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A TREATISE
ON
CHEMISTRY AND CHEMICAL
ANALYSIS
Prepared for Students of
The International Correspondence Schools
SCRANTON, PA.
Volume 111
QUALITATIVE ANALYSIS
WITH PRACTICAL QUESTIONS AND EXAMPLES
First Edition
SCRANTON
THE COLLIERY ENGINEER CO.
1900
*. *
» ^ *
" ' ' ^m* *• •rfrfrf « * * _, ^ ""
THE NEW YORK
PUBUC LIBRARY
AiTQn, LCMOX AND
TILDCM FOUMOATtONS
R 1«16 L
Copyright, 1899, by The Colliery Engineer Company.
Qualitative Analysis : Copyright, 1898, 1899, by The COLLIERY ENGINEER Company.
All rights reserved.
^ ^Pi;es% ptJ^T^ON & Mains
• • • •
• • ••
• • •
••• •
•••
• •
• • ••
• •
• • ••
• • • • •
:•:
• •••
••• • •
• •••• A ••• •*! I 1
•• ••• •••••••••
'V--'
CONTENTS.
Qualitative Analysis. Section, Page,
Definitions and Descriptions 10 1
Apparatus 10 4
Preparation of Reagents 10 8
Deportment of Metals with Reagents . . 10 11
Analysis of Mixed Solutions 10 51
Reactions of the Common Inorganic Acids 10 77
Reactions of the Common Organic Acids . 10 89
Reactions of the Rarer Inorganic Acids . 10 93
Reactions of the Rarer Organic Acids . . 10 104
Systematic Examination of Solutions for
Acids 10 110
Special Tests for Acids 10 115
Examination of Dry Substances ... 11 1
Examination in the Closed Tube ... 11 2
Examination on the Charcoal .... 11 9
Examination in the Flame 11 16
Examination in the Bead 11 17
Examination on the Platinum Foil ... 11 19
Examination with Sulphuric Acid ... 11 20
Solution of Solid Substances 11 25
Reactions of the Rare Elements ... 11 28
The Spectroscope 11 55
Analysis of Water 11 58
Examination of Urine 11 72
Common Inorganic Poisons 11 84
Detection of Arsenic . ;'• : \[ ^ \ • .-" .- - : : 11; : ^ 84
111 ' ' - , ,
iv CONTENTS.
Qualitative Analysis — Continued. Section. Page.
Detection of Phosphorus 11 91
Detection of Hydrocyanic Acid .... 1 1 1)0
Reactions of the Volatile Alkaloids . . 11 1)9
Reactions of the Non- Volatile Alkaloids .11 103
Questions and Examples. Section.
Qualitative Analysis, Parts 1 and 2 . . 10 and 11
«• . • • • • ••• • •
. ! ••• • • • «•* • '
«
* . A ■•• • f>
• •• • •
«,• • ••• ••• •• •
• » ^ • •• . • • " *
. • • • • • • •• •••
INDEX.
((
(I
78
81
115
89
96
Note. — All items in this index refer first to the section (see Preface, Vol. I) and then
to the page of the section. Thus, "Combustion 5 SG" means that combustion will be
found on page 86 of section 5.
Sec. Page,
Acid, hydrochloric, Deportment
with rea-
gents 10
" D e t e r m i-
nation of,
in urine.. 11
" Special tests
for 10
hydrocyanic, Deportment
with r e a-
gents 10
Determina-
tion of, in
food, dead
bodies,etc. 11
Special tests
for 10 119
hydroferricyanic. Deport-
ment with reagents
hydroferricyanic. Special
tests for 10 120
hy drof errocyanie. Deport-
ment with reagents 10 101
hydroferrocyanic. Special
tests for 10 120
hydrofluoric. Deportment
with reagents
hydrofluosilicic, Deport-
ment with reagents 10 103
hydrosulphocyanic, D e -
portment with reagents 10 100
hydrosulphocyanic. Spe-
cial tests for 10 119
hydrosulphuric, Deport-
ment with reagents 10
hydrosulphuric. Special
tests for.... 10 117
A.
Sec.
Page.
Abbreviations used
10
10
2
Acid,
Acetic, as reagent
10
((
" Deportment with
reagents
10
90
»t
arsenic, Special tests for. .
10
119
((
arsenious, Special tests
for
10
119
(t
benzoic. Deportment with
reagents
10
109
(4
boric, Deportment with
reagents
10
93
((
" Special tests for...
10
118
tl
carbonic, Deportment
with reagents
10
86
(t
" Determination
of, in water . .
11
68
((
" Special tests
for
10
117
t(
chloric. Deportment with
reagents
10
94
li
chromic. Deportment with
reagents
10
87
tl
" Special tests for
10
117
ii
citric, Deportment with
reagents
10
104
i(
formic. Deportment with
reagents
10
106
t(
hydr iodic, Deportment
with reagents
10
79
It
" Special tests
•
for
10
116
ii
hydrobromic. Deportment
with rea-
gents
10
70
il
" Special tests
for
10
115
ii
Hydrochloric, as reagent
10
8
10 102
10 96
83
VI INDEX.
Sec. Page.
Acid, hypochlorous. Deport-
ment with reagents 10 05
** malic, Deportment with
reagents 10 105
" Nitric, as reagent 10 8
" " Deportment with
reagents 10 84
" " Special tests for... 10 118
'* nitrous, Deportment with
reagents 10 99
" " Determination of,
in water 11 66
" oxalic. Deportment with
reagents 10 92
" phosphoric, Deportment
with rea-
gents 10 85
" " Determina-
tion of, in
urine 11
" " Special tests
for 10
" salicylic. Deportment with
reagents 10
" silicic, Deportment with
reagents 10
" " Special tests for.. 10
" Sulphuric, as reagent 10
" " Deportment
with rea-
gents 10
" " Determination
of, in urine.. 11
** " Examination
of solids with 11
" " Special tests
for 10
" sulphurous. Deportment
with rea-
gents 10
" " Special tests
for 10
" Tartaric, as reagent 10
" '* Deportment
with reagents 10
" thiosulphuric. Deport-
ment
with re-
agents.. 10 82
" " Special
tests for 10 116
Acids, Common inorganic 10 77
" *' organic 10 89
'* Examination of solutions
for 10 110
»♦ Grouping 10 112
" Rare inorganic 10 93
" " organic 10 104
83
117
10
91
Sec. Page.
Acids, Special tests for 10 115
Tables of 10 112
Albumin, Determination of, in
urine 11 78
Alkaloids 11 99
" Group 1 11 103
" Group II 11 107
" Group III 11 112
" Non-Volatile 11 103
" Volatile 11 99
Alloys, Examination of 11 23
Aluminum, Deportment with
reagents 10 31
" Detection of, in
mixed solutions 10 66
Ammonia, Determination of, in
water 11 64
Ammonium carbonate as rea-
gent 10 8
Chloride, as rea-
gent 10 8
Deportment with
reagents 10 44
Detection of, in
mixed solutions 10 74
hydrate as rea-
molybdate, as rea-
gent 10 11
oxalate as reagent 10 8
sulphate as rea-
gent 10 10
sulphide as rea-
gent 10 10
sulphide. Yellow,
as reagent 10 10
Analysis, Definition of 10 1
" of mixed solutions 10 51
" Qualitative, Definition
of 10 1
" " Methods
of 10 1
" Quantitative, Defini-
tion of 10 1
Antimony, Deportment with
reagents 10 23
'* Detection of, in
mixed solutions.. 10 62
Apparatus needed 10 4
" " for separations 10 51
Arsenic acid. Special tests for. . . 10 119
" compounds. Deport-
ment with reagents... 10 26
'* Determination of, in
food, dead bodies,
etc 11 84
" Determination of, in
water 11 70
81
117
106
98
118
8
81
80
20
116 /
^nalvs
INDEX.
Vll
Sec. Page,
Arsenic, Detection of, in mixed
solutions 10 62
Arsenious acid, Special tests for 10 119
" compounds, Deport-
ment with reagents 10 25
Atropine, Deportment with
reagents 11 116
B. Sec. Page.
Barium chloride as reagent 10 9
'* Deportment with rea-
gents 10 89
" Detection of, in mixed
solutions 10 71
" hydrate as reagent 10 11
Bead, Examination of solids in.. 11 17
Beads, Table of colors of 11 19
Benzoic acid. Deportment with
reagents 10 109
Beryllium, Deportment with
reagents 11 44
Bismuth, Deportment with
reagents 10 22
" Detection of, in mixed
solutions 10 59
Blowpipe 10 5
Blue glass 10 7
Borax bead. Examination of
solids in 11 17
Boric acid, Deportment with
reagents 10 93
" " Special tests for . . 10 118
Brucine, Deportment with rea-
gents 11 115
Brucke's test for sugar in
urine 11 77
Bunsen burner 10 4
C. Sec. Page.
Cadmium, Deportment with
reagents 10 20
" Detection of, in
mixed solutions . . 10 60
Ceesium, Deportment with rea-
gents 11 hi
Calcium, Deportment with rea-
gents 10 41
" Detection of, in mixed
solutions 10
" sulphate as reagent.... 10
Carbonic acid. Deportment with
reagents 10 86
" " Determination of,
in water 11 68
" " Special tests for.. 10 117
Cerium, Deportment with rea-
gents. 11 48
Sec. Page.
Charcoal 10 6
'* Examination of solids
on 11 9
Chloric acid, Deportment with
reagents 10 94
Chromic acid. Deportment with
reagents 10 87
" " Special tests for.. 10 117
Chromium, Deportment with
reagents 10 82
" Detection of, in
mixed solutions. . 10 65
Cinchonine, Deportment with
reagents 11 109
Citric acid, Deportment with
reagents 10 104
Closed tube. Examination of
solids in 11 2
Cobalt, Deportment with rea-
gents 10 84
" Detection of, in mixed
solutions 10 09
" nitrate as reagent 10 10
Cocaine,. Deportment with rea-
gents 11 106
Concentrating solutions 10 52
Conine, Deportment with rea-
gents 11 102
Copper, Deportment with rea-
gents 10 19
'* Detection of, in mixed
solutions 10 60
D. Sec. Page.
Definitions and descriptions 10 1
Deportment of metals with
reagents 10 11
Didymium, Deportment with
reagents 11 50
Dry substances, Examination of 11 1
71
10
F. S^c. Page.
Fehling's solution 11 75
Ferric compounds, Deportment
with reagents 10 80
Ferrous compounds. Deport-
ment with reagents 10
" sulphate as reagent.. 10
Flame, Examination of solids in 11
Formic acid, Deportment with
reagents 10 106
29
9
16
G. Sec. Page.
Gallium, Deportment with rea-
gents 11 47
Glass, Blue 10 7
Gold, Deportment with reagents 11 85
VIU
INDEX.
Group I
'* " Rare elements belong-
ing to
II
*' Rare elements belong-
ing to
Ill
" Rare elements belong-
ing to
IV
" Rare elements belong-
ing to
V
VI
VII
" Rare elements be-
longing to
reagents
separations
Grouping the acids
Groups, List of
Sec, Page.
10 55
((
it
it
((
it
(I
((
(t
it
(I
it
11
10
11
10
11
10
11
10
10
10
11
10
10
10
10
10
10
(t
l(
10
10
n. Sec.
Heller's test for albumin in urine 11
Hydriodic acid, Deportment
with rea-
gents
" " Special tests
for
Hydrobromic acid. Deportment
with rea-
gents
" " Special tests
for
Hydrochloric acid as reagent...
" Deportment
with rea-
gents
" Determina-
tion of, in ■
urine 11
" " Special tests
for 10
Hydrocyanic acid, Deportment
with rea-
gents 10
" " Determina-
tion of, in
food, dead
bodies,etc. 11
" " Special tests
for 10
Hydroferricyanic acid. Deport-
ment with reagents 10
Hydroferricyanic acid. Special
tests for 10
Hydroferrocyanic acid. Deport-
ment with reagents 10
29
56
81
63
41
68
41
70
73
73
53
53
53
112
53
Page.
79
79
116
Hydroferrocyanic acid. Special
tests for
Hydrofluoric acid, Deportment
with reagents
Hydrofluosilicic acid. Deport-
ment with reagents
Hydrogen sulphide as reagent..
Hydrosulphocyanic acid. De-
portment with reagents
Hydrosulphocyanic acid, Special
tests for
Hydrosulphuric acid. Deport-
ment with reagents
Hydrosulphuric acid. Special
tests for
Hypochlorous acid, Deportment
with reagents
Sec. Pagt
10 120
10 96
10
103
10
10
10
ICO
10
119
10
83
10
117
10 95
45
CO
I. S.c. P<^gc.
Indium, Deportment with rea-
gents 11
Inorganic acids. Common 10
" " Rare 10
Iridium, Deportment with rea-
gents 11
Iron, Deportment with reagents 10
" Detection of, in mixed sol u-
tions 10
87
29
10 79
L..
115
8
10 78
81
115
89
Lead acetate as reagent
" Deportment with reagents 10
" Detection of, in mixed solu-
tions 10
Lithium, Deportment with rea-
gents 11
65
Sec. Page.
10 9
14
56
53
it
((
96
119
102
120
101
M. S3C. Page.
Magnesium, Deportment with
reagents 10 43
Detection of, in
mixed solutions.. 10 73
sulphate as reagent 10 10
Malic acid. Deportment with rea-
gents 10 105
Manganese, Deportment with
reagents 10 37
" Detection of, in
mixed solutions... 10 70
Matrasses 10 7
Mercuric chloride as reagent — 10 9
compounds, Deport-
ment with reagents 10 18
compounds, Detec-
tion of, in mixed solu-
tions 10 59
t(
INDEX.
IX
Sec. Page.
Mercurous compounds, Deport-
in e n t with rea-
gents 10 16
** compounds, Detec-
tion of , in m i X e d - -
solutions 10 56
Metals and alloys, Examination
of 11 28
" Poisonous, in water 11 69
Mixed solutions. Analysis of . . . . 10 51
Molybdenum, Deportment with
reagents 11 88
Morphine, Deportment with rea-
gents 11 103
N. Sec. Page.
Narcotine, Deportment with rea-
gents 11 110
Nickel, Deportment with rea-
gents 10 85
" Detection of, in mixed
solutions 10 60
Nicotine, Deportment with rea-
gents 11 100
Nitric acid as reagent 10 8
** " Deportment with rea-
gents 10 84
" " Special tests for 10 118
Nitrous acid. Deportment with
reagents 10 99
" Determination of,
in water 11 66
Sec. Page.
Platinum foil, Examination of
solids on
11 19
i(
wire.
10
6
((
it
(t
it
It
(t
it
Poisonous metals, Determination
of, in water
Poisons, Common inorganic
Potassium chromate as reagent
cyanide as reagent
Deportment with
reagents
Detection of, in
mixed solution
ferricyanide as rea-
gent
ferrocyanide as
reagent
iodide as reagent ....
Precipitates, Washing
Preparation of solutions for
practice
Q. Sec. Page.
Qualitative analysis, Definition
of 10 1
" »* Methods
of 10 1
Quantitative analysis, Definition
of 10 1
Quinine, Deportment with rea-
gents 11 107
11
69
11
84
10
9
10
9
10
45
10
74
10
9
10
9
.10
9
10
52
10
75
o.
Sec. Page.
10 89
R.
Sec. Page.
Organic acids. Common
" " Rare 10 104
" matter. Determination
of, in water 11 67
Osmium, Deportment with rea-
gents 11 32
Oxalic acid, Deportment with
reagents 10 92
P. Sec. Page.
Palladium, Deportment with
reagents 11 31
Phosphoric acid, Deportment
with rea-
gents 10 85
" " Determina-
tion of, in
urine 11 81
" *' Special tests
for 10 112
Phosphorus, Determination of,
in food, dead bodies, etc 11 91
Platinum, Deportment with rea-
gents 11 36
Rare elements 11
Reaction, Definition of 10
Reactions, Table of 10
Reagent, Definition of 10
28
2
48
2
53
8
Reagents, Group 10
" Preparation of 10
Reports, How written 10 120
Rhodium, Deportment with
reagents 11 83
Rubidium, Deportment with re-
agents 11 54
Ruthenium, Deportment with
reagents 11 34
S. Sec. Page.
Salicylic acid. Deportment with
reagents 10 108
Selenium, Deportment with rea-
gents 11 89
Silicic acid, Deportment with
reagents., 10 98
" " Special tests for... 10 118
Silver, Deportment with rea-
gents 10 12
INDEX.
Sec, Page.
>t
i(
it
it
ct
tl
ii
CI
(i
it
Silver, Detection of, in mixed
solutions 10
*' nitrate as reagent 10
Sodium carbonate as reagent. ... 10
Deportment with rea-
gents 10
Detection of, in mixed
solutions 10
" hydrate as reagent 10
phosphate as reagent ... 10
tartrate acid as rea-
gent 10
Solids, Examination of 11
" Examination of, in the
bead 11
Examination of, in closed
tube 11
Examination of, in the
flame 11
Examination of, on char-
coal 11
Examination of, on plati-
num foil 11
Examination of, with sul-
phuric acid 11
Solution of 11
Solutions for practice. Prepara-
tion of 10
Spectroscope, The 11
Stannic compounds. Deportment
with reagents 10
Stannous chloride as reagents. . . 10
" compounds. Deport-
ment with reagents 10
Strontium, Deportment with
reagents 10
" Detection of, in
mixed solutions.. 10
Strychnine, Deportment with
reagents 11
Sugar, Determination of, in urine 11
Sulphuric acid as reagent 10
" Deportment with
reagents 10
" Determinationof,
in urine 11
" " Examination of
solids with 11
" " Special tests for 10
Sulphurous acid, Deportment
with reagents 10
" Special tests
for 10
(i
t(
it
56
9
9
46
74
9
9
11
1
17
2
16
9
19
20
25
75
55
28
9
27
40
71
112
75
8
81
80
30
116
»S
117
Sec. Page.
Tables of acids 10 112
Tartaric acid as reagent 10 10
*' " Deportment with
reagents 10 91
Tellurium, Deportment with
reagents 11 40
Thallium, Deportment with rea-
gents 11 29
Thiosulphuric acid. Deportment
with rea-
gents 10 82
" " Special tests
for 10 116
Thorium, Deportment with rea-
gents 11 51
Tin, Deportment with reagents. 10 27
" Detection of, in mixed solu-
tions 10 62
Titanium, Deportment with rea-
gents 11 41
Trommer 's test for sugar in urine 11 76
Tungsten, Deportment with rea-
gents 11 80
U. Sec. Page.
Uranium, Deportment with rea-
gents 11 43
Urine, Analysis of 11 72
Color of 11 72
Determination of albumin
in 11 78
Determination of hydro-
chloric acid in 11 81
Determination of phos-
phoric acid in 11 81
Determination of siijjar in 11 75
Determination of sulphu-
ric acid in 11 80
Reaction of 11 73
Samples for practice 11 8.?
Specific gravity of 11 73
Urinometer 11 74
(i
it
it
it
it
tt
it
it
T. Sec. Page.
Table of reactions 10 48
" showing colors of beads.. 11 19
V. Sec. Page.
Vanadium, Deportment with
reagents 11 42
AV. Sec. Page.
Washing precipitates 10 52
Water, Analysis of 11 58
" Determination of am-
monia in 11 64
" Determination of arsenic
in 11 70
" Determination of car-
bonic acid in 11 68
INDEX. XI
Sec. Page. Sec. Page.
Water, Determination of nitrous Yttrium, Deportment with rea-
acid in 11 CO gents 11 49
" Determination of organic
matter in 11 67
** Determination of poison- Z. Sec. Page.
ous metals in 11 69 Zinc, Deportment with rea-
gents 10 SO
" Detection of, in mixed
Y. Sec. Page. solutions 10 70
Yellow ammonium sulphide as Zirconium, Deportment with
reagent 10 10 reagents 11 47
QUALITATIVE ANALYSIS.
(PART 1.)
EN^TROD UCTOE Y.
DEFINITIONS AND DESCRIPTIONS.
1. Analysis. — Analysis in its most general sense is the
process of resolving more or less complex substances into
simpler ones. It is, therefore, the reverse of synthesis,
which consists in building up complex compounds from
simpler ones. Analysis consists in breaking these com-
pounds up into their component parts.
It is divided into qualitative and quantitative analysis.
Qualitative analysis is th^t branch of chemical science
which considers the methods of determining the elements
that compose a compound or mixture of compounds, with-
out reference to the quantities of these elements which the
substance contains.
Quantitative analysis takes up the subject where quali-
tative analysis leaves it, and determines the exact amount of
each element in a substance.
3. Methods of Qualitative Analysis. — There are two
methods of qualitative analysis, known as the wet method
and the dry method. The wet method, as its name implies,
deals with solutions, while the dry method de^\s with solids.
In most cases, separate quantities of these solids may be put
into solution, by methods to be described later, and to these
portions the wet method may also be applied.
§10
For notice of the copyright, see page immediately following the title page.
2 QUALITATIVE ANALYSIS. § 10
Each method has its advantages. The dry method is short
and simple in many instances, requires but little apparatus,
and, in case of some of the simpler substances, quickly
yields a result. Its use is almost indispensable in some cases,
but iii many instances* it only gives indications, which must
be confirmed by the wet method.
The wet method has the advantage that it is almost uni-
versally applicable, and its results are absolutely certain if
the work of obtaining them is properly done.
It is best to treat these two methods separately, so far as
possible, in describing them and in the early part of the
work, but after the student becomes familiar with them he
will find it a great advantage to combine the two.
3. Abbreviations Used. — In analytical work, certain
words occur so frequently that it is an advantage to use
abbreviations for them. The following is a list of the most
common ones used in this Course :
Ppt. — precipitate. Cone. — concentrate.
Pptd. — ^precipitated. Dil. — dilute.
Sol. — soluble. O. F. — oxidizing flame.
Insol. — insoluble. R. F. — reducing flame.
Sp. Gr. — specific gravity.
4. Reaction and Beagent. — A reaction is a chemical
change, and the substance that produces this change is
called a reagent.
Illustration. — If a small quantity of silver nitrate solution be placed
in a test tube and a few drops of hydrochloric acid added, a white pre-
cipitate of silver chloride is formed according to the equation :
AgNO^ -h HCl = AgCl + HNOz
This change is called a reaction, and the hydrochloric acid, which pro-
duced the change, is a reagent.
The attention of the student is called to the fact that when
a reagent is added to a metallic solution, the metallic com-
pound formed is similar in composition to the reagent.
Thus, if the reagent is a hydrate, a hydrate of the metal
will be produced ; a carbonate will form a carbonate of the
metal ; a sulphide produces a sulphide of the metal, etc. All
§ 10 QUALITATIVE ANALYSIS. 3
exceptions to this rule are given under ** Deportment of the
Metals with Reagents. "
6. Tlie Wet Method. — In wet analysis we determine
the constituents of a solution of a substance by the reactions
produced by certain common reagents. If there is but one
metal in the solution, this becomes a very simple matter.
About half an inch of the solution to be tested is placed
in a test tube and a small amount of the reagent is carefully
added, drop by drop, while the place where the two liquids
meet is closely watched. If no precipitate is formed, the
test tube is emptied, washed well with common water, and
rinsed out with distilled water. We are then ready to use a
fresh portion of the solution and test in the same way with
another reagent. A dirty test tube must never be used.
Neatness is essential in all successful analytical work.
If we obtain a precipitate, the first thing to be noted is its
color and general appearance. Its solubility may also help
to establish its identity. If we wish to test its solubility in
an excess of the reagent used to precipitate it, we pour out
all but a small portion, and to this add more of the reagent.
To test for its solubility in any other reagent, allow the
precipitate to settle to the bottom of the tube as much as
possible, pour off the supernatant liquid, retaining but a
small quantity of the precipitate in the tube ; to this add
the desired reagent, shake it up, and observe the result.
By observing the reactions of a few common reagents and
referring to the section on ** Deportment of the Metals with
Reagents," we can readily tell just what metal we have.
Illustration. — If we add a few drops of hydrogen sulphide to a
small quantity of a solution in a test tube and get a black precipitate,
we know the metal is either silver, lead, mercurous, mercuric, or
copper, for these are the only metals giving black precipitates with
hydrogen sulphide. If to a fresh portion of the solution we add
sodium hydrate and get a brown precipitate, we know the metal is
silver, for that is the only one, of the five metals mentioned, that gives
a brown precipitate with sodium hydrate.
When a result is obtained in this way it should always be
confirmed by the ether reactions given for the metal.
4 QUALITATIVE ANALYvSIS. § 10
6. It will be noted that some of the metals form two
series of compounds which differ widely from each other.
Thus, mercury forms mercurous and mercuric compounds,
which, in analytical chemistry, arc treated as though they
were salts of different metals.
APPARATUS NEEDED.
7. The only apparatus needed for the wet reactions,
when there is but one metal in the solution, will be some
test tubes, a set of reagents in properly labeled bottles, and
a good burner. A Bunsen burner is preferable for this pur-
pose, but where gas is not available, an alcohol lamp may
be made to serve in its stead.
It is desirable that the student should become familiar
with a few dry reactions in connection with the wet ones,
and for this purpose he will need a blowpipe, a small piece
of charcoal, a piece of platinum wire, a piece of platinum
foil, a pair of forceps, a piece of blue glass, and, as the work
proceeds, closed tubes, or matrasses, will be required.
8. The Burner. — A Bunsen burner, shown in Fig. 1, is
made with a perforated metal cylinder g near the base,
for regulating the air supply. In cases where the blowpipe
is not used, a full supply of air is admitted,
giving a non-luminous flame.
This consists of three parts: (1) An inner
zone of unbumed gas mixed with air, as seen
at afc ; (2) the outer mantle of burning gas
mixed with an excess of air, shown at^^^;
and (3) the luminous cone dfe.
The different parts of this flame have two
opposite effects. In the inner flame, the
unbumed gas, rich in carbon and hydrogen,
tends to reduce the substance, while the outer
Fig. 1. flame, by heating the substance in the pres-
ence of the oxygen of the air, tends to oxidize it.
A substance to be reduced should be held in the luminous
cone dfc^ as reduction is most rapidly accomplished here.
§10
QUALITATIVE ANALYSIS.
A substance to be oxidized should be held just within the
flame at b^ as this is the point of,- most rapid oxidation.
These points are meant when the reducing and oxidizing
flames are mentioned.
If a substance is merely to be heated, it is held in the
flame near the top, as this is the position of greatest heat.
Some substances are volatilized and give a characteristic color
to the flame, by which they may be recognized. For this
purpose the substance is held in the lower part of the outer
mantle ab c.
9. The Blowpipe. — By means of the blowpipe we obtain
an intensely heated flame, which may be directed where we
wish. There are several fonns of blowpipe, the simplest
being a small curved brass tube, termina-
ting in an orifice about the size of a small
needle. With this instrument, after blow-
ing a while, the moisture which accumulates
is blown into the flame. Several forms of
blowpipe have been devised to avoid this..
A good form is shown in Fig. 2. It con-
sists of five parts. The mouthpiece A is
usually made of hard rubber, and is pressed
against the lips when in use. It fits into
the tube B^ which in turn is fitted into the
moisture reservoir C The tip holder D fits
into the side of the moisture reservoir, and
the tip E fits on to this.
In using the blowpipe it is often neces-
sary to blow a steady stream of air through
it for several minutes, and the student
should practice until he can do this before
attempting any of the following operations.
To accomplish this, the mouthpiece is
pressed against the lips, and the cheeks
inflated. Then, by means of the muscles
of the cheeks, a steady stream of air is forced through the
blowpipe, while we breathe through the nostrils. The air
Fig. 2.
6
QUALITATIVE ANALYSIS.
§10
should never be forced from the lungs, as by this means we
cannot keep up a steady stream. This operation may seem
difficult at first, but by practice it will soon become easy.
In blowpipe work a rather small, luminous flame, obtained
by turning the metal cylinder so as to reduce the supply of
air, is used, and from this we can obtain either an oxidizing
or reducing flame, according to the method of using the
blowpipe. By placing the tip of the blowpipe just outside
Fig. 3.
Fig. 4.
of the flame and blowing, we get a long, slightly luminous
flame. A substance held at ^, Fig. 3, is rapidly reduced by
the unbumed gas.
To get an oxidizing flame, the tip of the blowpipe should be
placed just inside of the flame. Then, by blowing through
it, a long, blue flame is obtained which will rapidly oxidize
Q a substance held at the point B, Fig. 4, where it is
intensely heated in the presence of an excess of air.
10. Charcoal. — In blowpiping, a small piece of
fine-grained charcoal, made from soft wood, is largely
used as a support. Common charcoal is very unsatis-
factory, but the small blocks, for sale by all chemical
dealers, are very good for this purpose. A small cavity
is made in the charcoal, to hold the substance, and,
after using, it must be well scraped out before the next
operation.
11. Platinum Wire. — A short piece of fine plati-
num wire is essential in working by the dry method.
It is well to heat one end of a small glass tube in the
figTj. flame until it softens and begins to close ; then, without
§10
QUALITATIVE ANALYSIS.
withdrawing it from the flame, insert one end of the wire
and allow the glass to close over it, thus forming a handle
which does not readily transmit heat. The result is shown in
Fig. 5. The other end of the wire should be bent into a
loop about ^y inch in diameter.
This loop will serve to hold solid substances in the flame,
to hold a drop of solution in the flame in order to observe if
any color is thus imparted to it, and to hold the borax, or
microcosmic bead, to be described later.
When not in use, it is a good plan to place the wire in
dilute hydrochloric acid. Then, after burning it
off, it is nearly always clean and ready for use.
A good method of keeping the wire clean is to
insert the glass handle in the perforation of a cork
that is too large to go into a test tube, and by this
means suspend the wire in a test tube containing
hydrochloric acid, as shown in Fig. 6.
12. A small piece of platinum foil, which may
be bent into the form of a spoon, and a pair of
forceps with which to hold the foil, need
no description. It is only necessary to say
that platinum must never be heated in con-
tact with the heavy metals, such as lead,
mercury, etc., or their salts, for these will
alloy with the platinum and ruin it.
Fig. 6.
13. Blue Glass. — A small piece of blue glass,
which the operator may hold before his eye to look
through at the colored flames produced by some of
the metals, is indispensable when determining the
alkalies.
14. Matrasses. — Closed tubes, or matrasses, are
much used in analyzing solids, and may as well be
described here. They are made in several forms. A
good form may be made by cutting a piece of glass
tubing, having an inside diameter of about -f^ of an inch,
Fig. 7.
8 QUALITATIVE ANALYSIS. § 10
into pieces about 3 J inches long, and holding one end of each
piece in the flame till it softens and closes. The result is
shown in Fig. 7.
Solids may be dropped into this tube and heated at the
closed end, by holding it in the flame. To protect the fin-
gers from the heat, the tube may be held in the forceps, or
a piece of paper may be folded and wrapped around it near
the top, thus serving as a holder.
REAGENTS.
15. Preparation of Solutions. — In the outfit that
we furnish to students, all reagents except nitric, hydro-
chloric, and sulphuric acids, and ammonium hydrate — or
ammonia, as it is commonly called — are of the proper
strength for use. Those mentioned are needed in two
strengths, concentrate and dilute. The student is furnished
with the concentrate solutions, and from these he can make
the dilute solutions by adding a small portion of each to four
times its volume of water, and mixing them well. The sul-
phuric acid must be added to the water slowly while the
solution is constantly stirred, on account of the heat gener-
ated. In this, as in every case where water is mentioned,
distilled water should be used. When a reagent is mentioned,
the dilute solution is always meant unless the concentrate
solution is specified.
For the benefit of students that do not obtain our outfit,
the following directions are given for making up reagents:
Chemically pure substances should be used in every case.
Ammonium Carbonate. — Dissolve JOO grams of the solid
in 300 cubic centimeters of water and 100 cubic centimeters
of concentrate ammonium hydrate, and dilute to 500 cubic
centimeters with water.
Ammonium Chloride. — Dissolve 100 grams of the dry
salt in a sufficient amount of water — say 400 cubic centi-
meters — and then add water to make 500 cubic centimeters
of solution.
Ammonium Oxalate. — Add to 25 grams of the salt.
§ 10 QUALITATIVE ANALYSIS. 9
sufficient water to make 500 cubic centimeters of solution.
Allow it to stand until it dissolves, shaking it occasionally.
Sodium Hydrate. — Dissolve 40 grams of the solid in
water, and dilute this solution to 500 cubic centimeters with
water.
Sodium Carbonate. — Dissolve 100 grams of the dry salt,
or 270 grams of the crystals, in sufficient water to make
500 cubic centimeters of solution.
Sodium Phosphate. — -Dissolve 50 grams of acid sodium
phosphate Na^HPO^^\%HJD in sufficient water to make
500 cubic centimeters of solution.
Potassium Chromate. — Dissolve 50 grams in water and
add water to this solution to make it up to 500 cubic centi-
meters.
Potassium Ferricyanide. — To 50 grams of the solid, add
water enough to make 500 cubic centimeters of solution.
Potassium Ferrocyanide and Potassium Cyanide. —
These are made of the same strength and in the same man-
ner as potassium ferricyanide.
Potassium Iodide. — Dissolve 20 grams of the crystal-
lized salt in 500 cubic centimeters of water.
Barium Chloride. — Dissolve 25 grams of the solid in 500
cubic centimeters of water.
Silver Nitrate. — Dissolve 20 grams of the crystals in 500
cubic centimeters of water.
Lead Acetate. — Dissolve 50 grams of the dry salt in
water to which 1 cubic centimeter of acetic acid has been
added, using water enough to make 500 cubic centimeters of
the solution.
Mercuric Chloride. — Dissolve 25 grams of the crystals
in 500 cubic centimeters of water.
Stannous Chloride. — Dissolve 25 grams of the solid
stannous chloride in 75 cubic centimeters of concentrate
hydrochloric acid, and enough water to make 500 cubic
centimeters of solution. Some metallic tin should be kept
in the solution, which should be kept in a tightly stoppered
bottle.
Ferrous Sulphate. — To 75 grams of the crystals, add
10 QUALITATIVE ANALYSIS. § 10
water enough to make 500 cubic centimeters of solution.
To this add about 1 cubic centimeter of concentrate sul-
phuric acid and a little metallic iron, and keep the solution
from the air.
Cobalt Nitrate. — Dissolve 50 grams of the crystallized
salt in water, and dilute the solution to 500 cubic centimeters
with water.
Tartaric Acid. — Dissolve 100 grams of the solid tartaric
acid in water sufficient to make 500 cubic centimeters of
solution.
Acetic Acid. — Dilute the 33-per-cent. acid with twice its
volume of water to make the dilute acid.
Hydrogen Sulphide. — Generate the gas as described in
Experiment 50, Art. 105, Inorganic Chemistry, Part 1, and
lead it into water until the water is saturated, when it is
ready for use. The solution should be protected from the.
air.
Aimnonlum Sulplilde. — Lead hydrogen-sulphide gas
into a bottle two- thirds full of concentrate ammonium
hydrate, until it is saturated, which is indicated by the bub-
bles coming through the liquid undiminished in size. Fill
the bottle with concentrate ammonia and mix it well.
Before using, dilute this with twice its volume of water.
Yellow Ammonluin Sulphide. — This is made by adding
a small quantity of flowers of sulphur to the common ammo-
nium sulphide and shaking until dissolved. Enough sulphur
should be added to give the solution an amber color.
Ammonium Sulphate. — Dissolve 50 grams of the solid
ammonium sulphate in sufficient water to make 500 cubic
centimeters of solution. Its principal use is in separating
strontium and calcium.
Magnesium Sulphate. — Dissolve 50 grams of the crys-
tallized salt in water enough to make 500 cubic centimeters
of the solution.
Calcium Sulphate. — A saturated solution is always used.
It is prepared by repeatedly shaking up some finely pow-
dered calcium sulphate in a bottle of water, taking care to
have more of the sulphate than the water will dissolve.
§ 10 QUALITATIVE ANALYSIS. 11
Allow it to stand for some time and decant the clear liquid
for use.
Barium Hydrate. — To 25 grams of pure barium-hydrate
crystals, add sufficient water to make 500 cubic centimeters
of solution, and dissolve by the aid of heat. Filter into a
bottle provided with a good stopper, and close the bottle at
once to protect the solution from the air. The filtration is
performed as directed in Art. 99, Theoretical Chemistry,
Acid Sodium Tartrate. — A saturated solution is used.
It is prepared by placing in a bottle, about three-fourths
filled with water, a little more of the solid salt than will be
dissolved, and shaking repeatedly. Allow it to settle, and
decant the clear solution as it is needed.
Ammonium Molybdate. — This may be made by dissolv-
ing 25 grams of powdered ammonium molybdate in 75 cubic
centimeters of concentrate ammonia, by the aid of heat.
Pour this solution slowly, and with constant stirring, into a
mixture of 300 cubic centimeters of concentrate nitric acid
and 200 cubic centimeters of water. This solution should
be allowed to stand for at least 24 hours before using.
The directions in most cases are given for making 500 cubic
centimeters, merely because that is a convenient quantity.
More or less of any reagent may just as well be made, pro-
vided the proportions are not altered.
DEPORTMENT OF THE METALS WITH
REAGENTS.
INTRODUCTORY.
16, We now come to the deportment ^ or behavior^ of the
metals with reagents. The student should not attempt to
commit all these reactions to memory, but should make him-
self so familiar with them that he can readily distinguish any
of the metals by their reactions. For this purpose only a
12 QUALITATIVE ANALYSIS. § 10
few reactions will generally be necessary, but the results thus
obtained should always be confirmed by all the others given.
So far as possible^ it is desirable to perform each of the fol-
loioing operations, using known solutions before attempting"
to analyze unknozvn ones.
The student will soon learn to form groups of the metals
that are precipitated by the different reagents: as, for
instance, he will learn that only three metals, silver, lead,
and mercury, in the. mercurous form, are precipitated by
hydrochloric acid; five by sulphuric acid, etc. In this he
will be assisted by the table at the end of this section.
Each student should keep, in a note book, a complete
record of all work done. It is especially important that any-
thing that is not understood at the time should be recorded
in this book.
SIIiVER.
17. Silver is a white metal that fuses on the charcoal
before the blowpipe, forming a bright, metallic globule. It
does not volatilize, and no incrustation* is formed. To per-
form this and similar operations, a piece of the metal, about
twice as large as the head of a pin, is placed in a small cavity
in the charcoal, made to hold it, and the blowpipe flame is
directed upon it. In all blowpipe work, only small quanti-
ties of the substance treated must be used. Silver is only
very slowly acted upon by hydrochloric acid, forming insol-
uble silver chloride AgCL It dissolves slowly in dilute sul-
phuric acid, forming silver sulphate, and dissolves very
readily in nitric acid, forming silver nitrate AgNO^.
This solution may be used for the silver reactions, but it
is best to make a solution for this purpose from silver-nitrate
crystals. In the case of each of the metals, directions are
given for making a solution. Of course, any other solution
would give the same reactions, but the solution given is most
easily made, and is in the form in which we are most likely
to find the metal in actual analysis.
* By an incrustation 155 meant a deposit on the charcoal surrounding,
or near, the substance heated.
§ 10 QUALITATIVE ANALYSIS. 13
A silver solution may be made by dissolving about 2 grams
of silver-nitrate crystals in 100 cubic centimeters of water
and adding a drop or two of nitric acid. The acid is best
added by means of a dropper, which may be made by draw-
ing out a glass tube, and cutting it as shown in Fig. 35, The-
oretical Chemistry, When the small end of this tube is
dipped into the liquid, the liquid, of course, enters it, and
may be retained in the tube by pressing the finger closely
upon the upper end. If the finger is removed, the liquid
will be released, and by this means we can get any amount
of liquid we wish.
18, Reactions. — A silver solution gives the following
reactions:
1. Ammonium hydrate^ if added in very small amount to
a rather strong neutral solution of silver that does not con-
tain ammonium compounds, precipitates brown silver oxide
Agfi^ which is very soluble in an excess of the reagent.
As silver oxide is very soluble in ammonia, and its formation
is prevented by the presence of ammonium compounds, no
precipitate is usually obtained. Most silver solutions contain
free acid, hence, when ammonia is added, ammonium com-
pounds are formed, which prevent the formation of a pre-
cipitate.
2. Sodium hydrate precipitates brown silver oxide Agfi^
which is insoluble in an excess of the reagent, but very
soluble in ammonia.
3. Ammonium carbonate precipitates white silver carbon-
ate Ag^CO^^ which is easily soluble in excess.
4. Sodium carbonate gives a white precipitate of silver
carbonate Ag^CO^, which is insoluble in excess, but is readily
soluble both in nitric acid and ammonia.
6. Hydrogen sulphide precipitates black silver sulphide
Ag^S^ which is not easily dissolved in cold dilute acids, but
soluble in boiling dilute nitric acid.
6. Ammonium sulphide gives the same precipitate as
hydrogen sulphide. It may be well at this point to state that
in every case where hydrogen sulphide gives a precipitate,
14 QUALITATIVE ANALYSIS. § 10
ammonium sulphide gives the same. The reverse, how-
ever, is not true, as we shall see later.*
7. Hydrochloric acid precipitates white silver chloride
AgCly which slowly changes to brown upon exposure to sun-
light. It is insoluble in nitric acid, but is readily soluble in
ammonium hydrate, from which solution it is reprecipitated
by nitric acid.
8. Copper deposits metallic silver from its solutions. If
a small piece of copper be dropped into a silver solution, it
soon becomes gray, owing to the silver that is deposited on
it. Upon rubbing, it becomes bright.
9. Sodium phosphate precipitates yellow silver phosphate
Ag^PO^^ which is soluble in both nitric acid and ammonium
hydrate.
10. Potassium cyanide precipitates white silver cyanide
AgCN, which is soluble in excess of the reagent and in
ammonium hydrate, but insoluble in nitric acid.
LEAD.
19, Lead is a soft, white metal when freshly cut, but
soon tarnishes in the air. It fuses easily on the charcoal
before the blowpipe, giving the flame a pale, bluish tinge,
and depositing a yellow incrustation of the oxide PbO on
the charcoal. This incrustation is volatile, and may be
driven from place to place on the charcoal by directing the
blowpipe flame upon it.
Lead is only slightly acted upon by hydrochloric or sul-
phuric acid. It is best dissolved by adding a little concen-
trate nitric acid and then an equal volume of water and
heating if necessary.
A solution of the nitrate Pb{NO^^ may be made by dis-
solving about 3 grams of the solid lead nitrate in 100 cubic
* The reason for this is that sulphides of some of the metals are not
precipitated from acid solutions, but are precipitated from alkaline
ones. Ammonium sulphide, being a strong alkali, renders the solution
alkaline, and the precipitate is formed.
§ 10 QUALITATIVE ANALYSIS. 15
centimeters of water and adding a drop or two of nitric
acid.
30, Reactions. — A lead solution gives the following
reactions :
1. Ammonium hydrate precipitates white lead hydrate
Pb{OH)^^ which is insoluble in excess of the reagent.
2. Sodium hydrate precipitates white lead hydrate
Pb{OH)^^ which is easily soluble in excess of the reagent,
forming a solution of Pb{ONa)^,
3. Ammonium carbonate precipitates white basic lead
carbonate of varying composition.
4. Sodium carbonate gives the same precipitate as ammo-
nium carbonate.
6. Hydrogen sulphide precipitates black lead sulphide
PbS^ which is insoluble in dilute acids and alkalies when
cold, but is dissolved in boiling dilute nitric acid. Hot con-
centrate nitric acid converts it into white insoluble lead
sulphate. If we wish to obtain this white sulphate, there
must be no liquid present to dilute the acid.
6. Ammonium sulphide gives the same reactions as
hydrogen sulphide.
7. Hydrochloric acid precipitates white lead chloride
PbCl^^ which is slightly soluble in cold, and readily soluble
in hot, water. If this hot solution be allowed to cool, the
lead chloride separates in long, white crystals.
8. Sulphuric ^^/^ precipitates white lead sulphate PbSO^,
which is nearly insoluble in dilute acids, but may be dissolved
by adding tartaric acid and then a slight excess of concentrate
ammonia, and heating.
9. Potassium chromate precipitates yellow lead chromate
PbCrO^^ which is soluble in sodium hydrate, from which solu-
tion it is reprecipitated by nitric acid.
10. Potassium iodide precipitates yellow lead iodide PbT^^
which is soluble in boiling water. Upon cooling, it sepa-
rates from this solution in yellow crystals.
11. Potassium cyanide precipitates white lead cyanide
Pb{CN)^, which is insoluble in excess of the reagent, but is
soluble in nitric acid.
16 QUALITATIVE ANALYSIS. § 10
MERCURY.
31. Mercury is a heavy, white liquid. It is but slightly
acted upon by hydrochloric or sulphuric acid, but dissolves
readily in nitric acid. It forms two series of compounds,
known as mercur^^^.y and mercur^'. When mercury is dis-
solved in the cold, in dilute nitric acid, if there is an excess of
mercury present, mercurous nitrate HgJl^NO^^ is obtained.
If it is dissolved in an excess* of hot concentrate nitric acid,
mercuric nitrate Hg{NO^^ is formed.
These solutions could be properly diluted and used for the
reactions, but it is better to make up solutions as directed
later.
MERCUROUS COMPOUNDS.
22, A solution for the mercurous reactions may be made
by adding to 4 grams of solid mercurous nitrate 100 cubic
centimeters of water, and about 1 cubic centimeter of dilute
nitric acid ; then add a few drops of metallic mercury, and
heat gently, if necessary. A high temperature must be
avoided, and some metallic mercury should remain in the
solution, or it is likely to be partly changed to a mercuric
compound.
33, Reactions. — A mercurous solution gives the follow-
ing reactions:
1. Ammonium hydrate precipitates black amido-mer-
curous nitrate Hg^NH^NO^ from this solution. The precip-
itate is insoluble in an excess of the reagent.
2. Sodium hydrate precipitates black mercurous oxide
HgJDy which is insoluble in an excess of the reagent.
* By an excess of a reagent is meant more than is required to accom-
plish a certain object. When we speak of precipitating a metal with
an excess of a certain reagent, we mean to use more of the reagent
than would be required to unite with the metal to form a precipitate.
To render an alkaline solution acid, with an excess of a certain acid,
we would use more of that acid than would be required to neutralize
the alkali. When we say that a precipitate is soluble in an excess of a
reagent, we mean that when more of the reagent than is required to
form the precipitate is added, it dissolves the precipitate at first
formed.
§ 10 QUALITATIVE ANALYSIS. 17
3. Ammonium carbonate gives a white precipitate, which
rapidly changes to gray, and finally to black, upon standing.
4. Sodium carbonate gives a white precipitate, more or
less colored with yellow, owing to the fact that mercurous
solutions nearly always contain small quantities of mercuric
compoimds The carbonate precipitates are not important
in determining mercurous compounds.
5. Hydrogen sulphide precipitates black mercuric sulphide
HgS together with some free mercury. The precipitate is
not dissolved by any dilute acid, but dissolves slowly in hot
concentrate hydrochloric acid, and readily in aqua regia.
In this and similar operations, where aqua regia is used as
a solvent, add to a small quantity of the substance a half-
dozen drops of concentrate nitric acid, and then from two to
three times as much concentrate hydrochloric acid, and heat
if necessary. This mixture of concentrate acids is known as
aqua regia. It acts as a powerful solvent, dissolving many
substances that are not attacked by ordinary acids. It is the
only solvent for gold and platinum.
Boiling concentrate nitric acid converts the black mercuric
sulphide into a white, insoluble compound. The same pre-
cautions must be taken as described in Art. 20, 5.
6. Hydrochloric acid precipitates white mercurous chlo-
ride Hg^Cl^y which is insoluble in cold dilute acids, is slightly
acted upon by hot concentrate acids, and is readily dissolved
by aqua regia. Ammonia converts this white chloride into
black amido-mercurous chloride HgJSfHjOL
7. Potassium chromate precipitates brick-red basic mer-
curous chromate, which dissolves with difficulty in nitric
acid.
8. Potassium iodide in very small quantities precipitates
yellowish-green mercurous iodide HgJ^. If a little more of
the reagent is added and it is allowed to stand, the precipi-
tate changes into metallic mercury and bright-red potassium
mercuric iodide HgT^{KI)^,
9. Sulphuric acid precipitates white mercurous sulphate
HgJSO^^ which is dissolved with some difficulty in nitric acid.
10. Stannous chloride ^ when added in a very small amount,
18 QUALITATIVE ANALYSIS. § 10
precipitates white mercurous chloride HgjCl^. A little more
of the reagent partly reduces this, giving a gray mixture of
mercurous chloride and metallic mercury. An excess of
stannous chloride reduces the whole to a dark-gray, almost
black, precipitate of finely divided metallic mercury. The
white precipitate is seldom seen, but the gray mixture usually
is formed at once.
11. Sulphurous acid precipitates gray metallic mercury.
12. Copper^ when placed in a mercurous solution, precip-
itates metallic mercury, which forms a gray coating on the
copper. This may be rendered bright by rubbing with a dry
cloth, and is driven off by heat.
MERCURIC COMPOUNDS.
24, The solution of mercuric nitrate, which is obtained
when mercury is dissolved in an excess of hot concentrate
nitric acid, may be used for the following reactions, after
having the excess of acid evaporated off, and being properly
diluted with water; or a solution for the purpose may be
made by diluting some of the mercuric-chloride solution used
as a reagent with a little more than its own volume of water
and adding 2 or 3 drops of hydrochloric acid. But it is best
to make up a solution for this purpose by dissolving about
2 grams of dry mercuric nitrate in 100 cubic centimeters of
water to which 2 or 3 drops of concentrate nitric acid have
been added.
35, Reactions. — A mercuric solution gives the following
reactions:
1. Ammoniuvi hydrate precipitates white amido- mercuric
nitrate HgNH^NO^, which is somewhat soluble in an excess
of the reagent, and is readily dissolved by acids.
2. Sodium hydrate precipitates a brown basic salt, if a
very small quantity of the reagent is used. If more of the
reagent is added, yellow mercuric oxide HgO is formed.
This is easily dissolved by warm dilute acids.
§ 10 QUALITATIVE ANALYSIS. 19
3. Ammonium carbonate produces a white precipitate,
which is soluble in ammonia and in acids.
4. Sodium carbonate precipitates a reddish-brown basic
carbonate, probably HgCO^^dHgO.
5. Hydrogen sulphide gives a white precipitate when a
very small amovmt of reagent is added. If we continue to
add the reagent, the precipitate changes to yellow, reddish-
brown, and finally to black HgS. The white precipitate at
first formed is 2HgSjf/g(N0^)^, and this mixed with the
black HgS, in varying proportions, probably causes the inter-
mediate colors. The black HgS is insoluble in alkalies, and
in the acids used separately, but is dissolved by aqua regia.
6. Ammoniu7n sulphide gives the same precipitate as
hydrogen sulphide.
7. Potassium iodide precipitates red mercuric iodide Hgl^,
which is soluble in excess of the reagent.
8. Stannous chloride precipitates, at first, white mer-
curous chloride Hg^Cl^, An excess of the reagent reduces
this to gray metallic mercury.
9. Copper precipitates the mercury from mercuric solu-
tions the same as from mercurous ones.
COPPER.
36, Copper is a rather hard metal, with a peculiar red
color. It is malleable and ductile, and fuses with difficulty.
It is scarcely attacked by hydrochloric or sulphuric acid, but
is readily dissolved in nitric acid. A good solution for the
following reactions is made by dissolving from 1 ^ to 2 grams
of copper-sulphate crystals CuSO^.bH^Oin 100 cubic centi-
meters of water, and adding a drop or two of dilute sulphuric
acid.
37, Reactions. — A copper solution gives the following
reactions:
1. Ammonium hydrate precipitates a light-blue basic
compound, which is very soluble in excess, giving the
20 QUALITATIVE ANALYSIS. g 10
solution a deep-blue color, owing to the formation of a
soluble basic copper-ammonium sulphate.
2. Sodium hydrate precipitates light-blue copper hydrate
Cu(pil)^, which is insoluble in an excess of the reagent, but
soluble in ammonia and in acids. The precipitate is changed
by boiling into black, hydrated copper oxide, probably
2CuO,Cu(OH\.
3. Ammonium carbonate gives the same reaction as
ammonium hydrate.
4. Sodium carbonate precipitates blue basic copper car-
bonate CuCO^,Cu{OH)^y which is converted into black,
hydrated copper oxide by boiling.
6. Hydrogen sulphide precipitates black copper sulphide
CuS, which is easily soluble in warm nitric acid or potas-
sium cyanide,
G. Ammonium sulphide gives the same precipitate as
hydrogen sulphide.
7. Potassium cyanide precipitates greenish-yellow copper
cyanide Cu{CN)^, which is easily soluble in excess of the
reagent, forming a colorless solution. The copper is not
precipitated from this solution by hydrogen sulphide.
8. Potassium fcrrocyanide precipitates reddish-brown
copper fcrrocyanide Cu^Fe{CN)^, which is insoluble in dilute
acids.
9. If a small piece of solid copper chloride, or a drop of
the solution, supported on the loop of a platinum wire, be
held in the flame of a Bunsen burner, it imparts a blue color
to the flame, while the other volatile compounds of copper
color the flame green.
10. Iron^ when placed in a copper solution, slowly becomes
coated with the copper. If the solution is strong and slightly
acid, this action becomes quite rapid.
CADMIUM.
28. Cadmium is a white, rather soft metal, which easily
fuses on the charcoal before the blowpipe, depositing a
brown incrustation of the oxide CdO^ which is volatile, and
§ 10 QUALITATIVE ANALYSIS. 21
may be driven from place to place on the charcoal by direct-
ing the blowpipe flame upon it. Cadmium is slowly dis-
solved in hydrochloric or sulphuric acid, but is much more
readily dissolved by nitric acid, giving a solution of cadmium
nitrate Cd{NO^^. This solution may be used for the reac-
tions, after boiling off the excess of acid and diluting with
water, but it is better to make a solution for this purpose by
dissolving about 2 grams of cadmium nitrate crystals in 100
cubic centimeters of water and adding a drop of nitric acid.
29, Reactions. — A cadmium solution gives the follow-
ing reactions:
1. Ammonium hydrate does not usually give a precipitate
in ordinary cadmium solutions, but if a single drop of dilute
ammonia is added to a rather strong neutral solution, a white
precipitate of cadmium hydrate Cd{OH)^ is obtained. This
precipitate is very soluble in ammonia, and its formation is
prevented by the presence of ammonium salts.
2. Sodium hydrate precipitates white cadmium hydrate
Cd{OH)^, which is insoluble in excess of the reagent.
3. Ammonium carbonate precipitates white cadmium car-
bonate CdCO^^ which is quite readily dissolved in an excess
of the ordinary reagent, owing to the ammonia which it con-
tains. The precipitate would be but slightly attacked by the
carbonate alone.
4. Sodium carbonate precipitates white cadmium carbon-
ate CdCO^y which is insoluble in excess of the reagent, but
soluble in ammonia, potassium cyanide, and acids. Heating
the solution aids in the formation of the precipitate.
5. Hydrogen sulphide precipitates yellow cadmium sul-
phide CdS^ which is insoluble in cold dilute acids, ammonia,
ammonium sulphide, and potassium cyanide, but is dissolved
by boiling dilute acids.
6 Ammonium sulphide gives the same reaction as hydro-
gen sulphide.
7. Potassium chromate precipitates yellow basic cadmium
chromate, which is insoluble in sodium hydrate, but is dis-
solved by nitric acid.
i2 QUALITATIVE ANALYSIS. § 10
8. Potassium cyamdc docs not ordinarily produce a pre-
cipitate, but forms a soluble double cyanide of potassium
and cadmium Cd(CN)J(^KCN)^^ from which yellow cadmium
sulphide (CdS) may be precipitated by hydrogen sulphide.
BI8MUTH.
30, Bismuth is a rather hard, brittle metal, having a
white color with a sli^^htly reddish tinge. It fuses easily on
the charcoal before the blowpipe, forming a metallic globule,
and depositing a yellow incrustation of bismuth oxide Bi^O^,
It is not attacked by dilute hydrochloric and sulphuric acids,
but is readily dissolved in nitric acid, forming bismuth
nitrate Bi{NO^^. This solution may be used for the reac-
tions, after diluting with water and keeping just enough
nitric acid present to hold the salt in solution; or, we may
make a solution for the purpose by dissolving about 2 grams
of bismuth nitrate in about 1 cubic centimeter of dilute
nitric acid, and 15 or 20 cubic centimeters of water. If this
does not form a clear solution after heating, add nitric acid,
a few drops at a time, imtil it clears up. Then dilute to 100
cubic centimeters with water. If a precipitate forms during
dilution, add just nitric acid enough to dissolve it.
31, Reactions. — A bismuth solution gives the following
reactions :
1. Ainmoniuin hydrate precipitates white bismuth oxy-
hydrate BiOOH, which is insoluble in excess, but soluble
in warm hydrochloric or nitric acid.
2. Sodium hydrate gives the same reaction as ammonium
hydrate.
3. Ammonium carbonate precipitates white basic bismuth
carbonate Bi^O^CO^y which is insoluble in excess of the
reagent.
4. Sodium carbonate gives the same reaction as ammo-
nium carbonate.
5. Hydrogen sulphide precipitates dark-brown bismuth
sulphide Bi^S^^ which is insoluble in cold dilute acids, and
§ 10 QUALITATIVE ANALYSIS. 23
in ammonium sulphide, but is dissolved by boiling nitric
acid.
6. Ammonium sulphide gives the same reaction as hydro-
gen sulphide. In concentrate solutions these precipitates
look almost black.
7. Potassium chromate precipitates yellow basic bismuth
chromate Bi^O{CrO^^, which is insoluble in sodium hydrate,
but readily soluble in nitric acid; hence, in solutions which
contain much free acid, no precipitate is formed.
8. Stannous chloride^ in an excess of sodium hydrate, pre-
cipitates black bismuth oxide Bifi^, To get this precipitate,
add sodium hydrate to a little stannous chloride until the
precipitate at first formed is dissolved in excess. Then, to
this solution, add a little of the bismuth solution, a drop at a
time.
9. Water y in a large quantity, precipitates white bismuth
oxynitrate BiONO^ from solutions that are not too strongly
acid. To perform this operation, a test tube is nearly filled
with water, and 2 or 3 drops of the bismuth solution are
added to it. If this solution is not too strongly acid, a pre-
cipitate will be formed almost immediately. If it does not
appear in a few seconds, a little ammonium chloride should
be added, when, if the solution does not contain a large
amount of acid, a precipitate will form.
ANTIMOISTT.
33, Antimony is a hard, brittle, bluish-white metal, which
easily fuses on the charcoal before the blowpipe, depositing
a white volatile incrustation of antimony oxide Sbfi^^ while
dense white fumes of this oxide are given off.
Antimony is oxidized but is not dissolved by nitric acid,
and hydrochloric acid scarcely attacks it at all, but it is
dissolved in aqua regia. A solution for the following reac-
tions is best made by dissolving a trifle more than a gram
of the dry antimony chloride SbCl^ in hydrochloric acid and
water and diluting to 100 cubic centimeters. Just enough
24 QUALITATIVE ANALYSIS. § 10
acid should be added to dissolve the salt, and hold it in
solution.
33. Reactions. — An antimony solution gives the follow-
ing reactions:
1. Ammonium hydrate precipitates white antimonious
oxyhydrate SbOOH^ which is insoluble in excess of the
reagent.
2. Sodium hydrate precipitates white antimonious oxy-
hydrate SbOOHy which is easily dissolved by an excess of
the reagent.
3. Ammonium carbonate precipitates white antimonious
oxyhydrate SbOOH^ which is but slightly soluble in excess
of the reagent.
4. Sodium carbonate gives the same reaction as ammonia.
5. Hydrogen sulphide precipitates orange-red antimonious
sulphide Sb^S^, which is insoluble in cold dilute acids, but
soluble in hot concentrate hydrochloric acid, sodium hydrate,
or ammonium sulphide.
6. A^nmonium sulphide precipitates orange-red antimo-
nious sulphide SbJS^^ which is soluble in excess of the
reagent. From this solution the antimonious sulphide is
reprecipitated by hydrochloric acid.
7. Zinc^ when placed in a strongly acid solution of anti-
mony, precipitates the antimony as a black powder. If a
piece of platinum foil is placed in the solution in contact
with the zinc, the antimony will be deposited upon it, making
a black stain. This precipitate is insoluble in hydrochloric
acid.
8. Water y in large excess, precipitates white antimonious
oxychloride SbOCl, This precipitate is obtained in the same
manner as the precipitate which water gives with bismuth
(see Art 31, 9).
AKSEXIC.
34. Arsenic is a dark -gray, brittle solid, which easily
volatilizes on the charcoal before the blowpipe, without
fusing, yielding a white incrustation, and white fumes of
§ 10 QUALITATIVE ANALYSIS. 25
the oxide As^O^, which have a characteristic garlic odor.
Care must be taken not to inhale large quantities of these
fumes, as they are poisonous.
Arsenic is not readily dissolved by any single acid, but
aqua regia dissolves it easily, forming arsenic acid. It forms
two oxides, As^O^ and As^O^, which are acid^ while oxides
of the metals are basic. There are two series of compounds:
arsenites, which are arseni^;/^ compounds; and arsenates,
which are arsen/r compounds.
ARSENIOU8 COMPOUNDS.
35, A solution of sodium arsenite is the best for the
general reactions. It is made by dissolving about 1 gram
of sodium arsenite Na^HAsO^ in 100 cubic centimeters of
water.
36, Reactions. — An arsenious solution gives the follow-
ing reactions:
1. Hydrogen sulphide gives no precipitate if the solution
is neutral, but generally gives the solution a yellow color.
If a little hydrochloric acid is now added, a yellow precipi-
tate of arsenious sulphide As^S^ is at once formed, which
is soluble in ammonia, ammonium sulphide, or ammonium
carbonate, but is insoluble in hydrochloric acid, even when
concentrate.
2. Ammonium sulphide gives no precipitate in neutral or
alkaline solutions, but if a little hydrochloric acid is added to
the solution, yellow arsenious sulphide AsJS^ is formed, which
is readily soluble in excess of {NH^JS^ or in ammonia, but
is insoluble in hydrochloric acid.
3. Silver nitrate gives a slight, almost white precipitate
in neutral solutions, but, if a little ammonia is added, light-
yellow silver arsenite Ag^AsO^ is formed. A little more
ammonia dissolves the precipitate, as will also nitric acid.
4. Copper sulphate precipitates green copper arsenite
CuHAsO^^ which is soluble in acids and in ammonia.
26 QUALITATIVE ANALYSIS. § 10
5. Copper^ when placed in an arsenious solution to which
considerable hydrochloric acid has been added, becomes
coated with a gray film of copper arsenide Cu^As^ upon
boiling.
ARSENIC SOLUTIONS.
37. A good solution for the arsenic reactions is made
by dissolving about 1 gram of sodium arsenate Na^HAsO^ in
100 cubic centimeters of water.
38. Reactions. — An arsenic solution gives the following
reactions:
1. Hydrogen sulphide gives no precipitate with neutral
solutions, but if considerable hydrochloric acid is added, the
hydrogen sulphide slowly reduces the arsenic solution to
arsenious, and yellow arsenious sulphide AsJS^ is formed.
This reaction is greatly helped by heating the solution. If
the hydrogen-sulphide solution is very weak, it reduces the
solution slowly, so that the reaction only takes place after
some time, or may even fail entirely; but when a current
of hydrogen-sulphide gas is led through the solution, the
reaction takes place immediately. The AsJS^ is soluble in
ammonia and ammonium sulphide; but a little free sulphur,
thrown out* during the reduction, usually remains in the
solution, giving it a milky appearance. From this solution
As^S^ is reprecipitated by hydrochloric acid.
2. Ammonium sulphide gives no precipitate with neutral
solutions, but if sufficient hydrochloric acid is added, a yel-
low precipitate of arsenic sulphide AsJS^ is formed.
3. Silver nitrate^ when added to neutral arsenate solu-
tions, produces a characteristic reddish-brown precipitate of
silver arsenate Ag^AsO^, which is soluble in nitric acid and
in ammonia.
4. Magnesium sulphate^ under proper conditions, precipi-
tates white crystalline, magnesium-ammonium arsenate
MgNH^AsO^y^Hfi, which is soluble in nitric acid. To get
* The term "thrown out** means that an element is liberated from
its compounds, and remains undissolved in a solution.
§ 10 QUALITATIVE ANALYSIS. 27
this precipitate, a little magnesium-sulphate solution is placed
in a test tube, and precipitated with an excess of ammonia.
Just enough ammonium chloride is added to dissolve the pre-
cipitate thus formed, and a little of this solution is added to
a little arsenate solution in another test tube. If the solu-
tions are dilute, the precipitate forms slowly, but is hastened
by vigorous shaking.
TIN.
39. Tin is a soft, white, malleable metal that fuses easily
on the charcoal before the blowpipe, forming a metallic
globule and a slight, white incrustation. It is not readily
dissolved in the acids separately, but is dissolved in aqua
regia, forming a mixture of stannous and stannic chlorides.
Hot concentrate hydrochloric acid slowly dissolves it to a
solution of stannous chloride SnCL,
STANNOUS COMPOUNDS.
40. A solution for the stannous reactions is conveniently
made by adding 5 cubic centimeters of concentrate hydro-
chloric acid and 15 cubic centimeters of water to 1^ grams of
stannous chloride and heating till it dissolves. If the solu-
tion appears milky after heating, add 5 cubic centimeters of
hydrochloric acid and heat again, when it will clear up.
Dilute this solution to 100 cubic centimeters with water.
41. Reactions. — A stannous solution will give the fol-
lowing reactions :
1. A mmonium hydrate precipitates.white stannous hydrate
Sn{OH)^^ which is insoluble in excess of the reagent.
2. Sodium hydrate precipitates white stannous hydrate
Sn{OH)^^ which is soluble in excess of the reagent.
3. Ammonium carbonate precipitates white stannous
hydrate Sn{OH)^, which is insoluble in excess of the reagent.
4. Sodium carbonate gives the same reaction as ammo-
nium carbonate.
28 QUALITATIVE ANALYSIS. § 10
6. Hydrogen sulphide^ when added to solutions contain-
ing much free acid, at first colors the liquid brown, but if
more is added, a brown precipitate of stannous sulphide SnS
is formed. If but little free acid is present, the brown pre-
cipitate is formed at once.
6. ^;;/;«^;//«;« .y//^///^^ precipitates brown stannous sul-
phide SnS, The brown stannous sulphide precipitated by-
hydrogen or ammonium sulphide is soluble in yellow ammo-
nium sulphide. Hydrochloric acid precipitates yellow stan-
nic sulphide SnS^ from this solution. Yellow ammonium
sulphide is made by adding sulphur, in the form of powder,
to common ammonium sulphide and shaking till it is dis-
solved. It is a polysulphide of varying composition.
43. Stannous chloride acts as a reducing agent; that is,
it tends to change reducible compounds to a lower state of
oxidation, while it is changed to a stannic compound. Its
reaction with mercuric compounds (Art. 35, 8) is a good
example of this.
STANXIC COMPOUNDS.
43. A solution of stannic chloride SnCl^ may be used
for the stannic reactions. It is prepared by dissolving about
1^ grams of stannous chloride in 5 cubic centimeters of con-
centrate hydrochloric acid and 15 cubic centimeters of water.
Heat this to boiling and add potassium chlorate, a little at a
time, until the solution becomes distinctly yellow. Then
boil till the solution becomes clear, and the potassium chlo-
rate will have oxidized the stannous to stannic chloride.
After diluting to 100 cubic centimeters the solution is ready
for use.
44. Reactions. — A stannic solution gives the following
reactions :
1. Ammonium hydrate precipitates white stannic oxyhy-
drate, generally called metastannic acid SnO{OH)^, which
is insoluble in excess of the reagent
§ 10 QUALITATIVE ANALYSIS. 29
2. Sodium hydrate precipitates white stannic oxyhydrate
SnO{OH)^^ which is soluble in excess of the reagent and
in acids.
3. Ammonium carbonate precipitates white stannic oxy-
hydrate SnO{OH)^^ which is insoluble in excess of the
reagent, but soluble in acids.
4. Sodium carbonate gives the same reaction as ammo-
nium carbonate.
5. Hydrogen sulphide precipitates light-yellow stannic
sulphide SnS^y which is soluble in hot concentrate hydro-
chloric acid and in ammonium sulphide. From the solution
in ammonium sulphide, it is reprecipitated by hydrochloric
acid.
6. Ammonium sulphide precipitates yellow stannic sul-
phide SnS^^ which is easily dissolved by an excess of the
reagent. Hydrochloric acid reprecipitates it from this solu-
tion.
7 Zinc precipitates all the tin from both stannous and
stannic solutions that contain an excess of hydrochloric acid,
in the form of a dark-gray powder.
45. All compounds of tin, when mixed with sodium car-
bonate and placed on the charcoal before the blowpipe, are
easily reduced to a bright metallic globule.
IRON.
46. Iron is a gray, hard, tenacious metal that is only
fused at very high temperatures. It corrodes quite readily
in the air, forming oxides. It forms two series of com-
pounds, known as ferrous and ferric. It is easily dissolved
by hydrochloric, sulphuric, or nitric acid.
FERROUS COMPOUNDS.
47. For the reactions, a solution of ferrous sulphate is
the best. It is made by dissolving about 2 grams of the
crystals in 100 cubic centimeters of water to which half a
30 QUALITATIVE ANALYSIS. § 10
cubic centimeter of concentrate sulphuric acid is added.
This solution should be used when fresh, as all ferrous solu-
tions are oxidized to ferric in the air.
48. Reactions. — A ferrous solution gives the following
reactions:
1. Ammonium hydrate precipitates green ferrous hydrate
Fc{OH)^, Upon standing in the air for some time, this is
partially oxidized and assumes a reddish-brown color.
2. Sodium hydrate precipitates light-green ferrous hydrate
Fe{OH)^, which is insoluble in excess. On standing in the
air, its color changes to dark green and finally to reddish
brown, owing to oxidation to ferric hydrate Fe(OH).^ by the
oxygen of the air.
3. Ammonium carbonate precipitates white ferrous car-
bonate FeCO^y which almost immediately assumes a green
color, and upon standing in the air becomes a reddish brown,
owing to the formation of ferric hydrate.
4. Sodium carbonate gives the same reaction as ammo-
nium carbonate.
5. Hydroge7i sulphide does not precipitate iron or any of
the following metals from acid solutions. Ferric solutions
frequently, and some of the others more rarely, throw out
free sulphur, giving the solution a milky appearance.
6. A mmonium sulphide precipitates black ferrous sulphide
FeS, easily dissolved by hydrochloric or suT^huric acid.
7. Potassium ferrocyanide precipitates blue potassium
ferrous ferrocyanide K^Fe^'\CN)^. >
8. Potassium ferricyanide precipitates deep-blue ferrous
fcrricyanide Fe^"Fe,^"\CN)^^^ which is insoluble in dilute
acids.
FERRIC SOLUTIONS.
49. Ferric solutions may be obtained by dissolving
metallic iron in nitric acid, by oxidizing a ferrous salt by
means of an oxidizing agent, such as nitric acid or potassium
chlorate, or by dissolving a ferric s-ilt, sncli as ferric chloride,
in water, with the addition of a few drops of acid. A good
§ 10 QUALITATIVE ANALYSIS. 31
way to prepare a solution for the reactions is to dissolve
about 1^ grams of ferrous sulphate crystals in from 25 to
50 cubic centimeters of water, and heat to boiling. To this
boiling solution add a few drops of concentrate nitric acid,
and continue the boiling till the solution becomes a clear
yellow, adding a few more drops of nitric acid, if necessary,
to produce this change. The nitric acid completely oxidizes
the iron in hot solutions.
50. Reactions.— A ferric solution gives the following
reactions:
1. Ammonium hydrate precipitates reddish-brown ferric
hydrate Fc(OH)^, which is insoluble in excess of the
reagent, but soluble in acids.
2. Sodium hydrate gives the same reaction as ammonium
hydrate.
3. A mmonium carbonate precipitates reddish-brown ferric
hydrate Fe{OH)^^ and CO^ is set free. The precipitation is
aided by boiling.
4. Sodium carbonate gives the same reaction as ammo-
nium carbonate.
5. Ammonium sulphide reduces ferric compounds to
ferrous, and precipitates black ferrous sulphide FeS. Hydro-
chloric acid dissolves this readily, leaving the free sulphur,
thrown out during reduction, in the solution.
6. Potassium ferrocyanide precipitates dark -blue ferric
ferrocyanide Fe^"Fe^'{CN)^^^ which is insoluble in dilute
acids.
7. Potassium sulphocyanide imparts a deep-red color to
ferric solutions, due to the formation of soluble ferric sulpho-
cyanide Fe{SCN)^, This reaction is very delicate, mere
traces of a ferric compound giving a distinct color.
ALUMINUM.
51. Aluminum, or aluminium, is a white, very light,
malleable metal, that is scarcely acted on by nitric or sul-
phuric acid, but is quite easily dissolved in hydrochloric acid.
32 QUALITATIVE ANALYSIS. § 10
It is only fused at very high temperatures, and is very hard
to reduce from its compounds. Its valence is always III. A
solution for its reactions may be made by dissolving about
2^ or 3 grams of pure alum AlK^{SO^^,\lHfi in 100 cubic
centimeters of water and a drop or two of concentrate sul-
phuric acid.
52. Reactions. — An aluminum solution gives the fol-
lowing reactions :
1. Ammonium hydrate precipitates white aluminum
hydrate Al{OH)^^ which is insoluble in an excess of the
reagent, but is easily dissolved by acids.
2. Sodium hydrate precipitates white aluminum hydrate
Al{OH)^, which is soluble in an excess of the reagent.
From this solution aluminum hydrate is reprecipitated by
ammonium chloride, especially when boiled, but hydrogen
sulphide does not produce a precipitate in this solution.
3. Ammonium carbonate precipitates white aluminum
hydrate Al{OH)^^ which is insoluble in an excess of the pre-
cipitant, but is readily, dissolved by acids.
4. Sodium carbonate precipitates white aluminum hydrate
Al{OH)^, which is very slightly soluble in an excess of the
reagent.
6. Ammonium sulphide precipitates white aluminum
hydrate. To see this precipitate well, care must be taken.
A small quantity of the solution is placed in a test tube, and
a few drops of the reagent are added, allowing it to run
down the side of the inclined tube so that it will not mix
with the solution, but remain as a separate layer on the top.
The precipitate appears where the two liquids meet.
6. Sodium phosphate precipitates white aluminum phos-
phate AlPO^y which is insoluble in acetic add.
CHROMIUM.
53. Chromium is a hard, heavy metal, with a strong
affinity for oxygen. When acting as a base, it appears to be
trivalent, but it takes more oxygen, forming an acid radical.
§ 10 QUALITATIVE ANALYSIS. 33
A solution for the reactions may be made by dissolv-
ing about 2 grams of chrome alum CrK{SO^^,VlHfi in
100 cubic centimeters of water to which a drop or two of
sulphuric acid is added.
54. Reactions. — A solution of chromium gives the fol-
lowing reactions:
1. Ammonium hydrate precipitates greenish -blue chro-
mium hydrate Cr(OH)^, which is slightly soluble in excess
of the reagent. The part that diissolves gives the solution a
reddish color. It may be reprecipitated by boiling off the
excess of ammonia.
2. Sodium hydrate precipitates greenish-blue chromium
hydrate Cr{OH)^, which is soluble in excess of the reagent.
It may be reprecipitated from this solution by ammonium
chloride.
3. Ammonium carbonate precipitates greenish -blue basic
chromium carbonate of varying composition.
4. Sodium carbonate gives the same reaction as ammo-
nium carbonate.
5. Ammonium sulphide precipitates greenish-blue chro-
mium hydrate Cr{OH)^y which is very slightly soluble in an
excess of the reagent.
66. Chromium compounds impart a yellowish-green color
to the borax bead when hot, which changes to an emerald
green upon cooling. To get this bead, heat the loop of the
platinum wire and quickly dip it into borax, which will cling
to the heated wire. This is then heated in the hottest part
of the flame of a Bunsen burner, or in the blowpipe flame,
until it is thoroughly fused and looks like a glass bead. It is
now touched to a very small piece of a chromium compound,
which will adhere to the soft, hot bead, and is again placed
in the hottest part of the flame of the burner or the blow-
pipe until it is thoroughly fused. If the proper amount of the
substance was taken, the bead will now assume the green color.
The student must learn from experience the proper amount
to take, but should guard against taking too large a quantity.
A little of one of the chromium precipitates may be tested
34 QUALITATIVE ANALYSIS. § 10
on the bead in this way, or enough of a rather strong chro-
mium solution will adhere to the bead, especially if the bead
is dipped into it several times, to give it a good color.
66. All chromium compounds, when fused on the plati-
num foil with sodium carbonate and potassium nitrate, are
oxidized to chromates. To perform this operation, bend the
platinum foil into the form of a spoon and place upon it about
1 cubic centimeter of dry sodium carbonate, and a little more
than half as much potassium nitrate. To this add a piece
of the wet chromium precipitate about half as large as a pea,
or a much smaller piece of the dry compound. By means of
the forceps, hold this in the hottest part of the Bunsen flame
till it is thoroughly fused. When cool, place in a small
beaker, or other convenient vessel, and dissolve off the fusion
in equal parts of water and acetic acid, using only such a
quantity as is necessary to dissolve it, and boil till all carbon
dioxide is driven off. The chromium exists in the solution
as an alkaline chromate, and gives the solution a slight yel-
low color. From this solution, lead acetate precipitates
yellow lead chromate, which is easily soluble in sodium
hydrate.
COBALT.
57. Cobalt is a steel-gray, rather hard, malleable metal,
that is only fused at very high temperatures. It is slowly
dissolved in hydrochloric or sulphuric acid, but dissolves
readily in nitric acid. The solutions and crystalline salts are
red, but the anhydrous salts are blue. A solution of the
nitrate is best used for the reactions. It may be made by
dissolving about 2 grams of the crystals, Co(NO^)^y6H^O, in
100 cubic centimeters of water and adding a drop or two of
nitric acid.
58. Reactions. — A cobalt solution gives the following
reactions :
1. Aminonmm hydrate precipitates a blue basic cobalt
compound, which easily dissolves in excess of reagent to a
§ 10 QUALITATIVE ANALYSIS. 35
brown solution. The presence of much free acid, or of
ammonium salts, prevents the precipitation.
2. Sodium hydrate precipitates a blue basic compound
which is insoluble in excess. If the precipitate in the excess
of reagent be boiled, it changes to a pale-red precipitate of
cobalt ous hydrate Co{OH)^. This soon changes to brown,
owing to the formation of cobaltic oxide Cofi^.
3. Amviomum carbonate precipitates a reddish basic
cobalt carbonate, which is soluble in excess of the reagent,
forming a red solution.
4. Sodium carbonate precipitates a reddish basic cobalt
carbonate, which is insoluble in an excess of the reagent.
5. Ammonium sulphide precipitates black cobalt sulphide
CoSy which is but very slightly soluble in hydrochloric acid,
especially if it has been precipitated at a boiling tempera-
ture, but is dissolved by hot nitric acid.
6. Potassium nitrite gives a yellow precipitate, which is
probably potassium cobaltic nitrite, from acetic-acid solu-
tions. To get this precipitate, add ammonia to the solution
till a slight precipitate is formed. Dissolve this in a slight
but distinct excess of acetic acid, and to this solution add a
stick of the dry potassium nitrite from 1 to 2 inches long,
and stand aside for some time in a rather warm place. The
cobalt is completely precipitated from a strong solution in a
short time, and somewhat more slowly from a dilute one.
This is an important reaction, as it serves to separate
cobalt and nickel, the cobalt being all precipitated, while the
nickel remains in solution. Fresenius gives the probable
composition of the precipitate as %K^Co{NO,^^,ZHfi,
59. Compounds of cobalt impart a deep-blue character-
istic color to the borax bead, made as described under
** Chromium," Art. 55.
l>fICKEIi.
60. Nickel is a bright, hard, malleable metal with a
yellowish -white color. It is very hard to fuse, and is not
oxidized in the air at ordinary temperature, but slowly
36 QUALITATIVE ANALYSIS. § 10
oxidizes when ignited. It is slowly dissolved in hydrochloric
or sulphuric acid, and very readily in nitric acid.
A solution of the nitrate may be used for the reactions.
It is made by dissolving about 2 grams of the crystals
Nt{N0^)^,6H^0 in 100 cubic centimeters of water, and add-
ing a drop or two of nitric acid.
61. Reactions. — A nickel solution gives the following
reactions:
1. Ammonium hydrate gives a slight greenish precipitate,
which is very soluble in excess to a deep-blue solution. If
ammonium salts are present, or if the solution contains much
free acid, no precipitate is formed, but the blue solution
appears at once.
2. Sodium hydrate precipitates green nickel hydrate
Nt{OH)^, which is insoluble in excess of the reagent, but is
soluble in ammonium chloride.
3. Ammonium carbonate precipitates light-green basic
nickel carbonate, which is soluble in excess of the reagent.
4. Sodium carbonate precipitates light-green basic nickel
carbonate of variable composition, which is insoluble in
excess of the reagent.
5. Ammonium sulphide precipitates black nickel sulphide
NiS^ which is but slightly soluble in cold dilute hydrochloric
acid, but is readily dissolved by warm nitric acid.
ZINC.
63. Zinc is a bluish-white metal that tarnishes in the
air, owing to the formation of a thin coat of basic zinc car-
bonate. It is rather brittle and is fusible. On the charcoal
before the blowpipe, it fuses and deposits an incrustation of
zinc oxide ZnO^ which is yellow when hot and white when
cold.
Chemically pure zinc is only slowly attacked by hydro-
chloric or sulphuric acid, but is dissolved in nitric acid.
Common zinc, which contains small quantities of other
§ 10 QUALITATIVE ANALYSIS. 37
metals, dissolves readily in hydrochloric or sulphuric acid,
and is largely used in the laboratory for the preparation of
hydrogen, which is accomplished by dissolving zinc in one of
these acids.
A solution for the zinc reactions is conveniently prepared by
dissolving about 2 or 2^ grams of zinc sulphate ZnSO^y^Hfi
in 100 cubic centimeters of water to which is added a drop of
dilute sulphuric acid.
63. Reactions. — A zinc solution gives the following
reactions:
1. Ammonium hydrate precipitates white zinc hydrate
Zn{OH)^^ which is easily soluble in excess of the reagent.
From solutions containing much free acid or ammonium
salts the zinc is not precipitated by ammonia.
2. Sodium hydrate precipitates white zinc hydrate
Zn{OH)^y which is soluble in excess of the reagent. From
this solution the zinc is not reprecipitated by ammonium
chloride, but is reprecipitated by hydrogen sulphide.
3. Ammonium carbonate precipitates white basic zinc
carbonate, which is soluble in excess of the reagent.
4. Sodium carbonate precipitates white basic zinc car-
bonate, which is only slightly soluble in excess.
5. Ammonium sulphide precipitates white zinc sulphide
ZnS^ which is insoluble in excess, but easily soluble in
hydrochloric, sulphuric, and nitric acids. The precipitation
is hastened by the presence of ammonium chloride, and also
by warming.
6. Potassium ferrocyanide precipitates white zinc ferro-
cyanide ZnJFe{CN)^, which is insoluble both in acids and in
ammonia.
MANGAKESE.
64. Manganese is a dull-gray, very hard, brittle metal.
It only fuses at very high temperatures. It is rapidly
oxidized in moist air or water, and is readily dissolved by
acids.
A solutipu of manganese sulphate may be used for the
38 QUALITATIVE ANALYSIS. § 10
reactions. It is prepared by dissolving from 2 to 3 grams of
the crystals, MnSO^.lH^O, in 100 cubic centimeters of
water, and adding a drop or two of dilute sulphuric acid.
65. Reactions. — A manganese solution gives the fol-
lowing reactions;
1. Ammoniiun hydrate precipitates white manganese
hydrate Mn(pH)^ from solutions that do not contain much
free acid or ammonium salts. This rapidly changes to
brown MnOOH. If much ammonium chloride is present,
it prevents the immediate precipitation of the manganese,
but after oxidizing it sometimes separates slowly from the
solution.
2. Sodium hydrate precipitates white manganese hydrate
Mn{OH)^^ which is insoluble in excess, but slightly soluble
in ammonium chloride. Upon exposure to air the white
precipitate changes to brown, owing to the oxidation of the
manganese to MnOOH,
3. Ammonium carbonate precipitates white manganese
carbonate M?tCO^ In the air this precipitate slowly changes
to brown.
4. Sodium carbonate precipitates white manganese car-
bonate MnCO^^ which is insoluble in excess of the reagent,
but when freshly precipitated is soluble in ammonium
chloride.
5. Ammonium sulphide precipitates flesh-colored man-
ganese sulphide MnS, which is easily dissolved by acids.
6. If, to about half a cubic centimeter of lead dioxide in
a test tube, we add a few drops of manganese solution, and
then about 8 cubic centimeters of an acid made by mixing
equal volumes of concentrate nitric acid and water, and boil
the whole for about two minutes, permanganic acid HMnO^
is formed, which gives the liquid a distinct red color. This
may be seen as soon as the black insoluble matter has settled
to the bottom.
66. Manganese compounds impart an amethyst-red color
to the borax bead, when heated in the oxidizing flame. This
§ 10 QUALITATIVE ANALYSIS. 39
must be done as described under ** Chromium," Art. 55. If
this bead be reheated for some time in the reducing flame, it
loses its color, on account of the reduction of the manganese
to a colorless compound.
67. Compounds of manganese, when fused on platinum
foil with sodium carbonate and potassium nitrate, are oxidized
to manganates, and give a dark-green color to the fusion.
This should be done as described under ** Chromium,"
Art. 56.
BARIUM.
68. Barium compounds cannot be reduced on the char-
coal before the blowpipe, but when heated very high these
compounds become incandescent.
A good solution for the barium reactions is made by dis-
solving about 2 grams of barium chloride BaCl^ in 100 cubic
centimeters of water and adding a drop or two of dilute
hydrochloric acid.
69. Reactions. — A barium solution gives the following
reactions:
1. Afnmonuim hydrate does not give a precipitate with
barium, strontium, or calcium solutions.
2. Sodium hydrate does not give a precipitate from ordi-
nary barium solutions, but precipitates white barium hydrate
Ba^OH)^ from very strong solutions.
3. Ainmonium carbonate precipitates white barium car-
bonate Z^^COg, which is insoluble in ammonium chloride, but
soluble in hydrochloric acid. Heat aids the precipitation.
4. Sodium carbonate precipitates white barium car-
bonate BaCO^, which dissolves in hydrochloric acid with
effervescence.
5. Ammonium sulphide does not precipitate this or any
of the following metals.
6. Potassium chromate precipitates yellow barium chro-
mate, which is easily soluble in hydrochloric acid, but is
insoluble in sodium hydrate or acetic acid. From the hydro-
chloric-acid solution it is reprecipitated by ammonia.
40 QUALITATIVE ANALYSIS. § 10
7. Sulphuric acid precipitates white barium sulphate
BaSO^. The precipitate is formed immediately, and is
almost insoluble in all acids. A soluble sulphate may be
used instead of sulphuric acid, and the same result obtained.
Calcium sulphate precipitates barium sulphate from barium
solutions immediately.
8. Ammonium oxalate gives no precipitate in dilute solu-
tions, but in rather strong solutions it precipitates white
barium oxalate BaCfi^^ which is easily soluble in nitric,
hydrochloric, or acetic acid.
9. Sodium phosphate precipitates white hydrogen barium
phosphate HBaPO^ from neutral and alkaline solutions.
The precipitate is very soluble in hydrochloric, nitric, or
acetic acid, so that in a solution containing free acid, no
precipitate is formed. Such a solution may have the acid
neutralized by ammonia, after which it may be precipitated
by the phosphate.
70. All volatile barium compounds, as, for example, the
chloride, when brought into the flame, either in the solid or
liquid state, on the loop of a platinum wire, impart a charac-
teristic yellowish-green color to the flame.
STROISTTIUM.
71. Strontium is a brass-yellow metal, but is seldom seen
in the metallic form, owing to its great affinity for oxygen.
Its compounds can only be reduced to the oxide before the
blowpipe. At a high temperature this is luminous.
A solution for the wet reactions may be made by dissolving
about 2 grams of strontium nitrate in 100 cubic centimeters
of water to which a drop of nitric acid has been added.
72. Reactions. — A strontium solution gives the follow-
ing reactions :
1. Sodium hydrate precipitates, from moderately strong
solutions, white strontium hydrate Sr{OH)^, which is dis-
solved by adding water and boiling. In very dilute solu-
tions no precipitate is formed.
§ 10 '^ QUALITATIVE ANALYSIS. 41
2. Afnmoniunt carbonate precipitates white strontium
carbonate SrCO^^ which is only very slightly soluble in
ammonium chloride, but is soluble in hydrochloric, nitric, or
acetic acid. Warming aids in the precipitation.
3. Sodium carbonate gives the same precipitate as ammo-
nium carbonate.
4. Potassium ckromate precipitates yellow strontium
chromate SrCrO^ from rather strong neutral solutions. This
is easily dissolved by hydrochloric, nitric, or acetic acid, or
by a large amount of water, so that in dilute solutions, or
those containing much free acid, no precipitate is formed.
5. Sulphuric acid precipitates white strontium sulphate
SrSO^, which is very slightly soluble in water, so that in
very dilute solutions the precipitate does not appear imme-
diately. A saturated solution of calcium sulphate may be
used instead of sulphuric acid, in which case the precipitate
will appear after a few moments.
6. Sodium phosphate precipitates white hydrogen-stron-
tium phosphate HSrPO^ from neutral, and strontium phos-
phate SrJ^PO^^ from alkaline, strontium solutions. Both
are soluble in acids, so that in strongly acid solutions no
precipitate is formed.
7. Ammonium oxalate precipitates white strontium oxa-
late SrCfi^-t which is easily soluble in hydrochloric or nitric
acid, but only slightly soluble in acetic acid.
73. Strontium compounds that are volatile give a crim-
son color to the flame, when held in it on the loop of a plati-
num wire. The chloride is the most volatile of the ordinary
strontium compounds, so it is well to dip the substance into
hydrochloric acid just before placing it in the flame.
CALCIUM.
74. Calcium is a yellow metal, but on account of its
great affinity for oxygeh it is rare in the metallic state. Its
compounds can only be reduced to the oxide on the charcoal
42 QUALITATIVE ANALYSIS. g 10
before the blowpipe. This is infusible, and luminous at high
temperatures, giving what is l:nown as the calcium light.
A solution for the wet reactions may be prepared by dis-
solving about 2 grams of dry calcium chloride in 100 cubic
centimeters of water and adding a drop or two of hydro-
chloric acid.
75. Kcactlons. — A calcium solution gives the following
reactions :
1. Sodium hydrate precipitates white calcium hydrate
Ca{OH)^, which is slightly soluble in water. Hence, in very
dilute solutions no precipitate is formed.
2. Ammonium carbonate precipitates white calcium car-
bonate CaCO^, Heat aids the precipitation. The precipi-
tate is soluble in acids with effervescence.
3. Sodium carbonate precipitates white calcium carbonate
CaCO^^ which is easily dissolved by dilute acids.
4. Potassium chr ornate gives no precipitate with calcium
compounds.
5. Sulphuric acid precipitates white calcium sulphate
CaSO^ from concentrate solutions. As this is quite soluble
in water, unless the solution is very strong, the precipitate
forms slowly, and if the solution is dilute, no precipitate is
formed. Of course, calcium sulphate would not precipitate
calcium from its solutions.
6. Ammonium oxalate precipitates white calcium oxalate
CaCfi^^ which is insoluble in acetic acid, but easily soluble
in hydrochloric or nitric acid. The presence of free ammo-
nia and heating both favor the formation of this precipitate.
7. Sodium phosphate gives a white precipitate. If the
solution is slightly acid or neutral, this precipitate is HCaPO^y
but if the solution is alkaline, the precipitate is Ca^{PO^^,
It is easily dissolved by dilute acids, and is re precipitated by
ammonia.
76. All volatile calcium compounds, when held in the
Bunsen flame on the platinum wire, impart a brick-red color
to the flame. It is well to dip the substance in hydrochloric
§ 10 QUALITATIVE ANALYSIS. 43
acid just before placing it in the flame, in order to fonn vola-
tile calcium chloride. If the calcium gives a very strong
color to the flame it may be mistaken for strontium, but we
may distinguish between them by looking at the flame
through a blue glass, when the strontium flame appears
purple, or rose color, while the calcium flame only shows a
faint greenish-gray color.
MAGl^ESIUM.
77. Magnesium is a white metal that tarnishes very
slowly in dry air, but much more rapidly if the air is moist.
It bums in the air, with a dazzling white light, to magnesium
oxide MgO
A solution of magnesium sulphate may be used for the
wet reactions. It is made by dissolving about 3 grams of
the crystals MgSO^.lHJD in 100 cubic centimeters of water
and adding a drop or two of sulphuric acid.
78. Reactions. — A magnesium solution gives the fol-
lowing reactions:
1. Ammonium hydrate precipitates white magnesium
hydrate Mg{OH)^ from neutral solutions that are free from
ammonium salts. If the solution contains any considerable
amount of free acid or ammonium salts, no precipitate is
formed.
2. Sodium hydrate precipitates white magnesium hydrate
Mg{OH)^ from solutions that do not contain ammonium
salts. The precipitate is soluble in acids and in ammonium
chloride. From the solution in ammonium chloride the mag-
nesium hydrate may be slowly reprecipitated by continued
boiling.
3. Ammonium carbonate gives no precipitate under ordi-
nary conditions.
4. Sodium carbonate precipitates white basic magnesium
carbonate from solutions that do not contain ammonium
salts. Heat aids the formation of the precipitate. It is
44 QUALITATIVE ANALYSIS. § 10
soluble in ammonium chloride, and is prevented from form-
ing by the presence of ammonium salts.
5. Sodium phosphate gives no precipitate in acid solutions,
but in alkaline solutions the magnesium is completely
precipitated as white magnesium-ammonium phosphate
MgNH^PO^, which is easily dissolved by acids, and is repre-
cipitated from this solution by ammonium hydrate.
79. Magnesium compounds, when highly heated on the
charcoal before the blowpipe, are reduced to the white
infusible oxide, which is luminous at high temperatures. If
this is moistened with a drop of cobalt nitrate, and again
ignited, it assumes a pale-rose color, which is permanent,
and may be seen after cooling.
AMMO]«UM.
80. The ammonium group NH^ acts like a metal, form-
ing the base of all ammonium compounds, and is, conse-
quently, treated as a metal. When heated on the charcoal
or platinum foil, all ammonium compounds are either decom-
posed or volatilized, those that are decomposed giving the
peculiar odor of ammonia.
A solution for its reactions may be made by dissolving
2 or 3 grams of ammonium nitrate, or chloride, in 100 cubic
centimeters of water.
81. Reactions. — Ammonium compounds give the fol-
lowing reactions :
1. Acid sodium tartrate precipitates white acid ammo-
nium tartrate HNHjC^H^O^ from rather concentrate solu-
4 4 4
tions. It is very soluble in acids, and quite soluble in water,
so that in dilute solutions, or in those containing free acid,
no precipitate is formed. The precipitate is not formed at
once except in very strong solutions, but shaking favors its
formation. It is sometimes obtained from the solution pre-
pared as described above, but often fails. '
2. Platinum chloride precipitates yellow ammonium-
platinum chloride {NH^^PtCl^ from concentrate solutions.
§ 10 QUALITATIVE ANALYSIS. 45
This precipitate is insoluble in alcohol, but is dissolved by
water; hence, in dilute solutions no precipitate is formed.
Probably no precipitate can be obtained from the solution
described above, but the reaction is mentioned here as it is
important in later work.
3. Sodium hydrate^ when heated with any ammonium
compound, decomposes it, setting free NH^, This is by far
the best common test for ammonium, and, in fact, the only
sure one. To apply this test, place a little of the solution to
be tested in a test tube, add about an equal quantity of
sodium hydrate, and heat. Ammonia gas is set free, which
is recognized by its characteristic odor. If a piece of red
litmus paper is moistened and held at the mouth of the tube,
it is turned blue; or, if a drop of hydrochloric acid on a
glass rod is held at the mouth of the tube where the gas comes
in contact with it, white fumes of ammonium chloride NHJOI
are formed.
POTASSIUM.
82. Potassium is a soft, silver-white metal when freshly
cut, but tarnishes rapidly in air. It decomposes water,
forming potassium hydrate KOH and setting free hydrogen,
during which reaction heat enough is generated to ignite the
hydrogen, which bums with a violet flame.
A solution for the reactions may be made by dissolving
about 3 grams of potassium nitrate or chloride in 100 cubic
centimeters of water.
83. Reactions. — A potassium solution gives the follow-
ing reactions :
1. Acid sodium tartrate precipitates white acid potassium
tartrate KHC^H^O^ from neutral solutions that are not too
dilute. It is easily soluble in acids and alkalies, and less so
in water, so we cannot place a great deal of dependence upon
it. Its formation is favored by shaking.
2. Platinum chloride precipitates yellow potassium-plat-
inum chloride KJHCl^ from concentrate solutions. It is
insoluble in alcohol, but soluble in acids, alkalies, or water;
46 QUALITATIVE ANALYSIS. § 10
consequently, with the ordinary solution we may succeed or
fail in getting it.
84. Potassium compounds, when brought into a colorless
flame on a platinum wire, impart a bluish- violet color to the
flame. This is by far the best method of recognizing potas-
sium. Sodium and other impurities may partially obscure
this color, but when viewed through the blue glaSvS, their
colors are absorbed and the potassium flame appears a red-
dish-violet color. After a little practice this flame may be
identified with absolute certainty.
SODIUM.
85. Sodium is a soft, white metal that behaves much
like potassium, except that it produces no precipitates with
ordinary reagents. A solution may be made by dissolving
2 or 3 grams of sodium nitrate or chloride in 100 cubic centi-
meters of water.
86. As sodium gives no precipitates with ordinary rea-
gents, we depend upon the flame to enable us to recognize it.
This is easily done, as even small amounts of it impart an
intense yellow color to the flame, which is not obscured by
the presence of other elements. When viewed through a
blue glass, the yellow color is absorbed and the flame appears
almost colorless.
87. A crystal of potassium bichromate, when held close
to the sodium flame, appears transparent and almost colorless
in its light.
EXPIjAIS^ATIOX of TABTjE 1.
88. If the student has performed and studied each of the
reactions described imder the different metals, he is now
prepared to determine any single common metal in a solu-
tion, by means of these reactions. All the reactions neces-
sary to determine any of these metals have been described,
but the student will find that at first it is diflicult to remem-
ber the reactions, and much time would be lost in looking
3'
§ 10
/
■i.y*
QUALITATIVE ANALYSIS.
61
ANALYSIS OF MIXED SOLUTIONS.
90. We now have before us all the facts necessary to
make out a scheme by which we can separate and determine
several metals mixed together in a solution, but, as for this
work, we need some apparatus in addition to that already in
use, and as some of the oj^erations differ from any thus far
performed, we will describe these before proceeding to
describe the process.
91. Apparatus Needed for Separations. — In addition
to the apparatus already in use, we need a wash bottle, funnels,
support for funnels, filter paper, beakers,
a porcelain dish, a stirring rod, and a flask.
1. A wash bottle is made by fitting a
flask with a stopper that has two perfora-
tions. Through one of these perforations a
tube {by Fig. 8) is passed so that the lower
end just projects through the bottom of the
stopper. The upper part of the tube is
bent so that it forms an angle of about
G0°. Through the other perforation a tube
is passed, reaching nearly to the bottom of
the flask. The top of this tube is bent so
that it forms an angle of about 120°, and
the end is drawn out, leaving a small
opening. The tubes must fit tightly into the perforations
in the stopper. By blowing in the tube ^, the pressure of
the air forces the water in the flask up through the tube a
and out of the small opening in a fine jet that is very well
adapted to the purpose of washing precipitates, and of wash-
ing out small particles of substance that adhere to a beaker.
The tube a is often cut in two, about half way between the
bend and the tip, and the two parts held together by placing
over them a piece of rubber tubing that fits them closely.
This makes it much handier to direct the jet of water. As
hot water is often used in a wash bottle, the neck of the
flask is frequently covered, to protect the hand from the
Fig. 8.
62 QUALITATIVE ANALYSIS. § 10
heat. This may be done by wrapping it with a cord, or by
binding a ring of cork around it.
2. The funnels used in all ordinary analytical work must
be of glass. The ring of a retort stand serves very well for
a support in filtering.
3. Filter paper may be obtained from any chemical dealer,
either in sheets, or cut in disks, ready for use. The papers
4 inches in diameter (10 centimeters) are the best size for
qualitative work. The filter papers are folded as directed in
Art. 99, Theoretical Chemistry,
4. A nest of beakers, a porcelain dish, a common glass
stirring rod, and a flask require no description.
93. Washing Precipitates. — There are two methods of
washing precipitates, known as washing by decantation and
washing on the filter. In washing by decantation, the pre-
cipitate is allowed to settle to the bottom of the beaker and
the clear liquid is poured off, or decanted ; water is added,
the precipitate is stirred up with it, and then is allowed to
settle, and the water decanted. This may be repeated sev-
eral times, the water carrying off a large part of the remain-
ing impurity each time, until the precipitate is free from
foreign matter.
In washing on the filter, the precipitate is separated from
the liquid by means of filtration, as described in Art. 99,
Theoretical Chemistry, After all the liquid has passed
through, leaving the precipitate on the filter, a jet of water
from the wash bottle is directed around the top of the filter
paper, thus washing down any impurity that may be absorbed
by this part of the paper, and washing the precipitate down
nearer the cone of the paper. When a little more than
enough water to cover the precipitate has been added in this
way, allow it all to run through the filter before adding
more. By repeating this operation a few times, the water
carries all soluble matter through the filter, leaving the pre-
cipitate clean.
93. Concentrating Filtrates, or Solutions. — In sep-
arating the different metals, we precipitate some of them
§ 10 QUALITATIVE ANALYSIS. 53
from the solution, and then get others from the filtrate.
The water used in washing the precipitates, of course, goes
into the filtrates and in a short time our solution becomes
too large. To avoid this we must concentrate the solution,
and this is always done by evaporating off some of the water.
.This is rapidly accomplished by boiling the liquid. Liquids
in a beaker must always be heated over a wire gauze. Stand
the beaker on a gauze, resting on a tripod, and place the
burner under it. The flame must never be turned high
enough to reach around the side of the gauze and strike the
beaker, or it will probably crack it. This applies to heating
liquids in any glass vessel. The same care must be taken
when heating water in a wash bottle.
GROUP SEPARATIOl^S.
94. As has already been indicated, when there are sev-
eral metals in a solution, they are removed from the solution
in groups by means of the so called group reagents^ and the
metals in each group are then separated from each other.
There are six of these group reagents; and, by means of
them, all the common metals may be divided into seven
groups. The group reagents, in the order in which they are
used, are: hydrochloric acid^ hydrogen sulphide^ ammonium
hydrate^ ammonium sulphide^ ammonium carbonate^ and
sodium phosphate. There is no group reagent for the seventh
group, as it consists of the metals that are not precipitated
by any of the common reagents.
Group I consists of the metals that are precipitated as
chlorides by hydrochloric acid. They ar^ :
Silver white.
Lead (incompletely). ... **
Mercurous **
Group II consists of the metals left in the filtrate that are
precipitated as sulphides by hydrogen sulphide. On account
of tha solubility of lead chloride in water, some of the lead
is precipitated in the second group. This group is divided
64 QUALITATIVE ANALYSIS. § 10
into two divisions, depending^ upon the solubility of the sul-
phides in ammonium sulphide and ammonium hydrate. The
group is as follows:
Division A. Division B.
Insoluble in {NJI,y,S and NIUOH. Soluble in {A7/^hS and NH^OH.
Lead black. Antimony orange.
Mercuric ** Stannous brown.
Copper ** Stannic yellow.
Cadmium yellow. Arsenious **
Bismuth brown. Arsenic **
Group 111 consists of the remaining metals that are pre-
cipitated as hydrates by ammonium hydrate in the presence
of ammonium chloride. They are :
Iron reddish brown.
Chromium greenish blue.
Aluminum white.
Oroiii> IV consists of the remaining metals that are pre-
cipitated as sulphides by ammonium sulphide. They are:
Cobalt black.
Nickel **
Zinc white.
Manganese flesh color.
Group V consists of the metals not precipitated in any of
the previous groups, but that are precipitated as carbonates
by ammonium carbonate, in the presence of ammonium
chloride. They are :
Barium white.
Strontium **
Calcium **
Group VI contains but one metal. It is not precipitated
by any of the preceding group reagents, but is precipitated
by sodium phosphate in the presence of ammonia and ammo-
nium chloride. It is:
Magnesium white.
§ 10 QUALITATIVE ANALYSIS. 55
Group VII consists of the metals that are not precipitated
by any of the common reagents, but must be recognized by
special tests. They are:
Ammonium, Potassium, Sodium.
The rare metals are not treated here, as their treatment at
this time would complicate the work too much. They are,
therefore, taken up later and treated by themselves.
GROUP I.
95. About 20 cubic centimeters of the solution to be
analyzed are placed in the smallest beaker and about 3 drops
of concentrate hydrochloric acid added. If no precipitate is
formed, this portion ot the solution is ready for the next
step, and should be treated for Group II. If the solution
contains silver, lead, or mercurous compounds, they will be
precipitated, except in the case of very small quantities of
lead, which, on account of the solubility of its chloride in
water, may not be precipitated in this group, but will come
down in Group II. If a precipitate is formed, continue to add
hydrochloric acid gradually, and with constant stirring, till
all the metals of this group are precipitated, but taking care
not to add a large excess of the reagent. We can tell when
enough of the reagent has been added by allowing the pre-
cipitate to settle, and adding a drop or two of the reagent.
The precipitation is complete when this no longer produces
a precipitate in the clear liquid. Allow the precipitate to
settle, and filter as directed in Art. 99, Theoretical Chem-
istry^ and wash two or three times on the filter with cold
water. Receive the filtrate in the next to the smallest beaker
and set it aside, to be treated for Group II. It is best before
doing so, however, to add a drop or two of the reagent to
the filtrate, in order to be sure that the precipitation was
complete. If a precipitate is formed, it shows that the metals
of this group have not been perfectly separated, and the
reagent must be added till a precipitate is no longer formed.
This must then be filtered and the precipitates united. This
56 QUALITATIVE ANALYSIS. § 10
applies to the succeeding groups as well as to this one, but
in every case care must be taken not. to add a large excess
of the reagent.
Punch a hole in the apex of the filter with a stirring rod,
and wash the precipitate through into the small beaker with
hot water, using enough water to about half fill the beaker.
Place this on the gauze and heat it to boiling while stirring
it with a glass rod. If it all dissolves, there is only lead
present, which should be confirmed by adding a few drops
of sulphuric acid to a portion of it, and also by the other
reactions for lead. If the precipitate does not all dissolve,
it should be filtered while hot. The lead chloride will go
through in the filtrate, and the silver and mercurous chlo-
rides will remain on the filter. Test the filtrate for lead by
adding sulphuric acid, and by means of potassium chromate,
as described under ** Lead," in the ** Deportment of the
Metals With Reagents.** This may now be thrown away,
the beaker washed, and placed under the funnel. Ammo-
nium hydrate is now added to the precipitate on the filter.
If silver chloride is present, it is dissolved and runs through
the filter, forming a new filtrate, while the mercurous chlo-
ride is changed to a black, insoluble compound that remains
on the filter. Nitric acid is added to the ammoniacal filtrate,
or to a part of it, in sufficient quantity to render it slightly
acid, when silver, if present, will be reprecipitated as chlo-
ride. The blackening of the precipitate on the filter, when
ammonia is added, is proof of mercurous chloride ; but this
may be dissolved in a little aqua regia, and after evaporating
the excess of acid and diluting, it may be confirmed by the
use of stannous chloride, and by the other reactions for
mercury.
GROUP II.
96. The first filtrate from Group I, or the slightly acid
solution, if none of the members of Group I were present, is
now ready to be treated for Group II. But before treating
the whole of the solution with hydrogen sulphide, a small
portion in a test tube should be tried to see if any of the
g 10 QUALITATIVE ANALYSIS. 67
members of the second group are present. This may be
done by adding a little of the hydrogen -sulphide solution, if
proper precautions are taken to precipitate arsenic, if present.
But it is best to run a little of the gas through this solution.
If no precipitate is obtained in this side test, it is thrown
out, and the main part of the filtrate is ready to treat for
Group III. If a precipitate is obtained, it shows the presence
of second-group metals, and the solution must be treated with
hydrogen sulphide. The hydrogen- sulphide solution is too
dilute for this purpose, so we must use the gas. It is pre-
pared as described in Art. 105, Experiment 50, Inorganic
Chemistry, Part 1, and is led into the solution until the pre-
cipitation of the metals of Group II is complete. This will
generally take about 10 minutes. After a little practice the
student can tell when the operation is complete by removing
the beaker, blowing the gas away from the surface of the
liquid, and observing if a strong odor of hydrogen sulphide
is given off. If the odor is very strong, it indicates that the
precipitation is complete.
Allow the precipitate to settle, and then, without dis-
turbing the precipitate, lead a little more of the hydrogen
sulphide through the clear liqiiid, to be sure that the metals
of this group are completely precipitated. If a precipitate
is formed, the treatment with hydrogen sulphide must be
continued until precipitation is complete. Allow the precip-
itate to settle and pour as much as possible of the clear liquid
through the filter witliout disturbing the precipitate. When
the liquid has run through, wash the precipitate on to the
filter with hot water and wash twice on the filter with hot
water. Set the filtrate aside, to be treated for Group III,
The precipitate may contain metals of either Division A or
Division B, or may contain both. As the methods of sepa-
rating the metals of the two divisions differ, we should always
ascertain whether both divisions are present or not, and if
metals belonging to but one division are present, we should
learn to which division they belong before treating the whole
precipitate. To do this, remove a portion of the damp pre-
cipitate about as large as a small pea to a small porcelain
68 QUALITATIVE ANALYSIS. g 10
dish, and add about one cubic centimeter of ammonia, and
from half a dozen drops to half a cubic centimeter of yellow
ammonium sulphide, depending upon the color of the pre-
cipitate. If the precipitate is light colored, only a few drops
of the yellow sulphide is needed, or a little more of the com-
mon ammonium sulphide may be substituted; but if it is
rather dark, indicating that tin may be present, more of the
yellow sulphide must be used. In either case heat gently
and stir with a glass rod for a few minutes. If all the pre-
cipitate dissolves. Division B alone is present. If it does not
all dissolve, the insoluble part belongs to Division A.
This is filtered, washed once with hot water, and the filtrate
rendered slightly acid with hydrochloric acid. Sulphur will
be thrown out by the hydrochloric acid. If it merely makes
the solution milky, it may be disregarded, but if the solution
is colored yellow, it shows the presence of some of the mem-
bers of Division B, and in this case the two divisions must
be separated. If only metals belonging to one of the divisions
are present, the precipitate is at once treated as described for
the separation of the metals of that division.
97. Separation of the Tvro Divisions of Group II. —
The precipitate is removed, as completely as possible, from
the filter to a porcelain dish. If the precipitate is dark col-
ored, it may contain tin, and in that case from 2 to 3 cubic
centimeters of yellow ammonium sulphide are added, then
about an equal amount of common ammonium sulphide, and
finally a little more than enough ammonium hydrate to cover
the precipitate is added. In case the precipitate is light col-
ored, stannous sulphide must be absent, and in that case
only a few drops of the yellow sulphide should be added, and
the quantity of common ammonium sulphide should be
increased about the same amount that the yellow sulphide is
decreased. In either case, gradually heat the mixture, while
it is being stirred, until it begins to boil. By this time the
metals of Division B will all be in solution. Add to this
about twice its volume of hot water, and after allowing it to
stand for a few moments to settle, filter it, and wash several
§ 10 QUALITATIVE ANALYSIS. 59
times with hot water. The precipitate will now contain the
members of Division A, and the filtrate contains the metals
of Division B.
98. Separation of the Metals of Division A. — ^This
precipitate — or the original precipitate, if it were found to con-
tain only the metals of Division A — is removed as completely
as possible to a small porcelain dish, and covered with a
mixture of equal parts of concentrate and dilute nitric acid.
It should be heated slowly and with constant stirring until it
boils. The sulphides of lead, copper, cadmium, and bismuth
will be dissolved, while the sulphide of mercury remains as
a black, insoluble precipitate. Sulphur will also be thrown
out during the solution of the sulphides, but this may easily
be recognized, and is disregarded. It generally collects in a
pasty mass, which may be somewhat colored by small quan-
tities of undissolved sulphides. The excess of acid is evap-
orated off, and about 25 cubic centimeters of hot water is
added. Filter, and wash two or three times with hot water.
A black precipitate indicates mercury, but it should be con-
firmed by dissolving a little of the precipitate in aqua regia,
evaporating the excess of acid, diluting slightly, and testing
w4th stannous chloride. Other tests for mercury may also
be applied. The filtrate, containing the metals whose sul-
phides are soluble in nitric acid, is treated with a few drops
of sulphuric acid, to test for lead. If a precipitate is formed,
continue the addition of the sulphuric acid, drop by drop,
till all the lead is precipitated as sulphate. Filter, wash once,
and confirm the presence of lead by the solubility of the sul-
phate in tartaric acid and ammonia, as directed in Art. 20, 8.
A slight excess of ammonia is now added to the filtrate.
Bismuth, if present, will be precipitated as white bismuth
hydrate, while copper and cadmium, if present, form pre-
cipitates that are at once dissolved in excess. If the solution
assumes a deep-blue color, it is conclusive evidence of the
presence of copper. The precipitate, if one is formed, is
probably bismuth, but if the lead was not all removed, it will
be precipitated at this point, and if the third-group metals
60 QUALITATIVE ANALYSIS. § 10
were not thoroughly washed out of the original precipitate,
they may come down here, so we must confirm the presence
of bismuth. To do this, dissolve a little of the precipitate
in a few drops of hot concentrate hydrochloric acid in a test
tube, and drive off most of the acid by heating. Pour a few
drops of this solution, a drop at a time, into a test tube
nearly filled with cold water. If a white precipitate is
formed, it is conclusive evidence of the presence of bismuth;
but if too much acid were left in the bismuth solution, no
precipitate will be formed. In that case a little hydrogen
sulphide is added to the acid solution in the test tube of
water that failed to give a precipitate. A brown precipitate
confirms bismuth, while the absence of a brown precipitate
proves that it is not present.
The ammoniacal filtrate is next examined for copper and
cadmium. If it is colored blue, copper is present, but if
colorless, it shows the absence of copper. In that case, to
a small quantity of it in a test tube, add hydrogen sulphide,
which will precipitate cadmium, if present, as yellow cad-
mium sulphide. If the solution is blue, a little of it is taken
in a test tube, and just enough potassium -cyanide solution
added to entirely destroy the color. To this colorless solu-
tion add hydrogen sulphide, which will precipitate cadmium,
as yellow cadmium sulphide, but will not precipitate copper
from the cyanide solution.
In separating the cadmium and copper by this method,
traces of other metals are sometimes present, and give the
cadmium sulphide a dark color. For this reason some
chemists prefer the following method of separating them.
Render the filtrate from the bismuth slightly acid with
hydrochloric acid, and pass a current of hydrogen-sulphide
gas through it till the copper and cadmium are both com-
pletely precipitated. Filter and wash the precipitate two or
three times with hot water and a few drops of hydrogen-
sulphide solution. Remove the precipitate to a porcelain
dish as quickly as possible, in order to avoid the oxidizing
action of the air, treat it with warm dilute sulphuric acid,
and bring to boiling in order to expel the hydrogen sulphide
5 10
QUALITATIVE ANALYSIS.
61
generated by the action of the .sulplmric acid upon the sul-
phides. Cadmium sulphide will be dissolved, while copper
sulphide remains as a black insoluble compound. It should
be filtered at once, and the precipitate examined for copper,
by dissolving it in nitric acid and applying the reactions
given for copper. To test the filtrate for cadmium, add
ammonia in sufficient quantity to render the solution alkaline,
and then add just enough hydrochloric acid to render it dis-
tinctly acid, and again pass a current of hydrogen sulphide
through it, when cadmium, if present, will be precipitated
as yellow cadmium sulphide. This method is more difficult
to perform properly than the first method given.
99. Separation of the Metals of Division B.— 1. The
metals o£ Division B are in solution in the filtrate from the
metals of Division A. This filtrate is rendered acid with
hydrochloric acid, when more or less sulphur is thrown out,
depending on the amount of yellow ammonium sulphide
used, and the metals are precipitated as yellow or orange-
colored sulphides. The hydrochloric acid must be added as
long as a precipitate is formed. When precipitation is
complete, filter and wash the precipitate two or three times
with hot water. When the. water has run through, remove
the precipitate to a porcelain dish, and add enough concen-
trate hydrochloric acid to cover the precipitate. Heat until
I it has boiled for two or three minutes, w-hen the sulphides
I of tin and antimony will be dissolved and all the hydrogen
1 sulphide expelled. The arsenic will remain as a yellow sul-
[ pliide and some free sulphur will be thrown out.
n case the original precipitate contained only metals of
[ X)ivision B, it should not be treated with sulphides, but
I ^ould be transferred to a porcelain dish at once, and treated
\ with hydrochloric acid, as just described.
The hydrochloric- acid solution is diluted with about twice
I its volume of water, filtered, and the precipitate washed
I twice on the filter with hot water. The arsenic, if present,
\ will be in the precipitate, and antimony and tin in the fil-
I trate. Remove the precipitate to a small porcelain dish
62 QUALITATIVE ANALYSIS. § 10
and add a small amount of concentrate nitric acid. If the
precipitate is so small that it cannot be removed from the
filter, the part of the paper containing the precipitate may
be placed in the dish and the acid added. In either case,
heat until the precipitate is dissolved and most of the acid is
driven off; then add a little water and filter to remove free
sulphur and filter paper, receiving the filtrate in a test tube.
Then place a little magnesium sulphate in another test tube,
precipitate it with ammonia, using considerable excess, and
dissolve the precipitate thus formed by adding ammonium
chloride. To this solution add some of the filtrate from the
other tube, taking care that the solution remains alkaline,
and shake violently. A white, crystalline precipitate proves
the presence of arsenic.
Another method often used to confirm arsenic, is to remove
a little of the precipitate, supposed to be As^S^y to the char-
coal and heat it before the blowpipe. Dense white fumes,
with a garlic odor, prove the presence of arsenic.
To examine the acid filtrate for tin and antimony, place in
it several pieces of zinc, and when the acid begins to act on
them, place a piece of platinum foil in contact with one of the
pieces of zinc and leave it thus for a few seconds. If anti-
mony is present, some of it will be deposited on the platinum,
forming a black stain. Remove the platinum and allow the
acid to act on the zinc, until all chemical action ceases, and
some zinc remains undissolved. During this action some of
the antimony escapes as SbH^^ and the rest is deposited on
the zinc as metallic antimony, in the form of a black powder.
The tin is all deposited either as a gray powder or as a gray,
spongy mass of metallic tin. The pieces of zinc are now
removed and the adhering metals are washed back into the
dish and allowed to settle. Decant the clear liquid, and wash
two or three times by decantation, finally decanting as much
of the water as possible. Add a little concentrate hydro-
chloric acid and heat to boiling. The tin will dissolve to
stannous chloride, while the antimony remains unchanged.
Add a little water and filter, receiving the filtrate in a test
tube. This is tested for stannous chloride by means of
§ 10 QUALITATIVE ANALYSIS. 63
mercuric chloride, and by other reactions for stannous com-
pounds.
The antimony is further confirmed by dissolving a little of
the black powder in aqua regia, driving off the excess of acid,
diluting with water, and precipitating with hydrogen sul-
phide. If a white precipitate is formed when water is added
to dilute the solution, this in itself is proof of antimony.
2. The metals of this division are sometimes separated by
another method. In this case the precipitated sulphides of
Division B, after washing on the filter, are transferred to a
porcelain dish, a saturated solution of acid ammonium car-
bonate is added in sufficient quantity to cover the precipitate,
and this is heated for a few minutes, with constant stirring.
The arsenic is changed into the two soluble compounds,
ammonium sulphoarsenite and ammonium arsenite, while the
antimony and tin remain unchanged. Filter, and wash two
or three times with hot water. The precipitate will contain
the antimony and tin, and the arsenic will be in the filtrate.
The precipitate is removed to a porcelain dish, dissolved in
concentrate hydrochloric acid, and the tin and antimony sep-
arated as described in the first method.
The alkaline filtrate is treated with an excess of hydro-
chloric acid, when arsenic, if present, will be precipitated as
yellow arsenious sulphide. This is sufficient evidence of
arsenic, but it may be confirmed by either of the methods
previously given..
GROUP in.
100. The filtrate from Group II, or, in case the side test
showed that the solution did not contain any of the metals of
Group II, the filtrate from Group I is next treated for Group
III. If the second group has been precipitated from this
solution, it will contain hydrogen sulphide, which must be
expelled by boiling, before adding ammonia, or ammonium
sulphide will be formed, and the fourth group be precipitated
with the third. If the solution is growing too large, it is best
to boil it in a beaker, thus concentrating the solution at the
same time that the hydrogen sulphide is driven off. But if
64 QUALITATIVE ANALYSIS. § 10
the solution is not too large, it is best to boil it in a flask.
The student must be sure that all the hydrogen sulphide is
expelled before proceeding. The odor of the vapor is a good
indication, or a piece of filter paper saturated with a solution
of lead or silver, held in the vapor driven off by the heat, will
be colored as long as hydrogen sulphide is present. If sul-
phur is thrown out in the solution during this operation, it
should be filtered off before proceeding.
There are several things that may complicate the separa-
tion of the metals of this group. Manganese may be partially
precipitated with this group, and if phosphoric or oxalic acid
is present, the phosphates or oxalates of the alkaline earths
are either partly or wholly precipitated when ammonia is
added. In the presence of phosphoric acid, part of the iron
and aluminum are precipitated as phosphates, and barium,
strontium, calcium, and magnesium phosphates may also be
precipitated. When oxalic acid is present, the oxalates of
barium, strontium, and calcium are precipitated with this
group. Fortunately, these acids do not ordinarily occur in
solutions that are treated for the group separations, and the
student may never have to separate the metals in a solution
containing them, but in case he should meet them in a solu-
tion, methods for the treatment of this group, when they are
present, are given, after describing the ordinary method for
the separation of the metals of this group.
In any case the solution is heated to boiling and a few
drops of concentrate nitric acid are added, to oxidize ferrous
compounds to ferric. If a brown color is formed, continue
to add the acid, drop by drop, and boil till the solution
becomes clear. Now add about 10 cubic centimeters of
ammonium chloride, and then slowly add ammonium hydrate
in slight but distinct excess, while the solution is constantly
stirred. Continue the boiling for about one minute, and be
sure that the solution still smells distinctly of ammonia.
Filter as soon as the precipitate has partly settled, while the
solution is still hot, and wash two or three times with hot
water. The filtrate is now ready to be treated for Group
IV, and the precipitate should be tested for phosphoric and
§ 10 QUALITATIVE ANALYSIS. 65
oxalic acids. If they are found to be present, the precipitate
is treated as described later. If they are absent, the metals
are separated by the usual method.
101. Ordinary Method of Separating the Metals of
Group III. — If iron is present in the solution, some of the
manganese will generally be precipitated with the iron. To
test for manganese, remove a small portion of the precipitate
to the platinum foil, and fuse with sodium carbonate and
potassium nitrate, as directed in Art. 67. A dark-green
color proves the presence of manganese, which is sufficient
if we merely want to know whether it is present in the solu-
tion or not. But if we wish to separate it from the metals
of this group, the whole precipitate is removed to a beaker
and dissolved in about 25 cubic centimeters of hydrochloric
acid by the aid of heat. Bring this solution to boiling, pre-
cipitate with a slight excess of ammonia, and filter at once.
Wash the precipitate on the filter once with hot water, and
add this filtrate to the one previously obtained, to be treated
for Group IV. The precipitate will contain the metals of
Group III.
A small portion of the precipitate is dissolved in hydro-
chloric acid, the solution diluted a little, and potassium
ferrocyanide added, when iron, if present, will give a char-
acteristic blue precipitate, which is conclusive proof of the
presence of iron.
The remainder of the precipitate is now removed to a
beaker and dissolved in dilute hydrochloric acid, by the aid
of heat, using as little acid as possible. When all is dis-
solved, add considerable excess of sodium hydrate, and bring
to boiling. This will dissolve the aluminum hydrate at first
formed, while the iron and chromium remain as a precipi-
tate. Filter and wash two or three times with hot water on
the filter. Test the precipitate for chromium by fusing a
little of it on the platinum foil, as directed in Art. 56.
The bead test may also be used for both chromium and
manganese. There are two good methods of testing the
filtrate, and, as a rule, both should be used. They are :
66 QUALITATIVE ANALYSIS. § 10
1. Place a little of the alkaline filtrate in a test tube, add
ammonium chloride, shake well, and stand aside for a minute
or two. If aluminum is present, it will be precipitated as
white aluminum hydrate, but it may take a few moments to
collect so that it is readily seen.
2. Render the remainder of the filtrate slightly acid by
means of concentrate hydrochloric acid, add a slight excess
of ammonium carbonate, boil the solution a moment to expel
the liberated carbon dioxide, and allow to settle. If alu-
minum is present, it will be precipitated as white aluminum
hydrate. When the precipitate is first formed, it is almost
colorless, and may be overlooked unless the mixture is
examined carefully. After standing a while, it is much
more easily seen, especially when the tube, or beaker, is
moved sufficiently to cause the precipitate to move through
the liquid in which it is suspended. .
103. Treatment of Group III, When Phosplioric
Acid is Present. — To test for phosphoric acid, remove a
little of the original precipitate on the point of a knife
blade to a porcelain dish, and dissolve it in a drop or two of
nitric acid. Place about two or three cubic centimeters of
ammonium-molybdate solution in a test tube, heat it to the
boiling point, and add a drop or two of the solution obtained
by treating the precipitate with nitric acid. A yellow pre-
cipitate proves the presence of phosphoric acid, while the
absence of a yellow precipitate proves its absence.
When phosphoric acid is present, the precipitate is removed
to a porcelain dish and dissolved in the least necessary quan-
tity of hydrochloric acid, by the aid of heat, an excess of
sodium hydrate is added, and the whole is heated to boiling.
This dissolves the aluminum hydrate and phosphate, and the
other metals remain in the precipitate. Filter, wash once
with hot water on the filter, and test the filtrate for alumi-
num by the methods previously described.
Remove the precipitate to a porcelain dish, dissolve it in
concentrate nitric acid, and add an excess of pure tin foil.
Heat to boiling, and stir well. The phosphorus and tin
§ 10 QUALITATIVE ANALYSIS. 67
form an insoluble compound, while all the metals are
changed to soluble nitrates. Filter, wash with hot water,
and then throw away the precipitate, which contains only
the tin and phosphorus. Add about 10 cubic centimeters
of ammonium chloride to the filtrate, heat it to boiling, and
precipitate with a slight excess of ammonia. Filter, wash
once with hot water, and add the filtrate to the first filtrate,
to be treated for Group IV. Examine the precipitate for
iron and chromium, as previously directed.
103. Treatment of Group III, When Oxalic Acid
is Present. — To examine the precipitate for the presence
of oxalic acid, dissolve a small portion of it in a test tube, in
a few drops of concentrate nitric acid, add an excess of
sodium carbonate, and boil for a few moments. The metals
are precipitated as carbonates and hydrates, and the oxalic
acid unites with the sodium, forming soluble sodium oxalate.
Filter, acidify the filtrate with acetic acid, boil till all the
carbon dioxide is driven off, and add calcium chloride. If
oxalic acid is present, the calcium will be precipitated as
white calcium oxalate, which is insoluble in acetic acid, but
is readily dissolved by hydrochloric acid. In making this
test, care must be taken to render the filtrate distinctly acid
with acetic acid, and to boil till all carbon dioxide is expelled,
otherwise calcium carbonate will be precipitated, and this
will be mistaken for calcium oxalate.
If oxalic acid is found to be present, the precipitate is dis-
solved, and the aluminum removed, just as described in the
case where phosphoric acid is present. The precipitate
from the sodium hydrate is removed to a porcelain dish, an
exceiss of sodium carbonate added, and boiled for a minute
or two. The metals are thus changed to insoluble hydrates
and carbonates, and the oxalic acid unites with the sodium,
forming soluble sodium oxalate. Filter, and wash two or three
times with hot water. The filtrate may be thrown away.
Transfer the precipitate to a beaker, dissolve it in dilute
hydrochloric acid, bring to boiling, and precipitate the iron
and chromium with a slight excess of ammonia. Filter,
68 QUALITATIVE ANALYSIS. § 10
wash once on the filter with hot water, and add the filtrate
to the first filtrate from the separation of this group, which
is to be treated for the fourth group. The precipitate is
examined for iron and chromium by the methods already
described.
GROUP IV.
104. The filtrate from Group III, or, in case there were
none of the metals of Group III in the solution, the filtrate
from Group II, which failed to give a precipitate with
ammonia, is next treated for Group IV. But before adding
the group reagent to the whole quantity, a small amount is
taken out in a test tube and ammonium sulphide added, as
this will save boiling off the ammonium sulphide, and filter-
ing from sulphur, in case none of the metals of Group IV
are contained in the solution. If this side test yields no
precipitate, it is thrown out and the main filtrate is treated
for Group V. If we find, by the side test, that metals of
the fourth group are present, the filtrate from Group III is
heated to boiling and precipitated by ammonium sulphide.
It is important to avoid a large excess of this reagent, but a
sufficient quantity must be added to precipitate all the
metals of this group. It is difficult to tell when just enough
of the reagent has been added, but a sufficient quantity is
indicated if the solution retains a distinct odor of the reagent
after stirring a few moments. As a safeguard, the filtrate
must always be tested by adding to it a few drops of the
reagent, and if a precipitate is formed, the addition of the
reagent is continued till the precipitation is complete, and
this precipitate is added to and treated with the first one.
When the precipitation is complete, boil the contents of
the beaker for a moment, remove the beaker from the gauze,
allow the precipitate to completely settle, decant the clear
liquid as completely as possible through the filter, wash the
precipitate on to the filter with hot water, and wash twice on
the filter with hot water. Care must be taken to expose the
precipitate to the air as little as possible, as the air tends to
oxidize the sulphides to soluble sulphates. To avoid this, a
g 10 QUALITATIVE ANALYSIS. 69
drop or two of ammonium sulphide is sometimes added with
the water on the filter, but if the whole operation is per-
formed quickly, and with little exposure to the air, this is
generally unnecessary.
The filtrate is set aside to be treated for Group V, and the
precipitate is examined for the metals of Group IV. Ey
observdng the color of the precipitate, we may sometimes
avoid useless work. If the precipitate is light colored, only
zinc and manganese can be present, and in that case we dis-
solve the precipitate and proceed at once to separate the zinc
and manganese, as directed later. In case the precipitate is
black, all the metals of the group may be present, and wc
must examine the precipitate for all of them. To do this,
punch a hole in the apes of the filter with a stirring rod, and
wash the precipitate through into a beaker or porcelain dish,
using about 30 cubic centimeters of cold water. To this add
about 5 cubic centimeters of dilute hydrochloric acid, and
stir for a minute or two in the cold. The sulphides of zinc
and manganese are dissolved, while the sulphides of cobalt
and nickel are not attacked by tliis dilute acid. Filter, and
wash twice on the filter. The precipitate will contain the
cobalt and nickel, and the filtrate, the zinc and manganese,
if all were present. To learn if cobalt is present in the pre-
cipitate, the borax-bead test is used, as described in Art. 59,
Nickel also gives some color to the bead; so that, if a dis-
tinct blue is not obtained, the result should be rejected and
a further examination made. If the bead proves the absence
of cobalt, a little of the precipitate is dissolved in a few drops
of aqua regia, nearly all the acid driven off, a little water
added, and the solution thus made is tested for nickel by
adding sodium hydrate. A green precipitate proves the
presence of nickel. The other reactions for nickel may also
be used to further confirm it.
' When cobalt is present, it must be removed before wc can
test for the nickel. To do this, remove the pi'ecipitate to a
small porcelain dish — on a small portion of the filter if neces-
C'c it in a few drops of aqua regia. Evaporate
J, add about 1 cubic centimeter of water,
4
J
70 QUALITATIVE ANALYSIS. § 10
and filter into a test tube, using a little more water to wash
the filter paper, which should be very small. Neutralize this
solution with concentrate ammonia, then render it slightly,
but distinctly, acid with acetic acid, add a stick of potassium
nitrate that will reach nearly to the top of the solution, and
allow it to stand for several hours. The cobalt will all be
precipitated as a yellow powder, which will settle to the bot-
tom of the tube, and the clear liquid may be examined for
nickel by means of sodium hydrate, and by other tests.
The acid filtrate is next examined for zinc and manganese.
It is first boiled, to expel all hydrogen sulphide, then rendered
strongly alkaline with sodium hydrate, and heated to boiling.
Both zinc and manganese are at first precipitated as light-
colored hydrates. The manganese is quite rapidly oxidized
to a brown compound, while the zinc is dissolved in the
excess of sodium hydrate. Filter and test the precipitate
for manganese, and the filtrate for zinc. The precipitate
may be tested by means of the borax bea4, and also by fusing
part of it on the foil with sodium carbonate and potassium
nitrate. The filtrate may be tested by hydrogen sulphide.
If this gives a white precipitate, it is sufficient evidence of
zinc.
GROUP V.
105. The filtrate from the fourth group is boiled till the
ammonium sulphide is completely decomposed, and filtered
from sulphur, if any is deposited during the boiling. In case
there were no fourth-group metals in the solution, this boil-
ing will be unnecessary, as there will be no ammonium sul-
phide in the solution. We can tell when all the sulphide is
driven off in this case by the same methods that were used
for the purpose when the filtrate from the second group was
boiled to expel the hydrogen sulphide.
The clear filtrate is rendered distinctly alkaline with ammo-
nia, heated, and ammonium carbonate is added in sufficient
quantity to completely precipitate the barium, strontium, and
calcium, as carbonates. The contents of the beaker are boiled
for a few moments in order to change any acid carbonates
§ 10 QUALITATIVE ANALYSIS. 71
that may be formed at first, into normal carbonates, but this
boiling must not be continued more than a minute at the
outside, or the ammonium chloride in the solution will begin
to dissolve the carbonates by changing them to chlorides.
The precipitate is allowed to settle before filtering. It is
washed twice on the filter with hot water, and then examined
for the members of this group. The filtrate is set aside to be
treated for Group VI.
Remove the precipitate to a beaker and dissolve in a slight
excess of acetic acid, by the aid of gentle heat. Remove a
little of this solution to a test tube, and add potassium
chromate to test for barium. If a yellow precipitate is
formed, it shows the presence of barium. In this case, add
potassium chromate to the rest of the acetic-acid solution in
sufficient quantity to precipitate all the barium. Filter and
wash once or twice on the filter. A yellow precipitate at this
point is proof of barium, but it maybe confirmed by holding
a little of it on the loop of a platinum wire in a non-luminous
Bunsen flame and noting the color imparted to the flame.
It is well, after holding it in the flame for a while, to dip the
loop containing the dry precipitate into some dilute hydro-
chloric acid, and then return it to the flame. The acid will
partly dissolve the chromate, forming barium chloride, which
is quite volatile, and, therefore, colors the flame much more
distinctly. If desired, the rest of the chromate precipitate
may now be dissolved in dilute hydrochloric acid, and other
tests for barium applied.
The filtrate, which may contain strontium and calcium, is
precipitated by ammonia and ammonium carbonate, in exactly
the same way that the original group precipitation was made.
Filter, and wash the precipitate well to free it from the solu-
ble chromates. Dissolve the precipitate in a little hydro-
chloric acid, and make a preliminary flame test, by holding a
drop of the solution in the flame, on the loop of the platinum
wire. If strontium is present, there will be a flash of bright-
red light, while calcium imparts a brick -red color to the
flame. If the calcium solution is very strong, its flame may
be mistaken for the strontium flame.
72 QUALITATIVE ANALYSIS. § 10
To separate the strontium and calcium, dilute the solution
to from 50 to 75 cubic centimeters, and add ammonium sul-
phate. Strontium, if present, will be slowly precipitated as
white strontium sulphate, while the calcium remains in solu-
tion. After letting it stand for some time, for the precipi-
tate to form and settle, filter and test the precipitate for
strontium by means of the flame. If the color is not imparted
to the flame at once, the precipitate is held in the reducing
flame for a time, until the sulphate is partly reduced to sul-
phide. Then, if it is dipped in dilute hydrochloric acid
and quickly withdrawn, the sulphide is partly changed to chlo-
ride, which is quite volatile and colors the flame quickly and
distinctly.
The filtrate is now rendered distinctly ammoniacal, heated
to boiling, and ammonium oxalate added. If calcium is
present, a white, crystalline precipitate of calcium oxalate,
which is insoluble in acetic acid, is formed. This precipitate
proves the presence of calcium, while a failure to obtain this
precipitate proves its absence. If the precipitate is obtained,
however, it may be further verified by the color it imparts to
the flame, as in the case of barium and strontium.
106. Second Method of Separating Strontium and
Calcium. — Another method of separating strontium and
calcium, based upon the solubility of calcium sulphate in
ammonium sulphate, is sometimes used. In this method the
barium is removed by potassium chromate, the strontium and
calcium precipitated by ammonium carbonate, and washed
on the filter to free the precipitate from potassium chromate,
as described above. Dissolve this precipitate in the least
necessary quantity of hydrochloric acid, and add a little
water, but leave the solution quite concentrate. To this
solution add dilute sulphuric acid in sufficient quantity to
precipitate all the strontium and calcium as sulphates, and
allow it to stand for the precipitate to form and settle. Fil-
ter, and wash once on the paper. If only a trace of calcium
is present, the filtrate should be tested. Otherwise, it may
be disregarded.
§ 10 QUALITATIVE ANALYSIS. 73
Remove the precipitate to a porcelain dish, cover it with a
concentrate solution of ammonium sulphate,* and heat gently
for about 10 minutes, with frequent stirring. This will dis-
solve the calcium sulphate, while the strontium sulphate is
not acted upon. Filter, and wash two or three times, prefer-
ably with warm water. Test the precipitate for strontium
in the usual manner, and examine the filtrate for calcium by
means of ammonium oxalate, as described above.
GROUP VI.
107. If, at the time of the precipitation of the fifth
group, the boiling was not continued long enough, or exceeded
the proper time, the filtrate may contain traces of barium,
strontium, and calcium ; so, before treating this filtrate for
the sixth group, 2 or 3 drops of sulphuric acid and a like
amount of ammonium oxalate are added, and the solution
boiled for a few moments, taking care that it remains dis-
tinctly alkaline. If a slight precipitate forms, it is filtered
off. The filtrate can now only contain the sixth and seventh
groups. It should be concentrated to 75 or 100 cubic centi-
meters before precipitating. Add a few cubic centimeters
of concentrate ammonia, and then sodium phosphate; stir
well, and let stand for some time for the precipitate to form
and settle. If the solution is very dilute, this may require
several hours, and, at all events, the solution should stand
until it becomes perfectly cold. The presence or absence of
a precipitate at this point is proof of the presence or absence
of magnesium, but if a precipitate is formed, magnesium
may be confirmed by treating a little of it on the charcoal
before the blowpipe, as directed in Art. 79»
GROUP VII.
108. As the alkalies have been added to the solution in
the form of reagents, we cannot use the filtrate from the
sixth group to test for the members of the seventh, but must
♦Ammonium-sulphate solution for this purpose is made by dis-
solving about 15 grams of the solid in 30 cubic centimeters of water.
74 QUALITATIVE ANALYSIS. § 10
take small portions of the original solution. We should first
test for ammonium. To do this, take a small quantity of the
original solution in a test tube, add about an equal amount
of sodium hydrate, and boil. Ammonium compounds, when
present, are always decomposed, yielding ammonia gas NH^^
which is recognized by its odor, by the white fumes that are
formed when in contact with hydrochloric acid, and by its
power of turning red litmus paper blue. The odor is by far
the best proof, for nothing else has a similar odor.
A second small quantity of the original solution is now
taken, a clean platinum wire that has just been tested in the
flame to prove the absence of alkalies, is dipped into it and
the drop of solution adhering to the loop is brought into the
non-luminous flame.
Sodium is recognized by the intense yellow color that it
imparts to the flame, while potassium is recognized by the
violet color that is given to the flame by its compounds.
If both sodium and potassium are present in a solution,
the violet potassium flame is entirely obscured by the intense
yellow flame produced by the sodium. But if the flame is
viewed through a thick, blue (cobalt) glass, the yellow rays
of the sodium are entirely absorbed and the potassium flame
is distinctly seen. A still better method of recognizing
sodium and potassium, is by means of the spectroscope, which
will be described later.
GENERAL DIRECTIONS.
109. We now have before us a method by which any
number of the common metals may be recognized in, and
separated from, solutions containing a mixture of metals, but
the student should not expect to become an expert analyst from
merely reading directions. He should make up mixtures and
separate them according to the scheme given^ following direc-
tions as closely as possible.
The operations are described as carefully as possible, but
a student must perform each of them, with known solutions,
§ 10 QUALITATIVE ANALYSIS. 75
carefully observing the behavior of each metal or group of
metals, before he can be absolutely certain that his results
are correct when working on an unknown solution.
The student will also find that he can learn the method
much more easily and thoroughly by carrying out each
operation as he studies it, using the description given as a
guide in his work.
Mixed solutions for practice can easily be prepared by
mixing some of the solutions made as described for the reac-
tions of the separate metals. In doing this, certain simple
precautions must be taken ; as, for example, chlorides must
not be introduced into solutions containing first-group metals,
or these metals will at once be precipitated as chlorides.
Sulphates must not be added to solutions containing lead,
mercurous, barium, strontium, or calcium compounds, or
these metals will be precipitated as sulphates. Arsenites
and arsenates, under certain conditions, precipitate some of
the metals, so care should be exercised in making solutions
containing these. Much valuable experience will be acquired
in making up these solutions, if the work is done thoughtfully.
The student should not make up too complicated a solu-
tion at first. In fact, it is best to start with a solution con-
taining only metals of the first group, and after these have
been separated, make up more complicated mixtures, but
avoiding the more difficult operations until considerable
familiarity with the work has been acquired.
Each student is strongly advised to make up and analyze
the following list of solutions in their order^ using, in making
these mixtures, the solutions already made up for the reac-
tions of the separate metals. They should be used as soon as
possible after being made up, as some of them decompose upon
standing,
1. Lead, silver, and mercurous.
This is made by mixing equal parts of the nitrates of the
three metals,
2. Lead, bismuth, and cadmium.
This is made by mixing solutions of the nitrates of the
three metals in equal proportions.
76 QUALITATIVE ANALYSIS. § 10
3. Antitnonyy arsenic, and //;/.
To prepare this, mix antimony chloride, stannous chloride,
and sodium arsenite, in equal amounts. If a precipitate is
formed, dissolve it in the least necessary quantity of concen-
trate hydrochloric acid.
4. Iron, aluminum, and chromium.
This is made by mixing equal quantities of the solutions
of ferrous sulphate, common alum, and chrome alum. The
alums will introduce a little potassium or ammonium, or per-
haps both, and the student should examine the solution foi
these as well as for the constituents that were intentionally
introduced.
5. Aluminum, nickel, and zinc.
To prepare this, mix equal amounts of the solutions of
alum, nickel nitrate, and zinc sulphate. This solution, like
the preceding one, should be examined for potassium and
ammonium.
6. Barium, strontium, and calcium.
This is generally made by mixing barium chloride, stron-
tium nitrate, and calcium chloride, in equal quantities. Bui
either the chlorides or nitrates may be used equally well.
7. Magnesium, am^nonium, potassium, and sodium.
This solution is generally a mixture of equal parts of the
solutions of magnesium sulphate, and ammonium, potassium,
and sodium nitrates, but almost any compounds of these
metals will answer the purpose.
This list is given as a guide to the student in starting in
the group separations, and, after completing it, he should
make up and analyze a number of solutions, until he has
determined all of the metals, a few at a time, or he can gel
a friend to make up solutions for him, and thus analyze them
before knowing their composition.
The student must never forget to look for the alkalies,
whether he finds other metals in the solution or not. A por-
tion of the original solution should first be tested for ammo-
nium with sodium hydrate, and then another portion tested
for sodium and potassium in the flame.
The student should never attempt to separate the twc
§ 10 QUALITATIVE ANALYSIS. 77
divisions of the second group until he is thoroughly familiar
with the separation of the metals of each division, as this is
one of the most difficult operations in qualitative analysis.
The sulphides of some of the metals occasionally become
slimy at this point and pass through the filter. Boiling, and
allowing to settle again, sometimes remedies this, but, as a
rule, this portion of the solution must be thrown away, and
the analysis begun again with a fresh portion of the original
solution. However, after the student gains a little experi-
ence in chemical manipulation, this trouble will be very rare.
The separation of Group III, and subsequent groups, mthe
presence of phosphoric or oxalic acid, should never be
attempted until the operator is thoroughly familiar with all
the separations when they are absent.
While the main object in this, as in every part of the
work, is to become able to analyze substances, it is not the
only object. And, although definite directions are given for
the separation of the groups, the directions should not be fol-
lowed blindly and without thought. This system of sepa-
rating the metals is built upon the properties of their com-
pounds, and their deportment with reagents, as previously
described; and the many chemical relations, here brought
together in a small space, should be carefully studied. It is
only by such study that the student will acquire that knowl-
edge of chemical relations which is essential in all advanced
chemical work.
ACIDS.
COMMON INORGANIC ACIDS.
110. Having learned to recognize and separate the
metals, the next step is to learn to recognize the acids in a
similar manner. As most of the substances that a chemist
is called upon to analyze are compounds, he must be able to
determine the acid as well as the metal, and, in order to
have the conditions as nearly the same in practice as in actual
78 QUALITATIVE ANALYSIS. § 10
work, the acids should be determined in compounds rather
than to work on free acids.
The reactions for the common inorganic acids will be
given first, then the reactions for the common organic acids.
These will be followed by the reactions for the less common
inorganic and organic acids.
The student should verify and become familiar with the
reactions for the common acids, both inorganic and organic.
This can only be accomplished by actually performing the
operations, as in the case of the metals. '
The reactions for the less common acids are given more as
a matter of reference, so that if the student is called upon
to determine them at any time, he will have directions for
doing so.
HYDROCHL.ORIC ACID.
111. Hydrochloric acid HCl^ and all chlorides, except
lead, silver, and mercurous chlorides, are soluble in water.
Ammonium chloride or sodium chloride may be used for the
reactions.
1. Silver nitrate precipitates white silver chloride from
solutions of hydrochloric acid or chlorides. This precipitate
gradually turns to brown upon standing for some time in the
light, or is changed much more rapidly by heating. It is
soluble in ammonia or potassium cyanide, and is reprecipi-
tated from these solutions by nitric acid.
2. Lead acetate precipitates white lead chloride PbCl^
from solutions that are not too dilute. Lead chloride is some-
what soluble in cold water, so it is not completely precipi-
tated. It is soluble in hot water, and, upon cooling, crystal-
lizes from this solution in white needles.
3. Mercurous nitrate precipitates white mercurous chloride
Hg^Cl^, which is not dissolved by dilute acids, but is soluble
in hot concentrate nitric acid. Ammonia changes this pre-
cipitate to black amido-mercurous chloride Hg^NH^CL
4. Solid chlorides, when heated in a test tube with con-
centrate sulphuric acid, are decomposed, yielding free
hydrochloric acid, which may be recognized by its odor. If
§ 10 QUALITATIVE ANALYSIS. 79
a glass rod be dipped in ammonia, and then brought to the
mouth of the tube, dense white fumes of ammonium chloride
are formed.
HYDROBROMIC ACID.
112. Hydrobromic acid HBr forms compounds similar
to those of hydrochloric acid, but they are not so common.
All the common bromides, except those of silver, lead, and
mercury, are soluble in water. Potassium bromide or sodium
bromide may be used for the reactions.
1. Silver nitrate precipitates yellowish-white or light-
yellow silver bromide AgBr from solutions of bromides or
hydrobromic acid. This precipitate is insoluble in dilute
acids, dissolves with some difficulty in ammonia, but is easily
soluble in potassium cyanide.
2. Lead acetate precipitates white lead bromide PbBr^^
which is less soluble in water than the corresponding lead
chloride, but is dissolved by nitric acid.
3. Mercurous nitrate precipitates yellowish-white mercu-
rous bromide Hg^Br^.
4. Most bromides in the solid state, or in concentrate solu-
tions, when heated with concentrate sulphuric acid, are decom-
posed and give off a brownish-red vapor of free bromine.
5. All bromides, with the exception of silver bromide, are
decomposed when heated in a test tube with concentrate
nitric acid, yielding free bromine. If a solution of a bromide
is treated, it is colored yellow, yellowish red, or brownish
red, according to the degree of concentration. If a solid
bromide, or a very concentrate solution is treated with the
nitric acid, brownish-red vapors are given off, which collect
in the upper part of the tube in heavy, reddish globules of
free bromine. This is the most characteristic reaction for
hydrobromic acid.
IIYDRIODIC ACID.
113. The iodides correspond in many respects with the
chlorides and bromides, but many more of the iodides of the
heavy metals are insoluble in water than is the case with the
80 QUALITATIVE ANALYSIS. § 10
chlorides and bromides. The iodides of silver, lead, mer-
cury, bismuth, antimony, tin, and arsenic, are either insolu-
ble, or soluble with difficulty, in water. The others are more
or less easily dissolved. Potassium iodide is best used for
the reactions.
1. Silver nitrate precipitates yellowish- white silver iodide
Agl^ which becomes dark upon standing in the light. It is
insoluble in dilute nitric acid, and only slightly soluble in
ammonia, but is dissolved by potassium cyanide.
2. Lead acetate precipitates yellow lead iodide /&/„ which,
like lead chloride, is soluble in hot water.
3. Mercurous filtrate precipitates greenish-yellow mer-
curous iodide HgJ^^ which is soluble in excess of potassium
iodide ; hence, no permanent precipitate is formed until an
excess of mercurous nitrate has been added.
4. Mercuric chloride^ when added in the proper amount,
produces a scarlet precipitate of mercuric iodide Hgl^^ which
is soluble in an excess of either the potassium iodide or mer-
curic chloride, but is insoluble in nitric acid.
5. Copper sulphate mixed with sulphurous acid gives a
dirty-white precipitate of cuprous iodide CuJ^, Chlorides
and bromides are not precipitated by this reagent; hence, it
is a convenient method of testing for iodides in their pres-
ence. Instead of copper sulphate and sulphurous acid, we
may use a solution, made by mixing 1 part of copper sul-
phate with 2^ parts of ferrous sulphate, and dissolving them
in water, as this solution produces the same precipitate.
G. To test for iodine in a very dilute solution, acidify the
solution with sulphuric acid, add a few drops of starch solu-
tion or starch paste, * and then a few drops of a strong solu-
tion of potassium nitrate. If iodine is present, the solution
will assume a deep-blue color, owing to the formation of blue
starch iodide.
7. All iodides in the solid form, when heated with con-
centrate sulphuric acid in a test tube, are decomposed,
* Starch paste may be made by grinding up a little pure starch with
water, or a solution may be made as described in Art. 80, Experi-
ment 43, Inorganic Chemistry, Part 1.
§ 10 QUALITATIVE ANALYSIS. 81
yielding a characteristic violet vapor of iodine, which collects
in a solid mass on the sides of the upper part of the tube.
Near the edges, where the layer is very thin, this appears
violet, but where the layer is thicker it looks black.
SUL.PHURIC ACID.
114. Sulphuric acid H^SO^ is a very strong acid. It
forms stable compounds with the metals, and is not replaced
in these compounds by any other acid at ordinary tempera-
ture. All the normal sulphates, except lead, mercurous,
barium, strontium, and calcium sulphates, are readily soluble
in water. Sodium sulphate or magnesium sulphate may con-
veniently be used for the reactions.
1. Lead acetate precipitates white lead sulphate PbSO^,
which is only slightly attacked by water or dilute acids. It
may be dissolved in boiling concentrate hydrochloric acid.
1 1 is easily dissolved in alkaline ammonium tartrate, made by
treating the precipitate with tartaric acid and ammonia, as
described in Art. 20, 8, and from this solution the lead may
be precipitated by potassium chromate.
2. Mercurous nitrate precipitates white mercurous sul-
phate HgJSO^ from solutions that are not too dilute. This
is much less soluble in water than calcium sulphate ; hence,
is precipitated from more dilute solutions.
3. Barium chloride precipitates white barium sulphate
BaSO^, which is insoluble in all dilute, and but slightly
attacked by concentrate, acids. The presence of concentrate
acids, and of some salts, hinders the immediate formation of
the precipitate in very dilute solutions.
4. Some sulphates, when very highly heated in a glass
tube, give off sulphurous oxide SO^^ which is recognized by
its penetrating odor.
5. All sulphates in the solid form, when mixed with
sodium carbonate and fused on the charcoal before the blow-
pipe, are reduced to sulphides by the action of the carbon,
and the sulphur, or part of it, unites with the sodium, form-
ing sodium sulphide. If, after cooling, this mass is removed
82 QUALITATIVE ANALYSIS. § 10
to a silver coin, or other piece of silver, broken up,. and a
drop of water added, the solution of sodium sulphide will
attack the silver almost immediately, leaving a dark stain of
silver sulphide Ag^S.
This is not characteristic of sulphuric acid, but merely
shows the presence of sulphur. The other acids of sulphur
give the same reaction. It is very important, however, as it
shows that the compound is a salt of one of the acids of sul-
phur. It is generally spoken of as the coin test.
TIIIOSULPUURIC ACID.
115. Thiosulphuric acid H^S^O^ does not exist in the
free state, but its salts, the thiosulphates, which are often
erroneously called hyposulphites, are stable, and some of
them are important. Most of them are soluble in water.
Sodium thiosulphate may be used for the reactions.
1. Silver nitrate precipitates white silver thiosulphate
AgJSfi^y which changes rapidly to yellow, then brown, and
finally to black, owing to the formation of silver sulphide Ag^S,
The precipitate is easily soluble in excess of the thiosulphate.
2. Lead acetate precipitates white lead thiosulphate
PbSfi^, which is soluble in nitric acid.
3. Barium chloride precipitates white barium thiosulphate
BaSfi^ from rather strong solutions. It is decomposed by
hydrochloric acid, giving off sulphur dioxide, and throwing
out free sulphur in the solution, which it gives a yellowish
appearance. The precipitate is slightly soluble in water, so
in very dilute solutions no precipitate is formed.
4. Ferric chloride imparts a characteristic reddish- violet
color to solutions of thiosulphates. The color is not perma-
nent, but, upon standing, ferrous chloride is formed, and the
solution becomes colorless.
5. All thiosulphates are decomposed by hydrochloric or
sulphuric acid, giving sulphur dioxide and free sulphur.
The sulphur thrown out from thiosulphates is yellow, while
that from sulphites and sulphides is nearly always white.
6. Thiosulphates give the coin test the same as sulphates.
§ 10 QUALITATIVE ANALYSIS. 83
SUIiPHUROUS ACID.
116. Sulphurous acid H^SO^ is a weak, rather unstable
acid, and its salts are also rather unstable. The sulphites of
the alkalies are soluble in water, but the other sulphites are
only soluble with difficulty, or are insoluble. The sulphites,
especially in solution, when exposed to the air, are oxidized
to sulphates ; hence, we generally find sulphates mixed with
sulphites. Pure sodium sulphite Na^SO^ is a convenient salt
to use for the reactions.
1. Silver nitrate precipitates white silver sulphite Ag^SO.^^
which, upon standing, is decomposed into sulphuric acid and
metallic silver. This action is hastened by heating.
2. Lead acetate precipitates white lead sulphite PbSO^y
which is dissolved by nitric acid.
3. Barium chloride precipitates white barium sulphite
BaSO^ from neutral sulphite solutions. This is soluble in
hydrochloric acid ; but, as sulphates are nearly always present
in sulphites, an insoluble residue of barium sulphate gener-
ally remains. By filtering off this residue and adding a few
drops of concentrate nitric acid or chlorine water to the clear
filtrate, the sulphite will be oxidized to sulphate, and barium
sulphate will be precipitated. If this succeeds, it shows that
the solution contained sulphite. The oxidation and conse-
quent precipitation is aided by heating.
Barium chloride docs not precipitate free sulphurous acid.
4. All sulphites are easily decomposed by strong acids,
54elding sulphur dioxide. They are oxidized to sulphates by
chlorine oi bromine water, and, like all other sulphur com-
pounds, give the coin test.
HYDROSULPIIURIC ACID.
117. Hydrogen sulphide //^5 is a weak, unstable acid,
and on account of its acid properties is sometimes called
hydrosiilphiiric acid. It unites with bases, as we have seen,
to form sulphides. The sulphides of the alkalies and alka-
line earths are soluble in water. All the others are insolu-
ble. Sodium or ammonium sulphide may be used for the
84 QUALITATIVE ANALYSIS. § 10
wet reactions, and any sulphide that has been powdered may
be used for the dry ones.
1. Silver nitrate precipitates black silver sulphide Ag^S^
which is soluble in warm nitric acid.
2. Lead acetate precipitates black lead sulphide PbSy
which is soluble in warm nitric acid.
3. Mercurous nitrate precipitates black mercuric sulphide
HgS^ which is not dissolved by any single acid, but is soluble
in aqua regia. When treated as directed in Art. 23, 5, this
precipitate is changed to a white, insoluble compound by
nitric acid.
4. Nearly all the sulphides, either in the solid form or in
solution, are decomposed by heating with concentrate sul-
phuric acid, yielding hydrogen sulphide, which is readily
recognized by its odor or by the black color that it imparts
to a piece of filter paper moistened with lead solution.
NITRIC ACID.
118. Nitric acid HNO^ is a strong, stable acid, and forms
a large number of salts that are also stable. All the nitrates,
with the exception of a few basic ones, are soluble in water;
hence, we cannot use precipitation as a means of recognizing
nitric acid, and must resort to other reactions. Potassium
nitrate is a good salt to use for the reactions.
1. The best test for nitric acid in solution, and, in fact,
the only good ordinary test, is performed by mixing about
2 cubic centimeters, of the solution to be tested, with about
an equal amount of concentrate sulphuric acid in a test tube,
and cooling by holding the tube in water, or by allowing
water to run over the outside of it. When the solution has
reached about the temperature of the room, carefully pour a
solution of ferrous sulphate down the side of the inclined
tube, so that the solutions do not mix, but the ferrous sul-
phate forms a layer on top of the other solution. If the
solution contains a nitrate, a ring will be formed where the
two solutions meet, which will be variously colored accord-
ing to the amount of nitric acid present. If but a small
§ 10 QUALITATIVE ANALYSIS, 85
amount of nitrate is present, the ring will be light red, while
if the quantity is greater, it will be brown or almost black.
The color is caused by nitric oxide NO^ which is set free by
sulphuric acid, uniting with the ferrous sulphate, forming an
unstable compound. If the tube is shaken slightly, the liquids
will be mixed slightly at the points where they come in con-
tact, and the ring becomes wider. By heating, the compound
is broken up and the liquid becomes clear. At this time,
if much nitrate were present, brownish vapors of nitrogen
peroxide NO^ may be seen in the upper part of the tube.
2. As nitrites give the above reaction to a certain extent,
it is necessary to distinguish between nitric and nitrous acids.
To do this, place a small quantity of the solution in a test
tube, and add about half the volume of dilute sulphuric acid,
and small amounts of potassium-iodide solution and starch
paste. If nitric acid or a nitrate alone is present, no reac-
tion takes place. Now add a little metallic zinc. The hydro-
gen generated by the action of the sulphuric acid on the
zinc, reduces the nitric acid to nitrous acid ; this sets free
the iodine, which unites with the starch, forming blue starch
iodide. If nitrous acid is present, the blue color will be
produced at once when the reagents are added.
3. All nitrates are decomposed by heat. The nitrates of
the alkalies give off oxygen and are converted into nitrites
at first, but are changed to oxides at a higher temperature.
The nitrates of the heavy metals give off oxygen and nitric
peroxide at once, and are converted into the oxides of these
metals. If the nitrates are ignited in a small glass tube that
is closed at one end, the oxygen given off will ignite a spark
held at the mouth of the tube.
PHOSPHORIC ACID.
119. The phosphates of the alkalies are soluble in water.
Nearly all the others are insoluble. A solution of sodium
phosphate may be used for the reactions.
1. Silver nitrate precipitates light-yellow silver phos-
phate Ag^PO^^ which is soluble in nitric acid and in ammonia.
86 QUALITATIVE ANALYSIS. § 10
«
2. Lead acetate precipitates white lead phosphate
PbJ^PO^^y which is soluble in nitric acid, but insoluble in
acetic acid.
3. Barium chloride precipitates white barium phosphate
Ba^{PO^^, which is soluble in nitric or hydrochloric acid.
4. Magnesium sulphate precipitates white magnesium-
ammonium phosphate MgNH^PO^ from solutions of phos-
phates containing ammonia and ammonium chloride. In
order to avoid mistaking magnesium hydrate for magnesium
phosphate, it is best to add an excess of ammonium hydrate
to the magnesium sulphate, and then just enough ammo-
nium chloride to dissolve the precipitate thus formed. To
this solution add some of the solution to be tested, and shake
well. In case of dilute solutions, the precipitate is not
formed at once, so it should be allowed to stand for some
time. Agitation aids the formation of the precipitate.
5. Ammonium molybdate in nitric-acid solution, when
added in excess to a solution of phosphoric acid or a phosphate,
produces a yellow precipitate of ammonium phosphomolyb-
date, which varies in composition according to conditions. It
is soluble in ammonia, and also in phosphoric acid or phos-
phates; hence, no precipitate is formed imless there is an excess
of ammonium molybdate. The best way to make this test is to
place about 2 cubic centimeters of the molybdate solution in a
test tube, heat it almost to boiling, and add 2 or 3 drops of the
solution to be examined. If phosphoric acid is present in any
considerable amount, the yellow precipitate is formed almost
at once in this hot solution. Shaking also hastens precipita-
tion. Arsenates also give a yellow precipitate in hot solutions,
and silicates sometimes give a yellow color to the solution.
But neither arsenates nor silicates are so readily precipitated
as are phosphates, and they are easily distinguished by other
reactions.
CAHBONIC ACID.
130. Carbonic acid H.jCO^ is a weak acid that has never
been obtained in the uncombined state, except in very dilute
aqueous solution. Its anhydride, carbon dioxide, and its
§ 10 QUALITATIVE ANALYSIS. 87
salts, the carbonates, are common, and many of the salts are
important. The carbonates of the alkalies are soluble in
water. All other normal carbonates are insoluble in water.
Sodium carbonate is the most convenient salt to use for the
reactions.
1. Silver Jiitrate precipitates white silver carbonate
AgJ^O^^ which changes to brown silver oxide Agfi upon
boiling.
2. Lead acetate precipitates white lead carbonate PbCO^^
which is soluble in nitric acid, and also in acetic acid.
3. Barium chloride precipitates white barium carbonate
BaCO^, which is easily soluble, with effervescence, in hydro-
chloric acid.
4. All carbonates, either in the solid state or in solutions
that are not too dilute, are decomposed by dilute hydro-
chloric acid, with effervescence, due to the escaping carbon
dioxide. A drop of barium hydrate on a glass rod, held at
the mouth of the tube where the gas is escaping, will become
turbid, owing to the formation of white barium carbonate.
CHROMIC ACID.
121. Chromic acid H^CrO^ forms a large number of
salts, known as chromates. They are all colored compounds,
and are generally either yellow or red. The chromates of
the alkalies are soluble in water, while most of the other
chromates are insoluble. Potassium chromate serves well
for the reactions.
1. Silver nitrate precipitates red silver chromate
AgJI^rO^^i which is soluble in either nitric acid or ammonia.
2. Lead acetate precipitates yellow lead chromate
PbCrO^^ which is soluble in sodium hydrate, and is reprecip-
itated from this solution by nitric acid.
3. Mercurous nitrate precipitates red basic mercurous
chromate, which is insoluble in sodium hydrate, but is dis-
solved by nitric acid.
4. Barium chloride precipitates yellow barium chromate
88 QUALITATIVE ANALYSIS. § 10
BaCrO^^ which is soluble in nitric or hydrochloric acid, and
also in chromic acid.
6. Many of the dry chromates, when heated with concen-
trate hydrochloric acid in a test tube, are changed into chlo-
rides of chromium and the metal that acted as the base, and
free chlorine is given off.
6. A yellow normal chromate solution may be changed
to a red bichromate by adding an acid, preferably nitric
acid. The red bichromate thus formed may be changed
back to the yellow normal chromate by adding an excess of
ammonia.
7. All chromate solutions containing an excess of hydro-
chloric acid are reduced to green chromium chloride by
heating with sulphurous acid or alcohol. Sulphuric acid
serves instead of hydrochloric acid, and solutions in nitric
acid can be reduced, though with difficulty.
It is sometimes necessary to reduce chromates of the heavy
metals and put the solution thus obtained through the group
separations in order to be sure of the results obtained in the
dry way.
The chromate is dissolved in an acid that does not precip-
itate the metal acting as the base, alcohol is added, and the
solution is boiled until it becomes a deep green and all alco-
hol is expelled, which may be determined by the odor. The
solution is now diluted to the proper extent and put through
the group separations. The chromium, which has been
reduced to chromium chloride CrCl^^ if hydrochloric acid was
used, or chromium sulphate if sulphuric acid was the solvent,
will, of course, be precipitated in the third group, while the
metal that acted as a base will be precipitated in the group
to which it belongs.
8. If insoluble chromates are fused with sodium carbon-
ate to which a little potassium chlorate is added, chromates
of the alkalies are formed, which may be dissolved in water,
while the metals of the original chromates remain as insolu-
ble carbonates or oxides. The solution will give the reactions
for chromates. Or we may dissolve the fusion in acid, reduce
the solution, and proceed with the group separations as above.
§ 10 QUALITATIVE ANALYSIS. 89
COMMOK ORGANIC ACIDS.
13 3. Salts of a few of the organic acids are among the
most common substances, so the student should become
familiar with them. Reactions for four of the most common
are given here. If the student becomes thoroughly familiar
with these, he will have no trouble in determining the others,
if called upon to do so, by following the directions given for
their recognition, under the less common acids.
HYDROCYANIC ACID.
133. Hydrocyanic acid HCN is a weak acid that
scarcely reddens litmus paper, and its soluble salts have
an alkaline reaction. The cyanides of the alkalies and
alkaline earths, and mercuric cyanide, are soluble in water.
All other single cyanides are insoluble. The acid and
its salts are exceedingly poisonous, and should be handled
with great care. .Potassium cyanide may be used for the
reactions.
1. Silver nitrate precipitates white silver cyanide AgCN^
which is soluble in potassium cyanide; hence, no precipitate
is formed until silver nitrate is present in excess. The pre-
cipitate is soluble in ammonia, and is reprecipitated from this
solution by nitric acid.
2. Lead acetate precipitates white lead cyanide Pb{CN)^,
which is soluble in warm nitric acid.
3. Mix about 2 cubic centimeters of any cyanide solution,
about ^ cubic centimeter of ferrous sulphate, and 2 or 3 drops
of ferric chloride, in a test tube; add sodium hydrate until
the mixture is alkaline, and heat almost to boiling. Now
add hydrochloric acid till the solution gives an acid reaction,
and a deep-blue precipitate will be formed if the solution con-
tains much cyanide. If the solution is very dilute, a blue
coloration will be seen.
4. All cyanides are decomposed, without charring, by
heating in a test tube with concentrate sulphuric acid, when
00 QUALITATIVE ANALYSIS. § 10
they may be recognized by their characteristic odor, which
is similar to that of bitter almonds.
5. Solid cyanides, when heated in the closed tube, decom-
pose without charring.
ACETIC ACID.
124. Acetic acid C^HJD^ has a sharp, acid taste, and
strong, disagreeable odor, by which it is readily recognized
even in dilute solutions. Its salts, the acetates, are nearly
all soluble in water. Sodium acetate is a convenient salt to
use for the reactions.
1. Silver nitrate precipitates white silver acetate AgCJJfi^
from rather strong solutions of neutral acetates, or from
strong solutions of the acid. This precipitate is dissolved
rather easily in water and more readily in ammonia.
2. Mercurous fiitrate precipitates white mercurous acetate
Hg^C^Hfi^^ from neutral solutions of acetates that are not
too dilute, and from strong solutions of the free acid. The
precipitate is somewhat soluble in cold water, and is more
readily dissolved if the water is warm. It is also soluble in
excess of the reagent.
3. Ferric chloride colors a neutral acetate solution red,
owing to the formation of ferric acetate Fe{C^H^O^^. Upon
boiling, the iron is precipitated as brown basic acetate
Fe{OH)^{C^H^O^y which settles and leaves the supernatant
liquid clear.
If the ferric chloride is added to an acetic-acid solution a
faint red color is seen, which becomes deeper upon the addi-
tion of ammonia. If enough ammonia is added to just
neutralize the solution, and this is heated, the same reaction
is obtained as with neutral acetates.
4. Any acetate heated with concentrate sulphuric acid, is
decomposed, giving off free acetic acid, which is recognized
by its odor. If we modify this by adding concentrate sul-
phuric acid and a little alcohol, and heating, acetic ether is
formed during the decomposition. This is recognized by its
pleasant odor. In either case, the acetate does not char, as
a rule, and never to any great extent.
§ 10 QUALITATIVE ANALYSIS. 91
5. Solid acetates when heated in the closed tube are
decomposed without charring, yielding acetone, which may
be recognized by its odor, and leaving the oxide or carbonate
of the metal in the tube. In cases where the oxide of the
metal remains, carbon dioxide also escapes; and in case of
some of the weak bases some free acetic acid is driven off.
TARTARIC ACID.
135. Tartaric acid CJlfi^ is a colorless, crystalline
solid, with rather a pleasant acid taste. It dissolves quite
readily in water. Tartrates of the alkali metals, and a
few others, are soluble in water. Those that are insol-
uble in water are easily dissolved by nitric or hydrochloric
acid. Sodium-potassium tartrate may be used for the
reactions.
1. Silver nitrate gives no precipitate with free tartaric
acid, but in neutral solutions of tartrates it precipitates white
silver tartrate Ag^C JJ fi ^^ which is dissolved by either nitric
acid or ammonia. Boiling decomposes the precipitate, and
deposits black metallic silver.
2. Lead acetate precipitates white lead tartrate PbCJJfi^
from solutions of tartaric acid or tartrates. It dissolves easily
in nitric acid or ammonia.
3. Barium chloride precipitates white barium tartrate
BaC^HJD^ when added in excess. The precipitate is soluble
in nitric, hydrochloric, or acetic acid.
4. When tartaric acid or a tartrate in the solid state is
heated with concentrate sulphuric acid, it chars, owing to
the separation of carbon, and carbon monoxide is given
off. A characteristic odor like that of burned sugar may be
noted.
5. Solid tartaric acid and tartrates, when heated in the
closed tube, char and give off the characteristic odor resem-
bling that of burned sugar. A black residue of carbon is left
in the tube, mixed with the carbonate of the metal, if the
substance was a tartrate.
92 QUALITATIVE ANALYSIS. § 10
OXAL.IC ACID.
126. Oxalic acid CJIfi^ in the dry state is a white
powder. With 2 molecules of water it forms colorless crys-
tals. In either form it dissolves readily in water. The oxa-
lates of the alkalies are soluble, while most of the others are
insoluble in water. Ammonium oxalate is common, and
serves well for the reactions.
1. Silver nitrate precipitates white silver oxalate AgjOJ?^^
which is readily dissolved by ammonia, or hot concentrate
nitric acid. It is dissolved with some difficulty in dilute
nitric acid.
2. Barium chloride precipitates white barium oxalate
BaC^O^ from neutral solutions of oxalates. The precipitate
is easily dissolved by hydrochloric or nitric acid, and less
easily in acetic or oxalic acid, or ammonium chloride, and is
slightly soluble in water. Ammonia reprecipitates it from
its solutions in nitric or hydrochloric acid.
3. Calcium chloride^ or any other neutral calcium solution,
precipitates white calcium oxalate CaCfi^ from even very
dilute solutions of oxalates or oxalic acid. The precipitate
is almost insoluble in water, and is only very slightly soluble
in acetic or oxalic acid, but is easily dissolved in nitric or
hydrochloric acid. In very dilute solutions, the precipitate
is formed slowly, but is promoted by heating and by the
addition of ammonia.
4. Oxalic acid, and all oxalates in the dry state, when
heated with concentrate sulphuric acid, are decomposed with-
out charring. The sulphuric acid takes water from them,
and carbon monoxide and carbon dioxide are given off. The
carbon monoxide may be ignited at the mouth of the tube,
and bums with a blue flame, either at the mouth, or down in
the tube, depending upon the amount that is given off. The
carbon dioxide precipitates the barium from a drop of barium
hydrate held at the mouth of the tube on a glass rod, and
thus renders it turbid. The student should never fail to get
the tests for these two gases, as this is the most character-
istic reaction for oxalic acid.
5. In the closed tube the oxalates are all decomposed at
§ 10 QUALITATIVE ANALYSIS. 93
a red heat. If heated carefully, they do not char if pure.
Oxalic acid is decomposed into carbon monoxide, carbon
dioxide, and water. The oxalates of the alkalies, and of
barium, strontium, and calcium, are decomposed into carbon
monoxide and carbonates of the metals. The other oxalates
give off both carbon monoxide and carbon dioxide, and are
reduced to the oxides or to the metallic state, according to
the ease with which they are reduced. The carbon monox-
ide may be ignited, and bums with a blue flame.
127. Remarks. — The four acids given are the most com-
mon and important of the organic acids, and if the student
makes himself familiar with these, he will experience no diffi-
culty in determining others, should he be called upon to do so.
It will be noted that heating with concentrate sulphuric
acid is the most characteristic test for these acids. After a
little experience they may be determined with certainty by
this reaction alone ; but the result thus obtained should always
be confirmed by making use of the other reactions given.
The reactions for arsenious and arsenic acids, which are
quite common, have been given with the reactions for the
metals where they are usually found in the course of
analysis.
IiE88 COMMON INORGANIC AC1D8.
BORIC ACID.
128. Boric acid H^BO^ is rather weak in all its chemical
relations. It is soluble in water, and the solution reddens
litmus. It forms but a limited number of salts, and of
these, sodium biborate (borax) is the only very important
one. The salts of the alkalies are the only ones that are
readily soluble in water. Solutions of all the soluble borates
in water give an alkaline reaction.
1. Silver nitrate^ when added to a concentrate solution
of a normal borate of an alkali metal, gives a white precipi-
tate of %AgBO^,Hfi^ which has more or less of a yellow
tint, owing to the formation of a small quantity of silver
94 QUALITATIVE ANALYSIS. § 10
oxide Agfi. In concentrate solutions of the acid borates,
it gives a white precipitate of Ag^BjD^^. From dilute solu-
tions of the borates of the alkalies, brown silver oxide Ag^O
is precipitated. All of these precipitates are soluble in nitric
acid or ammonia. ' . ^r-
2. Lead acetate precipitates white lead metaborate
Pl\BO^^ from strong solutions. The precipitate is soluble
in an excess of the reagent.
3. Barium chloride precipitates white barium metaborate
Ba{BO^^ from strong solutions of normal borates. In acid
borates, the precipitate produced is Ba^B^fi^^^ which is also
white. Either precipitate is soluble in an excess of the
reagent, in ammonium salts, and in acids.
4. The best, and, in fact, the only reliable, test for boric
acid or borates is the characteristic green flame. If boric
acid is mixed with alcohol, and the latter ignited, the
boric acid will impart a green color to the flame at once; but
the borates are not volatile, and, consequently, do not color
the flame until we get the boric acid in a volatile form. To
do this, mix, in a porcelain dish, a little of the borate to be
tested with concentrate sulphuric acid; add some alcohol,
heat the contents of the dish, and ignite the alcohol. The
sulphuric acid sets boric acid free, and this colors the flame.
Boric acid does not usually appear to color the whole flame,
but gives to the flapie a green border. The delicacy of the
reaction is increased by stirring the contents of the dish.
5. If a borate is ground up with a mixture containing
about twice its bulk of acid potassium sulphate and about
half its bulk of calcium fluoride, a drop or two of water
added to form a paste, and this paste held on a platinum
wire in the flame of a Bunsen burner, it gives the flame a
green color for a moment.
CHLORIC ACID.
129. Chloric acid HCIO^^ in very concentrate solution,
is a slightly yellowish liquid, havmg an odor similar to that
of nitric acid. More dilute solutions are colorless and
§ 10 QUALITATIVE ANALYSIS. 95
odorless. All the chlorates are soluble in water; so no pre-
cipitates are obtained.
1. When solutions of chlorates are heated in a test tube
with concentrate hydrochloric acid, the liquid assumes a
greenish-yellow color, and greenish-yellow vapors of chlorine
tetroxide and free chlorine escape.
2. If a solution of a chlorate is colored light blue by a
solution of indigo in sulphuric acid, by adding a little dilute
sulphuric acid, and then carefully introducing a few drops of
a solution of sodium sulphite, the solution is decolorized.
The sulphurous acid of the sulphite takes oxygen from the
chlorate, setting free chlorine, or a lower oxide of it, which
destroys the color of the indigo.
3. Chlorates, when gently heated with concentrate sul-
phuric acid, are decomposed, yielding greenish-yellow explo-
sive fumes of chlorine tetroxide Clfi^, Great care must be
taken in performing this operation, as the chlorine tetroxide
explodes violently at a moderate temperature, often throw-
ing the acid some distance. Very small quantities should be
used, and the tube should always be held pointing away
from the. operator.
4. Nearly all chlorates, when heated in the closed tube,
give off oxygen, and are reduced to chlorides. The oxygen
will ignite a spark held at the mouth of the tube. The
chlorates of barium, strontium, and calcium g^ve off both
oxygen and chlorine, and are reduced to oxides.
HTPOCHLOROUS ACID.
130. Hypochlorous acid HCIO and the hypochlorites
are very unstable. Hypochlorous acid has never been
obtained, except in solution, but its salts are known, and cal-
cium hypochlorite, known as chloride of lime, or bleaching
powder, is important.
1. Stiver nitrate precipitates white silver chloride AgCl
from solutions of calcium hypochlorite, to which enough
nitric acid has been added so that it does not emit an odor
96 QUALITATIVE ANALYSIS. § 10
of chlorine. Silver hypochlorite is formed at first, but this
decomposes into silver chloride and silver chlorate almost
immediately.
2. Lead acetate precipitates white lead chloride PbCl^,
which soon decomposes, forming oxides of lead, giving the
precipitate a yellow color that gradually grows darker until
it becomes brown, owing to the formation of lead dioxide.
3. When hydrochlorites are treated with concentrate sul-
phuric or hydrochloric acid, they are decomposed, giving off
free chlorine, which may be recognized by its color and odor.
HYDROFLUORIC ACID.
131. Hydrofluoric acid HF is a colorless, corrosive
liquid with a penetrating odor. It fumes strongly in the
air, and attacks the tissues, causing sores that are difficult to
heal. It is distinguished from all other acids by its power
of decomposing silica and silicates that are insoluble in other
acids. The fluorides are stable compounds. Those of the
alkalies are quite readily dissolved by water, while all the
others are either insoluble or are dissolved with more or less
difficulty.
1. Silver nitrate precipitates white silver fluoride AgF
from rather strong solutions. It is somewhat soluble in
water, and easily dissolved by nitric acid, but is insoluble in
ammonia.
2. Lead acetate precipitates white lead fluoride PbF^,
which is almost insoluble in water, but is dissolved by nitric
acid.
3. Barium chloride precipitates white barium fluoride
BaF^ from solutions of hydrofluoric acid, but much more
readily from solutions of fluorides. The precipitate is almost
absolutely insoluble in water, but is dissolved by hydrochloric
or nitric acid.
4. Calcium chloride precipitates v»^hite calcium fluoride
CaF^, which is so transparent that it is often difficult to see
the precipitate at first. It is almost absolutely insoluble in
water and is only slightly attacked by acids in the cold. Hot
§ 10 QUALITATIVE ANALYSIS. 97
concentrate hydrochloric acid dissolves it more readily, but
only with great difficulty,
5. Nearly all fluorides are decomposed by warm concen-
trate sulphuric acid, yielding hydrofluoric acid in the gase-
ous state. If a fluoride is heated with concentrate sulphuric
acid in a platinum crucible, covered with a piece of glass,
coated with wax through which lines are traced so that the
liydrofluoric acid can come in contact with the glass, it
attacks the silicon of the glass, forming the volatile fluoride
of silicon SiF^, and thus etches the glass. After removing
the wax, the lines may be plainly seen.
6. A characteristic test for a fluoride may be made by
mixing about equal parts of the finely ground fluoride, and
powdered silicon dioxide SiO^. Place this mixture in a test
tube and add about twice its volume of concentrate sulphuric
acid. Fit the test tube with a perforated rubber stopper,
through which a bent delivery tube passes, as shown in Pig. 9.
The contents of the test tube are now heated, while the end
of the delivery tube is held under water. The volatile fluo-
ride of silicon StF^ that is formed passes through the delivery
98 QUALITATIVE ANALYSIS. § 10
tube into the water, where it produces a white, gelatinous
precipitate of silicic acid. At the end of the operation, first
remove the delivery tube from the water, then withdraw the
stopper from the test tube, and finally remove the test tube
from the flame.
Great care must be taken in performing this experiment.
Water must not be allowed to come in contact with the hot
sulphuric acid or it will cause an explosion, and the hot acid
that will be spattered about may cause much damage. The
operation must not be continued too long, or the hydrofluoric
acid may dissolve the bottom out of the test tube.
SILICIC ACID.
132. Silicic acid H^SiO^ is a gelatinous substance that
may be obtained in dilute aqueous solution, from which it
shows a great tendency to separate as a gelatinous precipi-
tate. It is a very weak acid in its chemical relations, and
will scarcely color litmus paper. The silicates of the alka-
lies are soluble, but all other silicates are insoluble in water.
Some of the silicates are soluble in acids, while others are
almost entirely insoluble. Silicic acid and the silicates are
not frequently met except in mineral analysis, where they
are very common. Most of the silicates are represented by
formulas that express their derivation from metasilicic or
polysilicic acids, but the reactions are the same for these as
for the normal silicic acid.
1. Lead acetate precipitates white lead silicate from solu-
tions of the alkali silicates. The precipitate is soluble in
nitric acid.
2. Barium chloride precipitates white barium silicate from
solutions of the silicates of the alkalies. The precipitate is
soluble in nitric or hydrochloric acid.
3. Concentrate hydrochloric acid precipitates white, gela-
tinous silicic acid from rather strong solutions of the alkali
silicates. If the solution is weak, the precipitate only appears
after standing some time, or on being concentrated.
§ 10 QUALITATIVE ANALYSIS. 99
4. Antmonium-molybdate solution, when heated with a
solution of a silicate, gives the solution a yellow color; and,
if the silicate solution is strong, a slight yellow precipitate
may be formed.
5. All silicates, when fused with sodium carbonate, yield
carbonates of the metal and sodium silicate. The sodium
silicate may be dissolved in water, while the carbonate of the
metal remains undissolved, or the metallic carbonates may
be dissolved in hydrochloric acid, while the silicic acid is
partially precipitated. The silicic acid is somewhat soluble
in water, but by removing it, or evaporating to dryness and
heating, water is driven off, and there is left silicic oxide
SiO^, which is insoluble in water and all acids except hydro-
fluoric acid.
If this silicic oxide is separated from the metals by filtra-
tion or decantation, and heated in a lead or plantinum dish
with a concentrate solution of hydrofluoric acid, it will be dis-
solved, forming volatile silicon tetrafluoride, which will be
driven off by the heat, leaving nothing in the dish except
traces of metallic compounds that were not perfectly sepa-
rated from the silicic oxide.
6. A very convenient test for a silicate depends upon the
formation of what is known as the silica skeleton^ in the
microcosmic bead, A bead is made of microcosmic salt (hydro-
gen-sodium-ammonium phosphate) in the same manner that
a borax bead is made ; a little of the silicate is added, and
the bead is brought into the hottest part of the blowpipe
flame. The metals form part of the fused portion of the
bead, while the silicic oxide (silica) remains undissolved and
floats in the bead. The bead is sometimes colored with a
little copper sulphate, to make the skeleton more easily seen.
NITROUS ACID.
133. Nitrous acid HNO^ is a blue, unstable liquid that
decomposes into nitric acid, nitrous oxide, and water, at
ordinary temperatures. It may be preserved at very low
100 QUALITATIVE ANALYSIS. § 10
temperatures. Its salts, the nitrites, are also rather unsta-
ble. Most of them are soluble in water.
1. Silver filtrate gives a white precipitate in rather strong
solutions of the alkali nitrites. The precipitate is slightly-
soluble in cold water, and is much more easily dissolved if
the water is heated.
2. Ferrous sulphate produces a slight yellowish or green-
ish-yellow coloration in neutral nitrite solutions. This is
changed to a deep-brown color upon the addition of acetic
acid. If the ferrous sulphate contains free sulphuric acid,
the brown color is produced at once.
3. If a few drops of a mixture of potassium iodide, starch
paste, and dilute sulphuric acid, are added to a solution of a
nitrite, a deep-blue color is immediately produced, owing to
the formation of blue starch iodide. This is a very delicate
reaction when properly handled, and shows the presence of
nitrites in even very dilute solutions: The potassium iodide
must be free from iodate, and the mixture of potassium
iodide, starch, and sulphuric acid must remain colorless
until added to the nitrite solution, or the reaction shows
nothing. The sulphuric acid may be considerably diluted if
necessary.
4. Nitrites, when heated with concentrate sulphuric or
hydrochloric acid, are decomposed, and brownish-red fumes
of nitric oxide are given off.
HYDROSUL.PHOCYANIC ACID.
1 34. Hydrosulphocyanic acid HSCN^ or hydrothiocyanic
acidy as it is also called, is an oily liquid with a penetrating
odor, somewhat similar to that of acetic acid. It mixes with
water, forming a very poisonous liquid with an acid reaction.
Upon standing, it is gradually dissociated, and hydrocyanic
acid is formed during the decomposition. It unites with all
bases, forming sulphocyanides, all of which are soluble in
water, except those of silver, lead, and mercury.
1. Silver nitrate precipitates white, curdy silver sulpho-
§ 10 QUALITATIVE ANALYSIS. 101
cyanide AgSCN^ which is insoluble in dilute nitric acid, but
is soluble in ammonia.
2. Lead acetate precipitates yellowish lead sulphocyanide
Pb{SCN)^y which is changed to a white basic compound by
boiling.
3. Mercurous nitrate gives a white precipitate of mercu-
rous sulphocyanide Hg^{SCN)^, or a gray precipitate of mer-
curic sulphocyanide Hg{SCN)^ and free mercury, depending
tipon the degree of concentration and the proportions in
which the two liquids are mixed. The white mercurous
sulphocyanide may be changed to the gray precipitate of
mercuric sulphocyanide and mercury by boiling.
4. Copper sulphate precipitates greenish-black copper
sulphocyanide Cu{SCN)^ from strong solutions of the alkali
sulphocyanides. In dilute solutions, it produces an emerald-
green coloration, but no precipitate.
5. Ferric-chloride solution, acidulated with hydrochloric
acid, imparts a blood-red color to solutions of sulphocyanides,
but does not produce a precipitate. The color is due to the
formation of red, soluble ferric sulphocyanide Fe{SCN)^.
The color is not injured by hydrochloric acid, but is destroyed
by mercuric chloride.
6. When a sulphocyanide is heated with nitric acid, a
violent decomposition takes place, during which nitric and
carbonic oxides are given off, and sulphuric acid is formed.
HYDROFERROCYANIC ACID.
135. Hydroferrocyanic acid H^Fe{CN)^ is a colorless,
crystalline substance that readily dissolves in water, giving
a liquid with a strong acid reaction. The ferrocyanides of
the alkalies and alkaline earths are soluble, while most of the
others are insoluble in water. They are all decomposed by
ignition in the closed tube, and if they are not quite dry,
hydrocyanic acid, carbon dioxide, and ammonia are given
off. If perfectly dry, nitrogen, and sometimes cyanogen,
escape.
102 QUALITATIVE ANALYSIS. § 10
1. Silver nitrate precipitates white silver ferrocyanide
AgJ'e^CN)^^ which is insoluble in nitric acid, and in ammo-
nia in the cold, but is dissolved by potassium cyanide.
2. Lead acetate precipitates white lead ferrocyanide,
which has the formula Pb^Fe{CN)^^ and is not dissolved by
dilute nitric acid.
3. Copper sulphate precipitates reddish-brown copper
ferrocyanide Cu^Fe{CN)^^ which is insoluble in dilute
acids.
4 Ferric chloride precipitates dark-blue ferric ferrocy-
anide /v/''/^f3^(CA^),g, which is insoluble in dilute mineral
acids, but may be dissolved in a large excess of potassium
ferrocyanide, giving a deep-blue solution. The precipitate
is known as Prussian blue.
5. If Prussian blue is heated with an ammoniacal solution
of silver, ferric oxide is precipitated, and silver cyanide is
formed, and remains in solution. If the ferric oxide is sep-
arated, and the solution acidified with nitric acid, white
silver cyanide is thrown down.
6. All solid ferrocyanides, when heated with 1 part of
water and 3 or 4 parts of concentrate sulphuric acid, are
decomposed, yielding hydrocyanic acid, which may be rec-
ognized by its odor.
HYDROFERRICYANIC ACID.
136. Hydroferricyanic acid H^Fe{CN)^ is soluble in
water, and many of its salts are also soluble. The ferricy-
anides, like the ferrocyanides, are all decomposed upon igni-
tion in a closed tube, and in a similar manner.
1. Silver nitrate precipitates orange or reddish-brown
silver ferricyanide Ag^Fe{CN)^^ which is insoluble in nitric
acid, but is dissolved by ammonia or potassium cyanide.
2. Copper sulphate precipitates yellowish-green copper
ferricyanide Cu^FeJi^CN)^^, which is insoluble in dilute hydro-
chloric acid.
3. Ferric chloride does not produce a precipitate in pure
ferricyanide solutions, but gives the solution a dark coloration ;
§ 10 QUALITATIVE ANALYSIS. 103
but as ferricyanides often contain ferrocyanides, a precipitate
is frequently obtained that is due to impurity. A precipi-
tate will also be formed if the ferric chloride contains ferrous
compounds.
4. Ferrous sulphate precipitates blue ferrous ferricyanide
Fe^Fe^"(CN)^^^ which is insoluble in dilute inorganic acids.
The precipitate is known as Turnbults blue.
5. All ferricyanides are decomposed when heated with
1 part of water and 3 parts of concentrate sulphuric acid, and
yield hydrocyanic acid, in the same manner that the ferrocy-
anides do.*
HirDROFL.UOSIL.ICIC ACID.
137. Hydrofluosilicic acid H^SiF^ is a white, deliques-
cent substance that readily dissolves in water, forming a
strongly acid liquid. It may be obtained by leading silicon
tetrafluoride 5/7^^ into water, when hydrofluosilicic and silicic
acids are formed. Its salts are called silicofluorides. Most
of them are soluble in water.
1. Lead acetate^ when added in excess to hydrofluosilicic
acid or a silicofluoride solution, gives a white precipitate of
lead silicofluoride PbSiF^,
2. Barium chloride precipitates white barium silicofluoride
BaSiF^^ which is insoluble in dilute acids.
3. Ammonium hydrate added in excess to solutions of
hydrofluosilicic acid or its salts, decomposes them, forming
insoluble silicic and soluble ammonium fluoride.
4. All solid silicofluorides, when heated with concentrate
sulphuric acid, are decomposed with the evolution of silicon
tetrafluoride and hydrofluoric acid. If a drop of water on a
glass rod is held at the mouth of the tube, it becomes turbid,
owing to the formation of silicic acid. Care must be taken
* It will be noticed that hydrocyanic acid was treated as an organic
acid, while the other cyanogen acids are treated among the inorganic
acids. This is largely an arbitrary division, as all these acids are
allied to both organic and inorganic compounds. Hydrocyanic acid
seems to have more organic than inorganic properties, while in the
other acids the inorganic properties appear to predominate.
104 QUALITATIVE ANALYSIS. g 10
not to let the water come in contact with the hot sulphuric
acid, and if the operation is performed in a test tube, it must
not be continued too long or the hydrofluoric acid may
dissolve the tube.
liESS COMMON ORGANIC ACIIWS.
CITRIC ACID.
138. Citric acid C^Hfi^ is obtained in colorless crystals
having 1 molecule of water. It dissolves in water readily,
forming a liquid with a pleasant acid taste. The citrates of
the alkalies, and a number of others, are soluble in water.
1. Silver nitrate precipitates white silver oWxdX^AgJJJIjO^
from solutions of the normal citrates of the alkalies. If rather
a large quantity of this precipitate is boiled with a small
amount of water, it is decomposed with the separation of
metallic silver.
2. Lead acetate^ when added in excess to a solution
of citric acid or a citrate, precipitates white leiad citrate
PbJ^CJIfi^^y which is soluble in ammonia that is free from
carbonate.
3. Barium hydrate^ added in excess to a rather strong
citric acid solution, precipitates white barium citrate
Ba(CJiJD^^, As this precipitate is somewhat soluble in
water, it is not obtained in dilute solutions.
4. Mix about equal parts of citric acid and glycerine, and
heat gently until the mixture begins to puff up. Dissolve
this mass in ammonia, evaporate off the excess, and add
2 or 3 drops of a solution, consisting of 1 part of red, fuming
nitric acid and 4 parts of water. The solution assumes a
green color, which is changed to blue by gently heating.
A drop or two of hydrogen peroxide may be used instead
of nitric acid. This reaction may be used to detect small
quantities of citric acid in the presence of oxalic, tartaric,
and malic acids.
5. Citric acid, and all citrates in the solid state, when
§ 10 QUALITATIVE ANALYSIS. 105
heated with concentrate sulphuric acid, are decomposed,
yielding, at first, carbon monoxide, then carbon dioxide and
acetone also, while the solution remains clear; finally the
solution blackens, and sulphur dioxide is given off. In
order to get these gases in the above order, the mixture
should be heated slowly. Carbon monoxide may be recog-
nized by its blue flame, carbon dioxide by its property of
rendering turbid a drop of barium hydrate, and acetone and
sulphur dioxide by their characteristic odors.
6. Citric acid and citrates, when heated in the closed
tube, char, and emit pungent acid fumes that are readily
distinguished from those given off by tartaric acid when it
carbonizes.
7. Calcium chloride does not produce a precipitate in
solutions of free citric acid, but if enough ammonium or
sodium hydrate is added to neutralize the solution, white
calcium citrate CaJ^CJIfi^^ is thrown down, provided the
solution is not too dilute.
MALIC ACID.
139. Malic acid C^Hfi^ is a deliquescent, crystalline
substance that readily dissolves in water. Most of the
malates are also soluble in water.
1. Silver nitrate precipitates white silver malate
AgrjO ^H jO ^ from solutions of normal malates of the alkalies.
The precipitate becomes slightly gray upon standing for
some time, or more readily by boiling.
2. Lead acetate precipitates white lead malate PbCJIfi^
from solutions of malic acids or malates. If the solution is
acid, precipitation is promoted by rendering the solution just
neutral, with ammonia, but taking care to avoid an excess,
for the precipitate is soluble both in malic acid and in
ammonia. It is also soluble in acetic acid. If the solution,
in which the precipitate is suspended, is boiled, part of the
precipitate is dissolved and the rest will melt into a mass
that resembles resin fused under water.
106 QUALITATIVE ANALYSIS. § 10
3. If calcium chloride, ammonium chloride, and ammonia
are added to a solution of malic acid or a malate, no precipi-
tate is formed even if the solution is boiled. This serves to
distinguish between malic acid and citric acid.
4. Lime water ^ prepared with boiling water, gives no pre-
cipitate with malic acid or malates even upon boiling.
5. MaHc acid, when heated with nitric acid, is decom-
posed with the evolution of carbon dioxide and formation
of oxalic acid.
G. When heated in the closed tube, malic acid is decom-
posed into fumaric acid, water, and maleic anhydride CJifi^,
Water and maleic anhydride are first driven off, and then
the fumaric acid is volatilized and condenses upon the upper
part of the tube where it is cool, forming a crystalline subli-
mate. This is a characteristic reaction for malic acid.
7. If a solution of malic acid in a test tube is acidified
with a few drops of sulphuric acid, a little potassium
bichromate added, and the contents of the tube heated to
boiling, an odor resembling that of fresh apples is obtained.
This reaction may be used to detect malic acid in the pres-
ence of citric acid.
8. If malic acid, or a malate in the solid form, is care-
fully heated with concentrate sulphuric acid, carbon mon-
oxide and carbon dioxide are given off at first; then the acid
turns brown, and finally black, and sulphur dioxide is
evolved. The carbon monoxide and carbon dioxide are
recognized, in the usual manner, by the blue flame and drop
of barium hydrate. The sulphur dioxide is recognized by
its characteristic penetrating odor.
FORMIC ACID.
140. Formic acid CHfi^ is a colorless, corrosive liquid
that fumes slig"htly in the air and has a very penetrating
odor. All formates are soluble in water. One of their
most characteristic properties is the power of reducing com-
pounds of the heavy metals, either to the metallic condition
or to a lower state of oxidation.
g 10 QUALITATIVE ANALYSIS. 107
1. Silver nitrate gives no immediate precipitate in solu-
tions of free formic acid or dilute sohitioiis of formates. In
concentrate solutions of alkali formates, white silver for-
mate AgCHO^ is thrown down. This precipitate rapidly
assumes a dart color, owing to its rediiction to metallic sil-
ver. If the test of formic acid or formate that failed to give
a precipitate at iiret, is allowed to stand, or is heated, metal-
lic silver separates as a gray powder, or as a coating on the
sides of the test tube. This reduction is prevented by an
excess of ammonia.
3. Mcrcurous nitrate gives no precipitate in solutions of
free formic acid, but in strong solutions of alkali formates,
white glistening mercurous formats /;^,(C//f?,), separates.
This precipitate rapidly becomes gray, owing to the reduc-
tion to metallic mercury. The precipitate is completely
reduced after standing for same time ia th^ cold, but, by
heating, complete reduction is accomplished almost immedi-
ately.
^ 3, Mercuric chloride, free from hydrochloric acid, when
heated with a solution of formic acid or a formate, is reduced,
and mercurous chloride HgJJl^ separates as a white precipi-
tiite before the solution reaches the boiling point. This
reaction serves to distinguish formic from acetic acid. It is
hindered or prevented by the presence of hydrochloric acid
or alkali chlorides.
4. ■. Ferric chloride, when added to a neutral formate solu-
tion imparts a deep-red color to the solution. The same
result may be obtained by adding ferric chloride to formic
acid, and then just neutralizing with ammonia. This reac-
tion is similar to the reaction of ferric chloride with acetic
acid.
5. Formic acid and all solid formates, when heated with
concentrate sulphuric aci 1, arc decomposed, the sulphuric acid
extracting water, and setting free carbon monoxide, which
escapes with effervescence, atid, when ignited, bums with
a blue flame. The solution does not carbonize, but remains
clear, unless some organic impurity is present. When for-
mates or formic a;id are heated with concentrate sulphuric
108 QUALITATIVE ANALYSIS. §10
acid and alcohol, ethyl formate is evolved, which is recog-
nized by its pecviliar odor, resembling that of rum.
6. All formates, when ignited in the closed tube, char,
and give oflE carbon monoxide, which, when ignited, burns
with a blue flame. In many cases carbpn dioxide is also
given off, which renders the ignition of the carbon monoxide
difficult. Carbonates, oxides, or metals are left in the tube.
SALICYLIC ACID.
141. Salicylic acid C^Hfi^ is a colorless, odorless, crys-
talline substance that dissolves but slightly in cold water,
more readily in hot water, and very freely in alcohol and
other organic solvents. It forms two series of salts, known
as normal and basic salts. Most of the normal salts are
readily dissolved by water, while many of the basic salts are
but slightly soluble in that medium.
1. Lead acetate precipitates nvhite lead salicylate
Pb(C^Hfi^^ from normal alkali salicylate solutions. The
precipitate is soluble in an excess of lead acetate or acetic
acid, but not in ammonia. It may be dissolved by heating
in the solution from which it was precipitated, and, upon
cooling, will separate in crystals.
2. Ferric chloride^ in very dilute solution, when added in
small amount to a water solution of salicylic acid or one of
its salts, imparts a deep- violet color to the solution. This
is a very characteristic reaction, but it is hindered by the
presence of some other organic acids, and prevented by
hydrochloric acid or ammonia.
3. If a solution of salicylic acid in methyl alcohol (wood
alcohol) is heated with about half its volume of concentrate
sulphuric acid, methyl salicylate is formed, which is recog-
nized by its characteristic odor of wintergreen oil, of which
it is the chief constituent. A solution of salicylic acid in
ordinary alcohol, when heated with concentrate sulphuric
acid, yields ethyl salicylate, which has an odor similar to
that of methyl salicylate.
510
QUALITATIVE ANALYSIS.
109
4. Salicylic acid, when carefully heated in a closed tube,
is not decomposed, but sublimes, forming needle-shaped
crystals on the cool portion of the tube. If quickly ignited
at a high temperature, it is decomposed into phenol and
carbon dioxide.
BENZOIC ACID.
143. Benzoic acid 6*,//,(9, is a white, crystalline sub-
stance that, when strictly pure, is odorless, but generally has
a faint aromatic odor, due to the presence of small quantities
of impurity. It is very sparingly soluble in cold water,
more freely in hot water, and dissolves readily in alcohol.
Most of the benzoates are soluble in water, but a few, having
weak bases, are insoluble.
1. Lead acetate gives no precipitate with free ben-
zoic acid, but, from rather strong solutions of the alkali
benzoates, it precipitates lead benzoate Pb(C^Hfi^^,
which is soluble in excess of lead acetate and also in
acetic acid.
2. Ferric-chloride solution, carefully mixed with a little
very dilute ammonia until it takes on a brownish-red color,
but remains clear, precipitates flesh-colored basic ferric
benzoate Fe^{C^HJJ^,Fcfi^, which is decomposed by hydro-
chloric acid, with separation of benzoic acid. This reac-
tion serves to distinguish between benzoic and salicylic
acids.
3. Benzoic acid i i dissolved in concentrate sulphuric acid
without decomposition. It is precipitated unchanged from
its solution in sulphuric acid by the addition of water.
4. Strong mineral acids, when added to concentrate solu-
tions of the soluble benaoates, take the place of the benzoic
acid that is thrown out as a glistening, white powder. Ben-
zoic acid may be obtained in the same way from insoluble
benzoates, by adding an acid that forms a soluble salt with
the base with which it is united.
5. Pure benzoic acid, when heated in a closed tube, vola-
tilizes completely, leaving the tube clean; but there are
110 QUALITATIVE ANALYSIS. § 10
generally organic impurities present, which remain in the
tube as a charred residue. The acid vapor giyen off has an
irritating effect on the tissues, and when inhaled provokes
coughing.
SYSTEMATIC EXAMINATION OP SOIiUTIONS FOR
ACIDS.
143. It would be a difficult matter to formulate a scheme
for the detection and separation of acids in a solution, simi-
lar to the one used for the metals, which would be so
complete, exact, and practical ; and, fortunately, this is
unnecessary, for the frequently occurring acids are few in
number, and, as a rule, only one, or, at most, but two or
three, will be found in any one solution. In a great majority
of cases, after determining the metals in a solution — which
should always be done first — enough will be known of the
composition of the solution so that we may proceed at once
to apply special tests for the acids. In this part of the work,
more than in any of the preceding, the student must apply
all his knowledge of chemistry, and consider carefully the
full significance of each reaction, and of each fact which he
discovers as he proceeds, or he will make much unnecessary
work for himself. For instance, it would be a waste of time
and chemicals to examine a neutral or acid solution, in which
silver or mercurous compounds had been found, for hydro-
chloric, hydrobromic, or hydriodic acid, for these compounds
cannot exist in such a solution in the presence of these acids.
For the same reason, it would be useless to look for sul-
phuric acid in a solution containing barium or other metals
whose sulphates are insoluble, or to examine a neutral solu-
tion containing calcium for phosphoric or oxalic acid.
All solutions should be tested with litmus paper before the
analysis is commenced, or erroneous conclusions may be
drawn. For instance, silver chloride may exist in ammo-
niacal solution, or phosphates and oxalates of the alkaline
earths may exist in acid solution.
It sometimes happens that the separation of the metals
§ 10 QUALITATIVE ANALYSIS. Ill
from a solution gives no clue to the acid or acids, and it
becomes desirable to pursue a systematic course for their
detection. This is accomplished by dividing them into three
groups, by means of reagents. The first group is composed
of those acids that are precipitated by barium chloride, the
second contains those that are not precipitated by barium
chloride but are precipitated by silver nitrate, and the third '
group is made up of those acids that are not precipitated by
either of these reagents. Tables 2 and 3 give the color and
solubility of the precipitates produced by these reagents, and
as lead acetate helps to classify the acids, a table (4) is given
showing the color and sclubility of precipitates produced
by this reagent.
144. Preparation of the Solution. — In many cases,
preparation is not required, but if the solution contains
metals that would interfere with the reactions, they must be
removed by precipitation. The solution should be slightly
acid ; if it is alkaline or neutral, just enough nitric acid is
added to give an acid reaction with test paper. To remove
the metals of the first and second groups, lead hydrogen-
sulphide gas through the solution until they are all precipi-
tated. Then filter and boil the filtrate until all the hydrogen
sulphide is expelled. If metals of the third, fourth, and fifth
groups are present, add to the solution a slight excess of
sodium carbonate, boil for a moment, and filter. The filtrate
will contain the acids, freed from such metals as would inter-
fere with their determination. Render this slightly acid with
nitric acid, and boil till all carbon dioxide is expelled; then
add dilute ammonia, drop by drop, imtil a point is reached
at which the solution does not give a reaction with either red
or blue litmus paper. It is now ready to be examined foi the
acids. If chromic acid was present, and was reduced by the
hydrogen sulphide, this fact must be noted. The solution
is now divided into three equal parts. The first portion is
treated with barium chloride, the second with silver nitrate,
and the third with lead acetate. The precipitates produced
in each case are g^ven in the accompanying tables.
112
QUALITATIVE ANALYSIS.
§10
TABLE 8.
ACIDS PRECIPITATED BY BARIUM CHIiORIDE.
Acid.
Color of Precipitate.
Solubility.
SulDhuric
White.
Insoluble in HCl.
Soluble in HCl
with
Thiosulphuric
White.
evolution of SO^
free sulphur.
, and
Sulphurous
White.
Soluble in HCl
evolution of SO^
with
Phosphoric
White.
Soluble in HCl.
Carbonic
White.
Soluble in HCl
effervescence.
with
Chromic
Yellow.
White.
Soluble in HCl.
Soluble in HCl.
Hydrofluoric ......
•
White (from con-
Boric
centrate solu-
tion).
Soluble in HCl.
Silicic.
White.
White.
Soluble in HCl.
Insoluble in HCl.
Hydrofluosilicic. . . .
Oxalic
White.
White.
Soluble in HCl.
Soluble in HCL
Tartaric
Citric and malic acids belong in this group, but must be recognized
by special reactions.
145. Grouping the Acids. — In a majority of cases,
the precipitates produced by these reagents will indicate the
acid present, and it only remains to confirm it by the reac-
tions given for that acid. In some cases, it may be of advan-
tage to have the acids classed in groups, and for this reason
the acids that are likely to be met are arranged in three
groups, according to the plan before indicated. If the stu-
dent has done his work thoroughly up to this point, he will
experience no difficulty in determining the rarer acids, if
called upon to do so, and as they would merely serve to com-
plicate matters, if introduced here, they will be difr-^garded.
§10
QUALITATIVE ANALYSIS.
113
TABLE 3.
ACIDS PRECIPITATED BY SILVER NITRATE.
Acid.
Hydrochloric
Hydrobromic
Hydriodic
Thiosulphuric.
Sulphurous
Hydrosulphuric. .
Phosphoric
Carbonic
Chromic.
Silicic. . .
Nitrous.
Hypochlorous.
Boric.
• • • •
Hydrocyanic
H y drosulphocyanic.
Hydroferrocyanic . .
Hydroferricyanic. . .
Oxalic
Tartaric,
Formic.
Color of Precipitate.
White.
Yellowish white.
Yellow.
White, turns
black on stand-
ing.
White, turns
gray on boiling.
Black.
. Yellow.
White.
Red.
Yellow.
White (from con-
centrate solu-
tions).
White.
White (from con-
centrate solu-
tions).
White.
White.
White.
Yellow.
White.
White.
Solubility.
Insoluble in HNO^,
Insoluble in HNO^,
Insoluble in HNO..
Soluble in UNO,.
Soluble in HNO,.
Insoluble in cold dilute
HNO^.
Soluble in HNO^.
Soluble in HNO^, with
effervescence.
Soluble in HNO^.
Soluble in HNO^.
Soluble in HNO,.
Insoluble in HNO^.
Soluble in HNO,,
9
Insoluble in HNO^.
Insoluble in cold dilute
HNO,.
Insoluble in HNO^.
Insoluble in HNO^,
Soluble in HNO^,
Soluble i n HNO,.
Boiling precipitates
gray metallic silver.
Precipitates gray met-
allic silver upon
standing for some
time in the cold or
more readily upon
heating.
Benzoic and salicylic acids are classed in the second group, but must
be recognized by their special reactions.
114
QUALITATIVE ANALYSIS.
§10
TABLE 4.
ACIDS PRECIPITATED BY LEAD ACETATE.
Acid.
Color of Precipitate.
Solubility.
Hydrochloric. . . .
White.
Soluble in hot water.
Hydrobromic
White.
Soluble in HNO^.
Hydriodic
Yellow.
Soluble in hot water.
Sulphuric
White.
Insoluble in HNO^.
Thiosulphuric . . .
White.
Soluble in HNO,.
Sulphurous
White.
Soluble in HNO-^.
Hydrosulphuric. .
Black.
Solublein warm HNO^
Phosphoric
White.
Soluble in HNO^.
Carbonic
White.
Soluble in HNO,, with
effervescence.
Chromic
Yellow.
Soluble in concentrate
HNO,.
Boric
White.
White.
Soluble in HNO .
Hydrofluoric
Soluble in HNO,.
Hypochlorous . . .
White, turning to
brown on standing.
Silicic
White.
White.
Soluble in UNO .
Hydrocyanic
Soluble in HNO,.
Hydroferrocyanic
White.
Insoluble in HNO,.
Oxalic
White.
White.
Soluble in HNO .
Tartaric
Soluble in HNO,.
Citric
White.
White.
White.
Malic
Salicylic
Benzoic
White, from alkali
benzoates.
The four rare organic acids given in this table are precipitated as
given if the conditions are right, but other reactions must be depended
upon to identify them.
The acids of the first group are those precipitated by
barium chloride. They are: sulphuric^ thiosulphuric^ sul-
phurous^ chromic, phosphoric, carbonic, boric, hydrofluoric^
silicic, oxalic, and tartaric acids.
§ 10 QUALITATIVE ANALYSIS. 115
The second group is composed of the acids that are not
precipitated by barium chloride, but form precipitates with
silver nitrate. This group contains: hydrochloric^ hydro-
bromicy hy dr iodic ^ hydrosulphuric^ hydrocyanic, kydroferro-
cyanicy hy dr oferr icy ante ^ and hydrosulphocyanic acids.
The third group contains those acids that are not precipi-
tated by either of these reagents. They are; nitric^ chloric^
and acetic acids.
Nitrous acid is also sometimes classed in this group, but
generally in the second group. By looking at its reactions
it will be seen that its classification is doubtful.
It must be remembered that we cannot use the filtrate
from the first group of acids to test for the second group,
for in that case the barium chloride, added as the first rea-
gent, will precipitate the silver of the silver nitrate as silver
chloride. Separate solutions must always be used, and \\\
applying tests for the acids of the third group, some of the
original solution must be used.
SPECIAL TESTS FOR ACIBS.
146. Having iiow located the acid within very narrow
limits, special tests are next applied. One or two of the
most characteristic tests for each of the common acids are
given in the- folio wing list. After determining the acid by
one of these tests, it should always be confirmed by the
other reactions given for that acid. ' '
1. Hydrochloric acid, when treated with silver nitrate,
gives a white precipitate of silver chloride AgCl^ which is
easily dissolved by ammonia, and is repreci pita ted by nitric
acid. Sodium thiosulphate also dissolves the precipitate.
2. Hydrobromic acid, treated with silver nitrate, gives
yellowish-white silver bromide AgBr, which is dissolved
with some difficulty in ammonia, but readily by sodium
thiosulphate. .
116 QUALITATIVE ANALYSIS. § 10
The most characteristic test for hydrobromic acid in the
case of a solid bromide is made by heating it in a test tube
with concentrate nitric acid, when reddish-brown vapors of
bromine are given off, and condense in the upper part of the
tube, forming red globules. This test may be applied to all
solid bromides except the bromide of silver, and can also be
applied to concentrate solutions.
3. Hydriodic acid gives yellowish silver iodide Agl
when treated with silver nitrate. The precipitate is almost
insoluble in dilute ammonia, but is dissolved somewhat by
concentrate ammonia, and is readily soluble in sodium
thiosulphate.
A chloride may be recognized in the presence of bromides
and iodides by precipitating all of them with an excess of
silver nitrate, and dissolving the silver chloride with a mix-
ture of equal parts of dilute ammonia and water. After
filtering, the silver chloride may be reprecipitated from the
alkaline filtrate by nitric acid. To distinguish bromides
and iodides when all three acids are present, place a small
quantity of the solution in a test tube, add a few drops of
colorless carbon bisulphide, which will form a globule, and
then add a saturated solution of chlorine water, drop by
drop, and shake the tube frequently. The chlorine water
will first set the iodine free, and this w^'ll give the globule a
violet tint; a few more drops of chlorire water destroys this
color, and sets bromine free, imparting a yellow color to
the globule, which is in turn destroyed by an excess of the
chlorine water.
4. Sulphuric acid, when treated with barium chloride,
gives white barium sulphate BaSO^, which is insoluble in all
acids. Lead acetate precipitates white lead sulphate PbSO^y
which may be dissolved by adding tartaric acid, and then
rendering alkaline with strong ammonia.
5. Thiosulphuric acid, when treated with silver nitrate,
gives, at first, a white precipitate that turns brown, and finally
§ 10 QUALITATIVE ANALYSIS. U7
becomes black, owing to its reduction to silver sulphide Ag'^S.
All thiosutphatea are decomposed by hydrochloric acid, yield-
ing sulphur dioxide and free sulphur
6. Sulphurous acid, when treated with silver nitrate,
precipitates white silver sulphite A^^SO,, which is decom-
posed into gray metallic silver and sulphuric add by boiling-
All sulphites are decomposed by hydrochloric acid, yielding
sulphur dioxide, which is recognized by its odor,
7. Ilj-drosiilphuric Aeld. — Nearly all sulphides are
decomposed when heated with concentrate sulphuric acid,
and yield hydrogen sulphide, which is recognized by its
odor. All precipitates of acids containing sulphur, when
fused on the charcoal with sodium carbonate, form sodium
sulphide. If this fusion is placed on a piece of silver, ground
up, and a drop or two of water added, it leaves a black stain
on the silver, due to the formation of silver sulphide.
8. Phosphoric Acid. — ^If a drop or two of phosphoric
acid, or a solution of a phosphate in nitric acid, are added
to about 2 cubic centimeters of hot ammonium-molybdate
solution in a test tube, a yellow precipitate of ammonium
phosphomolybdate is formed at once. This precipitate is
soluble in ammonia, and is re precipitated by nitric acid.
Arsenious and arsenic acids, if present, must be removed by
hydrogen sulphide before applying this test, as they also
give yellow precipitates, though not so readily as phosphoric
acid.
9. Carhonic AeUI. — Hydrochloric acid decomposes all
carbonates with effervescence, which is due to escaping
carbon dioxide. Effervescence indicates a carbonate, and
this conclusion may be confirmed by testing the escaping
gas with a drop of barium hydrate on a glass rod. Carbon
dioxide renders the barium hydrate turbid.
10. Chromic Acid. — Yellow normal chromates are
changed to red bichromates by rendering them acid with
118 QUALITATIVE ANALYSIS. § 10
nitric or hydrochloric acid. The red bichromates are changed
to yellow normal chromates by ammonia. All chromates, in
solutions containing free acid, are reduced to green chromium
compounds when heated with alcohol or sulphurous acid.
The borax-bead test is also a good one; but, when it is
applied, it must be remembered that all compounds contain-
ing chromium, either in the base or in the acid, give the
color to the bead. Compounds containing chromium in the
base are green, while the chromates are yellow or red.
11. Nitric Acid. — To the solution to be tested for nitric
acid, add an equal volume of concentrate sulphuric acid, and
cool by allowing water to run over the outside of the test
tube. When cool, hold the tube in an inclined position and
carefully add 1 or 2 cubic centimeters of ferrous sulphate, in
such a manner that the liquids do not mix, but the sulphate
forms a separate layer above the solution to be tested. If
nitric acid is present, a dark ring will be formed where the
two solutions meet. This test is sometimes varied by drop-
ping a crystal of ferrous sulphate into the solution instead
of adding the ferrous-sulphate solution. In this case, the
crystal is surrounded by a dark color that gradually spreads
to the rest of the solution.
12. Boric Acid. — Mix the substance to be tested for boric
acid with concentrate sulphuric acid, in a porcelain dish ; add
alcohol, stir, and heat the contents of the dish, and then
ignite the alcohol. The characteristic green flame is con-
clusive proof of boric acid. The free acid gives the flame
without being mixed with sulphuric acid, b)it nearly all the
borates are non-volatile.
13. Silicic Acid. — Solutions to be tested for silicic acid
may be rendered distinctly acid with hydrochloric acid, and
evaporated to dryness in a porcelain dish. The residue is
treated with hydrochloric acid to dissolve any metals present,
and silicic oxide will remain as an undissolved residue. This
may be separated from the solution, removed to a platinum
§ 10 QUALITATIVE ANALYSIS. 119
crucible, and dissolved in hydrofluoric acid. Upon heating,
the silicon tetrafluoride formed is volatilized, leaving the
crucible empty.
For solid silicates, the silica skeleton in the microcosmic
bead, described in Art. 13S, 6, gives an easy means of
recognizing the acid. This reaction may be performed,
using any precipitate obtained from silicic acid.
14. Arsenious and Arsenic Adds. — These acids have
been treated among the metals where they are always found
in the course of analysis. Arsenious acid is precipitated at
once from acid solutions by hydrogen sulphide, as yellow
arsenious sulphide. Arsenic acid is first reduced to arseni-
ous by the hydrogen sulphide, and is then precipitated. Heat
promotes the reduction and precipitation. They may be
further identified by their reactions with silver nitrate.
Neutral solutions of arsenites produce a yellow, and arsenates
a red, precipitate.
15. Hydrocyanic Acid. — To test a solution of hydro-
cyanic acid, mix about 2 cubic centimeters of it in a test tube
with from half a dozen to a dozen drops of ferrous sulphate
and 2 or 3 drops of ferric chloride, add sodium hydrate till
the mixture is distinctly alkaline, and heat nearly to boiling.
Then add hydrochloric acid in sufficient quantity to produce
a distinctly acid reaction. If much hydrocyanic acid is
present, a deep-blue precipitate will be formed, and if but
little of the acid is present, it will give a blue coloration.
This test may be applied to insoluble cyanides by first fusing
them with sodium carbonate. During the fusing, the hydro-
cyanic acid unites with sodium, forming soluble sodium cya-
nide. This is dissolved in about 2 cubic centimeters of water
and the solution treated as described above. The reaction
with silver nitrate, which is similar to that of hydrochloric
acid, is quick and simple, and may serve to identify this acid
in many cases.
16. Hydrosulpliocyanic acid imparts an intense red
coloration to a dilute solution of ferric chloride. The color
120 QUALITATIVE ANALYSIS. § 10
is not injured by hydrochloric acid, but is destroyed by
mercuric chloride.
17. Hydroferrocyanlc Acid. — In acid solutions of hydro-
ferrocyanic acid or ferrocyanides, ferric chloride produces a
dark-blue precipitate of ferric ferrocyanide Fe^'"Fe^"{CN)^^
known as Prussian blue.
18. Hydroferrlcyanlc acid, and solutions of ferricya-
nides, when treated with ferrous sulphate, yield a blue pre-
cipitate of ferrous ferricyanide 7v/"/v/'(CiV)„, which is
insoluble in dilute acids. This precipitate is known as Tum-
buirs blue.
147. Writing Reports. — In reporting analyses, the stu-
dent should adopt a neat and uniform system of writing his
results. In commercial work, the exact form adopted is a
matter of personal preference, but in sending analyses of the
substances, sent with the Question Paper, to the Schools, the
following forms should always be followed. In order to
illustrate the method of using these blanks, analyses are
reported on the forms.
1. Where one metal is to be determined in a solution.
Question No
Reagent.
Precipitate.
Conclusion.
L H^S,
2. NaOH,
Black.
Yellow.
^g^ Pf>^ tig{piis)y Hg(ic)^ or Cu, Pos-
sibly Bi or Sn,
Hg{tc).
•
Remarks. — Mercury in the mercuric condition was indi-
cated as above, and confirmed by the usual reactions. There-
fore, No is a solution of a mercuric compound.
[Signature, etc. ]
§10
QUALITATIVE ANALYSIS.
121
2. Determination of several metals in a solution.
Question No
Group.
Precipitate.
Conclusion.
I.
n.
in.
IV.
V.
VI.
VIL
White.
Black.
None.
Light colored.
None.
None.
Odor of NH^.
No flame test.
j Possible metals — Ag^Pb^Hg{ous),
I Metals found — Ag.
j Possible metals — All of the group.
\ Metals found — Bi^ Cu.
j Possible metals — None.
1 Metals found — None.
j Possible metals — Mn^ Zn.
{ Metals found — Zn.
j Possible metals — None.
( Metals found — None.
j Possible metals — None.
( Metals found — None.
( Ammonium is present, but sodium
( and potassium are not.
Remarks. — The above metals were found and confirmed
in the usual manner. The solution contains a mixture of
compounds of silver, bismuth, copper, zinc, and ammonium.
[Signature, etc.]
3. When metal and acid arc both determined.
Question No
METAL.
Reagent.
1. H^S.
2. NaOH.
Precipitate.
Black.
Blue, black on boiling.
Conclusion.
Ag, Pb, Hg{pus\ Hg(ic\ Cu.
Possibly Bi or 5;/.
Cu,
REMARKa — Copper was determined as shown above, and
confirmed by the other reactions for copper.
122
QUALITATIVE ANALYSIS.
§10
ACID.
Reagent.
1. BaCl^.
2. Pb{C,HfiX
Precipitate.
White, insoluble in acids.
White, soluble in tartaric
acid and ammonia.
Conclusion.
Acid of the first
group. Probably
f
Remarks. — Sulphuric acid was found as above|, and con-
firmed by the coin test and other reactions. '
Conclusion. — The compound is copper sulphate CuSO^.
[Signature, etc.]
QUALITATIVE ANALYSIS.
(PART 2.)
EXAMEN^ATION OF DRY SUBSTAI^^CES,
PREIilMIKABY REMARKS.
1. As we now have before us all the information neces-
sary for the analysis of any common inorganic substance in
solution, the next step will be the analysis of dry substances.
The dry reactions are short and simple, and in many cases
yield positive results very quickly. In case of some complex
substances that do not give positive results by this method,
clues are obtained that render their analysis by the wet
method much easier, after putting them into solution by one
of the methods given later.
In this, as in every part of the work, the student should
not merely follow directions, but should make use of all of
his knowledge of chemistry, and study carefully the cause of
each phenomenon that he observes. Physical properties,
such as the color and form of many substances, give valu-
able indications in regard to their composition, and in some
cases the substances are so strongly indicated in this way
that it is only necessary to confirm them by a few reactions.
But as a rule, a systematic course of treatment should be
pursued. The most common operations are six in number,
and are generally applied in the following order:
§11
For notice of the copyright, sec page immediately following the title page.
2 QUALITATIVE ANALYSIS. § 11
1. Heat the substance in a closed tube,
2. Heat the substance on the charcoal before the bloivpipe,
3. Heat the substance in the non-luminous flame on a loop
of platinum wire,
4. Heat the substance in the borax or microcosmic bead.
5. Fuse the substance on the platinum foil with sodium
carbonate and potassium nitrate,
6. Heat the substance with concentrate sulphuric acid in
a test tube.
One of these tests will show that the substance is one of a
number of compounds. The next will reduce the possible
number, or perhaps indicate the compound, and each suc-
ceeding test reduces the number, until we arrive at a result.
It seldom happens that all six tests are applied to any one
substance, for, when a previous test has shown that a certain
operation will not yield, any information, it is, of course,
omitted.
The above scheme is based upon the supposition that the
substance is not a metal or an alloy. If its appearance indi-
cates that it is one of these, it is treated by a method to be
given later.
EXAMINATION IN THE CliOSEB TUBE.
3. If the substance is in the form of a powder, or in
small crystals, it is ready for analysis; if in lumps or large
crystals, it must first be pulverized. A small quantity of it
is introduced into the tube and shaken down into the closed
end. The quantity should not exceed half an inch in the
bottom of the tube. This is heated gently at first, and
finally at the highest temperature of the Bunsen flame.
The points to be observed are :
1. If water is driven off and condenses in the upper part
of the tube,
2. If any gas escapes,
3. If there is any change of color,
4. If sublimation takes place.
§ 11 QUALITATIVE ANALYSIS. 3
5. If the substance fuses.
6. If the substance carbonizes,
3. Water Is Expelled. — If water is driven oflf, it shows
that the substance belongs to one of the following classes:
1. Substances containing water of crystallization. Many
of these fuse at first, and solidify as the water is driven off.
Some of them, especially alums, borates, and phosphates,
swell up as the water is being driven off.
2. Hydrates^ or compounds cofitaining chemically combined
water^
3. Salts that contain mechanically enclosed water ^ in which
case they usually decrepitate.*
4. Deliquescent substances.
5. Ammonium salts that are decomposed with the forma-
tion of water. Ammonium nitrate is the most common of
these, and in its case nitrous oxide Nfi is formed at the same
time, and will ignite a spark on the end of a splinter held at
the mouth of the tube. The reaction of the water that con-
denses in the tube should always be tested with litmus paper.
An alkaline reaction indicates the presence of ammonium com-
pounds, and an acid reaction indicates a salt of a volatile acid.
Ciertain minerals possess the property of decrepitating
without giving off water, when heated.
4. A Gas or Vapor is Evolved. — If a gas or vapor is
given off, the color, odor, and reaction with litmus paper
should be observed. It should also be tested to see if it is
combustible, and if it will rekindle a spark on the end of a
splinter.
The most common gases given off at this point are the
following :
1, Oxygen is recognized by its power of reigniting a
glowing spark on the end of a splinter of wood, when it is
* By saying that a substance decrepitates is meant that when heated
it breaks up violently into small pieces, which tend, if not confined, to
fl)" some distance. This is usually accompanied with a crackling
• sound.
.■ft**"'**'.
4 QUALITATIVE ANALYvSIS. § 11
held at the mouth of the tube. It indicates nitrates, chlo-
rates, metallic peroxides, or oxides of the noble metals.
2. Sulphur dioxide is recognized by its odor and its acid
reaction. It is produced when sulphites and some sulphates
are decomposed by heat, and also when some sulphates and
sulphides are mixed and ignited.
3. Nitrogen peroxide is known by its brownish-red color
and peculiar odor, and indicates nitrates or nitrites — espe-
cially those of the heavy metals.
4. Carbon dioxide indicates carbonates or oxalates of
metals that are reducible. The gas is odorless, colorless,
and non-combustible. It is recognized by its property of
rendering turbid a drop of barium hydrate, and by extin-
guishing a spark held in the mouth of the tube.
5. Carbon monoxide indicates oxalates or formates. It is
recognized by the blue flame with which it bums when
ignited. In the case of formates of easily reducible metals,
and of a number of oxalates, carbon dioxide is also given off,
and this makes it difficult to ignite the carbon monoxide.
Formates often char to a considerable extent in the closed
tube, while this is very rare with oxalates. When mixed
with a little manganese dioxide and a few drops of water on
a watch glass, and a little concentrate sulphuric acid is
added, oxalates give off carbon dioxide, while formates do
not. This gives us a convenient method of distinguishing
between these two acids.
6. Chlorine^ bromine^ and iodine indicate certain chlorides,
hypochlorites, bromides, and iodides, which are broken up
by heat. They may be recognized by their odor and color.
Chlorine is yellowish green ; bromine, brownish red ; and
iodine, violet. If given off in any considerable quantity,
iodine forms a black sublimate in the upper part of the tube.
7. Hydrogen ciilphide indicates sulphides that contain
water, or thiosulphates. It is readily recognized by its odor,
and, if evolved in sufficient quantity, when ignited, bums
with a pale-blue flame having a red mantle, forming sulphur
dioxide and water.
8. Cyanogen and hydrocyanic acid indicate cyanides that
§ 11 QUALITATIVE ANALYSIS. 5
are decomposed by heat. They are known by their peculiar
odor, similar to that of bitter almonds. Cyanogen, when free
from other gases, will burn with a crimson flame, if ignited.
9. Ammonia, which is recognized by its odor and alkaline
reaction, indicates ammonium salts. Nitrogenous organic
matter or cyanides containing water may also give it off ; but
in this case the substance usually chars, and the ammonia is
generally mixed with other vapors having disagreeable
odors.
10. Nitrous oxide indicates ammonium nitrate, or an
ammonium salt mixed with a nitrate. It is recognized by its
power of supporting combustion, which is almost as great as
that of oxygen. If ammonium nitrate alone is present, its
decomposition products will be completely volatilized, leav-
ing the tube clean.
5. A Change of Color. — If the substance changes
color, the colors before heating, while hot, and after cooling,
should be observed.
1. If the substance changes from white to yellow when
hot, and becomes white again upon cooling, it indicates zinc
oxide ZnOy or a compound of zine, like the carbonate, which
is readily reduced to oxide when heated.
2. A change from white or light yellow to yellowish
brown when hot, turning to dirty light yellow upon cooling,
indicates stannic oxide SnO^,
3. If the substance changes from light yellow to yellowish
red or brownish red when hot, returning to yellow on cool-
ing, and fuses at a high temperature, it indicates lead
oxide PbO,
4. A change from red to brown when hot, turning red
again on cooling, indicates red lead oxide Pbfi^, Intense
heat expels part of the oxygen from this, forming the yellow
oxide PbO,
5. A change from white or light yellow to orange yellow
or reddish brown when hot, turning to pale yellow on cool-
ing, indicates bismuth oxide Bifi^,
G. A change from a light yellowish color to dark brown,
6 QUALITATIVE ANALYSIS. § 11
remaining dark brown after cooling, indicates manganons
oxide MnOy or a compound, as the carbonate, which is
readily reduced to oxide by heat.
7. A change from yellow to dark brown, turning light
reddish brown on cooling, indicates cadmium oxide CdO^ or
a compound, such as the carbonate, that is reduced to the
oxide by heat.
8. A change from light blue or light green to black, with
the evolution of water, when hot, remaining black when cold,
indicates a hydrate or carbonate of copper, changing to oxide,
or a similar change in the corresponding compounds of
nickel.
9. A change from brownish red to black when hot, turn-
ing to brownish red again upon cooling, indicates ferric
oxide Fe^Oy
10. A change from grayish white to black when hot indi-
cates ferrous carbonate FeCO^.
11. A change from yellow to dark orange, the substance
fusing at an intens3 heat, indicates potassium or sodium
chromate.
12. A change from light red to dark red, and then almost
black upon raising the temperature, turning light red again
upon cooling, indicates mercuric oxide HgO, In this case,
intense ignition decomposes the compound, with the evolu-
tion of oxygen and the formation of a sublimate of metallic
mercury in the upper part of the tube.
6. A Sublimate is Formed. — If a sublimate forms, it
shows the presence of a volatile body. By observing the
color and other properties of the sublimate, many substances
may be recognized.
The most common substances givmg a white sublimate are
as follows :
1. Ammonium salts, which may be verified by the char-
acteristic odor of ammonia given ojff when the substance is
heated with a few drops of sodium hydrate.
2. Mercurous chloride, which sublimes without fusing, is
yellow when hot, but turns to white on cooling.
§ 11 QUALITATIVE ANALYSIS. 7
3. Mercuric chloride first fuses, then fills the tube with
dense white fumes that condense in the upper part of the
tube in the form of a white crystalline sublimate. .
4. Lead chloride fuses to a yellow liquid and then vola-
tilizes, forming a white sublimate that is volatilized with
difficulty.
5. Arsenious oxide volatilizes without fusing, and forms
a white crystalline sublimate. If a little powdered charcoal
is introduced into the tube, and heat applied, it reduces the
oxide, and a dark arsenic mirror is produced.
6. Antimonious oxide fuses to a yellow liquid, and sub-
limes at a bright-red heat in the form of brilliant, white,
needle-shaped crystals.
7. Oxalic acid gives off thick fumes that are irrita-
ting, and provoke coughing when inhaled. They condense
in the upper part of the tube, forming a white crystalline
sublimate.
8. Salicylic acid, when gently heated, volatilizes without
decomposition, forming a white crystalline sublimate. It
may be recognized by the odor of phenol, which is given off
when it is quickly and intensely heated.
9. Benzoic acid is volatilized by heat, without decompo-
sition, giving off irritating fumes that induce coughing
when inhaled. The fumes condense in the upper portion of
the tube, forming a white crystalline sublimate.
The most common substances giving a yellow sublimate are
as follows :
1. Sulphur is dark red when hot, but becomes yellow
again on cooling. When heated to rather a high tempera-
ture in the presence of air, it burns to sulphur dioxide. It
may indicate free sulphur, or may result from the decompo-
sition of a metallic persulphide, such as FeS^, *^^a^5» ^^c*
2. Arsenious sulphide gives a sublimate that is red while
hot, but usually turns to yellow upon cooling.
3. Mercuric iodide forms a yellow crystalline sublimate,
that turns red when rubbed with a glass rod, probably owing
to a change in crystalline form.
8 QUALITATIVE ANALYSIvS. § 11
The common substances giving a dark-colored sublimate
are as follows :
1. Iodine gives off violet vapors that condense on the
sides of the tube, forming a black sublimate that often
appears to have a violet tinge at the edges, where the subli-
mate is very thin.
2. Mercury and amalgams form globules in the tube. In
many cases these globules are very minute, and give the
sublimate the appearance of a gray mirror.
3. Mercuric sulphide yields a black sublimate that becomes
red when rubbed with a glass rod.
4. Arsenic and arsenides give a brownish-black shining
mirror, but no globules are formed. The vapors that are
given off have the characteristic garlic odor by which arsenic
may always be recognized.
7. The Substance May Fuse Without Apparent
Decomposition. — This indicates some compound of one of
the alkalies, or one of a few compounds of the alkaline
earths, such as a nitrate, a chloride, or a bromide. If, upon
intense ignition, a gas is given off, and small fragments of
charcoal dropped in the tube are energetically attacked when
they come in contact with the fused mass, a nitrate or chlo-
rate is indicated. The gas evolved in this case is oxygen.
8. The Substance Carbonizes. — If the substance car-
bonizes, or chars, it shows the presence of organic matter.
This is always accompanied by the evolution of gases, and
by water that is usually either acid or alkaline to litmus
paper. If the substance is entirely composed of organic
matter, it will be completely consumed when ignited on the
platinum foil. Much may be learned of the composition of a
substance by noting the odor of the evolved gas. An odor
like that of burning hair indicates an organic compound con-
taining nitrogen. The odor of acetone indicates an acetate.
An odor like that of burnt sugar indicates a tartrate. If the
residue in the tube effervesces when treated with dilute acid,
and the original substance did not effervesce when similarly
treated, it shows that the substance was composed of an
§11
QUALITATIVE ANALYSIS.
organic :icid combined with an alkali, or alkaline -earth
metal, and that this has been reduced to a carbonate by the
heat. I£ this carbonate is soluble in water and gives an
alkaline reaction with litmus paper, we may assume that the
organic acid was combined with an alkali metal. If the car-
bonate is insoluble in water, it indicates that the acid was
united to an alkaline- earth metal.
Compounds containing an organic acid combined with a
metal that is easily reduced, often leave the imcombined
metal in the tube. In this case the oxygen of the oxide is
removed by the carbon that is thrown out during the reac-
tion, leaving the metal, and much or all of the carbon unites
with the oxygen, leaving little or none in the tube.
9. The Substance Remains Unchanged. — If the sub-
Stance is not altered by the heat, it shows the absence of
organic matter, salts containing water of crystallization or
constitution, compounds that are easily fused, those that
change color when heated, and volatile compounds, except
carbon dioxide, which may be given oif without being
observed in any way except by applying a test at the mouth
of the tube.
EXAMINATION" ON TIIB CHARCOAL.
10. Place a little of the substance to be tested in a small
cavity that has been made for the purpose in a piece of fine-
grained, sjft-wood charcoal, and by means of the blowpipe,
direct the flame upon it, heating gently at first, and after-
wards to the highest temperature obtainable. One of the
objects of this treatment is to see if the substance is fusible,
and it should be noted whether the substance fuses easily,
with diflSculty, or is infusible. After trying this, the sub-
stance should be exposed to the inner, or reducing, flame, to
see if it can be reduced to the metallic state by the combined
action of the inner blowpipe flame and the carbon of the
charcoal. Most of the reactions observed in the closed tube
will be repeated on the charcoal, and a number of others
J
10 QUALITATIVE ANALViSIS. § 11
added. The phenomena here observed may lead to the
direct detection of the composition of the substance, or
reduce the number of possible compounds within very nar-
row limits.
11. The Substance Decrepitates. — This indicates one
of a number of crystalline substances, some of which contain
water of crystallization, or substances containing water
mechanically enclosed. Of the crystalline substances that
decrepitate, sodium chloride (common salt) is probably the
most common.
13. The Substance I>eflasrrates. — If the substance
deflagrates (i. e., burns violently), a nitrate or chlorate is
indicated, and more particularly nitrates and chlorates of the
alkalies. Deflagration is caused by the carbon of the char-
coal uniting with the oxygen set free when chlorates or
nitrates are decomposed by the heat. The residue left on
the charcoal should be tested. If the substance was a
nitrate, a carbonate will be left on the charcoal, and may be
recognized by treating part of it with dilute hydrochloric
acid, when it will effervesce. If the substance was a chlorate,
a residue of chloride will be left on the charcoal, and may be
identified by one of the tests for hydrochloric acid.
13. The Substance Fuses. — If the substance fuses and
penetrates the charcoal, or forms a bead in the cavity, with-
out giving an incrustation, gas, or odor, and without changing
color, a salt of an alkali, or one of a few compounds of the
alkaline earths, is indicated. To distinguish between these,
first place a small quantity of the substance in a test tube,
add a little strong solution of sodium hydrate, and heat. If
an ammonium compound is present, ammonia will be evolved,
and is recognized by its odor. Next, bring a little of the
substance into the flame on the loop of a platinum wire, and
observe the color imparted to the flame, both with and with*
out the blue glass. After holding it in the flame for a short
time, dip it into hydrochloric acid, and again bring -it into
the flame, The colors imparted to the flame by the metals
§ 11 QUALITATIVE ANALYSIS. 1!
are: sodium, yellow; potassium, violet: barium, green;
n; and calcium, brick red.
14. The Sabstance Tolatllizes. — If the substance
volatilizes, it indicates one of the. compounds of mercury,
arsenic, antimony, or ammonium, or organic substances.
The student should be very careful not to inhale much of
the vapors given off by these compounds, as they are very
injurious. It is a good plan to make it a rule not to breathe
any of the vapors produced by substances that give subli-
mates in the closed tube; or, if we do so in order to detect
the odor in the case of arsenic, to be very careful not to
inhale much.
15. A Metallic Globule Is Formed.— 1. If, upon the
sustained application of a strong flame for some time, a metal-
lic globule is obtained, and no incrustation is formed, it indi-
cates that the substance was a compound of gold, copper,
silver, or tin. If the globule is yellow, gold is indicated; if
red, it indicates copper; and silver or tin is indicated if a
white globule is formed. In the case of tin and silver,
incrustations are formed, but they are often so slight as to
be overlooked, and so are mentioned here. The compounds
of platinum, iron, cobalt, and nickel are also rediiced; but,
if pure, these metals cannot be fused into globules by the
blowpipe flame.
3. A white, soft, and malleable metallic globule, with a
yellow volatile incrustation that becomes lighter colored
upon cooling, indicates a compound of lead. In this case
th^'iflame is usually colored blue when the incrustation is
volatilized, especially if the reducing flame is used.
3. If the metallic globule is white, hard, and brittle, and
fuses easily, and the incrustation is dark orange yellow when
hot, but changes to lighter yellow upon cooling, and is
volatile, but does not color the flame, a compound of bismuth
is indicated.
'4. A metallic globule that is easily fused and slowly
volatilized, together with a reddish-brown incrustation that
12 QUALITATIVE ANALYSIS. g U
volatilizes without coloring the flame, indicates a compound
of cadmiuni,
5. If the metallic globule is white, hard, and brittle, and
the incrustation is white and volatile, a compound of anti-
mony is indicated.
6. If a white, rather hard, but malleable globule is formed
and a very slight, dark-red incrustation is deposited, silver
compounds are indicated. If small quantities of lead and
antimony are present, the incrustation will be crimson.
7. A bright, readily fusible metallic globule that is malle-
able, together with an incrustation that closely surrounds
the globule and is faint yellow while hot, but becomes white
upon cooling, indicates a compound of tin. The incrustation
is often very slight, and the metallic globule is only obtained
by persistent heating in the reducing flame, or by special
treatment to be described later.
16. An Incrustation Is Formed Wltliout a Metallic
Globule. — It will be noted that some of the metals that were
mentioned as giving metallic globules are also mentioned
here. The reason for this is that some of the compounds of
these metals may yield a metallic globule, while it is impos-
sible to obtain it from others by ordinary means; hence, they
must be treated under both heads.
1. A white incrustation that forms on the charcoal at
some distance from the test, and volatilizes very easily when
heated, giving a garlic odor, indicates a compound of arsenic.
3. A reddish-brown incrustation that volatilizes easily
before the flame without imparting a color to it, indicates a
compound of cadmium,
3. A white incrustation that forms rather near the test,
and is so volatile that it may be driven from place to place
on the charcoal, indicates a compound of antimony.
4. A dark reddish-yellow incrustation that becomes lemon
yellow on cooling, and may he volatilized without coloring
the flame, indicates a compound of bismuth.
In the case of antimony and bismuth, metallic globules are
usually — though not always — formed.
«
§ 11 QUALITATIVE ANALYSIS. 13
5. An incrustation that is deposited rather near the test,
is yellow while hot, but turns to white upon cooling, and is
volatilized with difficulty, indicates a compound of zinc.
C. An incrustation that surrounds the test closely, is
yellowish white while hot, and white when cold, and is not
volatile, indicates a compound of tin.
7. A reddish-brown incrustation that imparts a deup-green
color to the flame indicates a compound of tiiallium.
17. An Infusible Metal. — If the substance does not
give an incrustation, but is reduced to the metallic state
without forming a globule, owing to the infusibility of the
metal, a compound of platinum, iron, chromium, cobalt,
nickel, or manganese is indicated. By heating a little of the
metal in the borax or microcosmic bead, chromium, cobalt,
and manganese may be identified, and the others more or
less clearly indicated.
18. A White, Lamlnous, Infusible Mass.— If a white
mass that is infusible, and is incandescent when highly heated,
is formed on the charcoal, either at once or after water is
expelled, it indicates a compound of tin, aluminum, zinc,
barium, strontium, calcium, magnesium, silicic oxide, or,
possibly, a silicate. A drop or two of cobalt- nitrate solution
should be added, and the mass again heated in the oxidizing
blowpipe flame to the highest temperature obtainable. By
this means the test is general!}' given a characteristic color,
1. B/ue indicates aluminum oxide, or a compound that
has been reduced to the oxide, a phosphate of an alkaline-
earth metal, or possibly silicic oxide, or a silicate.
2. Green indicates an oxide of zinc or tin, or one of their
compounds that has been reduced to the oxide. Stannic
oxide is colored rather a bluish green.
3. Rose color indicates magnesium oxide that may have
been formed by the reduction of some other compound on
the charcoal. Magnesium phosphate gives a violet -colored
residue.
4. Gray indicates an oxide of barium, strontium, calcium,
14
QUALITATIVE ANALYSIS.
§11
one of their compounds that has been reduced to the oxide,
or, possibly, silica, or a silicate. If a small piece of the
test, placed on a piece of red litmus paper, and moistened
with a drop of water, colors the paper blue, it indicates
barium, strontium, or calcium, as the oxides of these metals
give an alkaline reaction. The same test may be applied in
the case of magnesium, as its oxide is also alkaline. To dis-
tinguish between barium, strontium, and calcium, moisten a
small piece of the test on a platinum wire with hydrochloric
acid, dry it carefully near the flame, moisten again with
hydrochloric acid, and bring it into the outer flame, when
the metal will impart its characteristic color to the flame.
The colors imparted by strontium and calcium are very
similar under certain circumstances, and care should be
taken to distinguish between them.
Silicic oxide (silica) and silicates may be recognized by
heating a small portion of the substance in a microcosm ic
bead, when the silica skeleton will be formed if silicon is
present.
19. A Colored Mass. — If a colored residue that is only
slightly luminous when heated is left on the charcoal, it indi-
cates a compound of copper, iron, chromium, cobalt, nickel,
or manganese, or some compound of sulphur. The metals
named may be distinguished from one another with a fair
degree of accuracy by means of the borax or microcosmic
bead, and by fusing on the platinum foil with sodium car-
btHiate and potassium nitrate, as previously described.
If a compound of sulphur is present, it may be recognized
by mixing some of the substance with sodium carbonate and
fusing it on the charcoal, when sodium sulphide is formed,
which, when ground up on a piece of silver and moistened
with a drop or two of water, will deposit a black stain of
silver sulphide. In performing this operation, it is some-
times necessary to heat the mixture, at the highest tempera-
ture obtainable, with the reducing blowpipe flame for some
time, in order to reduce the compound and form sodium
sulphide.
§ 11 QUALITATIVE ANALYSIS. 15
30. In the case of oxides and other easily reducible com-
pounds, such as nitrates, the substance will be reduced to the
metallic state when heated alone on the charcoal, in the
reducing blowpipe flame, if it is a compound of a reducible
metal ; but, in case of compounds that are difficult to reduce,
such as sulphates, sulphides, chlorides, phosphates, etc., the
reduction is greatly facilitated by adding sodium carbonate.
By this means double decomposition is induced, and the
oxide is formed, and from this we may be able to obtain the
metal. In many cases reduction is greatly aided by mixing
the substance with about twice its volume of potassium
cyanide, and heating this mixture in the reducing blowpipe
flame on the charcoal, or by heating the substance with a
mixture of sodium carbonate and potassium cyanide. If a
metallic globule is obtained by any of these methods, it
should be examined as to its color, hardness, brittleness, and
malleability. In case the globule is sufficiently large, it may
be removed from the charcoal with the forceps, placed on a
smooth piece of steel, and examined with the aid of a ham-
mer. If the globules are small, they should be scraped out,
together with the adhering charcoal, into a small mortar, a
little water added, and the charcoal loosened from the metal
by gently rubbing with a pestle. The charcoal is then care-
fully washed out by means of water, and the metal left in
the mortar, where it may be examined by means of the
pestle, or it may be removed to the smooth steel and a
hammer used, as in the case of large globules. If the metal
is yellow, gold is indicated; copper is indicated if the metal
is red; silver is white; tin, grayish white; cadmium, bluish
white; lead, whitish gray; bismuth, reddish gray; and anti-
mony, gray. Lead and tin are soft and malleable ; gold a::d
cadmium are harder than lead and tin, but not very hard,
and are malleable; copper and silver are rather hard, but are
malleable, and bismuth and antimony are hard and brittle.
After examining the globule in this way, it is best to dis-
solve it in acid, and apply the wet reactions. It is impossible
to reduce the alkalies and alkaline-earth metals tp the metal-
lic state by any treatment on the charcoal.
16 QUALITATIVE ANALYSIS. § 11
Many of the reactions observed in the closed tube will also
appear when the substance is heated on the charcoal, and
indicate the same things here that they do in the closed tube.
Thus, ammonia, which is always recognized by its odor,
indicates a compound of ammonium, etc.
EXAMINATION IN THE FliAME.
21. As we have already seen, a number of substances
impart characteristic colors to the flame when heated in it;
and, as the operation is simple and quickly performed, it
gives us a good method of determining these substances. In
performing this operation, be sure that the platinum wire is
perfectly clean, by burning it off till it does not color the
flame, after it has been suspended in hydrochloric acid; and,
while hot, bring the loop in contact with some small particles
of the substance to be tested. They will adhere to the hot
wire, and may be brought into the outer flame, when they
will impart the characteristic color to the flame, if the sub-
stance is one that colors the flame. If the substance does
not color the flame, it should be dipped in hydrochloric acid,
and brought into the flame again. If it does not color the
flame now, dip it into sulphuric acid, and again bring it into
the outer flame, as this is necessary in order to set free phos-
phoric or boric acid. When compounds of sodium are pre-
sent, they give such an intense color as to often obscure the
colors of the other substances, so that it is very often neces-
sary to view the flame through a blue glass. The following
colors when obtained are quite characteristic :
1. Yellow indicates a compound of sodium. It is often
so intense that it is impossible to see the colors imparted to
the flame by other substances that may be present; so, when
a flame is colored an intense yellow, it should be viewed
through a blue glass, when the yellow rays will be absorbed
and other shades will appear.
2. Violet indicates a compound of potassium.
3. Bright red or crimson indicates a comptound of
§ 11 QUALITATIVE ANALYSIS. 17
strontium or lithium. There is a shght difference in these
dames, which serves to indicate more or less clearly to the
experienced chemist which metal is present; but this reaction
alone cannot be depended on to identify either of these
metals with certainty; they may, however, be distinguished
easily by other means, as lithium forms no compounds insol-
uble in water, while strontium forms many.
4. Brick red indicates a comixjund of calcium. Under
certain conditions, the color imparted to the flame by calcium
compounds is almost as bright a red as that given by stron-
tium or lithium, but this is rather unusual.
5. Blue indicates a compound of lead, antimony, arsenic,
or copper chloride CuCl^. All compounds of copper, except
the chloride, impart a green color to the flame.
6. Green indicates a compound of barium, copper, thal-
lium, molybdenum, manganese chloride, boric acid, or phos-
phoric acid. Molybdenum gives a rather yellowish -green
color to the flame; volatile compounds of boric acid impart
a bright green, which often lasts but a moment, and phos-
phoric acid a rather pale green. Borates and phosphates
must be treated with sulphuric acid before trying the flame
reaction. Phosphates may sometimes fail to color the flame,
btit borates always impart a green color, especially if treated
with sulphuric acid and alcohol and ignited in a porcelain
dish, as described in treating the reactions of boric acid.
EXAMINATION IN THE BEAD.
33. Compounds of many of the metals, when heated in
the borax or microcosmic bead, impart a color to the bead
by which these metals are indicated. The colors imparted by
three of these metals — chromium, cobalt, and manganese —
are bo distinctive as to be conclusive proof of the presence of
these metals, and the others may be recognized with toler-
able certainty by this test, after the operator has become
familiar with them. In making Ihis test, first be sure the
wire is perfectly clean; then, whib it is hot, dip the loop
L
18 QUALITATIVE ANALYSIS. § 11
into powdered borax, or microcosmic salt, and heat the por-
tion that adheres to the hot wire until it fuses into a clear,
transparent bead ; and while this is hot bring it in contact
with a few small particles of the substance to be tested^
which will adhere to the soft, hot bead. Only a very small
quantity of the substance sh,()uld be taken for this purpose.
Now heat the bead containing the substance, in the oxidizing
flame, until it is thoroughly fused, and observe the color of
the bead when hot, while cooling, and after it is cold. Then
hpld the bead in the reducing* flame for some time, and note
any change that may take place either while the bead is hot
or after -it -cools. The following . are- the most important
metals that give colored beads, with the colors which they
impart.
A blue bead in both the oxidizing and the reducing flaipe,
that appears more clearly colored upon cooling, indicates
cobalt.
An amethyst-red bead showing the color much better after
cooling, and becoming colorless, but not quite clear, when
heated in the reducing flame, indicates manganese.
A green bead, in both the oxidizing and the reducing
flame, that becomes particularly clear and distinct upon cool-
ing, indicates chromium.
A bead that in the oxidizing flame is bluish green when
hot, and blue when cold, and becomes red in the reducing
flame after considerable of the substance has been added,
indicates copper.
A bead that in the oxidizing flame is brownish red, and
changes to yellow or becomes colorless upon cooling, and in
the reducing flame is red while hot, yellow while cooling,
and yellowish green when cold, indicates iron.
A bead that in the oxidizing flame is red when hot, but
becomes yellowish brown, yellow, or even colorless upon
coolmg, and in the reducing flame is reddish brown when hot,
and becomes gray and opaque when cool, indicates nickel.
A bead that in the oxidizing flame is yellow when hot
and becomes lighter colored — sometimes almost colorless —
on cooling, and in the reducing flame is yellow or almost
11
QUALITATIVE ANALYSIS.
19
colorless when hot, and gray and opaque when cold, indicates
bismuth.
An infusible skeleton floating in the fused bead indicates
silicic oxide or a silicate. For the silicates, a microcosmic
bead must be used.
A bead that, when heated in the oxidizing flame, is light
yellow or opal while hot, and turbid when cold, and becomes
whitish gray in ;the reducing flame, indicates silver.
In the' case of sulphides and arsenides, the substance
should be heated on the charcoal with the blowpipe until the
sulphur or arsenic is driven off, as these may interfere with
the bead reaction to a certain extent, and a little of the
residue is used in the bead.
The most important of the bead reactions may be given in
the form of a table for convenience:
TABLE 1.
O. R MetaL
Blue Co
Amethyst Mn
Green Cr
Hot, — Bluish green }
Cold. — Blue f
Hot, — Brownish red (
Cold, — Yellow or colorless )
Hot.— Red )
Cold -^YeWow )
//^/.—Yellow I
Cold, — Light yellow )
R. F.
Blue
Colorless
Green
Cu Red when cold
Fe
Ni
Bi
\
jrHot.—}
\ Cold. —
j Hot,— I
} Cold —
Hot.-
Cold,
Hot.
Cold,
Hot,
Cold.
Red
-Yellowish green
Red
Gray and opaque
Light yellow
Gray and opaque
EXAMINATION ON THE PI^ATINUM FOIIi,
33. Examination on the foil is only resorted to in cases
where chromium or manganese has been indicated by some of
the preceding tests, when it is used to confirm these metals.
Care must be taken not to fuse compounds of such metals
as lead or mercury on the foil, or they will alloy with the
20 QUALITATIVE ANALYSIS. § 11
platinum and destroy the foil. To perform this operation,
mix a little of the substance with about its own volume
of potassium nitrate, and three times its volume of
sodium carbonate, on the foil, and heat till it is thoroughly
fused. If manganese is present, it is oxidized to manganate
and gives the fusion a deep-green color, which is a very
characteristic reaction for manganese. When the fusion is
dissolved in boiling water, the manganese is precipitated as
a brown oxide. If a chromium compound is present, it will
be oxidized to chromate of sodium or potassium, and will
give the fusion more or less of a yellow tint. In this case
the fusion should be dissolved in equal parts of acetic acid
and water, the solution boiled until all carbon dioxide is
expelled, and lead acetate added. If chromium is present,
yellow lead chromate will be precipitated. The precipitate
is soluble in sodium hydrate, and is reprecipitated from this
solution by nitric acid. The fusion is dissolved in acetic acid
and water, rather than water alone, in order to break up the
carbonate and expel the carbon dioxide, which, if present,
would precipitate the lead as carbonate, and obscure the
reaction with the chromate.
EXAMINATION WITH SULPHITRIC ACID.
24. Treatment with sulphuric acid is for the pur-
pose of detecting the acid present, and much may be
learned of the composition of a substance by this means.
To make this test, place a small amount of the substance in
a test tube, add about 2 or 3 cubic centimeters of concentrate
sulphuric acid ; heat gently at first, then gradually raise the
heat to the boiling point. During this heating, some of the
following gases may be liberated, which will lead tO the
identification of the acid.
1. A colored gas is given off. It maybe:
Chlorine^ which is recognized by its yellowish-green color
and peculiar, penetrating odor, indicates a hypochlorite, a
mixture of a chloride and a nitrate, or a chloride and a
§ 11 QUALITATIVE ANALYSIS. 21
peroxide. These latter may suffer double decomposition, dur-
ing which chlorine is liberated. A greenish-yellow explosive
mixture of chlorine and chlorine tetroxide indicates a chlo-
rate. In case a chlorate has been indicated by a previous
reaction, only a very little of the sample should bs taken, as
a larger quantity is likely to cause a violent explosion,
which is dangerous, as it may spatter the hot concentrate
acid.
Yellowish vapors of bromine^ which are generally mixed
with some hydrobromic acid, may be recognized by their
color and odor, and indicate a bromide. In case a bromide
is thus indicated, a small quantity of the substance should
be heated with concentrate nitric acid, which decomposes
all bromides, except the bromide of silver, giving off reddish
vapors that condense in red globules in the upper part of the
tube.
Dark-red vapors of chromium oxychloride CrO^Cl^ indicate
a mixture of a chloride and a chromate.
Reddish-brown fumes of nitrogen tetroxide N^O^^ which
are recognized by their color and odor, and which indicate a
nitrite. Nitrites are decomposed in the same way when
heated with dilute sulphuric acid.
Violet vapors of iodine^ which condense, forming a black
solid in the upper part of the tube, and show the presence
of an iodide.
2. A colorless gas with an odor may be given off. The
most common are;
Hydrochloric^ or, possibly, hydrobromic^ acid. These are
recognized by their odors, and by the white fumes that arc
produced when they come in contact with a drop of ammo-
nia held at the mouth of the tube on a glass rod. They
indicate salts of these acids. Hydrobromic acid is always
more or less decomposed by the heat of the reaction, and
brownish vapors of bromine may be seen.
Hydrofluoric acid^ known by its penetrating odor and
white fumes, but especially by its power of etching glass,
shows the presence of a fluoride.
Sulphur dioxide^ known by its penetrating odor, like that
22 QUALITATIVE ANALYSIS. § 11
of burning sulphur matches, indicates a sulphite or thiosul-
phate.
Hydrogen sulphide^ recognized by its disagreeable odor,
and its property of blackening a piece of filter paper that
has been moistened with a solution of lead or silver, indi-
cates a sulphide.
Nitric acid^ which is indicated by its odor, and by the
brown fumes that are given off when a small crystal of fer-
rous sulphate is dropped into the tube, indicates a nitrate.
In this case the contents of the tube should be cooled, and
ferrous-sulphate solution cautiously added, when the charac-
teristic brown ring will be formed where the two solutions
meet.
Hydrocyanic acid, which is recognized by its peculiar odor,
similar to that of bitter almonds, indicates a cyanide.
Acetic acid, which is recognized by its odor, indicates an
acetate. In this case a little of the substance should be
heated with concentrate sulphuric acid and alcohol, when
acetic ether, having an agreeable odor somewhat like that of
ripe apples, is evolved.
A gas having an odor like that of burnt sugar, accom-
panied by a charring of the substance, indicates tartaric acid
or one of its compounds.
3. A colorless^ odorless gas may be evolved. It may be ;
Oxygen, which is recognized by its power of igniting a
spark on the end of a splinter when held in the mouth of
the tube, indicates a peroxide, a chromate, or a permanga-
nate.
Carbon dioxide, which is evolved with effervescence, and
renders turbid a drop of barium hydrate or of lime water,
held at the mouth of the tube on a glass rod, indicates a
carbonate. In this case a little of the substance should be
treated in a test tube with hydrochloric acid, as all carbonates
are decomposed by hydrochloric acid, with effervescence.
A few of the mineral carbonates, however, show but slight
effervescence if the acid is dilute.
Carbon monoxide, which is recognized by its burning with
a blue flame when ignited at the mouth of the tube, indicates
§ 11 QUALITATIVE ANALYSIS. 23
an organic compound or a ferrocyanide. Oxalic acid or
an oxalate gives both carbon monoxide and carbon diox-
ide, without any charring of the substance. Both of these
gases should be identified in the case of an oxalate, by the
blue flame, and the reaction with a drop of barium hydrate.
Tartrates give ofiP first carbon monoxide, then begin to char
and give off a mixture of carbon monoxide and sulphur
dioxide, and, finally, the contents of the tube become thick
and black, and jdeld an odor like that of burnt sugar. Formic
acid and formates, when heated with concentrate sulphuric
acid, are decomposed with the formation of water and carbon
monoxide ; the latter escapes with effervescence, and burns
with a blue flame. If heated with concentrate sulphuric
acid and alcohol, ethyl formate is evolved, and is recognized
by its peculiar rum-like odor. Citric acid at first yields
carbon monoxide, then carbon monoxide mixed with carbon
dioxide, which is recognized by its reaction with barium
hydrate, and acetone, indicated by its odor. During this
time the solution remains clear; but, upon continued heat-
ing it assumes a dark color, and sulphur dioxide is given off.
If a white insoluble precipitate is formed during the treat-
ment with sulphuric acid, lead, mercurous, barium, strontium,
or calcium compounds are indicated.
26. Metals and Alloys. — If the appearance of the sub-
stance indicates that it is a metal or an alloy, it should be
examined as to color, hardness, and malleability, and then
small portions of it tested with hydrochloric acid, to see if
hydrogen is liberated, and with nitric acid, to see if nitrogen
dioxide is evolved. If these gases are given off, they prove
the substance to be a metal or an alloy. A small portion of
the metal should next be heated on the charcoal before the
blowpipe. Its behavior here may lead directly to its recog-
nition, or suggest some special test by which it may be
identified.
After these preliminary tests, a small portion of the metal
is treated in a test tube with a mixture of equal quantities
of concentrate nitric acid and water, and heat is applied, if
24 QUALITATIVE ANALYSIS. § 11
necessary. By this means all the metals may be classified as
follows ;
1. Metals that are not acted on by nitric acid, consisting
of gold and platinum.
2. Metals that are oxidized by nitric acid, but whose
oxides are not soluble to any considerable extent in an excess
of the acid, or in water. This group consists of tin and anti-
mony; and, in the presence of these metals, arsenic, and
sometimes bismuth, form compounds that are insoluble in
nitric acid and water.
3. Metals that, when treated with nitric acid, form nitrates
that are soluble in an excess of the acid, or in water. This
class includes all the metals, except those mentioned above.
In any case, evaporate most of the excess of acid, and
dilute the substance remaining in the tube with about four
times its volume of water. If a clear solution is formed, it
may be subjected at once to treatment for the group separa-
tions. If a metal remains unattacked by the acid, it is fil-
tered off, and the filtrate tested for metals that may have
been dissolved ; the metal on the filter is then dissolved in
aqua regia, and the solution tested for gold and platinum, as
directed in the next section, after most of the excess of acid
has been driven off by heating carefully, and the solution
has been diluted with about four times its volume of water.
If a white insoluble mass is formed, it must be filtered off,
and the filtrate examined for metals that may have gone into
solution. The precipitate will probably be the oxide of tin
or antimony, or possibly one or both of these, together wnth
arsenic or bismuth. And, in addition to these, the precipi-
tate may contain undissolved gold or platinum. After wash-
ing it two or three times on the filter, it is removed to a
porcelain dish and heated with yellow ammonium sulphide.
If not all dissolved, filter, wash well on the filter, and treat
the filtrate for the separation of tin, antimony, and arsenic,
as described in Art. 97, Qualitative Analysis^ Part 1. The
precipitate may contain gold, platinum, and bismuth. Dis-
solve it in aqua regia, drive off most of the excess of acid,
dilute with water, heat almost to boiling, and lead a current
§ 11 QUALITATIVE ANALYSIS. 25
of hydrogen sulphide through the hot solution until the
metals are completely precipitated as sulphides. Filter,
remove the precipitate to a porcelain dish, and heat some
time with a mixture of equal parts of concentrate nitric acid
and water. This will dissolve the bismuth sulphide, and
leave the sulphides of gold and platinum unattacked. Filter,
and test the filtrate for bismuth. Then dissolve the pre-
cipitate in aqua regia, and test for gold and platinum, as
directed in Art. 39, et seq. If both gold and platinum are
present, they are separated by means of oxalic acid.
SOIiUTION OF SOIilD SUBSTANCES,
26. As all solid substances, except simple ones that yield
positive results in the dry way, should be* dissolved, and the
solutions subjected to wet analysis, to confirm the results
obtained by the dry method, the means of getting them into
solution becomes a matter of importance. The method to
be pursued will depend on the dry reactions, and it is impos-
sible in a work of this kind to consider every possible case
separately, but a general outline may be given from which
the student may select the method suited to any particular
case. All substances may be divided into three classes, as
follows :
1. Substances soluble in zvater,
2. Substances insoluble in water y but soluble in an acid.
3. Substances decomposed by fusing with carbonates.
As complex substances may contain compounds belonging
to each of these classes, a small portion should be heated in
a test tube with water, the filtrate tested for compounds that
may have gone into solution, and the residue treated with
acids. The excess of acid should be driven off after this
operation, the substance diluted with water, filtered, the
filtrate tested for substances that may have been dissolved,
and the residue, if any remains, fused with carbonates of
sodium and potassium. By this treatment, all compoimds
may be dissolved.
26 QUALITATIVE ANALYSIS. § 11
As the treatment of metals and alloys has already been
described, they will not be considered here.
37. Substances Soluble In Water, — Unless the dry
reactions have clearly shown that such treatment would be
useless, the first operation should be to boil a little of the
substance thoroughly in a test tube with water. All sub-
stances that have been fused, must be ground to a fine pow-
der before treatment. If an imdissolved residue remains, it
should b3 filtered off, and the clear filtrate examined for
compounds that may have been dissolved. The principal
substances dissolved by water are :
1. All chlorates, hypochlorites, acetates, and formates.
2. All chlorides, bromides, and iodides, except those of
silver, lead, and mercury in the mercurous condition.*
3. All nitrates and nitrites, except a few basic nitrates.
4. All sulphates, with the exception of lead, mercurous,
barium, strontium, and calcium sulphates.
5. The alkalies and all their compounds, except metanti-
monate of sodium and potassium silicofluoride.
G. The chromates of copper, zinc, manganese, ferric
iron, and mercury in the mercuric condition.
7. Oxalates of chromium, aluminum, antimony, ferric
iron, and tin in the stannic condition.
8. Sulphides of the alkaline earths. The sulphides of
calcium and magnesium sometimes dissolve with difficulty.
In addition to these, the cyanides, arsenites, arsenates,
acid carbonates, and oxides of the alkaline earths are par-
tially dissolved in water. Calcium sulphate may also be
partly dissolved in a large quantity of water.
28, Substances Insoluble In Water. — If the substance
is insoluble in water, a portion should be placed in a test
tube, concentrate hydrochloric acid added, and the contents
of the tube boiled, if necessary. By this means many sub-
stances insoluble in water are changed to soluble chlorides,
♦Cuprous chloride, bromide, and iodide are insoluble in water; but,
as they are not common, and are rapidly oxidized to soluble cupric
compounds, they may generally be disregarded.
§ 11 QUALITATIVE ANALYSIS. 27
and water is formed, or the acid, if volatile, is driven off, or,
if non-volatile, remains in solution.
If this treatment fails to decompose the substance, a small
quantity of it should be heated in a test tube with concen-
trate nitric acid. This will oxidize some insoluble com-
pounds, forming soluble ones; as, mercurous chloride is
oxidized to mercuric, etc..
If the substance is not dissolved by either of these acids
separately, it should be boiled with aqua regia. If this fails
to dissolve the substance, it must be fused with a carbonate
or subjected to some special treatment in order to get it into
solution. In each case the excess of acid should be driven
off, water added, the substance filtered, and the clear filtrate
tested to see if a part of the substance has been dissolved.
In case the substance is dissolved by one of these acids,
the excess of acid is driven off, the substance diluted with
four or five times its volume of water, and subjected to
examination for the metals in the wet way.
39. Substances Fused With Carbonates. — Most sub-
stances are decomposed by acids, but a few — including anhy-
drous silicates, and sulphates of barium, strontium, and,
possibly, calcium, although the latter is usually dissolved,
partly by water and partly by acids — remain undissolved,
and must be put into solution by some other means. The
most general method of doing this is to fuse the substance
with about six times its weight of a mixture of equal parts
of sodium and potassium carbonates. By this means the
substances are decomposed, the acid of the substance unites
with sodium or potassium, forming soluble alkali salts, and
the metal is changed to carbonate. The fusion is made in a
platinum vessel, usually the foil, and must be continued
until chemical action ceases and the fusion becomes quiet.
Substances that would alloy with platinum must not be
treated in this manner.
The fusion after cooling is transferred to a lest tube or a
small beaker, and boiled with water until it is thoroughly
disintegrated. The acid, which is combined with an alkali,
28 QUALITATIVE ANALYSIS. § 11
will now be in solution, and the carbonate or oxide of the
metal will remain undissolved. Filter, and test the filtrate
for the acid ; then dissolve, in hydrochloric acid, the residue
that remains on the filter, and test this solution for the
metal.
Pulverized silicates that are insoluble in the acids used
may be decomposed by hydrofluoric acid, and this method
must be resorted to when the alkalies are to be determined.
Insoluble cyanides, ferrocyanides, and ferricyanides are
best dissolved by fusing in a porcelain crucible, with about
five times their weight of a mixture of equal parts of sodium
and potassium carbonates. The acid unites with the alka-
lies, forming soluble cyanide, ferrocyanide, or ferricyanide
of sodium and potassium, and carbonates or oxides of the
metals are formed. After disintegrating the fusion in hot
water, and filtering, the acid may be determined in the
filtrate. Then the precipitate is dissolved in nitric acid, and
the metals determined in this solution.
30. We now have before us all the principal dry reac-
tions, and the general methods of dissolving solid substances.
After this has been done, the results obtained in the dry
way should always be confirmed by the wet reactions.
When an acid is used in dissolving a substance, this solution
cannot be used in testing for the acid, for the reactions for
the acid used in dissolving the substance will, of course, be
obtained.
THE RARE ELEMENTS.
31. The rare elements arrange themselves in the same
groups as the common metals, but the distinction between
the groups is not so sharp as in the case of the common
metals; and, as their treatment at that point would have
greatly complicated the work, they were reserved for special
treatment in a separate section. The most important reac-
tions, by which these elements may readily be recognized,
are given here.
§ 11 QUALITATIVE ANALYSIS. 29
GROUP I.
Thallium Tl Tungsten W
32. Thallium. — Thallium is a soft white metal, and is
often found in minute quantities associated with sulphides of
the other metals, as in copper and iron pyrites. It forms
two series of compounds — thallous and thallic — but the latter
are very unstable, and are readily reduced to thallous com-
pounds. It is readily dissolved by dilute nitric or sulphuric
acid, but is only slightly acted upon by hydrochloric acid.
Thallium is not completely embraced in this group, as thal-
lous chloride is slightly, and thallic chloride easily, soluble in
water, so that, in dilute solutions of thallous, or ordinary
solutions of thallic, compounds, the metal passes on to the
fourth group, where it is completely precipitated by ammo-
nium sulphide.
1. Thallic compounds are reduced to thallous compounds
with the separation of free sulphur when treated with hydro-
gen sulphide.
2. Sodium and ammonium hydrates and carbonates precip-
itate brown, gelatinous compounds from thallic solutions, but
give no precipitates with ordinary thallous solutions. The
carbonates give white precipitates with very strong thallous
solutions.
3. Potassium iodide precipitates light-yellow thallous
iodide Tllivora thallous solutions. In thallic solutions the
same precipitate is formed, and iodine is set free.
4. Hydrochloric acid precipitates white thallous chloride
from thallous solutions that are not very dilute, but gives no
precipitate with thallic compounds.
5. Ammonium sulpliide precipitates black thallous sul-
phide Tl^S from thallium solutions. Hydrogen sulphide
produces the same precipitate from solutions that do not
contain inorganic acids, but the presence of inorganic acids
prevents this precipitate.
6. All thallium compounds are readily reduced when
heated on the charcoal before the blowpipe, and deposit a
30 QUALITATIVE ANALYSIS. § 11
dark-violet or black incrustation that is volatile and imparts
a green color to the flame.
7. Thallium compounds are best recognized by the deep
emerald-green color that they impart to the flame, or by
means of the spectroscope. The thallium spectrum consists
of one green line. In many cases the flame or the line can
only be seen for a short time.
33, Tungsten. — Tungsten is a white, hard, brittle ele-
ment that is classed with the metals principally on account
of its weight and some other physical properties. In nearly
all its chemical relations it acts as a non-metal. Its oxygen
compounds are all acid. Magnesium tungstate and the
alkali tungstates are soluble. All the others are insoluble
in water, and many of them in acids. The insoluble tung-
states are best decomposed by fusing with carbonates of
sodium and potassium, when soluble tungstates of the
alkalies are foimed.
1. Hydrochloric or/^ precipitates white //, WO^^Hfiirova
cold solutions, and yellow //, WO^ from hot solutions. These
precipitates are insoluble in an excess of acid, but soluble in
ammonia.
2. Hydrogen sulphide^ when led through a solution of a
tungstate that is rendered distinctly acid, reduces the tung-
state to a lower oxide, and gives the solution a blue color.
3. Ammonium sulphide gives no precipitate in neutral
or alkaline solutions of tungstates, but, if an excess of the
sulphide is added and then the solution is rendered acid,
a light-brown precipitate of tungsten trisulphide WS^ is
formed.
4. Stannous chloride gives a yellow precipitate that
changes to a fine blue color when hydrochloric acid is added
and heat is applied. This is a very characteristic reaction
for tungsten.
5. Metallic zinc and hydrochloric acid added to a tung-
state solution produce a blue color, owing to reduction of
the tungsten to a lower oxide Wfi^,
6. All tungsten compounds, when heated for some time
§ 11 QUALITATIVE ANALYSIS. 31
in the reducing flame, in the microcosmic bead, impart a
blue color to the bead. If iron is introduced, the bead
assumes a blood-red color ; but the blue color is restored by
adding a little tin foil, and heating again.
GROUP n.
DIVISION A.
Palladium Pd Rhodium Rh
Osmium Os Ruthenium Ru
34. These rare elements occur associated with platinum
almost exclusively. They are all completely precipitated by
hydrogen sulphide, and are insoluble in ammonium sulphide
and alkaline hydrates, hence they are completely compre-
hended in this group.
35. Palladium. — Palladium always occurs associated
with platinum, and is nearly always present, in small quan-
tities, in platinum ores. It is obtained from the residue
that is left when platinum is extracted from its ores. It is
lighter than platinum, is white, malleable, and ductile, and
only fuses at very high temperatures. It is more easily
oxidized, and is less dense than platinum. It has both
divalent and tetravalent relations, but the compounds in
which it acts as a divalent element are much more common
and stable. It is not dissolved by hydrochloric acid, and is
only slightly acted on by nitric acid, but is readily dissolved
to PdCl^ by aqua regia.
1. Ammonium hydrate precipitates, from palladium solu-
tions, flesh-colored palladamnionium chloride Pd{NH^^Cl^^
which dissolves in an excess of ammonia, especially when
heated, forming a colorless solution from which it is repre-
cipitated in yellow crystals by hydrochloric acid.
2. Sodium hydrate precipitates a brown basic salt that is
slightly soluble in an excess of the reagent.
32 QUALITATIVE ANALYSIS. § 11
3. Hydrogen sulphide precipitates black palladious sul-
phide PdS from slightly acid solutions of palladium. The
precipitate is insoluble in ammonium sulphide, but dissolves
slowly in hot concentrate hydrochloric acid, and readily in
aqua regia.
4. Ammonium sulphide gives the same reaction as hydro-
gen sulphide.
5. Mercuric cyanide precipitates yellowish-white palladi-
ous cyanide Pd{CN)^ from neutral or slightly acid solutions.
The precipitate is slightly soluble in hydrochloric acid, and is
readily dissolved by ammonia. This reaction is very char-
acteristic, and it is important as the means of separating
palladium from the residuary solution in the platinum
process. The cyanide is decomposed by heat, leaving the
palladium in the spongy form. This is known o.^ palladium
sponge,
G. Stannous chloride in the presence of free hydrochloric
acid gives the solution at first a red color, which quickly
changes to brown, and finally becomes greenish. Upon the
addition of considerable water, this changes to reddish brown.
7. Potassium iodide precipitates black palladious iodide
/V/,, which is soluble in considerable excess of the precipi-
tant, forming a dark-brown solution. This reaction is very
characteristic.
8. Potassium sulphocyanide does not precipitate palla-
dium, even after the addition of sulphurous acid. This gives
us the best means of separating palladium from copper.
36. Osmium. — Osmium is a very rare element, but it
occasionally occurs in platinum ores alloyed with iridium. It
is usually obtained as a black or gray powder, with metallic
luster, and is the most infusible metal known. Metallic
osmium, osmious oxide OsO, osmium trioxide Osfi^^ and
osmic oxide OsO^ are all readily oxidized to osmium tetroxide
OsO^ when heated in the air. This is a very volatile com-
pound, with an exceedingly irritating and offensive odor,
similar to that of chlorine and bromine, and gives us the
best means of recognizing osmium.
g 11 QUALITATIVE ANALYSIS. 33
If a little osmium is held in the outer non-luminous flame
on a platinum wire, it makes the flame exceedingly lumi-
nous. By this means the presence of osmium is indicated in
alloys of osmium and iridium. If only minute quantities of
osmium are present, the flame is only rendered highly
luminous. for a very short time; but, by holding the alloy in
the reducing flame for a time, and then returning it to the
outer flame, this may be repeated.
Fuming nitric acid and aqua regia dissolve osmium, forming
the tetroxide. The application of heat hastens the solution,
and volatilizes the tetroxide, which is recognized by its odor.
Osmium tetroxide, when heated with water, first fuses,
and then slowly dissolves to a colorless liquid, with an
unpleasant, irritating odor.
1. Hydrogen sulphide gives this solution a dark-brown
color; and when an acid is added, a dark-brown precipitate
of osmium sulphide OsS^ is formed. This is insoluble in
ammonium sulphide and alkali hydrates.
2. Sulphurous acid produces at first a yellow color, which,
upon the addition of more of the reagent, changes to reddish
brown, then green, and finally blue.
3. Zinc^ added to an acid solution, precipitates metallic
osmium.
4. All compounds of osmium, when ignited in hydrogen,
yield the metal, but, when ignited on the charcoal in the
oxidizing flame, yield volatile osmium tetroxide, which is
recognized by its odor.
37. RUodium. — Rhodium occurs in very small quanti-
ties in platinum ores. In the compact form it is a silver- white,
malleable metal, which fuses with great difficulty, and is
insoluble in all acids. When precipitated from solution it is
a gray powder, dissolving somewhat in concentrate nitric
acid. A solution of rhodium is best obtained by fusing the
metal or one of its salts in acid potassium sulphate, and dis-
solving the fusion in water or hydrochloric acid. The solu-
• tion in watei is yellow, and the hydrochloric-acid solution
is red.
34 QUALITATIVE ANALYSIS. § 11
1. Sodium hydrate precipitates yellow rhodium hydrate
Rh{OH)^yH^Oy which is changed to dark brown or black
Rh{OH\ by boiling.
2. Hydrogen sulphide^ when led through a hot rhodium
solution for some time, precipitates brown rhodium sulpho-
hydrate RhJ^SH)^ which is insoluble in alkali sulphides and
in single acids, but is dissolved by aqua regia. When this
precipitate is boiled with considerable water, it is decom-
posed into hydrogen sulphide H^S and rhodium sulphide
R/t^S^.
3. Zinc, added to ah acid solution, precipitates black
metallic rhodium.
38. Ruthenium. — Ruthenium, like the other rare
metals of this group, is chiefly found associated with plati-
num. In the compact form it is a grayish-white brittle
metal that is exceedingly difficult to fuse. When precipi-
tated, it is a grayish-black powder. It is scarcely acted upon
by aqua regia, and is unaffected when fused with acid potas-
sium sulphate. A solution of ruthenium is best obtained by
fusing for some time with a larg^ excess of potassium nitrate.
After cooling, the fused mass dissolves in water to an orange-
colored solution of potassium ruthenate KJiuO^. A few
drops of nitric acid precipitate dark-brown . ruthenium
trioxide RuJD^, which is dissolved in hot concentrate hydro-
chloric acid. . This solution is used for the following
reactions:
1. Hydrogen sulphide, when led through this solution for
some time, produces a light-colored precipitate of .unknown
composition. Upon continued treatment, the precipitate
becomes darker, and when nearly black, if the precipitate is
filtered off, a deep sky-blue filtrate is obtained.
3. Ammonium sulphide precipitates brownish- black ruthe-
nium tristilphide Ru^S^, which is almost insoluble in an
excess of the reagent.
3. Potassium iodide, added to a cold solution, slowly pre-
cipitates black ruthenic iodide Rul^. -If added to a hot
solution, the black precipitate is formed at once.
§ 11 QUALITATIVE ANALYSIS. 35
4. Zinc^ added to the acid solution of the chloride, at first
imparts a blue color to the solution, owing to the reduction
to ruthenious chloride, and finally precipitates black metallic
ruthenium.
DIVISION B.
Gold Au Platinum Pt Iridium Ir
Molybdenum Mo Selenium Se Tellurium Te
39. Gold. — Gold is usually found in the metallic state.
In this condition it is recognized by its yellow color, malle-
ability, and insolubility. It is insoluble in any single acid,
but is readily dissolved by aqua regia, forming. ^wC/g. It
acts both as a monovalent and as a trivalent element, but in
most of its compounds it is trivalent.
1. Hydrogen sulphide precipitates brownish-black gold
sulphide Au^S^ from a cold solution of the trichloride. The
precipitate dissolves slowly in colorless ammonium sulphide,
but more readily in yellow ammonium sulphide, and the
solution is promoted by heating. It is not dissolved by any
single acid^ but dissolves readily in aqua regia.
2. Ammonium sulp/tide pveci-pitsites brownish-black gold
sulphide Au^S^, which dissolves in an excess of the reagent,
especially when heated. It dissolves more readily in yellow
ammonium sulphide, and is still more easily dissolved by
yellow sodium sulphide.
3. Ferrous sulphate reduces the gold chloride, and pre-
cipitates metallic gold, in a very finely divided reddish-
brown powder. When held up and looked at towards the
light, the liquid in which the gold is suspended appears
bluish by the transmitted light.
4. Stannous chloride^ which contains some stannic chlo-
ride, produces a purple precipitate, known as ** purple of
Cassius." This precipitate is decomposed, with the separa-
tion of metallic gold, by hydrochloric acid. The mixture of
stannous and stannic chlorides is obtained by adding a few
drops of chlorine water to stannous chloride.
6. Sulphurous acid reduces the chloride, and finely divided
3G QUALITATIVE ANALYSIS. 1 11
metallic gold separates, and is suspended in the solution.
Upon boiling, this settles to the bottom of the tube as a
black powder.
6. Oxalic acidy when heated with a solution of gold chlo-
ride that does not contain too much free acid, reduces the
gold to the metallic state, and gives off carbon dioxide, some-
times with effervescence. After decanting the liquid, the
gold may be fused into a metallic globule. This is best done
in a porcelain crucible. The reaction with oxalic acid affords
the best means of separating gold from other metals, espe-
cially platinum.
40. Platinum. — Platinum in the compact form is a
rather hard, very malleable and ductile, steel-gray metal that
fuses only at very high temperatures, and is insoluble in any
single acid, but dissolves in aqua regia. Platinum sponge is
dull gray, and precipitated platinum is a black powder,
known as platinum black. When platinum is dissolved in
aqua regia, if an excess of hydrochloric acid is present,
platinum chloride PtCl^ is formed. After driving off the
excess of acid by gentle heat, and diluting with water, a
solution is obtained that is suitable for the following reac-
tions:
1. Hydrogen sulphide ^ when led into a cold platinum
solution, at first colors the solution brown, and then slowly
precipitates brownish-black platinum sulphide PtS^. If the
solution is heated, the precipitate forms at once. Ammo-
nium and sodium sulphides, especially when heated, dissolve
this precipitate, but the solution is slow, and it is difficult to
dissolve it completely. Hot concentrate nitric acid slowly
dissolves the precipitate that is formed in the cold, but
scarcely acts on the sulphide precipitated from hot solutions.
It dissolves in aqua regia.
3. Ammonium sulphide precipitates brownish-black plati-
num sulphide PtS.^^ which is slightly soluble in an excess of
the reagent, and more easily dissolved by yellow ammonium
or sodium sulphide. Heat aids the solution.
3. Ferrous sulphate does not produce a precipitate in
§ 11 QUALITATIVE ANALYSIS. 37
solutions of platinum chloride, except upon long-continued
boiling, in which case platinum finally separates.
4. Stannous chloride does not precipitate platinum from
its solutions, but imparts a dark-red or reddish-brown color
to the solution.
5. Potassium iodide^ when added in excess to an ordinary-
platinum solution, produces a dark-red coloration. If the
solution is very dilute, a rose-red color is obtained.
6. Oxalic acid does not precipitate platinum from its
solutions. This gives us the best means of separating gold
and platinum. If, to a solution of these metals that contains
a slight excess of hydrochloric acid, oxalic acid is added and
the solution boiled, all the gold will be precipitated and the
platinum will remain in the solution. After the gold is fil-
tered off, the platinum may be precipitated as sulphide, or
we may add ferrous sulphate to the solution, render it alka-
line with sodium hydrate, then add hydrochloric acid, and
heat, when the platinum will be precipitated as platinum
black.
41. Iridium. — Iridium is found associated with other
metals in platinum ores, especially with osmium as an alloy
of osmium and iridium known as osmiridium. In the com-
pact condition it is a heavy, steel-gray, brittle metal that
fuses only at very high temperatures. In compact form, or
when reduced from its compounds by hydrogen at a red
heat, all acids, even aqua regia, fail to dissolve it — a fact
that serves to distinguish it from gold and platinum. When
precipitated from a solution, or when alloyed with a large
amount of platinum, aqua regia dissolves it, forming the
tetrachloride IrCl^, Acid potassium sulphate oxidizes, but
does not dissolve it, thus serving to distinguish it from rho-
dium. When fused with potassium nitrate, it is oxidized,
and may be partially dissolved in water. If the fusion is
heated with aqua regia, the iridium is completely dissolved,
forming a dark-red solution of iridic chloride IrCl^.
1. Hydrogen sulphide at first reduces the iridic chloride
to iridious chloride Irfil^^ and sulphur is thrown out. The
38 QUALITATIVE ANALYSIS. § 11
solution assumes an olive-green color. But, upon continued
treatment, brown iridious sulphide Ir^S^ is precipitated.
2. Ammonium sulphide precipitates brown iridious sul-
phide Ir^S^^ which is easily dissolved in an excess of the
reagent.
3. Zinc^ added to a solution of iridic chloride containing
free hydrochloric acid, reduces it and deposits metallic
iridium as a black powder.
4. Ferrous sulpliate^ sulphurous acid, and oxalic acid do
not precipitate iridium.
«
42. Molybdenum. — Molybdenum is found in small
quantities as molybdenum sulphide and as lead molybdate.
All its compounds when heated in the air are changed to
molybdic oxide AToO^y which is soluble in ammonia. If
hydrochloric acid is added to this solution, it precipitates the
white oxide, which dissolves in more of the acid. This solu-
tion gives the following reactions:
1. Hydrogen sulphide at first gives the solution a blue
color, and then precipitates dark-brown molybdenum sul-
phide MoS^s w^hile the supernatant liquid becomes green.
The precipitation is not complete in the cold, but, by heat-
ing the solution and treating for some time with hydrogen-
sulphide gas, the molybdenum is all precipitated. The pre-
cipitate dissolves in alkali sulphides, and is reprecipitated
from this solution by hydrochloric acid.
2. Zinc, when added to the hydrochloric-acid solution,
soon develops a blue, green, or brown color, depending on
the degree of concentration of the solution.
3. Stannous chloride imparts a blue, green, or brown
color to the solution, depending on the amount of the reagent
added, and the concentration of the solution.
4. Ferrous sulphate, containing free sulphuric acid, gives
the solution a blue color that is permanent.
5. Sodium phosphate, added to a molybdate solution con-
taining a little free nitric acid, produces at once, or upon
gently heating, a yellow precipitate of phosphomolybdate,
which is insoluble in nitric acid, but is soluble in an excess
§ 11 QUALITATIVE ANALYSIS. 39
of the reagent. Ammonia also readily dissolves the precipi-
tate, and from this solution it is reprecipitated by nitric
acid.
6. All molybdenum compounds, when heated in the
oxidizing blowpipe flame on the charcoal, deposit an incrus-
tation of molybdic oxide, which is yellow when hot, and
white or yellowish white when cold.
43. Selenium. — Selenium is classed with the non-
metals. It occurs principally as lead selenide PbSe. In
many respects it resembles sulphur. Selenium and most of
its compounds are soluble in nitric acid or aqua regia, but
the selenides of lead and silver dissolve with difficulty. All
selenium compounds, when fused with a mixture of sodium
carbonate and potassium nitrate, form alkaline selenates that
are soluble in water, and the solution remains clear when
acidified with hydrochloric acid. If the solution is boiled
with hydrochloric acid, chlorine is given off, and selenic
acid is reduced to selenious acid. This solution gives the
following reactions:
1. Hydrogen sulphide^ conducted into a cold solution,
produces a yellow precipitate that is probably a mixture of
finely divided selenium and free sulphur. If led into a hot
solution, a reddish-yellow precipitate of selenium sulphide
SeS^ is obtained. This is soluble in ammonium sulphide.
2. Stannous chloride precipitates finely divided selenium,
which remains suspended in the liquid for some time, giving
the solution a reddish color. It finally settles to the bottom
in the form of a reddish-gray powder.
3. Sulphurous acid gives the same reaction as stannous
chloride.
4. Barium chloride^ added to a selenious acid or a selenite
solution in which the excess of hydrochloric acid has been
neutralized, precipitates white barium selenite BaSeO^y
which is soluble in nitric and in hydrochloric acid.
5. Selenium is most readily recognized by heating any of
its compounds on the charcoal in the reducing blowpipe
flame, when a red incrustation is formed, and a putrid odor
40 QUALITATIVE ANALYSIS. § 11
similar to that of decaying horseradish is observed. The
incrustation is volatilized by the blowpipe flame, and gives
off the characteristic putrid odor.
44, Tellurium. — Tellurium has many of the physical
properties of the metals, and on this account is sometimes
classed with them. But, chemically, it acts as a non-metal,
and is generally classed as such. It resembles sulphur and
selenium, and belongs to this group of elements. It occurs
in small quantities in nature, combined with gold, silver, or
lead. It is white and brittle, fuses easily, and may be sub-
limed in the closed tube. Tellurium is insoluble in hydro-
chloric acid, but dissolves readily in nitric acid, forming
tellurous acid //, TV (9,. If this solution is poured into water,
the tellurous acid is precipitated. Tellurous acid H^TeO^
and its anhydride TeO^ are readily dissolved by hydrochloric
acid, and this solution gives the following reactions :
1. Hydrogen sulphide precipitates dark-brown tellurous
sulphide 7V5„ which dissolves readily in ammonium sul-
phide.
2. Stannous chloride^ sulphurous aeid, or zinc^ added to a
rather strongly acid solution, precipitates the tellurium as a
black powder. This action is aided by warming the solution.
3. Sodium hydrate or carbonate precipitates white tel-
lurium hydrate, which is soluble in an excess of the reagent.
4. Solid tellurium compounds, when heated on the char-
coal before the blowpipe, deposit a white incrustation of tel-
lurous oxide TV (9,, which has a yellowish color when hot.
5. Tellurium compounds, when fused on the charcoal
with sodium carbonate, form soluble sodium telluride, which,
when placed on a piece of silver and moistened, gives a
black stain, similar to that produced by sulphur compounds.
6. When held in the flame on a loop of platinum wire,
tellurium imparts a bluish-green color to the flame.
7. If a little finely pulverized telluride ore is covered
with water in a porcelain dish, a little mercury added, and
then some sodium amalgam, the water is given a violet color
by sodium telluride going into solution.
§ 11 QUALITATIVE ANALYSIS. 41
GROUPS III AND IV.
45, As the distinction between the third and the fourth
group is not sharp, it is much better to disregard it entirely
and treat the two groups as one. This is rendered more
practicable in this case by the fact that it is seldom necessary to
make a general separation of the rare elements. In a great
majority of cases, it is only necessary to determine the pres-
ence of one or a very few of them, which may be done by
applying the reactions given for the separate elements.
This division includes:
Titanium Ti Vanadium V Uranium U
Beryllium Be Indium In Gallium Ga
Zirconium Zr Cerium Ce Yttrium Y
Didymium Di Thorium Tk
46. Titanium. — Titanium occurs in quite large quanti-
ties in nature, in clay and some iron ores, and in a number
of minerals. It is not used in commerce, and, conse-
quently, is not frequently met in the laboratory. It is most
frequently met in the form of titanic oxide TiO^, Titanic
oxide is not dissolved by any acid except hydrofluoric
acid, and somewhat in concentrate sulphuric acid. When
the solution in hydrofluoric acid is evaporated with sul-
phuric acid, it is neither decomposed nor volatilized. The
best means of obtaining a solution of titanium is to fuse the
oxide for some time with acid potassium sulphate. The
fused mass will dissolve in moderately warm water, but, if
the solution is boiled, metatitanic acid is precipitated. The
solution as obtained above may be used for the following
reactions.
1. Ammonium hydrate precipitates white, flocculent
titanic acid H^TiO^^ which is insoluble in excess, but is
dissolved by hydrochloric or dilute sulphuric acid.
2. Sodium hydrate gives the same reaction as ammonia.
3. Sodium thiosulphate^ when boiled with rather a dilute
solution of titanium, precipitates it completely as metatitanic
acid.
42 QUALITATIVE ANALYSIS. § 11
4. Ammonium sulphide precipitates white titanic acid
H^TiO^y which is insoluble in excess of the reagent, but is
dissolved by hydrochloric or sulphuric, acid.
5. Ztnc^ added to an acid solution of titanium, produces
a blue or violet coloration, and, after standing for some
time, a blue precipitate separates. Upon standing, this
precipitate gradually changes to white. If sodium hydrate
is added to the blue solution before the precipitate begins
to separate, blue titanium hydrate is precipitated, and on
standing gradually changes to white titanic acid.
6. Potassium ferrocyanide gives a reddish-yellow precip-
itate.
7. Potassium ferricyanide produces a yellow precipitate.
8. Titanic acid dissolves quite readily in the microcosmic
bead, when held in the outer flame near the point of the
inner flame, forming a clear colorless bead, that becomes
opaque when held at the point of the outer flame. If,
instead of holding the bead at the point of the outer flame,
it is held for some time in the reducing flame, it is colored
yellow while hot, red while cooling, and violet when cold.
47. Vanadium. — ^Vanadium occurs chiefly combined
with lead, and in some iron and copper ores. It is known in
several stages of oxidation. VOy F^C^j, and F(9, are known,
but vanadic oxide V^O^^ the anhydride of vanadic acid, is the
principal oxide. All the lower oxides are oxidized to vanadic
oxide, or vanadic acid, by nitric acid or aqua regia, or when
fused with potassium nitrate or heated in the air. Vanadic
oxide, or acid, dissolves in a large amount of water to a red
liquid, or in sulphuric acid to a red or yellow liquid. Moder-
ately dilute sulphuric acid dissolves all of the oxides. In this
acid, vanadious oxide VO dissolves to a blue solution, vana-
dium trioxide Vfi^ to a green solution, and the dioxide VO^
to a blue solution. The reddish or yellow solution of vanadic
acid in sulphuric acid gives the following reactions:
1. Ammonium hydrate produces a brown precipitate that
dissolves in an excess ot the reagent to a yellowish-brown
solution.
§ 11 QUALITATIVE ANALYSIS. 43
2. Sodium hydrate gives the same reaction as ammonia.
3. Hydrogen sulphide reduces the vanadic acid to vana-
dium dioxide, and thus colors the solution blue, while free
sulphur ^separates.
4. Ammonium sulphide precipitates brown vanadium sul-
phide V^S^y which dissolves with some difficulty in an excess
of the reagent to a reddish-brown liquid. From this solution
sulphuric acid reprecipitates the brown vanadium sulphide.
5. ZinCy added to the acid solution, which is warmed,
reduces the vanadic acid, forming at first a blue solution
that changes to green, and finally to violet or blue.
6. Sulphurous acid reduces the vanadic acid to vanadium
dioxide, which imparts a blue color to the solution.
7. Potassium ferrocyanide produces a green, flocculent
precipitate that is insoluble in acids.
8. Vanadium compounds dissolve in the borax bead in
both the oxidizing and the reducing flame, forming clear
beads. When a small quantity is heated in the oxidizing
flame, a colorless bead is produced, but if much vanadium is
present the bead will have a yellow color. If a bead con-
taining a small quantity of vanadium is heated in the redu-
cing flame, a green bead is obtained, while, if more vana-
dium is present, the bead will be brown when hot, and turn
green upon cooling.
48. Uranium. — Uranium occurs in small quantities in
nature, principally in pitchblende. There are two oxides,
uranous oxide UO^ and uranic oxide UO^^ and two series of
salts. The uranous salts are green, and the uranic com-
pounds are yellow. The latter are by far the more common.
Most of the uranic salts are soluble in water, and those that
are insoluble in water dissolve in hydrochloric or sulphuric
acid.
1. Ammonium hydrate ^ added to uranic solutions,
produces a yellow precipitate of ammonium uranate
{NH^^U^O^y which is insoluble in an excess of the reagent.
2. Sodium hydrate precipitates yellow sodium uranate
Na^Ufi^y which is insoluble in excess of the reagent.
44 QUALITATIVE ANALYSIS. § 11
3. In uranous solutions, ammonium and sodium hydrates
give reddish-brown precipitates.
4. Ammonium sulphide precipitates, from neutral solu-
tions or acid solutions after neutralizing, brown uranic oxy-
sulphide, which is insoluble in pure colorless ammonium
sulphide, but dissolves in yellow ammonium sulphide to a
brown solution. The precipitate is dissolved by ammonium
carbonate, or by acids. Even acetic acid dissolves it. If
the precipitate is boiled in the liquid from which it was pre-
cipitated, the oxysulphide is decomposed into uranous sul-
phide US^ and free sulphur.
5. Ammonium carbonate precipitates yellow ammonium-
uranium carbonate {NH^^UOjl^CO^^y which readily dissolves
in an excess of the reagent. From this solution the uranium
is completely precipitated by sodium hydrate, especially
when boiled.
6. Potassium ferrocyanide produces a reddish-brown pre-
cipitate that looks much like copper ferrocyanide, but is dis-
tinguished from it by being soluble in ammonia, forming a
yellow solution.
7. Zinc^ added to an acid solution, imparts a green color
to the liquid, especially when it is heated. This color is due
to the reduction of the uranic to a green uranous compound.
8. Uranium compounds, heated in the borax bead in the
reducing flame, impart a green color to the bead that is seen
best after the bead cools. Heated in the oxidizing flame,
the bead is colored yellow when hot, and assumes a fine yel-
lowish-green color when cold.
49. Beryllium. — Beryllium occurs in nature almost
entirely as a silicate. It is associated with aluminum in
beryl and emerald. In many respects the compounds of
beryllium resemble those of aluminum, but it is divalent,
and, therefore, cannot form alums. The soluble beryllium
compounds have a sweetish, astringent taste, and give an
acid reaction with litmus paper. Most of the silicates are
decomposed when heated with concentrate sulphuric acid,
and all are readily decomposed when fused with four or five
§ 11 QUALITATIVE ANALYSIS. 45
times their weight of mixed carbonates of sodium and potas-
sium. From solutions of beryllium salts the following reac-
tions are obtained :
1 . A mmonium hydrate precipitates white, flocculent beryl-
lium hydrate Be{OH)^^ which is only slightly soluble in an
excess of th« reagent. The precipitate looks very much like
aluminum hydrate.
2. Sodium hydrate precipitates white beryllium hydrate
Be{OH)^^ which dissolves readily in an excess of the reagent,
and the solution remains clear upon boiling, but if consider-
able water is added, and the boiling continued, beryllium
hydrate separates. In this respect it differs from aluminum.
3. Ammonium carbonate precipitates white beryllium car-
bonate BeCO^^ which dissolves in a considerable excess of
the reagent. This is one of the best methods of distinguish-
ing between beryllium and aluminum. If this solution is
diluted with water, and boiled for some time, the beryllium
is precipitated as a basic carbonate.
4. Sodium carbonate precipitates white beryllium carbon-
ate BeCO^y which is slightly soluble in excess.
5. Ammonium sulphide precipitates white beryllium
hydrate Bc{OH\.
6. Oxalic acid and oxalates do not precipitate beryllium
from its solutions, which fact distinguishes it from a number
of the other rare metals.
7. Beryllium is separated from aluminum by fusing the
mixture with twice its weight of hydrogen-potassium fluoride,
and treating the fusion with hydrofluoric acid and water.
The beryllium dissolves in thivS, while the aluminum remains
as insoluble potassium-aluminum fluoride.
8. Beryllium compounds, when heated on the charcoal
before the blowpipe, yield a mass that is somewhat luminous.
When this is moistened with cobalt nitrate, and reignited,
it assumes a gray color. In this it differs from aluminum,
whose compounds, when similarly treated, are colored blue.
50. Indium. — Indium is found in small quantities, asso-
ciated with tungsten, and in the blende obtained in certain
46 QUALITATIVE ANALYSIS. § 11
localities. It is soft, ductile, fuses easily, and resembles
platinum in color. In the air, or in contact with water, it
oxidizes, but not quite so rapidly as zinc. The metal dis-
solves slowly in cold dilute hydrochloric or sulphuric acid,
but much more readily if heat is applied. It dissolves
readily in cold dilute nitric acid. It is trivalent in all its
compounds, and its salts are nearly all colorless. They dis-
solve in water or acids, forming colorless solutions.
1. Amtno?tium hydrate precipitates white indium hydrate
In{OH)^, which is insoluble in excess of the reagent.
2. Sodium hydrate precipitates white indium hydrate
In{OH)^, which dissolves in an excess of the reagent. From
this solution the indium hydrate slowly separates when it is
boiled, or when ammonium chloride is added.
3. Ammonium carbonate precipitates white indium car-
bonate I^J^CO^^, which is soluble in excess of the reagent,
and is reprecipitated from this solution by boiling.
4. Sodium carbonate gives the same precipitate as ammo-
nium carbonate, but it is insoluble in excess of the sodium
carbonate.
5. Hydrogen sulphide precipitates, from neutral solutions
or those containing only acetic acid, yellow indium sulphide
InJS^, The presence of free inorganic acids prevents the
precipitation.
6. Ammonium sulphide produces a white precipitate of
unknown composition. If the yellow indium sulphide is
boiled with yellow ammonium sulphide, it becomes white,
and partly dissolves. Upon cooling, a white precipitate
separates from this solution.
7. Zific^ added to an acid solution, precipitates the metal
in white shining scales.
8. Indium, when heated on the charcoal, fuses to a bright
metallic globule, and deposits an incrustation that is dark
yellow when hot, and light yellow when cold, and is only
volatilized with difficulty.
9. Indium compounds, held in the colorless flame on a
loop of platinum wire, impart a violet-blue color to the
flame. Viewed through the spectroscope, this flame gives
§ 11 QUALITATIVE ANALYSIS. 47
two characteristic blue lines. These are the brighest when
the chloride is used, but in this case they only last a short
time. The lines given by the sulphide are less bright, but
are much more persistent.
51. Gallium. — Gallium occurs in very small quantities
in some zinc ores. It is a white, hard, slightly malleable
metal that dissolves slowly in hot nitric acid, and readily in
hydrochloric acid. Its salts are colorless, and the nitrate,
chloride, and sulphate readily dissolve in water to colorless
solutions.
1. Ammonium hydrate precipitates white gallium hydrate
Ga{OH)^^ which is soluble in excess of the precipitant.
2. Sodium hydrate gives the same reaction as ammonium
hydrate.
3. Ammonium carbonate produces a white precipitate that
is soluble in excess of the reagent.
4. Hydrogen sulphide does not give a precipitate in solu-
tions containing free mineral acids, but precipitates white
gallium sulphide GaJS:^ from acetic-acid solutions.
5. Ammonium sulphide precipitates white gallium sul-
phide, which is insoluble in an excess of the reagent.
6. Potassium f err ocyanide produces a light, bluish colored
precipitate that dissolves more easily in water than in hydro-
chloric acid.
7. When gallium compounds are held in the Bunsen flame,
they give a spectrum consisting of one rather indistinct violet
line ; but when a spark passes from the positive terminal of
an induction coil to the surface of a gallium solution, under
which the negative terminal is dipped, the spectrum pro-
duced consists of two distinct violet lines. This is the most
distinctive reaction for gallium, and the one that led to its
discovery.
52. Zirconium. — Zirconium occurs as a silicate in a few
rare minerals. It is tetravalent, and forms a white infusible
oxide ZrO^^ which is luminous when heated. The native
minerals are decomposed by fusing, in powdered form, for
48 QUALITATIVE ANALYSIS. § 11
some time, with four or five times their weight of sodium
carbonate, forming sodium zirconate. The zirconium is dis-
solved by treating the fused mass with hydrochloric acid,
leaving insoluble silicic acid, which may be filtered off.
With this solution the following reactions may be obtained:
1. Amvioiiiinn hydrate precipitates white zirconium
hydrate Zr{OH)^, which is insoluble in an excess of the
reagent.
2. Sodium hydrate gives the same reaction as ammonium
hydrate.
3. Ammonium carbonate precipitates a white basic car-
bonate that is soluble in considerable excess of the precip-
itant. Upon boiling this solution, white, gelatinous zirco-
nium hydrate separates.
4. Sodium carbonate gradually precipitates a white basic
carbonate that is slightly soluble in an excess of the reagent.
5. Ammonium sulphide precipitates white, flocculent
zirconium hydrate, which is not dissolved by an excess of
the reagent, nor by alkali hydrates.
6. Oxalic acid ox ammonium oxalate precipitates white,
crystalline zirconium oxalate, which is soluble in an excess
of the reagent. From this solution, ammonium hydrate
reprecipitates the zirconium oxalate.
7. Sodium thiosulphate, when boiled with a zirconium
solution, precipitates white zirconium thiosulphate, even
from dilute solutions.
8. Hydrogen peroxide precipitates zirconium in the form
of a white, bulky hydrate, probably Zr{OH)^.
9. Hydrofluoric acid does not precipitate zirconium from
its solutions, which fact serves to distinguish it from yttrium
and thorium.
63. Cerium. — Cerium occurs in small quantities in
nature, principally as cerous silicate in cerite, and as cerous
phosphate in monazite. It exhibits two degrees of valence,
forming, with oxygen, cerous oxide CeJD^ and eerie oxide
CeO^. The cerous salts are stable, but eerie salts are readily
decomposed, forming cerous compounds. The cerous salts
§ 11 QUALITATIVE ANALYSIS. 49
and their solutions are white or colorless, while eerie com-
pounds and solutions are yellow or red.
Most compounds of cerium may be dissolved by treating
the finely powdered compound for some time with concen-
trate hydrochloric acid. All of its compounds may be decom-
posed by fusing the pulverized compound with about five
times its weight of sodium carbonate. Upon treating the
fusion with hydrochloric acid, the cerium dissolves to a color-
less solution of cerium chloride CeCl^,
1. Ammonium hydrate precipitates a white basic com-
pound that is insoluble in an excess of the reagent.
2. Sodium hydrate gives a white precipitate, probably
Cc{OH\,
3. A mmonium carbonate precipitates white cerous carbon-
ate CeJl^CO^^, which is only slightly soluble in an excess of
the reagent.
4. Oxalic acid^ added to a solution that does not contain
too much free acid, precipitates white cerous oxalate, which
is insoluble in an excess of the reagent, but dissolves in a
large excess of hydrochloric acid.
5. Sodium thiosulphate does not precipitate cerous solu-
tions, even when heated with the concentrate solution, but
does form a precipitate with ceric-nitrate solutions.
6. Ceric solutions have a yellow color, but are reduced to
cerous compounds by sulphurous acid, and the color is thus
destroyed.
7. Cerium oxides are dissolved in the borax bead. In the
oxidizing flame the bead is colored yellowish red while
hot, and gets lighter colored upon cooling, and sometimes
becomes colorless. In the reducing flame the bead is color-
less.
54. Yttrium. — Yttrium occurs as a silicate in gadoli-
nite and a few other rare minerals. A solution of yttrium
may be obtained by fusing the silicate with sodium and
potassium carbonates, and dissolving the fusion in hydro-
chloric acid. Yttrium forms the oxide YJD^ known asyttria.
It is slightly soluble in cold nitric, hydrochloric, or sulphuric
.o^i*
50 QUALITATIVE ANALYSIS. § 11
acid, and dissolves completely in these acids when heated for
some time. Its salts and solutions are colorless. Yttrium
solutions give the following reactions :
1. A ntmonium hydrate precipitates white yttrium hydrate
V{OfI)^y which is insoluble in an excess of the reagent, but
dissolves in mineral acids. The precipitate also dissolves
slowly in ammonium carbonate, and from this solution, it is
reprecipitated by boiling.
2. Sodium hydrate gives the same reaction as ammonium
hydrate.
3. Ammonium carbonate produces a white precipitate
that is somewhat soluble in an excess of the reagent. From
this solution it is reprecipitated by boiling.
4. Sodium carbonate gives a white precipitate that is
slightly soluble in an excess of the precipitant, but dissolves
more readily in ammonium carbonate, arid is reprecipitated
from this solution by boiling.
5. A 7nmonium sulphide precipitates white yttrium hydrate
Y{OH)^, which is insoluble in an excess of the reagent, but
dissolves in ammonium carbonate or in strong mineral acids.
6. Oxalic acid precipitates white yttrium oxalate
F,(C,(?J3, which is insoluble in excess of the reagent, but is
partly dissolved by heating with ammonium oxalate. If this
solution is diluted and cooled, the oxalate again separates
almost completely. The precipitate also dissolves with some
difficulty in hydrochloric acid.
7. Hydrofluoric acid pt*oduces a white gelatinous precip-
itate that is insoluble in excess of the reagent, and in water.
Before it has bjen heated it dissolves in mineral acids, but
after heating it can only be decomposed by concentrate sul-
phuric acid. .
8. When heated on the charcoal before the blowpipe,
yttrium oxide is luminous, and emits a white light without
fusing.
65. Dldymlum. — Didymiiim is found associated with
cerium in cerite. It may be separated from cerium by pre-
cipitating both the metals as oxalates from a solution obtained
§ 11 QUALITATIVE ANALYSIS. 51
as described under cerium, and heating the precipitate, after
it is dry, until the oxalates are broken up, forming oxides;
then, by treating the mixed oxides with nitric acid, the
didymium is dissolved to a rose-colored solution, while the
cerium remains as an insoluble residue.
1. Ammonium hydrate precipitates a white basic salt that
is insoluble in excess of the reagent, but is dissolved by
hydrochloric acid.
2. Sodium hydrate gives the same reaction as ammonium
hydrate.
3. Ammonium carbonate produces a white precipitate
that is insoluble in an excess of the reagent, but is soluble in
hydrochloric acid.
4. Sodium carbofiate gives the same reaction as ammo-
nium carbonate.
5. Oxalic acid precipitates white didymimn oxalate
DiJ^C^O^^y which is slightly soluble in cold hydrochloric
acid, and dissolves quite readily when the acid is heated.
6. Didymium oxide, when ignited on the charcoal before
the blowpipe, appears pure white; but, if a few drops of
concentrate nitric acid are added, and it is again ignited at
a rather low temperature, it becomes dark brown, owing
to the formation of the peroxide DiO^. If tins is. again
intensely ignited, it changes to the white oxide Di^O^.
7. In the oxidizing flame, didymium oxide dissolves in the
microcosmic bead, giving it an amethyst color. The color dis-
appears when the bead is held in the reducing flame. It scarcely
colors the borax bead, unless large quantities are added.
66. Thorium. — Thorium is a rare metal, and is found
in nature, principally as a silicate, in thorite, monazite, etc.
The oxide 77/(9,, commonly called thoria^ is important, as if is
the chief constituent used in the mantle of the Welsbach light.
The native minerals and the artificial compotmds are decom-
posed by treating with rather concentrate sulphuric acid.
1. A mmonium hydrate precipitates white thorium hydrate
Th[OH)^, which is insoluble in an excess of the reagent.
The precipitate is soluble in all inorganic acids while it is
62 QUALITATIVE ANALYSIS. § 11
moist, but after heating it is only decomposed by rather
concentrate sulphuric acid.
2. Sodium hydrate gives the same reaction as ammonium
hydrate.
3. Ammonium carbonate precipitates a white basic
thorium carbonate, which dissolves readily in an excess of
the reagent, in a strong solution, but with difficulty if the
solution is dilute. Upon heating this solution, the basic
carbonate is reprecipitated.
4. Sodium carbonate precipitates a white basic carbonate,
which is soluble in an excess of the reagent, especially if the
solution is strong.
5. Oxalic acid precipitates white thorium oxalate
Th{C^O^^y which is insoluble in an excess of the reagent, but
dissolves in a boiling concentrate solution of ammonium
oxalate, and is not reprecipitated when the solution is diluted
and cooled. The precipitate also dissolves slightly in dilute
inorganic acids, and readily in ammonium acetate containing
free acetic acid.
6. Hydrofluoric acid precipitates white thorium fluoride
ThF^^ which is gelatinous at first, but upon standing changes
to a powder. It is insoluble in an excess of the reagent and
in water.
7. A mmonium sulphide precipitates white thorium hydrate
Th{OH)^, which is insoluble in an excess of the reagent, but
is dissolved by mineral acids, if treated while still moist.
8. Sodium thiosulphate, when boiled with a rather strong
solution of thorium, precipitates white thorium thiosulphate,
mixed with free sulphur, but the precipitation is not com-
plete, and the precipitate may be colored by the sulphur.
9. Potassium sulphate^ in concentrate solution, when
boiled with a solution of thorium, precipitates the thorium
completely as white potassium-thorium sulphate, which is
insoluble in an excess of the reagent, and dissolves with
difficulty in cold water, but easily in hot water.
10. Thoria is white or gray. When heated on the char-
coal before the blowpipe, it is incandescent, and emits an
exceedingly brilliant white light
§ 11 QUALITATIVE ANALYSIS. 53
GROUP VII.
Lithium Li Ccesium Cs Rubidium Rb
5'7« liltMum. — Lithium occurs quite widely distributed
in nature, but in very small quantities. It is found in many
mineral waters, in the ashes of some plants, and in sev-
eral minerals. In some ways it acts like a fifth, and in some
ways like a sixth, group metal, but a majority of its chemical
relations place it in this group. The hydrate and the car-
bonate of lithium dissolve with some difficulty in cold water,
but more readily in warm water. Hydrates and carbonates,
however, do not precipitate lithium from ordinary solutions.
Acid sodium tartrate and platinum chloride do not precipi-
tate lithium from its solutions.
1. Sodium phosphate, when boiled with a rather strong
lithium solution that has been rendered alkaline with sodium
hydrate, precipitates white crystalline lithium phosphate
Li^PO^, which settles quickly. The precipitate dissolves
readily in hydrochloric acid, and when this solution is ren-
dered alkaline by ammonia, no precipitate is formed when
cold, but when heated the lithium phosphate again separates.
In this, lithium differs from the alkaUne earths, and also
differs from them in that, when the phosphate is heated on
the charcoal before the blowpipe^ it fuses and is absorbed
into the pores of the charcoal.
2. Ammonium fluoride, when added to a rath-er strong
lithium solution, together with an excess of ammonia, gradu-
ally precipitates white lithium fluoride LiF. As fluorides of
the other alkalies are easily soluble in a mixture of equal
parts of ammonium hydrate and water, while it requires
3,500 parts of this mixture to dissolve lithium fluoride, this
method may be employed in separating lithium from the
other alkalies.
3.* All volatile lithium compounds (especially the chloride)
impart a bright-red color to the flame, and this is probably
the most used of any method in determining lithium. In the
presence of large quantities of sodium, the color imparted to
the flame by a small amount of lithium is masked by the
54 QUALITATIVE ANALYSIS. § 11
yellow sodium flame, and a blue glass must be used to absorb
the yellow rays, as in the case of potassium.
4. The best method of detecting small quanties of lithium
is by means of the spectroscope. The.lithium spectrum con-
sists of a bright-red line and a faint-yellow line.
58. Ceeslum and Rubidium. — Caesium and rubidium
are quite widely distributed in nature, but in very minute
quantities. They are very closely allied, and resemble potas-
sium, both in compounds and in the color that they impart
to the flame.
1. Platmum chloride precipitates these metals in the form
of double chlorides of the metals and platinum, similar to
potassium-platinum chlorides. These precipitates are not
nearly so soluble in water as the corresponding double salt
of potassium.
2. Caesium carbonate is soluble in absolute alcohol, while
rubidium carbonate is insoluble in that medium, but they
cannot be completely separated by this means.
3. Probably the best method of separating these metals
is by means of stannic chloride. To do this, add stannic
chloride to the hot concentrate solution containing consider-
able strong hydrochloric acid. The caesium is precipitated
as caesium-stannic chloride, while the rubidium remains in
solution. The precipitate is washed with concentrate hydro-
chloric acid.
4. Volatile compounds of caesium and rubidium impart a
violet color, similar to that of potassium, to the non-lumi-
nous flame; but, when this is viewed through the spectro-
scope, the spectra of the two metals are very distinct.
Caesium gives two brilliant sky-blue lines and a less distinct
red line. Rubidium gives two indigo-blue lines and two
bright-red lines. As the flames (and consequently the lines)
produced by the chlorides of these metals are more distinct
than those produced by the other compounds, the chlorides
should always be used.
59. There are a number of rare elements that are not
treated here. As many of the rare elements have only
§ 11 QUALITATIVE ANALYSIS. 55
lately been discovered, and their reactions have not been
thoroughly studied, it is impossible to treat them in a Paper
of this kind at the present It has lately been discovered
that some of the substances here treated as elements are
really composed of two or more closely related elements;
but, as they have not yet been separated and studied, it is
only possible at the present time to treat them as elements.
It is altogether probable that the chemistry of the rare
elements will be changed very materially within the next
few years.
THE SPECTROSCOPE,
ITS USK IN ANALYSIS.
60. In studying the reactions of the metals, the color that
is imparted to the flame by the vapors of many oi them is
made use of in recognizing them ; and in several cases in
this Paper the spectrum of the metal is spoken of. In every
case where a color is imparted to a flame, the reaction
becomes much more distinctive if the spectroscope is used.
The spectroscope is made in several forms, but the principle
is the same in all. We have seen, in Art. 145, et seq.,
Physics, that, when light passes through a glass prism, it is
separated into its primary colors, and each color is refracted,
forming a certain angle with the incident ray. Upon this
principle, which is explained in Art. 150, et seq. , Physics, the
spectroscope is constructed. A common form of spectro-
scope is shown in Fig. 1. It consists of a tube a, at the end
of which there is a narrow slit through which the light
passes to a lens in the tube, which throws it on the flint-
glass prism b in the form of a narrow band, owing to the
narrow slit through which it has passed. This prism refracts
the light at a certain angle, depending on its color, and this
line of refracted light is viewed through the tube c, which
contains a lens and acts as a telescope. The spectroscope is
usually supplied with a tube d, containing a scale that may
QUALITATIVE ANALYSIS.
\n
be thrown into the spectrum by the liyhl c at the end of the
tube. By this means, tlie spectrum, when viewed through
the tube c, appears in connection with the scale, so that the
exact position of the lines may be noted. The lines pro-
duced by any metal always appear in exactly the same place
when the same instnmient is used. The instrument is gen-
erally mounted on a brass support, as shown in the figure.
The whole of the spectrum cannot be seen at once ; hence, the
tube c is made so that it may be turned, bringing the different
parts of the spectrum successively into view. In some
instruments the tube e is made stationary, and the prism is so
arranged tliat it may be rotated, thus accomplishing the same
object. The prism is usually enclosed in a metal covering,
through which the ends of the tube a, c, and (/ pass.
If the Eunsen burner f is burning with a non-luminous
flame, the spectrum appears blank and is devoid of lines,
but if a little sodium compound is brought into the flame it
at once assumes a yellow color, and a bright-yellow line is
r
I
I
1^
f
. •■ • |.
. 1 •- •
■ -^iL'-fc-^ -'-■■
^.(.\ *'■■
SH
QUALITATIVE ANALYSIS.
57
a in tiie spectrum. This is such an extremely delicate
I reaction that STmSfloif part of a millij^ram of sodium may be
I detected with accuracy by this means. It is such a deUcate
I reaction that it is difficult to obtain a flame that will not give
r this yellow line, owinjj to the sodium floating in the air in
[ the form of dust. The colors imparted to the flame by most
lof the metals are not single colors, but combinations of dif-
I ferent colors. Thus, the violet flame of potassium contains
I red and violet rays, and produces a dark-red line near one
I end of the spectrum and a violet line near the other. The
I ted line is much the stronger of the two, and if only a very
I Httle potassium is present, the violet line is very faint or may
I not be seen at all. In the same way the lithium flame,
I which appears bright red, contains some j-ellow rays, and its
[■ Bpectrum consists of a bright- red line and a faint-yellow line.
I Ab the tube c contains a lens and acts as a telescope, it should
[.always be focused before using, so that the lines of the spcc-
rtrum appear perfectly clear and distinct. No two metals
1 impart exactly the same color to the iiame; hence, the spec-
I tram of each is absolutely distinct, as regards the position of
its lines. For this reason, when several metals are brought
I into the flarae at once, either in the solid form or in solution,
I the spectra in no wise interfere with one another, provided
I the slit in the tube ti is made narrow enough for the colors
I to appear as mere lines rather than as bands; in this way,
I several metals may be detected at once with absolute cer-
I talnty. For instance, sodium, potassium, and lithium often
I occur in very small quantities in mineral waters, and the
1 Spectroscope is used in detecting them. For this purpose a
I Httle pure hydrochloric acid is added, and the water is
I evaporated nearly to dryness, A drop of this concentrated
Ipolution is held in the flame on the loop of a clean platinum
I wire, and the flame examined by the spectroscope. If the
[ water contains these three metals alone, the spectra will
appear as shown in Plate I, If only these three metals are
sent in the solution, their spectra will appear as shown in
the illustration, and no other lines will be seen ; but usually the
water contains other metals, and these may be determined
J
at Lh(i siime time, by comparing the lines observed wiili
those produced by other metals, as shown in Plate II.
It has been stated that the colors imparted to the flanie
are due to highly heated vapors; hence, volatile compounds
must be used in working with the spectroscope. The chlorides
of the metals are generally the most volatile, and nitrates rank
next. Carbonates are usually ditBcult to volatilize, bnt are
easily changed to chlorides by means of hydrochloric acid.
Silicates must be decompo.sed by means of a flux, usually
sodium carbonate, and some substances should be held in the
reducing flame and then dipped in hydrochloric acid, thus
forming chlorides. In the case of very volatile compounds,
such as lithium and thallium chlorides, the spectrum, although
lasting only a short time, is very brilliant.
61, In Plate II the spectra of the metals that are often
determined by means of the spectroscope arc given. As the
flame is colored by highly heated luminous vapors, metals
that do not ordinarily color the flame, if heated to a temper-
ature high enough to volatilize thciii, impart colors to the
flame and consequently produce spectra by which they may
be recognized. But in all such cases the wet reactions
suffice for the determination of these metals, and it is much
easier and simpler to determine them in this way than it is
to get the heat necessary to volatihze them. Hence, the use
of the spectroscope in analysis is usually restricted to the
determination of the alkalies, a few of the rare elements that
are easily volatilized, and, iu some cases, barium, strontium,
and calcium.
ANALYSIS OF WATEK.
63. As water is never pure, unless specially prepared,
but alwaj's contains some substances in solution, the quality
of the water depends upon the quantity of these substances
contained in it; hence, a quantitative analysis is usually
required to determine the fitness of a water for drinking
and cooking purposes. But for many purposes all that is
required is a qualitative examination, and by this means we
\7-
§ 11 QUALITATIVE ANALYSIS. 59
can learn much of the fitness of a water for drinking
purposes by noting whether much or little of the various
constituents are present, as indicated by the production of a
mere coloration, a slight, or a copious, precipitate, when the
reagents are added. In this way, after some practice, quite
an accurate opinion can be formed in regard to the amounts
of substances present, and the consequent character of the
water. In the case of poisonous substances, whose mere
presence is sufficient to condemn the water, their qualitative
determination alone is required.
63. Treatment of tlie Sample. — There are several
methods of proceeding with the analysis of water, and all
methods are modified to suit the particular case. In choos-
ing his mode of procedure, the chemist should be governed
largely by circumstances. If something is known of the
source and character of the water, the method of analysis
should be made to suit the particular case. A method that
is very commonly employed is as follows : If the water is
clear, about 1 liter is taken for the analysis, and is evaporated
in a large, perfectly clean porcelain dish, ^ddmg in successive
portions, if necessary, until all is in the dish, and then evap-
orating until the bulk is reduced to about 250 cubic centi-
meters. During this evaporation, as a rule, a precipitate
will be formed, consisting of the metals that were held in
solution by free carbonic acid, or in the form of bicarbon-
ates. Allow the dish and contents to cool, and filter through
a perfectly pure filter, bringing as much of the precipitate
as possible on to the paper. Add a small amount of pure,
recently distilled water to the dish, and, after washing out
the dish with it, pour it on to the filter, thus washing the
part of the precipitate that has been brought on to the paper.
Repeat this two or three times, and then proceed to examine
the precipitate and the filtrate.
64. Examination of tlie Precipitate. — The precipitate
usually contains some of the following constituents: calcium
carbonate, magnesium carbonate, ferric hydrate which is
precipitated by boiling a solution of ferrous carbonate,
CO
QUALITATIVE ANALYSIS.
S"
silica, calcium phosphate, ferric phosphate, ferric silicate,
and, sometimes, calcium sulphate, if the water contains
much of this substance.
Place the porcelain dish, which still contains much of the
precipitate, under the funnel, break the point of the filter
with a clean glass rod or platinum wire, and wash the pre-
cipitate into the dish with a small quantity of hot, dilute
hydrochloric acid. At this point, effervescence is usually
observed, due to the escape of carbon dioxide, when the car-
bonates are decomposed by the acid. Heat the dish and
contents to complete the solution as far as possible, and pro-
ceed as follows:
1. Take a small portion of the solution, which often is
not quite clear, in a test tube or on the lid of a porcelain
crucible, and add a few drops of potassium sulphocyanide.
A red coloration shows the presence of iron,
2. Evaporate the rest of the solution to dryness on a water
bath, in a small porcelain
dish, A water bath for this
purpose may be made by
placing the porcelain dish
on a beaker, or other suit-
able vessel, containing water,
as shown in Fig. 2, and heat-
ing the water to boiling. The
steam from the boiling water,
coming against the bottom of
the dish, evaporates the solu-
tion quite rapidly, A piece
of folded paper or some other
substance should be placed
over the edge of the beaker,
to make a small space be-
tween the beaker and the
dish, for the escape of steam,
and the water in the beaker
must be replenished as it
evaporates. When the solution in the dish is evaporated
§ 11 QUALITATIVE ANALYSIS. 61
to dryness, moisten the residue with hydrochloric acid, heat
it gently, add water, and continue the heating until the
soluble portion is dissolved. If an insoluble residue remains,
it can only be silica, but may be further tested with hydro-
fluoric acid, if desired.
3. Evaporate a few cubic centimeters of the filtrate
nearly to dryness in a test tube, add a few drops of nitric
acid, and test for phosphoric acid with ammonium molybdate.
4. To another small portion in a test tube, add a few drops
of hydrochloric acid, boil, and then add a little barium-
chloride solution. A white insoluble precipitate shows the
presence of sulphuric acid.
5. Heat the remainder of the solution to boiling, and add
ammonia in sufficient quantity to render the solution alka-
line, but avoid a large excess. If a precipitate is formed,
filter, and examine the precipitate for iron and aluminum by
methods previously described. Heat the clear filtrate to
boiling, add from 3 to 5 cubic centimeters of ammonium
oxalate, and a like amount of ammonium hydrate; boil for a
few seconds, and stand aside for 4 or 6. hours. A white
precipitate shows the presence of calcium, which was present
in the water in the form of bicarbonate, or also of sulphate,
if the portion just tested contained sulphuric acid.
G. Filter off the calcium oxalate, and evaporate the filtrate
to a small bulk, if necessary, after making sure that all the
calcium was precipitated. To the concentrated filtrate, add
about 6 cubic centimeters of a solution of sodium-ammonium
phosphate (microcosmic salt), and then about half its volume
of ammonia; stir well, and stand in a cool place for 10 or
12 hours. A white precipitate shows the presence of mag-
nesium, which was in the water in the form of carbonate or
bicarbonate. The precipitate sometimes adheres to the sides
of the beaker in the form of colorless crystals that cannot
be seen until the liquid is poured out.
66. Examination of tlie Filtrate. — 1. To about
10 cubic centimeters of the filtrate, add 1 or 2 cubic centi-
meters of nitric acid, and, after mixing thoroughly, add silver
62 QUALITATIVE ANALYSIS. § 11
nitrate, when chlorine, if present, will be precipitated as
white silver cliloride. This is sufficient proof of chlorine,
but, if any considerable precipitate is formed, it may be con-
firmed by dissolving in ammonia, and re precipitating with
nitric acid.
2. To another portion of about 10 cubic centimeters, add
1 cubic centimeter of nitric acid, evaporate the whole to
about one-half cubic centimeter, and test for phosphoric acid
with ammonium molybdate.
3. Evaporate about 30 cubic centimeters of the filtrate to
a small bulk, and test its reaction with litmus paper. If the
reaction is alkaline, and a drop or two of it, placed on a watch
glass, effervesces when .brought in contact with a drop of
acid, and, if calcium carbonate is precipitated when calcium
chloride is cautiously added to a portion of the alkaline solu-
tion, the water contains a carbonate of an alkali metal.
Evaporate the rest of this test to dryness on the water bath,
boil the residue with alcohol, filter, evaporate the filtrate
to dryness, dissolve the residue in a very little water, and
test this solution for nitric acid with diphenylamine or ani-
line sulphate.
A diphenylamine solution is made by treating about
2 milligrams of the crystals with 5 cubic centimeters of con-
centrate sulphuric acid, adding an equal volume of w^ater,
and mixing the solution thus formed with about 5 cubic
centimeters of concentrate sulphuric acid. To test for nitric
acid, place about half a cubic centimeter of this solution on a
watch glass, and add a drop or two of the liquid to be tested.
If nitric acid is present, a blue line will be formed where the
liquids meet.
The anilme-sulphate solution is made by adding about half
a dozen drops of aniline to 15 cubic centimeters of dilute
sulphuric acid, and then adding this solution drop by drop to
about 40 cubic centimeters of concentrate sulphuric acid. If
about 1 cubic centimeter of this solution is placed on a watch
glass, and a drop or two of a liquid containing nitric acid is
added, a red color is produced.
Very often a drop or two of the original water, or of a
§ 11 QUALITATIVE ANALYSIS. 63
somewhat concentrated solution, is added to one of these
reagents, to test for nitric acid ; but the method described,
although rather long, is usually to be recommended on
account of its greater accuracy.
4. To the remainder of the original filtrate, add about
5 cubic centimeters of hydrochloric acid, and evaporate at first
over the Bunsen flame, and finally to dryness on the water
bath. Moisten the residue with hydrochloric acid, warm
gently, add water, bring into solution by the aid of heat, and
filter off the insoluble silica, which is nearly always present.
To a little of this filtrate in a test tube, add a few drops of
hydrochloric acid and then barium chloride. A white insol-
uble precipitate shows the presence of sulphuric acid. Ren-
der the rest of the filtrate distinctly alkaline with ammonia,
add about 5 cubic centimeters of ammonium oxalate, bring
to boiling, add 1 or 2 cubic centimeters of ammonia, and
stand in a warm place for about 5 hours for the precipitate
to collect and settle. A white precipitate shows the pres-
ence of calcium. Filter, and test a portion of the filtrate for
magnesium, by ammonia and sodium-ammonium phosphate,
as previously described. The rest of the solution is tested
for the alkalies. This may be done in several ways. The
shortest, and probably the most satisfactory, method of test-
ing is to evaporate the solution nearly to dryness, holding a
drop of it in the non-luminous flame, and noting the color
imparted by the solution, using the blue glass, or, still bet-
ter, examining the flame by means of the spectroscope. In
case a spectroscope is not accessible, it may be necessary to
adopt another method for potassium. Sodium is always
recognized by the yellow color it imparts to the flame, but,
in the presence of large quantities of sodium, a small amount
of potassium may be overlooked, even when the flame is
examined through a blue glass; hence, in the presence of
much sodium, if no potassium is found by the flame reaction,
the following method should be employed :
Evaporate the test to dryness, and heat it carefully over
the flame until all ammonium compounds are volatilized.
Heat the residue with from 10 to 30 cubic centimeters of
C4 QUALITATIVE ANALYSIS. g 11
water, depending upon the amount of residue, and to this
solution add a few drops of barium chloride. If this pro-
duces a precipitate, continue the addition drop by drop as
long as a precipitate is formed, apply heat, add a little pure
barium or calcium hydrate, bring to boiling, and filter off
the precipitate. To the filtrate, add a few drops of ammonia
and then pure ammonium carbonate drop by drop as long as
a precipitate forms; heat gently, filter off the precipitate,
evaporate the filtrate to dryness, and ignite gently until all
ammonium compounds are expelled. Dissolve the residue
in a few cubic centimeters of water, add 2 or 3 drops of
ammonia and a few drops of ammonium carbonate, and
heat gently to precipitate small quantities of the alkaline
earths that may still be present. Filter off any precipitate
that may be formed, evaporate the filtrate to dryness, and care-
fully ignite till the last traces of ammonium salts are driven
off. If the work has been properly done up to this point,
the residue can contain only sodium and potassium, and will
completely dissolve in 1 or 2 cubic centimeters of water to a
clear solution. If this fails, the alkaline earths have not
been completely removed, and the treatment with ammonia
and ammonium carbonate must be repeated. If the solution
in a very small amount of water is clear, add to it a few drops
of platinum chloride, and heat gently on the water bath until
the mixture is almost syrupy; then add about 20 cubic centi-
meters of alcohol, and continue the heat over the water bath
for a minute or two. If a heavy yellow powder remains
undissolved, it shows the presence of potassium.
5. If a spectroscope is available, a very good method of
testing for the alkalies is to evaporate from 200 to 500 cubic
centimeters of the water, with the addition of a little hydro-
chloric acid, almost to dryness, and examine this concentrated
solution by means of the spectroscope. In this way we
avoid the chance of introducing alkalies into the water with
the reagents.
66. Examination for Ammonia. — In testing for
ammonia, place a fresh sample, consisting of about 300 cubic
§ 11 QUALITATIVE ANALYSIS. 05
centimeters of the original water, in a flask or glass cylinder,
add 2 cubic centimeters of a saturated solution of sodium
carbonate, and 1 cubic centimeter of a solution of sodium
hydrate, made by dissolving 1 part of dry sodium hydrate
in 2 parts of water. Stopper the flask, shake well, and allow
the precipitate to settle. Pour from 50 to 100 cubic centi-
meters of the clear liquid through a clean filter into a glass
cylinder or large test tube, and add 1 cubic centimeter of
Nsssler's solution. * A yellow coloration, or, perhaps, a slight
reddish-brown turbidity upon the addition of another cubic
centimeter of the solution, shows the presence of ammonia.
This operation must be carried on in a room free from
ammonia vapors, for this is so delicate a reaction that the
small amount of ammonia in the air would bj sufficient to
give the reaction.
67. Separation of Ammonia In Different Conditions.
In many cases the determination of ammonia as just described
is all that is required, but in a large number of cases it is a
matter of importance to know in what condition the ammonia
exists in the water. It occurs in water in two conditions,
(I) as ammonia that is merely dissolved in the water and
is known as free ammonia; and (2) ammonia that is being
formed by the decomposition of nitrogenous organic matter,
known as albuminoid ammonia.
To distinguish between these, place 500 cubic centimeters
of the water to be tested in a perfectly clean retort or flask,
and connect it with a condenser, as shown in Fig. 25, Theo-
retical Chemistry. Heat the water in the retort or flask to
boiling, and receive the distillate in a glass cylinder. When
^ •
*To make Nessler's solution, add about 800 cubic centimeters of
water to 35 gprams of potassium iodide and 13 grams of mercuric chlo-
ride; heat to boiling, and continue the heat till solution is complete.
Remove the solution from the heat, and when quite cold, add a sat-
urated solution of mercuric chloride, drop by drop, until a precipi-
tate begins to form that does not dissolve when stirred. Now add
160 grams of potassium hydrate, or 120 grams of sodium hydrate, and
water enough to make the solution up to 1 liter. When the hydrate is
all dissolved, add a few more drops of mercuric chloride, and allow the
precipitate to settle. The clear liquid should have a slight yellowish
color, and if colorless, a little more mercuric chloride must be added.
66 QUALITATIVE ANALYSIS. § 11
about 50 cubic centimeters have passed over, remove the
cylinder and add 1 or "Z cubic centimeters of Nessler's solu-
tion. A yellow color at this point shows the presence of free
ammonia. Continue the distillation until about 200 cubic
centimeters of the water have passed over. Then remove
the hght and add 50 cubic centimeters of a solution of potas-
sium hydrate and potassium permanganate.* Return the
burner, and continue the distillation. When 50 cubic centi-
meters of the water have passed over, add 2 cubic centimeters
of Nessler's solution. A yellow color shows the presence of
albuminoid ammonia, but the absence of a yellow color does
not prove its absence. If albuminoid ammonia is present,
some of it nearly always comes over with the first 50 cubic
centimeters of the distillate, but we cannot state positively
that the water contains no albuminoid ammonia until three
portions of the distillate, of 50 cubic centimeters each, have
been tested in this manner.
68. Nitrous Acid. — To test for nitrous acid, it is usually
sufficient to measure 50 cubic centimeters of the water into a
suitable vessel, add 1 cubic centimeter of dilute sulphuric
acid, 1 cubic centimeter of potassium-iodide solution, and a
little starch solution. The formation of a blue color, either
at once or after a few moments, indicates a relatively large
amount of nitrous acid, but, if the color docs not appear for
some time^ it indicates that only a small quantity is present,
while a failure to obtain a blue color, even after several
hours, indicates that the water is free from nitrous acid.
In performing this operation, bright daylight, and espe-
cially direct sunlight, should be avoided, or a blue color will
probably be produced even if no nitrous acid is present.
And it is best to treat 50 cubic centimeters of a water, known
to be free from nitrous acid, in the same manner and at the
* To make this solution, dissolve 50 grams of potassium hydrate and
2 grams of potassium permanganate in 250 cubic centimeters of water.
Boil until about one-fourth of the liquid is evaporated, in order to drive
off any ammonia that may be present, and then add enough water,
which is strictly pure and free from ammonia, to make 250 cubic centi-
meters of solution.
§ 11 QUALITATIVE ANALYSIS. 67
same time that the water to be tested is treated. This
method is very simple, and its results are quite reliable, but
not absolutely certain, as the water may contain substances
that interfere with the reaction. To avoid this source of
error, we may place about 300 cubic centimeters of the water
to be examined in a retort or flask, add a little acetic acid,
and distil it as in the preceding article, in testing for ammo-
nia. Nitrous acid, if present, will come over in the first
50 cubic centimeters of the distillate, and this may be tested
with potassium iodide and starch solution as just described,
or still better with a solution of sulphanilic acid and naph-
thylamine in acetic acid. To make this solution, dissolve
one-half a gram of sulphanilic acid in 150 cubic centimeters
of acetic acid. Then boil one- tenth of a gram of naphthyl-
amine with 20 cubic centimeters of water, and decant the
colorless liquid, from the violet-colored residue, into 150 cubic
centimeters of acetic acid. Mix these two solutions, and, if
the resulting mixture is colored, add zinc dust, and shake
till the color is destroyed. Allow the solution to settle,
decant the clear liquid, and keep it in a well stoppered
bottle.
If a little of this solution is added to the distillate, and the
mixture heated to 70° or 80°, it will assume a rose color if
nitrous acid is present.
69, Organic Matter. — To test for organic matter in
water, it is usually sufficient to evaporate about 200 cubic
centimeters of the original sample to dryness on the water
bath, and heat the residue over the Bunsen burner, gently
at first, and gradually increasing the temperature. If there
is any considerable amount of organic matter present, the
residue will become brown or black, and a burnt odor is
generally observed. If the water contains carbonates, and
the residue has not been heated too strongly, carbon dioxide
with a burnt odor will generally be given off when the resi-
due is treated with dilute hydrochloric acid.
70, Decaying Matter. — A simple test for decaying
organic matter may be made by filling a rather large bottle
68 QUALITATIVE ANALYSIS. § 11
to two-thirds its capacity with the water to be tested, cover-
ing it with the hand, shaking it well, and noting if any odor
is evolved. If hydrogen sulphide is present, it will probably
mask any other odor. In this case place a fresh sample of
the water in the bottle, add a little copper sulphate, cover
with the hand, shake well, and note the odor.
If hydrogen sulphide is found in applying this test, we
should seek to confirm it by means of reagents, although it
often happens that the odor evolved is a more delicate test
than any of the wet reactions. To test water in the wet way
for hydrogen sulphide, nearly fill a rather large white bottle
with the water to be tested, and add a few drops of a strong
solution of lead acetate in sodium hydrate. If this produces
a white precipitate, a few drops of a strong solution of cop-
per chloride in water must be substituted. Place the bottle
on a sheet of white paper, and look down through it towards
the white surface. If a black precipitate or a brown colora-
tion is produced by either of these reagents, it shows the
presence of hydrogen sulphide in greater or less amount.
This coloration may be produced either by free hydrogen
sulphide dissolved in the water or by the sulphide of an
alkali; hence, if the water is alkaline, indicating the probable
presence of an alkaline sulphide, the following method of
distinguishing between the two should be employed : Close a
rather large bottle, half filled with the water, with a cork,
to the bottom of which is fastened a piece of filter paper that
has been saturated with a solution of lead acetate and then
moistened with a drop or two of ammonium carbonate.
Allow the bottle thus stoppered to stand for several hours,
and shake at frequent intervals, taking care not to allow any
of the water to spatter on to the paper. Hydrogen sulphide
will give the paper a brown color, but the sulphide of an
alkali will not affect it unless it comes in contact with the
water.
71, CarlK>nlc Acid and Blcarbonates. — To a rather
large sample of the freshly drawn water, add a little lime
water, a drop at a time. If the water contains free carbonic
§ 11 QUALITATIVE ANALYSIS. 69
acid, a white precipitate of calcium carbonate will be formed
at first, and upon stirring will be dissolved by the free car-
bonic acid, forming calcium bicarbonate ; but, upon the addi-
tion of a few more drops of the lime water, a permanent
precipitate of calcium carbonate will be formed. If the
water does not contain free carbonic acid, but does contain
bicarbonates, a permanent precipitate will be formed at
once.
73. Poisonous Metals. — The poisonous metals most
frequently found in water are lead, copper, and zinc. To
examine the water for these, place about 1 liter of the water
in a tubulated retort, and add about 10 cubic centimeters of
dilute hydrochloric acid ; direct the neck of the retort steeply
upwards, leave the tubulure open, and evaporate the water
to about 100 cubic centimeters. If a precipitate forms dur-
ing this concentration, it is filtered off. As it may contain
lead, add to it a little tartaric acid, then a slight excess of
ammonia, boil, filter, and test the filtrate for lead with hydro-
gen sulphide. Lead hydrogen sulphide through the first
filtrate, to precipitate copper and lead, filter, and, if any con-
siderable precipitate is formed, treat it for the separation of
these metals, as described in the separation of the metals
of Group II. If only a slight precipitate is formed, more of
the water must be evaporated and treated in the same way,
in order to get enough of the precipitate, so that it can be
separated. Boil the filtrate, or the solution if no precipitate
was formed, to expel all traces of hydrogen sulphide, and, if
sulphur separates during the boiling, filter it off. To the
clear liquid, add a few drops of concentrate nitric acid and
3 or 4 cubic centimeters of ammonium chloride, heat to boil-
ing, and add a slight excess of ammonia. If a precipitate
forms, filter it off, and if of any considerable size, examine
it for iron and chromium, for iron, if present in any consider-
able quantity, is injurious to the health, and chromium is
quite poisonous.
Add just enough acetic acid to the filtrate to render it acid,
and lead a current of hydrogen sulphide through it. A white
TO
QUALITATIVE ANALYSIS.
8"
precipitate shows the presence of zinc. Or the usual method
of analysis may be followed, and ammonium sulphide added
instead of acetic acid and hydrogen sulphide.
Arsenic sometimes occurs dissolved in water, and when
present should never be overlooked. Marsh's test is nearly
always used in examining water for arsenic. It may be
performed as described in Art. 74, Inorganic Chemistry,
Part 2. Or, a somewhat simpler form of apparatus may be
used, as shown in Fig, 3. To test the water for arsenic,
pure zinc is placed in the evolution flask a and covered with
pure water. Connect the apparatus, and pour about half as
much concentrate sulphuric acid through the funnel tube b
as there is water in the flask. The hydrogen evolved passes
out through the drj-ing tube c, which is filled with granulated
calcium chloride, and thence through a hard-glass tube that
has been drawn out at a point d. After enough hydrogen has
been evolved to drive all the air out of the apparatus, so that
there is no danger of its containing an explosive mixture of
air and hydrogen, bring a Bunsen burner under the tube at
(/, and ignite the hydrogen at e. If, after several trials, no
§ 11 QUALITATIVE ANALYSIS. 71
black spot is deposited on a piece of cold porcelain by the
flame e, and no mirror is deposited on the tube between
d and e, we may assume that our materials are free from
arsenic. Now through the funnel tube b add a few cubic
centimeters of the water that has been concentrated as just
described, taking care not to introduce any air with the
water, and after a few moments test the flame e with a piece
of cold porcelain. The tube must be kept at a red heat at d,
and the flame at e must be repeatedly tested for several
mmutes. If, at the end of fifteen minutes, the flame has not
deposited a black spot on the cold porcelain, and no mirror
has been formed between d and e, we can safely assume that
the water is free from arsenic, but if either of these phenom-
ena is observed, it shows the presence of arsenic.
If antimony were present in the water, it would give the
mirror in the tube and a black stain on the porcelain, but, as
antimony is not likely to occur in water, and as its compounds
are also poisonous, it is not necessary as a rule to distinguish
between antimony and arsenic. If it is desired to learn which
IS present, this is easily done, for the stain produced by arsenic
is brownish black and has a- bright luster, while the stain
produced by antimony is a dull deep black. The stain pro-
duced by arsenic is immediately dissolved by a solution
containing a mixture of sodium hypochlorite and sodium
chloride, while the stain deposited by antimony is only dis-
solved very slowly, or not at all, by this solution.
73, Tlie Water is Turbid.— In case the water to be
examined is not clear, part of the tests must be made on the
water in its original condition and part after it has cleared.
Fill a large bottle with the water, stopper it tightly, and
stand it aside in a cool, dark place until perfectly clear.
Draw off the necessary quantity of the clear water by
means of a siphon, and treat it as described in Arts.
63, 64, 65, 69, and 71, Then, using fresh samples of
the water in its original turbid condition, test for ammonia
as described in Art. 66, for nitrous acid according to Art.
68, for decaying matter according to Art. 70, and for
72 QUALITATIVE ANALYSIS. § 11
poisonous metals according to Art. 73. In the case of
turbid waters, the distillation method must be used for
nitrous acid.
It is often desirable to know the character of the solid
matter in water. In order to learn this, filter off the sedi-
ment that remained in the bottle in which the water was
set aside to become clear, treat it with hydrochloric acid,
filter off the insoluble matter, which nearly always remains,
and subject the filtrate to treatment for the group separa-
tions. Fuse the insoluble residue with sodium carbonate,
dissolve the fusion in hydrochloric acid, and put this solution
also through the group separations.
EXAMINATIOIf OF UKINE.
74, Urine is the most important vehicle through which
waste matter escapes from the body ; hence, it always con-
tains salts and organic matter. The constituents of normal
urine vary considerably, both in character and quantity, so
that, to obtain complete information in regard to the char-
acter of a sample of urine, a quantitative examination is
required. But certain constituents that are never present in
health are found in urine in case of disease ; hence, we may
learn much from a qualitative examination. The compo-
sition of the urine varies at different times in the day;
hence, a sample representing the average for twenty-four
hours should be taken for analysis. The quantity of urine
passed in twenty-four hours varies considerably, but averages
from 1,200 to 1,500 cubic centimeters.
75, Color. — The first step in the examination of urine
is usually to note its color. In health the colot may be
light yellow, lemon yellow, or amber. As, in health, the
quantity of coloring matter passed remains comparatively
constant, while the total amount of urine passed varies
greatly, it necessarily follows that the less urine passed, the
darker will be its color, owing to the strong solution of
§ 11 QUALITATIVE ANALYSIS. 73
coloring matter that is thus obtained. Hence, normal urine
may vary considerably in color, but, if very light or very
dark colored, disease is indicated. To determine the color
of a sample of urine, it is merely necessary to place some of it
in a colorless-glass vessel and compare the shade with the
colors given in VogeVs scale of urine tints in Plate IIL
76. Reaction. — Usually the second operation in the
examination of urine is to test its reaction with litmus paper.
Normal urine should be slightly acid, but shortly after a meal
it may be neutral or even slightly alkaline. The total urine
passed in twenty- four hours should surely have an acid reac-
tion; if alkaline, it shows that the urine has decomposed
before passing, and consequently indicates a deranged condi-
tion of the system. Urine containing much albumin is often
alkaline ; hence, if a sample of urine is alkaline, this is taken
as an indication of Bright's disease. To test the reaction of
urine, two pieces of litmus paper should be used, one red
and the' other blue. As the reaction is usually only faintly
acid or alkaline, the paper should not be strongly colored, or
the urine may not be strong enough to change the color.
With paper that is only faintly colored the reaction is much
more delicate. The urine should not be allowed to stand
longer than necessary before taking its reaction, as it is
likely to decompose, especially if it stands in a warm place,
and a urine that is originally acid may thus become alkaline.
77, Specific Gravity. — As urine is a solution of solid
substances in water, it is always heavier than water. The
specific gravity depends on the amount and character of the
solid matter passed, and upon the quantity of urine. The
amount of solid matter will be the same whether a large or a
small amount of urine is passed ; hence, if the quantity of
urine is small, the solution will be concentrate, and the
specific gravity high, while, if the quantity of urine is large,
the solution will be dilute, and the specific gravity will con-
sequently be low. In health the specific gravity of urine
may vary from 1.005 to 1.025; while in case of disease it
74
QUALITATIVE ANALYSIS.
Ml
varies from 1.002 to l.OliO. Sugar, which is present in the
urine in case of diabetes, gives it a high sijecific gravity.
Hence, if the speciiic gravity is more than about 1.028, the
urine should at once be tested for sugar. The test for
specific gravity is usually made with a hydrometer, which
is graduated from l.OflO to l.OOU,
known as a ttrinomftiT. To make
this test, a sample of urine is
I.MS placed in a cylinder, and the
, urinometer is lowered into it, as
a shown in Fig, 4. The urinometer
' will sink into the urine up to some
" point on the graduated stem, and
" the reading on the stem at the
surface of the liquid is the specific
gravity. The urinometer is just
like the hydrometer described in
Art. 43, Physics, except that it is
graduated from 1.000 to 1.0(10.
and many urinometers contain a
thermometer in the stem. All of
ISillHL ((^d) them- are made to take the specific
V™ jiiiiilR^ ^^P" gravity of the urine at a certain
tenijjerature, generally 15°, and,
^"'' ^ as the urine is usually warmer
than this, it must be cooled to this temperature before it is
tested. This may readily be done by holding the cylinder
containing the urine in cold water, or by allowing cold
water to run over the outside of the cylinder; but care must
be taken not to allow any water to get into the urine, or its
specific gravity will be reduced. The urinometer is nearly
always used in taking the specific gravity of urine, on account
of the ease and rapidity with which it }'ields a result; but if
there should be an error in the graduation of the urinometer,
all results obtained with it would be erroneous; hence, when
great accuracy is desired, ths specific gravity is also taken
by means of a bulb, or specific-gravity bottle, as described in
Art. 36, P/ij/sics.
§ 11 QUALITATIVE ANALYSIS. 75
From the specific gravity of urine, the approximate quan-
tity of solid matter that it contains may be calculated. The
last two figures of the specific gravity multiplied by 2^ gives
the approximate weight, in grams, of solid matter in 1 liter
of the urine.
Illustration. — The specific gravity of a sample of urine is 1.010.
To find how much solid matter it contains, multiply 10 by 2^; thus,
10 X 2^ = 23J grams in 1 liter. If the amount of urine passed in
24 hours is known, the approximate quantity of solid matter passed
may readily be found from this result, by a simple calculation.
78, Sugar. — Sugar is found in the urine of patients
suffering from diabetes, and urine containing sugar is fre-
quently spoken of as diabetic urine. Sugar occurs in urine
in the form of glucose y or grape sugar. It probably never
occurs in normal urine, and certainly never in any consider-
able amount; hence, if sugar enough to give a distinct reac-
tion is found in urine, it is a certai.i indication of disease.
There are several methods of testing for sugar in urine, but
probably Fehling*s solution is most commonly employed for
this purpose.
1. Determination by Fehlin^s Solution. — Fehling*s solu-
tion is an alkaline solution of copper. To make it, dissolve
34. G52 grams of pure crystallized copper sulphate in sufficient
water to make 500 cubic centimeters of solution, and keep in
a well stoppered bottle. Thjn dissolve 173 grams of pure
crystallized neutral sodium tartrate in 480 grams "of a solu-
tion of sodium hydrate, having a specific gravity of 1.14;
dilute to 500 cubic centimeters, and keep this solution also
in a well stoppered bottle. These solutions are mixed in
equal proportions just before using, but must be kept in
separate bottles until they are to be used, as decomposition
takes place when they are mixed and allowed to stand. To
use the Fehling solution, pour 1 cubic centimeter of the
solution of sodium tartrate and sodium hydrate into a rather
large test tube, add an equal amount of the copper-sulphate
solution, dilute this to 10 cubic centimeters, and heat to
boiling. If the solution has been prepared according to the
directions given, it should remain clear; if a precipitate
76 QUALITATIVE ANALYSIS. § 11
fomis, the solution is useless, and a new one must be made
up. If the chemicals used in preparing the solution are
pure, and it is prepared as directed, it will remain clear.
After boiling the solution for a few seconds, remove it from
the flame, and at once add the urine to be tested, a few
drops at a time. When about 1 cubic centimeter of the
urine has been added, the mixture should again be heated to
boiling, but the boiling must not be continued more than a
few seconds. Continue the gradual addition of the urine,
keeping the solution as near the boiling point as practicable,
until 10 cubic centimeters have been added, and again boil
the solution for a few seconds. If the solution remains
unchanged after this treatment, it is quite safe to assume
that the urine is free from sugar, for sugar when present
acts as a reducing agent, destroying the color of the solution,
and precipitating red cuprous oxide Cufi, If any considera-
ble amount of the red cuprous oxide is precipitated, it is
proof of the presence of sugar. In experienced hands this is
a very accurate test, but, like other tests for sugar in urine,
it only yields reliable results when properly performed.
Hence, the beginner should always confirm his results, by
repeating the determination or by another test.
2. Trommer's Test. — To 8 or 10 cubic centimeters of the
urine in a large test tube, add one-third of its bulk of sodium
hydrate, made by dissolving 10 grams of solid sodium
hydrate in 30 cubic centimeters of water, and then add, a
drop at a time, a solution of copper sulphate, made by dis-
solving 5 grams of the pure crystals in 50 cubic centimeters of
water. After the addition of each drop of the copper sul-
phate, the solution should be shaken, and if the precipitate
at first formed dissolves, this is evidence of sugar, but is not
conclusive. Continue the addition of copper sulphate until a
slight permanent precipitate is formed, and then heat the solu-
tion just to the boiling point, and remove it at once from the
flame. If sugar is present, a precipitate of yellow cuprous
hydrate is formed. This soon changes to red cuprous oxide,
which settles to the bottom or sides of the tube.
One of these methods is nearly always used in testing for
§ 11 QUALITATIVE ANALYSIS. 77
sugar in urine, but care must be taken in using them, or
erroneous results will be obtained. If the boiling is con-
tinued long when the copper solution is added, it may be
decolorized, or a slight precipitate may even be formed when
the urine does riot contain sugar, as other constituents of the
urine have the power of reducing copper sulphate, when
boiled with it for some time. Albumin, if present, inter-
feres with the reduction of copper; hence, it must be
removed, by one of the methods given later, before one of
these methods can be employed. To avoid these sources of
error, the following exact method is sometimes used :
3. Brucke's Method, — To 50 cubic centimeters of the urine
in a beaker, add 60 cubic centimeters of a solution of neu-
tral lead acetate, made by dissolving C grams of the solid
lead acetate in sufficient water to make GO cubic centimeters
of solution. This precipitates most of the substances that
would interfere with the reaction, and leaves the sugar in
solution. Filter, wash the precipitate on the filter once or
twice with cold water, and to the filtrate add ammonia, in
slight, but distinct, excess. This precipitates the sugar as
lead saccharate {PbO)j^CJi^JD^^. Allow the precipitate to
settle, wash twice by decantation with cold water, then filter
and wash on the filter with cold water until the washings
give no reaction with red litmus paper. Wash the precipi-
tate from the filter into a beaker, using about 75 cubic centi-
meters of water, and pass a current of hydrogen sulphide
through the liquid in which the precipitate is suspended, as
long as a black precipitate of lead sulphide is formed. The
hydrogen sulphide breaks up the lead saccharate, precipita-
ting the lead as sulphide, and the sugar goes into solution.
Filter off the lead sulphide, and wash the precipitate two or
three times with cold water. Boil the filtrate until all hydro-
gen siilphide is expelled, and the volume of the liquid is
reduced to about 50 cubic centimeters. If any sulphur sepa-
rates in the solution during the boiling, filter it off, and stand
the clear liquid aside for at least twenty-four hours for any
uric acid that it may contain to separate in crystals. A little
of the clear liquid, which is now freed from substances that
78 QUALITATIVE ANALYSIS. § 11
would interfere with the reaction, is decanted, or filtered off,
and tested with Fehling's solution, as previously described.
79, Albumin. — Whether albumin ever occurs in strictly
normal urine or not, is a question that has not been settled.
But if present in normal urine, it is only in minute quanti-
ties, while in case of some diseases, especially Bright's dis-
ease, the urine may contain large quantities of it. In testing
for albumin, the sample should be perfectly clear, and if the
urine is cloudy or contains a sediment, it should be filtered
before testing. There are several methods of testing for
albumin in urine. Those most frequently used are here
given.
1. Testing by Heat, — To test for albumin by means of
heat, half fill a test tube with perfectly clear urine, and
gently heat the upper part of the liquid to a temperature of
75° or 80°, and examine the sample in a good light to see if
any difference in transparency between the upper and lower
parts of the sample can be observed. If much albumin is
present, it is usually precipitated by the heat in the upper
part of the tube, while in the lower part, where the sample
is still comparatively cool, but little or no precipitation is
observed. Now continue heating until it boils, and finally
bring the whole sample to boiling. If a precipitate is
formed, or the sample becomes turbid, it is due to the
presence of albumin or phosphates of the alkaline earths.
To distinguish between these, add about half a cubic centi-
meter of nitric acid, drop by drop, when the precipitate, if it
is a phosphate, will dissolve, while albumin is unchanged or
may become more distinct.
If the sample of urine tested is strongly alkaline, probably
no precipitate will be formed until the nitric acid is added,
even though it contains considerable albumin; and, if it is
strongly acid, a soluble modification of albumin may be
formed that will not be precipitated until the sample is neu-
tralized with sodium hydrate. Hence, we must be governed
in our mode of procedure by the reaction of the urine. If
the urine is acid to litmus paper, and a sample, when treated
§ 11 QUALITATIVE ANALYSIS. 79
as just described, gives no precipitate, a second quantity, in
a test tube, should be neutralized with sodium hydrate, and
then treated as directed above.
2. Heller's Test. — Heller's test depends upon the coagu-
lation of albumin by nitric acid, when the two liquids are
brought in contact without mixing. To make this test,
place a few cubic centimeters of strong, colorless nitric acid
in a test tube, and add an equal amount of the clear urine to
be tested, allowing it to run down the side of the inclined
tube, so that it will not mix with the nitric acid. If much
albumin is present, a white band will be formed at the point
where the two liquids meet, which varies in thickness
according to the quantity of albumin present. If a precipi-
tate is not formed at once, the tube and contents should be
set aside for several hours.
Some chemists prefer to place the urine in the tube first,
and add the acid to it, and this may be done by inclining the
tube containing the urine, and pouring the nitric acid care-
fully down the side of the tube, when the two liquids will
form separate layers, and the white ring or band will be
formed where they meet. This test is sometimes modified,
by getting the two layers as described, and then heating
cautiously, taking care not to allow the liquids to mix more
than is necessary. As in the case of the test by heat, if the
urine is strongly acid, the test by nitric acid may fail to
produce a precipitate, even though the urine contains con-
siderable albumin, on account of the formation of so called
acid albumin, which is soluble in acids. Consequently, if
the urine is acid to litmus paper, and gives no reaction for
albumin by Heller's test, as just described, a fresh sample
of it should be neutralized with sodium hydrate, and the test
repeated on this neutral sample.
When nitric acid stands in contact with urine, it acts on
the coloring matter, forming a dark ring that grows darker
on standing, and if albumin is present, and coagulated by
the nitric acid, it is often colored more or less by these col-
oring matters, which have been rendered dark by the acid.
3. These tests have been modified in a number of ways
80 QUALITATIVE ANALYSIS. § 11
by different chemists. A very good method is as follows;
Fill a test tube to about one-third its capacity with the clear
urine to be tested, and heat it to the boiling point ; remove
it from the flame, and, without allowing it to cool, pour
about 1 cubic centimeter of colorless nitric acid down the
side of the inclined tube, so that it forms a separate layer.
If a white band does not form after standing for some time,
heat the solution carefully at first, so that the two liquids
remain separate, and finally shake them up so that the acid
is thoroughly mixed with the urine, and allow the tube to
stand for several hours.
As albumin is rather difficult to determine, and in many
cases is very important, a single test should never be relied
on ; but, if two of the tests given are used, and the reaction
of the urine taken into account, it is scarcely possible to
make a mistake.
The determinations given are the principal qualitative tests
applied to urine, but it occasionally happens that qualitative
determinations of sulphuric, hydrochloric, and phosphoric
acids are required. For these constituents the following
tests are recommended :
80, Sulphuric Acid. — Sulphuric acid occurs in normal
urine combined with sodium and potassium, forming sul-
phates of these metals. Normally, about 2 grams of sul-
phuric acid are passed daily. To determine sulphuric acid,
place about 25 cubic centimeters of the urine to be tested in
a small beaker, add about 1 cubic centimeter of concentrate
hydrochloric acid, and then 8 or 10 cubic centimeters of
barium-chloride solution, and stir well. A white precipi-
tate shows the presence of sulphuric acid. Something may
be learned of the quantity of sulphuric acid present by this
reaction. If the solution becomes milky, it shows that the
urine contains about the normal amount of sulphuric acid,
while a creamy appearance and consistency shows an increase,
and a mere cloudiness a decrease, in the quantity. Hydro-
chloric acid must always be added before the barium chloride,
or barium phosphate may also be formed. If the urine is
I 11 QUALITATIVE ANALYSIS. 81
not clear, or if a precipitate is formed when the hydrochloric
acid is added, it must be filtered and the clear filtrate tested
for sulphuric acid.
81. HydrocMoric Acid. — Hydrochloric acid occurs in
urine chiefly combined with sodium, in the form of sodium
chloride, but also in smaller quantities, combined with potas-
sium and ammonium. In normal urine, the amount passed
in 24 hours should contain from 10 to 16 grams of chlo-
rides. To test for hydrochloric acid, place about 25 cubic
centimeters of the clear inline in a small beaker, add about
half a cubic centimeter of dilute nitric acid to keep the phos-
phates in solution, and then 2 or 3 drops of silver-nitrate
solution. If the urine contains from -J- to 1 per cent, of
chlorides, this will form curdy lumps of white silver chloride
which do not readily break up, or else give the solution a
milky appearance when it is gently agitated. If curdy lumps
of precipitate are not formed, but the solution becomes
equally milky throughout, it shows that the urine contains
less than the normal amount of chlorides, while a failure to
get a precipitate shows the absence of chlorides.
A small amount of albumin in the urine does not usually
interfere with the determination of the normal quantity of
hydrochloric acid, but if much albumin is present, or if the
quantity of hydrochloric acid is small, it is necessary to
remove the albumin before testing for hydrochloric acid.
To do this, heat the sample of urine to boiling, add a few
drops of nitric acid, allow the albumin thus precipitated to
settle, and filter it off. To the clear filtrate add a little more
nitric acid, and then silver nitrate, as just directed. This
determination is sometimes important in the case of certain
acute diseases. In these cases the disappearance of chlorides
from the urine indicates a change for the worse, while their
reappearance always denotes improvement. In the case of
acute pneumonia, the appearance of chlorides in the urine is
frequently the first indication of recovery.
83, Phospliorlc Acid, — Phosphoric acid is contained in
urine in the form of calcium and magnesium phosphates
82 QUALITATIVE ANALYSIS. § 11
(known as earthy phosphates), and alkaline phosphates, prin-
cipally acid sodium phosphate. There are two common
methods of determining the phosphates:
1. Place in a small beaker about 25 cubic centimeters of
the urine to be tested, render it slightly, but distinctly, alka-
line with ammonia, heat gently until a precipitate begins to
form, stir well, and stand aside for an hour or so, for the
precipitate to collect and settle, taking care that the solution
remains alkaline. If earthy phosphates are present, they
will be precipitated from this alkaline solution. If the urine
is normal, the precipitate will be white; but if abnormal col-
oring matters are present, they will be precipitated with the
phosphates, and give their color to the precipitate. The
precipitate of earthy phosphates is filtered off, and the filtrate
is tested for alkaline phosphates. To do this, add from
5 to 8 cubic centimeters of magnesium solution,* stir well,
and stand aside for a few moments. Then stir again, and
note the appearance of the sample. The phosphoric acid of
the alkaline phosphates is precipitated as pure white mag-
nesium-ammonium phosphate; and, if the liquid has a milky
apearance, a normal amount of phosphoric acid is present.
If the liquid is more creamy in appearance, it shows an
excess of phosphoric acid, while a mere cloudiness shows a
decreased amount. If no precipitate or only a slight one is
formed, the solution should be allowed to stand for several
hours and then be again examined.
It frequently happens that the total phosphoric acid is all
that is required. In this case, place about 25 cubic centi-
meters of the urine in a small beaker, render it alkaline with
ammonia, heat gently, and slowly add about 8 cubic centi-
meters of magnesium solution, with constant stirring.
2. We have seen that silver nitrate precipitates phos-
phoric acid from neutral solutions, and this fact is sometimes
made use of in determining phosphoric acid. This is done
* To make majarnesium solution for this purpose, dissolve 1 gram of
magnesium sulphate in 8 cubic centimeters of water, add 1 gram of
ammonium chloride, and, when all is dissolved, add 1 cubic centimeter
ot concentrate ammonia.
§ 11 QUALITATIVE ANALYSIS. 83
as follows: Place about 25 cubic centimeters of the sample
in a beaker, add about 1 cubic centimeter of nitric acid, and
precipitate the hydrochloric acid with an excess of silVer
nitrate. Stir well, and filter off the silver chloride. The
filtrate contains the phosphoric acid in acid solution, together
with the excess of silver nitrate added to precipitate the hydro-
chloric acid. To the clear filtrate, add ammonia, drop by drop,
with constant stirring, until the neutral point is just reached,
when silver phosphate is precipitated. As silver phosphate
is soluble in ammonia, a few more drops will dissolve it,
and from this solution it may be repreci pita ted by adding
nitric acid, a drop at a time, until the solution is just neutral.
If it is desired to do so, the earthy phosphates may be
removed by heat and ammonia. The filtrate is rendered acid,
and the alkaline phosphates determined by this method. As
this test only yields good results when carefully and properly
applied, the first method is recommended, especially for
beginners, but it is a good plan to confirm the results thus
obtained by the second method.
83. Samples for Practice. — In examining urine for
sugar and albumin, only negative results are ordinarily
obtained; hence, the student is advised to make up samples
containing these substances, in order to become familiar with
their reactions. This may be done by dissolving small quan-
tities of these substances in water, and adding these solutions
to samples of normal urine. A solution containing sugar
may readily be made by dissolving about 1 gram of grape
sugar, or glucose (the kind of sugar that occurs in urine),
in 50 cubic centimeters of water, and adding this to an
equal amount of lu'ine. A solution containing albumin
is not quite so easily prepared, but may be made quite
readily as follows: Add the white of an egg to about
100 cubic centimeters of cold water, stir it well for some
time, and allow the part that does not dissolve to settle.
After the undissolved portion has completely subsided, pour
the clear liquid, which contains albumin in solution, into an
equal volume of urine.
84 QUALITATIVE ANALYSIS. § 11
COMMON INORGANIC POISONS.
84. The chemist is often called upon to determine if a
substance contains a certain poison, and this section is
designed to enable the student to answer such a question,
and to give him a certain familiarity with the methods
employed in such cases. Obviously, an exhaustive treatment
of the subject of poisons would be out of place in a Paper of
this character, hence, only the common poisons will be
treated. But, if the student makes himself familiar with
the determination of the poisons treated in this Paper, he
will be able to determine any of the less common ones, by
referring to one of the books on this subject. The most
common inorganic poisons are arsenic, phosphorus, and
hydrocyanic acid, or a cyanide.
ARSENIC.
85, Preliminary Examination. — Arsenic is the most
frequently used of the poisons,* and generally in the form of
arsenious oxide (white arsenic), which is very dangerous, as
small doses are fatal, and it is almost tasteless, so that its
presence cannot be detected in this way. The sample for
analysis may be almost any ordinary substance — a food,
vomit, or even a stomach. In case wilful poisoning is sus-
pected, it is desirable to learn, if possible, in what form the
arsenic was administered.
1. If food, vomit, or some similar substance is submitted
for analysis, mix it well, set aside from one-third to one-half
for further examination, or to confirm the results obtained,
and mix the rest in a rather large, perfectly clean porcelain
dish, with two or three times its volume of water. Stir well
with a glass rod, allow the heavy solid matter to settle, and
pour the liquid, together with the light suspended matter,
into a second porcelain dish. Stir the solid matter with a
glass rod, and feel over the bottom of the dish with the rod
§ 11 QUALITATIVE ANALYSIS. 85
for any gritty particles of solid matter. Pour the liquid from
the second dish back into the first, stir well, allow it to settle,
and again pour the liquid into the second porcelain dish. To
the solid matter in the first dish add an equal volume of
water, stir well, allow it to stand a moment for any heavy
grains of solid matter to settle, pour the rest of the contents
of the dish, ascompletelyaspossiblewithout disturbing such
grains, into the second dish, and examine the bottom of the
dish that has just been emptied, for white grains of arsenious
oxide, or black grains or scales of metallic arsenic.
If _such grains are found, remove a few of them, and dry
them between folds of filter paper. If black grains are
found, introduce them into a closed tube and heat over the
Bunsen burner, when a black mirror on the cool part of the
tube shows the presence of metallic arsenic. If white grains
are found, introduce them into a closed tube that is drawn
out to a point, as shown in Fig. 5, so that they fall to the
point a, and drop in a splinter of freshly ignited charcoal,
which will be held at the point b. Now heat the charcoal
to redness, and then chang'e the position of the tube so that
the white grains are heated at the same time, when, if
arsenious oxide is present, a black mirror will be formed at c.
Whether such grains arc foimd or not, wash the contents of
the first dish into the second, and treat as directed in
Art. 86.
If a stomach is to be analyzed, empty the contents into
a porcelain dish, turn the stomach inside out, and search the
I lining for white or black grains or scales, which are often
found adhering to, or embedded in, the membrane, and are
frequently indicated by red spots. If such grains are found,
examine them for arsenic and arsenious oxide, as just
described. Then cut the stomach into small pieces, mix it
■ thoroughly with the contents in the dish, and proceed as
^E''directed in examination No. 1.
t
86 QUALITATIVE ANALYSIS. § 11
86. Method for the Determination of Arsenic in
Any Form. — The reaction of the mixture in the porcelain
dish is next ascertained by means of litmus paper, and, if
acid, just enough pure sodium carbonate is added to render
it neutral, and the whole is evaporated to a pasty consistence
over the water bath. If the sample contained alcohol, the
evaporation must be continued until this is completely driven
off. A quantity of hydrochloric acid, of about 1.12 Sp. Gr.,
about equal in weight to the amount of solid substance
taken for analysis, is added, together with distilled water,
if necessary, in order that the hydrochloric acid shall not
exceed one-third of the total liquid present. Add about
2 grams of potassium chlorate, and heat the mixture on the
water bath. When the liquid has attained the temperature
of the water bath, add more potassium chlorate at intervals
of 5 or 10 minutes, in portions of ^ gram to 2 grams, and
stir it well. Replace the water that has evaporated from
time to time. Continue this treatment until the contents of
the dish have become nearly homogeneous and fluid, and
have assumed a light-yellow color that is retained when the
substance is heated for 20 or 30 minutes longer, without the
further addition of potassium chlorate.
When this point is reached, add about 1 gram of potassium
chlorate, stir, and immediately remove the dish from the
water bath. When the dish and contents have become per-
fectly cold, filter, and wash the residue well with hot water.
The residue may contain metallic mercury, albuminate of
mercury, lead sulphate, and possibly lead chloride, basic
bismuth chloride, and stannic oxide. It should be marked
Ppt. 1, and set aside to be examined for these metals, as
described in Art. 87. The filtrate and washings are usually
kept separate. Heat the filtrate on the water bath, with the
renewal of the water as it evaporates, until the odor given
off by the chlorate has disappeared. Evaporate the washings
on the water bath to about 100 cubic centimeters, and add
this to the filtrate, which has been evaporated so that the
total amount of liquid is from three to four times the volume
of the hydrochloric acid added. Transfer the liquid to a
§ 11 QUALITATIVE ANALYSIS. 87
flask, heat it to about 70° on the water bath, and while at
this temperature, conduct a slow stream of hydrogen sul-
phide through it for about 12 hours. Then remove the flask
from the water bath, and allow the mixture to cool while the
gas is still passing through it. When the contents of the
flask have become cool, withdraw the delivery tube from the
flask, and wash it with ammonia, allowing the washings to
run into a beaker. Acidulate the ammoniacal washings with
hydrochloric acid, and add this to the contents of the flask.
Cover the flask loosely with filter paper, and stand it in a
moderately warm place for from 6 to 12 hours. Collect the
precipitate on a small filter, and wash thoroughly with water
containing a little hydrogen sulphide. Saturate the filtrate
and washings with hydrogen sulphide, and evaporate to a
small bulk over the water bath. If any precipitate is formed
during the evaporation, filter it off, wash well, and add it to
the main precipitate. The filtrate should be examined for
the metals of the third, fourth, and fifth groups. The pre-
cipitate contains the arsenic, together with any other metals
of the first and second groups that may be present, and gen-
erally some organic matter. Remove the precipitate and
filter to a small porcelain dish, and heat it on the water bath
until perfectly dry. Add pure fuming nitric acid (which
must be free from chlorine), drop by drop, until the precipi-
tate is thoroughly moistened, and again evaporate to dryness
on the water bath. Moisten the precipitate with pure con-
centrate sulphuric acid, heat for about 2 hours on the water
bath, and then on the sand bath at a moderate temperature,
gradually raising the temperature until white fumes begin
to escape. The mass should now be easily broken up, and a
small portion of it when stirred with a little water should
not impart any considerable color to the fluid. If it gives a
brown color to the water, or if the mass should have a brown,
oily appearance, add some small pieces of pure dry filter
paper, and heat the mass till white fumes again begin to
come off, and then allow the dish and contents to become
nearly cold. Add a mixture of 1 part of concentrate hydro-
chloric acid and 8 parts of water, and heat on the water bath
88 QUALITATIVE ANALYSIS. § 11
for about 1 hour, stirring occasionally. Filter, wash well
with hot water containing a little hydrochloric acid, and
finally with boiling water. The undissolved portion on the
filter, which may contain lead, mercury, tin, bismuth, and
antimony, should be marked Ppt. 2, and set aside for exam-
ination according to Art. 87.
The filtrate is removed to a flask, and hydrogen sulphide
again conducted through it, exactly as described in the first
precipitation, by hydrogen sulphide. The precipitate, which
is now free from organic matter, is collected on a small filter
and washed. It will contain all the arsenic, and perhaps
some other metals as sulphides. If the precipitate is yellow,
and a small portion of it, when shaken in a test tube with
ammonium carbonate, completely dissolves, arsenic alone is
present. In this case, dissolve it in ammonia, evaporate the
solution to dryness on the water bath, add a little fuming
nitric acid, heat, then add concentrate sulphuric acid, and
evaporate on the sand bath imtil all nitric acid is expelled, and
white fumes begin to come off. Allow the residue to cool, add
from 5 to 10 cubic centimeters of sulphurous acid, evaporate
the excess on the water bath, and examine the resulting
solution for arsenic by one of the methods to be given later.
If the precipitate contains other metals than arsenic,
remove the filter, together with the precipitate, to a small
porcelain dish, pour ammonia over the precipitate, add a few
drops of ammonium sulphide, and remove the filter, washing
it thoroughly with as little water as possible. Heat the dish
and contents on the water bath while stirring the mixture.
Filter, wash, and mark the residue Ppt. 3, to be examined
according to Art. 87. Evaporate the filtrate to dryness on
the water bath, add a little pure fuming nitric acid, and
again evaporate until nearly dry. To the residue add a little
sodium hydrate, and then sodium-carbonate solution in slight
excess. Now add a mixture of 1 part of sodium carbonate
and 2 parts of sodium nitrate; evaporate to dryness over
the water bath, remove to a Bunsen flame, and gradually
increase the heat until the substance fuses. Allow the
fusion to cool, add cold water, and stir frequently until the
§ 11 QUALITATIVE ANALYSIS. 89
mass is thoroughly disintegrated, when all the arsenic will
be dissolved. If a residue remains undissolved, filter it off,
wash, and examine it for antimony and tin. To the filtrate
add pure dilute sulphuric acid until the reaction is strongly
acid, evaporate nearly to dryness on the water bath, add a
little more dilute sulphuric acid, and heat on the sand bath
until heavy white fumes begin to come off. Ccfol the residue,
add from 5 to 10 cubic centimeters of sulphurous acid, and
heat on the water bath till most of the excess of sulphurous
acid is driven off. Add a little water to make a clear solu-
tion, and test for arsenic by one of the following methods:
1. Marsh's Test. — This test is applied in exactly the same
manner as described in Art. 73, The solution prepared as
directed above is added in the same way as the water is
added, and the black mirror or stain shows the presence of
arsenic. Only a little of the arsenic solution should be
added at a time, for, if much is added, it may cause violent
action, which would interfere with the test, or perhaps cause
its loss, through foaming over. In many cases a solution of
arsenic may be tested directly by this method, without the
long preparation above described, but when absolutely
accurate results are desired, and organic matter is present,
the above directions should be carefully followed.
2. Fresejiins" and von Babo's Method, — Add a little water
to the solution obtained as described above, transfer it to a
small flask, heat to 70°, and precipitate the arsenic by a cur-
rent of hydrogen sulphide, as previously directed, except
that in this case all the arsenic will be precipitated in
G hours. Filter, wash well, and, if much is present, dry the
filter and precipitate, remove the thoroughly dry precipitate
to a porcelain boat, and proceed directly with its reduction.
If the precipitate is too small to be removed from the filter,
dissolve it while wet with a little ammonia; allow the solu-
tion to run into a porcelain crucible, add from | to ^ gram
of dry sodium carbonate, evaporate to dryness on the water
bath, and remove the dry residue, or the precipitate as
obtained above, to a porcelain boat ^, Fig. 6, mix it with
about twice its weight of pure potassium cyanide and 5 or
90
QUALITATIVE ANALYSIS,
§"
C times its wfight of pure dry sodium carbonate, and place
the boat and contents in a hard-glass tube, drawn out at one
end. Connect the apparatus as shown in Fig. 6, and after
the tube is thoroughly filled with carbon dioxide — -generated
by the action of hydrochloric acid on marble, in the Kipp
apparatus a, and washed by concentrate sulphuric acid in the
fl;:sk b — gently heat the tube throughout its entire length, to
be sure all moisture is driven off. Then regulate the flow
of carbon dioxide so that it passes through the flask b at the
rate of about one bubble per second, gradually heat the tube
to redness near the point (/, where it begins to narrow, then
place a second burner under the boat at r, gradually increas-
ing the heat until the tube is bright red and the contents of
the boat are thoroughly fused, continuing the heat until all
the arsenic is driven off. The arsenic will be deposited on
the tube just beyond the burner ;it the point d, and in the
narrow part of the tulie, forming a metallic mirror. If any
arsenic IS not deposited on the tube, but escapes, it may be
detected by its gariic odor. In this determination the carbon
dioxide should always be generated in Kipp's, or some similar
generator, so that its flow may be properly regulated.
87. Ilxamination of the Resldxies or Precipitates.
Although the main object of this process is the determination
of arsenic, the insoluble residues obtained while carrying it
§ 11 QUALITATIVE ANALYSIS. 91
out should be examined for other poisonous metals. This
may be done as follows :
1. Examination of Ppt, 1. — This residue may contain
lead, mercury, bismuth, and tin. When dry, remove it to a
porcelain dish, add red fuming nitric acid, and evaporate
almost to dryness on the water bath. Add water and a little
common nitric acid, and continue the heating for some time;
then filter, dilute the filtrate, precipitate with a current of
hydrogen sulphide, and examine the precipitate for the
metals mentioned above, as directed under the group separa-
tions in Qualitative Analysis^ Part 1. The precipitate may
contain a little lead, and should be examined for it.
2. Examination of Ppt. 2, — This residue may contain
lead, mercury, antimony, and possibly tin and bismuth.
Remove it to a small porcelain dish, add an excess of aqua
regia, heat for some time on the water bath, and finally boil
down to a small bulk on the sand bath or over the flame.
Add water and a little hydrochloric acid, bring the solution
to boiling, and if an insoluble residue remains, filter it off.
Precipitate the metals from the filtrate by a current of
hydrogen sulphide, and examine the precipitate as directed
under the group separations in Qualitative Analysis^ Part 1.
3. Examination of Ppt. S, — This residue may contain
lead, mercury, and possibly copper. Remove it to a porce-
lain dish, and heat on the water bath with a mixture of
equal parts of concentrate and dilute nitric acid, for half an
hour, and then bring to boiling on the sand bath or over the
flame. Mercury will not be attacked by this acid, but other
metals that may be present will be dissolved. Dilute, filter,
and examine the precipitate and filtrate, as directed under
the separation of the metals of the second group in Qualita-
tive Analysis^ Part 1.
PHOSPHORUS.
88. Preliminary Examination for Phosphorus. —
Phosphorus has been quite largely used in poisoning
mice, etc., and its poisonous properties have become quite
92 QUALITATIVE ANALYSIS. § 11
generally known. Consequently, the chemist is occasionally
called upon to examine the contents of a stomach, an article
of food, or some similar substance, for phosphorus. In such
cases the chemist should direct his attention exclusively to
the detection of phosphorus in the free state. Merely find-
ing phosphoric acid would not prove anything, for this is a
constituent of nearly all animal and vegetable bodies. In
examining a substance for phosphorus, there should be no
unnecessary delay, for in the air the phosphorus is oxidized
to phosphorous acid, and finally to phosphoric acid.
The first step in the examination of a substance for unoxi-
dized phosphorus is to ascertain if its presence is indicated
by the odor of the substance, or by phosphorescence when
the sample is stirred in a perfectly dark room. These tests
furnish strong indications, but cannot be depended on, as the
odor and phosphorescence may both be due to other sub-
stances. Next, place a little of the sample in a small flask,
and, if dry, moisten it with water. In the mouth of the
flask, loosely fit a cork to which is fastened a strip of filter
paper saturated with a neutral solution of silver nitrate, and
heat the flask and contents to about 40°. If the paper is not
colored after an hour of this treatment, it is scarcely possible
that free phosphorus is present, and it is hardly necessary to
proceed further with the examination, but the result may be
confirmed by one of the following methods. If the paper is
blackened, phosphorus is indicated but not proved, as the
blackening may be caused by other substances. Conse-
quently, in this case, the substance must be further exam-
ined by one of the following methods.
89. Examination by Means of I>lstillatlon With
Water. — Mix a rather large portion of the sample with
water and a little dilute sulphuric acid in the flask a^ Fig. 7,
and connect it w^ith a Liebig condenser b c. Place a screen
ef of some opaque material between the flask and the con-
denser to prevent the light of the lamp falling upon the
condenser, and distil the contents of the flask, receiving the
distillate in a flask d. This experiment must be performed
in
QUALITATIVE ANALYSIS.
in a dark room. If thu substance contains free phosphorus,
there will be seen a strong luminous riny that usually moves
up and down ne:ir the
point b where the steam
enters the cooled part of
the tube. Samples that
contain only very small
quantities of phosphorus
usually prodticc a luminous
ring that may be seen con-
tinuously for half an hour.
If much phosphorus is
present, it will collect in
small globules in the bot-
tom of the flask (t and may
be further examined. If
phosphorus has Ix^en intro-
duced into the substance
in the form of phosphor-
us matches, an oxidizii;g
agent will always be pres-
ent. In this case a little
ferrous sulphate should be ^"^' ^"
added with the sulphuric acid, in order to destroy the oxidi-
zing agent; and if hydrogen sulphide is present, a little ferric
chloride should also be added. Ether, alcohol, oil of turpen-
tine, and many other ethereal oils prevent the luminosity so
long as they are present. Ether and alcohol are soon distilled
over, and the luminosity will then appear, but many of the
ethereal oils prevent it permanently, and when they are pres-
ent the method described in Art. 90 should be employed.
Instead of the apparatus shown in Fig. 7, the ordinary
form of distilling app;iratus shown in Fig. 25, Theoretical
Chemistry, may be used ; but the form shown in Fig. 7 is
better for this purpose.
90. Examination by Drlvlngr Off Phosphorus In a
Current of Carbon Dioxide. — The method just described
k
91
QUALITATIVE ANALYSIS.
511
in Art. 89 is easily carried out, and yields conclusive results
even with minute quantities of phosphorus, when substances
that prevent the reaction are absent. But as a number of
substances prevent the formation of a luminous ring, when-
ever this reaction fails a portion of the sample should be
treated as follows:
Place the substance in a flask, add water, and then dilute
sulphuric acid until the reaction of the liijnid is distinctly
acid. Fit the flask d. Fig. 8, with a stopper having two per-
forations, through one of which a glass tube c passes nearly
to the bottom of the flask; and through this tube pass a
slow current of carbon dioxide,, which has been generated in
the Kipp apparatus a, and washed in the flask b containing
concentrate sulphuric acid. Connect the tube c, which
passes through the other perforation, and through which the
gas passes from the flask d, with a U tube/" containing a
neutral solution of silver nitrate, so that the gas passes
through this solution. When t!ie flask t/is thoroughly filled
with carbon dioxide, place it on the water bath_f, and, while
heated on the bath, pass a slow current of carbon dioxide
through it for several hours. If the substance contains
phosphorus, it will be carried over unoxidized, by the carbon
dioxide, and form a black precipitate of silver phosphide
and metallic silver, when it comes in contact with the silver-
nitrate solution. If no precipitate is formed in the U tube
gll
QUALITATIVE ANALYSIS.
95
after several hours, free phosphorus is not present, and the
operation need not be carried further. If a black precipitate
is formed, it is an indication of phosphorus, but is not con-
clusive, as it may be formed by other substances, and must
be further examined. In this case, filter the contents of the
tube, wash the precipitate well with water, and proceed as
follows :
Place some zinc in the two-necked Woulff bottle a. Pig. 9,
and add dilute sulphuric acid through tlie funnel tube b,
which must be large enough to hold more than the total
amount of acid added. Lead the hydrogen thus generated
through the U tube c, which contains pumice stone satu-
rated with a concentrate solution of potassium hydrate, to
absorb any hydrogen sulphide that may be present. Con-
nect the tube leading from the U tube with a tube having a
platinum tip at e, by means of a piece of rubber tubing over
which a screw pinch cock d is fitted, and by means of this
pinch cock regulate the flow of hydrogen so that it will bum
at e with a steady flame. If this flame is colorless, and does
not produce a green coloration when allowed to impinge on
a piece of cold porcelain, the gas is free from hydrogen
phosphide. Now wash the precipitate, supposed to contain
k
96 QUALITATIVE ANALYSIS. § 11
silver phosphide, into the generator a^ through the funnel
tube b. If this precipitate contains phosphorus, hydrogen
phosphide will be formed in the generator, and in a few
moments the inner cone of the flame will become green, and
an emerald-green coloration will be imparted to the cold
porcelain.
HYDROCYANIC ACID.
91. Preliminary ICxamination. — If an article of food,
the contents of a stomach, or some other substance is to be
examined for hydrocyanic acid or a cyanide — most frequently
potassium cyanide — which has the same effect as the acid,
there should be as little delay as possible, as hydrocyanic
acid is quite readily decomposed and may be lost, and it has
been claimed, but not thoroughly demonstrated, that hydro-
cyanic acid is formed during the decomposition of animal
matter. If the sample for examination does not have an
odor of its own, the presence of hydrocyanic acid will be
revealed by its well known odor; but, if the substance with
which it is mixed has a strong odor, that of the hydrocyanic
acid may be completely hidden. In any event, the odor
alone cannot be depended on, as nitrobenzol and benzaldehyde
have odors somewhat similar to that of hydrocyanic acid.
Mix a small portion of the sample with water, filter, and
test part of the filtrate with ferric chloride for ferrocyanides
and sulphocyanides, and the other part with ferrous sulphate
for ferricyanides. Then proceed with the examination
according to the information obtained by these tests.
93. Examination for Hydrocyanic Acid When Fer-
rocyanides, Ferricyanides, and Sulphocyanides Are
Absent. — If the preliminary examination has shown that fer-
rocyanogen, ferricyanogen, and sulphocyanogen compounds
are absent, mix the substance w^ith water, add a solution of
tartaric acid until the substance has a strong acid reaction,
and introduce it into the retort a. Fig. 10, through the
tubulure b. Tightly stopper the tubulure, and lower the
retort into a vessel c containing a solution of calcium
^11
■ QUALITATIVE ANALYSIS.
97
chloride, so that it does not touch the bottom of the vessel.
Slant the neck of the retort upwards, and heat the calcium-
chloride bath until the contents of the retort begin to boil.
Lead the vapors through a Liebig condenser, the lower end
of which is connected with a tube that passes throug;h one of
the perforations of a doubly perforated stopper that is closely
fitted into the top of the cylinder d. Through the other
]ierforation of this stopper pass a tiibe that leads to the U tiibe
e, containing a dilute solution of pure sodium hydrate, to
absorb ;;ny hydrocyanic acid that may pass over. When
about 10 cubic centimeters of diHtillatc have collected in the
cylinder (/, replace it with another cylinder, divide the dis-
tillate into three parts, and test them as follows:
1. To one-third of the distillate in a test tube, add a httle
ferrous -sulphate solution, a drop of ferric-chloride solution,
and then enough sodium hydrate to give the liquid an alka-
line reaction, when, if hydrocyanic acid ispresent, agreenish-
blue precipitate will be formed that consists of a mixture of
ferric ferrocyanide and the hydrates of iron. Now add
hydrochloric acid, which will dissolve the hydrates of iron,
and leave a bhie precipitate of ferric ferrocyanide, or, if only
k
98 QUALITATIVE ANALYSIS. § 11
a minute quantity of hydrocyanic acid is present, a greenish
solution will be left in the tube, from which a slight blue
precipitate will settle upon standing.
2. Place a second portion of the distillate in a porcelain
dish, add a drop of sodium-hydrate solution, then sufficient
yellow ammonium sulphide to impart a yellowish color to
the solution, and slowly evaporate to dryness on the water
bath. If the solution contained hydrocyanic acid or a
cyanide, the residue in the dish will contain sodium sulpho-
cyanide.. Dissolve this residue in a little water, add 4 or
5 drops of hydrochloric acid, allow it to stand a few minutes,
and then add a few drops of ferric chloride. A red colora-
tion shows the presence of a sulphocyanide that has been
formed from hydrocyanic acid by the above treatment. In
case the red color is not permanent, or a violet color is
formed, more of the ferric chloride must be added to produce
a permanent red color.
3. To the third portion of the filtrate, add a few drops of
potassium-nitrite solution, about 3 drops of ferric chloride,
and then just enough dilute sulphuric acid to change the
color of the ferric salt formed from brown to light yellow.
Heat the solution carefully, until it just commences to boil,
and, after allowing it to cool, add ammonia in slight excess,
to precipitate the excess of iron. Filter off the precipitate,
and to the filtrate, Avhich' should still contain free ammonia,
add a few drops of hydrogen sulphide. If the solution con-
tained hydrocyanic acid, potassium nitroprusside will be
formed, and the hydrogen sulphide acting upon this imparts
a violet color to the solution.
The second filtrate that collects in the cylinder should be
tested in the same manner, and finally the contents of the
U tube should be subjected to the same tests.
93. Determination of Hydrocyanic Acid When
Ferrocyanides, Ferricyanides, or Sulphocyanides Are
Present. — If the preliminary examination has shown the
presence of ferrocyanogen, ferricyanogen, or sulphocyanogen
compounds, mix the sample with water, add a little tartaric
§ 11 QUALITATIVE ANALYSIS. 99
acid, and then sodium carbonate until the sample is slightly
alkaline. Introduce the sample into a retort, and heat over
the water bath to about (but not exceeding) 60"*, while leading
a slow current of washed carbon dioxide through the tubulure,
nearly to the bottom of the retort. The carbon dioxide should
be generated in a Kipp apparatus, and washed in concentrate
sulphuric acid. Collect the distillate in a cylinder to which
a U tube containing sodium hydrate is attached, as shown in
Fig. 10, and subject the distillate to the tests described in
Art 92.
THE ALKALOIDS.
94. The detection and separation of the alkaloids is
much more difficult than the detection and separation of the
metals. This is due to several causes. Reagents do not give
the same sharp distinction between the alkaloids that is seen
in the case of the metals, and, as the alkaloids form a com-
paratively new field of chemistry, and have not been
thoroughly studied, in many cases the reactions are not under-
stood, and only the outward appearance known, so that the
conditions that may modify these reactions are not known.
As new alkaloids, of whose reaction nothing is known, are
continually being discovered, anything like a complete treat-
ment of this subject is impossible at the present time. Only
a few of the most common alkaloids, therefore, will be
treated in this course. This will be sufficient for the average
student, but if a student wishes to know more of this subject,
after making himself familiar with the alkaloids treated in
this Paper, he will be in a position to widen his range of
knowledge in this field, by reading and investigation.
YOLATIIiE AMCALOIDS.
95. The volatile alkaloids are liquids at ordinary tem-
peratures. They may be volatilized either in the pure state
or when mixed with water, and, consequently, are obtained
100 QUALITATIVE ANALYSIS. § 11
in the distillate when their salts are distilled with strong
fixed bases and water. When their vapors come in contact
with the vapor of a volatile acid, they form a white cloud,
similar to that formed by ammonia and hydrochloric acid.
The most common volatile alkaloids are nicotine and conine.
They are most easily detected when in the pure state, and,
consequently, should be obtained as nearly as possible in
that condition before applying tests for them. To do this,
add sodium-hydrate solution to the aqueous solution of the
alkaloids, and distil them in a current of hydrogen, which
has been generated in a Kipp apparatus, and lead into the
retort containing the solution. Neutralize the distillate with
oxalic acid, and evaporate slowly. Dissolve the oxalate of
the alkaloid in alcohol, filter off any residue that may be
present, and evaporate the solution. Treat the residue with
water, add sodium-hydrate solution, shake this mixture with
ether, separate the ethereal solution, and allow the ether to
evaporate at about 20°, leaving the pure alkaloid.
96. Nicotine. — Nicotine in the pure state is a colorless,
oily liquid, with a disagreeable odor. It is found in the
tobacco plant, especially in the leaves and seeds. When
allowed to stand in the air, it assumes a yellowish or brownish
color. When heated to boiling (247°) in the air, it partially
decomposes, but may b3 distilled in an atmosphere of hydro-
gen without decomposition. It mixes with water in all
proportions, and dissolves easily in alcohol or ether.
Nicotine has a pungent taste, and is very poisonous. It
acts as a moderately strong base, precipitating metals as
hydrates, and forming salts with acids. Most of these salts
are non- volatile, and easily soluble in water or alcohol, but
insoluble in ether. They are odorless, but have a strong
taste of tobacco.
1. A solution of nicotine in water, or a nicotine salt
mixed with sodium hydrate, when shaken with ether, forms
a solution of nicotine in ether. If this ethereal solution is
removed to a watch glass, and the ether evaporated at a
temperature of about 20°, the nicotine will remain on the
§ 11 QUALITATIVE ANALYSIS. 101
watch glass in drops or streaks. If this is now heated, the
nicotine will be volatilized, forming white fumes, with a
strong, disagreeable odor.
2. Platinum chloride^ when added to a rather strong
solution of nicotine or one of its salts, produces a light-
yellow, flocculent precipitate that dissolves upon heating;
but, if the heat is continued, an orange-yellow crystalline
precipitate soon separates from this solution. If the solution
is rather weak and contains free hydrochloric acid, the pre-
cipitate may not form for some time, and from a rather
strong solution in alcohol, containing a little free hydro-
chloric acid, a yellow precipitate forms at once.
3. Gold chloridey when added to a solution of nicotine or
one of its salts, in water, forms a reddish-yellow precipitate
that is slightly soluble in hydrochloric acid.
4. Iodine solutiony^ when added in small quantity to a
solution of nicotine in water, produces a yellow precipitate
that, upon standing, dissolves in the solution. If a little
more of the iodine solution is added to this solution, a bright
reddish-brown precipitate is formed that also disappears
upon standing. If iodine solution is added to a solution of
a nicotine salt, the reddish-brown precipitate is formed at
once.
5. Picric acid, when added in excess to a solution of
nicotine in water, or to a neutral solution of a nicotine salt,
produces a yellow precipitate that is soluble in hydrochloric
acid.
6. Tannic acid^ added to an aqueous solution of nicotine,
produces a white precipitate that is soluble in hydrochloric
or sulphuric acid.
7. Silver nitrate^ when added to a solution of nicotine in
water or alcohol, slowly imparts a brown color to the solu-
tion, and finally a black precipitate separates.
8. Concentrate stilphtiric acid^ or 7iitric acid of 1. 2 Sp. Gr. ,
dissolves nicotine in the cold to a colorless solution, but
nitric acid of 1.3 Sp. Gr. forms a red solution.
* To make this solution, dissolve about 20 grams of potassium iodide
in water, add 13 grams of iodine, stir, and dilute to 1 liter.
102 QUALITATIVE ANALYSIS. § 11
9. When a drop of nicotine is gently warmed with 4 or
6 drops of hydrochloric acid of 1.12 Sp. Gr., it forms a brown
solution. If to this a drop of nitric acid of 1.4 Sp. Gr. is
added, after the solution has become cool, it gives the solution
a reddish- violet color that gradually changes to red.
10. If a few drops of a solution of nicotine in water, or of
a neutral solution of nicotine hydrochloride, are added to an
excess of mercuric-chloride solution, a white, flocculent pre-
cipitate is produced that is soluble in ammonium chloride or
hydrochloric acid.
97. Conine. — Conine is a colorless, oily liquid that
becomes brown when exposed to the air. It occurs in the
spotted hemlock, especially in the green seed. When heated
in the air to the boiling point (about 168°), it partly decom-
poses and becomes brown, but may be distilled unaltered in
an atmosphere of hydrogen. It is only slightly soluble in
water, but dissolves readily in alcohol or ether, and its solu-
tions have a strong alkaline reaction. Conine is a strong
base. It slowly volatilizes at ordinary temperatures, giving
off poisonous vapors with a pungent, stupefying odor, which
give dense white fumes with the vapor of a volatile acid.
It precipitates metals as hydrates in a manner similar to
ammonia, and with the acids it forms salts that are soluble
in water or alcohol, but are insoluble, or nearly so, in ether.
1. When an aqueous solution of a conine salt is mixed
with sodium hydrate, and this mixture is shaken with ether,
the conine dissolves in the ether. If this ethereal solution
is now evaporated on a watch glass at about 25°, the conine
will remain on the watch glass in yellowish, oily drops.
2. Platinum chloride does not produce a precipitate in
solutions of conine salts, even when concentrate.
3. Gold chloride^ when added to a rather strong solution
of conine hydrochloride, produces a light, yellowish precipi-
tate that is insoluble in hydrochloric acid.
4. Iodine solution acts in the same way with a conine
solution that it does with nicotine.
5. Picric acidy in concentrate solution, when added to
§ 11 QUALITATIVE ANALYSIS. 103
conine that is covered with a little water, produces a yellow
precipitate ; but, if the solution is at all dilute, no precipitate
is formed.
6. Silver nitrate^ when added to a solution of conine in
alcohol, yields a grayish-brown precipitate at once.
7. Mercuric chloride^ when added in excess to a conine
solution, produces a white precipitate that is soluble in
hydrochloric acid. •
8. Chlorine water ^ when added to conine that is covered
with a little water, produces a white precipitate that dissolves
easily in hydrochloric acid.
9. Concentrate sulphuric acid^ or nitric acid of 1.4 Sp. Gr. ,
dissolves conine in the cold without coloration.
NOK-VOLATIIjE AliKAIiOIBS.
Solid alkaloids that cannot be distilled with water.
GROUP I.
Non-volatile alkaloids that are precipitated from solutions of their
salts by sodium hydrate^ and dissolve in an excess of the reagent.
Morphine Cocaine
98. Morphine. — Morphine is a white crystalline sub-
stance obtained from opium, the dried juice of the seed
capsules of the poppy. It is very slightly soluble in cold
water, but dissolves somewhat more freely in hot water; it
dissolves somewhat more readily in alcohol, but is most
readily dissolved by amyl alcohol, especially when hot. Its
solutions have a bitter taste and an alkaline reaction. It
unites with acids, neutralizing them and forming salts that
are easily soluble in water and most of them also in alcohol.
Morphine and its salts are poisonous.
1, Sodium hydrate or ammonia precipitates morphine
from solutions of its salts, in the form of a white crystalline
powder. Shaking promotes the formation of this precipi-
tate, which is generally slow in separating. It dissolves
very readily in an excess of sodium hydrate, less easily in
104 QUALITATIVE ANALYSIS. § 11
ammonia, and with difficulty in ammonium carbonate. If
the solution in sodium hydrate is shaken with ether, but
very little of the morphine will be taken up; it is all dis-
solved, however, when shaken with warm amyl alcohol.
2. Sodium carbonate precipitates morphine as a white
powder that is insoluble in an excess of the reagent. Con-
sequently, if carbon dioxide is led into the solution of mor-
phine in sodium hydrate, it will precipitate the morphine by
changing the sodium hydrate to carbonate.
3. Sodium bicarbonate precipitates morphine, in the form
of a white powder, from neutral solutions of its salts, but
does not form a precipitate in acid solutions.
4. Picric acid^ when added to a concentrate neutral solu-
tion of a morphine salt, produces a yellow precipitate that
dissolves quite readily in water. Hence, no precipitate is
formed in neutral solutions.
5. Tannic acid^ when added to an aqueous solution of a
morphine salt, produces a white precipitate that dissolves
readily in acids.
6. Concentrate nitric acid, when added to morphine or one
of its salts, in the dry state or in concentrate solution, pro-
duces a reddish-yellow color that is not changed by the addi-
tion of stannous chloride. Nitric acid does not impart a
color to dilute solutions in the cold, but if heated, they
assume a yellowish color.
7. If morphine is dissolved in pure, concentrate sulphuric
acid in the cold, and a small fragment of potassium nitrate
is added, a brown coloration is produced at the point of con-
tact. Sometimes the color is reddish at first, but rapidly
changes to brown. If the sulphuric-acid solution of the
morphine is allowed to stand for 15 hours in the cold, or is
heated for half an hour at 100°, before adding the potassium
nitrate, and is then cooled and a small piece of potassium
nitrate added, it imparts a blood-red color to the solution.
Sometime^ the potassium nitrate gives the solution a violet
color at first, but this rapidly changes to red,
8. If a little morphine is dissolved in concentrate sul-
phuric acid, a little sodium arsenate added, and the solution
§ 11 QUALITATIVE ANALYSIS. 105
heated, it assumes a reddish-brown color. If this solution is
cooled, and water is slowly added, the color changes first to
red and then to green. If this green solution is shaken with
ether, it gives the ethereal solution a reddish-violet color.
If shaken with chloroform, a deep-violet color is produced.
9. If a small quantity of morphine is dissiolved in about
1 cubic centimeter of concentrate hydrochloric acid, a drop
of concentrate sulphuric acid added, and the solution is
placed on a watch glass and evaporated over the water bath,
a purple residue remains on the glass. If, to this residue, a
few drops of hydrochloric acid are added, and then enough
saturated solution of sodium bicarbonate to render it neutral
or slightly alkaline, a drop or two of a solution of iodine in
alcohol will impart a green color to the solution. Ether,
when shaken with this solution, dissolves the coloring matter,
forming a layer of solution with a reddish- violet color.
10. A simple test for morphine may be made by mixing
a little of the morphine with about six times its weight of
white sugar, and adding a few drops of concentrate sulphuric
acid to this mixture. The solution thus obtained will have
a red color that changes to green, and finally to brownish
yellow. If a morphine solution is to be tested, to a small
portion add as much white sugar as it will dissolve, and
then a few drops of concentrate sulphuric acid. The addi-
tion of a drop or two of bromine water is said to increase the
delicacy of this reaction.
11. If a small fragment of morphine or a morphine salt is
added to a small quantity of a solution, containing about 1 gram
of ammonium molybdate in 10 cubic centimeters of concen-
trate sulphuric acid, in a porcelain dish, and broken up with
a stirring rod, it gives the solution a violet color that gradu-
ally changes to green, while the edge of the solution appears
blue. If this is now stirred, the color changes to a brownish
green, and finally to deep blue. I f a drop of rather dilute solu-
tion of a morphine salt is added to the molybdate solution, a
blue ring is formed that gradually extends to the whole of the
solution. The solution of ammonium molybdate in sulphuric
acid must be freshly prepared, as it rapidly decomposes.
106 QUALITATIVE ANALYSIS. § 11
99. Cocaine. — Cocaine is a white crystalline substance
obtained from coca leaves. It has a bitter taste, and pos-
sesses the property of destroying the sense of feeling. It
dissolves slightly in water, more easily in alcohol, and still
more readily in ether. Its solutions have an alkaline reac-
tion. It dissolves readily in acids, forming salts, most of
which are soluble in water and alcohol, but insoluble, or
nearly so, in ether.
1. Sodium hydrate, when added to a solution of a cocaine
salt, produces a white precipitate that is slightly soluble in
an excess of the reagent.
2. Ammonium hydrate gives a reaction similar to sodium
hydrate, but the precipitate dissolves much more readily in
an excess of the ammonia. If a little ether is shaken with
the solution in ammonia, it takes up the cocaine, which will
be deposited in needles when this ethereal solution is evap-
orated in the air.
3. Sodium carbonate^ added to a solution of a cocaine
salt, produces a white precipitate that is insoluble in an
excess of the reagent.
4. Tannic acid, added to a solution of cocaine that con-
tains hydrochloric acid, produces a yellow precipitate that
forms a resinous mass when shaken, or upon standing.
5. Mercuric chloride, when mixed with a solution of a
cocaine salt, produces a white precipitate that is soluble in
hydrochloric acid, ammonium chloride, or alcohol.
6. Stannous chloride, when added to a concentrate solu-
tion of a cocaine salt, produces a curdy, white precipitate that
is soluble in nitric acid.
7. Concentrate stilphuric acid dissolves cocaine to a color-
less solution that is not colored by nitric acid or nitrates.
Molybdic acid and white sugar also fail to produce character-
istic colors.
8. Nitric acid of 1. 4 Sp. Gr. dissolves cocaine or its salts to
a colorless solution. I f this solution is evaporated on the water
bath, and a few drops of a solution of potassium hydrate in
alcohol are added to the residue, the whole being stirred, a
characteristic odor, similar to that of peppermint, is given off.
§ 11 QUALITATIVE ANALYSIS. 107
9. Potassium chromate^ when added to a rather strong
solution of cocaine that contains a very little free hydro-
chloric acid, precipitates yellow cocaine chromate, which is
soluble in an excess of hydrochloric acid, or in a large quan-
tity of water.
10. If a little cocaine is dissolved in about 1 cubic centi-
meter of concentrate sulphuric acid, a quantity of potassium
iodate, amounting to about three times the weight of the
cocaine, is added, and the whole is heated on the water bath ;
it first assumes a yellow color, then green streaks appear
that grow darker, and gradually spread to the whole of the
liquid, and finally the whole solution becomes brown.
11. If cocaine and concentrate hydrochloric acid are
sealed in a strong glass tube, and heated on the water bath
for 3 or 4 hours, the cocaine will be decomposed, and methyl
alcohol and benzoic acid will be formed. If considerable
cocaine was present, white crystals of benzoic acid will sepa-
rate when the tube is allowed to cool.
12. If a little cocaine solution is added to 2 or 3 cubic
centimeters of chlorine water, and to this a few drops of
palladium chloride are added, a red precipitate is formed.
100. Separation of Morphine and Cocaine. — Cocaine
may be separated from morphine by rendering a solution of
their salts just alkaline with ammonia, and shaking with
petroleum ether. This extracts the cocaine, but does not
dissolve the morphine. The cocaine is obtained by evapo-
rating the petroleum-ether solution.
GROUP n.
Non-volatile alkaloids that are precipitated by sodium hydrate^ and
are insoluble in an excess of the reagent, and are also
precipitated by sodium bicarbonate^ even
from acid solutions.
Quinine . Cinchonine Narcotine
101. Quinine. — Quinine is a white crystalline substance
foimd in cinchona bark. It is slightly soluble in water, but
dissolves more readily in alcohol or ether. It is exceedingly
108 QUALITATIVE ANALYSIS. § 11
bitter, and its solutions are alkaline. It unites with acids,
forming neutral and acid salts. The neutral salts are spar-
ingly soluble in cold water, but more readily soluble in hot
water or alcohol, while the acid salts dissolve readily in
water.
1. Sodium hydrate precipitates quinine from solutions of
its salts, in the form of a white powder, which is insoluble in
an excess of the reagent.
2. Ammonium hydrate produces a white precipitate that
is slightly soluble in an excess of the reagent. If the mixture
containing the precipitate formed by ammonia is shaken
with ether, to which about 2 per cent, of alcohol is added,
the precipitate is dissolved and two clear layers of liquid are
formed.
3. Sodium carbonate precipitates quinine in the form of a
white powder that is insoluble, or but slightly soluble, in an
excess of the reagent
4. Sodium bicarbonate^ when added to a rather strong
neutral or acid solution of a quinine salt, produces a white
precipitate that is very slightly soluble in an excess of the
reagent.
5. Tannic acid, when added to an aqueous solution of a
quinine salt, produces a white precipitate that is soluble in a
little hydrochloric acid, and is reprecipitated by the addition
of more hydrochloric acid. The precipitate is also soluble in
acetic acid.
6. Concentrate sulphuric acid dissolves quinine and its
salts to a colorless or faintly-yellowish solution. If this
solution is cautiously heated, it becomes yellow, and finally
brown.
7. Nitric acid of 1.4 Sp. Gr. dissolves quinine and its
salts to a colorless solution that generally has a bluish opal-
escence, and turns yellow when heated.
8. If, to a solution of a quinine salt, about one-sixth its
volume of strong chlorine water is added, and then ammonia
is added slowly until the reaction of the solution is alkaline,
an emerald-green coloration is produced. This test may be
varied by adding chlorine water, then potassium ferrocyanide,
§ 11 QUALITATIVE ANALYSIS. 109
and finally ammonia, when the solution will assume a deep-red
color that rapidly changes to brown. The addition of acetic
acid to the red solution destroys the color, but it may be
restored by the careful addition of ammonia. This is a
delicate and characteristic reaction, but is prevented by the
presence of morphine.
9. If a drop of water is added to a small piece of potas-
sium hydrate and this is fused, and, while still warm, a
solution of quinine in alcohol is added, the alcohol evaporated
off, and the residue gently heated, a green color is imparted
to the mass. Other alkaloids give similar, but not the same,
colors.
10. A characteristic test for quinine may be made by
dissolving a little of the sulphate in acetic acid, adding a
little alcohol, and then a solution of iodine in alcohol until
the solution has a brownish-yellow color, when a black pre-
cipitate will separate, either at once or after standing a few
minutes.
102. Clnclionlne. — Cinchonine is a white crystallin
substance, found in cinchona bark, together with quinine
and other bases. It is almost insoluble in water, and but
slightly soluble in alcohol containing water, but somewhat
more readily in absolute alcohol, especially when hot. It is
most readily dissolved in a mixture consisting of 3 parts of
chloroform and 1 part of alcohol. Its solutions have a bitter
taste and an alkaline reaction. Cinchonine neutralizes acids
completely, forming salts that have a bitter taste, are soluble
in water and alcohol, but insoluble, or nearly so, in ether.
1. Sodium hydrate precipitates cinchonine from solutions
of its salts, in the form of a white powder that is insoluble in
an excess of the reagent.
2. A mmonium hydrate gives the same reaction as sodium
hydrate.
3. Sodium carbonate^ when added to a solution of a cin-
chonine salt, produces a white precipitate that is insoluble in
an excess of the reagent.
4. Sodium bicarbonate precipitates cinchonine, in the
110 QUALITATIVE ANALYSIS. § ll
form of a white powder, from moderately strong solutions of
its salts.
5. Tannic acid^ when added to an aqueous solution of a
cinchonine salt, produces a white precipitate that dissolves
in a little hydrochloric acid, and is reprecipitated if more
hydrochloric acid is added. It is also soluble in acetic acid.
(Compare Art. 101, 5.)
6. Concentrate sulphuric acid dissolves cinchonine to a
colorless solution that becomes brown, and finally black, when
heated.
7. If cinchonine is dissolved in concentrate sulphuric
acid, and a little concentrate nitric acid is added, the solu-
tion remains colorless in the cold ; but, when heated, it first
becomes yellowish, then brown, and finally black.
8. If, to a solution of a cinchonine salt, about one-fifth its
volume of strong chlorine water is added, and then ammonia,
until the reaction of the liquid is alkaline, a yellowish- white
precipitate is formed.
9. If a little potassium hydrate is fused, with the addition
of a drop of water, a little solution of cinchonine in alcohol
is added, and the residue is carefully heated, after evapora-
ting the alcohol, a reddish-brown or violet color is at first
imparted to the mass, which, upon the continued application
of heat, changes to bluish green, and vapors with a pungent
odor are evolved.
10. Potassium f err ocyanide^ when added to a neutral solu-
tion of a cinchonine salt, or one containing but little free
acid', precipitates yellow, flocculent cinchonine ferrocyanide.
If an excess of the reagent is added and the mixture is
gently heated, the precipitate dissolves, but, upon cooling, it
separates again in golden-yellow crystals.
103. Narcotlne. — Narcotine is a white crystalline sub-
stance obtained from opium. It is almost insoluble in water,
and only sparingly soluble in alcohol and ether, but dissolves
readily in chloroform. Narcotine is tasteless, but its solu-
tions are exceedingly bitter, and do not color litmus paper.
It dissolves readily in acids, forming salts that have an acid
g 11 QUALITATIVE ANALYSIS. Ill
reaction and are bitter. Most of the salts are soluble in water,
alcohol, and ether. When solutions of the salts are shaken
with chloroform, the narcotine is dissolved in it, even in the
presence of a free acid.
1. Sodium hydrate precipitates narcotine from solutions
of its salts, in the form of a white crystalline powder that is
insoluble in an excess of the reagent.
3. Ammonium hydrate precipitates narcotine in the form
of a white powder that is insoluble in an excess of the
reagent. If the liquid containing this precipitate is shaken
with considerable ether, the ether dissolves the precipitate,
and two clear layers of liquid are formed. If some of the
ethereal solution is allowed to evaporate on a watch glass,
the narcotine will remain as a white crystalline powder.
3. Sodium carbonate precipitates narcotine from its sohi-
tions in the fonn of a white crystalline powder that is insolu-
ble in an excess of the reagent.
4. Sodium bicarboiiate gives the same reaction as sodium
carbonate.
5. Tannic acid does not produce a precipitate in neutral
solutions of narcotine salts, but sometimes gives the solution
a milky appearance. If a drop of hydrochloric acid is added,
a precipitate is formed that dissolves when heated, and
separates again when the solution is cooled,
6. Chlorine water imparts a greenish- yellow color to
solutions of narcotine salts. If ammonia is now added, the
color is changed to reddish yellow, and becomes stronger.
7. Concentrate sulphuric acid 6^?&o\\c.?,naxco^\n&, forming
a solution with a greenish-yellow color that soon changes to
pure yellow. If this solution is heated, various colors are
produced, depending on the amount of narcotine present. If
considerable narcotine is present, the solution at first
assumes an orange color, then becomes blue, and sometimes
purple streaks form. If the solution is now allowed to cool,
it assumes a red color, but if heated nearly to boiling, it
becomes reddish violet. If the sulphuric acid contains but
very little narcotine, a crimson color is seen instead of blue.
8. If a little narcotine isdissulved in concentrate sulphuric
I
112 QUALITATIVE ANALYSIS. § 11
acid, and heated until it assumes a reddish color, and, after
cooling, a drop of ferric chloride is added, at the point
where the ferric chloride enters the liquid a red color is
formed that shades off to violet ; after about 10 minutes, the
red color spreads to the rest of the liquid.
9. Nitric acid of 1.4 Sp. Gr. dissolves narcotine to a
reddish-yellow solution. During the solution, heat is gener-
ated and reddish fumes are evolved. If the solution is now
heated over the Bunsen flame, more fumes are given off, and
the solution becomes clear yellow.
10. A solution containing 10 milligrams of ammonium
molybdate in 1 cubic centimeter of concentrate sulphuric
acid dissolves narcotine to a green solution that rapidly
changes to red.
104, Separation of Quinine, Cinclionine, and Nar-
cotine. — If an acid solution of these alkaloids is shaken w4th
chloroform, the narcotine will be dissolved in the chloroform
and form a separate layer of clear liquid, while the quinine
and cinchonine remain in the acid solution. If the chloro-
form solution is removed and evaporated in the air, the nar-
cotine remains as a white powder. Now render the solution,
containing quinine and cinchonine, alkaline with ammonia,
and shake it with ether that contains about 2 per cent, of
alcohol. This will precipitate the cinchonine, and dissolve
the quinine, which may be obtained in the same manner as
the narcotine. The precipitated cinchonine may then be
obtained from the liquid.
GROUP III.
Non-volatile alkaloids that are precipitated by sodium hydrate^ and
are insoluble in an excess of the reagent^ but are not pre-
cipitated from acid solutions by sodium bicarbonate.
Strychnine Brucine Atropine
105, Stryelinine. — Strychnine is an exceedingly poison-
ous, white crystalline substance found in various varieties of
strychnos, but especially in the beans of the strychnos nux
§ 11 QUALITATIVE ANALYSIS. 113
vomica. It has an alkaline reaction, and is very bitter. It is
almost insoluble in water, alcohol, or ether, but dissolves in
chloroform and acetic ether. It neutralizes acids, forming
salts, most of which are soluble in water and alcohol, but
are insoluble in ether and chloroform. They all have an
extremely bitter taste, and are exceedingly poisonous.
1. Sodium hydrate precipitates strychnine from solutions
of its salts, in the form of a white crystalline powder that is
insoluble in an excess of the reagent. If the solution is
very dilute, the precipitate only separates after some time.
2. Ammonium hydrate precipitates strychnine in the
form of a white powder that is soluble in an excess of the
reagent. But if this solution is allowed to stand for some
time, it again separates, in the form of white needles.
3.. Sodium carbonate gives the same reaction as sodium
hydrate.
4. Sodium bicarbonate slowly precipitates strychnine
from neutral solutions, in the form of fine white needles
that are insoluble in an excess of the reagent. But, if a
drop of acid is added, the precipitate dissolves in the car-
bonic acid that is liberated, even if the solution remains
alkaline. In acid solutions, sodium bicarbonate produces no
precipitate.
5. Tannic acid, when added to a solution of a strychnine
salt, produces a white precipitate that is insoluble in hydro-
chloric acid.
6. CJilorine water ^ when added to a solution of a strych-
nine salt, produces a white precipitate that dissolves in
ammonia to a colorless solution.
7. Mercuric chloride, added to a solution of a strychnine
salt, produces a white precipitate that dissolves when
heated, and is reprecipitated in white needles upon cooling.
8. Potassium sulphocyanide, when added to a strong solu-
tion of a strychnine salt, produces a white crystalline pre-
cipitate that is only slightly soluble in an excess of the rea-
gent. In dilute solutions this precipitate is only formed
after standing for some time.
9. Cerium dioxide, when added to a solution of strychnine
114 QUALITATIVE ANALYSIS. § 11
in concentrate sulphuric acid, produces a deep-blue color
that slowly changes to violet, and finally to red.
10. Concentrate sulphuric acid dissolves strychnine to a
colorless solution. If, to a little of this solution in a porce-
lain dish, a little dry potassium chromate is added, it imparts
a blue color to the solution that changes to red, and finally
to reddish yellow. The same reaction is produced by man-
ganese dioxide, but, in this case, it takes place more slowly.
This reaction may be varied in several ways. If a solution,
made by dissolving 10 milligrams of potassium chromate in
5 cubic centimeters of water, and adding 15 grams of con-
centrate sulphuric acid, is placed in a test tube, and a
solution of strychnine is added, so that it forms a separate
layer, a bluish-violet band will be formed where the two-
liquids come in contact. The same reaction is obtained if a
little solid strychnine or one of its salts is sprinkled on the
acid -chromate solution. Morphine, if present, interferes
with this reaction. This may be partly overcome by placing
a few small particles of the strychnine on a watch glass,
covering with a dilute solution of potassium dichrom ate, and
stirring well. By this means the strychnine is slowly con-
verted into strychnine chromate, which is almost insoluble.
Pour off the liquid, wash the residue once with water, pour
off as much of this as possible, and absorb the rest with a
piece of filter paper. By this treatment the strychnine
chromate is obtained as a solid in the dish, and most of the
morphine is removed, if only a small amount was present.
Now, if a little concentrate sulphuric acid is brought into the
dish, bluish- violet streaks are formed. The best method of
obtaining this reaction when morphine is present is to treat
the concentrate aqueous solution of the salts with potassium
chromate, when the strychnine will be precipitated as strych-
nine chroniate, and the morphine will remain in solution.
Filter the strychnine chromate, wash at once with cold
water, and dry it. If the dry precipitate is rubbed off the
paper into a porcelain dish, and treated with concentrate
sulphuric acid, a bluish-violet color is produced at once.
11. Nitric acid of 1.4 Sp. Gr. dissolves strychnine to a
g H QUALITATIVE ANALYSIS. 115
colorless solution that turns yellow when heated. A little
potassium chlorate added to the cold colorless solution gives
it a purple color,
106> Bmctne. — Brucine is a white crystalline substance
found associated with strychnine in the stiychnos nux
vomica. It is but slightly soluble in water or ether, hut
dissolves readily in alcohol. It is very poisonous, and is
extremely bitter. It neutralizes acids completely, forming
salts that dissolve readily in water. Like the free alkaloid,
the salts are poisonous and very bitter.
1. Sodium hydrate precipitates brucine from soliitions of
its salts in the form of a white, granular, or crystalline pre-
cipitate that is insoluble in an excess of the reagent.
2. Ammonium hydrate produces a white precipitate that
at first has an oily appearance, but becomes crystalline upon
standing. When first precipitated this is soluble in an excess
of the reagent, but if the solution thus obtained is allowed to
stand for some time, the precipitate again separates in the
form of crystals that do not dissolve in more of the reagent.
3. Sodium carbonate produces the same reaction as sodium
hydrate.
4. Sodium bicarbonate produces a white, silky precipitate
of brucine, which is insoluble in an excess of the reagent, but
is dissolved by a drop of acid. '
6. Tannic acid produces a dirty white precipitate that is
insoluble in hydrochloric acid, but dissolves in acetic acid.
6. Chlorine water, when carefully added to the solution
of a brucine salt, imparts a bright-red color to the solution.
If ammonia is now added, the color changes to brownish
yellow. If a little chlorine water is added to solid brucine,
it dissolves to a red liquid that becomes colorless if more
chlorine water is added. If this colorless solution is evap-
orated to dryness on the water bath, it deposits a red residue.
1. Mercuric chloride, added to a solution of a brucine
salt, produces a white, granular precipitate,
8. Mercurous nitrate that contains as little free acid as
possible, when added to the solution of a brucine salt, leaves
I ^
116 QUALITATIVE ANALYSIS. § 11
the solution colorless. But if this is now gently heated on
the water bath, it gradually assumes a red color. This reac-
tion serves well to detect brucine in the presence of strych-
nine, which is not colored by mercurous nitrate.
9. Potassium sulphocyanide^ when added to a strong solu-
tion of a brucine salt, produces a white, granular precipitate.
The same precipitate separates from more dilute solutions
after standing some time.
10. Concentrate sulphuric acid^ when added in small
amounts to a little brucine, dissolves it, forming a rose-
colored solution that soon changes to yellow. If a little
sulphuric acid containing nitric acid* is added, the liquid at
first assumes a red color that soon changes to yellow.
11. Concentrate nitric acid dissolves brucine and its salts
to bright-red solutions that soon change to yellowish red,
and, when heated, become yellow. If stannous chloride is
added to a solution that has been heated imtil it is yellow,
it assumes a deep- violet color, and, if the solution is concen-
trate, a violet precipitate separates. The violet color will
be imparted to solutions that have been quite largely diluted
with water. Colorless ammonium sulphide produces the
same reaction as stannous chloride, and hydrogen sulphide
produces a violet color at first, but, upon continued treat-
ment, the solution finally becomes green.
12. If a little brucine is dissolved in acetic acid, the solu-
tion diluted with water, and lead dioxide added, a rose color
is imparted to the liquid.
107. Atropine. — Atropine is a white crystalline sub-
stance found in the deadly nightshade. It is only slightly
soluble in water or ether, but dissolves readily in alcohol and
chloroform. It is poisonous, has a bitter taste that is very
persistent, and an alkaline reaction. It unites with acids,
forming salts that are easily soluble in water or alcohol, but
insoluble, or nearly so, in ether.
* This mixture of acids, known as ErdmantC s acid mixture^ is made
by mixing 6 drops of strong nitric acid with 100 cubic centimeters of
water, and adding 10 drops of this mixture to 20 grams of concentrate
sulphuric acid.
§ 11 QUALITATIVE ANALYSIS. 117
1. Sodium hydrate precipitates part of the atropine from
strong aqueous solutions of its salts, in the form of a white
powder, that is insoluble in an excess of the reagent.
2. Ammonium hydrate^ added to a rather strong solution
of an atropine salt, produces a white precipitate that is
soluble in an excess of the reagent.
3. Sodium carbonate gives the same reaction as sodium
hydrate.
4. Sodium bicarbonate does not produce a precipitate in a
solution of an atropine salt.
5. . Gold chloride^ when added to an aqueous solution of
an atropine salt, produces a yellow precipitate that gradually
becomes crystalline upon standing.
6. Tannic acid, added to an aqueous solution of an atro-
pine salt, produces a white, curdy precipitate that is soluble
in hydrochloric acid and in ammonia.
7. Mercuric chloride, dissolved in water, when added to a
solution of atropine in alcohol, produces a yellow precipitate
that changes to orange red when gently heated.
8. If a little atropine in a porcelain dish is covered with
concentrate sulphuric acid, and heated until it begins to
froth and turn brown, an odor similar to that of wild-plum
blossoms is given off. If a small piece of potassium dichro-
mate is now added, the odor becomes similar to that of the
wild rose, and if the heating is continued, an odor similar to
that of bitter almonds is given off. The odor of flowers may
also be obtained by bringing a little atropine in contact with
a few chromic-acid crystals, and gently heating until the
chromic acid begins to turn green.
9. If atropine is mixed with concentrate sulphuric acid in
a porcelain dish, and a little solid potassium nitrite is stirred
into this mixture, it assumes a yellow or orange color. If
a few drops of a solution of potassium hydrate in absolute
alcohol are now added, the mixture assumes a reddish- violet
color that soon changes to pink.
10. If a little atropine or an atropine salt in a porcelain
dish is covered with fuming nitric acid, and the mixture is
evaporated to dryness on the water bath, a colorless residue
118 QUALITATIVE ANALYSIS. § 11
remains, which assumes a violet color that changes to red, if
a drop of potassium hydrate dissolved in absolute alcohol is
added to the residue after it becomes cold. Strychnine
and some other compoimds give similar reactions, but not
the same.
108. Separation of Stryclinine, Brucine, and Atro-
pine. — Strychnine may be separated from brucine and atro-
pine by shaking these alkaloids with cold absolute alcohol,
when the brucine and atropine will be dissolved, and the
strychnine, which is insoluble in cold absolute alcohol, may
be filtered off. Brucine and atropine may be separated by
shaking an alkaline solution containing them with petroleum
ether, which dissolves the brucine, and leaves the atropine.
The brucine may be obtained by separating the layer of
petroleum ether, and evaporating it at a rather low tempera-
ture. If the solution, separated from the petrolemn ether,
which contains the atropine, is shaken with ether, the atro-
pine will be dissolved, and may be obtained by separating
the ethereal solution and evaporating it in the air.
Strychnine and brucine occur together in nature, and are
often found together in commerce. When only these two
alkaloids are present, they may be separated by placing the
dry substance in a porcelain dish, and covering it with strong
chlorine water, when brucine will be dissolved to a red solu-
tion, and the strychnine will remain tmchanged.
A SERIES
OF
QUESTIONS AND EXAMPLES
Relating to the Subjects
Treated of in this Volume.
It will be noticed that the various Question Papers that
follow have been given the same section numbers as the
Instruction Papers to which they refer. No attempt should
be made to answer any of the questions or to solve any of
the examples until the Instruction Paper, having the same
section number as the Question Paper in which the questions
or examples occur, has been carefully studied.
QUALITATIVE ANALYSIS.
(PART 1.^
(1) Define qualitative analysis.
(2) What metals impart the following colors to the borax
bead: {a) green, (^) blue, and {c) amethyst in the oxidi-
zing flame, and colorless in the reducing flame ?
(3) What is aqua regia, and how is it made ?
(4) What are the two methods of qualitative analysis ?
(5) Express, in the form of an equation, the reaction
that takes place when silver nitrate is precipitated by hydro-
chloric acid.
(6) Describe the separation of the metals of the third
group when phosphoric and oxalic acids are absent.
(7) What metals are precipitated by hydrochloric acid ?
(8) What part of the flame of a Bunsen burner acts (a) as
an oxidizing flame ? {b) as a reducing flame ?
(9) How are (a) oxidation and {b) reduction accomplished
by the flame of a Bunsen burner ?
(10) What metal imparts a crimson color to the flame ?
(11) What metals give black precipitates when their solu-
tions are treated with hydrogen sulphide ?
(12) Describe the method of determining the members
of the seventh group.
§10
For notice of the copyright, see page immediately following the title page.
2 QUALITATIVE ANALYSIS. § 10
(13) What metal, when fused with sodium carbonate and
potassium nitrate, imparts a deep-green color to the fusion ?
(14) Name the metals that are not precipitated from acid
solutions by hydrogen sulphide, but are precipitated by
ammonium sulphide, giving the color of the precipitate
formed in each case.
(15) What metals are precipitated by sulphuric acid ?
(16) Describe briefly the best method of distinguishing
between solutions of zinc and aluminum.
(17) Express, in the form of an equation, the reaction
that takes place when sulphuric acid is added to a solution
of barium chloride.
(18) How are precipitates washed ?
(19) Define {a) reagent and (6) reaction.
(20) Name the group reagents in the order in which they
are used.
(21) What is the most characteristic test for the common
organic acids ?
(22) When hydrogen sulphide produces a precipitate in
the solution of a metal, what compound of the metal is
formed ?
(23) What metals are precipitated as hydrates by ammo-
nium sulphide ?
(24) What is the most characteristic test for bromides ?
(25) How are solutions concentrated ?
(26) What metals are precipitated in the form of hydrates
by sodium carbonate ?
(27) What is the best test for ammonium compounds ?
(28) What metals are precipitated from their solutions by
a large excess of water ?
(29) What metals are precipitated as yellow sulphides by
hydrogen sulphide ?
§ 10 QUALITATIVE ANALYSIS. 3
(30) Give a list of the metals composing each of the
groups.
(31) How are the acids divided into groups ?
(32) How are cobalt and nickel separated ?
(33) {a) What is the color of the precipitate formed when
a solution of antimony chloride is treated with hydrogen
sulphide ? (d) Express this reaction by an equation.
(34) If a compound is fused with sodium carbonate on
the charcoal, and the fusion when placed on a piece of silver
and moistened with water produces a black stain on the
silver, what is learned of the composition of the compound ?
(35) How would you distinguish between barium, stron-
tium, and calcium in solutions ?
(36) Briefly describe the most characteristic test for phos-
phoric acid.
(37) What is indicated when the original fourth-group
precipitate is light colored ?
(38) Complete the following equation, and name the fac-
tors and products of the reaction :
^^SO^ + Na^HPO^ + NHfiH = ?
(39) What is the color and composition of the precipi-
tates formed when sodium hydrate is added to the following
solutions: (pi) silver? (b) lead? {c) mercurous? (d) mercuric?
{e) copper ?
(40) What color is imparted to the flame by volatile
barium compounds ?
(41) Describe the precipitate formed when hydrogen sul-
phide is slowly added to a mercuric solution.
(42) If a compound, when heated with concentrate sul-
phuric acid, gives off carbon monoxide and carbon dioxide,
and does not char, what acid is indicated ?
(43) Solutions of copper and nickel have similar colors.
What is the simplest way to distinguish between them ?
4 QUALITATIVE ANALYSIS. § 10
(44) How would you test for nitric acid in a solution ?
(45) Complete the following equation, and name the
factors and products of the reaction :
2Na^HAsO^ + ^H^S-{-4:HCl = ?
(46) What metals form white precipitates when ammo-
nium sulphide is added to their solutions ?
(47) How may ferrous solutions be changed to ferric ?
(48) Why is ammonium chloride added to the solution
before precipitating the third group with ammonia ?
(49) What metals are not precipitated by ammonium sul-
phide ?
(50) What common metals form two series of salts ?
(51) What odor is given off when acetates are heated
{a) with concentrate sulphuric acid ? (b) with concentrate
sulphuric acid and alcohol ?
(52) What metals, when their solutions are treated with
hydrogen sulphide, produce black precipitates that are
changed to white, insoluble compounds by heating with con-
centrate nitric acid ?
(53) {a) When hydrogen sulphide is added to an acid
solution of an arsenious compound, what precipitate is
formed ? (b) In what is this precipitate soluble ?
(54) Complete the following equation:
(55) How does lead behave when heated on the charcoal
before the blowpipe ?
(56) What metal is precipitated from its solutions by
hydrogen sulphide, in the form of a yellow sulphide that is
insoluble in ammonium sulphide ?
(57) Briefly describe the most characteristic test for
hydrochloric acid.
(58) If a substance, when heated on the charcoal before
§ 10 QUALITATIVE ANALYSIS. 5
the blowpipe, gives off white fumes with a garlic odor, what
is indicated ?
(59) What precipitates are obtained when the following
solutions are treated with barium chloride: (a) a sulphate?
{b) a thiosulphate ? (c) a sulphite ?
(60) If the precipitates obtained as described in the last
question are pure, how do they act when treated with hydro-
chloric acid ?
(61) How may chromates be reduced ?
(62) When hydrogen sulphide is added to a mercurous
solution, (a) what is the color and composition of the precipi-
tate ? {b) In what is it soluble ?
(63) Describe a blowpipe.
ACTUAL ANALYSIS.
Note. — ^With this Question Paper the student receives twelve
2-ounce bottles of solutions for analysis. About one-third the contents
of each bottle should be sufficient for the analysis, but more is given
in order that the work may be verified. The student should not
attempt to analyze these samples until he is thoroughly familiar with
the Instruction Paper, and has analyzed a number of solutions that he
has made up himself, for these samples can only be duplicated at the
student's expense.
SINGLE METALS.
(64) What metal, in solution, is contained in bottle labeled
*' Qualitative Analysis, Part 1, Question G4" ?
{65) What metal is contained in bottle labeled ** Qualita-
tive Analysis, Part 1, Question 65 " ?
{6(j) What metal is contained in bottle labeled ** Qualita-
tive Analysis, Part 1, Question 66 *' ?
(67) What metal is contained in bottle labeled ** Qualita-
tive Analysis, Part 1, Question 67 " ?
6 QUALITATIVE ANALYSIS. § 10
MIXTURES.
(68) What metals are contained in bottle labeled ** Qual-
itative Analysis, Part 1, Question 68 '* ?
(69) What metals are contained in bottle labeled ** Qual-
itative Analysis, Part 1, Question 69 *' ?
(70) What metals are contained in bottle labeled ** Qual-
itative Analysis, Part 1, Question 70 '* ?
COMPOUNDS.
(71) What compound (metal and acid) is contained in
bottle labeled *' Qualitative Analysis, Part 1, Question 71 ** ?
(72) What compound is contained in bottle labeled
** Qualitative Analysis, Part 1, Question 72 *' ?
(73) What compound is contained in bottle labeled
** Qualitative Analysis, Part 1, Question 73" ?
(74) What compound is contained in bottle labeled
** Qualitative Analysis, Part 1, Question 74" ?
(75) What compound is contained in bottle labeled
** Qualitative Analysis, Part 1, Question 75 " ?
QUALITATIVE ANALYSIS.
(PART 2.)
(1) What are the principal operations performed in the
analysis of substances by the dry method ?
(2) If a white, luminous, infusible mass is obtained
when a substance is heated on the charcoal, (a) what does
this indicate ? {d) What should be the next step in the
analysis ?
(3) If the infusible mass mentioned in the last question
assumes a rose color when ignited with cobalt nitrate, what
is indicated ?
(4) (a) What is the first step in the examination of
urine ? (d) How is this accomplished ?
(5) (a) What odor is observed when an acetate is heated
with concentrate sulphuric acid ? (d) What should be the
next step in this case ?
(6) How are the alkaloids divided into groups ?
(7) In what form should a substance be, when analyzed
by the dry method ?
(8) If a substance heated on the charcoal fuses and pene-
trates the charcoal, (a) what is indicated ? {d) How would
you distinguish the bases that may be present ?
§11
For notice of the copyright^ see page immediately following the title page.
2 QUALITATIVE ANALYSIS. § 11
(9) If a substance is fused on the charcoal with sodium
carbonate, and the fusion when placed on a piece of silver
and moistened with water produces a black stain, what is
indicated ?
(10) How may we obtain a solution of a substance that
is insoluble in water and acids ?
(11) Into what two classes are the phosphates that occur
in urine divided ?
(12) Name the common volatile alkaloids.
(13) What points should be observed when a substance is
heated in the closed tube ?
(14) (a) What is indicated if a substance deflagrates
when heated on the charcoal before the blowpipe ? (^) What
further information is obtained if a residue of chloride is
deposited on the charcoal ?
•
(15) What are the principal points to be observed when a
substance is heated on the charcoal before the blowpipe ?
(16) What metals may be recognized by fusing their com-
pounds on 'the platinum foil with sodium carbonate and
potassium nitrate ?
(17) If a substance effervesces when treated with con-
centrate sulphuric acid, (a) what is indicated ? (d) What
should be the next step in the examination in this case ?
(18) For what is thorium important ?
(19) {a) What is the principle of the spectroscope ? (b) In
what cases is it used ?
(20) If a substance when heated in the closed tube gives
off a gas having the odor of bitter almonds, what is indi-
cated ?
(21) What is indicated if a gas having an alkaline reac-
tion and the odor of ammonia is evolved when a substance is
heated in the closed tube ?
§ 11 QUALITATIVE ANALYSIS. 3
(22) If a substance volatilizes when heated on charcoal,
giving off fumes with a garlic odor, (a) what is indicated ?
(b) If the substance is yellow, and the odor of burning
sulphur is also given off, what additional information is
obtained ?
(23) If a solid heated with concentrate sulphuric acid
gives off a mixture of gases that give a blue flame when
ignited, and render a drop of barium hydrate turbid when
held at the mouth of the tube, what is indicated ?
(24) How are the metals classified with regard to their
solubility ?
(25) What rare elements belong to Group VII ?
(26) Briefly describe the method of determining arsenic
in water ?
(27) (a) What is the reaction of normal urine, and
(l?) how is it determined ?
(28) How may strychnine and brucine be separated ?
(29) (a) What compounds yield carbon monoxide when
heated with concentrate sulphuric acid, and {d) how is the
carbon monoxide recognized ?
(30) What rare elements are found in Division B of
Group II ?
(31) What poisonoiis metals are most frequently found in
water ?
(32) How would you test for nitric acid or nitrates in
drinking water?
(33) Of what common non-volatile alkaloids is Group II
composed ?
(34) If a substance, when heated in the closed tube,
changes color from white to yellow when hot, and becomes
white again upon cooling, what is indicated ?
(35) If a substance when heated on the charcoal yields
a white, malleable, metallic globule, surrounded v/ith a
6 QUALITATIVE ANALYSIS. § 11
(64) Describe the phenomena observed when brucine is
treated {a) with concentrate nitric acid and stannous chloride;
(d) with concentrate nitric acid and hydrogen sulphide.
(66) What rare elements belong in Group I ?.
(66) Between what limits does the specific gravity of
urine vary (a) in health ? {b) in disease ?
(67) (a) Where is titanium found in nature ? (b) Give a
characteristic test by which it may be recognized.
(68) In a case where poisoning by phosphorus is sus-
pected, why would it not be sufficient to treat the sample
with an oxidizing agent, and then test for phosphoric acid ?
ACTUAL ANALYSIS.
(69) What metal is contained in the box labeled ** Quali-
tative Analysis, Part 2, Question 69 " ?
(70) What compound is contained in the box labeled
'* Qualitative Analysis, Part 2, Question 70" ?
(71) What metal is contained in the box labeled ** Quali-
tative Analysis, Part 2, Question 71 ** ?
(72) What compound is contained in the box labeled
'* Qualitative Analysis, Part 2, Question 72" ?
(73) What compound is contained in the box labeled
** Qualitative Analysis, Part 2, Question 73 " ?
(74) What compound is contained in the box labeled
** Qualitative Analysis, Part 2, Question 74" ?
(75) What compound is contained in the box labeled
** Qualitative Analysis, Part 2, Question 75 " ?
(76) What compound is contained in the box labeled
** Qualitative Analysis, Part 2, Question 76 " ?
§ 11 QUALITATIVE ANALYSIS. 7
(77) What double salt is contained in the box labeled
'* Qualitative Analysis, Part 2, Question 77 " ?
(78) What powdered mineral is contained in the box
labeled ** Qualitative Analysis, Part 2, Question 78 " ?
(79) What fertilizer is contained in the box labeled
•* Qualitative Analysis, Part 2, Question 79 " ?
(80) What pigment is contained in the box labeled
'* Qualitative Analysis, Part 2, Question 80 " ?
4
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