possibly be present, it
is not indispensable to test for the above enumerated acids at this
stage of the analytical process ; still, as it is often interesting to
know the presence of these acids at once, more especially in cases
where a somewhat large proportion of some alkaline earth has been
found in the precipitate produced by sulphide of ammonium, a
method for the detection of the acids in question will be found
appended by way of supplement to the method for the detection
of the bases.
Remove the precipitate from the filter with a small spatula, or 152
by rinsing it off with the washing-bottle, and pour over it cold dilute
hydrochloric acid in moderate excess.
a. A RESIDUE REMAINS. Filter, and treat the filtrate as 153
directed in 6 (154). The residue, if it is black, may contain
sulphide of nickel, and sulphide of cobalt, and besides these,
sulphur and silicic acid. Wash, and examine a sample of it in
conjunction with phosphate of soda and ammonia before the
blowpipe, in the outer flame. If a silica skeleton remains un-
dissolved, ( 150, 8), this proves the presence of silicic acid.
If the color of the bead is blue, COBALT is present ; if reddish,
turning yellow on cooling, NICKEL. Should the color leave you
in doubt, incinerate the filter containing the remainder of the
residue, and test for cobalt and nickel by means of nitrite of
potassa, as directed 192, 1, b, (3, bb (149).
b. No RESIDUE is LEFT (except perhaps a little sulphur, 154
which may separate) : absence of nickel and cobalt, at least
in any notable proportion.
Boil the solution until the sulphuretted hydrogen is expelled,
and then proceed as follows :
p2
212 ACTUAL EXAMINATION COMPLEX COMPOUNDS. [ ]92.
a. Mix a small portion of tlie solution with dilute sul- 155
phuric acid. If a precipitate forms, this may consist of
sulphates of BARYTA and STRONTIA, possibly also of sulphate of
lime. Filter, wash the precipitate, decompose it by boiling
or fusion with carbonated alkali, wash the carbonates pro-
duced, dissolve them in hydrochloric acid, and test the solu-
tion as directed 193. Mix the fluid which has not been
precipitated by dilute sulphuric acid, or the fluid filtered
from the precipitate produced, with 3 volumes of spirit of
wine. If a precipitate forms, this consists of sulphate of
LIME. Filter, dissolve in water, and add oxalate of ammonia
to the solution, as a confirmatory proof of the presence of
lime.
/3. Heat a somewhat larger sample with some nitric acid, 156
and test a small portion of the fluid with sulphocyanide of
potassium for IRON;* mix the remainder with sesqui-
chloride of iron in sufficient quantity to make a drop of the
fluid give a yellowish precipitatet when mixed, on a watch-
glass, with a drop of ammonia ; concentrate the fluid now until
there is only a small quantity left ; add to this some water,
then a few drops of solution of carbonate of soda, just sufficient
to nearly neutralize the free acid, and lastly carbonate of
baryta in slight excess; stir the mixture, and let it stand
in the cold until the fluid above the precipitate has become
colorless. Filter now the precipitate (aa) from the solu-
tion (bb), and wash.
aa. Boil the precipitate for some time with solution of 157
soda, filter, and test the filtrate for ALUMINA,:}: by heating
with chloride of ammonium in excess. The part of the
precipitate insoluble in solution of soda is examined for
CHROMIUM, as directed in 192, 1, a, j3, aa (141).
bb. Mix the solution with some ammonia and sulphide
of ammonium.
aa. No precipitate forms : absence of manganese and 158
zinc. Mix the solution containing chloride of barium
with dilute sulphuric acid in slight excess, boil, filter,
supersaturate with ammonia, and mix with oxalate of
ammonia. If a precipitate of oxalate of LIME forms,
filter, and test the filtrate with phosphate of soda for
MAGNESIA.
/3/3. A precipitate forms. Filter, and proceed with 159
the filtrate according to the directions of aa (158)
* Whether the iron was present as sesquioxide or as protoxide, must be ascertained by
testing the original solution in hydrochloric acid with ferricyanide of potassium and sul-
phocyanide of potassium.
t The addition of sesquichloride of iron is necessary, to effect the separation of phos-
phoric acid and silicic acid which may be present.
If the solution contains silicic aeid, the precipitate taken for alumina may contain also
silicic acid. A simple trial with phosphate of soda and ammonia, on a platinum wire,
in the blowpipe flame, will show whether the precipitate really contains silicic acid.
Should this be the case, ignite the remainder of the supposed alumina precipitate
on the cover of a platinum crucible, add some acid sulphate of potassa, fuse the
mixture, and treat the fused mass with water, which will dissolve the alumina, leaving
the silicic acid undissolved ; precipitate the alumina from the solution by ammonia.
193.] DETECTION OF OXIDES.
213
The precipitate may consist of sulphide of manganese
and sulphide of zinc, and may contain traces also of
sulphide of cobalt and sulphide of nickel. Wash it
with water containing some sulphide of ammonium, and
then treat it with acetic acid, which will dissolve the
sulphide of MANGANESE, if any is present, leaving the
other sulphides undissolved. Filter, boil the filtrate
with solution of soda, and test the precipitate, which
may form, with carbonate of soda in the outer blow-
pipe flame for MANGANESE. Free the residuary part of
the precipitate, which acetic acid has failed to dissolve,
by washing, from the acetic acid solution still adhering
to it, and then treat it with dilute hydrochloric acid,
which will dissolve the zinc, if any is present. Filter,
add some nitric acid to the filtrate, and concentrate
the mixture considerably by boiling then add to it
solution of soda in excess, boil, filter, if necessary,
and test the filtrate with sulphide of ammonium for
ZINC. Should a precipitate insoluble in solution of
soda remain in the last operation, or should the dilute
hydrochloric acid have left a black residue, test this
precipitate and residue for COBALT and NICKEL, if you
have not already previously detected the presence of
these bodies ; compare 192, 1, b, fl (148 and 149).
y. If you have found alkaline earths in a and /3, and 160
wish to know the acids in combination with which they have
passed into the precipitate produced by sulphide of ammo-
nium, this may be ascertained by making the following expe-
riments with the remainder of the hydrochloric acid solu-
tion :
aa. Test a small portion of it for PHOSPHORIC ACID, by 161
means of molybdic acid ( 143, 11).
bb. Mix another portion with carbonate of soda in
excess, boil for some time, filter, and test one-half of the
filtrate for OXALIC ACID, by acidifying it with acetic acid,
and adding solution of sulphate of lime ; the other half
for BORACIC ACID, by slightly acidifying it with hydro-
chloric acid, and testing with turmeric paper ( 145 and
146).
cc. Evaporate a third portion in a small dish or in a 162
watch-glass, dry the residue thoroughly, and then treat
with hydrochloric acid. If there was any SILICIC ACID in
the solution, this will be left undissolved.
dd. Precipitate the remainder with ammonia, filter,
wash and dry the precipitate, and examine it for FLUORINE
according to 147, 5.
193.
(Separation and Detection of the Oxides of Group II., which are pre-
cipitated by Carbonate of Ammonia in Presence of Chloride of
Ammonium, viz., Baryta, Strontia, Lime).
To A SMALL PORTION OF THE FLUID IN WHICH AMMONIA AND
214 ACTUAL EXAMINATION COMPLEX COMPOUNDS. [ 193.
SULPHIDE OF AMMONIUM HAVE FAILED TO PRODUCE A PRECIPITATE,
OR OF THE FLUID FILTERED FROM THE PRECIPITATE FORMED, ADD
CHLORIDE OF AMMONIUM, IF THE SOLUTION CONTAINS NO AMMO-
NIACAL SALT, THEN CARBONATE OF AMMONIA AND SOME CAUSTIC
AMMONIA, AND HEAT FOR SOME TIME VERY GENTLY (not to
boiling).
1. No PRECIPITATE FORMS: absence of any notable quantity of 163
baryta, strontia, and lime. Traces of these alkaline earths may,
however, be present ; to detect them, add to another portion of the
fluid some sulphate of ammonia (prepared by supersaturating
dilute sulphuric acid with ammonia) : if the fluid becomes turbid, it
contains traces of BARYTA ; add to a third portion some oxalate of
ammonia ; if the fluid turns turbid which reaction may perhaps
require some time to manifest itself traces of lime are present.
Treat the remainder of the fluid as directed 194, after having
previously removed the traces of lime and baryta which may have
been found, by means of the reagents that have served to effect
their detection.
2. A PRECIPITATE is FORMED. Presence of LIME, BARYTA, or 164
STRONTIA. Fitter, test portions of the filtrate with sulphate and
oxalate of ammonia, for traces of lime and baryta, which it may pos-
sibly still contain, remove such traces, should they be found, by
means of the said reagents, and examine the fluid, thus perfectly
freed from baryta, strontia, and lime, for magnesia according to
the directions of 194. Wash the precipitate produced by car-
bonate of ammonia, dissolve it in the least 'possible amount of
dilute hydrochloric acid, and add to a small portion of the fluid
some solution of sulphate of lime (not too little).
a. No precipitate is formed, NOT EVEN AFTER THE LAPSE OF
SOME TIME. Absence of baryta and strontia; presence of
LIME. To remove all doubt, mix another sample with oxalate
of ammonia.
b. A precipitate is formed ~by solution of sulphate of lime.
a. It is formed immediately ; this indicates BARYTA. Be- 165
sides this, strontia and lime may also be present.
Evaporate the remainder of the hydrochloric acid solu-
tion of the precipitate produced by carbonate of ammonia to
dryness, digest the residue with strong alcohol, decant the
fluid from the undissolved chloride of barium, dilute with an
equal volume of water, mix with a few drops of hydrofluo-
silicic acid which throws down the small portion of baryta
that had dissolved in form of chloride of barium allow the
mixture to stand for some time ; filter, evaporate the
alcoholic solution to dryness, dissolve the residue in water,
and test a portion of the fluid with a dilute solution of
sulphate of potassa ( 96, 3). If a precipitate forms imme-
diately, or in the course of half an hour, the presence of
STRONTIA is demonstrated. In that case, let the fluid with
the precipitate in it stand at rest for some time, then filter,
and add ammonia and oxalate of ammonia to the filtrate.
The formation of a white precipitate indicates LIME. If
sulphate of potassa has failed to produce a precipitate, the
remainder of the solution of the residue left upon evapora-
194, 195.] EXAMINATION FOR MAGNESIA. 215
tion of the alcoholic fluid is tested at once with ammonia
and oxalate of ammonia for lime.
ft. It is formed only after some time. Absence of baryta, 166
presence of STRONTIA. Mix the remainder of the hydro-
chloric acid solution with sulphate of potassa, let the mix-
ture stand for some time, then filter, and test the filtrate with
ammonia and oxalate of ammonia for LIME.
(Examination for Magnesia.)
To A PORTION OF THE FLUID IN WHICH CARBONATE, SULPHATE, AND
OXALATE OF AMMONIA HAVE FAILED TO PRODUCE A PRECIPITATE ( 193,
1 [163] ), OR OF THE FLUID FILTERED FROM THE PRECIPITATES FORMED
( 193, 2 [164]), ADD AMMONIA, THEN SOME PHOSPHATE OF SODA,
AND, SHOULD A PRECIPITATE NOT AT ONCE FORM, RUB THE INNER
SIDES OF THE VESSEL WITH A GLASS ROD, AND THEN LET THE
MIXTURE STAND FOR SOME TIME.
1. No PRECIPITATE is FORMED : absence of magnesia. Evapo- 167
rate another portion of the fluid to dryness,* and ignite gently. If
a residue remains, treat the remainder of the fluid the same
as the sample, and examine the residue, which by the moderate
ignition to which it has been subjected has been freed from ammonia,
for potassa and soda, according to the directions of 195. If no
residue is left, this is a proof of the absence of the fixed alkalies ;
pass on to 196.
2. A PRECIPITATE is FORMED : presence of MAGNESIA. As testing 168
for alkalies can proceed with certainty only after the removal of
magnesia, evaporate the remainder of the fluid to dryness, and
ignite until all ammoniacal salts are removed. Warm the residue
with water, add baryta-water, prepared from the crystals, as long
as a precipitate continues to form, boil, filter, add to the fil-
trate a mixture of carbonate of ammonia with some caustic
ammonia in slight excess, heat for some time gently, filter, evapo-
rate the filtrate to dryness, adding some chloride of ammonium dur-
ing the process (to convert into chlorides the caustic alkalies that
may have formed), ignite the residue gently, then dissolve it in
a little water, precipitate, if necessary, once more, with ammonia
and carbonate of ammonia, evaporate again, and if a residue
remains, ignite this gently, and finally examine it according to the
directions of 195.
195.
(Examination for Potassa, and Soda.)
YOU HAVE NOW TO EXAMINE FOR POTASSA AND SODA THE GENTLY
IGNITED RESIDUE, FREE FROM SALTS OF AMMONIA AND ALKALINE
EARTHS, WHICH HAS BEEN OBTAINED IN 194, 1 (167), OR m
194, 2 (168). ,.,
Dissolve it in a little water, filter, if necessary, evaporate until
* The most convenient way is to conduct the evaporation in the cover of a platinum
crucible.
216 EXAMINATION FOR AMMONIA. [ 196, 197.
there is only a small quantity of fluid left, and transfer one half of
this to a watch-glass, leaving the other half in the porcelain dish.
1. To the one-half in the porcelain dish add, after cooling, a few 169
drops of solution of bichloride of platinum. If a yellow, crystal-
line precipitate forms immediately, or after some time, POTASSA is
present. Should no precipitate form, evaporate to dryness at a
gentle heat, and treat the residue with a very small quantity of
water or, if chlorides alone are present, with a mixture of water and
alcohol, when the presence of minute traces of potassa will be
revealed by a small quantity of a heavy yellow powder being left
undissolved.
2. To the other half of the fluid (in the watch-glass) add some 170
antimonate of potassa. If this produces at once or after some time
a crystalline precipitate, SODA is present. If the quantity of
soda present is only very trifling, it often takes twelve hours
before minute crystals of autimouate of soda will separate ;
you must therefore always wait full that time for the possible
manifestation of the reaction, before deciding, from its non-appear-
ance, that no soda is present. As regards the form of the crystals,
consult 91.
196.
(Examination for Ammonia.)
There remains still the examination for ammonia. Triturate 171
some of the body under examination, or, if a fluid, a portion of
the latter, together with an excess of hydrate of lime, and, if
necessary, a little water. If the escaping gas smells of ammonia, if
it restores the blue color of reddened litmus paper, and forms white
fumes with hydrochloric acid vapors, brought into contact with
it by means of a glass rod, AMMONIA is present. The reaction is the
most sensitive, if the trituration is made in a small beaker, and the
latter covered with a glass plate with a slip of moistened turmeric
or moist reddened litmus paper adhering to the under side.
Complex Compounds.
A, 1. SUBSTANCES SOLUBLE IN WATER.
DETECTION OF ACIDS.*
I. In the Absence of Organic Acids.
197.
Consider, in the first place, which are the acids that form with
the bases found compounds soluble in water, and let this guide
you in the examination. To students the table given in Ap-
pendix IV. will prove of considerable assistance.
1. The ACIDS of ARSENIC, as well as CARBONIC ACID, HYDROSUL- 172
PHURIC ACID, CHROMIC ACID, and SILICIC ACID, have generally been
detected already in the course of testing for the bases j compare
also 181, 1 and 2.
* Consult also Section III.
197.] DETECTION OF ACIDS. 217
2. Add to a portion of the solution chloride of barium or, if
lead, silver, or suboxide of mercury are present, nitrate of baryta,
and, should the reaction of the fluid be acid, add ammonia to
neutral or slightly alkaline reaction.
a. No PRECIPITATE is FORMED : absence of sulphuric acid, 173
phosphoric acid, chromic acid, silicic acid, oxalic acid, arsenious
and arsenic acids, as well as of notable quantities of boracic
acid and hydrofluoric acid.* Pass on to 3 (175).
b. A PRECIPITATE is FORMED. Dilute the fluid, and add 174
hydrochloric acid ; if the precipitate does not redissolve, or at
least not completely, SULPHURIC ACID is present.
3. Add nitrate of silver to a portion of the solution. If this fails 175
to produce a precipitate, test the reaction, and add to the fluid, if
it is acid, some dilute ammonia, taking care to add the reagent
so gently and cautiously that the two fluids do not intermix ; if the
reaction is alkaline, on the other hand, add with the same care
some dilute nitric acid, instead of ammonia, and watch attentively,
whether a precipitate or a cloud forms in the layer between the
two fluids.
a. NO PRECIPITATE IS FORMED IN THE LAYER BETWEEN THE 176
TWO FLUIDS, NEITHER IMMEDIATELY NOR AFTER SOME TIME.
Pass on to 4 (181) '> there is neither chlorine, bromine, iodine,
cyanogen,t ferro- and ferricyanogen present, nor sulphur ; nor
phosphoric acid, arsenic acid, arsenious acid, chromic acid,
silicic acid, oxalic acid \ nor boracic acid, if the solution was
not too dilute.
b. A PRECIPITATE is FORMED. Observe the color J of it, 177
then add nitric acid, and shake the mixture.
a. The precipitate redissolves completely : absence of
chlorine, bromine, iodine, cyanogen, ferro- and ferricyanogen,
and also of sulphur. Pass on to 4 (181)'
ft. A residue is left : chlorine, bromine, iodine, cyanogen, 178
ferro- or ferricyanogen may be present ; and if the residue
is black or blackish, HYDROSULPHURIC ACID or a soluble
METALLIC SULPHIDE. The presence of sulphur may, if
necessary, be readily established beyond doubt, by mixing
another portion of the solution with some solution of sul-
phate of copper.
aa. Test another portion of the fluid for IODINE, and
subsequently for BROMINE, by the methods described in
157.
bb. Test a small portion of the fluid with sesqui- 179
chloride of iron for FERROCYANOGEN ; and, if the color of
the silver precipitate leads you to suspect the presence of
* If the solution contains an ammoniacal salt in somewhat considerable proportion, the
non-formation of a precipitate cannot be considered a conclusive proof of the absence ot
these acids, since the baryta salts of most of them (not the sulphate), are, m prei
ammoniacal salts, more or less soluble in water.
t That the cyanogen in cyanide of mercury is not indicated by nitrate of i
been mentioned 181, 5 (73). . r , j
J Chloride, bromide, cyanide, and ferrocyanide of silver, and oxalate, silicate, an
borate of silver are white ; iodide of silver, tribasic phosphate, and arsemte vei
are yellow ; arsenate of silver and ferricyanide of silver are brownish-red ; chromate o
silver is purple-red j sulphide of silver black.
218 DETECTION OF ACIDS. [ 197.
FERRICYANOGEN, test another portion for this latter
substance with sulphate of iron. If the original solu-
tion has an alkaline reaction, some hydrochloric acid
must be added before the addition of the sesquichloride
of iron, or the sulphate of iron.
cc. CYANOGEN, if present in form of a simple metallic
cyanide soluble in water, may usually be readily re-
cognised by the smell of hydrocyanic acid which the body
under examination emits, and which is rendered more
strongly perceptible by addition of a little dilute sulphuric
acid. If no ferrocyanogen is present, the presence of
cyanogen may be ascertained by the method given in
155, 6.
dd. Should bromine, iodine, cyanogen, ferrocyanogen, 180
ferricyanogen, and sulphur not be present, the preci-
pitate which nitric acid has failed to dissolve, consists of
CHLOKIDE of silver.
However, should the analytical process have revealed
the presence of any of the other bodies, a special
examination for chlorine may become necessary, viz.,
in cases where the quantity of the precipitate will not
enable the operator to pronounce with positive certainty
on the presence or absence of the latter element.* In
such cases, which are of rare occurrence, however, the
method given in 157 is resorted to.
4. Test another portion for NITRIC ACID, by means of sulphate of 181
iron and sulphuric acid ( 159).
5. To ascertain whether CHLORIC ACID is present, pour a little con-
centrated sulphuric acid over a small sample of the solid body under
examination : ensuing yellow coloration of the acid resolves the
question in the affirmative ( 160). You have still to test for
phosphoric acid, boracic acid, silicic acid, oxalic acid, and chromic
acid, as well as for hydrofluoric acid. For the first five acids
test only in cases where both chloride of barium and nitrate of
silver have produced precipitates in neutral solutions. Compare
also foot note to 197, 2, a.
6. Test for PHOSPHORIC ACID, by adding to a portion of the fluid 182
ammonia in excess, then chloride of ammonium and sulphate
of magnesia ( 143, 7). Very minute quantities of phosphoric
acid are detected most readily by means of rnolybdic acid ( 143,
7. To effect the detection of OXALIC ACID and HYDROFLUORIC
ACID, add chloride of calcium to a portion of the solution. If this
produces a precipitate which is not redissolved by addition of
acetic acid, one or both bodies are present. Examine therefore now
a sample of the original substance for fluorine, according to the
directions of 147, 5, another sample for oxalic acid, by the method
given in 146, 7.
8. Acidulate a portion of the fluid slightly with hydrochloric 183
* Supposing, for instance, the solution of nitrate of silver to have produced a copious
precipitate insoluble in nitric acid, and the subsequent examination to have shown mere
traces of iodine and bromine, the presence of chlorine may be held to be demonstrated
without requiring additional proof.
198.] DETECTION OF ACIDS. 219
acid, and then test for BORACIC ACID, by means of turmeric paper
9. Should SILICIC ACID not yet have been found in the course
of testing for the bases, acidulate a portion of the fluid with hydro-
chloric acid, evaporate todryness, and treat the residue with hydro-
chloric acid ( 150, 3).
10. CHROMIC ACID is readily recognised by the yellow or red
color of the solution, and by the purple-red color of the precipi-
tate produced by nitrate of silver. If there remains the least
doubt on the point, test for chromic acid with acetate of lead and
acetic acid ( 138).
Complex Compounds.
A, 1. SUBSTANCES SOLUBLE IN WATER.
DETECTION OF ACIDS.
II. In Presence of Organic Acids.
198.
1 . The examination for inorganic acids, inclusive of oxalic acid, 184
is made in the manner described in 197. As the tartrates
and citrates of baryta and oxide of silver are insoluble in water,
tartaric acid and citric acid can be present only in cases where both
chloride of barium and nitrate of silver have produced precipitates
in the neutral fluid j still, in drawing a conclusion, you must bear
in mind that the said salts are slightly soluble in solutions of
salts of ammonia.
The examination for the organic acids is conducted as follows :
2. Make a portion of the fluid feebly alkaline by addition of am- 185
monia, filter, if necessary, add some chloride of ammonium, then
chloride of calcium, shake vigorously, and let the mixture stand at
rest from ten to twenty minutes.
a. No PRECIPITATE IS FORMED, NOT EVEN AFTER THE LAPSE
OF SOME TIME. Absence of tartaric acid ; pass on to 3.
b. A PRECIPITATE IS FORMED IMMEDIATELY, OR AFTER SOME 186
TIME. Filter, wash, and keep the filtrate for further examina-
tion according to the directions of 3.
Digest and shake the precipitate with solution of soda,
without applying heat, then dilute with a little water, filter, and
boil the filtrate some time. If a precipitate separates, TARTARIC
ACID may be assumed to be present. Filter hot, and subject
the precipitate to the ammonia and nitrate of silver test
described in 162, 8.
3. Mix the fluid in which chloride of calcium has failed to pro-
duce a precipitate, or that which has been filtered from the precipi-
tate in which latter case some more chloride of calcium is to be
added with alcohol.
a. No PRECIPITATE is FORMED. Absence of citric acid and 187
malic acid. Pass on to 4.
b. A PRECIPITATE is FORMED. Filter and treat the filtrate 188
as directed in 4. As regards the precipitate, treat this as
follows :
220 DETECTION OF ACIDS. [ 198.
After -washing with some alcohol, dissolve on the filter in
a little dilute hydrochloric acid, add ammonia to the filtrate to
feebly alkaline reaction, and then boil for some time.
a. THE FILTRATE REMAINS CLEAR. Absence of citric acid.
Probable presence of MALIC ACID. Add alcohol again to the
fluid, and test the lime precipitate in the manner directed
165, to make sure whether malic acid is really present
or not.
ft. A HEAVY, WHITE PRECIPITATE IS FORMED. Presence 189
of CITRIC ACID. Filter boiling, and test the filtrate for
malic acid in the same manner as in a. To remove all
doubt as to whether the precipitate is citrate of lime
or not, it is advisable to dissolve once more in some hy-
drochloric acid, to supersaturate again with ammonia,
. and to boil ; if the precipitate really consisted of citrate of
lime, it will now be thrown down again. (Compare
164, 3.)
4. Heat the filtrate of 3, b (188) (or the fluid in which addition 190
of alcohol has failed to produce a precipitate, 3, a [187])? to expel
the alcohol, neutralize exactly with hydrochloric acid, and add ses-
quichloride of iron. If this fails to produce a light brown, floccu-
lent precipitate, neither succinic nor benzoic acid is present. If a
precipitate of the kind is formed, filter, digest, and heat the washed
precipitate with ammonia in excess ; filter, evaporate the filtrate
nearly to dryness, and test a portion for SUCCINIC ACID with chloride
of barium and alcohol ; the remainder for BENZOIC ACID with hydro-
chloric acid ( 169). Benzoic acid may generally be readily detected
also in the original substance, by pouring some dilute hydrochloric
acid over a small portion of the latter, which will leave the benzoic
acid undissolved ; it is then filtered and heated on platinum foil
( 168, 1).
5. Evaporate a portion of the solution to dryness if acid, after 191
previous saturation with soda introduce the residue, or a portion
of the original dry substance into a small tube, pour some alcohol
over it, add about an equal volume of concentrated sulphuric acid,
and heat to boiling. Evolution of the odor of acetic ether de-
monstrates the presence of ACETIC ACID. This odor is rendered
more distinctly perceptible by shaking the cooling or cold mixture.
6. To effect the detection of FORMIC ACID, add to a portion of 192
the solution nitrate of silver in not too small a proportion, then
soda until the fluid is exactly neutralized, and boil . If formic acid
is present, reduction of the silver to the metallic state ensues ( 171,
4). The reaction with nitrate of suboxide of mercury may be had
recourse to as a conclusive test ( 171, 4).*
* In presence of chromic acid the reduction of oxide of silver and of suboxide of mercury
is not a positive proof of the presence of formic acid. In cases where the two acids are
present, the following method must be resorted to : Mix the original solution with some
nitric acid, add oxide of lead in excess, shake the mixture, filter, add to the filtrate dilute
sulphuric acid in excess, and distil. Test the distillate as directed 172. In presence
of tartaric acid also it is the safest way to distil the formic acid first, with addition of
dilute sulphuric acid.
199.] .DETECTION OF ACIDS. 221
Complex Compounds.
A, 2. SUBSTANCES INSOLUBLE IN WATER, BUT SOLUBLE IN HYDRO-
CHLORIC ACID, NITRIC ACID, OR NITROHYDROCHLORIC ACID.
DETECTION OF THE ACIDS.
I. In the Absence of Organic Acids.
199.
In the examination of these compounds attention must be directed,
to all acids, with the exception of chloric acid. Cyanogen com-
pounds and silicates are not examined by this method. (Com-
pare 202 and 203.)
1. CARBONIC ACID, SULPHUR (in form of metallic sulphides), ARSE- 193
NIOUS ACID, ARSENIC ACID, and CHROMIC ACID, if present, have been
found already in the course of the examination for bases j NITRIC
ACID, if present, has been detected in the course of the preliminary
examination, by the ignition of the powdered substance in a glass
tube( 174).
2. Mix a sample of the substance with 4 parts of pure carbonate 194
of soda and potassa, and, should it contain a metallic sulphide, add
some nitrate of soda \ fuse the mixture in a platinum crucible if
there are no reducible metals present, in a porcelain crucible if re-
ducible metals are present ; boil the fused mass with water, and
add a little nitric acid, leaving the reaction of the fluid, however,
still alkaline ; heat again, filter, and proceed with the filtrate accord-
ing to the directions of 197, to effect the detection of all the
acids which were combined with the bases.*
3. As the phosphates of the alkaline earths are only incompletely 195
decomposed by fusion in conjunction with carbonate of soda and
potassa, it is always advisable in cases where alkaline earths are
present, and phosphoric acid has not yet been detected, to dissolve
a fresh sample of the body under examination in hydrochloric acid
or nitric acid, and test the solution for PHOSPHORIC ACID with
molybdic acid.
4. If in the course of the examination for bases, alkaline earths
have been found, it is also advisable to test a separate portion of
the body under examination for FLUORINE, by the method described
in 147, 5.
5. That portion of the substance under examination which is 196
treated of in 199, 2 (194), can be tested for SILICIC ACID only
in cases where the fusion has been effected in a platinum crucible ;
in cases where a porcelain crucible has been used, it is necessary to
examine a separate portion of the body for silicic acid, by evaporat-
ing the hydrochloric or nitric acid solution.
6. Examine a separate sample of the body for OXALIC ACID as
directed in 200, 3.
* If the body examined has been found to contain a metallic sulphide, a separate por-
tion of it must be examined for sulphuric acid, by heating it with hydrochloric acid,
filtering, adding water to the filtrate, and then testing the fluid with chloride of barium.
222 DETECTION OP ACIDS. [ 200, 201.
Complex Compounds.
A, 2. SUBSTANCES INSOLUBLE IN WATER, BUT SOLUBLE IN HYDRO-
CHLORIC ACID, NITRIC ACID, OR NITROHYDROCHLORIC ACID.
DETECTION OP THE ACIDS.
II. In Presence of Organic Acids.
200.
1. Conduct the examination for inorganic acids according to the 197
direction of 199.
2. Test for ACETIC ACID as directed 198, 5 (191).
3. Dissolve a portion of the compound under examination in the 198
least possible amount of hydrochloric acid, filter, if necessary, and
test the undissolved residue which may be left, for BENZOIC ACID by
application of heat ; add to the filtrate solution of carbonate of soda
in considerable excess, and, besides this, also a little solid carbonate
of soda, boil the mixture for a few minutes, and then filter the fluid
from the precipitate. In the filtrate you have now all the organic
acids in solution, combined with soda. Acidify the filtrate with
hydrochloric acid, heat, and proceed according to the direction of
198.
Complex Compounds.
B. SUBSTANCES INSOLUBLE OR SPARINGLY SOLUBLE BOTH IN WATER
AND IN HYDROCHLORIC ACID, NITRIC ACID, OR NITROHYDRO-
CHLORIC ACID.
DETECTION OF THE BASES, ACIDS, AND NON-METALLIC ELEMENTS.
201.
To this class belong the following bodies and compounds. 199
SULPHATE OP BARYTA, SULPHATE OF STRONTIA, and SULPHATE OF
LIME.*
SULPHATE OF LEADt and chloride of lead.{
CHLORIDE OF SILVER, bromide of silver, iodide of silver, cyanide
of silver, 1 1 ferro- and ferricyanide of silver.^]"
SILICIC ACID and many SILICATES.
Native alumina, or alumina which has passed through a process
of intense ignition, and many aluminates.
Ignited sesquioxide of chromium and chrome-ironstone (a com-
pound of sesquioxide of chromium and protoxide of iron).
* Sulphate of lime passes partially into the solution effected by water, and often com-
pletely into that effected by acids.
*f Sulphate of lead may pass completely into the solution effected by acids.
Chloride of lead can here only be found if the precipitate insoluble in acids has not
been thoroughly washed with hot water.
|| Bromide, iodide, and cyanide of silver are decomposed by boiling with nitrohydro-
chloric acid, and converted into chloride of silver; they can accordingly be found here
only in cases where the operator has to deal with a substance which as nitrohydrochloric
acid has failed to effect its solution is examined directly by the method described in this
paragraph { 201).
U With regard to the examination of these compounds, compare also 202.
201.] DETECTION OP BASES, ACIDS, ETC. 223
Ignited, and native binoxide of tin (tin-stone).
Some metaphosphates and some arsenates.
FLUORIDE OF CALCIUM and a few other compounds of fluorine.
SULPHUR.
CARBOX.
Of these compounds those printed in small capitals are more
frequently met with. As the silicates perform a highly important
part in mineral analysis, a special chapter ( 203 206) is devoted
to them.
The substance Bunder examination which is insoluble in water
and in acids is in the first place subjected to the preliminary
experiments here described in a e, if the quantity at your disposal
is not absolutely too small to admit of this proceeding ; in cases
where the quantity is insufficient for the purpose, the operator
must omit this preliminary examination, and at once pass on to 1,
bearing in mind, however, that the body may contain all the afore-
said substances and compounds.
a. Examine closely and attentively the physical state and con- 200
dition of the substance, to ascertain whether you have to deal
with a homogeneous mass or with a mass composed of dis-
similar particles ; whether the body is sandy or pulverulent,
whether it has the same color throughout, or is made up of
variously-colored particles, &c. The microscope, or even a simple
magnifying glass, will be found very useful at this stage of the
examination.
b. Heat a small sample in a glass tube sealed at one end. If 201
brown fumes arise, and SULPHUR sublimes, this is of course a proof
of the presence of that substance.
c. If the substance is black, this indicates, in most cases, the pre- 202
sence of carbon (wood-charcoal, pit-coal, bone-black, lamp-black,
graphite, &c). Heat a small sample on platinum foil over the blow-
pipe flame ; if the substance which blackens the fingers is con-
sumed, this may be held to be a positive proof of the presence of
CARBON in some shape or other. Graphite, which may be readily
recognised by its property of communicating its blackish-gray color
to the fingers, to paper, &c., requires the application of oxygen for
its easy combustion.
d. Warm a small sample, together with a small lump of cyanide 203
of potassium and some water, for some time, filter, and test the
filtrate with sulphide of ammonium. The formation of a brownish-
black precipitate shows that the substance under examination con-
tains a compound of SILVER.
e. If an undissolved residue has been left in d, wash this tho- 204:
roughly with water, and, if white, sprinkle a few drops of sul-
phide of ammonium over it j if it turns black, salts of LEAD are
present. If, however, the residue left in d is black, heat it with
some acetate of ammonia, adding a few drops of acetic acid, filter,
and test the filtrate for LEAD, by means of sulphuric acid and
hydrosulphuric acid.*
The results obtained by these preliminary experiments serve to
guide the operator now in his further course of proceeding.
* The presence of lead in silicates, e. g. in glass containing lead, cannot be detected by
this method.
224 DETECTION OF BASES, ACIDS, ETC. [ 201.
1, a. SALTS OF LEAD ARE NOT PRESENT. Pass on to 2 (206)- 205
b. SALTS OF LEAD ARE PRESENT. Heat the substance re-
peatedly with a concentrated solution of acetate of ammonia,
until the salt of lead is completely dissolved out. Test a por-
tion of the nitrate for CHLORINE, another for SULPHURIC ACID,
and the remainder for LEAD, by addition of sulphuric acid in
excess, and by hydrosulphuric acid. If acetate of ammonia
has left a residue, wash this, and treat it as directed in 2.
2, a. SALTS OF SILVER ARE NOT PRESENT. Pass on to 3. 206
b. SALTS OF SILVER ARE PRESENT. Digest the substance
free from lead, or which has been freed from that metal by
acetate of ammonia, repeatedly with cyanide of potassium
and water, at a gentle heat (in presence of sulphur, in the
cold), until all the salt of silver is removed. If an undis-
solved residue is left, wash this, and then proceed with it
according to the directions of 3 (207)- Of the filtrate, which
contains cyi nide of potassium, mix the larger portion with
sulphide of ammonium, to precipitate the silver. Wash the
precipitated sulphide of silver, then dissolve it in nitric acid,
dilute the solution, and add hydrochloric acid, to ascertain
whether the precipitate really consisted of sulphide of silver.
Test another small portion of the nitrate for SULPHURIC
ACID.* *
3, a. SULPHUR is NOT PRESENT. Pass on to 4. 207
b. SULPHUR is PRESENT. Heat the substance free from silver
and lead in a covered porcelain crucible until all the sulphur
is expelled, and, if a residue is left, treat this according to the
directions of 4 (208).
4, Mix the substance free from silver, lead, and sulphur with 208
2 parts of carbonate of soda, 2 parts of carbonate of potassa, and
1 part of nitrate of potassa, f heat the mixture in a platinum crucible
until the mass is in a state of calm fusion, place the red hot crucible
on a thick, cold iron plate, and let it cool. By this means you will
generally succeed in removing the fused mass from the crucible in
an unbroken lump. Soak the mass now in water, boil, filter, and
wash the residue until chloride of barium no longer produces a
precipitate in the washings. (Add only the first washings to the
filtrate.)
a. The solution obtained contains the acids which were 209
present in the substance decomposed by fluxing (208)- But it
may, besides these acids, contain also such bases as are soluble
in caustic alkalies. Proceed as follows :
a. Test a small portion of the solution for SULPHURIC
ACID.
/3. Test another portion with molybdic acid for PHOS-
PHORIC ACID and ARSENIC ACID. If a yellow precipitate
* As the carbonate of potassa contained in the cyanide of potassium may have pro-
duced a total or partial decomposition of any sulphates of the alkaline earths which
happened to be present.
f* Addition of nitrate of potassa is useful even in the case of white powders, as it
counteracts the injurious action of silicate of lead, should any be present, upon the
platinum crucible. In the case of black powders, the proportion of nitrate of potassa
must be correspondingly increased, in order that carbon, if present, may be consumed as
completely as possible, and that any chrome-ironstone existing iu the compound, may be
more thoroughly decomposed.
201.] DETECTION OP BASES, ACIDS, ETC. 225
forms, remove the arsenic acid which may be present with
hydrosulphuric acid, and then test once more for phosphoric
acid.
y. Test another portion for FLUORINE ( 147, 7).
& If the solution is yellow, CHROMIC ACID is present.
To remove all doubt on the point, acidify a portion of the
solution with acetic acid, and test with acetate of lead.
e. Acidify the remainder of the solution with hydrochloric 210
acid, evaporate to dryness, and treat the residue with hydro-
chloric acid and water. If a residue is left which refuses
to dissolve even in boiling water, this consists of SILICIC ACID.
Test the hydrochloric acid solution now in the usual way
for those bases which, being soluble in caustic alkalies, may
be present.
b. Dissolve the residue left in 4 (208) in hydrochloric acid 211
(effervescence indicates the presence of alkaline earths), and
test the solution for the bases as directed in 188. (If much
silicic acid has been found in e (210), it is advisable to evapo-
rate the solution of the residue to dryness, and to treat the
residuary mass with hydrochloric acid and water, in order that
the silicic acid remaining may also be removed as completely
as possible.)
5. If you have found in 4 that the residue insoluble in acids 212
contains a silicate, treat a separate portion of it according to the
directions of 205, 2 (228), to ascertain whether or not this sili-
cate contains alkalies.
6. If a residue is still left undissolved upon treating the 213
residue left in 4 with hydrochloric acid (211)? this may consist
either of silicic acid, which has separated, or of an undecomposed
portion of sulphate of baryta ; it may, however, also be fluoride of
calcium, and if it is dark- colored, chrome-ironstone, as the last-
named two compounds are only with difficulty decomposed by
the method given in 4. I would therefore remind the student
that fluoride of calcium may be readily decomposed by means of sul-
phuric acid ; and, as regards the decomposition of chrome-ironstone,
I can recommend the following method, first proposed by Hart :
Project the fine powder into 8 times the quantity of fused
borax, stir the mixture frequently, and keep the crucible for half-
an-hour at a bright red heat. Add now to the fusing mass car-
bonate of soda so long as effervescence continues, and then
finally add 3 times the weight of the chrome-ironstone of a mix-
ture of equal parts of carbonate of soda and nitrate of potassa,
whilst actively stirring the mixture with a platinum wire. Let the
ma >s cool, and, when cold, boil it with water.
7. If the residue insoluble in acids contained silver, you have 214
still to ascertain whether that metal was present in the original
substance as chloride, bromide, iodide, &c., of silver, or whether
it has been converted into the form of chloride of silver by the
treatment employed to effect the solution of the original substance.
For that purpose, treat a portion of the original substance with
boiling water until the soluble part is completely removed ; then
treat the residuary portion in the same way with dilute nitric
acid, wash the undissolved residue with water, and test a small
i. Q
226 ANALYSIS OF INSOLUBLE CYANIDES, FE11ROCYANIDES, ETC. [ 202,
sample of it for silver according to the directions of 201, d
(203)- If silver is present, proceed to ascertain the salt-radical
with which the metal is combined ; this may easily be effected
by boiling the remainder of the residue in the first place with
rather dilute solution of soda, filtering, and testing the filtrate, after
acidifying it, for ferro- and ferricyanogen. Digest the washed residue
now with finely granulated zinc and water, with addition of some
sulphuric acid, and filter after the lapse of ten minutes. You may
now at once test the filtrate for chlorine, bromine, iodine, and
cyanogen ; or you may first throw down the zinc with carbonate of
soda, in order to obtain the salt-radicals in combination with sodium.
SECTION II.
PRACTICAL COURSE
IN PARTICULAR CASES.
I. SPECIAL METHOD OP EFFECTING THE ANALYSIS OF CYANIDES,
FERROCYANIDES, ETC., INSOLUBLE IN WATER, AND ALSO OF INSO-
LUBLE MIXED SUBSTANCES CONTAINING SUCH COMPOUNDS.*
202.
THE analysis of ferrocyanides, ferricyanides, <fec., by the common 215
method is often attended by the manifestation of such anomalous
reactions as easily to mislead the analyst. Moreover, acids often,
fail to effect their complete solution. For these reasons it is ad-
visable to analyze them, and mixtures containing such compounds,
by the following special method :
Treat the substance with water until the soluble parts are en-
tirely removed, and boil the residue with strong solution of potassa
or soda ; after a few minutes ebullition add some carbonate of soda,
and boil again for some time filter, should a residue remain, and
wash the latter.
1. The residue, if any has been left, is now free from cya- 216
nogen, unless the substance under examination contains cyanide
of silver, in which case the residue would of course still contain
cyanogen. Examine the residue now by the common method,
beginning at _178, 2 (34).
2. The solution or filtrate, which, if combinations of com- 217
pound cyanogen radicals were originally present, contains
these combined with alkali metals, may also contain other
acids, which have been separated from their bases by the process
of boiling with carbonate of soda, and lastly also, such oxides
as are soluble in caustic alkalies.
* Before entering upon this course of analysis, consult the special remarks to the
paragraph ( 202), page 274, in the Third Section.
203.] ANALYSIS OF SILICATES. 227
Treat the solution as follows :
a. Mix the alkaline fluid with a sufficient quantity of hydro- 218
sulphuric acid.
a. No permanent precipitate is formed. Absence of zinc
and lead. Pass on to b.
ft : A permanent precipitate is formed. Add to the fluid
a little yellow sulphide of sodium, heat moderately, filter,
wash the precipitate, and treat the nitrate as directed in b.
Dissolve the washed precipitate in nitric acid, and examine
the solution for copper, lead, zinc, and other metals of the
fourth group, which may, in the same way as copper, have
passed into the alkaline solution, by the agency of organic
matters.
b. Mix the alkaline fluid, which contains now also sulphide 219
of an alkali metal, with nitric acid to acid reaction, and, if
necessary, add once more hydrosulphuric acid.
a. No precipitate is formed. Absence of mercury and of
the oxides of the sixth group. Pass on to c.
ft. A precipitate is formed. Filter, wash the precipitate,
and then examine it for mercury, and the metals of the sixth
group, according to the directions of 189.
c. The fluid, acidified with nitric acid, and therefore abun- 220
dantly supplied with nitrates of alkalies, may still contain
the metals which, in combination with cyanogen, form com-
pound radicals (iron, cobalt, manganese, chromium), and, besides
these, also alumina. You have to test it also for cyanogen,
respectively, ferrocyanogen, cobalticyaiiogen, &c., and for other
acids. Divide it, therefore, into two portions, a and ft. Ex-
amine a for the acids according to the directions of 197.
(Cobalticyanide may be recognised as such by its giving with
salts of nickel greenish, with salts of manganese and zinc white
precipitates.)
Evaporate ft to dryness, and heat the residue to fusion. Pour
'the fused mass upon a piece of porcelain, boil with water, filter,
and examine the residue for IRON, MANGANESE, COBALT, and
ALUMINA. Test a portion of the filtrate (if yellow) for CHROMIC.
ACID, the remainder for ALUMINA which may have passed par-
tially or completely into the solution, through the agency of
the caustic alkalies formed, in the process of fusion, from the
nitrates of the alkalies present.
II. ANALYSIS OF SILICATES.
203.
Whether the body to be analyzed is a silicate, or contains one, is 221
ascertained by the preliminary examination with phosphate of soda
and ammonia before the blowpipe; since, in the process effusion, the
metallic oxides dissolve, whilst the separated silicic acid floats about
in the liquid bead as a transparent, swollen mass.
The analysis of the silicates differs, strictly speaking, from the
common course only in so far as the preliminary treatment is con-
cerned, which is required to effect the separation of the silicic acid
from the bases, and to obtain the latter in solution.
Q 2
228 .ANALYSIS OF SILICATES. [ 20l.
The silicates and double silicates are divided into two distinct
classes, which require respectively a different method of analysis ;
viz., (1) silicates decomposable by acids (hydrochloric acid, nitric acid,
sulphuric acid) and (2) silicates which are not decomposed by acids.
To ascertain to which of these two classes a silicate belongs, re-
duce it to a very fine powder, and digest a portion with hydrochloric
acid at a temperature near the boiling point. If this fails to decom-
pose it, try another portion with tolerably concentrated sulphuric
acid, and apply heat. If this also fails, after some time, to produce
the desired effect, the silicate belongs to the second class. Whether
decomposition has been effected by the acid or not may generally be
learned from external indications, as a colored solution forms almost
invariably, and the separated gelatinous, flocculent, or finely-pul-
verulent hydrate of silicic acid takes the place of the original heavy
powder which grated under the glass rod with which it was stirred ;
the separated hydrate of silicic acid will, after filtering and washing,
dissolve in boiling solution of potassa or soda, which affords an addi-
tional means of identification.
Before proceeding further, test a portion of the pulverized com-
pound also for water, by heating it in a perfectly dry glass tube.
If the substance cou tains hygroscopic moisture it must first be dried
by protracted exposure to a temperature of 212 F. Apply a gentle
heat at first, but ultimately an iutense heat, by means of the blow-
pipe ; you may also conveniently combine with this a preliminary
examination for fluorine ( 147, 8).
A. SILICATES DECOMPOSABLE BY ACIDS.
204.
a. Silicates decomposable by hydrochloric acid or ly nitric acid*
1. Digest the finely pulverized silicate with hydrochloric acid at 222
a temperature near the boiling point, until complete decomposition
is effected, filter off a small portion of the fluid, evaporate the re-
mainder, together with the silicic acid suspended therein, to dry-
ness, and expose the residue to a temperature somewhat exceeding
212 F., with constant stirring, until no more, or very few, hydrochloric
acid fumes escape ; allow it to cool, moisten the residue with hydro-
chloric acid, or as the case may be, with nitric acid, afterwards add
a little water, and heat gently for some time.
This operation effects the separation of the silicic acid, and the
solution of the bases in the form of chlorides. Filter, wash the
residue thoroughly, and examine the solution by the common
method, beginning at 188.t To be quite safe, the residuary silicic
acid may be digested with ammonia, filtered, and the filtrate tested
for silver, by supersaturation with nitric acid.
2. As in silicates, and more particularly in those decomposed by 223
* Nitric acid is preferable to hydrochloric acid in cases where compounds of silver or
lead are present.
f Minute traces of titanic acid are occasionally met with in silicates. The titanic acid
present passes into the hydrochloric acid solution, if the separation of the silicic acid has
been effected on the water-bath, and is subsequently thrown down with the bases precipi-
table by ammonia (sesquioxide of iron and alumina). Upon igniting the precipitate,
and then treating it with concentrated hydrochloric acid, the greater portion of the titanic
acid remains undissolved. On filtering it, the washings generally look milky when pass-
ing through the filter. It is more closely examined before the blowpipe ; compare 103
(H. Rose}.
205-] ANALYSIS OF SILICATES. 229,
hydrochloric acid, there are often found other acids, as well as
metalloids, the following observations and instructions must be
attended to, that none of these substances may be overlooked :
a. SULPHIDES of METALS and CARBONATES are detected in the
process of treating with hydrochloric acid.
/3. If the separated silicic acid is black, and turns sub-
sequently white upon ignition in the air, this indicates the
presence of CARBON or of ORGANIC SUBSTANCES. In presence of
the latter, the silicates emit an empyreumatic odor upon being
heated in a glass tube.
y. Test the portion of the hydrochloric acid solution filtered
off before evaporating (222), for PHOSPHORIC ACID (ARSENIC
ACID, which may happen to be present), and SULPHURIC ACID,
by means of molybdic acid, and phloride of barium.
e). BORACIC ACID is best detected by fusing a portion 224
of the substance in a platinum spoon with carbonate of soda
and potassa, boiling the fused mass with water, and examining
the solution for boracic acid by the method given in 145, 6.
. With many silicates, boiling with water is sufficient to dis-
solve the metallic CHLORIDES present, which may then be readily
detected in the filtrate by means of solution of nitrate of
silver: the safest way, however, is to dissolve the mineral in
dilute nitric acid, and test the solution with nitrate of silver.
. Metallic FLUORIDES, which often occur in silicates in
greater or smaller proportion, are detected by the methods
described 147.
b. Silicates which resist the action of hydrochloric acid, but are de-
composed by concentrated sulphuric acid.
Heat the finely pulverized mineral with moderately concentrated 225
pure sulphuric acid (best in a platinum dish), finally drive off the
sulphuric acid, boil the residue with hydrochloric acid, dilute, filter,
and treat the filtrate as directed 1 88 ; and the residue, which, besides
the separated silicic acid, may contain also sulphates of the alkaline
earths, &c,, according to the directions of 201. If you wish to exa-
mine silicates of this class for acids and salt-radicals, treat a separate
portion of the substance according to the directions of 205.
B. SILICATES WHICH ARE NOT DECOMPOSED BY ACIDS.
205.
As the silicates of this class are most conveniently decomposed by 226
fusion with carbonate of soda and potassa, the portion so treated
cannot, of course, be examined for alkalies. The analytical process
is therefore properly divided into two principal parts, viz., a portion
of the mineral is examined for the silicic acid and the bases, with
the exception of the alkalies, whilst another portion is specially
examined for the latter. Besides these, there are some other ex-
periments required, to obtain information as to the presence <
absence of other acids. .
1. Detection of the silicic acid and the bases, with the exception oj t/ie
alkalies. . , , on _
Reduce the mineral to a very fine powder, mix this with 4 227
parts of carbonate of soda and potassa, and heat the mixture in a
230 ANALYSIS OF SILICATES. [ 205.
platinum crucible over a gas or Berzelius spirit-lamp, until the mass
is in a state of calm fusion. Put the red-hot crucible on a thick, cold
iron plate, and let it cool there ; this will generally enable you to
remove the fused cake from the crucible, in which case break the
mass to pieces, and keep a portion for subsequent examination for
acids. Put the remainder, or, if the mass still adheres to the cru-
cible, the latter, with its contents, into a porcelain dish, pour water
over it, add hydrochloric acid, and heat gently until the mass is dis-
solved, with the exception of the silicic acid, which separates in flakes.
Remove the crucible from the dish, if necessary, evaporate the con-
tents of the latter to dryness, and treat the residue as directed
204, 1 (222)-
2. Detection of the alkalies.
To effect this, the silicates under examination must be decom- 228
posed by means of a substance free from alkalies. Hydrofluoric
acid or a metallic fluoride answers this purpose best ; but fusion
with hydrate of baryta will also accomplish the end in view.
a. DECOMPOSITION BY MEANS OF A METALLIC FLUORIDE. Mix
1 part of the very finely pulverised mineral with 5 parts
of fluoride of barium, or pure, finely pulverized fluoride of
calcium, stir the mixture in a platinum crucible with concen-
trated sulphuric acid to a thickish paste, and heat gently for
some time in a place affording a free escape to the vapors ;
finally heat a little more strongly, until the excess of sulphuric
acid is completely expelled. Boil the residue now with water,
add chloride of barium cautiously as long as a precipitate con-
tinues to form, then baryta-water to alkaline reaction, boil,
filter, mix with carbonate of ammonia and some ammonia as
long as a precipitate forms, and proceed exactly as directed
194, 2 (168).
b. DECOMPOSITION BY MEANS OF HYDRATE OF BARYTA. Mix 229
1 part of the very finely pulverized substance with 4 parts of
hydrate of baryta, expose the mixture for half an hour in a pla-
tinum crucible to the strongest possible heat of a good Berzelius
or gas-lamp, and treat the fused or agglutinated mass with
hydrochloric acid and water until it is dissolved ; precipitate
the solution with ammonia and carbonate of ammonia,, filter,
evaporate to dryness, ignite, dissolve the residue in water, pre-
cipitate again with ammonia and carbonate of ammonia, filter,
evaporate, ignite, and test the residue for potassa and soda as
directed 195. If the residue still contains magnesia, this
may be readily removed, by adding to the aqueous solution of
the residue, a little finely pulverized oxide of mercury,
evaporating to dryness, igniting the dry mass, and then treat-
ing it with water, which will dissolve the alkalies as chlorides,
and leave the magnesia undissolved.
3. Examination for fluorine, chlorine, boracic acid, phosphoric
acid, arsenic acid, and sulphuric acid.
Use for this purpose the portion of the fused mass reserved in 230
205, 1 (227)> r ? if necessary, fuse a separate portion of the
finely pulverized substance with 4 parts of pure carbonate of soda
and potassa until the mass flows calmly ; boil the fused mass with
water, filter the solution, which contains all the fluorine as fluoride
of sodium, all the chlorine as chloride of sodium, all the boracic acid
206, 207.] ANALYSIS or SILICATES. 231
as borate, all the sulphuric acid as sulphate, all the arsenic acid as
arsenate, and at least part of the phosphoric acid as phosphate of
soda, and treat the nitrate as follows :
a. Acidify a small portion of it with nitric acid, and test for
chlorine with nitrate of silver.
b. Test another portion for boracic acid as directed $ 205 2
a (224).
c. Test a third portion, after addition of hydrochloric acid,
with molybdate of ammonia for phosphoric acid and arsenic
acid.
d. To effect the detection of the fluorine, treat the remainder
of the filtrate as directed 147, 7.
C. SILICATES WHICH ARE PARTIALLY DECOMPOSED BY ACIDS.
206.
Most of the native rocks and minerals are mixtures of several 231
silicates, of which the one is often decomposed by acids, the other
not. If such minerals were analyzed by the same method as the
absolutely insoluble silicates, the analyst would indeed detect all the
elements present, but the analysis would afford no satisfactory in-
sight into the actual composition of the mineral.
It is, therefore, advisable to examine separately those parts of
the mineral which show a different deportment with aoids. For
this purpose digest the very finely pulverized mineral for some
time with hydrochloric acid at a very gentle heat, then evaporate
to dry ness, and expose to a temperature somewhat exceeding 212F.,
with stirring, until no more, or very few, hydrochloric acid vapors
are evolved ; let the residue cool, moisten it when cold with hydro-
chloric acid, heat gently with water, and filter.
The filtrate contains the bases of the decomposed part of the
mixed mineral ; examine this as directed 204. The residue con-
tains, besides the silicic acid separated from these bases by the
action of the hydrochloric acid, that part of the mixed mineral
which has resisted the action of the acid. Boil this residue with an
excess of solution of carbonate of soda, filter hot, and wash, first
with hot solution of carbonate of soda, finally with boiling water.
Treat the residuary undecomposed part of the mineral, from which
the admixed free silicic acid has thus been removed, according to
the instructions given in 205. In cases where it is of no conse-
quence or interest to effect the separation of the silicic acid of the
part decomposed by acids, you may omit the laborious treatment
with carbonate of soda, and may proceed at once to the decomposi-
tion of the residue.
III. ANALYSIS OF NATURAL WATERS.
207.
In the examination of natural waters the analytical process is 232
simplified by the circumstance that we know from experience the
elements and compounds which are usually found in them. Now,
although a quantitative analysis alone can properly inform us as to
the true nature and character of a water, since the differences be-
232 ANALYSIS OF FEESH WATERS. [ 08.
tween the various waters are principally caused by the different pro-
portions in which the several constituents are respectively present,
a qualitative analysis may yet render very good service, especially if
the analyst notes with proper care, whether a reagent produces a
faint or a distinctly marked turbidity, a slight or a copious precipi-
tate, since these circumstances will enable him to make an approxi-
mate estimation of the relative proportions in which the several
constituents are present.
I separate here the analysis of the common fresh waters (spring-
water, well-water, brook-water, river-water, &c.) from that of the
mineral waters, in which we may also include sea- water ; for,
although no well-defined limit can be drawn between the two
classes, still the analytical examination of the former is necessarily
far more simple than that of the latter, as the number of substances
to be looked for is much more limited than in the case of mineral
waters.
A. ANALYSIS OF FRESH WATERS (SPRING- WATER, WELL-WATER,
BROOK WATER, RIVER- WATER, &c.).
208.
We know from experience that the substances to be had regard 233
to in the analysis of such waters are the following :
a. BASES : Potassa, soda, ammonia, lime, magnesia, protoxide of
iron.
6. ACIDS, &c. : Sulphuric acid, phosphoric acid, silicic acid, car-
bonic acid, nitric acid, chlorine.
c. ORGANIC MATTERS.
d. MECHANICALLY SUSPENDED SUBSTANCES : Clay, &c.
The fresh waters contain indeed also other constituents besides
those enumerated here, as may be inferred from the origin and for-
mation of springs, &c., and as has, moreover, been fully established
by the results of analytical investigations ;* but the quantity of
such constituents is so trifling that they escape detection, unless
hundreds of pounds of the water are subjected to the analytical pro-
cess. I omit, therefore, here the mode of their detection, and refer
to 209.
1. Boil the carefully collected water in a glass flask or retort 234
to one half. This generally produces a precipitate. Pass the fluid
through a perfectly clean filter (free from iron and lime), wash the
precipitate well, after having removed the filtrate, and then examine
both as follows :
a. Examination of the precipitate.
The precipitate contains those constituents of the water 235
which were only kept in solution through the agency of free
* Chatin (" Journ. de Pharm. etde Chim.," 3 Ser. t. xxvii. p. 418) found iodine in all
fresh-water plants, but not in land plants, a proof that the water of rivers, brooks,
ponds, &c., contains traces, even though extremely minute, of metallic iodides.
According to Marchand ("Compt. Rend.," t. xxxi. p. 495), all natural waters contain
iodine, bromine, and lithia. Van Ankum has demonstrated the presence of iodine in
almost all the potable waters of Holland. And it may be affirmed with the same cer-
tainty that all, or at all events most, natural waters contain compounds of strontia,
fluorine, &c.
208.] ANALYSIS OF FRESH WATERS. 233
carbonic acid, or, as the case may be, in the form of bicar-
bonates, viz., carbonate of lime, carbonate of magnesia, hydrated
sesquioxide of iron (which was in solution as bicarbonate of
protoxide of iron, and precipitates upon boiling as sesquioxide,
and if phosphoric acid is present, also in combination with that
acid), phosphate of lime ; and besides, silicic acid, and some-
times also sulphate of lime, if that substance is present in large
proportion ; and clay which was mechanically suspended in the
water.
Dissolve the precipitate on the filter in the least possible
quantity of dilute hydrochloric acid (effervescence indicates
the presence of CARBONIC ACID), and mix separate portions of
the solution :
a. With sulphocyanide of potassium : red coloration indi-
cates the presence of IRON ;
/3. With ammonia ; warm, filter, if necessary, mix the 236
filtrate with oxalate of ammonia, and let the mixture stand
for some time in a warm place. The formation of a white
precipitate indicates the presence of LIME in the form of
carbonate, or also in that of sulphate if sulphuric acid is de-
tected in y. Filter, mix the filtrate again with ammonia,
add some phosphate of soda, stir with a glass rod, and let
the mixture stand for twelve hours. The formation of a
white, crystalline precipitate, which is often visible only on
the sides of the vessel when the fluid is poured out, indicates
the presence of MAGNESIA (carbonate of) ;
y. With chloride of barium, and let the mixture stand
for twelve hours in a warm place. The formation of a pre-
cipitate which, when very inconsiderable, is best seen if the
supernatant clear fluid is cautiously decanted, and the small
quantity remaining shaken about in the glass indicates the
presence of SULPHURIC ACID.
<). Add some of the fluid to a solution of molybdate of 237
ammonia, acidified with hydrochloric acid, and boil. The
appearance of a yellow color, or the formation of a yellow
precipitate, indicates the presence of PHOSPHORIC ACID.*
b. Examination of the filtrate.
a. Mix a portion of the filtrate with a little hydrochloric 238
acid and chloride of barium. The formation of a white pre-
cipitate, which makes its appearance at once or perhaps only
after standing some time, indicates SULPHURIC ACID.
/3. Mix another portion with nitric acid, and add nitrate
of silver. A white precipitate or a white turbidity, indi-
cates the presence of CHLORINE.
y. Test a portion of the filtrate for PHOSPHORIC ACID as in
a, S (237).
<). Evaporate another and larger portion of the filtrate until 239
* In default of molybdate of ammonia, evaporate the remainder of the hydrochloric
acid solution of the precipitate to dryness, redissolve the residue in a little hydrochloric
acid and water, filter the solution, and mix the filtrate with carbonate of soda until it is
nearly neutralized, then with acetate of soda and a very small quantity of sesquicbloride
of iron. The formation of a white precipitate, which generally becomes visible only after
long standing, indicates the presence of PHOSPHORIC ACID.
234 ANALYSIS OF FRESH WATERS. [ 208.
highly concentrated, and test the reaction of the fluid.
If it is alkaline, and a drop of the concentrated clear solu-
tion effervesces when mixed on a watch-glass with a drop of
acid, a CARBONATE of an alkali is present. Should this be the
case, evaporate the fluid to perfect dryness, boil the residue
with spirit of wine, filter, evaporate the alcoholic solution to
dryness, dissolve the residue in a little water, and test the
solution for NITRIC ACID as directed 159, 5, or by the
method given in 159, 8, which is still more delicate.
e. Mix the remainder of the filtrate with some chlo-
ride of ammonium, add ammonia and oxalate of ammonia,
and let the mixture stand for a considerable time. The
formation of a precipitate indicates the presence of LIME.
Filter, and test,
aa. A small portion with ammonia and phosphate of
soda for MAGNESIA.
bb. Evaporate the remainder to dryness, heat the resi-
due to redness, remove the magnesia, which may be pre-
sent ( 194), and test for POTASSA and SODA, according
to the directions of 195.
2. Acidify a tolerably large portion of the filtered water with 240
pure hydrochloric acid, and evaporate nearly to dryness ; divide the
residue into 2 parts, and,
a. Test the one part with hydrate of lime for AMMONIA (com-
pare 196).
b. Evaporate the other part to dryness, moisten with
hydrochloric acid, add water, warm, and filter, if a residue
remains. The residue may consist of SILICIC ACID, and of CLAY
which has been mechanically suspended in the water ; these
two substances may be separated from each other by boiling
with solution of carbonate of soda. The precipitate is often
dark-colored from the presence of organic substances ; but it
becomes perfectly white upon ignition.
3. Mix another portion of the water, fresh taken from the well, 241
&c., with lime-water. If a precipitate is thereby produced, FREE
CARBONIC ACID or BiCARBONATES are present. If the former is pre-
sent (free carbonic acid), no permanent precipitate is obtained when
a larger portion of the water is mixed with only a small amount of
lime-water, since in that case soluble bicarbonate of lime is formed.
4. To detect the presence of ORGANIC MATTERS, evaporate a portion 242
of the water to dryness, and gently ignite the residue : blackening
of the mass denotes the presence of organic substances. If this ex-
periment is to give conclusive results, the evaporation of the water,
as well as the ignition of the residue, must be conducted in a glass
flask or a retort.
5. If you wish to examine the MATTERS MECHANICALLY SUSPENDED 243
in a water (in muddy brook or river-water, for instance), fill a large
glass bottle with the water, cork securely, and let it stand at rest
for several days, until the suspended matter has subsided ; remove
now the clear supernatant fluid with the aid of a syphon, filter the
remainder, and examine the sediment remaining on the filter. As
this sediment may consist of the finest dust of various minerals,
treat it first with hydrochloric acid, and examine the part insoluble
209, 210.] ANALYSIS OF MINERAL WATERS. 035
in that menstruum in the manner directed 203 (Analysis of
Silicates).
B. ANALYSIS OF MINERAL WATERS.
209.
The analysis of mineral waters embraces a larger number of con- 244
stituents than that of fresh water. The following are the principal
of the additional elements to be looked for :
LlTHIA, BARYTA, STRONTIA, ALUMINA, PROTOXIDE OF MANGANESE,
BORACIC ACID, BROMINE, IODINE, FLUORINE, HYDROSULPHURIC ACID,
CRENIC ACID and APOCRENIC ACID.
The^ analyst has, moreover, to examine the muddy ochreous or
hard sinter-deposits of the spring for ARSENIOUS ACID, ARSENIC ACID,
OXIDE OF COPPER, OXIDE OF LEAD, and the oxides of other heavy
metals. The greatest care is required in this examination, to ascer-
tain whether these oxides come really from the water, and do
not proceed from metal pipes, stopcocks, &c.* The absolute purity
of the reagents employed in these delicate investigations must also
be ascertained with the greatest care.
1. EXAMINATION OF THE WATER.
a. OPERATIONS AT THE SPRING.
210.
1. Filter the water at the spring, if not perfectly clear, through 245
Swedish filter paper, and collect the filtrate in large bottles with
glass stoppers. The sediment remaining on the filter, which con-
tains, besides the nocculent matter suspended in the water, also
those constituents which separate at once upon coming in contact
with the air (hydrate of sesquioxide of iron, and compounds of ses-
quioxide of iron with phosphoric acid, silicic acid, arsenic acid), is
taken to the laboratory, to be examined afterwards according to the
directions of 212.
2. The presence of FREE CARBONIC ACID is usually sufficiently 246
visible to the eye. However, to convince yourself by positive re-
actions, test the water with fresh-prepared solution of litmus, and
with lime-water. If carbonic acid is present, the former acquires a
wine-red color ; the latter produces turbidity, which must disappear
again upon addition of the mineral water in excess.
3. Free HYDROSULPHURIC ACID is most readily detected by the 247
smell. For this purpose half fill a bottle with the mineral water,
cover with the hand, shake, take off the hand, and smell the bottle.
In this way distinct traces of hydrosulphuric acid are often found,
which would escape detection by reagents. However, if you wish
to have some visible reactions, fill a large white bottle with the
water, add a few drops of solution of acetate of lead in solution of
soda, place the bottle on a white surface, and look in at the top, to
* Compare " Chemische Untersuchung der wichtigsten Mineral wasser des Herzogthums
Nassau," von Professor Dr. Fresenius ; I. Der Kochhrunnen zu Wiesbaden; II. Die
Mineralquellen zu Ems ; III. die Quellen zu Schlangenbad ; IV. die Quellen zu Langen-
schwalbacb. ; published at Wiesbaden, by Kriedel und Niedner. 1850-1855.
236 ANALYSIS OF MINERAL WATERS. [ 211.
see whether the water acquires a brownish color or deposits a
blackish precipitate ; or half fill a large bottle with the water, and
close with a cork to which is attached a small slip of paper, pre-
viously steeped in ' solution of acetate of lead and then moistened
with a little solution of carbonate of ammonia; shake the bottle
gently from time to time, and observe whether the paper slip
acquires a brownish tint in the course of a few hours. If the
addition of the solution of acetate of lead to the water has im-
parted a brown color to the fluid or produced a precipitate in it,
whilst the reaction with the paper slip gives no result, this indi-
cates that the water contains an alkaline sulphide, but no free
hydrosulphuric acid.
4. Mix a wineglass-full of the water with some tannic acid, 248
another wineglass-full with some gallic acid. If the former imparts
a blue violet, the latter a red violet color to the water, PROTOXIDE
OF IRON is present. Instead of the two acids, you may employ in-
fusion of galls, which contains them both.
b. OPERATIONS IN THE LABORATORY.
211.
As it is always desirable to obtain even in the qualitative exami-
nation some information as to the quantitative composition of a
mineral water, i. e. as to the proportions in which the several consti-
tuents are contained in it, it is advisable to analyze a comparatively
small portion for the principal constituents, and to ascertain, as far
as may be practicable, the relative proportions in which these
constituents exist, and thus to determine the character of the
water ; and then to examine a very large amount of the water for
those elements which are present only in minute quantities. For
this purpose proceed as follows :
1. EXAMINATION FOR THOSE CONSTITUENTS OF THE WATER WHICH 249
ARE PRESENT IN LARGER QUANTITIES. Boil about 31bs. of the
clear water, or of the nitrate, brought from the spring, in a glass
flask for 1 hour, taking care, however, to add from time to time
some distilled water, that the quantity of liquid may remain un-
diminished, and thus the separation of any but those salts be pre-
vented which owe their solution to the presence and agency of
carbonic acid. Filter after an hour's ebullition, and examine the
precipitate and the filtrate as directed 208.
2. EXAMINATION FOR THOSE FIXED CONSTITUENTS OF THE WATER 250
WHICH ARE PRESENT IN MINUTE QUANTITIES ONLY. Evaporate a
large quantity (at least 20 Ibs.) of the water in a silver or porce-
lain dish to dry ness ; conduct this operation with the most
scrupulous cleanliness in a place as free as possible from dust. If
the water contains no carbonate of an alkali, add pure carbonate of
potassa to slight predominance. The process of evaporation may
be conducted in the first place over a gas-lamp, but ultimately the
sand-bath must be employed. Heat the dry mass to very faint
redness ; if in a silver dish, you may at once proceed to ignite it ;
but if you have it in a porcelain dish, first transfer it to a silver
or platinum vessel before proceeding to ignition. If the mass
211-] ANALYSIS OF MINERAL WATEUS. 237
turns black in this process, ORGANIC MATTERS may be assumed to
be present.*
Mix the residue thoroughly, that it may have the same composi-
tion throughout, and then divide it into 3 portions, one (c) amount-
ing to about one-half, and each of the other two (a and b) to one-
fourth. ,
a. EXAMINATION FOR IRON, PHOSPHORIC ACID (ARSENIC
ACID).
Warm the portion a with some water, add perfectly pure 251
hydrochloric acid in moderate excess, digest for some time at a
temperature near the boiling point, filter through paper
washed with hydrochloric acid and water, and test.
a. A sample for IRON, by means of sulphocyanide of
potassium.
/3. Treat the remainder with hydrosulphuric acid, let the
fluid saturated with that acid stand for twenty-four hours,
filter from the separated sulphur, concentrate the filtrate by
boiling, and test it with molybdate of ammonia for PHOS-
PHORIC ACID.
7 . If the sulphur deposited in /3 is not perfectly white,
treat it as directed 212, 1, a, a (263), in order to detect the
arsenic, copper, &c., which may be present.
b. EXAMINATION FOR FLUORINE.
Heat the portion b with water, add chloride of calcium as 252
long as a precipitate continues to form, let deposit ; filter the
fluid from the precipitate, which consists chiefly of carbonate
of lime and carbonate of magnesia. After having washed and
dried the precipitate, ignite, then pour water over it in a
small dish, add acetic acid in slight excess, evaporate on the
water-bath to dryness, heat until all smell of acetic acid has
disappeared, add water, heat again, filter the solution of the
acetates of the alkaline earths, wash, dry or ignite the residue,
and test it for FLUORINE as directed 147, 5.
c. EXAMINATION FOR THE REMAINING CONSTITUENTS PRESENT 253
IN MINUTE QUANTITIES.
Boil the portion c repeatedly with water, filter, and wash
the undissolved residue with boiling water. You have now a
residue (a), and a solution (/?).
a. The residue consists chiefly of carbonate of lime, car- 254
bouate of magnesia, and in the case of chalybeate springs
hydrate of sesquioxide of iron. But it may contain also
minute quantities of BARYTA ,STRONTIA, ALUMINA, and PROT-
OXIDE OF MANGANESE, and must accordingly be examined for
these substances.
Put the residue in a platinum or porcelain dish, pour
water over it, add hydrochloric acid to slightly acid reaction,
then 4 or 5 drops of dilute sulphuric acid, evaporate to
dryness, moisten with hydrochloric acid, then add water,
* This inference is, however, correct only if the water has been effectually protected
from dust during the process of evaporation ; if this has not been the case, and you
yet wish to ascertain beyond doubt whether organic matters are present, evaporate a sepa-
rate portion of the water in a retort. If you find organic matter, and wish to know
whether it consists of crenic acid or of apocrenic acid, treat a portion of the residue
as directed 212, 3.
238 ANALYSIS OF MINERAL WATERS. [ 211.
warm gently, filter, and wash the residue which is left un-
dissolved.
cia, EXAMINATION OF THE RESIDUE INSOLUBLE IN HY- 255
DROCHLORIC ACID FOR BARYTA AND STRONTIA.
This residue will generally consist of silicic acid ; but it
may contain also sulphates of the alkaline earths and
carbon. If there is much silicic acid present, remove
this in the first place, as far as practicable, by boiling with
dilute solution of soda ; filter, wash the residue, if any
has been left, dry, incinerate the filter in a platinum
crucible, add some carbonate of soda and potassa and, in
presence of carbon, some nitrate of potassa, and ignite
for some time. If the residue contains but little
silicic acid, the treatment with solution of soda may be
omitted, and the fusion with carbonate of potassa and
soda, &c., at once proceeded with. Boil the fused mass
with water, filter, wash thoroughly, dissolve the residue
(which must have been left, if sulphates of the alkaline
earths were present) on the filter in the least possible
quantity of dilute hydrochloric acid, add an equal volume
of spirit of wine, then some pure hydrofluosilicic acid,
and let the mixture stand 12 hours. If in the course or
at the end of the 12 hours a precipitate makes its ap-
pearance, this denotes the presence of BARYTA. Filter, and
warm the filtrate in a platinum dish, adding from time
to time some water, until the spirit of wine is quite
driven off. Mix the fluid now with saturated solu-
tion of sulphate of lime. If this produces a precipitate,
whether after some time or after several hours' standing,
this precipitate consists of sulphate of STRONTIA. To
make quite sure, examine it before the blowpipe (see
95, 7).
bb. EXAMINATION OF THE HYDROCHLORIC ACID SOLU- 256
TION FOR PROTOXIDE OF MANGANESE AND ALUMINA.
Mix the solution in a flask with some pure chloride of
ammonium, add ammonia until the fluid is just turning
alkaline, then some yellow sulphide of ammonium, close
the flask, and let it stand for 12 hours in a moderately
warm place. If a precipitate has formed at the end of
that time, filter, dissolve the precipitate in hydrochloric acid,
boil, add solution of potassa ( 30, c) in excess, boil again,
filter, and test the filtrate for ALUMINA ;* the residue with
carbonate of soda before the blowpipe for MANGANESE.
/3. The alkaline solution contains the salts of the alkalies, 257
and usually also magnesia and traces of lime. You have to
examine it now for NITRIC ACID,T BORACIC ACID, IODINE,
* You are not justified in regarding this substance as an ingredient of the water,
except in cases where the process of evaporation has been conducted in a platinum or silver
dish, but not in a porcelain dish.
+ The nitric acid originally present may have been destroyed by the ignition of the
residue in 211, 2 (250), u*fce latter contained organic matter. If you have reason
to fear that such has been the case, and you have not already found nitric acid in
211, 1, examine a larger portion of non-ignited residue for that acid, according to the
directions of 211, 2, c, p, aa (258)-
211.] ANALYSIS OF MINERAL WATERS. 239
BROMINE, and LITHIA. Evaporate the fluid until highly
concentrated, let it cool, and place the dish in a slanting
position, that the small quantity of liquid may separate
from the saline mass ; pour a few drops of the concentrated
solution in a watch-glass, acidify very slightly with hy-
drochloric acid, and test with turmeric paper for BORACIG
ACID. Pour back into the dish the remainder of the liquid,
of which you have just tested a few drops, evaporate,
with stirring, to perfect dryness, and divide the residuary
powder into 2 portions, one (aa) of two-thirds, the other (66)
of one-third.
aa. EXAMINE THE LARGER PORTION FOR NITRIC ACID, 258
IODINE, AND BROMINE.
Put the powder into a flask, pour pure spirit of wine of
90 per cent, over it, boil on the water bath, and filter
hot ; repeat the same operation a second and a third time.
Mix the alcoholic extract with a few drops of solution of
potassa, distil the spirit of wine off to within a small quantity,
and let cool. If minute crystals separate, these may con-
sist of nitrate of potassa ; pour off the fluid, wash the
crystals with some spirit of wine, dissolve them in a very
little water, and test the solution for nitric acid, best
by means of brucia ( 159, 8). Evaporate the alcoholic
solution now to dryness. If you have not yet found
nitric acid, dissolve a small portion of the residue in
a very little water, and examine the solution for that
acid. Treat the remainder of the residue or, if it
has been unnecessary to search for nitric acid, the entire
residue, three times with warm alcohol, filter, evaporate
the filtrate to dryness, dissolve the residue in a very little
water, add some starch-paste, acidify slightly with sul-
phuric acid, and test for iodine by adding some nitrite of
potassa in solution, or a drop of solution of hyponitric
acid in sulphuric acid. After having carefully observed
the reactions, test the same fluid for bromine with
ether and chlorine water in the manner described in
1ST.
bb. EXAMINE THE SMALLER PORTION FOR LITHIA.
Warm the smaller portion of the residue, which. 259
if lithia is present, must contain that alkali as car-
bonate or phosphate, with water, add hydrochloric acid to
distinctly acid reaction, evaporate nearly to dryness, and
then mix with pure spirit of wine of 90 per cent,
which will separate the greater portion of the chloride
of sodium, and give alt the lithia in the alcoholic solu-
tion. Drive off the alcohol by evaporation, dissolve the
residue in water mixed with a few drops of hydrochloric
acid, add a little sesquichloride of iron, then ammonia
in slight excess, and a small quantity of oxalate of ammonia,
and let the mixture stand for sometime ; then filter off the
fluid, which is now entirely free from phosphoric acid and
lime'; evaporate the filtrate to dryness, and gently ignite
the residue, until the salts of ammonia are expelled;
240 ANALYSIS OF MINERAL WATERS. [ 212.
treat the residue with some chlorine water (to remove the
iodine and bromine) and a few drops of hydrochloric acid,
and evaporate to dryness ; add a little water and (to remove
the magnesia) some finely divided oxide of mercury, eva-
porate to dryness, and gently ignite the residue, until the
chloride of mercury is completely driven off ; treat the
residue now with a mixture of absolute alcohol and anhy-
drous ether, filter the solution obtained, concentrate the
filtrate by evaporation, and set fire to the alcohol. If it
burns with a carmine flame, LITHIA is present. By way
of confirmation, convert the lithia found into phosphate
of LITHIA.*
3. If you have not yet clearly detected ammonia in 1 (249)> add 260
to a large quantity of the water hydrochloric acid to acid reaction,
and concentrate the fluid considerably by boiling in a retort. Add
now, through the tubular neck of the retort, an excess of milk of
lime, made with recently calcined hydrate of lime, boil, and conduct
the vapor into a flask containing very dilute hydrochloric acid,
which is kept cool by surrounding it with ice or with very cold
water ; evaporate the contents almost to dryness, and then
test for ammonia with hydrate of lime or with bichloride of
platinum.
2. EXAMINATION OF THE SINTER-DEPOSIT.
212.
1. Free the ochreous or sinter-deposit from impurities, by picking, 261
sifting, elutriation, &c., and from the soluble salts adhering to it, by
washing with water; digest a large quantity (about 200 grammes)
of the residue with water and hydrochloric acid (effervescence :
CARBONIC ACID) until the soluble part is completely dissolved ; dilute,
cool, filter, and wash the residue.
a. Examination of tJie filtrate.
a. Saturate the larger portion of the filtrate nearly with 262
carbonate of soda, add a few drops of dilute sulphuric
acid, and let the mixture stand for 24 hours at a gentle
heat. If a precipitate is found to have formed after this
time, filter, wash the precipitate, pour hydrosulphuric acid
over it, that you may not overlook the possible presence of
sulphate of lead, and test for BARYTA and STRONTIA as directed
211, 2, c, a, aa (255). Boil the fluid filtered from this
precipitate with sulphite of soda if necessary, with addi-
tion of some hydrochloric acid, as the fluid must always
remain acid to reduce the sesquioxide of iron to protoxide,
and the arsenic acid, which may be present, to arsenious
acid ; heat finally, until all sulphurous acid is expelled, and
conduct for some hours a slow stream of washed hydrosul-
phuric acid gas into the fluid ; let the latter now stand in
a moderately warm place, until the smell of hydrosulphuric
acid has become quite faint. If a precipitate has formed, 263
* The precipitate designated in 92 as phosphate of soda and lithia, is 3 Li 0, P O t
(Mayer, "Annal. d. Chem. u. Pharm.," 98, 193).
21--] ANALYSTS OF MINERAL WATERS. 241
filter, wash, and digest with dilute solution of soda and
some sulphide of sodium ; filter, and mix the filtrate with
hydrochloric acid to acid reaction. If a precipitate is pro-
duced, test,
a. A portion of it for ARSENIC, with cyanide of potas-
sium and carbonate of soda in a stream of carbonic acid.
b. Treat the remainder as directed 190, that traces
of ANTIMONY and TIN, which may be present, may not
be overlooked.
If a residue has been left upon treating the precipitate 264
produced by hydrosulphuric acid with solution of soda and
sulphide of sodium, boil it, together with the filter, with a
very little dilute nitric acid, filter, wash, and examine
the contents of the filter, as directed in 212, a, a (262),
for sulphate of lead, sulphate of baryta, and sulphate
of strontia (the two latter salts are more soluble in solution
of sesquichloride of iron than in solution of protochloride
of iron. Mix the filtrate (the nitric acid solution) with
some pure sulphuric acid, evaporate on the water-bath to
dryness, and treat the residue with water. If this leaves
an undissolved residue, the latter consists of sulphate of
LEAD. To make quite sure, filter, wash the residue, treat
it with hydrosulphuric acid water, and observe whether
that reagent imparts a black color to it. Test the fluid fil-
tered from the sulphate of lead which may have separated,
a with ammonia, b with ferrocyanide of potassium, for
COPPER.
Of the fluid filtered from the precipitate produced by 265
hydrosulphuric acid, examine in the first place, after having
expelled the hydrosulphuric acid by boiling, a portion with
molybdate of ammonia for PHOSPHORIC ACID; mix the
remainder in a flask with chloride of ammonium, ammonia,
and yellowish sulphide of ammonium, close the flask, and
let it stand in a moderately warm place until the fluid
above the precipitate looks no longer greenish, but yellow;
filter, and wash the precipitate with water to which some
sulphide of ammonium has been added. Dissolve the washed
precipitate in hydrochloric acid, separate the SILICIC ACID by
evaporation, moisten the residue with hydrochloric acid, add
water, warm, and test the solution for ALUMINA, IRON, MAN-
GANESE, and ZINC, according to the directions of 192, 1.
Examine now the fluid filtered from the precipitate pro-
duced by sulphide of ammonium, for LIME and MAGNESIA
in the usual way.
/3. Mix a portion of the hydrochloric acid solution with
chloride of barium, and let the mixture stand 12 hours
in a warm place. The formation of a white precipitate indi-
cates the presence of SULPHURIC ACID.
b. Examination of the residue.
This consists usually of silicic acid, clay, and organic mat- 268
ters, but it may also contain sulphate of baryta and sulphate
of strontia. Boil in the first place with solution of soda or
potassa, to dissolve the SILICIC ACID; then fuse the residue
I. R
242 ANALYSIS OF SOILS. [ 213.
with carbonate of soda and potassa, and a little nitrate of
potassa. Boil the mass, wash the residue, and then dissolve
it in some hydrochloric acid ; boil the solution, add ammonia,
filter the fluid from the ALUMINA, &c., which may precipitate,
evaporate the filtrate to dryness, gently ignite the residue, re-
dissolve it in very little water, with addition of a drop of
hydrochloric acid, and test for BARYTA and STRONTIA as directed
211, 2, c, a, aa (255>
2. As regards the examination for FLUORINE, the best way is to 267
take for this purpose a separate portion of the ochreous or sinter-
deposit. Ignite (which operation will also reveal the presence of
organic matters), stir with water, add acetic acid to acid reaction,
evaporate until the acetic acid is completely expelled, and proceed as
described in 211, 2, b (252).
3. Boil the ochreous or sinter-deposit for a considerable time with 268
concentrated solution of potassa or soda, and filter.
a. Acidify a portion of the filtrate with acetic acid, add
ammonia, let the mixture stand 12 hours, and then filter
the fluid from the precipitate of alumina and hydrated silicic
acid, which usually forms ; again add acetic acid to acid
reaction, and then a solution of neutral acetate of copper.
If a brownish precipitate is formed, this consists of APO-
CRENATE of copper. Mix the fluid filtered from the precipitate
with carbonate of ammonia, until the green color has changed
to blue, and warm. If a bluish-green precipitate is produced,
this consists of CRENATE of copper.
b. If you have detected arsenic, use the remainder of the
alkaline fluid to ascertain whether the arsenic existed in the
sinter as arsenious acid or as arsenic acid. Compare 133, 6.
IV. ANALYSIS OF SOILS.
213.
Soils must necessarily contain all the constituents which are found
in the plants growing upon them, with the exception of those sup-
plied by the atmosphere and the rain. When we find, therefore, a
plant the constituent elements of which are known, growing in
a certain soil, the mere fact of its growing there gives us some
insight into the composition of that soil, and may accord-
ingly save us, to some extent, the trouble of a qualitative-
analysis.
Viewed in this light, it would appear quite superfluous to make
a qualitative analysis of soils still capable of producing plants ; for
it is well known that the ashes of plants contain almost invariably
the same constituents, and the differences between them are caused
principally by differences in the relative proportions in which the
several constituents are present. But if, in the qualitative analysis
of a soil, regard is had also in so far as may be done by a simple
estimation to the quantities and proportions of the several con-
stituent ingredients, and to the state and condition in which they
are found to be present in the soil, an analysis of the kind, if com-
bined with an examination of the physical properties of the soil,
14.] ANALYSIS OF SOILS. 243
and a mechanical separation of its component parts * may <nve
most useful results, enabling the analyst to judge sufficiently
of the condition of the soil, to supersede the necessity of a quan-
titative analysis, which would require much time, and is a far more
difficult task.
As plants can only absorb substances in a state of solution, it is
a matter of especial importance, in the qualitative analysis of a soil
to know which are the constituents that are soluble in water ; which
those that require an acid for their solution (in nature principally
carbonic acid) ; and, finally, which those that are neither soluble in
water nor in acids, and are not, accordingly, in a position for the
time being to afford nutriment to the plant. With regard to the
insoluble substances, another interesting question to answer is,
whether they suffer disintegration readily, or slowly and with diffi-
culty^ or whether they altogether resist the action of disintegrating
agencies ; and also what are the products which they yield upon
their disintegration^
In the analysis of soils, the constituents soluble in water, those
soluble in acids, and the insoluble constituents must be examined
separately. The examination of the organic portion also demands
a separate process.
The analysis is therefore properly divided into the following four
parts :
1. Preparation and Examination of the Aqueous Extract.
214.
About two pounds (1000 grammes) of the air-dried soil are used 269
for the preparation of the aqueous extract. To prepare this ex-
tract quite clear is a matter of some difficulty ; in following the
usual course, viz., digesting or boiling the earth with water, and then
filtering, the fine particles of clay are speedily found to impede the
operation, by choking up the pores of the filter ; they also almost
invariably render the filtrate turbid, at least the portion which passes
through first. I have found the following method the most practical. J
Close the neck of several middle-sized funnels with small filters of
coarse blotting paper, moisten the paper, press it close to the sides
of the funnels, and then introduce the air-dried soil, in small lumps
ranging from the size of a pea to that of a walnut, but not pulverized
or even crushed ; fill the funnels with the soil to the extent of
about two-thirds. Pour distilled water into them, in sufficient
quantity to cover the soil; if the first portion of the filtrate is
turbid, pour it back 011 the filter. Let the operation proceed
quietly. When the first quantity of the fluid has passed, fill the
* With regard to the mechanical separation of the component parts of a soil, and the
examination of its physical properties and chemical condition, compare Fr. Schulze's
paper " Anleitung zur Untersuchung der Ackererden auf ihre wichtigsten physikalischen
Eigenschaften und Bestandtheile." Journal f. prakt. Chemie, Vol. 47, p. 241.
t For more ample information on this subject I refer the reader to Frcsenius' " Chemie
fiir Landwirthe, Forstmanner und Cameralisten j" published at Brunswick, by F. Vieweg
and Son, 1847, p. 485.
+ Recommended byjpr. Scliulze " Anleitung zur Untersuchung der Ackererden auf ihre
wichtigsten physikalischen Eigenschaften und Bestandtheile." Journ. f. prakt. Chemie,
Vol. 47, p. 241.
44 ANALYSIS OF SOILS. [ 214.
funnels a second, and after this a third time. Collect the several fil-
trates in one vessel. Treat the contents of one of the funnels repeatedly
with hot water, in order to remove the soluble matter as far as
practicable, the lixiviated soil being required for the preparation of
the acid extract.
a. Concentrate two-thirds of the aqueous solution by cau- 270
tiously evaporating in a porcelain dish, filter off a portion, and
test its reaction ; put aside a portion of the filtrate for the
subsequent examination for organic matters, according to the
directions of 4. Warm the remainder, and add nitric acid.
Evolution of gas indicates the presence of an ALKALINE CAR-
BONATE. Then test with nitrate of silver for CHLORINE, b.
Transfer the remainder of the concentrated fluid, together with
the precipitate which usually forms in the process of concen-
tration, to a small porcelain, or, which is preferable, a small
platinum dish, evaporate to dryness, and cautiously heat the
brownish residue over the lamp until complete destruction of
the organic matter is effected. In presence of NITRATES this
operation is attended with deflagration, which is more or less
violent according to the greater or smaller proportion in which
these salts are present, c. Test a small portion of the gently
ignited residue with carbonate of soda before the blowpipe for
MANGANESE, d. Warm the remainder with water, add some
hydrochloric acid (effervescence indicates the presence of CAR-
BONIC ACID), evaporate to dryness, heat a little more strongly, to
effect the complete separation of the silicic acid, moisten with
hydrochloric acid, add water, warm, and filter. The washed
residue generally contains some carbon, and also a little clay
if the aqueous extract was not perfectly clear and lastly SILICIC
ACID. To detect the latter, make a hole in the point of the
filter, rinse the residue through, boil with solution of carbonate
of soda, filter, saturate with hydrochloric acid, evaporate to
dryness, and treat the residue with water, which will leave the
silicic acid undissolved.
e. Test a small portion of the hydrochloric acid solution 271
with chloride of barium for SULPHURIC ACID ; another portion
with molybdate of ammonia for PHOSPHORIC ACID ; a third por-
tion with sulphocyanide of potassium for SESQUIOXIDE OF
IRON. Add to the remainder a few drops of sesquichloride of
iron (to remove the phosphoric acid), then ammonia cautiously
until the fluid is slightly alkaline, warm a little, filter, throw
down the LIME from the filtrate by means of oxalate of am-
monia, and proceed for the detection of MAGNESIA, POTASSA, and
SODA, in the usual way, strictly according to the directions of
194.
f. Alumina is not likely to be found in the aqueous extract. 272
(Fr. Schulze never found any). However, if you wish to test
for it, boil the ammonia precipitate obtained in e (271)
with pure solution of soda or potassa, filter, and test the fil-
trate with chloride of ammonium.
g. If you have detected iron, test a portion of the remaining 273
third of the aqueous extract with ferricyanide of potassium,
another with sulphocyanide of potassium, both after previous
215, 216.] ANALYSIS OF SOILS. 245
addition of some hydrochloric acid : this will indicate the degree
of oxidation in which the iron is present. Mix the remainder
of the aqueous extract with a little sulphuric acid, evaporate
on the water-bath nearly to dryness, and test the residue for
AMMONIA, by adding hydrate of lime.
2. Preparation and Examination of the Acid Extract.
215.
1. Heat about 50 grammes of the soil from which the part soluble 274
in water both cold and hot has been removed as far as prac-
ticable* (see 214), with moderately strong hydrochloric acid
(effervescence indicates CARBONIC ACID) for several hours on the
water-bath, filter, and make the following experiments with the
filtrate, which, owing to the presence of sesquichloride of iron,
has in most cases a yellow color :
Test a small portion of it with sulphocyanide of potassium for 275
SESQUIOXIDE OF IRON, another with ferrocyanide of potassium for
PROTOXIDE OF IRON.
2. Test a small portion with chloride of barium for SULPHURIC
ACID, another with molybdate of ammonia for PHOSPHORIC ACID.
3. Mix a larger portion of the filtrate with ammonia to neutra- 276
lize the free acid, then with yellowish sulphide of ammonium ;
and let the mixture stand in a warm place until the fluid looks
yellow; then filter, and test the filtrate in the usual way for LIME,
MAGNESIA, POTASSA, AND SODA.
4. Dissolve the precipitate obtained in 3 (276), in hydrochloric 277
acid, evaporate the solution to dryness, moisten the residue with
hydrochloric acid, add water, warm, filter, and examine the filtrate
according to the directions of 192, 2 (150), for IRON, MANGANESE,
ALUMINA, and, if necessary, also for lime and magnesia, which may
have been thrown down by the sulphide of ammonium, in combina-
tion with phosphoric acid.
5. The separated SILICIC ACID obtained in 4 is usually colored
by organic matter. It must, therefore, be ignited to obtain it pure.
" 6. If it is a matter of interest to ascertain whether the hydro- 278
chloric acid extract contains ARSENIC ACID, OXIDE OF COPPER, &c.,
treat the remainder of the solution first with sulphite of soda,
then with hydrosulphuric acid, as directed in 223, 1, and 2.
7. Should you wish to look for FLUORINE, ignite a fresh portion
of the earth, and then proceed according to the directions of 205.
3(230).
3. Examination of the Inorganic Constituents insoluble in Water
and Acids.
216.
The operation of heating the lixiviated soil with hydrochloric 279
acid (215 [274]) leaves still the greater portion of it undissolved.
If you wish to subject this undissolved residue to a chemical exaini-
* Complete lixiviation is generally impracticable.
246 ANALYSIS OF SOILS. [ 217.
nation, wash, dry, and sift, to separate the large and small stones
from the clay and sand ; moreover, separate the two latter from
each other by elutriation. Subject the several portions to the ana-
lytical process given for the silicates ( 203).
4. Examination of the Organic Constituents of the Soil.*
217.
The organic constituents of the soil, which exercise so great an
influence upon its fertility, both by their physical and chemical
action, are partly portions of plants in which the structure may still
be recognised (fragments of straw, roots, seeds of weeds, <fec.), partly
products of vegetable decomposition, which are usually called by the
general name of HUMUS, but differ in their constituent elements and
properties, according to whether they result from the decay of the
nitrogenous or non-nitrogenous parts of plants whether alkalies or
alkaline earths have or have not had a share in their formation
whether they are in the incipient or in a more advanced stage of
decomposition. To separate these several component parts of humus
would be an exceedingly difficult task, which, moreover, would
hardly repay the trouble ; the following operations are amply suffi-
cient to answer all the purposes of a qualitative analysis of the
organic constituents of a soil.
a. Examination of the Organic Substances soluble in Water.
Evaporate the portion of the nitrate of 214, a (270), which has 280
been put aside for the purpose of examining the organic constituents,
on the water-bath to perfect dryness, and treat the residue with
water. The ulmic, humic, and geic acids, which were in the solu-
tion in combination with bases, remain undissolved, whilst crenic
acid and apocrenic acid are dissolved in combination with ammonia ;
for the manner of detecting the latter acids, see 212, 3 (268).
b. Treatment with an Alkaline Carbonate.
Dry a portion of the lixiviated soil, and sift to separate the 281
fragments of straw, roots, &c., together with the small stones, from
the finer parts; digest the latter for several hours, at a tem-
perature of 176 1 9 4 F., with solution of carbonate of soda, and
filter. Mix the nitrate with hydrochloric acid to acid reaction. If
brown flakes separate, these proceed from ulmic acid, humic acid, or
geic acid. The larger the quantity of ulmic acid present the lighter,
the larger that of humic acid or geic acid, the darker the brown
color of the flakes.
c. Treatment with Caustic Alkali.
Wash the soil boiled with solution of carbonate of soda (b) with 282
water, boil several hours with solution of potassa, replacing the water
* Compare Fresenius 1 "Chernie fur Landwirthe, Forstmanner und Cameralisten ;"
published at Brunswick, by F. Vieweg and Son, 1847, 282285.
218, 219.] DETECTION OF INORGANIC SUBSTANCES. 247
in proportion as it evaporates, dilute, filter, and wash. Treat the
brown fluid as in b. The ulmic and humic acids which separate
now, are new products resulting from the action of boiling solution
of potassa upon the ulmine and humine originally present.
Y. DETECTION OF INORGANIC SUBSTANCES IN PRESENCE OF
ORGANIC SUBSTANCES.
218.
The impediments which the presence of coloring, slimy, and other
organic substances throw in the way of the detection of inorganic
bodies, and that the latter can often be effected only after the total
destruction of the organic admixture, will be readily conceived, if
we reflect that in dark colored fluids changes of color or the forma-
tion of precipitates escape the eye, that slimy fluids cannot be filtered,
<fec. Now, as these difficulties are very often met with in the ana-
lysis of medicinal substances, and more especially in the detection of
inorganic poisons in articles of food or in the contents of the stomach,
and, lastly, also in the examination of plants and animals, or parts
of them, for their inorganic constituents, I will here point out the
processes best adapted to lead to the attainment of the object in
view, both in the general way and in special cases.
1. General Rules for the Detection of Inorganic Substances in Presence of
Organic Matters, which by their Color, Consistence, <kc., impede the
Application of the Reagents, or obscure the Reactions produced.
219.
We confine ourselves here, of course, to the description of the
most generally applicable methods, leaving the adaptation of the
modifications which circumstances may require in special cases, to
the discretion of the analyst.
1. THE SUBSTANCE UNDER EXAMINATION DISSOLVES IN WATER, BUT 283
THE SOLUTION IS DARK COLORED OR OF SLIMY CONSISTENCE.
a. Boil a portion of the solution with hydrochloric acid, and
gradually add chlorate of potassa, until the mixture is decolor-
ized and perfectly fluid j heat until it no longer exhales
the odor of chlorine, then dilute with water, and filter. Ex-
amine the filtrate in the usual way, commencing with 188.
Compare also 223.
b. Boil another portion of the solution for some time with
nitric acid, filter, and test the filtrate for SILVER, POTASSA, and
HYDROCHLORIC ACID. If the nitric acid succeeds in effecting
the ready and complete destruction of the coloring and slimy
matters, &c., this method is often altogether preferable to all
others.
c. ALUMINA and SESQUIOXIDE OF CHROMIUM might escape de-
tection by this method, because ammonia and sulphide of am-
monium fail to precipitate these oxides from fluids containing
non- volatile organic substances. Should you have reason to
suspect the presence of these oxides, deflagrate a third portion
of the substance with nitrate of potassa and some carbonate of
21<S DETECTION OP INORGANIC POISONS. [ 220.
soda, and boil the fused mass with solution of soda. The
alumina is now found by acidifying with nitric acid, and
then adding ammonia ; the chromium as alkaline chromate
in the nitrate, by means of acetate of lead, after addition of
acetic acid.
2. BOILING WATER FAILS TO DISSOLVE THE SUBSTANCE, OK EFFECTS 284
ONLY PARTIAL SOLUTION ; THE FLUID ADMITS OF FILTRATION.
Filter, and treat the filtrate either as directed 187, or, should it
require decolorization, according to the directions of 219, 1. The
residue may be of various kinds.
a. IT is FATTY. Remove the fatty matters by means of
ether, and should a residue be left, treat this as directed 173.
b. IT is RESINOUS. Use alcohol instead of ether, or apply
both liquids successively.
c. IT is OF A DIFFERENT NATURE, e.g., woody fibre, &c.
a. Dry, and ignite a portion of the dried residue in a porce-
lain or platinum vessel, until total or partial incineration
is effected ; boil the residue with nitric acid and water, and
examine the solution as directed 187, III. (109) ; if &
residue has been left, treat this according to the directions
of 201.
(3. Examine another portion for the heavy metals, in the
manner directed 219, 1, a ; since in a, besides the com-
pounds of mercury which may be present, arsenic, cadmium,
zinc, &c., may volatilize.
y. Test the remainder for ammonia, by triturating it
together with hydrate of lime.
3. THE SUBSTANCE DOES NOT ADMIT OF FILTRATION OR ANY OTHER 285
MEANS OF SEPARATING THE DISSOLVED FROM THE UNDISSOLVED PART.
Treat the substance in the same manner as the residue in 2. As
regards the charred mass (2 a), it is often desirable to boil the
mass, carbonized at a gentle heat, with water, filter, examine
the filtrate, wash the residue, incinerate it, and examine the
ash.
2. Detection of Inorganic Poisons in Articles of Food, in Dead
Bodies, &c., in Chemico-legal Cases*
220.
The chemist is sometimes called upon to examine an article of 286
food, the contents of the stomach of an individual, a dead body, &c.,
with a view to detect the presence of some poison, and thus to esta-
blish the fact of a wilful or accidental poisoning ; but it is more fre-
quently the case that the question put to him is of a less general
nature, and that he is called upon to. determine whether a certain
substance placed before him contains a metallic poison ; or, more
pointedly still, whether it contains arsenic, or hydrocyanic acid,
or some other particular poison as it may be that the symptoms
* Compare: a. Fresenius, "die Stellung des Chemikers bei gerichtlich chemiscben
Untersuchungen," &c. (Annal. der Chemie uud Pharm. 49, 275) ; and b. Fresenius and
v. Babtfs " Abhandlung iiber ein neues, unter alien Umstanden sicheres Verfahren zur
Ausmittelung und quantitativen Bestimmung des Arsens bei Vergiftungsfallen. " Annal.
der Chemie und Pharmacie, 49, 287.
. DETECTION OF ARSENIC. 249
point clearly in the direction of that poison, or that the examining
magistrate has, or believes he has, some other reason to put this
question.
It is obvious that the task of the chemist will be the easier, the
more special and pointed the question which is put to him. How-
ever, the analyst will always act most wisely, even in cases where he
is simply requested to state whether a certain poison, e. g. arsenic, is
present or not, if he adopts a course of proceeding which will not
only permit the detection of the one poison specially named, the
presence of which may perhaps be suspected on insufficient grounds,
but will moreover inform him as to the presence or absence of other
similar poisons.
But we must not go too far in this direction either ; if we were
to attempt to devise a method that should embrace all poisons, we
might unquestionably succeed in elaborating such a method at* the
writing-desk j but practical experience would but too speedily con-
vince us that the intricate complexity inseparable from such a
course, must necessarily impede the easy execution of the process,
and impair the certainty of the results, to such an extent indeed,
that the drawbacks would be greater than the advantages derivable
from it.
Moreover, the attendant circumstances permit usually at least a
tolerably safe inference as to the group to which the poison belongs.
Acting on these views, I give here,
1. A method which ensures the detection of the minutest traces
of arsenic, allows of its quantitative determination, and permits at
the same time the detection of all other metallic poisons.
2. A method to effect the detection of hydrocyanic acid, which
leaves the substance still fit to be examined both for metallic poisons
and for vegeto-alkalies.
3. A method to effect the detection of phosphorus, which does
not interfere with the examination for other poisons.
This Section does not, therefore, profess to supply a complete
guide in every possible case or contingency of chemico- legal investi-
gations. But the instructions given in it are the tried and proved
results of my own practice and experience. Moreover, they will be
found sufficient in most ca-es, the more so as I shall append to the
Section on the vegeto-alkalies the description of a process by which
the detection of these latter poisons in criminal cases may be
effected.
I. METHOD FOR THE DETECTION OP ARSENIC (WITH DUE REGARD TO
THE POSSIBLE PRESENCE OF OTHER METALLIC POISONS.
221.
Of all metallic poisons arsenic is the most dangerous, and at the 287
same time the one most frequently used, more particularly for the
wilful poisoning of others. And again, among the compounds of
arsenic, arsenious acid (white arsenic) occupies the first place,
because (1) It kills even in small doses ; (2) It does not betray
itself, or at least very slightly, by the taste ; and (3) It is but too
readily procurable.
250 DETECTION OF ARSENIC. [ 222.
As arsenious acid dissolves in water only sparingly and 011
account of the difficulty with which moisture adheres to it very
slowly, the greater portion of the quantity swallowed exists usually
in the body still in the undissolved state ; as, moreover, the smallest
grains of it may be readily detected by means of an exceedingly
simple experiment ; and lastly, as no matter what opinion may be
entertained about the normal presence of arsenic in the bones, &c.
this much is certain, that at all events arsenious acid in grains or
powder is never normally present in the body, the particular care
and efforts of the analyst ought always to be directed to the detec-
tion of the arsenious acid in substance and this end may indeed
usually be attained.
A. Method for the Detection of undissolved Arsenious Acid.
222.
1. If you have to examine some article of food, substances re- 288
jected from the stomach, or some other matter of the kind, mix the
whole as uniformly as may be practicable, reserve one-third for
unforeseen contingencies, and mix the other two-thirds in a porcelain
dish with distilled water, with a stirring rod ; let the mixture stand
a little, and then pour off the fluid, together with the lighter sus-
pended particles, into another porcelain dish. Repeat this latter
operation several times, if possible, with the same fluid, pouring
it from the second dish back into the first, &c. Finally, wash once
more with pure water, remove the fluid, as far as practicable, and
try whether you can find in the dish small, white, hard grains which
feel gritty and grate under the glass rod. If not, proceed as directed
223. But if so, put the grains, or part of them, on blotting-paper,
removing them from the dish with the aid of pincers, and try the
deportment of one or several grains upon heating in a glass tube,
and of some other grains upon ignition with a splinter of charcoal
(compare 131, 11). If you obtain in the former experiment a
white crystalline sublimate, in the latter a lustrous arsenical mirror,
the fact is clearly demonstrated that the grains selected and examined
consisted really of arsenious acid. If you wish to determine the
quantity of the poison, unite the contents of both dishes, and pro-
ceed as directed 223.
2. If a stomach is submitted to you for analysis, empty the con-
tents into a porcelain dish, turn the stomach inside out, and (a),
search the inside coat for small, white, hard, sandy grains. The
spots occupied by such grains are often reddened ; they are also
frequently found firmly imbedded in the membrane, (b) Mix the
contents in the dish uniformly, put aside one-third for unforeseen
contingencies, and treat the other two-thirds as in 1. The same
course is pursued also with the intestines. In other parts of
the body with the exception perhaps of the pharynx and oeso-
phagus arsenious acid cannot be found in grains, if the poison
has been introduced through the mouth. If you have found grains
of the kind described, examine them as directed in 1 ; if not, pro-
ceed according to the instructions of 223.
223.] DETECTION OP ARSENIC. 251
B. Method for the Detection of Arsenic in whatever Form of Combination it
may exist, which allows also a Quantitative Determination of that Poison,
and permits at the same time the Detection of other Metallic Poisons
which may be present.*
223.
If you have found no arsenious acid by the method described in 289
A, evaporate the mass in the porcelain dish, which has been diluted
by washing with water (see A, 1), on the water-bath, to a pasty
consistence. If you have to analyze a stomach, intestinal tube, &c.,
cut this into pieces, and add two-thirds to the mass in the dish.
In examining other parts of the body (the lungs, liver, &c.), cut
them also into pieces, and use two-thirds for the analysis. The pro-
cess is divided into the following parts, t
1. Decolorization and Solution.
Add to the matters in the porcelain dish an amount of pure 290
hydrochloric acid about equal to, or somewhat exceeding the
weight of the dry substances present, and sufficient water to
give to the entire mass the consistence of a thin paste. Heat
the dish now on the water-bath, adding every five minutes
about two grammes (half a drachm) of chlorate of potassa to the
hot fluid, with stirring, and continue the same operation until the
contents of the dish show a light-yellow color and a perfectly homo-
geneous appearance, and are quite fluid. When this point is
attained, add again a portion of chlorate of potassa, and then remove
the dish from the water-bath. When the contents are quite cold,
transfer them cautiously to a linen strainer or to a white filter,
according to the greater or less quantity of substance ; allow the
whole of the fluid to pass through, and put the filtrate aside. Wash
the residue well with hot water, and dry it ; then mark it I., and
reserve for further examination, according to the instructions
of 223, 8 (303)- Evaporate the washings on the water-bath
to about 3 or 4 oz. (about 100 grm.), add this, together with any
precipitate that may have formed therein, to the principal fil-
trate, and then add to the united fluid, which is still very acid,
some solution of sulphite of soda, with stirring, until the odor of
sulphurous acid becomes distinctly perceptible. Then heat the mix-
ture again gently on the water-bath until the excess of the sul-
phurous acid is expelled, which will take about an hour.
2. Treatment of the Solution with Hydrosulphuric Acid (Separation
of the Arsenic as Tersulphide, and, respectively, of all the
Metals of Groups V. and VI. in form of Sulphides).
When the fluid obtained in 1, and which amounts to about twice 291
in
* This method is essentially the same as that which I have elaborated and published
1844, jointly with L. v. Babo ; compare " Annal. der Chemie und Pharmacie, Bd. 49,
p. 308. I have since that time had frequent occasion to apply it ; I have also had it tried
by others, under my own inspection, and I have invariably found it to answer the purpose
perfectly.
t I think I need hardly observe that in such extremely delicate experiments the
vessels and reagents used in the process must be perfectly free from arsenic, from heavy
metals in general, and indeed from every impurity.
252 DETECTION OF ARSENIC. [ 223.
or three times the quantity of hydrochloric acid used, is quite cold,
pour it into a beaker, transmit through it, for about 12 hours, a
slow stream of washed hydrosulphuric acid gas, rinse the delivery
pipe with some ammonia, add the ammoniated solution thus ob-
tained to the principal fluid, cover the beaker lightly with unsized
paper, and put it in a moderately warm place (about 86 F.), until
the odor of hydrosulphuric acid has nearly disappeared. Collect the
precipitate obtained in this manner on a moderately sized filter,
and wash, until the washings are quite free from chlorine. Con-
centrate the filtrate and washings somewhat, mix the fluid in a
flask with ammonia to alkaline reaction, then with sulphide of
ammonium, closely cork the flask, which must now be nearly full,
and reserve for further examination according to the instructions of
223, 9 (307).
3. Purification of the Precipitate produced by Hydrosulphuric
Acid.
Thoroughly dry the precipitate obtained in 2 which, besides 292
organic matters, must contain, in form of tersulphide, the whole of
the arsenic present in the analyzed substance, as well as, in form of
sulphides, all the metals of Groups Y. and VI. which may happen
to be present together with the filter, in a small porcelain dish,
heated on the water-bath; add pure fuming nitric acid (perfectly
free from chlorine), drop by drop, until the mass is completely
moistened, and then evaporate on the water-bath to dryness.
Moisten the residue uniformly all over with pure hydrated sul-
phuric acid, previously warmed ; then heat for two or three hours
on the water-bath, and finally on the air- sand- or oil-bath at a some-
what higher, though still moderate temperature (338 F.), until the
charred mass becomes friable, and a small sampleof it to be returned
afterwards to the mass when mixed with water and then allowed
to subside, gives a colorless fluid ; should the fluid standing over
the sediment show a brownish tint, or the residue, instead of being
friable, consist of a brown, oily liquid, add to the mass some
cuttings of pure Swedish filtering paper, and continue the appli-
cation of heat. By attending to these rules you will always
completely attain the object in view, viz., the destruction of the
organic substances, without loss of any of the metals. Warm the
residue on the water-bath, with a mixture of 8 parts of water and
1 part of hydrochloric acid, filter, wash the undissolved part tho-
roughly with hot, distilled water, with addition of a little hydro-
chloric acid, and add the washings, which must be concentrated if
necessary, to the filtrate.
Dry the washed carbonaceous residue, then mark it II., and re-
serve for further examination according to the instructions given in
223, 8, b (304).
4. PRELIMINARY EXAMINATION FOR ARSENIC AND OTHER METALLIC
POISONS OP GROUPS V. AND YI. (Second Precipitation with
Hydrosulphuric Acid).
The clear fluid obtained in 3 contains all the arsenic which 293
may have been present, in form of arsenious acid, and may con-
223.] DETECTION OF ARSENIC. 253
tain also tin, antimony, mercury, copper, bismuth, and cadmium.
Supersaturate a small portion of it cautiously and gradually with
a mixture of carbonate of ammonia and some ammonia, and observe
whether a precipitate is thereby produced. Acidify the super-
saturated sample of the fluid with hydrochloric acid, which will
redissolve the precipitate that may have been produced by am-
monia ; then return the sample to the fluid, and treat the latter
with hydrosulphuric acid in strict accordance with the directions
of 2 (291).
This process may lead to three different results, which are to
be carefully distinguished.
a. The hydrosulphuric acid fails to produce a precipitate ; 294
but subsequently, after the fluid treated as directed in 2 (291)
has stood for some time, a trifling white or yellowish-white
precipitate separates. In this case probably no metals of
Groups Y. and VI. are present. Nevertheless, treat the
filtered and washed precipitate as directed in. 5 (297) > to
guard even against overlooking the minutest traces of ar-
senic, &c.
6. A precipitate is formed, of a pure yellow color like that 295
of tersulphide of arsenic. Take a small portion of the fluid,
together with the precipitate suspended therein, add some
ammonia, and shake the mixture for some time, without
application of heat. If the precipitate dissolves readily and,
with the exception of a trace of sulphur, completely, arid if, in
the preliminary examination (293)? carbonate of ammonia
has failed to produce a precipitate, arsenic alone is present,
and no other metal (tin or antimony), at all events, no quantity
worth mentioning. Mix the solution of the small sample in
ammonia with hydrochloric acid to acid reaction, return
the acidulated sample to the fluid from which it was
taken, and which contains the yellow precipitate produced
by the hydrosulphuric acid, and proceed as directed in 5
(297)- If, on tne other hand, the addition of ammonia
to the sample completely or partially fails to redissolve
the precipitate, or if, in the preliminary examination (293),
carbonate of ammonia has produced a precipitate, there is
reason to suppose that another metal is present, perhaps with
arsenic. In this latter case also, add to the sample in the test-
tube hydrochloric acid to acid reaction, return the acidulated
sample to the fluid from which it was taken, which contains
the yellow precipitate produced by the hydrosulphuric acid,
and proceed as directed in 6 (298)-
c. A precipitate is formed, which is not yellow. In that 296
case you have to assume that other metals are present,
perhaps with arsenic. Proceed as directed in 6 (298)-
5. Treatment of the Yellow Precipitate produced by Hydrosulphuric
Acid, in Gases where the Results of the Examination in 4 b (295)
lead to the Assumption that Arsenic alone is present. Determina-
tion of the Weight of the Arsenic.
As soon as the fluid precipitated according to the directions of 297
4 (293) has nearly lost the smell of sulphuretted hydrogen transfer
254 DETECTION OF AESENIC. [ 223.
the yellow precipitate to a small filter, wash thoroughly, pour
upon the still moist precipitate solution of ammonia, and wash
the filter on which, in this case, nothing must remain undis-
solved, except sulphur thoroughly with dilute ammonia; eva-
porate the ammoniacal fluid in a small, accurately tared porce-
lain dish, on the water-bath, dry the residue at 212 F. until
its weight suffers no further diminution, and weigh. If it is
found, upon reduction, that the residue consisted of perfectly pure
tersulphide of arsenic, calculate for every part of it 0*8049 of
arsenious acid, or 0'6098 of arsenic. Treat the residue in the dish
according to the instructions given in 7 (300)-
G. Treatment of the Yellow Precipitate produced ~by Hydro sulphuric
Acid, in Gases where the Results of the Examination in 4, b (295)>
or in 4. c (296); lead to the Assumption that another Metal is
present perhaps with Arsenic. Separation of the Metals from
each other. Determination of the Weight of the Arsenic.
If you have reason to suppose that the precipitate produced by 298
hydrosulphuric acid (293) contains other metals, perhaps with
arsenic, proceed as follows : As soon . as the precipitation is
thoroughly accomplished, and the smell of sulphuretted hydrogen
nearly disappeared, pour the precipitate on a small filter, wash
thoroughly, perforate the point of the filter, and rinse the contents
with the washing-bottle into a little flask, using the least possible
quantity of water for the purpose ; add to the fluid in which the
precipitate is now suspended, first ammonia, then some yellowish
sulphide of ammonium, and let the mixture digest for some time at a
gentle heat. Should part of the precipitate remain undissolved,
filter this off, wash, perforate the filter, rinse off the residuary
precipitate, mark it III., and reserve for further examination
according to the instructions given in 223, 8, c (305)- Evaporate
the filtrate, together with the washings, in a small porcelain dish, to
dryness. Treat the residue with some pure fuming nitric acid
(free from chlorine), nearly expel the acid by evaporation, and
then add, as C. Meyer was the first to recommend, gradually,
and in small portions at a time, a solution of pure carbo-
nate of soda until it predominates. Add now a mixture of
1 part of carbonate and 2 parts of nitrate of soda, in suffi-
cient, yet not excessive quantity, evaporate to dryness, and heat
the residue very gradually to fusion. Let the fused mass cool, and,
when cold, extract it with cold water. If a residue remains
undissolved, filter, wash with a mixture of equal parts of spirit 299
of wine and water, mark it IV., arid reserve for further exa-
mination, according to the directions of 223, 8, d (306)- Mix
the solution, which must contain all the arsenic as arsenate of soda,
with the washings, previously freed from alcohol by evaporation,
add gradually and cautiously pure dilute sulphuric acid to strongly
acid reaction, evaporate in a small porcelain dish, and, when the fluid
is tolerably concentrated, add again sulphuric acid, to see whether
the quantity first added has been sufficient to expel all nitric and
nitrous acids ; heat now very cautiously until heavy fumes of hy-
drated sulphuric acid begin to escape; then let the liquid cool,
223.] DETECTION OP ARSENIC. 55
and, when cold, add a little of a concentrated ^solution of sulphurous
acid in water; warm until the excess of the sulphurous acid is driven
off, and then conduct hydrosulphuric acid into the fluid. If arsenic
is present, a yellow precipitate will form. When the precipitate
has completely subsided, and the fluid has nearly lost the smell of
sulphuretted hydrogen, filter, wash the precipitate, dissolve it in
ammonia, and proceed with the solution as directed in 5, (297), to
determine the weight of the arsenic.
7. Deduction of the Sulphide of Arsenic.
The production of metallic arsenic from the sulphide, which may 300
be regarded as the keystone of the whole process, demands the
greatest care and attention. The method recommended in 131,
12, viz., to fuse the arsenical compound, mixed with cyanide of
potassium and carbonate of soda, in a slow stream of carbonic
acid gas, is the best and safest, affording, besides the advantage of
great accuracy, also a positive guarantee against the chance of con-
founding the arsenic with some other body, more particularly anti-
mony ; on which account it is more especially adapted for medico-
legal investigations.
As regards the process of reduction, either proceed at once with
the sulphide of arsenic, or previously convert the latter into arsenic
acid (see 301). In the former case take care, if possible, not to
use the whole of the residue in the dish, obtained by the evapo-
ration of the ammoniacal solution, but only a portion of it, so that
the process may be repeated several times, if necessary. Should the
residue be too trifling to admit of being divided into several por-
tions, dissolve it in a few drops of ammonia, add a little carbonate of
soda, and evaporate on the water-bath to dryness, taking care to
stir the mixture during the process ; divide the dry mass into
several portions, and proceed to reduction.
Otto* recommends to convert the sulphide first into arsenic acid, 301
and then to reduce the latter with cyanide of potassium. The fol-
lowing is the process given by him to effect the conversion of the sul-
phide into the acid ; pour concentrated nitric acid over the sulphide
of arsenic in the dish, evaporate, and repeat the same operation several
times, if necessary, and then remove every trace of nitric acid by
repeatedly moistening the residue with water, and drying again ;
when the nitric acid is completely expelled, treat the residue with a
few drops of water, add carbonate of soda in powder, to form an
alkaline mass, and thoroughly dry this in the dish, with frequeot
stirring, taking care to collect the mass within the least possible
space in the middle of the dish. The dry mass thus obtained is
admirably adapted for reduction. I can, from the results of my
own experience, fully confirm this statement of Otto; but I must
once more repeat, that it is indispensable for the success of the
operation that the residue should be perfectly free from every trace
of nitric acid or nitrate ; otherwise deflagration is sure to take place
during the process of fusion with cyanide of potassium, and, of
course, the experiment will fail.
* " Anleitung zur Ausmittelung Jer Gifte," von Dr. Fr. Jid. Otto, p. 33.
256 DETECTION OF ARSENIC. [ 223.
When the operation is finished, cut off the reduction tube at c (see 302
Fig. 30), set aside the fore part, which contains the arsenical mirror,
put the other part of the tube into a cylinder, pour water over it, and
let it stand some time; then filter the solution obtained, add to the
filtrate hydrochloric acid to acid reaction ; then again some hydro-
sulphuric acid, and observe whether this produces a precipitate. In
cases where the reduction of the sulphide of arsenic has been
effected in the direct way, without previous conversion to arsenic
acid, a trifling yellow precipitate will usually form ; had traces of
antimony been present, the precipitate would be orange-colored
and insoluble in carbonate of ammonia. When all the soluble
salts of the fused mass have been dissolved out, examine the
metallic residue, which may be left behind, according to the
directions of 133, 1, for traces of tin and antimony; these
being the only metals that can possibly be present if the instruc-
tions here given have been strictly followed. Should appreciable
traces of these metals, or of either of them, be found, proper de-
duction and correction must be made in calculating the weight of
the arsenic.
8. Examination of the reserved Residues, marked severally I., II.,
III., and IV., for other Metals of the Fifth and Sixth Groups.
a. Residue I. Compare 223, 1 (290)-
This may contain chloride of silver and sulphate of lead, 303
possibly also binoxide of tin. Incinerate the residue (I.) in a
porcelain dish, burn the carbon with the aid of some nitrate
of ammonia, extract the residue with water, dry the part left
undissolved, and then fuse it with cyanide of potassium in a
porcelain crucible. When the fused mass is cold, treat it with
water until all that is soluble in it is completely removed ;
warm the residue with nitric acid, and proceed as directed in
179.
b. Residue II. Compare 223, 3 (292).
The carbonaceous residue which is obtained by the purifica- 304
tion of the crude sulphide by means of nitric acid and sulphuric
acid, may more particularly contain lead, mercury, and tin ;
antimony and bismuth may also be present.
Heat the residue for some time with nitrohydrochloric acid,
and filter the solution ; wash the undissolved residue with
water mixed with some hydrochloric acid, add the washings to
the filtrate, and treat the dilute fluid thus obtained with
hydrochloric acid ; should a precipitate form, examine this
according to the instructions given in 189. Incinerate the
residue insoluble in nitrohydrochloric acid, fuse the ash in con-
junction with cyanide of potassium, and proceed with the fused
mass as directed in 8, a (303)-
224.] DETECTION OF HYDROCYANIC ACID. 257
c. Residue III. Compare 223, 6 (298).
Examine the precipitate insoluble in sulphide of ammonium 3Q5
for the metals of the fifth group according to the instructions
given in 191.
d. Residue IV. Compare 223, 6 (299). ong
This may contain tin and antimony, perhaps also copper.
Proceed as directed 190, 2, b (123). If the color of the re-
siaue was black (oxide of copper), treat the reduced metals
according to the instructions given in 179.
9. Examination of the Filtrate reserved 233, 2 (291), /or Metals of
the Fourth and Third Groups, especially for Zinc and Chromium.
a. As we have seen in 223, 2 (291), the fluid filtered from 3Q7
the precipitate produced by hydrosulphuric acid, and tempo-
rarily reserved for further examination, has already been mixed
with sulphide of ammonium. The addition of this reagent
to the filtrate is usually attended with the formation of
a precipitate, consisting of sulphide of iron and phosphate
of lime, but which may possibly also contain sulphide of zinc.
Filter the fluid from this precipitate, and treat the filtrate as
directed in b (308) ; wash the precipitate with water mixed
with some sulphide of ammonium, dissolve by warming with
hydrochloric acid, and boil the solution with nitric acid, to
convert the protoxide of iron into sesquioxide ; add, if neces-
sary, sufficient sesquichloride of iron for carbonate of soda
to produce a brownish-yellow precipitate in a sample of the
fluid ; neutralize almost completely with carbonate of soda,
precipitate with carbonate of baryta, and filter ; the precipi-
tate contains all the sesquioxide of iron and all the phos-
phoric acid. Concentrate the filtrate, precipitate the baryta
with dilute, sulphuric acid, filter, add to the filtrate ammonia
to alkaline reaction, and precipitate with sulphide of ammo-
nium the zinc which may be present. For the further exami-
nation of the precipitate, see 105.
b. If the analyzed substance contained chromium, this will 308
be found in the fluid filtered from the precipitate produced by
sulphide of ammonium, 223, 2 (291). Compare 223, 9,
a (307). If you wish to ascertain whether chromium is really
present, evaporate the filtrate to dryness, mix the residue with
3 parts of nitrate of potassa and 1 part of carbonate of soda,
put the mixture into a Hessian crucible and heat to moderate
redness. Allow the fused mass to cool, and, when cold, boil
with water : yellow coloration of the fluid shows the presence
of alkaline chromate, and accordingly of chromium. For con-
firmatory tests, see 138.
II. METHOD FOB THE DETECTION OF HYDROCYANIC ACID.
224.
In cases of actual or suspected poisoning with hydrocyanic acid, 309
I. s
258 DETECTION OF HYD110CYANIC ACID. [ 224.
where it is required to separate that acid from articles of food or
from the contents of the stomach, and thus to prove its presence,
it is highly necessary to act with the greatest expedition, as the
hydrocyanic acid speedily undergoes decomposition. Still this de-
composition is not quite so rapid as is generally supposed, and indeed
it requires some time before the complete decomposition of the whole
of the acid present is effected.*
Although hydrocyanic acid betrays its presence, even in minute
quantities, by its peculiar odor, still this sign must never be looked
upon as conclusive. On the contrary, to adduce positive proof of
the presence of the acid, it is always indispensable to separate it,
and to convert it into certain known, compounds.
The method of accomplishing this is based upon distillation of
the acidified mass, and examination of the distillate for hydrocyanic
acid. Now, as the non-poisonous salts, ferro- and ferricyanide of
potassium, on distillation, likewise yield a distillate containing
hydrocyanic acid, it is, of course, indispensable as Otto very pro-
perly observes first to ascertain whether one of these salts may
not be present. For this purpose, stir a small portion of the
mass to be examined with water, filter, acidify the filtrate with
hydrochloric acid, and test a sample of it with sesquichloride of
iron, another with sulphate of protoxide of iron. If no blue pre-
cipitate forms in either, soluble ferro- and ferricyanides are not pre-
sent, and you may safely proceed as follows :
Test, in the first place, the reaction of the mass under examina- 310
tion ; if necessary, after mixing and stirring it with water. If it is
not already strongly acid, add solution of tartaric acid until the
fluid strongly reddens litmus paper ; introduce the mixture into a
retort, and place the body of the retort, with the neck pointing
upwards, in an iron or copper vessel, but so that it does not touch
the bottom, which should, moreover, by way of precaution, be
covered with a cloth ; fill the vessel with a solution of chloride of
calcium, and apply heat, so as to cause gentle ebullition of the con-
tents of the retort. Conduct the vapors passing over, with the aid
of a tight-fitting tube, bent at a very obtuse angle, through a Liebigs
condensing apparatus, and receive the distillate in a small, weighed
flask. When about half-an-ounce of distillate has passed over, re-
move the receiver, and replace it by a somewhat larger flask, also
previously tared. Weigh the contents of the first receiver, and
proceed as follows :
a. Mix one-fourth of the distillate with solution of potassa 311
or soda to strongly alkaline reaction, and then add a small
quantity of solution of sulphate of protoxide of iron, mixed
with a little sesquichloride of iron.
b. Treat another fourth as directed 155, 7, to convert the 312
hydrocyanic acid into sulphocyanide of iron. As the distillate
might, however, contain acetic acid, do not neglect to add some
* Thus I succeeded in separating a notable quantity of hydrocyanic acid from the sto-
mach, of a man who had poisoned himself with that acid in very hot weather, and whose
intestines were handed to me full 36 hours after death. A dog was poisoned with,
hydrocyanic acid, and the contents of the stomach, mixed with the blood, were left for
24 hours exposed to an intense summer-heat, and then examined : the acid was still
detected.
DETECTION OF PHOSPIIOEUS. 259
hydrochloric acid after the sesquicliloride of iron, in order
to neutralize the adverse influence of the acetate of ammonia.
Compare 155, 7.
c. If the experiments a and 6 have demonstrated the pre- 313
sence of hydrocyanic acid, and you wish now also to approxi-
mately determine its quantity, continue the distillation, until
the fluid passing over contains no longer the least trace of
hydrocyanic acid ; add one-half of the contents of the second
receiver to the remaining half of the contents of the first, mix
the fluid with nitrate of silver, then with ammonia until it
predominates, and finally with nitric acid to strongly acid reac-
tion. Allow the precipitate which forms to subside, filter on a
tared filter, dried at 212F., wash the precipitate, dry it tho-
roughly at 212 F., and weigh. Ignite the weighed precipitate
in a small porcelain crucible, to destroy the cyanide of silver,
fuse the residue with carbonate of soda and potassa to effect
the decomposition of the chloride of silver which it may con-
tain boil the mass with water, filter, acidify the filtrate with
nitric acid, and precipitate with nitrate of silver ; determine
the weight of the chloride of silver which may precipitate, and
deduct the amount found from the total weight of the chloride
and cyanide of silver : the difference gives the quantity of the
latter ; by multiplying the quantity found of the cyanide of
silver by O2017, you find the corresponding amount of an-
hydrous hydrocyanic acid ; and by multiplying this again by
2 as only one-half of the distillate has been used you find
the total quantity of hydrocyanic acid which was present in
the examined mass.
Instead of pursuing this indirect method, you may also deter- 314
mine the quantity of the hydrocyanic acid by the following direct
method : Introduce half of the distillate into a retort, together
with powdered borax ; distil to a small residue, and deter-
mine the hydrocyanic acid in the distillate as cyanide of
silver. Hydrochloric acid can no longer be present in this
distillate, as the soda of the borax retains it in the retort
( Wackenroder).
III. METHOD FOR THE DETECTION OF PHOSPHORUS.
225.
Since phosphorus paste has been employed to poison mice, &c., 315
and the poisonous action of lucifer matches has become more ex-
tensively known, phosphorus has not unfrequently been resorted
to as an agent for committing murder. The chemist is therefore
occasionally called upon to examine some article of food, or the
contents of a stomach, for this substance. It is obvious
that, in cases of the kind, his whole attention must be directed
to the separation of the phosphorus in the free state, or to pro-
ducing such reactions as will enable him to infer the presence of
free phosphorus ; since the mere finding of phosphorus in form of
phosphates would prove nothing, as phosphates invariably form
constituents of animal and vegetable bodies.
s 2
260
DETECTION OF PHOSPHORUS.
[ 225.
K Mitech&rlich, who has published the latest treatise on the 316
subject,* recommends the following method as the simplest and
best:f
Mix the substance under examination with water and some sul-
phuric acid, and subject the mixture to distillation in a flask, A
(see .Fig. si). This flask is connected with an evolution tube, b, and
Fig. 31.
the latter again with a glass cooling or condensing tube, c c c, which
passes through a perforated cork a, in the bottom of a cylinder, B,
into a glass vessel, C. Cold water runs from D, through a stop-
cock, into a funnel, i, which extends to the bottom of B ; the
warmed water flows off through g.
Now, if the substance in A contains phosphorus, there will ap-
pear, in the dark, in the upper part of the condensing tube
at the point r, where the aqueous vapors distilling over enter that
part of the tube, a strong luminosity, usually a luminous ring.
If you take for distillation 5 oz. of a mixture containing only
of a grain of phosphorus, and accordingly only 1 part of
* "Journal fur prakt. Chemie," vol. 66, p. 238.
I have tried this method, and found it to answer perfectly.
226.] ANALYSIS OF ASHES. 261
phosphorus in 100,000 parts of mixture, you may distil over 3 oz.
of it which will take at least half-an-hour without the lumi-
nosity ceasing ; Mitscherlich, in one of his experiments, stopped
the distillation after half-an-hour, allowed the flask to stand
uncorked a fortnight, and then recommenced the distillation :
the luminosity was as strong as at first. If the fluid contains sub-
stances which prevent the luminosity of phosphorus in general,
such as ether, alcohol, or oil of turpentine, no luminosity is
observed so long as these substances continue to distil over. In
the case of ether and alcohol, however, this is soon effected, and
the luminosity accordingly very speedily makes its appearance ; but
it is different with oil ot turpentine, which exercises a lasting pre-
ventive influence upon the manifestation of this reaction.
After the termination of the process, globules of phosphorus 317
are found at the bottom of the receiver, C. MitscJierlich obtained
from 5 oz. of a mixture containing ^ grain of phosphorus, so
many globules of that body that the one-tenth part of them would
have been amply sufficient to demonstrate its presence. In medico-
legal investigations these globules should first be washed with
alcohol, and then weighed. A portion may afterwards be sub-
jected to a confirmatory examination, to make quite sure that
they really consist of phosphorus : the remainder, together with a
portion of the fluid which shows the luminosity upon distillation,
should be sent in with the report.
3. Examination of the Inorganic Constituents of Plants, Animal*, or Parts
of the same, of Manures, &c. (Analysis of Ashes.)
226.
A. PREPARATION OF THE ASH.
It is sufficient for the purposes of a qualitative analysis to in- 318
cinerate a comparatively small quantity of the substance which it is
intended o examine for its inorganic constituents ; the substance
must previously be most carefully cleaned. The incineration is
effected best in a small clay muffle, but it may be conducted also
in a Hessian crucible placed in a slanting position, or, under certain
circumstances, even in a small porcelain or platinum dish. The heat
must always be moderate, to guard against the volatilization of cer-
tain constituents, more especially of metallic chlorides. It is not
always necessary to continue the combustion until all the carbon is
consumed. With ashes containing a large proportion of fusible
salts, as, e. g. the ash of beetroot molasses, it is even advisable to
effect, in the first place, complete carbonization, then to boil the
charred mass with water, and finally to incinerate the washed and
dried residue. For further particulars see Quantitative Analysis,
3rd Edition, 250.
B. EXAMINATION OP THE ASH.
As the qualitative analysis of the ash of a vegetable substance 319
is usually undertaken, either as a practical exercise, or for the
purpose of determining its general character, and the state or
condition in which any given constituent may happen to be pre-
262 ANALYSIS or ASHES. [ 226.
sent, or also with a view to make, as far as practicable, an approxi-
mate estimation of the respective quantities of the several constituents,
it is usually the best way to examine separately ; (1) the part so-
luble in water ; (2) the part soluble in hydrochloric acid ; and (3)
the residue which is insoluble in either menstruum. This can be
done the more readily, as the number of bodies to which regard must
be had in the analysis is only small, and the several processes may
accordingly be expeditiously performed.
a. Examination of the Part soluble in Water.
Boil the ash with water, filter, and whilst the residue is being
washed, examine the solution as follows :
1. Add to a portion, after heating it, hydrochloric acid in excess, 320
warm, and let the fluid stand at rest. Effervescence indicates CAR-
BONIC ACID, combined with alkalies ; odor of hydrosulphuric acid
indicates the SULPHIDE of an ALKALI METAL, formed from an alkaline
sulphate by the reducing action of the carbon. Turbidity from
separation of sulphur, with odor of sulphurous acid, denotes a HYPO-
SULPHITE (which occurs occasionally in the ash of coal). Filter,
if necessary, and add to the filtrate or to the fluid if no filtration
is required some chloride of barium ; the formation of a white
precipitate indicates the presence of SULPHURIC ACID.
2. Evaporate another portion of the solution until it is reduced 321
to a small volume, add hydrochloric acid to acid reaction efferves-
cence indicates the presence of CARBONIC ACID evaporate now to
dryness, and treat the residue with hydrochloric acid and water.
The portion left undissolved consists of SILICIC ACID. Filter, add
ammonia, chloride of ammonium, and sulphate of magnesia j the
formation of a white precipitate indicates the presence of PHOS-
PHORIC ACID. Instead of this reaction, you may also mix the fluid
filtered from the silicic acid with acetate of soda, and then cautiously
add, drop by drop, sesquichloride of iron, or you may test with
molybdate of ammonia ( ] 43).
3. Add to another portion of the solution nitrate of silver as 322
long as a precipitate continues to form ; warm gently, and then
cautiously add ammonia : if a black residue is left, this consists of
sulphide of silver, proceeding from the sulphide of an alkali metal,
or from a hyposulphite. Mix the ammoniacal solution now after
previous filtration if necessary cautiously with nitric acid until it
is exactly neutralized. If this produces a bright yellow precipitate,
the phosphoric acid found in 2 was present in the tribasic, if a
white precipitate, it was present in the bibasic form. Add more
nitric acid. This effects the solution of the phosphate of silver
precipitate. But if CHLORINE (iodine,* bromine) is present, a
portion of the precipitate remains undissolved, or the fluid appears
turbid.
4. Acidify a portion of the solution with hydrochloric acid, and 323
then make it alkaline with ammonia ; mix the alkaline fluid with
oxalate of ammonia, and let it stand at rest. The formation . of a
* To detect the iodine in aquatic plants, dip the plant in a weak solution of potassa
(Chatiri), dry, incinerate, treat with water, and examine the aqueous solution as directed
211, 2, c, ft aa (258).
22G.] ANALYSIS OF ASHES. 263
white precipitate indicates LIME. Filter, and mix the nitrate with
ammonia and phosphate of soda ; the formation of a crystalline pre-
cipitate, which often becomes visible only after long standing, indi-
cates MAGNESIA. Magnesia is often found in distinctly appreciable,
lime only in exceedingly minute, quantity, even when alkaline car-
bonates and phosphates are present.
5. For POTASSA and SODA examine as directed S 195.
b. Examination of the Part soluble in Hydrochloric Acid.
Warm the residue left undissolved by water with hydrochloric 324
acid* effervescence indicates CARBONIC ACID, combined with alka-
line earths ; evolution of chlorine denotes OXIDES OF MANGANESE
evaporate to dryness, and heat a little more strongly, to effect the
separation of the silicic acid ; moisten the residue with hydrochloric
acid and some nitric acid, add water, warm, and filter.
1. Test with hydrosulphuric acid. If this produces any other
than a perfectly white precipitate, you must examine it in the usual
way. The ashes of plants occasionally contain COPPER ; if the
plant has been manured with excrements deodorized by nitrate
of lead, they may contain LEAD ; other metals are also occasionally
found.
2. Mix a portion of the original solution with carbonate of soda, 325
as long as the precipitate formed redissolves upon stirring ; then
add acetate of soda, and some acetic acid. This produces, in most
cases, a white precipitate of PHOSPHATE OF SESQUIOXIDE OF IRON. If
the fluid in which this precipitate is suspended is reddish, there is
more sesquioxide of iron present than corresponds to the phosphoric
acid ; if it is colorless, add sesquichloride of iron, drop by drop,
until the fluid looks reddish. (From the quantity of the precipitate
of phosphate of sesquioxide of iron formed you may estimate the
PHOSPHORIC ACID present.) Heat to boiling,t filter hot, and mix
the filtrate, after addition of ammonia, with yellowish sulphide of
ammonium, in a stoppered flask ; should a precipitate form, after
long standing, examine this before the blowpipe for MANGANESE, and
the fluid filtered from it for LIME and MAGNESIA, in the usual way
(226, B,a, 4 [323]).
c. Examination of the Residue insoluble in Hydrochloric Acid.
The residue insoluble in hydrochloric acid contains,
1. The silicic acid, which has separated on treating with hydro- 326
chloric acid.
2. Those ingredients of the ash which are insoluble in hydro-
chloric acid. These are, in most ashes, sand, clay, carbon ; sub-
stances, therefore, which are present in consequence of defective
cleaning or imperfect combustion of the plants, or matter derived
from the crucible. It is only the ashes of the stems of cereals and
others abounding in silicic acid, that are not completely decomposed
by hydrochloric acid.
* If the residue still contains much carbon, after further incineration.
f If this should fail to decolorize the fluid, add some more acetate ot soda.
26 i ADDITIONAL REMARKS. [To 173 176.
Boil the washed residue with solution of carbonate of soda in 327
excess, filter hot, wash with boiling water, and test for silicic acid
in the filtrate by evaporation with hydrochloric acid. If the ash
was of a kind to be completely decomposed by hydrochloric acid, the
analysis may be considered as finished for the accidental admix-
ture of clay and sand will rarely interest the analyst sufficiently to
warrant a more minute examination by fluxing. But, if the ash
abounded in silicic acid, and it may therefore be supposed that the
hydrochloric acid has failed to effect complete decomposition, evapo-
rate half of the residue insoluble in solution of carbonate of soda,
with pure solution of soda in excess, in a silver or platinum dish, to
dryness. This decomposes the silicates of the ash, whilst but
little affecting the sand. Acidify now with hydrochloric acid,
evaporate to dryness, &c., and proceed as in b (324). For the de-
tection of the alkalies use the other half of the residue. Compare
205, 2 (228).
SECTION III.
EXPLANATORY NOTES AND ADDITIONS TO THE
SYSTEMATIC COURSE OF ANALYSIS.
I. ADDITIONAL REMARKS TO THE PRELIMINARY EXAMINATION.
To 173176.
THE inspection of the physical properties of a body may, as already
stated 173, in many cases enable the analyst to draw certain general
inferences as to its nature. Thus, for instance, if the analyst has a
white substance before him, he may at once conclude that it is not
cinnabar, or if a light substance, that it is not a compound of lead, &c.
Inferences of this kind are quite admissible to a certain extent ; but
if carried too far, they are apt to mislead the operator, by blinding
him to every reaction not exactly in accordance with his preconceived
notions.
As regards the examination of substances at a high temperature,
platinum foil or small iron spoons may also be used in the process ;
however, the experiment in the glass tube gives, in most cases, results
more clearly evident, and affords, moreover, the advantage that volatile
bodies are less likely to escape detection, and that a more correct and
precise notion can be formed of the nature of the heated substance, than
exposure on platinum foil or in an iron spoon will permit. In the case
of minerals it is always advisable to extend the examination in the dry
way, also to fluorine ( 147, 8). To ascertain the products of oxidation
of a body, it is sometimes advisable also to heat it in a short glass-tube,
open at both ends, and held in a slanting position ; small quantities of a
metallic sulphide, for instance, may be readily detected by this means.
(Compare 156, 6.)
With respect to the preliminary examination by means of the blow-
To 177 179.] ADDITIONAL REMARKS. 265
pipe, I have to remark that the student must avoid drawing positive
conclusions from pyrochemical experiments, until he has acquired some
practice in this branch of analytical chemistry. A slight incrustation
of the charcoal support, which may seem to denote the presence of a cer-
tain metal, is not always a conclusive proof of the presence of that
metal ; nor would it be safe to assume the absence of a substance simply
because the blowpipe flame fails to effect reduction, or solution of nitrate
of protoxide of cobalt fails to impart a color to the ignited mass, &c.
The blowpipe reactions are, indeed, in most cases, unerring, but it is not
always easy to produce them, and they are moreover liable to suffer
modification by accidental circumstances.
The student should never omit the preliminary examination ; the
notion that this omission will save time and trouble, is very erroneous.
II. ADDITIONAL EEMARKS TO THE SOLUTION OF SUBSTANCES, ETC.
To 177179.
It is a task of some difficulty to fix the exact limit between substances
which are soluble in water and those that are insoluble in that men-
struum, since the number of bodies which are sparingly soluble in water
is very considerable, and the transition from sparingly soluble to in-
soluble is very gradual. Sulphate of lime, which is soluble in 430 parts
of water, might perhaps serve as a limit between the two classes, since
this salt may still be positively detected in aqueous solution, by the deli-
cate reagents which we possess for lime and sulphuric acid.
When examining an aqueous fluid by evaporating a few drops of it
upon platinum foil, to see whether it holds a solid body in solution, a
very minute residue sometimes remains, which leaves the analyst in
doubt respecting the nature of the substance ; in cases of the kind test,
in the first place, the reaction of the fluid with litmus papers ; in the
second place, add to a portion of it a drop of solution of chloride of
barium ; and lastly, to another portion some carbonate of soda. Should
the fluid be neutral, and remain unaltered upon the addition of these
reagents, the analyst need not examine it any further for bases or acids ;
since if the fluid contained any of those bases or acids which principally
form sparingly soluble compounds, the chloride of barium and the car-
bonate of soda would have revealed their presence. The analyst may
therefore feel assured that the detection of the substance of which the
residue left upon evaporation consists, will be more readily effected in
the class of bodies insoluble in water.
If water has dissolved any part of the substance under examination,
the student will always do well to examine the solution both for acids
and bases, since this will lead more readily to a correct apprehension of
the nature of the compound an advantage which will amply counter-
balance the drawback of sometimes meeting with the same substance
both in the aqueous and in the acid solution.
The following substances (with few exceptions) are insoluble in water,
but soluble in hydrochloric acid or in nitric acid : the phosphates, arse-
nates, arsenites, borates, carbonates, and oxalates of the earths and metals ;
and also several tartrates, citrates, malates, benzoates, and succinates ;
the oxides and sulphides of the heavy metals; alumina, magnesia; many
of the metallic iodides and cyanides, &c. Nearly the whole of these
266 EXPLANATION OF THE ANALYTICAL COURSE. [To 180 201.
compounds are, indeed, decomposed, if not by dilute, by boiling concen-
trated hydrochloric acid * but this decomposition gives rise to the for-
mation of insoluble compounds when oxide of silver is present, and of
sparingly soluble compounds in the presence of suboxide of mercury and
lead. This is not the case with nitric acid, and accordingly the latter
effects complete solution in many cases where hydrochloric acid has left
a residue. But, on the other hand, nitric acid leaves, besides the bodies
insoluble in any simple acid, teroxide of antimony, binoxide of tin, bin-
oxide of lead, &c., undissolved, and fails also to effect the complete
solution of many other substances.
Substances not soluble in water are, therefore, treated as follows : try
to dissolve them in dilute or concentrated hydrochloric acid, cold or
boiling if this fails to effect complete solution, try to dissolve a fresh
portion in nitric acid j if this also fails, treat the body with aqua regia,
which is an excellent solvent, more particularly for metallic sulphides.
To examine separately the solution in hydrochloric acid or in nitric
acid, on the one hand, and that in nitrohydrochloric acid on the other,
is, in most cases, unnecessary.
With regard to the solution of metals and alloys, I have to remark
that, upon boiling them with nitric acid, white precipitates will fre-
quently form, although neither tin nor antimony be present. Inexpe-
rienced students often confound such precipitates with the oxides of
these two metals, although their appearance is quite different. These
precipitates consist simply of nitrates sparingly soluble in the nitric acid
present, but readily soluble in water. Consequently the analyst should
ascertain whether these white precipitates will dissolve in water or not,
before he concludes them to consist of tin or antimony.
III. ADDITIONAL REMARKS TO THE ACTUAL EXAMINATION.
To 180201.
A. GENERAL REVIEW AND EXPLANATION OF THE ANALYTICAL COURSE.
a. DETECTION OF THE BASES.
The classification of the bases into groups, and the methods which
serve to detect and isolate them individually, have been fully explained
in Part I., Section III. The systematic course of analysis, from 180 to
196, is founded upon this classification of the bases j and as a correct
apprehension of it is of primary importance, I will here subjoin a brief
explanation of the grounds upon which this division rests. Respecting
the detection of the several bases individually, I refer the student to
the recapitulations and remarks in 91, 98, 102, 111, 117, 122, 127,
and 133.
The general reagents which serve to divide the bases into principal
groups are HYDROCHLORIC ACID, HYDROSULPHURIC ACID, SULPHIDE OF
AMMONIUM, and CARBONATE OF AMMONIA ; this is likewise the order of
succession in which they are applied. Sulphide of ammonium performs
a double part.
Let us suppose we have in solution the whole of the bases, together
* For tlie exceptions, see 5 201.
To 180 201.] EXPLANATION OF THE ANALYTICAL COURSE. 267
with arsenious and arsenic acids, and also phosphate of lime which
latter may serve as a type for the salts of the alkaline earths, soluble in
acids, and reprecipitated unaltered by ammonia.
Chlorine forms insoluble compounds only with silver and mercury ;
chloride of lead is sparingly soluble in water. The insoluble subchloride
of mercury corresponds to the suboxide of that metal. If, therefore, we
add to our solution :
1. Hydrochloric Acid,
we remove from it the metallic oxides of the first division of the fifth
group, viz., the whole of the OXIDE OF SILVER and the whole of the SUB-
OXIDE OF MERCURY. From concentrated solutions, a portion of the LEAD
may likewise precipitate as chloride j this is, however, immaterial, as a
sufficient quantity of the lead remains in the solution to permit the sub-
sequent detection of this metal.
Hydrosulphuric acid completely precipitates the oxides of the fifth
and sixth group from solutions containing a free mineral acid, since the
affinity of the metallic radicals of these oxides for sulphur, and that of
the hydrogen for oxygen, are sufficiently powerful to overcome the affinity
between the metal and the oxygen, and that between the oxide and a
strong acid, EVEN THOUGH THE ACID BE PRESENT IN EXCESS. But none
of the other bases are precipitated under these circumstances, since those
of the first, second, and third group form no sulphur compounds insoluble
in water j and the affinity which the metallic radicals of the oxides of
the fourth group possess for sulphur, combined with that manifested by
hydrogen for oxygen, is not sufficiently powerful to overcome the affinity
of the metal for oxygen and of the oxide for a strong acid, IF THE LATTER
IS PRESENT IN EXCESS.
If, therefore, after the removal of the oxide of silver and suboxide of
mercury, by means of hydrochloric acid, we add to the solution, which
still contains free hydrochloric acid,
2. Hydrosulphuric Acid,
we remove from it the remainder of the oxides of the fifth, together
with those of the sixth group, viz., OXIDE OF LEAD, OXIDE OF MERCURY,
OXIDE OF COPPER, TEROXIDE OF BISMUTH*, OXIDE OF CADMIUM, TEROXIDE
OF GOLD, BINOXIDE OF PLATINUM, PROTOXIDE OF TIN, BINOXIDE OF TIN,
TEROXIDE OF ANTIMONY, ARSENIOUS ACID, and ARSENIC ACID. All the
other oxides remain in solution, either unaltered, or reduced to a lower
degree of oxidation, e. g., sesquioxide of iron to protoxide ; chromic acid
to sesquioxide of chromium, &c.
The sulphides corresponding to the oxides of the sixth group com-
bine with basic metallic sulphides (the sulphides of the alkali metals),
and form with them sulphur salts soluble in water ; while the sulphides
corresponding to the oxides of the fifth group do not possess this pro-
perty, or possess it only to a limited extent.* If, therefore, we treat
the whole of the sulphides precipitated by hydrosulphuric acid from an
acid solution, with
* Sulphide of mercury combines with sulphide of potassium and sulphide of sodium,
but not with sulphide of ammonium ; sulphide of copper dissolves a little in sulphide of
ammonium, but not in sulphide of potassium or sulphide of sodium.
268 EXPLANATION OF THE ANALYTICAL COURSE. [To 180201.
3. Sulphide of Ammonium (or, in certain cases, Sulphide of Sodium),
the sulphides* of mercury, lead, copper, bismuth, and cadmium remain
undissolved, whilst the other sulphides dissolve as double compounds of
sulphide of GOLD, PLATINUM, ANTIMONY, TIN, ARSENIC, with SULPHIDE OF
AMMONIUM (or, as the case may be, SULPHIDE OF SODIUM), and precipi-
tate again from this solution upon the addition of an acid, either un-
altered, or, as regards the protosulphide of tin, and the tersulphide of
antimony, in a state of higher sulphtiration these two compounds
taking up sulphur from the yellow sulphide of ammonium. The
rationale of this precipitation is as follows : The acid decomposes the
sulphur salt formed. The sulphur base (sulphide of ammonium or sul-
phide of sodium) transposes with the constituents of the water, forming
an oxygen base (oxide of ammonium or soda) and hydrosulphuric acid ;
the former combines with the acid added, the latter escapes, and the
liberated electro-negative sulphide (sulphur acid) precipitates. If the
acid is an hydracid, its radical combines with the ammonium, its
hydrogen with the sulphur. Sulphur precipitates at the same time, the
sulphide of ammonium containing generally an excess of that element.
The analyst must bear in mind that this eliminated sulphur makes
the precipitated sulphides appear of a lighter color than they are
naturally.
The alkalies, the alkaline earths, alumina, and sesquioxide of chromium
have remained in solution, because their sulphur compounds are soluble
in water, or because their salts are not affected in the least by hydro-
sulphuric acid ; the sulphides corresponding to the oxides of the fourth
group are insoluble in water, and would have been precipitated accord-
ingly by hydrosulphuric acid, but for the free acid present. If, there-
fore, this free acid is removed, **. e., if the solution is made alkaline, and
then treated with hydrosulphuric acid, or, what answers both purposes
at once, if
4. Sulphide of Ammonium,
is added to the solution,* the sulphides corresponding to the oxides of
the fourth group will precipitate : viz., the SULPHIDES OF IRON, MANGA-
NESE, COBALT, NICKEL, and ZINC. But in conjunction with them,
ALUMINA, SESQUIOXIDE OF CHROMIUM, and PHOSPHATE OF LIME, are
thrown down, because the affinity which the oxide of ammonium pos-
sesses for the acid of the salt of alumina or of sesquioxide of chromium,
or for that which keeps the phosphate of lime in solution, causes the
elements of the sulphide of ammonium to transpose with those of the
water, thus giving rise to the formation of oxide of ammonium and of
hydrosulphuric acid. The former combines with the acid, the latter
escapes, being incapable of entering into combination with the liberated
oxides or with the phosphate of lime, the oxides and the lime-salt
precipitate.
There remain now in solution only the alkaline earths and the
alkalies. The neutral carbonates of the former are insoluble in water,
* After previous neutralization of the free acid by ammonia, to prevent unnecessary
evolution of hydrosulphuric acid ; and the addition also, if necessary, of chloride of am-
monium, to prevent the precipitation of magnesia by ammonia.
TO 180201.] EXPLANATION OP THE ANALYTICAL COURSE. 269
whilst those of the latter are soluble in that menstruum. If therefore
we now add
5. Carbonate of Ammonia,
and apply a gentle heat, in order to decompose the bicarbonates which
may have formed, the whole of the alkaline earths ought to precipitate.
This is, however, the case only as regards BARYTA, STRONTIA, and LIME ;
of magnesia we know that, owing to its disposition to form double com-
pounds with salts of ammonia, it precipitates only in part ; and that
the presence of an additional salt of ammonia will altogether prevent its
precipitation. To guard against any uncertainty arising from this
cause, chloride of ammonium is added previously to the addition of the
carbonate of ammonia, and thus the precipitation of the magnesia is
altogether prevented.
We have now in solution magnesia and the alkalies. The detection of
magnesia may be effected by means of phosphate of soda and ammonia ;
but its separation requires a different method, since the presence of
phosphoric acid would impede the further progress of the analysis.
The process which serves to effect the removal of the magnesia is based
upon the insolubility of that earth in the pure state. The substance
under examination is accordingly ignited in order to expel the salt of
ammonia, and the magnesia is then precipitated by means of baryta, the
alkalies, together with the newly formed salt of baryta and the excess of
the caustic baryta added, remaining in solution. By the addition of
carbonate of ammonia, the compounds of baryta are removed from the
solution, which now only contains the fixed alkalies, the salt of ammonia
formed, and the excess of the salt of ammonia added. If the salts of
ammonia are then removed by ignition, the residue consists of the fixed
alkalies alone. This method of separating the baryta affords the advan-
tage over that of effecting the removal of that earth by means of sul-
phuric acid, that the alkalies are obtained in the most convenient form
for their subsequent individual detection and isolation, viz., as chlorides.
But as carbonate of baryta is slightly soluble in salts of ammonia, and
gives, upon evaporation with chloride of ammonium, carbonate of baryta
and chloride of barium, it is usually necessary, after the expulsion of
the salts of ammonia by ignition, to precipitate it once more with car-
bonate of ammonia, in order to obtain a solution perfectly free from
baryta. Lastly, to effect the detection of the ammonia, a fresh portion
of the substance must of course be taken.
b. DETECTION OF THE ACIDS.
Before passing on to the examination for acids and salt- radicals, the
analyst should first ask himself which of these substances may be ex-
pected to be present, from the nature of the detected bases and the class
to which the substance under examination belongs with respect to its
solubility in water or acids, since this will save him the trouble of
unnecessary experiments. Upon this point I refer the student to the
table in Appendix IV., in which the various compounds are arranged
according to their several degrees of solubility in water and acids.
The general reagents applied for the detection of the acids are, for the
inorganic acids CHLORIDE OF BARIUM and NITRATE OF SILVER, for the
270 EXPLANATION OP THE ANALYTICAL COURSE. [To 180 201.
organic acids CHLORIDE OF CALCIUM and SESQUICHLORIDE OP IRON. It is
therefore indispensable that the analyst should first assure himself
whether the substance under examination contains only inorganic acids,
or whether the presence of organic acids must also be looked for. The
latter is invariably the case, if the body, when ignited, turns black,
owing to separation of carbon. In the examination for bases the
different reagents serve to effect the actual separation of the several
groups of bases from each other ; but in the examination for acids they
serve simply to demonstrate the presence or absence of the acids belong-
ing to the different groups.
Let us suppose we have an aqueous solution containing the whole of
the acids, in combination with soda, for instance.
Baryta forms insoluble compounds with sulphuric acid, phosphoric
acid, arsenious acid, arsenic acid, carbonic acid, silicic acid, boracic
acid, chromic acid, oxalic acid, tartaric acid, and citric acid ; fluoride of
barium also is insoluble or, at least, difficultly soluble j all these com-
pounds are soluble in hydrochloric acid, with the exception of sulphate
of baryta. If, therefore, to a portion of our neutral or, if necessary,
neutralized solution, we add,
1. Chloride of Barium,
the formation of a precipitate will denote the presence of at least one
of these acids. By treating the precipitate with hydrochloric acid, we
learn at once whether sulphuric acid is present or not, as all the salts
of baryta being soluble in this menstruum, with the exception of the
sulphate, a residue left undissolved by the hydrochloric acid can consist
only of the latter salt. When sulphate of baryta is present, the
reaction with chloride of barium fails to lead to the positive detection of
the whole of the other acids enumerated. For upon filtering the hydro-
chloric solution of the precipitates and supersaturating the filtrate with
ammonia, the borate, tartrate, citrate, &c., of baryta do not always fall
down again, being kept in solution by the chloride of ammonium formed.
For this reason, chloride of barium cannot serve to effect the actual
separation of the whole of the acids named, and except as regards sul-
phuric acid, we set no value upon this reagent as a means of effecting
their individual detection. Still it is of great importance as a reagent,
since the non-formation of a precipitate upon its application in neutral
or alkaline solutions, proves at once the absence of so considerable a
number of acids.
The compounds of silver with sulphur, chlorine, iodine, bromine,
cyanogen, ferro- and ferricyanogen, and of the oxide of silver with phos-
phoric acid, arsenious acid, arsenic acid, boracic acid, chromic acid,
silicic acid, oxalic acid, tartaric acid, and citric acid, are insoluble in
water. The whole of these compounds are soluble in dilute nitric acid,
with the exception of the chloride, iodide, bromide, cyanide, ferro-
cyanide, ferricyanide, and sulphide of silver. If, therefore, we add
to our solution, which, for the reason just now stated, must be perfectly
neutral,
2. Nitrate of Silver,
and precipitation ensues, this shows at once the presence of one or
several of the acids enumerated ; chromic .acid, arsenic acid, and several
TO 180201.] EXPLANATION OF THE ANALYTICAL COTJUSE. 271
others, which form colored salts with silver, may be individually re-
cognised ^with tolerable certainty by the mere color of the precipitate.
By treating the precipitate now with nitric acid, we see whether it con-
tains any of the haloid compounds of silver, as these latter remain un-
dissolved, whilst all the oxide salts dissolve. Nitrate of silver fails to
effect the complete separation of those acids which form with oxide of
silver compounds insoluble in water, from the same cause which renders
the separation of acids by chloride of barium uncertain, viz. the ammo-
niacal salt formed prevents the reprecipitation of several of the salts of
silver by ammonia, from the acid solution. Nitrate of silver, besides
effecting the separation of chlorine, iodine, bromine, cyanogen, &c., and
indicating the presence of chromic acid, &c., serves, like the chloride of
barium, to demonstrate at once the absence of a great many acids, where
it produces no precipitate in neutral solutions.
The deportment which the solution under examination exhibits with
chloride of barium and with nitrate of silver, indicates therefore at once
the further course of the investigation. Thus, for instance, where
chloride of barium has produced a precipitate, whilst nitrate of silver has
failed to do so, it is not necessary to test for phosphoric acid, chromic
acid, boracic acid, silicic acid, arsenious acid, arsenic acid, oxalic acid,
tartaric acid, and citric acid, provided always the solution did not
already contain salts of ammonia. The same is the case if we obtain a
precipitate by nitrate of silver, but none by chloride of barium.
Returning now to the supposition which we have assumed here, viz.,
that the whole of the acids are present in the solution under examina-
tion, the reactions with chloride of barium and nitrate of silver would
accordingly have demonstrated already the presence of SULPHUKIC ACID,
and led to the application of the special tests for CHLORINE, BROMINE,
IODINE, CYANOGEN, FERROCYANOGEN, FERRICYANOGEN, and SULPHUR;*
and there would be reason to test for all the other acids precipitable by
these two reagents. The detection of these acids is based upon the
results of a series of special experiments, which have already been fully
described and explained in the course of the present work : the same
remark applies to the rest of the inorganic acids, viz., nitric acid and
chloric acid.
Of the organic acids, oxalic acid, paratartaric acid, and tartaric acid,
are precipitated by chloride of calcium in the cold, in presence of
chloride of ammonium ; the two former immediately, the latter often
only after some time ; but the precipitation of citrate of lime is pre-
vented by the presence of salts of ammonia, and ensues only upon ebulli-
tion or upon mixing the solution with alcohol ; the latter agent serves
also to effect the separation of malate of lime from aqueous solutions.
If, therefore, we add to our fluid,
3. Chloride of Calcium and Chloride of Ammonium,
OXALIC ACID, PARATARTARIC ACID, and TARTARIC ACID are precipitated,
but the lime-salts of several inorganic acids, which have not yet been
separated, phosphate of lime for instance, precipitate along with them.
We must therefore select for the individual detection of the precipitated
organic acids such reactions only as preclude the possibility of con-
* For the separation and special detection of these substances, I refer to 157.
272 SPECIAL REMARKS AND ADDITIONS. [To 187.
founding the organic acids with the inorganic acids that have been
thrown down along with them. For the detection of oxalic acid we
select accordingly solution of sulphate of lime, with acetic acid ( 146) ;
to effect the detection of the tartaric and paratartaric acids, we treat the
precipitate produced by chloride of calcium with solution of soda, since
the lime-salts of these two acids only are soluble in this menstruum in
the cold, but insoluble upon ebullition.
Of the organic acids we have now still in solution citric acid and malic
acid, succinic acid and benzoic acid, acetic acid and formic acid. CITRIC
ACID and MALIC ACID precipitate upon addition of alcohol to the fluid
filtered from the oxalate, tartrate, &c., of lime, and which still contains
an excess of chloride of calcium. Sulphate and borate of lime invariably
precipitate along with the malate and citrate of lime, if sulphuric acid
and boracic acid happen to be present ; the analyst must therefore care-
fully guard against confounding the lime precipitates of these acids with
those of citric acid and malic acid. The alcohol is now removed by
evaporation, and,
4. Sesquichloride of Iron
added. This reagent precipitates SUCCINIC ACID and BENZOIC ACID, in
combination with sesquioxide of iron, whilst FORMIC ACID and ACETIC
ACID remain in solution. The methods which serve to effect the sepa-
ration of the several groups from each other, and the individual detec-
tion of the various acids, have been fully described and explained in the
former part of this work.
B. SPECIAL REMARKS AND ADDITIONS TO THE SYSTEMATIC COURSE
OF ANALYSIS.
To 187.
At the commencement of 187, the analyst is directed to mix neutral
or acid aqueous solutions with hydrochloric acid. This should be done
drop by drop. If no precipitate forms, a few drops are sufficient, since
the only object in that case is to acidify the fluid in order to prevent the
subsequent precipitation of the metals of the iron group, by hydrosul-
phuric acid. In the case of the formation of a precipitate, some chemists
recommend that a fresh portion of the solution should be acidified with
nitric acid. However, even leaving the fact out of consideration that
nitric acid also produces precipitates in many cases in a solution of
potassio-tartrate of antimony, for instance I prefer the use of hydro-
chloric acid, i.e. the complete precipitation by that acid of all that is
precipitable by it, for the following reasons : 1. Metals are more rea-
dily precipitated by hydrosulphuric acid from solutions acidified with
hydrochloric acid, than from those acidified with nitric acid ; 2. In
cases where the solution contains silver, suboxide of mercury, or lead,
the further analysis is materially facilitated by the total or partial pre-
cipitation of these three metals in the form of chlorides ; and 3. This
latter form is the best adapted for the individual detection of these three
metals when present in the same solution. Besides, the application of
hydrochloric acid saves the necessity of examining whether the mercury,
which may be subsequently detected with the other metals of the fifth
To 188.] SPECIAL REMARKS AND ADDITIONS. j>73
group, was originally present in the form of oxide or in that of suboxide
1 hat the lead, if present in large proportion, is obtained partly in the
form of a chloride, and partly in the precipitate produced by hydro-
sulphuric acid in the acid solution, can hardly be thought an objection
to the application of this method, as the removal of the larger portion of
the lead from the solution, effected at the commencement, will only serve
to facilitate the examination for other metals of the fifth and sixth
groups.
As already remarked, a basic salt of teroxide of antimony may separate
from potassio-tartrate of antimony, for instance, or from some other
analogous compound, and precipitate along with the insoluble chloride
of silver and subchloride of mercury, and the sparingly soluble chloride
of lead. This precipitate, however, is readily soluble in the excess of
hydrochloric acid which is subsequently added, and exercises therefore
no influence whatever upon the further process. The application of heat
to the fluid mixed with hydrochloric acid is neither necessary nor even
advisable, since it might cause the conversion of a little of the preci-
pitated subchloride of mercury into chloride.
Should bismuth or chloride of antimony be present, the addition of
the washings of the precipitate produced by hydrochloric acid to the
first filtrate will cause turbidity, if the amount of free hydrochloric
acid present is not sufficient to prevent the separation of the basic
salt. This turbidity exercises, however, no influence upon the
further process, since hydrosulphuric acid as readily converts these
finely-divided precipitates into sulphides, as if the metals were in actual
solution.
In the case of alkaline solutions, the addition of hydrochloric acid
must be continued until the fluid shows a strongly acid reaction. The
substance which causes the alkaline reaction of the fluid combines with
the hydrochloric acid, and the bodies originally dissolved in that acid
separate. Thus, if the alkali was present in the free state, oxide of zinc,
for instance, or alumina, &c., may precipitate. But these oxides re-
dissolve in an excess of hydrochloric acid, whereas chloride of silver
would not redissolve, and chloride of lead only with difficulty. If a
metallic sulphur salt was the cause of the alkaline reaction, the sulphur
acid, e. g., tersulphide of antimony, precipitates upon the addition of the
hydrochloric acid, whilst the sulphur base, e. </., sulphide of sodium, trans-
poses with the constituents of the hydrochloric acid, forming chloride of
sodium and hydrosulphuric acid. If an alkaline carbonate, a cyanide,
or the sulphide of an alkali metal was the cause of the alkaline reaction,
carbonic acid, hydrocyanic ticid, or hydrosulphuric acid escapes. All
these phenomena should be carefully observed by the analyst, since they
not only indicate the presence of certain substances, but demonstrate
also the absence of entire groups of bodies.
To 188.
A judicious distribution and economy of time is especially to be studied
in the practice of analysis ; many of the operations may be carried on
simultaneously, which the student will readily perceive and arrange for
himself.
In cases where the analyst has simply to deal with metallic oxides
of the sixth group e. g., teroxide of antimony and of the fourth or fifth
274 SPECIAL HEM ARKS AND ADDITIONS. [To 191, 202.
group e. g., iron or bismuth he need not precipitate the acidified solu-
tion with hydrosulphuric acid, but may, after neutralization, at once add
sulphide of ammonium in excess. The sulphide of iron, &c., will in that
case precipitate, whilst the antimony, &c., will remain in solution, from
which they will, by addition of an acid, at once be thrown down as ter-
sulphide of antimony, &c. This method has the advantage that the fluid
is diluted less than is the case where solution of hydrosulphuric acid is
employed, and that the operation is performed more expeditiously and
con veniently than is the case where hydrosulphuric acid gas is conducted
into the fluid. Finally, I must once more remind the student that the
perfect purity of the reagents, and their application in correct quantity,
rank amongst the most indispensable conditions of successful analysis.
This applies more particularly to hydrosulphuric acid, especially when
used in the gaseous form. In such cases, students often lose sight
of the circumstance that hydrosulphuric acid gas fails to precipitate
highly acid solutions unless they be previously diluted with water.
To 191.
Besides the methods described in the systematic course to distinguish
between cadmium, copper, lead, and bismuth, the following process will
also be found to give highly satisfactory results. Add carbonate of soda
to the nitric acid solution as long as a precipitate continues to form, then
solution of cyanide of potassium in excess, and heat gently. This effects
the complete separation of lead and bismuth in the form of carbonates,
whilst copper and cadmium are obtained in solution in the form of
cyanide of copper and potassium, and cyanide of cadmium and potassium.
Lead and bismuth may now be readily separated from one another by
means of sulphuric acid. The separation of the copper from the cadmium
is effected by adding to the solution of the cyanides of these two metals
in cyanide of potassium, hydrosulphuric acid in excess, gently heating,
and then adding some more cyanide of potassium, in order to redissolve
the sulphide of copper which may have precipitated along with the
sulphide of cadmium. A residuary yellow precipitate (sulphide of
cadmium), insoluble in the cyanide of potassium, demonstrates the
presence of cadmium. Filter the fluid from this precipitate, and add
hydrochloric acid to the filtrate, when the formation of a black preci-
pitate (sulphide of copper) will demonstrate the presence of copper.
To 202.
The analysis of cyanogen compounds is not very easy in certain cases,
and it is sometimes a difficult task even to ascertain whether we
have really a cyanide before us or not. However, if the reactions of
the substance under examination upon ignition ( 174, A, I. 2, e [8])
be carefully observed, and also whether upon boiling with hydro-
chloric acid any odor of hydrocyanic acid is emitted ( 178, 2 [34])>
the presence or absence of a cyanide will generally not long remain a
matter of doubfc.
It must above all be borne in mind that the insoluble cyanogen com-
pounds occurring in pharmacy, &c., belong to two distinct classes. Viz.,
they are either SIMPLE CYANIDES, or COMPOUNDS OF METALS WITH FERRO-
CYANOGEN or some other analogous compound radical.
To 202.] SPECIAL REMARKS AND ADDITIONS. 275
All the simple cyanides are decomposed by boiling with concentrated
hydrochloric acid, into metallic chlorides and hydrocyanic acid Their
analysis is therefore never difficult. But the ferrocyariides, &c., to which
indeed the method described 202 more exclusively refers, suffer by
acids such complicated decompositions that their analysis by means of
acids is a task not so easily accomplished. Their decomposition by
potassa (or soda) is far more simple. The alkali yields its oxygen to the
metal combined with the ferrocyanogen, &c., the oxide thus formed pre-
cipitates, and the reduced potassium or sodium forms with the liberated
radical soluble ferrocyanide, &c., of potassium (or sodium, as the case may
be). But several oxides are soluble in an excess of potassa, as, e. #., oxide of
lead, oxide of zinc, &c. If, therefore, the double ferrocyanide of zinc
-and potassium, for instance, is boiled with solution of caustic potassa, it
dissolves completely in that menstruum, and we may assume that the
solution contains ferrocyanide of potassium, and oxide of zinc dissolved
in potassa. Were we to add an acid to this solution, we should of course
simply re-obtain the original precipitate of the double ferrocyanide of
zinc and potassium, and the experiment would consequently be of no
avail. To prevent this failure, conduct hydrosulphuric acid into
the solution in potassa. This serves to convert into sulphides all
the heavy metals which the potassa holds in solution as oxides. Those
sulphides which are insoluble in potassa, such as sulphide of lead, sul-
phide of zinc, &c., precipitate, whilst those which are soluble in alkaline
sulphides, such as bisulphide of tin, tersulphide of antimony, <fcc., remain
in solution, and separate only upon the addition of an acid.
The fluid filtered from the precipitated oxides and sulphides accord-
ingly always contains the cyanogen as ferrocyanide, &c., of potassium
provided, of course, the analyzed compound is really a double ferro-
cyanide, &c. From most of these compounds ferrocyanide, ferri-
cyanide, chromicyanide, and manganocyanide of potassium the cyanogen
partly separates as hydrocyanic acid, upon boiling the solutions with
sulphuric acid, and may thus be readily detected by this means, should
the direct way of detecting the radicals not succeed. But the cobalti-
cyanide of potassium is not decomposed by sulphuric acid, and the analyst
is accordingly directed to effect the detection of the compound radical in
that salt by means of solution of nickel, manganese, zinc, &c. By fusion
with nitrate of potassa, all these double compounds suffer decomposition,
cobalticyanide of potassium not excepted. The reason why the fusion
of these double compounds with nitrate of potassa should be preceded
by evaporation with an excess of nitric acid, is simply to prevent the
occurrence of explosions. Caution is always highly advisable in this
operation.
If you simply wish to examine for certain bases in simple or com-
pound cyanides, and for that purpose to destroy the cyanogen compound,
mix the body under examination with 3 parts of sulphate and 1
part of nitrate of ammonia, and heat in a porcelain crucible under a
chimney, to carry off the fumes. Complete decomposition ensues even
at a moderate heat, the whole of the cyanide volatizing in form of
cyanide of ammonium and products of the decomposition of the latter,
whilst the metals are left behind as sulphates (Bolley).
T 2
APPENDIX.
I.
DEPORTMENT OF THE MOST IMPORTANT MEDICINAL ALKALOIDS WITH
REAGENTS, AND SYSTEMATIC METHOD OF EFFECTING THE DETECTION
OF THESE SUBSTANCES.
227.
THE detection and separation of the vegeto-alkalies, or alkaloids, is a
task of far greater difficulty than that of most of the inorganic bases.
Although this difficulty is in some measure owing to the circumstance
that scarcely one of the compounds which the alkaloids form with other
substances is absolutely insoluble or particularly characterized by its
color or any striking property, yet the principal cause of it must be
ascribed to the want of accurate and minute investigations of the salts
and other compounds of the alkaloids, and of the products of their
decomposition. We consequently generally see and apprehend the
reactions only in their external manifestation, but without being able to
connect them with the causes producing them, which makes it impos-
sible to understand all the conditions which may exercise a modifyicg
influence.
Although therefore, in the present imperfect state of our knowledge
of these bodies, an attempt to define their deportment with reagents, and
base thereon a method of effecting their separation, or, at least, their
individual detection in presence of each other, must of necessity fall
very short of perfection, yet, having made a great many experiments on
the nature and behavior of these substances, I will attempt here, for
the benefit of young chemists, and more particularly pharmaceutists, to
describe in some measure the reactions which the most important of the
alkaloids manifest with other bodies, and to lay down a systematic method
of effecting their individual detection.
The classification of the alkaloids into groups, which I have adopted,
is based upon their deportment with certain general reagents. I have
verified by numerous experiments the whole of the reactions described
in the succeeding paragraphs.
I. VOLATILE ALKALOIDS.
The volatile alkaloids are fluid at the common temperature, and may
be volatilized in the pure state as well as when mixed with water.
They are accordingly obtained in the distillate when their salts are dis-
tilled with strong fixed bases and water. Their vapors, when brought in
contact with those of volatile acids, form a white cloud.
223.]
APPENDIX. 277
1. NICOTIA, or NICOTINE (C 10 H y N).
228.
1. Nicotia, in its pure state, forms a colorless, oily liquid, of 1-048
sp. gr. ; the action of air imparts a yellowish or brownish tint to it.
It boils at 482 F., suffering, however, partial decomposition in the
process ; but, when heated in a stream of hydrogen gas, it distils over
unaltered, between 212 and 392 F. It is miscible in all proportions
with water, alcohol, and ether.
Nicotia has a peculiar, disagreeable, somewhat ethereal, tobacco-like
odor, an acrid, pungent taste, and very poisonous properties. Dropped
on paper, it makes a transparent stain, which slowly disappears ; it
turns turmeric paper brown, and reddened litmus paper blue. Con-
centrated aqueous solution of nicotia shows these reactions more dis-
tinctly than the alkaloid in the pure state.
2. Nicotia has the character of a pretty strong base ; it precipitates
metallic oxides from their solutions, and forms salts with acids. The
salts of nicotia are freely soluble in water and alcohol, insoluble in ether ;
they are inodorous, but taste strongly of tobacco ; part of them are
cry stall izable. Their solutions, when distilled with solution of potassa, give
a distillate containing nicotia. By neutralizing this with oxalic acid,
and evaporating, oxalate of nicotia is produced, which may be freed
from any admixture of oxalate of ammonia, by means of spirit of wine,
in which the former salt is soluble, the latter insoluble.
3. If an aqueous solution of nicotia, or a solution of a salt of nicotia
mixed with solution of soda or potassa, is shaken with etJier, the nicotia
is dissolved by the ether ; if the latter is then allowed to evaporate on a
watch-glass, the nicotia remains behind in drops and streaks ; on warming
the watch-glass, it volatilizes in white fumes of strong odor.
4. Bichloride of platinum produces in aqueous solutions of nicotia
whitish-yellow, flocculent precipitates. On heating the fluid containing
the precipitate, the latter dissolves, but upon continued application of
heat it very speedily separates again in form of an orange-yellow, crys-
talline, heavy powder, which, under the microscope, appears to be com-
posed of roundish crystalline grains. If a rather dilute solution of
nicotia, supersaturated with hydrochloric acid, is mixed with bichloride
of platinum, the fluid at first remains clear ; after some time, however,
the double salts separate in small crystals (oblique, four-sided prisms),
clearly discernible with the naked eye.
5. Ter chloride of gold produces a reddish-yellow, flocculent precipitate,
sparingly soluble in hydrochloric acid.
6. Solution of iodine in iodide of potassium and water, when added in
small quantity to an aqueous solution of nicotia, produces a yellow
precipitate, which after a time disappears. Upon further addition
of iodine solution, a copious, kermes-colored precipitate separates ; but
this also disappears again after a time.
7. Solution of tannic acid produces a copious, white precipitate,
which redissolves upon addition of hydrochloric acid ; but if a large
quantity of hydrochloric acid is then added to the solution, an abundant
precipitate again makes its appearance.
8. If an aqueous solution of nicotia is added to a solution of chloride
278 APPENDIX. [ 229.
of mercury in excess, an abundant, flocculent, white precipitate is formed.
If solution of chloride of ammonium is now added to the mixture in
sufficient quantity, the entire precipitate, or the greater part of it, redis-
solves. But the fluid very soon turns turbid, and deposits a heavy, white
precipitate.
2. CONIA, or CONINE (C 16 H 16 N).
229.
1. Conia forms a colorless, oily liquid, of 0-89 sp. gr. ; the action of
the air imparts to it a brown tint. In the pure state it boils at about
392 F. ; when heated in a stream of hydrogen gas, it distils over
unaltered ; but when distilled in vessels containing air, it turns brown
and suffers partial decomposition ; with aqueous vapors it distils over
freely. It dissolves sparingly in water, 100 parts of water of the com-
mon temperature dissolving 1 part of conia. The solution turns turbid
on warming. Conia is miscible in all proportions with alcohol and ether.
The aqueous and alcoholic solutions manifest strong alkaline reaction.
Conia has a very strong, pungent, repulsive odor, which affects the head,
a most acrid and disagreeable taste, and very poisonous properties.
2. Conia is a powerful base ; it accordingly precipitates metallic oxides
from their solutions, in a similar way to ammonia, and forms salts with
acids. The salts of conia are soluble in water and in spirit of wine, but
nearly insoluble in ether. The solutions of the salts turn brownish upon
evaporation with partial decomposition of the conia. The dry salts of
conia do not smell of the alkaloid ; when moistened, they smell only
feebly of it ; but upon addition of solution of soda, they at once emit a
strong conia odor. When salts of conia are distilled with solution of
soda, the distillate contains conia. On neutralizing this with oxalic
acid, evaporating to dryness, and treating the residue with spirit of wine,
the oxalate of conia formed is dissolved, whilst any oxalate of ammonia
that may be present is left undissolved. As conia is only sparingly
soluble in water, and dissolves with still greater difficulty in solutions
of alkalies, a concentrated solution of a salt of conia turns milky, upon
addition of solution of soda. The minute drops which separate unite
gradually, and collect on the surface.
3. If an aqueous solution of a salt of conia is shaken with solution of
soda and ether, the conia is dissolved by the ether. If the latter is then
allowed to evaporate in a watch-glass, the conia is left behind in yel-
lowish-colored, oily drops.
4. Concentrated nitric acid imparts a fine blood-red tint to conia;
sulphuric acid, a purple-red color, which subsequently turns to olive-
yellow.
5. Terchloride of gold produces a yellowish- white precipitate, insoluble
in hydrochloric acid ; chloride of mercury, a copious white precipitate,
soluble in hydrochloric acid. Bichloride of platinum does not precipitate
aqueous solutions of salts of conia, the conia compound corresponding
to ainmonio-bichloride of platinum being insoluble in spirit of wine and
ether, but soluble in water.
6. With solution of iodine in iodide of potassium and water, and
with solution of tannic acid, conia comports itself the same as nicotia.
7. Chlorine water produces in a mixture of water and conia a strong,
white turbidity.
230.] APPENDIX. 279
The volatile alkaloids are easily recognised when pure; the great
object of the analyst must accordingly always be to obtain them
in that state. The way of effecting this is the same for nicotia as
for conia, and has already been given in the foregoing paragraphs,
viz., to distil with addition of solution of soda, neutralize withoxalic
acid, evaporate, dissolve in alcohol, evaporate the solution, treat the
residue with water, add solution of soda, shake the mixture with ether,
and let the latter evaporate spontaneously. Conia is distinguished from
nicotia chiefly by its odor, its sparing solubility in water, and its com-
portment with chlorine.
II. NON-VOLATILE ALKALOIDS.
The non- volatile alkaloids are solid, and cannot be distilled over with
water.
FIRST GROUP.
NON-VOLATILE ALKALOIDS WHICH ARE PRECIPITATED BY POTASSA OB
SODA FROM THE SOLUTIONS OF THEIR SALTS, AND REDISSOLVE READILY
IN AN EXCESS OF THE PRECIPITANT.
Of the alkaloids of which I purpose to treat here, one only belongs to
this group, viz.,
+
MORPHIA, or MORPHINE (C 34 H 19 N 6 = Mo).
230.
+
1. Crystallized morphia (Mo + 2 aq.) usually appears in the form of
colorless, brilliant, four- sided prisms, or, when obtained by precipitation,
as a white crystalline powder. It has a bitter taste, and dissolves very
sparingly in cold, but somewhat more readily in boiling water. Of cold
alcohol it requires about 90 parts by weight for solution ; of boiling
alcohol from 20 to 30 parts. The solutions of morphia in alcohol as
well as in hot water manifest distinctly alkaline reaction. This alkaloid is
nearly insoluble in ether. At a moderate heat the crystallized morphia
loses the two equivalents of water.
2. Morphia neutralizes acids completely, and forms with them the
SALTS OF MORPHIA. These salts are readily soluble in water, and in
spirit of wine, but insoluble in ether ; their taste is disagreeably bitter.
Most of them are crystallizable.
3. Potassa and ammonia precipitate from the solutions of salts of
+
morphia generally only after some time Mo + 2 aq., in the form of a
white crystalline powder. Stirring and friction on the sides of the vessel
promote the separation of the precipitate, which redissolves with great
readiness in an excess of potassa, but more difficultly in ammonia. It
dissolves also in chloride of ammonium and, though with difficulty only,
in carbonate of ammonia.
4. Carbonate of potassa and carbonate of soda produce the same pre-
cipitate as potassa and ammonia, but fail to redissolve it upon addition
in excess. Consequently if a fixed alkaline bicarbonate is added to a
solution of morphia in caustic potassa, or if carbonic acid is conducted
280 APPENDIX. [ 231.
into the soution, Mo + 2 aq. separates, especially after previous ebul-
lition in the form of a crystalline powder. A more minute inspection,
particularly through a inagnifying-glass, shows this powder to consist of
small acicular crystals; seen through a glass which magnifies 100 times,
these crystals present the form of four-sided prisms.
5. Bicarbonate of soda and bicarbonate of potassa speedily produce in
solutions of neutral salts of morphia a precipitate of hydrated morphia,
in the form of a crystalline powder. The precipitate is insoluble in an
excess of the precipitants. These reagents fail to precipitate acidified
solutions of salts of morphia in the cold.
6. The actiou of strong nitric acid upon morphia or one of its salts,
in the solid state or in concentrated solutions, produces a fluid varying
from red to yellowish-red. Dilute solutions do not change their color
upon addition of nitric acid in the cold, but upon heating they acquire a
yellow tint.
7. Neutral sesquichloride of iron imparts to neutral solutions of salts
of morphia a beautiful dark blue color, which disappears upon the addi-
tion of an acid. If the solution contains an admixture of animal or
vegetable extractive matters, or of acetates, the color will appear clouded
and less distinct.
8. If iodic acid is added to a solution of morphia or of a salt of mor-
phia, IODINE separates. In concentrated aqueous solutions the separated
iodine appears as a kerrnes-brown precipitate, whilst to alcoholic and
dilute aqueous solutions it imparts a brown or yellowish-brown color.
The addition of starch-paste to the fluid, no matter whether made before
or after that of the iodic acid, considerably heightens the delicacy of the
reaction, since the blue tint of the iodide of starch remains still percep-
tible in exceedingly dilute solutions, which is not the case with the brown
color imparted by iodine. As other nitrogenous bodies (albumen, caseine,
fibrine, &c.) likewise reduce iodic acid, this reaction has only a relative
value.
SECOND GROUP.
NON-VOLATILE ALKALOIDS WHICH ARE PRECIPITATED BY POTASSA FROM
THE SOLUTIONS OF THEIR SALTS, BUT DO NOT REDISSOLVE TO A PER-
CEPTIBLE EXTENT IN AN EXCESS OF THE PRECIPITANT, AND ARE PRE-
CIPITATED BY BICARBONATE OF SODA EVEN FROM ACID SOLUTIONS,
if the latter are not diluted in a larger proportion than 1 : 100;
Narcotina, Quina. Cinchonia.
+
a. NARCOTINA, or NARCOTINE (C 46 H 25 N O 14 = Na).
231.
+
1. Crystallized narcotina (Na + aq.) appears usually in the form of
colorless, brilliant, straight rhombic prisms, or, when precipitated by
alkalies, as a white, loose, crystalline powder. It is insoluble in water.
Alcohol and ether dissolve it sparingly in the cold, but somewhat more
readily upon heating. Solid narcotina is tasteless, but the alcoholic and
ethereal solutions are intensely bitter. Narcotina does not alter vege-
table colors. At 338 F. it fuses, with loss of 1 eq. of water.
2. Narcotina dissolves readily in acids, combining with them to salts.
23 2.] APPENDIX. 281
These salts have invariably an acid reaction. Those with weak acids are
decomposed by a large amount of water, and, if the acid is volatile, even
upon simple evaporation. Most of the salts of narcotina are amorphous,
and soluble in water, alcohol, and ether ; they have a bitter taste.
3. Pure alkalies, and alkaline carbonates and bicarbonates, immediately
+
precipitate from the solutions of salts of narcotine (Na + aq.) in the
form of a white powder, which, seen through a lens magnifying 100
times, appears an aggregate of small crystalline needles. The precipi-
tate is insoluble in an excess of the precipitarits. If a solution of
narcotina is mixed with ammonia, and ether added in sufficient quan-
tity, the narcotina which has separated upon the addition of the am-
monia, redissolves in the ether, and the clear fluid presents two distinct
layers. If a drop of the ethereal solution is evaporated in a watch-
glass, the residue is seen, upon inspection through a lens magnifying
100 times, to consist of small, distinct, elongated, and lance-shaped
crystals.
4. Concentrated nitric acid dissolves narcotina to a colorless fluid,
which acquires a pure yellow tint upon application of heat.
5. Concentrated sulphuric acid dissolves narcotina to a yellow fluid,
which turns brown upon application of heat. A solution of narcotina
in concentrated sulphuric acid containing a slight admixture of nitric
acid, appears of an intense blood-red color, which disappears altogether
upon the addition of a somewhat larger amount of nitric acid.
6. If the solution of a salt of narcotina is mixed with chlorine water,
it acquires a yellow color, slightly inclining to green ; if ammonia is
then added, a much more intensely colored, yellowish-red fluid is
obtained.
7. If narcotina or one of its salts is dissolved in an excess of dilute
sulphuric acid, some finely levigated binoxide of manganese added, the
mixture heated to boiling, and kept in ebullition for the space of several
minutes, the narcotina absorbs oxygen and is converted into opianic
acid, cotarnine (a base soluble in water), and carbonic acid. Ammonia
will now of course fail to precipitate narcotiua from the filtrate.
b. QUINA, or QUININE (C 40 H 24 N 2 4 = Q).
232.
4-
1. Crystallized quina (Q + 2aq.) appears either in the form of fine
crystalline needles of silky lustre, which are frequently aggregated into
tufts, or as a loose white powder. It is sparingly soluble in cold, but
somewhat more readily in hot water. It is readily soluble in spirit of
wine, both cold and hot, but less so in ether. The taste of quina is in-
tensely bitter ; the solutions of quina manifest alkaline reaction. Upon
exposure to heat it loses the 2 eq. of water.
2. Quina neutralizes acids completely. The salts taste intensely
bitter ; most of them are crystallizable, and for the greater part readily
soluble in water and in spirit of wine. Acid solutions reflect a bluish
tint.
3. Potassa, ammonia, and the neutral carbonates of the alkalies, pro-
duce in solutions of salts of quina (if they are not too dilute) a white,
2S2 APPENDIX. [ 233.
loose, pulverulent precipitate of hydrated quina, which immediately
after precipitation appears opaque and amorphous under the micro-
scope, but assumes, after the lapse of some time, the appearance of an
aggregate of crystalline needles. The precipitate redissolves only to a
scarcely perceptible extent in an excess of potassa, but more readily in
ammonia. It is hardly more soluble in fixed alkaline carbonates than
in pure water. If a solution of quina is mixed with ammonia, ether
added, and the mixture shaken, the quina which has separated upon the
addition of the ammonia, redissolves in the ether, and the clear fluid
presents two distinct layers. In this point quina differs essentially from
cinchonia; by means of this reaction the former may therefore be readily
detected in presence of the latter, and separated from it.
4. Bicarbonate of soda also produces both in neutral and acid solu-
tions of salts of quina a white precipitate. In acidified solutions con-
taining 1 part of quina to 100 parts of acid and water, the precipitate
forms immediately; if the proportion of the quina to the acid and
water is as 1 : 150, the precipitate separates only after an hour or two,
in the form of distinct needles, aggregated into groups. If the propor-
tion is as 1 : 200, the fluid remains clear, and it is only after from twelve
to twenty-four hours' standing that a slight precipitate makes its appear-
ance. The precipitate is not altogether insoluble in the precipitant, and
the separation is accordingly the more complete, the less the excess of
the precipitant ; the precipitate contains carbonic acid.
5. Concentrated nitric acid dissolves quina to a colorless fluid, turning
yellowish upon application of heat.
6. The addition of cldorine water to the solution of a salt of quina
fails to impart a color to the fluid, or, at least, imparts to it only a very
faint tint ; but if ammonia is now added the fluid acquires an intensely
emerald-green color. If, after the addition of the chlorine water some
solution of ferrocyanide of potassium is added, and after this a few drops
of ammonia or some other alkali, the fluid acquires a magnificent deep
red tint, which, however, speedily changes to a dirty brown. This
reaction is delicate and characteristic. Upon addition of an acid* to
the red fluid, the color vanishes, but reappears afterwards upon cautious
addition of ammonia. (0. Livonius' Letters ; A. Vogel.)
7. Concentrated sulphuric acid likewise dissolves pure quina and pure
salts of quina to a colorless fluid, which does not acquire any coloration
upon being heated to the point of incipient evaporation of the sulphuric
acid, but turns afterwards yellow, and finally brown. Sulphuric acid
containing an admixture of nitric acid dissolves quina to a colorless or
very faint yellowish fluid.
+
c. CINCHONIA, or CINCHONINE (C 40 H 24 N" 2 2 = Ci).
233.
1. Cinchonia appears either in the form of transparent, brilliant, four-
sided prisms, or fine white crystalline needles, or, when precipitated
from concentrated solutions, as a loose white powder. At first it appears
tasteless, but after some time the bitter taste of the bark becomes per-
ceptible. It is nearly insoluble in cold water, and dissolves only with
* Acetic acid answers the purpose best.
2 34.] APPENDIX. 283
exceeding difficulty in hot water ; it dissolves sparingly in cold dilute
spirit of wine, more readily in hot spirit of wine, arid the most freely
in absolute alcohol. From hot alcoholic solutions the greater portion of
the dissolved cinchonia separates upon cooling in a crystalline form.
Solutions of cinchonia taste bitter, and manifest alkaline reaction. Cin-
chonia is insoluble in ether.*
2. Cinchonia neutralizes acids completely. The salts have the bitter
taste of the bark ; most of them are crystallizable ; they are generally
more readily soluble in water and in spirit of wine than the correspond-
ing quina compounds. Ether fails to dissolve them.
3. Cinchonia, when heated cautiously, fuses at first without loss of
water ; subsequently white fumes arise which, like benzoic acid, con-
dense upon cold substances, in the form of small brilliant needles, or as
a loose sublimate, a peculiar aromatic odor being exhaled at the same
time. If the operation is conducted in a stream of hydrogen gas, long,
brilliant prisms are obtained (Hlasiwetz).
4. Potassa, ammonia, and the neutral carbonates of the alkalies produce
in solutions of salts of cinchonia a white, loose precipitate of CINCHONIA,
which does not redissolve in an excess of the precipitants. If the solu-
tion was concentrated, the precipitate does not exhibit a distinctly
crystalline appearance, even though viewed through a lens magnifying
200 times ; but if the solution was so dilute that the precipitate formed
only after some time, it appears under the microscope to consist of dis-
tinct crystalline needles aggregated into star-shaped tufts.
5. Bicarbonate of soda and bicarbonate of potassa precipitate cin-
chonia in the same form as in 4, both from neutral and acid solutions,
but not so completely as the simple carbonates of the alkalies. In solu-
tions containing 1 part of cinchonia to 200 parts of water and acid, the
precipitate still forms immediately ; its quantity increases after standing
some time.
6. Concentrated sulphuric acid dissolves cinchonia to a colorless fluid,
which upon application of heat first acquires a brown, and finally a
black color. Addition of some nitric acid leaves the solution colorless
in the cold, but upon application of heat the fluid, after passing through
the intermediate tints of yellowish-brown and brown, turns finally
black.
7. The addition of chlorine water to the solution of a salt of cinchonia
fails to impart a color to the fluid ; if ammonia is now added, a yel-
lowish-white precipitate is formed.
Recapitulation and Remarks.
234.
The alkaloids of the second group are altered or precipitated by
various other reagents besides those mentioned above; the reactions
are, however, not adapted to effect their individual detection and sepa-
ration. Thus, for instance, bichloride of platinum produces in solutions
of the salts of the three alkaloids belonging to this group, a yellowish-
* The cinchonia of commerce usually contains in admixture another alkaloid, called
cinchotina, which is soluble in ether. This alkaloid crystallizes in large rhomboidal crys-
tals of brilliant lustre, which fuse at a high temperature, and cannot be sublimed, even
in a stream of hydrogen gas (Hlasiwetz).
2S4 APPENDIX. [ 235.
wLite precipitate, chloride of mercury a white precipitate, tincture of
galls a yellowish-white, flocculent precipitate, &c.
Narcotina and quina being soluble in ether, whilst cinchonia is inso-
luble in that menstruum, the former may be most readily separated by
this means from the latter alkaloid. For this purpose the analyst need
simply mix the solution of the three alkaloids with ammonia in excess,
then add ether, and separate the solution of quina and narcotine from
the undissolved cinchonia. If the ethereal solution is now evaporated,
the residue dissolved in hydrochloric acid and a sufficient amount of
water to make the dilution as 1 : 200, and bicarbonate of soda is then
added, the narcotina precipitates, whilst the quina remains in solution.
By evaporating the solution, and treating the residue with water, the
quina is obtained in the free state.
THIRD GROUP.
NON-VOLATILE ALKALOIDS WHICH ARE PRECIPITATED BY POTASSA FROM
THE SOLUTIONS OF THEIR SALTS, AND DO NOT REDISSOLVE TO A PER-
CEPTIBLE EXTENT IN AN EXCESS OF THE PRECIPITANT ; BUT ARE NOT
PRECIPITATED FROM (even somewhat concentrated) ACID SOLUTIONS BY
THE BICARBONATES OF THE FIXED ALKALIES : Strychnia, Brucia,
Veratria.
+
a. STRYCHNIA, or STRYCHNINE (C tt H 24 N 2 4 = Sr).
235.
1. Strychnia appears either in the form of white, brilliant rhombic
prisms, or, when produced by precipitation or rapid evaporation, as a
white powder. It has an exceedingly bitter taste. It is nearly inso-
luble in cold, and barely soluble in hot water. It is insoluble in abso-
lute alcohol and ether, and difficultly soluble in dilute spirit of wine.
It does not fuse when heated. It is exceedingly poisonous.
2. Strychnia neutralizes acids completely. The salts of strychnia are,
for the most part, crystallizable ; they are soluble in water. All the
salts of strychnia have an intolerably bitter taste and are exceedingly
poisonous.
3. Potassa and carbonate of soda produce in solutions of salts of
strychnia white precipitates of strychnia, which are insoluble in an excess
of the precipitants. Viewed through a lens magnifying one hundred
times the precipitate appears as an aggregate of small crystalline needles.
From dilute solutions the strychnia separates only after the lapse of some
time, in the form of crystalline needles, which are distinctly visible even
with the naked eye.
4. Ammonia produces the same precipitate as potassa. The preci-
pitate redissolves in an excess of ammonia, but after a short time or if
the solution is highly dilute, after a more considerable lapse of time the
strychnia crystallizes from the ammoniacal solution in the form of needles,
which are distinctly visible with the naked eye.
5. Bicarbonate of soda produces in neutral solution of salts of strychnia
a precipitate of strychnia, which separates in fine needles shortly after
the addition of the reagent, and is insoluble in an excess of the preci-
pitant. But upon adding one drop of acid (so as to leave the fluid still
alkaline) the precipitate dissolves readily in the liberated carbonic acid.
236.] APPENDIX. 285
The addition of bicarbonate of soda to an acid solution of strychnia causes
no precipitation, and it is only after the lapse of twenty-four hours, or
even a longer period, that strychnia crystallizes from the fluid in distinct
prisms, in proportion as the free carbonic acid escapes. If a concen-
trated solution of strychnia, supersaturated with bicarbonate of soda, is
boiled for some time, a precipitate forms immediately ; from dilute
solutions this precipitate separates only after concentration.
6. tSidphocyanide of potassium produces in concentrated solution of
salts of strychnia immediately, and in dilute solutions after the lapse of
some time, a white crystalline precipitate, which appears under the
microscope as an aggregate of flat needles, truncated or pointed at an
acute angle, and is but little soluble in an excess of the precipitant.
7. On putting a drop of concentrated sulphuric acid in a watch-glass,
and adding to it some strychnia or a little of a salt of strychnia, solution
ensues without any particular reaction ; but if a drop of solution of
chromate of potassa is now added to the fluid, the latter instantly
acquires a deep blue color, which speedily changes to red (Otto). If the
strychnia is rubbed together with binoxide of lead and concentrated
sulphuric acid containing 1 per cent, of nitric acid, the mass acquires
first a blue, then a violet color, which changes to red, and, finally, to
greenish-yellow (_/. Marchand). The former reaction (Otto's) loses in
distinctness, or even altogether fails to manifest itself, if the substance
contains admixtures of some other organic compounds, e.g., quina, sugar
(Brieger). But by the second method (Marchand's) strychnia may be
clearly detected even when mixed with much sugar. Ferricyanide of
potassium also will produce the same reaction ( W. Davy) ; with this
oxidizing agent the change from violet to red and yellow takes place
more slowly.
8. Chloride of mercury produces in solutions of salts of strychnia a
white precipitate, which changes after some time to crystalline needles
aggregated into stars, and distinctly visible through a lens. Upon
heating the fluid these crystals redissolve, and upon subsequent cooling
of the solution the double compound recrystallizes in distinct needles.
9. Strong chlorine water produces in solution of salts of strychnia a
white precipitate, which dissolves in ammonia to a colorless fluid.
10. Concentrated nitric acid dissolves strychnia and its salts to a color-
less fluid, which becomes yellow upon the application of heat.
b. BRUCIA, or BRUCINE (C 46 H 26 N 2 8 = Br).
+ 236 -
1. Crystallized brucia (Br + 7 aq.) appears either in the form of trans-
parent, straight rhombic prisms, or in that of crystalline needles aggre-
aated into stars, or as a white powder composed of minute crystalline
scales. Brucia is difficultly soluble in cold, but somewhat more readily
in hot water. Both absolute and dilute alcohol dissolve it freely, but it
is insoluble in ether. Its taste is intensely bitter. When heated, it
fuses with loss of its water of crystallization.
2 Brucia neutralizes acids completely. The salts of brucia are readily
soluble in water, and of an intensely bitter taste. Most of them are
C13 3. Vofowsa'and carbonate of soda throw down from solutions of salts
286 APPENDIX. [ 237.
of brucia a white precipitate of brucia, which, is insoluble in an excess of
the precipitant. Viewed under the microscope, immediately after pre-
cipitation, it appears to consist of very minute grains ; but, upon further
inspection, these grains are seen with absorption of water to suddenly
form into needles, which latter subsequently arrange themselves into
concentric groups. These successive changes of the precipitate may be
traced distinctly even with the naked eye.
4. Ammonia produces a whitish precipitate in solutions of salts of
brucia, which appears at first like a number of minute drops of oil, but
changes subsequently witli absorption of water to small needles. The
precipitate redissolves, immediately after separation, very readily in an
excess of the precipitant, but after a very short time or, in dilute
solutions, after a more considerable lapse of time the brucia, combined
with crystallization water, crystallizes from the ammoniacal fluid in
small concentrically grouped needles, which addition of ammonia fails to
redissolve.
5. Bicarbonate of soda produces in neutral solutions of salts of brucia
a precipitate of brucia, combined with crystallization water ; this pre-
cipitate separates after the lapse of a short time, in form of concentrically
aggregated needles of silky lustre, which are insoluble in an excess of
the precipitant, but dissolve in free carbonic acid (compare strychnia).
Bicarbonate of soda fails to precipitate acid solutions of salts of brucia ;
and it is only after the lapse of a considerable time that the alkaloid
separates from the fluid in regular and comparatively large crystals, in
proportion as the carbonic acid escapes.
6. Concentrated nitric acid dissolves brncia and its salts to intensely
red fluids, which subsequently acquire a yellowish-red tint, and turn com-
pletely yellow upon application of heat. Upon addition of protochloride of
tin or sulphide of ammonium to the fluid heated to this point, no matter
whether concentrated or after dilution with water, the faint yellow color
changes to a most intense violet.
7. Addition of chlorine water to the solution of a salt of brucia imparts
to the fluid a fine bright red tint ; if ammonia is then added, the red
color changes to yellowish-brown.
8. Concentrated sulplmric acid dissolves brucia to a faint rose-colored
fluid.
9. Sulphocyanide of potassium produces in concentrated solutions of
salts of brucia immediately, and in dilute solutions after some time, a
granular crystalline precipitate, which, when viewed under the micro-
scope, appears composed of variously aggregated polyhedral crystalline
grains. Friction applied to the sides of the vessel promotes the separa-
tion of the precipitate.
10. Chloride of mercury also produces a white granular precipitate,
which, when viewed under the microscope, appears composed of small
round crystalline grains.
c. VERATRIA, or VERATRINE (C 34 H 22 K O 6 ) Ve.
237.
1. Yeratria appears generally as a pure white, yellowish or greenish-
white powder, of acrid and burning, but not bitter taste ; it is ex-
ceedingly poisonous. Yeratria acts with great energy upon the mem-
238.] APPENDIX. 287
branes of the nose ; even the most minute quantity of the powder
excites the most violent sneezing. It is insoluble in water; in alcohol
it dissolves readily, but more sparingly in ether. At a gentle heat it
fuses like wax, and solidifies upon cooling to a transparent yellow
mass.
2. Yeratria neutralizes acids completely. Some salts of veratria are
crystalhzable, others dry up to a gummy mass. They are soluble in
water, and of acrid and burning taste.
Z.^Potassia, ammonia, and the simple carbonates of the alkalies pro-
duce in solutions of salts of veratria a flocculent, white precipitate, which,
viewed under the microscope, immediately after precipitation, does not
appear crystalline. After the lapse of a few minutes, however, it alters
its appearance, and small scattered clusters of short prismatic crystals are
observed, instead of the original coagulated flakes. The precipitate does
not redissolve in an excess of potassa, and of carbonate of potassa. It is
slightly soluble in ammonia, in the cold, but the dissolved portion
separates again upon application of heat.
4. With bicarbonate of soda and bicarbonate of potassa the salts of
veratria comport themselves like those of strychnia and brucia. How-
ever, upon boiling, the veratria separates readily, even from dilute
solutions.
5. If veratria is acted upon with concentrated nitric acid, it agglu-
tinates into small resinous lumps, which afterwards dissolve slowly in the
acid. The solution presents a faint reddish-yellow color.
6. If veratria is treated with concentrated sulphuric acid, it also
agglutinates at first into small resinous lumps ; but these dissolve with
great readiness to a pale yellow fluid, the color of which gradually
increases in depth and intensity, and changes afterwards to a reddish-
yellow, then to an intense blood-red, subsequently to crimson, and finally
to violet.
7. Sulphocyanide of potassium produces only in concentrated solutions
of salts of veratria flocculent-gelatiuous precipitates.
8. Addition of chlorine-water to the solution of a salt of veratria
imparts to the fluid a yellowish tint, which, upon addition of ammonia,
changes to a faint brownish color. In concentrated solutions chlorine
produces a white precipitate.
Recapitulations and Remarks.
238.
The alkaloids of the third group also are precipitated by many other
reagents besides those above-mentioned, as, for instance, by tincture of
galls, bichloride of platinum, &c. But as these reactions are common to
all, they are of little importance in an analytical point of view.
Strychnia may be separated from brucia and veratria by means of
absolute alcohol, since it is insoluble in that menstruum, whilst the two
latter alkaloids readily dissolve in it. The identity of strychnia is best
established by the reaction with sulphuric acid and chromate of potassa,
or with binoxide of lead or ferricyanide of potassium ; also by the form
of its crystals when thrown down by alkalies viewed under the micro-
scope ; and lastly, by the form of the precipitate which sulphocyanide of
potassium and chloride of mercury produce in solutions of its salts.
288 APPENDIX. [ 239241.
Brucia and veratria are not readily separated from one another, but may
be detected in presence of each other. The identity of brncia is best
established by the reactions with nitric acid and protochloride of tin or
sulphide of ammonium, or by the form of the precipitate which ammonia
produces in solutions of salts of brucia. Yeratria is sufficiently dis-
tinguished from brucia and the other alkaloids which we have treated of,
by its characteristic deportment at a gentle heat, and also by the form
of the precipitate which alkalies produce in solutions of its salts. To
distinguish veratria in presence of brucia, the reaction with concentrated
sulphuric acid is employed.
To these alkaloids I will add salicine, although this substance does not
properly belong to the same class of chemical compounds.
239.
SALICINE (C 26 H 18 O u ).
1. Salicine appears either in the form of white crystalline needles and
scales of silky lustre, or, when the crystals are very small, as a powder
of silky lustre. It has a bitter taste, is readily soluble in water and in
alcohol, but insoluble in ether.
2. No reagent precipitates salicine as such.
3. If salicine is treated with concentrated sulphuric acid, it aggluti-
nates into a resinous lump, and acquires an intensely blood-red color,
without dissolving in the acid ; the color of the sulphuric acid is at first
unaltered.
4. If an aqueous solution of salicine is mixed with hydrochloric acid
or dilute sulphuric acid, and the mixture boiled for a short time, the
fluid suddenly becomes turbid, and deposits a finely granular crj^stalline
precipitate (saliretine).
SYSTEMATIC COURSE FOR THE DETECTION OF THE ALKALOIDS TREATED
OF IN THE PRECEDING PARAGRAPHS, AND OF SALICINE.
240.
The analytical course which I am now about to describe is based upon
the supposition that the analyst has to examine a concentrated aqueous
solution effected by the agency of an acid of one or several of the non-
volatile alkaloids, which solution is free from any admixture of substances
that might tend to obscure or modify the reactions. For the modifica-
tions which the presence of coloring or extractive matters, &c., requires,
I refer to 243.
I. DETECTION OF THE ALKALOIDS, AND OF SALICINE, IN SOLUTIONS
SUPPOSED TO CONTAIN ONLY ONE OF THESE SUBSTANCES.
241.
1. Add dilute solution of potassa or soda drop by drop to a portion of
the aqueous solution, until the fluid acquires a scarcely perceptible alka-
line reaction ; stir, and let the- fluid stand for some time.
a. No PRECIPITATE is FORMED ; this proves the total absence of the
alkaloids, and indicates the presence of SALICINE. To set all doubt at
~- APPENDIX. 289
rest, test the original substance with concentrated sulphuric acid and
also with hydrochloric acid. Compare 239.
b. A PRECIPITATE is FORMED. Add solution of potassa or soda, drop
by drop, until the fluid manifests a strongly alkaline reaction.
a. The precipitate redissolves : MORPHIA. To arrive at a positive
conclusion on this point, test another portion of the solution with
iodic acid (230, 8), and a portion of the original substance with
nitric acid ( 230, 6).
/3. The precipitate remains undissolved : Presence of an alkaloid
of the second or third group. Pass on to 2.
2. Add to a second portion of the original solution two or three drops
of dilute sulphuric acid, and then a saturated solution of bicarbonate of
soda until the acid reaction is just neutralized ; vigorously rub the inside
of the vessel, and allow the mixture to stand for half an hour.
a. No PRECIPITATE is FORMED : Absence of narcotina and cinchonia.
Pass on to 3.
b. A PRECIPITATE is FORMED : Narcotina, cinchonia, and perhaps also
quina, as the precipitation of the latter substance by bicarbonate of soda
depends entirely upon the degree of dilution of the fluid. Add to a
portion of the original solution ammonia in excess, then a suflicient
quantity of ether, and shake the mixture.
a. The precipitate which forms at first upon the addition of the
ammonia redissolves in the ether, and the clear fluid presents two
distinct layers : narcotina or quina. To distinguish between the
two, test a fresh portion of the original solution with chlorine water
and ammonia. If the solution turns green, QUINA, if yellowish-red,
NARCOTINA is present.
/3. The precipitate which forms upon the addition of ammonia does
not redissolve in the ether : CINCHONIA. The deportment of cinchonia
at a high temperature may serve as a conclusive test ( 233, 3).
3. Put a portion of the original substance, or of the residue remaining
upon the evaporation of the solution, in a watch-glass, and treat with
concentrated sulphuric acid.
a. A rose-colored solution is obtained, which becomes intensely red
upon addition of nitric acid : BRUCIA. The reaction with nitric acid and
protochloride of tin is resorted to as a conclusive test ( 236, 6).
b. A yellow solution is obtained, the color of which gradually changes
to yellowish-red, then to blood-red, and turns finally crimson : VERATRIA.
c. A colorless fluid is obtained, which remains colorless after standing
for some time.
Add to the fluid a drop of chromate of potassa ; if this imparts to it a
deep blue color, STRYCHNIA is present ; if it leaves the fluid unaltered,
QUINA is present. The reaction with chlorine water and ammonia is
resorted to as a conclusive test.
II. DETECTION OF THE ALKALOIDS, AND OF SALICINE, IN SOLUTIONS
SUPPOSED TO CONTAIN SEVERAL OR ALL OF THESE SUBSTANCES.
242.
1. Add to a portion of the aqueous solution dilute solution of potassa
or soda, drop by drop, until the fluid acquires a scarcely perceptible alka-
line reaction ; stir, and let the fluid stand for some time.
a. No PRECIPITATE is FORMED j this proves the total absence of the
I. u
200 APPENDIX. [ 242.
alkaloids, and indicates the presence of SALICINE. To remove all doubt
on. the point, test the original substance with concentrated sulphuric acid,
and with hydrochloric acid. Compare 241, 1, a.
b. A PRECIPITATE is FORMED i add solution of potassa or soda, drop by
drop, until the fluid manifests a strongly alkaline reaction.
a. The precipitate redissolves. Absence of the alkaloids of the
second and third group. Presence of MORPHIA is indicated. The
reactions with iodic acid ( 230, 8), and with nitric acid ( 230, 6),
are resorted to as conclusive tests. Examination for salicine, see 4.
/3. The precipitate does not redissolve, or at least not completely.
Filter, and treat the precipitate as directed in 2. Saturate the
nitrate with carbonic acid, or mix it with bicarbonate of soda or
bicarbonate of potassa, and boil nearly to dryness. Treat the residue
with water ; if it dissolves completely, this is a sign that no morphia
is present ; but if there is an insoluble residue left, this indicates
the presence of morphia. The reactions with iodic acid ( 230, 8),
and with nitric acid ( 230, 6), are resorted to as conclusive tests.
2. Wash the filtered precipitate of 1, b, j3 t with cold water, dissolve in
a slight excess of dilute sulphuric acid, and add solution of bicarbonate
of soda to the fluid until the acid reaction is neutralized ; stir the mix-
ture, vigorously rubbing the sides of the vessel, and allow the fluid to
stand for an hour.
a. No PRECIPITATE is FORMED. Absence of narcotina and cinchonia.
Boil the solution nearly to dryness, and treat the residue with cold water.
If it dissolves completely, pass on to 4 ; but if an insoluble residue is
left, examine this for quina of which a minute quantity might be
present and for strychnia, brucia, and veratria, according to the direc-
tions of 3.
b. A PRECIPITATE is FORMED. This may contain narcotina, cinchonia,
and also quina, compare 241, 2, b. Filter, and treat the filtrate as
directed 242, 2, a. Wash the precipitate with cold water, dissolve in
a little hydrochloric acid, add ammonia in excess, and then a sufficient
quantity of ether.
a. The precipitate which forms at first upon the addition of the
ammonia redissolves completely in the ether, mid the clear fluid pre-
sents two distinct layers. Absence of cinchonia ; presence of quiiia
or narcotina. Evaporate the ethereal solution, dissolve the residue
in a little hydrochloric acid and a sufficient amount of water to
make the dilution at least as 1 : 200 ; add bicarbonate of soda to
neutralization, and allow the fluid to stand for some time. The
formation of a precipitate indicates the presence of NARCOTIXA.
Filter, and test the precipitate with chlorine water and ammonia
( 231, 6). Evaporate the filtrate, or the fluid if no precipitate has
been formed, to dryness, and treat the residue with water. If part
of it remains undissolved, wash this, dissolve in hydrochloric acid,
and add chlorine water and ammonia. Green color : QUINA.
/3. The precipitate produced by the ammonia does not redissolve in
tlie etJier, or at least not completely : CINCHONIA. Quina or narcotiua
may also be present. Filter, and examine the filtrate for quina and
narcotina as in a. The precipitate consists of cinchonia, and may
be further examined according to 233, 3.
3. Wash the insoluble residue of 242, 2, a, with water, dry on the
water- bath, and digest with absolute alcohol.
243.] APPENDIX. 291
a. IT DISSOLVES COMPLETELY : absence of strychnia ; presence of (quina)
brucia or veratria. Evaporate the alcoholic solution on the water-bath
to dryness, and, if quina has already been detected, divide the residue
into two portions, and test one part for BRTJCIA, with nitric acid and
protochloride of tin ( 236, 6), and the other for VERATRIA, by means of
concentrated sulphuric acid ( 237, 6) ; but if no quina has as yet been
detected, divide the residue into three portions, a, b, and c ; examine a
and b for BRUCIA and VERATRIA, in the manner just stated, and c for quina,
with chlorine-water and ammonia. However, if brucia is present, dis-
solve c in hydrochloric acid, add ammonia and ether, let the mixture
stand for some time, evaporate the ethereal solution, and examine the
residue for quina.
b. It does not dissolve, or at least not completely : presence of STRYCHNIA ;
perhaps also of (quina) brucia and veratria. Filter, and examine the
filtrate for (QUINA) BRUCIA and VERATRIA as directed 242, 3, a. The
identity of the precipitate with strychnia is demonstrated by the reaction
with sulphuric acid and chromate of potassa ( 235, 7).
4. Mix a portion of the original solution with hydrochloric acid, and
boil the mixture for some time. The formation of a precipitate indicates
the presence of SALICINE. To set all doubt on this point at rest, test the
original substance with concentrated sulphuric acid ( 239, 3).
DETECTION OP THE ALKALOIDS, IN PRESENCE OF COLORING AND
EXTRACTIVE VEGETABLE OR ANIMAL MATTERS.
243.
The presence of mucilaginous, extractive, and coloring matters renders
the detection of the alkaloids a task of considerable difficulty. These
matters obscure the reactions so much that we are even unable to deter-
mine by a preliminary experiment, whether the substance under exami-
nation contains one of the alkaloids we have treated of in the foregoing
paragraphs, or not. I will now give several methods by means of which
the separation of the alkaloids from such extraneous matters may be
effected, and their detection be made practicable. Which of^these
methods to select will, of course, always depend upon the particular
circumstances of the case.
1. STAS'S METHOD FOR EFFECTING THE DETECTION CF POISONOUS
ALKALOIDS.*
a If you have to look for the suspected organic bases in the contents
of the stomach or intestines, or in articles of food, or in pulpy matters
in general, heat the suspected substance with double its weight of strong
alcohol, acidified with from 0'5 grm. to 2 grm. of tartaric acid or
oxalic acid, to from 158 F. to 167 F. When quite cold, filter, and wash
the undissolved part with strong alcohol, adding the washings t<
lt lf 'you have to deal with the heart, liver, lungs, or similar organs cut
them into fine shreds, moisten with the acidified alcohol, Fes, and
repeat the same operation, until the soluble parts are completely ex-
tracted ; collect the fluids obtained, and filter.
* -Bulletin do 1'Academie de Medecine de ^ f '
Pharm " XXIV 313 " Jahresbericht" von Licbig und Kopp, 1851, P- o*u.
u 2
292 APPENDIX. [ 243.
b. Concentrate the alcoholic fluid at a temperature not exceeding 95
"P., and, if no insoluble matter separates, continue to evaporate nearly to
dryness. Conduct this process, either under a bell-glass over sulphuric
acid, with or without rarefaction of the air, or in a tubular retort, through
which a current of air is passed. If fatty or other insoluble matters
separate in the process of concentration, pass the concentrated fluid
through a moistened filter, and evaporate the filtrate nearly to dryness,
conducting the process, as above, either under a bell-glass or in a retort.
c. Digest the residue with cold absolute alcohol, filter, wash the in-
soluble residue thoroughly with alcohol, and let the alcoholic solution
evaporate in the air or in vacuo ; dissolve the acid residue in a little
water, and add bicarbonate of soda as long as effervescence ensues.
d. Add to the mixture four or five times its volume of ether, and
shake ; then allow it to stand at rest ; let a little of the supernatant
ether evaporate spontaneously in a watch-glass. If this leaves oily
streaks upon the glass, which gradually collect into a drop, and emit,
upon the application of a gentle heat, a disagreeable, pungent, and stifling
odor, there is reason to infer the presence of a liquid volatile base ; whilst
a solid residue or a turbid fluid, with solid particles suspended in it, in-
dicates a non-volatile, solid base. In the latter case, the base may
emit a disagreeable animal smell, but not a pungent odor, as with
volatile bases. The blue color of reddened litmus paper is permanently
restored. If no residue is left, add to the fluid some solution of soda or
potassa, and shake with repeatedly renewed ether, which will now dis-
solve the base. It follows from the assumption that the bases present
will pass into the ethereal solution, that Stass method is principally
calculated for the detection of the poisonous alkaloids which are soluble
in ether, though some of them only difficultly. The following are the
vegeto-alkalies which Stas enumerates as discoverable by his method :
Conia, Nicotina, Aniline, Picoline, Petinine, Morphia, Codeia, Brucia,
Strychnia, Yeratria, Colchicia, Delphia, Emetine, Solania, Aconita,
Atropia, and Hyoscyamia.
a. There is reason to infer the presence of a, volatile base.
Add to the contents of the vessel from which you have taken the small
portion of ether for evaporation in the watch-glass, one or two cubic
centimetres of strong solution of potassa or soda, shake the mixture, let
it stand at rest, pour the supernatant fluid into a flask, and treat the
residue again three or four times with ether, until the last portion
poured off leaves no longer a residue upon evaporation. Mix the ethe-
real fluid with some dilute sulphuric acid until the well-shaken fluid
manifests acid reaction; allow the mixture to stand at rest, decant
the supernatant ether from the acid aqueous fluid, and treat the latter
once more with ether in the same way.
aa. Mix the residual acid solution (which may contain sulphates
of ammonia, nicotina, aniline, picoline, and petinine, indeed which
must contain these bases, if they are present in the examined sub-
stances, since their compounds with sulphuric acid are quite inso-
luble in ether ; and in which, if conia is present, the greater part
of the latter alkaloid is also found) with concentrated solution of
soda or potassa in excess, and treat with ether, which will again
dissolve the liberated bases ; decant the ether, and leave it to spon-
taneous evaporation, at the lowest possible temperature ; place the
dish with the residue in vacuo over sulphuric acid. In this process
^43.] APPENDIX. 293
the ether and ammonia escape, leaving the volatile organic base
behind in the pure state. The nature of the organic base is then
finally ascertained.
bb. The ether decanted from the acid solution contains the animal
matters which it has removed from the alkaline fluid. It leaves
therefore, upon spontaneous evaporation, a trifling, faint yellow re-
sidue of nauseous odor, which contains also some sulphate of conia,
if that base was present in the examined matter.
/3. There is reason to infer the presence of a solid base.
Add a few drops of alcohol to the ethereal solution obtained by treat-
ing with ether the previously acid residues mixed either simply with
bicarbonate of soda, or first with that reagent and then with solution of
soda or potassa (see c and d), and leave the mixture to spontaneous
evaporation. If this fails to give the base in a distinctly crystalline
form and sufficiently pure, add a few drops of water feebly acidified with
sulphuric acid, which will usually serve to separate the mass into a fatty
portion, adhering to the dish, and an acid aqueous solution, which con-
tains the base as a bisulphate. Decant or filter, wash with a little
slightly acidified water, and evaporate the solution to a considerable
extent, under a bell-glass over sulphuric acid. Mix the residue with a
highly concentrated solution of pure carbonate of potassa, treat the mix-
ture with absolute alcohol, decant, and let the alcoholic fluid evaporate,
which will generally leave the base behind in a state of perfect purity or
nearly so.
This method, which gives very satisfactory results with alkaloids
soluble in ether, and especially with volatile alkaloids, may lead to mis-
takes in the case of those alkaloids which are insoluble or only sparingly
soluble in ether, as, e. g., morphia, the solution of which in caustic
alkalies, when shaken with ether, will hardly yield any of the alkaloid
to the latter fluid. Never neglect, therefore, to mix the alkaline fluid
obtained in d after repeated extraction with ether, and subsequent
addition of some more solution of soda, to dissolve the morphia, which
may have separated, and after evaporation of the ether still present
with a concentrated solution of chloride of ammonium, and let the
mixture stand in the open air. If morphia is present, it will separate in
the form of crystals.*
2. MERCK'S METHOD OF EFFECTING THE DETECTION OF ALL
NON-VOLATILE ALKALOIDS.
Mix the substance under examination with concentrated acetic acid
to strongly acid reaction, and let the mixture digest for several hours.
Then strain the fluid from the solid part, squeeze the latter, and wash it
with water acidified with acetic acid ; evaporate the whole of the fluid
obtained to dryness on the water-bath. Boil the residue first with pure
spirit of wine, then with spirit of wine containing some acetic acid ;
evaporate the solutions thus obtained nearly to dryness on the water-
bath, dilute with water, add carbonate of soda to feebjy alkaline reac-
tion, evaporate to the consistence of syrup, and allow it to stand at rest
for 24 hours ; then dilute again with water, and filter the fluid from the
precipitate formed ; wash the latter with water, digest with concentrated
* Otto " Instructions how to detect Poisons." The facts stated are fully borne out
by the results of experiments made in my own laboratory.
2S.4 APPENDIX. [ 24-3.
acetic acid, dilute with, water, and decolorize with pure blood charcoal.
Examine the decolorized fluid in the usual way for the alkaloids. As
the charcoal may retain alkaloids, do not omit examining it by the
method given below, in 3.
3. METHOD OF EFFECTING THE DETECTION OF STRYCHNIA IN BEER,
BY Graham AND A. W. Hofmann*
This method, which is based on the known fact that a solution of a
salt of strychnia, when mixed and shaken with animal charcoal, yields
its strychnia to the charcoal, will undoubtedly be found applicable also
for the detection of other alkaloids. The process is conducted as fol-
lows :
Shake 2 ounces of animal charcoal, with half-a-gallon of the aqueous
neutral or feebly acid fluid under examination ; let the mixture
stand for from 12 to 24 hours, with occasional shaking, filter, wash
the charcoal twice with water, and then boil for half-an-hour with
8 ounces of spirit of wine of 80 90 per cent., avoiding loss of alcohol
by evaporation. Filter the spirit of wine hot from the charcoal, and
distil the filtrate ; add a few drops of solution of potassa to the residual
watery fluid, shake with ether, let the mixture stand at rest, and then
decant the supernatant ether. The ethereal fluid leaves, upon sponta-
neous evaporation, the strychnia in a sufficient state of purity to admit
of its further examination by reagents (see 235).
II.
GENERAL PLAN OF THE ORDER AND SUCCESSION IN WHICH
SUBSTANCES SHOULD BE ANALYZED FOR PRACTICE.
It is not a matter of indifference whether the student, in analyzing
for the sake of practice, follows no rule or order whatever in the selec-
tion of the substances which he intends to analyze, or whether, on the
contrary, his investigations and experiments proceed systematically.
Many ways, indeed, may lead to the desired end, but one of them
will invariably prove the shortest. I will, therefore, here point out a
course which experience has shown to lead safely and speedily to the
attainment of the object in view.
Let the student take 100 compounds, systematically arranged (see
below), and let him analyze these compounds successively in the order
in which they are placed. A careful and diligent examination of these
will be amply sufficient to impart to him the necessary degree of skill in
practical analysis. When analyzing for the sake of practice only, the
student must above all things possess the means of verifying the results
obtained by his experiments. The compounds to be examined ought,
therefore, to be mixed for him by a friend who knows their exact com-
position.
A. From 1 to 20.
AQUEOUS SOLUTIONS OF SIMPLE SALTS : e. g., sulphate of soda, nitrate of
lime, chloride of copper, &c. These investigations will . serve to teach
the student the method of analyzing substances soluble in water, which
contain but one base. In these investigations it is only intended to
* "Chem. Soc. Quart. Journ.," V. 173.
213.] .APPENDIX. 295
ascertain which base is present in the fluid under examination ; but
neither the detection of the acid, nor the proof of the absence of all other
bases besides the one detected, is required.
B. From 21 to 50.
SALTS, ETC., CONTAINING ONE BASE AND ONE ACID, OR ONE METAL AND
ONE METALLOID (in form of powder) : e.g., carbonate of baryta, borate of
soda, phosphate of lime, arsenites, chloride of sodium, bitartrate of
potassa, acetate of copper, sulphate of baryta, chloride of lead, &c. These
investigations will serve to teach the student how to make a preliminary
examination of a solid substance, by heating in a tube or before the blow-
pipe ; how to convert it into a proper form for analysis, i.e., how to dis-
solve or decompose it ; how to detect one metallic oxide, even in sub-
stances insoluble in water ; and how to demonstrate the presence of one
acid. The detection of both the base and the acid is required, but it is
not necessary to prove that no other bodies are present.
C. From 51 to 65.
AQUEOUS on ACID SOLUTIONS OF SEVERAL BASES. These investigations
will serve to teach the student the method of separating and distinguishing
several metallic oxides from each other. The proof is required that no
other bases are present besides those detected. No regard is paid to the
acids.
D. From 66 to 80.
DRY MIXTURES OF EVERY DESCRIPTION. A portion of the salts should.
be organic, another inorganic ; a portion of the compounds soluble in
water or hydrochloric acid, another insoluble ; e. g., mixtures of chloride
of sodium, *" carbonate of lime, and oxide of copper ; of phosphate of
magnesia and ammonia, and arsenious acid; oftartrate of lime, oxalate
of lime, and sulphate of baryta ; of phosphate of soda, nitrate of ammonia,
and acetate of potassa, &c.
These investigations will serve to teach the student how to treat mix-
tures of different substances with solvents ; how to detect several acids
in presence of each other ; how to detect the bases in presence of phos-
phates of the alkaline earths ; and they will serve as a general intro-
duction to scientific and practical analyses. All the component parts
must be detected, and the nature of the substance ascertained.
E. From 81 to 100.
NATIVE COMPOUNDS, ARTICLES OF COMMERCE, &c. Mineral and
other waters, minerals of every description, soils, potash, soda, alloys,
colors, &c.
III.
ARRANGEMENT OF THE RESULTS OF THE ANALYSES PERFORMED
FOR PRACTICE.
The manner in which the results of analytical investigations ought to
be arranged is not a matter of indifference. The following examples
will serve to illustrate the method which I have found the most suitable
in this respect.
296
APPENDIX.
PLAN OF ARRANGING THE EESULTS OF EXPERIMENTS, oSTos. 1 20.
Colorless fluid of qieutral reaction.
HC1
HS
NH 4 S
N H. 0, C O 2 and
no precipitate,
no precipitate,
no precipitate,
KH 4 C1
consequently no
noPbO
noEeO
a ivhite precipitate,
AgO
,,HgO
Mn O
consequently either
Hg 2
CuO
,,NiO
BaO,SrO,orCaO,
,,Bi0 3
,,CoO
no precipitate by
,,CdO
,,ZnO
solution of sul-
phate of lime,
,,As0 3
A1 O 3
consequently
As 5
Cr" 2 3
LIME.
Sb O
Confirmation by
,,SnO,
means of
,,SnO
,,AuO,
,,Pto 2
,,Fe 2 3
PLAN OF ARRANGING THE RESULTS OF EXPERIMENTS, Nos. 21 50.
White powder, fusing in the water of crystallization upon application of
heat, and then remaining unaltered soluble in water reaction neutral.
HC1
HS
NH 4 S
NH 4 0,CO.,,
PO 5 ,2NaO,HOand
no preci-
no preci-
no precipi-
andNH 4 ,Cl
NH 4
pitate.
pitate.
tate.
no precipi-
a white precipitate,
tate.
consequently
MAGNESIA.
The detected base being MgO, and the analyzed substance being
soluble in water, 01, I, Br, S0 3 , N0 6 , A, &c., are the only acids or
metalloids that can be present. The preliminary examination has proved
the absence of the organic acids and of nitric acid.
Pa Cl produces a white precipitate which H Cl fails to dissolve j con-
sequently SULPHURIC ACID.
APPENDIX.
297
^
s
e
yellow tin
rder upon c
nitric acid.
acquiring a perma
rustation with white
acid, readily soluble
H rl
O 2 O
.Bfiii
gj.siii
'2n.22
.
f< ~
.
| 111 111
^ 111.3 1-J ^
6 .-
W ^ ^ c3
S O
.S
,
rf i o
* ,1
P-M N
o
298 APPENDIX,
IY.
TABLE
OF THE
MORE FREQUENTLY OCCURRING FORMS AND
COMBINATIONS OF THE SUBSTANCES TREATED OF IN THE
PRESENT WORK,
ARRANGED
"WITH ESPECIAL REGARD TO THE CLASS TO WHICH THEY RESPECTIVELY BELONG
ACCORDING TO THEIR SOLUBILITY
WATER, IN HYDROCHLORIC ACID, IN NITRIC ACID,
OR IN NITROHYDROCHLORIC ACID.
PRELIMINARY REMARKS.
The class to which the several compounds respectively belong accord-
ing to their solubility in water or acids (see 177), is expressed by
figures. Thus 1 or I means a substance soluble in water ; 2 or II a
substance insoluble in water, but soluble in hydrochloric acid, nitric acid,
or nitrohydrochloric acid; 3 or III a substance insoluble in water, in
hydrochloric acid, and in nitric acid. For those substances which stand
as it were on the limits between the various classes, the figures of the
classes in question are jointly expressed : thus 1 2 signifies a substance
difficultly soluble in water, but soluble in hydrochloric acid or nitric
acid ; 1 3 a body difficulty soluble in water, and of which the solubility
is not increased by the addition of acids ; and 2 3 a substance insoluble
in water, and difficultly soluble in acids. Wherever the deportment of
a siibstance with hydrochloric acid differs materially from that which it
exhibits with nitric acid, this is stated in the notes.
The Roman figures denote officinal and more commonly occurring
compounds.
The haloid salts and sulphur compounds are placed in the columns of
the corresponding oxides. The salts given are, as a general rule, the
neutral salts ; the basic, acid, and double salts, if officinal, are mentioned
in the notes j the small figures placed near the corresponding neutral or
simple salts refer to these.
APPENDIX. 299
Cyanogen, chloric acid, citric acid, malic acid, benzoic acid, succinic
acid, and formic acid, are of more common occurrence in combination
with a few bases only, and have therefore been omitted from the table.
The most frequently occurring compounds of these substances are :
cyanide of potassium I, ferrocyanide of potassium I, ferricyanide of
potassium I, sesqui-ferrocyanide of iron (Prussian blue) III, ferrocyanide
of zinc and potassium II III, chlorate of potassa I, the citrates of the
alkalies I, the malates of the alkalies I, malate of sesquioxide of iron I, the
benzoates of the alkalies I, the succinates of the alkalies I, and the
formates of the alkalies I.
300
APPENDIX.
INDEX OF THE SOLUBILITY
KO
NaO
NH 4
BaO
SrO
CaO
MgO
Al,0,
MnO
FeO
Fe 8 3
CoO
NiO
Zi
I
I
I
I
1
I-II
II
II
2
2
II
II
II
I]
s
I
I
I
I
1
I-II
2
II
II
2
2,5
9
-18
2
Cl
I
I
I,
I
I
I
1
1
I
I
I,,
I
I
1
I
I
1
1
1
1
1
1
1
1
1
1
so s
I,
I
1,3
III
III
I-III
I
I,M3
I
I
I
1
I
I
N0 5
I
I
I
I
I
1
1
1
1
1
1
I
1
1
P0 5
1
I,o
1,0
2
2
11,4
2
2
2
II
2
2
2
CO,
I,
I,,
I
II
II
II
II
II
II
2
2
I]
C 8 3
Is
1
I
2
2
II
2
2
2
1-2
1-2
2
2
B0 3
1
2
2
2
2
2
2
2
2
2
2
2
_
T
1.
2
2
II
1-2
1
1-2
1-2
Is
1
2
As0 5
I
1
1
2
2
2
2
2
2
2
2
2
2
As0 3
I
1
1
2
2
2
2
2
2
CrO s
I
1
1
2
2
2
1
2
1
1
2
2
1
NOTES.
1. SULPHATE of potassa and alumina I.
2. Bicarbonate of potassa I.
3. Binoxalate of potassa I.
4. Tartarized borax (bitartrate of potassa and borate of soda) I.
5. Bitartrate of potassa I-II.
6. Tartrate of potassa and ammonia I.
7. Tartrate of potassa and soda I.
8. Tartrate of potassa and sesquioxide of iron I.
9. Tartrate of antimony and potassa I.
10. Phosphate of soda and ammonia I.
1 1. Bicarbonate of soda I.
1 2. Sesquichloride of iron and chloride of ammonium I.
1 3. Sulphate of alumina and ammonia I.
14. Basic phosphate of lime II.
15. Sulphide of cobalt is pretty readily decomposed by nitric acid, b
very difficultly by hydrochloric acid. This substance is n
officinal.
APPENDIX.
301
SUBSTANCES IN WATER OR ACIDS.
CdO
PbO
SnO
SnO g
BiO,
CuO
Hg 2
HgO
AgO
Pt0 2
Au0 3
SbO s
Cr a 3
2
H,8
2
2&3
2
II 22
II
II
2
2
35
II & III
2
II
2 20
2 20
2
9
^23
II
II
2 30
2 3l
H 36
1
1
I-III
I
1
I
IM
II-III
I*
III
*S2 -33
Is,
I 37
I&III
1
I-II
2
1
II
II
3
o s
I
II-III
1
1
I
1-2
1 M
I-II
'1
2
I&III
ro s
1
I
I,,
I
I*
I
I
1
I
o s
2
2
2
2
2
2
2
2
2
II
2
II
2
2
2
8 3
2
2
2
1
2
2
2
2
2
1-2
1
3
1-2
2
2
2
2
1
2
1
1,9
1
1
1
1,6
1-2
1
1
1
1
1-2
2
1-2
2
1
1-2
2
2
I
1
s0 5
2
2
2
2
2
2
2
2
s0 3
2
II
2
2
2
2
rO,
1
II-III
2
2
2
2
1-2
2
2
2
16. The same applies to sulphide of nickel.
17. Sulphide of zinc is readily soluble in nitric acid, somewhat more
difficultly soluble in hydrochloric acid.
18. Minium is converted by hydrochloric acid into chloride of lead ;
by nitric acid into oxide, which redissolves in an excess of the
acid, and into brown binoxide of lead, which is insoluble in
nitric acid.
19. Trisacetate of lead I.
20. Proto- and bisulphide of tin are decomposed and dissolved by
hydrochloric acid ; by nitric acid they are converted into
binoxide, which is insoluble in an excess of the acid. Sub-
limed bisulphide of tin dissolves only in nitrohydrochloric
acid.
21. Basic nitrate of teroxide of bismuth II.
22. Ammoniated oxide of copper 1.
23. Sulphide of copper is difficultly decomposed by hydrochloric acid,
but with facility by nitric acid.
24. Chloride of copper and ammonium I.
25. Sulphate of copper and ammonia I.
302 APPENDIX.
26. Basic acetate of copper, partially soluble in water, and completely
in acids.
27. Basic nitrate of suboxide of mercury and ammonia II.
28. Ammonio-chloride of mercury II.
29. Basic sulphate of oxide of mercury II.
30. Sulphide of silver soluble only in nitric acid.
31. Bisulphide of platinum is not affected by hydrochloric acid, and
but little by boiling nitric acid j it dissolves in hot nitrohydro-
chloric acid.
32. Bichloride of platinum and chloride of potassium 1 3.
33. Bichloride of platinum and chloride of ammonium 1 3.
34. Terchloride of gold and chloride of sodium I.
35. Teroxide of antimony is soluble in hydrochloric acid, but not in
nitric acid.
36. Tersulphide of antimony and sulphide of calcium I II.
37. Basic terchloride of antimony II.
38. Tartrate of ter oxide of antimony and potassa I.
APPENDIX.
303-
V.
TABLE OF WEIGHTS AND MEASURES.
GRAMMES.
1
2
3
4
5
6
7
8
9
CENTIGRAMMES.
1
2
3
4
5
6
7
8
CENTIMETRES.
1
2
3
4
5
6
7
8
GRAINS.
DECIGRAMMES.
] 5-4846
1
30-8692
2
46-3038
3
61-7384
4
77-1730
5
92-6076
6
108-0422
7
123-4768
8
138-9114
9
GRAINS.
MILLIGRAMMES.
1543
1
3086
2
4630
3
6173
4
7717
5
9260
6
1-0804
7
1-2347
8
1-3891 i
9
INCHES.
DECIMETRES.
39-37
1
78-74
2
118-11
3
157-48
4
196-85
5
236-22
5
275-59
7
314-96
8
354-33
9
INCHES.
MILLIMETRES.
3937
1
7874
2
1-1811
3
1-5748
4
1-9685
5
2-3622
6
2-7559
7
3-1496
8
3-5433
9
GRAINS.
1-5434
3-0869
4-6304
6-1738
7-7173
9-2607
10-8042
12-3476
13-8911.
GRAINS.
0154
0308
0463
0617
0771
0926
1080
1234
1389
INCHES.
3-937
7-874
11-811
15-748
19-685
23-622
27-559
31-496
35-433
INCHES.
03937
07874
11811
15748
196S5
23622
27559
31496
35433
One kilogramme
One cubic centimetre
One litre
15434 grains.
0-0610 cubic inch.
61-0271 cubic inches.
ALPHABETICAL INDEX.
A.
Acetic acid (as reagent) ... 26
deportment with reagents 164
detection of, in simple com-
pounds . . 192, 195
in complex com-
pounds 220
Acids as reagents ... 23
Actual examination . . . 183
Alcohol (as reagent) ... 23
Alkaloids, detection of . . 288
in food, &c. 291
Alkaline solutions, examination of 198
Alloys, examination of . . 178, 180
Alumina, deportment with reagents . 78
detection of, in soluble simple
compounds 187, 188, 193
in soluble complex
compounds 209, 210, 212
in insoluble complex
compounds . . .222
phosphate (see phosphate of
alumina).
Ammonia (as reagent) ... 37
deportment with reagents . 68
detection of, in simple com-
pounds .... 188
in complex com-
pounds . 216
in soils . .245
in fresh waters 234
in mineral waters 240
carbonate of (as reagent) . 45
molybdate of (as reagent . 47
oxalate (as reagent) . . 43
Antimony, detection of, in alloys . 183
properties of . .109
teroxide of, detection of, in
simple compounds . 185
in complex compounds 205
in sinter deposits . 241
in food, &c. . 256, 257
deportment with re-
agents . . . 109
Apocrenic acid, detection of, in soils . 24 6
in mineral waters 242
PAGE
Apparatus and utensils . . .16
Arsenic, properties of . . .112
acid, deportment with reagents 121
produced from arsenious acid . 118
the tersulphide 118
Arsenious acid, deportment with re-
agents 112
Arsenious and arsenic acids, detection of,
in simple compounds . 185
in complex compounds . 204
in mineral waters . 237
in food, &c. . . . 249
Arsenious from arsenic acid, to distin-
guish 125
Ashes of plants, animals, manures,
&c., examination of . . . 261
B.
Baryta, detection of, in soluble simple
compounds
in insoluble simple
compounds
in soluble complex
compounds
in insoluble com-
plex compounds
in mineral waters
in sinter deposits .
carbonate of (as reagent)
deportment of, with reagents .
hydrate of (as reagent)
nitrate of (as reagent)
water (as reagent) .
Bases (as reagents) .
188
197
214
222
238
240
51
71
60
51
38
34
19
Benzoic acid, detection of, in simple
compounds . 192
in complex com-
pounds . . 220
deportment with reagents 163
Bismuth, detection of, in alloys . . 179
in articles of
food, &c. 256, 257
properties of . 100
teroxide, deportment of, with
reagents . . . .100
306
ALPHABETICAL INDEX.
PAGE
Bismuth, teroxide, detection of, in simple
compounds 18 5, 186
in complex com-
pounds 206, 207
hydrated (as reagent) 40
Blowpipe 12
flame ... 14, 15
Boracic acid, deportment, with re-
agents . . .136
detection of, in simple
compounds . .191
in complex com-
pounds . 219
in silicates 229, 231
in mineral wa-
ters . .238
Borax (as reagent) .... 62
Bromine, deportment with reagents . 146
detection of . . 190, 217
Brucia, deportment with reagents . 285
detection of, in simple com-
pounds . 289
in complex com-
pounds . 291
C.
Cadmium, properties of . .101
oxide, detection of, in simple
compounds 184
in complex
compounds 206, 207
deportment with re-
agents . . .101
Carbon, detection of, in compound
bodies . 223
in silicates . 229
properties of . . .142
Carbonic acid, deportment with reagents 142
detection of, in simple
compounds 189
in complex
compounds 216, 221
in soils 244, 245
in well and
mineral waters 234, 235
Charcoal for blowpipe experiments . 1 5
Chloric acid, detection of . . 191,218
deportment with reagents 156
Chloride of ammonium (as reagent) . 47
of barium (as reagent) . . 50
of calcium (as reagent) . 52
of mercury (as reagent) . 55
of silver (as reagent) . . 64
Chlorine (as reagent) . . . .28
deportment with reagents . 145
detection of, in soluble simple
compounds 1 90, 195
in insoluble sim-
ple compounds 196
in soluble com-
plex com-
pounds . 217, 218
in insoluble com-
plex compounds
222, 224, 225
PAGE
Chloride, detection of, in soils . . 244
in fresh and mi-
neral waters . 233
in silicates 229, 230
Chrome iron-stone, analysis of . . 225
Chromic acid, deportment with reagents 128
detection of, in simple
compounds 389,194
in complex com-
pounds 216, 219, 221
in insoluble com-
pounds . . 225
Chromium, sesquioxide, deportment
with reagents . . .79
detection of, in soluble sim-
ple com-
pounds 186, 188
in complex com-
pounds 209, 212
Cinchonia, deportment with reagents . 282
detection of, in simple com-
pounds . 289
in complex com-
pounds . 290
Citric acid, deportment with reagents . 159
detectioa of, in simple com-
pounds 191, 195
in complex
compounds . 220
Cobalt, properties of . . . .86
protoxide, deportment with re-
agents . 86
detection of, in sim-
ple compounds . 186
in complex com-
pounds 210, 211
nitrate (as reagent) . . 63
Conia, deportment with reagents . 278
Copper (as reagent) . . . .40
properties of . . . .98
oxide, deportment with reagents 98
detection of, in simple com-
pounds . 185
in complex
compounds 206
in sinter de-
posits 241, 242
sulphate (as reagent) . . 55
Crenic acid, detection of, in soils . 246
in mineral waters 242
Crystallization 5
Cyanide of potassium (as reagent)
in the moist way 48
in the dry way . 61
Cyanides, insoluble in water, analysis of 226
Cyanogen, detection of, in simple com-
pounds . 190
in complex com-
pounds 217, 218
D.
Decantation
Deflagration .
Distillation
Distilling apparatus
12
10
ALPHABETICAL INDEX.
307
Edulcoration
Ether (as reagent)
Evaporation
F.
23
49
Ferricyanide of potassium (as reagent)
Ferricyanogen, detection of, in simple
compounds . 190
in complex com-
pounds
217, 226, 227
Ferrocyanide of potassium (as reagent) 49
Ferrocyanogen, detection of, in simple
compounds . 190
in complex
compounds
217, 226, 227
Filtering paper . . . . 7
stands ... 7
Filtration . . v . . 6
Flame, parts of ... 13
Fluoride of calcium (as reagent) . 60
Fluorine, detection of, in simple com
pounds 190, 194
in complex com-
pounds 218, 221
in insoluble com-
pounds 222, 225
in mineral waters 237
in sinter deposits 242
in silicates 229, 230
Fluxing 11
Formic acid, deportment with reagents 166
detection of, in simple com-
pounds . 192
in complex
compounds 220
Funnels . >..... . . 7, 19
Fusion ...... 11
G.
Gas-lamp . .... 17
Geic acid, detection of, in soils . .246
Georgina paper . . . .57
Gold, properties of . . . .104
detection of, in alloys . .183
terchloride of (as reagent) . . 56
teroxide, deportment with re-
agents . . .104
detection of, in simple
compounds 186
in complex
compounds 205
H.
Humic acid, detection of, in soils . 246
Hydriodic acid, deportment with re-
agents . .- t J - . . 148
Hydrobromic acid, deportment with re-
agents . .146
Hydrochloric acid (as reagent) . . 27
deportment with re-
agents . . 145
PAGE
Hydrocyanic acid, deportment with re-
agents . . 150
detection of, in simple
compounds 190
in complex com-
pounds 217, 218
in organic mat-
ters . . 257
Hydroferricyanic acid, deportment with
reagents 151
Hydroferrocyanic acid, deportment with
reagents 151
Hydrofluoric acid, deportment with re-
agents 138
Hydrofluosilicic acid (as reagent) . 29
deportment with
reagents . .132
Hydrosulphuric acid (as reagent) . 30
deportment with
reagents . 152
detection of, in sim-
ple compounds 189
in complex com-
pounds
216, 217, 221
in mineral waters 235
Hypochlorous acid, deportment with re-
agents . . . . .154
Hyposulphurous acid, deportment with
reagents . 130
Ignition . . . . . .10
Indigo solution (as reagent) . . 58
Inorganic bodies, detection of, in pre-
sence of organic bodies . .247
Iodine, detection of, in simple com-
pounds 190, 194
in complex com-
pounds 217, 225
in mineral waters 239
properties of. . . .148
Iron (as reagent) . . . .40
properties of . .87
protoxide, deportment with reagents 87
detection of, in simple
compounds . 186
in complex com-
pounds 210, 212
in soils . . 244
in well and mi-
neral waters
233, 237
sulphate of protoxide (as reagent) 52
sesquichloride (as reagent) . . 53
sesquioxide, deportment with re-
agents . 89
detection of, in simple
compounds . 184
in complex com-
pounds
201, 210, 212
in soils . 244, 245
in well and mine-
ral waters 233, 237
308
ALPHABETICAL INDEX.
PAGE
L.
Lead, deportment with reagents . . 95
oxide, detection of, in soluble simple
compounds 184, 185
in insoluble simple
compounds . 196
in soluble complex
compounds
198, 199, 201
in insoluble complex
compounds 222, 223
in organic matters . 256
in sinter deposits . 241
acetate (as reagent) ... 54
Lime, deportment with reagents . . 73
detection of, in soluble simple
compounds . 188
in soluble complex
compounds 214, 215
in insoluble simple
compounds . 196
in insoluble complex
compounds . 222
in soils . . 244, 245
in well and mineral
waters . . 233
sulphate (as reagent) . . 51
water (as reagent) ... 39
Lithia, deportment with reagents . 70
detection of, in mineral waters 239
Litmus-paper . . ^ , . 57
M.
Magnesia, deportment with reagents . 74
detection of, in simple com-
pounds . 188
in complex com-
pounds . 215
in soils . 244, 245
in well and mi-
neral waters . 233
sulphate of (as reagent) . 52
Malic acid, detection of,
in simple compounds 192
in complex compounds 220
deportment with reagent . 160
Manganese, deportment of 83
protoxide, detection of, in
simple compounds . 186
in complex compounds 209, 213
in soils . . . 244, 245
in well and mineral waters,
237, 238
protoxide, deportment with
reagents . . . 83
Marsh's apparatus . . . .115
Mercury, detection of, in articles of
food, &c. . . .256
properties of . . .94
chloride (as reagent) . . 55
oxide, deportment with re-
agents . . .97
detection of, in soluble
simple com-
pounds . 185
Mercury, oxide, detection of, in soluble
complex compounds . 207
suboxide, deportment with
reagents . . .94
detection of, in sim-
ple com-
pounds 184
in complex
compounds 198
nitrate of (as re-
agent) . . 54
Metallic poisons, detection of, in ar-
ticles of food, &c. . 248
Mineral waters, analysis of . . 235
Molybdic acid, deportment with re-
agents 125
Morphia, deportment with reagents . 279
detection of, in simple com-
pounds . 289
in complex com-
pounds . 290
N.
Narcotina, deportment with reagents . 280
detection of, in simple com-
pounds . 289
in complex com-
pounds . 290
Nickel, properties of . . . .84
protoxide, deportment with re-
agents . . 84
detection of, in simple
compounds 186
in complex
compounds,
210, 211
Nicotia, deportment with reagents . 277
Nitric acid (as reagent) . . .25
deportment with reagents . 155
detection of, in simple com-
pounds, 191, 194
in complex com-
pounds, 218, 221
in soils . . 244
in well and mi-
neral waters,
234, 239
Nitrohydrochloric acid (as reagent) . 29
Nitrous acid, deportment with reagents 154
0.
Oxalic acid, properties of . . .137
deportment with reagents . 137
detection of, in simple com-
pounds, 190, 191, 193
in complex com-
pounds . 213, 218
Oxidizing flame . . . .14
Oxygen acids (as reagents) . 23, 24
bases (as reagents) . 34, 35
P.
Palladium, protoxide of, deportment
with reagents . .103
sodio-chloride as reagent . 56
ALPHABETICAL INDEX.
309
Paratartaric acid, deportment with re-
agents 162
Phosphate of soda and ammonia (as
reagent) 63
Phosphates of alkaline earths, detec-
tion of, in simple compounds . 193
in complex compounds, 210, 221
Phosphate of alumina, detection of,
in simple compounds . . .193
in complex compounds . 212, 213
Phosphoric acid, bibasic, deportment
with reagents . 135
monobasic . .135
tribasic . . .132
detection of, in simple
compounds,
190, 193
in complex
compounds,
213, 218, 221, 224
in soils . 244
in mineral
waters, 233, 237
in silicates,
229, 230, 231
132
259
19
179
105
56
Phosphorus, properties of
in articles of food, &c.
Pincers .....
Platinum, detection of, in alloys
properties of
bichloride of (as reagent)
binoxideof, deportment wit]
reagents
detection in sim
pie com-
pounds
in complex
compounds
crucibles and their use
foil and wire
Porcelain dishes and crucibles
Potassa (as reagent) .
antimonate (as reagent)
bichromate (as reagent)
nitrite (as reagent)
sulphate (as reagent)
deportment with reagents
detection of, in simple com-
pounds .
in complex com-
pounds 215, 216
in well and mi-
neral waters .
in silicates
in soils
Potassium, ferricyanide of (as reagent)
ferrocyanide of (as reagent)
sulphocyanide of (as reagent)
Precipitation .....
Preliminary examination of solid bodies
of fluids
105
186
205
11, 19
16, 19
19
35
4G
4G
4G
43
188
234
230
244
49
49
50
5
174
179
Q.
Quina, detection of, in simple compounds 289
PAGE
Quina, detection of, in complex com-
pounds . . . .290
deportment with reagents . 281
R.
Racemic acid, deportment with reagents 162
Reagents ...... 20
Reducing flame . . . ' . 14
Retorts ...... 19
S.
288
288
290
129
227
143
178
Salicine, deportment with reagents
detection of, in simple com
pounds.
in complex com
pounds
Selenious acid, deportment with re
agents . . . .
Silicates, analysis of . . .
Silicic acid, deportment with reagents
detection of, by the blow-
pipe . .
in soluble com-
pounds 187, 190
in insoluble simple
compounds 193, 194
in soluble complex
compounds 210, 219
in insoluble com-
plex compounds 222
in soils . 244, 245
in well and mine-
ral waters . 234
Silver, detection of, in articles of food,
&c ..... 256, 257
properties of . . . .93
oxide of, deportment with re-
agents . . 93
detection of, in simple
compounds,
183, 196
in complex com-
pounds 198, 222
nitrate (as reagent) . 53
Sinter deposits, analysis of . .240
Soda (as reagent) . . . .35
deportment with reagents . . 67
detection of, in simple compounds 188
in complex com-
pounds . 215, 216
in well and mineral
waters . .234
in silicates . . 230
in soils . . 244, 245
acetate of (as reagent) . . 44
biborate of (as reagent) . . 62
carbonate of (as reagent) . . 44
nitrate of (as reagent) . . 60
phosphate of (as reagent) . . 43
sulphite of (as reagent) . . 45
and ammonia, phosphate of (as
reagent) . . . .63
and potassa, carbonate of (as re-
agent) ..... 58
Sodio-protochloride of palladium (as
reagent) ..... 56
310
ALPHABETICAL INDEX.
PAGE
Soils, analysis of .... 242
Solubility, table indicating degrees of . 300
Solution 3
of bodies for analysis . .180
Spirit- lamps . . . . 16, 17
Strontia, deportment with reagents . 72
detection of, in soluble simple
compounds . 188
in insoluble simple
compounds 196, 197
in soluble complex
compounds . 214
in insoluble com-
plex compounds 222
in mineral waters,
237, 238
in sinter deposits . 240
Strychnia, deportment with reagents . 284
detection of, in simple com-
pounds . . 289
in complex com-
pounds . . 291
Sublimation . . . . .11
Succinic acid, detection of, in simple com-
pounds . 192
in complex
compounds 220
deportment with reagents 162
Sulphate of lime (as reagent) . 51
Sulphide of ammonium (as reagent) 41
iron ... 30
sodium (as reagent) . 42
Sulphides, metallic, detection of, in sim
pie compounds, 189, 194
detection of, in com-
plex compounds,
217, 221
detection of, in sili-
cates . . 229
Sulphocyanide of potassium (as reagent) 50
Sulphur acids (as reagents) . 24, 30
bases (as reagents) . 35, 41
detection of, in insoluble com-
plex compounds . . 223
properties of . . .152
Sulphuretted hydrogen (see hydrosul-
phuric acid)
water (as reagent) 30
Sulphuric acid (as reagent) . . 24
deportment with re-
agents . . .131
detection of, in soluble
simple com-
pounds . 189
in soluble com-
plex compounds
217, 221
in insoluble sim-
ple compounds
195, 196
in insoluble
complex com-
pounds . . 224
in soils . 244, 245
Sulphuric acid, detection of, in well and
mineral waters 233
in silicates 229, 230
Sulphurous acid, deportment with re-
agent 129
T.
Tartaric acid (as reagent) ... 27
deportment with reagent 158
detection of, in simple corn-
compounds . 191
in complex com-
pounds . 219
Test tubes . ... 19
Tin, properties of . . .106
binoxide, deportment with reagents 108
detection of, in soluble sim-
ple compounds 184
in soluble complex
compounds . 205
in insoluble com-
pounds 222, 223
in articles of food,
&c. . 256, 257
protochloride (as reagent) . . 55
protoxide, deportment with re-
agents . . .106
detection of, in simple
compounds 185
in complex
compounds 205
in articles of
food, &c. 256, 257
Titanic acid, deportment with reagents 80
Turmeric paper . . . .58
TL
Ulmic acid, detection of, in soils . 246
Uranium, sesquioxide of, deportment
with reagents . . . . 92
V.
Veratria, deportment with reagents . 286
detection of, in simple com-
pounds . 289
in complex com-
pounds . 291
W.
Washing 8
bottles . . . 8, 19
Water (as reagent) .... 22
bath 9
Waters, analysis of natural . . 231
Well-water, analysis of ... 232
Z.
Zinc (as reagent) . . . . 40
properties of . . .82
oxide of, deportment with reagents 82
detection of, in simple compounds
187, 193
in complex compounds
209, 210, 213
in sinter deposits . 241
THE END.
LONDON
SAVILL AND EDWARDS, PRINTERS, CHANDOS STREET,
COVENT GARDEN.
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