James Freeman Sellers.

An elementary treatise on qualitative chemical analysis online

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decomposed by dilute HC1, with separation of gelati-
nous H 4 SiO 4 .

2. HC1 added, drop by drop, to the solution of a sili-
cate, precipitates gelatinous H 4 SiO 4 , which, on evapora-
tion to dryness, is decomposed with the formation of
silicic anhydride, SiO 2 .

3. Fused with Na 2 CO 3 on a platinum foil until bub-
bles of gas cease to escape, most insoluble silicates are
changed by metathesis to sodium silicate and a metallic
carbonate or oxide. If the fused mass is then boiled
with dilute HC1 and filtered, the filtrate will contain



132 CHEMICAL ANALYSIS

the chloride of the metal and the residue will consist of
H 4 Si0 4 :-

(a) Ba 2 SiO 4 + 2 Na 2 CO 3 = 2 BaCO 3 + Na 4 SiO 4 ;

(b) BaC0 3 4- 2HC1 - BaCl 2 + H 2 O + CO 2 ;
(<?) Na 4 SiO 4 + 4HC1 = H 4 SiO 4 + 4NaCl.

4. HF in an aqueous solution, or in gaseous form,
decomposes SiO 2 with evolution of silicon tetrafluoride,
SiF 4 :_

SiO 2 + 4HF = SiF 4 + 2H 2 O.

If a silicate is mixed with three parts of NH 4 F or
five parts of CaF 2 , moistened with concentrated H 2 SO 4 ,
and then heated till fumes cease to escape, the silicic
acid is decomposed and expelled :

(a) H 2 S0 4 + 2NH 4 F = (NH 4 ) 2 SO 4 + 2HF;

(b) 6HF + Na 2 SiO 3 = Na 2 SiF 6 + 3 H 2 O ;

(c) Na 2 SiF 6 + H 2 SO 4 = Na 2 SO 4 + 2HF + SiF 4 .

5. Metaphosphate bead dissolves the metallic parts of
the silicates, but not the SiO 2 , which remains floating
in the fused bead. As SiO 2 is not affected, the outline
of the particle of the silicate remains intact, giving
rise to the so-called "skeleton bead."

ANALYSIS OF SILICATES

There are two classes of silicates important in analytical chem-
istry silicates decomposed by acids, and those not decomposed
by acids :

First class : Silicates decomposed by acids. This is not a very
numerous class, composed for the most part of the soluble alkali
metal silicates and a few less soluble single and double silicates
of other metals. The analysis of this class is quite simple. This



ACIDS OF GROUP I 133

is accomplished by treatment of the silicates with HC1, which by
metathesis form soluble chlorides of the metals and colloidal
silicic acid.

Second class : Silicates not decomposed by acids. This consti-
tutes by far the more numerous class, including the natural sili-
cates. Many natural silicates contain the alkali metals combined
with other metals. The varieties of feldspar are representatives
of this kind.

The analysis of silicates riot decomposed by acids is usually
conducted by one of three methods :

Method 1. Fusion with alkali-metal carbonates. By metath-
esis, soluble silicates and carbonates of the metals of the original
silicates are formed, which resulting salts are then decomposed
by HC1 (see reactions above). Finely powder the silicate, mix
with about 3 parts of Na 2 CO 3 , or fusion mixture, and heat to quiet
fusion in a platinum crucible or foil. When cool, boil the mass
in water. Filter, evaporate to a small bulk, and add concentrated
HC1. H 2 SiO 3 will precipitate as a gelatinous mass. If it is desired
to test for the presence of alkali metals in the silicate, this method
cannot be used, as the carbonates of these metals are added as
a flux.

Method 2} (Method of J. Lawrence Smith.) Fusion with
NH 4 C1 and CaCO 3 . An insoluble silicate like feldspar, contain-
ing alkali metals, may be converted into soluble alkali-metal
chlorides and some insoluble hydroxides, by heating to redness
in a covered platinum crucible with 1 part NH 4 C1 and 8 parts
powdered CaCO 3 . In all fusions it is necessary for both the
substance and the flux to be reduced to very fine powders, and
intimately mixed.

Method 3. Fusion with BaO. Fuse in a platinum crucible a
mixture of 1 part of the powdered silicate and 4 parts BaO.
Digest the mass in a little water to detach it from the crucible,
and then dissolve in HC1. Add NH 4 OH till alkaline, filter,
evaporate to dryness, and ignite.



134 CHEMICAL ANALYSIS

Sulphurous Acid, H 2 S0 3 (salt for study, sodium sulphite,

Na 2 S0 3 ).

1. BaCIs precipitates white barium sulphite, BaSO 3 ,
soluble in dilute HC1.

2. Nascent hydrogen reduces sulphites to sulphides,
which are decomposed by an excess of HC1 with evolu-
tion of H 2 S, detected by its odor, or with Pb(C 2 H 3 O 2 ) 2 .

3. HgS decomposes sulphites with separation of
sulphur.

4. HC1 decomposes sulphites with evolution of SO 2 ,
detected by its odor and by the production of a white
precipitate of calcium sulphite with lime water.

Sulphuric Acid, H 2 S0 4 (salt for study, sodium sulphate,
Na 2 S0 4 ).

1. BaC^ precipitates white barium sulphate, BaSO 4 ,
insoluble in water or acids ; decomposed by fusion with
Na 2 CO 3 in a platinum crucible or foil, sodium sulphate
and barium carbonate being formed :

Na 2 CO 3 + BaSO 4 = Na 2 SO 4 + BaCO 3 .

In like manner, the other insoluble sulphates, SrSO 4 ,
CaSO 4 , and PbSO 4 , are decomposed by fusion with
Na 2 CO 3 or by boiling with its solution.

2. Pb(C 2 H 3 2 ) 2 precipitates white lead sulphate, PbSO 4 ,
almost insoluble in dilute HNO 3 ; soluble in hot con-
centrated HC1. 1

3. Fused with Na 2 CO 3 on charcoal, sulphates are
reduced to sulphides. If the mass is moistened with
very dilute HC1 and placed on a bright silver coin, the
latter will be stained black.



ACIDS OF GROUP I 135

Phosphoric Acid, H 3 P0 4 (salt for analysis, sodium phos-
phate, HNa 2 P0 4 ).

1. BaC^ precipitates white barium phosphate, HBaPO 4 ,
or Ba 3 (PO 4 ) 2 , if the solution contained a normal phos-
phate, soluble in HC1 and HNO 3 .

2. MgS0 4 in presence of NH 4 OH and NH 4 C1 precipi-
tates white crystalline ammonium magnesium phos-
phate, NH 4 MgPO 4 , soluble in acids. (Compare with
NH 4 MgAs0 4 .)

3. (NH 4 ) 2 Mo0 4 in HNO 3 solution precipitates, in
the cold, yellow ammonium phospho-molybdate,
(MoO 3 ) 12 -(NH 4 ) 3 PO 4 . (Compare with behavior of the
same reagent toward arsenates.)

4. FeCl 3 in presence of NaC 2 H 3 O 2 precipitates yellow
ferric phosphate, FePO 4 , soluble in strong acids and
excess of FeCl 3 ; insoluble in HC 2 H 3 O 2 .

Boric Acid, H 3 B0 3 (salt for study, borax, Na 2 B 4 7 ).

1. BaCl 2 precipitates white sodium barium borate,
Na 2 Ba 5 (BO 3 ) 4 , soluble in acids, except H 2 SO 4 .

2. 1^804 precipitates from hot solutions of borates, on
cooling, crystalline boric acid, H 3 BO 3 .

3. Alcohol, added to free boric acid or to a borate with
concentrated H 2 SO 4 and then kindled, burns with a
green flame, especially upon stirring the mixture.

4. Turmeric paper, immersed in a slightly acid (HC1)
solution of boric acid or a borate and then dried,
shows a reddish tint which is turned blue by NaOH.



136 CHEMICAL ANALYSIS

Oxalic Acid, H 2 C 2 4 (salt for study, sodium oxalate,
Na 2 C 2 4 ).

1. BaC^ precipitates from neutral solutions white
barium oxalate, BaC 2 O 4 , somewhat soluble in dilute
NH 4 C1 and many organic acids; soluble in HC1 and
HN0 3 .

2. Lime water and soluble calcium salts precipitate white
calcium oxalate CaC 2 O 4 , soluble in HC1 and HNO 3 ;
insoluble in organic acids.

3. Concentrated H 2 S0 4 , heated with oxalic acid or an
oxalate, removes water, and the compound is decom-
posed into CO 2 and CO :

H 2 C 2 4 4- H 2 S0 4 = C0 2 + CO + H 2 S0 4 -H 2 0.

If in sufficient quantity the CO gas can be burned with
its characteristic blue flame.

4. Heating decomposes all oxalates with formation of
carbonates or oxides of the metals, and evolution of CO
or CO 2 .

Tartar ic Acid, H 2 C 4 H 4 6 (salt for study, potassium tar-
trate, K 2 C 4 H 4 6 ).

1. BaCl 2 (or, better, CaCl 2 ) from neutral solutions
precipitates white barium (or calcium) tartrate, soluble
in acids, except H 2 SO 4 .

2. AgN0 3 precipitates white silver tartrate,
Ag 2 C 4 H 4 O 6 , soluble in NH 4 OH. On warming this
solution, black metallic silver is deposited. If the
Ag 2 C 4 H 4 O 6 be carefully redissolved in the least possible
amount of NH 4 OH, and if this solution be heated gently






ACIDS OF GROUP I 137

in a test-tube, a mirror of metallic silver will be depos-
ited on the walls of the tube. AgNO 3 precipitates
Ag 2 C 4 H 4 O 6 only from neutral solutions. This reaction
distinguishes tartaric from most other organic acids.

3. Heated in a closed tube, tartrates char and emit
inflammable vapors with the odor of burnt sugar.
Commingled with the carbon residue is also a carbon-
ate, detected by effervescence on adding HC1.

Hydrofluoric Acid, HF (salt for study, ammonium fluoride,

NH 4 F).

1. BaC^ precipitates white barium fluoride, BaF 2 ,
soluble with difficulty in HC1 and HNO 3 .

2. Concentrated H 2 S0 4 mixed to a paste with powdered
fluorides and warmed in a platinum vessel expels gas-
eous HF :

2NH 4 F + H 2 S0 4 = (NH 4 ) 2 SO 4 + 2HF.

If the vessel is loosely covered for an hour with a
watch-glass which previously has been coated with wax
through which some lines have been cut with a sharp
instrument, the lines will be seen to have been etched
into the glass upon removal of the wax. The reaction
involved is identical with No. 4, under silicic acid.

DETECTION OF THE ACIDS OF GROUP I

The analysis for acids cannot be made by following a
systematic scheme of separation, such as is used in the
analysis for metals ; on the contrary, the presence or
absence of each acid must be established chiefly by
individual tests applied to the original material.



138 CHEMICAL ANALYSIS

For convenience the members of Group I may be
classified as follows :

Sub-group I H 2 CrO 4 , H 2 CO 3 , H 4 SiO 4 , H 2 SO 3 .
These acids are decomposed, in solution, by HC1 and
H 2 S.

Sub-group II H 2 SO 4 , H 3 PO 4 , H 3 BO 3 , H 2 C 2 O 4 ,
H 2 C 4 H 4 O 6 , HF. These acids are not decomposed by
HC1 or H 2 S.

Neutralize a small portion of the original solution,
and add some BaCl 2 (or Ba(NO 3 ) 2 , if metals of Group I
are present). A precipitate confirms the presence of
one or more acids of Group I. Divide a larger portion
of the original solution into four parts :

Part I, for chromic acid. A yellow color indicates
chromic acid, confirmed by acidifying with HC 2 H 3 O 2
and adding Pb(C 2 H 3 O 2 ) 2 .

Part II, for carbonic acid. Add II Cl and warm.
An effervescence of an odorless gas indicates the
presence of CO 2 . Confirm by testing with lime
water.

Part III, for sulphurous acid. Add HC1 and warm.
Effervescence with odor of burning sulphur indicates
the presence of SO 2 , confirmed by passing the gas
through lime water.

Part IV, for silicic acid. Add dilute HC1, drop by
drop. A gelatinous precipitate indicates H 4 SiO 4 , con-
firmed by evaporating to dryness and testing with the
metaphosphate bead.

If any of these acids are present, they must be
removed from solution before testing for the members
of Sub-group II. H 2 CrO 4 is destroyed by H 2 S, in



ACIDS OF GROUP I 139

presence of HC1 ; H 2 CO 3 and H 2 SO 3 are driven off by
boiling with HC1; and H 4 SiO 4 is removed by evapo-
ration with HC1.

The solution, thus freed of members of Sub-group I,
is now neutralized exactly with NH 4 OH, free of
(NH 4 ) 2 CO 3 , and its examination is continued as
follows :

To a small portion BaCl 2 is added. If no precipitate
is formed, all members of Sub-group II are absent. If
a precipitate is formed which dissolves on the addition
of HC1, H 2 SO 4 is absent, but other members may be
present. If a precipitate is formed which does not
dissolve in HC1, H 2 SO 4 (possibly other acids) is present.
In either of the latter cases it is necessary to test indi-
vidually for the remaining acids of the group in small
portions of the solution.

Part I, for phosphoric acid. Add a few drops of the
solution to a strong HNO 3 solution of (NH 4 ) 2 MoO 4 , and
warm gently. A yellow crystalline precipitate confirms
the presence of H 3 PO 4 .

Part II, for boric acid. Acidify some of the solution
with HC1 and test with turmeric paper. Evaporate
another portion almost to dryness, add alcohol and con-
centrated H 2 SO 4 , and kindle. A green flame confirms
the presence of H 3 BO 3 .

Part III, for oxalic acid. Add lime water and boil
the white precipitate with HC 2 H 3 O 2 . If the precipitate
fails to dissolve, it confirms the presence of H 2 C 2 O 4 .

Part IV, for tartaric acid. Neutralize the solution
and add CaCl 2 . If a white precipitate occurs, filter, dry
the residue, and heat in a closed tube. Charring with



140 CHEMICAL ANALYSIS

the odor of burnt sugar, and effervescence of the residue
with HC1, confirm the presence of H 2 C 4 H 4 O 6 .

Part V, for hydrofluoric acid. Evaporate the solution
to dryness, transfer the residue to a platinum crucible,
add concentrated H 2 SO 4 , and cover with a watch-glass.
If the gas etches the glass cover, the presence of HF
is confirmed.



CHAPTER XIV

ACIDS OF GROUP II: HYDROCHLORIC, HYDROBROMIC,
HYDRIODIC, HYDROCYANIC, HYDROFERROCYANIC,
HYDROFERRICYANIC, SULPHOCYANIC, AND HYDRO-
SULPHURIC ACIDS

CHARACTERISTIC : Insolubility of their silver salts in dilute
nitric acid.

GROUP REAGENT : Silver nitrate.

REACTIONS

Hydrochloric Acid, HC1 (salt for study, sodium chloride,

NaCl).

1. AgN0 3 precipitates white silver chloride, AgCl,
insoluble in dilute acids; soluble in KCN, NH 4 OH,
and in boiling solution of ammonium "sesqui" car-
bonate.

2. Pb0 2 or Mn0 2 with concentrated H 2 SO 4 expels chlo-
rine gas, detected with starch-KI paper.

3. K 2 Cr 2 7 with concentrated H 2 SO 4 gives red
fumes, condensing to a brown liquid, chromic oxy-
chloride, CrO 2 Cl 2 , changing to yellow (NH 4 ) 2 CrO 4
on the addition of NH 4 OH. The dry chloride
should be triturated with K 2 Cr 2 O 7 crystals, and dis-
tilled with concentrated H 2 SO 4 in a small retort
(25 c.c.).

141



142 CHEMICAL ANALYSIS

Hydrobromic Acid, HBr (salt for study, potassium
bromide, KBr).

1. AgN0 3 precipitates yellow silver bromide, AgBr,
insoluble in dilute acids and in ammonium " sesqui "
carbonate; soluble in NH 4 OH and KCN.

2. Pb0 2 with concentrated H 2 SO 4 expels brown vapors
of bromine, identified by their odor and color.

3. K 2 Cr 2 7 with concentrated H 2 SO 4 expels bromine,
which is decolorized by NH 4 OH, forming NH 4 Br.

4. Chlorine liberates bromine, detected in small quan-
tities by coloring carbon disulphide or chloroform
brownish-red. Mix the bromide solution with about
1 c.c. of CS 2 , then add dilute chlorine water, drop by
drop, and shake well. The globules of CS 2 will assume
a reddish tint. An excess of chlorine should be avoided,
lest it combine with bromine to form colorless bromine
chloride, BrCl.

Hydriodic Acid, HI (salt for study, potassium iodide, KI).

1. AgN0 3 precipitates yellow silver iodide, Agl,
insoluble in dilute acids, NH 4 OH and ammonium
"sesqui" carbonate; soluble in KCN.

2. Pb0 2 with concentrated HC 2 H 3 O 2 liberates violet
iodine, turning starch paper blue.

3. K2Cr 2 7 with concentrated H 2 SO 4 liberates iodine.

4. Chlorine water liberates iodine, turning starch
paper blue. An excess of chlorine will decolorize
the paper by formation of iodine chloride, IC1.

5. KN0 2 in concentrated H 2 SO 4 liberates iodine.
Into a clear solution of starch paste and an iodide, dip



ACIDS OF GEOUP II 143

a glass rod moistened with a solution of KNO 2 in con-
centrated H 2 SO 4 . The liquid in contact with the rod
becomes blue. It is necessary to keep the reagent cold,
as iodized starch becomes colorless in hot water.

Hydrocyanic Acid, HCN (salt for study, potassium cya-
nide, KCN).

1. AgN0 3 precipitates white silver cyanide, AgCN,
soluble in excess of KCN, forming the salt KAg(CN) 2 .
AgCN is also soluble in NH 4 OH and boiling HC1.

2. FeS0 4 , with a few drops of FeCl 3 , added to the solu-
tion of a cyanide in weak NaOH, precipitates a bluish-
green mixture of ferrous ferric hydroxide, Fe 3 O 2 (OH) 4 ,
and Prussian blue. Fe 3 O 2 (OH) 4 can be dissolved with
dilute HC1, leaving the Prussian blue intact.

3. (NH 4 ) 2 S x (a few drops) and a drop of NaOH added
to a cyanide solution, form ammonium sulphocyanate,
NH 4 CNS, on heating. Evaporate the solution to dry-
ness and test by dissolving in dilute HC1 and adding
FeCl 3 solution. A deep red coloration shows the pres-
ence of HCNS, derived from HCN : -

(NH 4 ) 2 S X + 4 KCN = 4 KCNS + (NH 4 ) 2 S(z - 4).

4. HNaC0 3 heated with a cyanide expels HCN gas,
identified by its odor and the rose color of its flame.

Hydroferrocyanic Acid, H 4 Fe(CN) 6 (salt for study, potas-
sium ferrocyanide, K 4 Fe(CN) 6 ).

1. AgN0 3 precipitates white silver ferrocyanide,
Ag 4 Fe(CN) 6 , soluble in KCN; insoluble in NH 4 OH
and HN(X.



144 CHEMICAL ANALYSIS

2. FeCl 3 precipitates Prussian blue (see Iron, p. 10T).

3. CuS0 4 precipitates brown cupric ferrocyanide,
Cu 2 Fe(CN) 6 (see Copper, p. 84).

Hydroferricyanic Acid, H 3 Fe(CN) 6 (salt for study, potas-
sium ferricyanide, K 3 Fe(CN) 6 ).

1. AgN0 3 precipitates orange-red silver ferricyanide,
Ag 3 Fe(CN) 6 , soluble in NH 4 OH and KCN; insoluble
in HN0 3 .

2. FeS0 4 precipitates Turnbull's blue (see Iron, p. 107).

Sulphocyanic Acid, HCNS (salt for study, potassium
sulphocyanate, KCNS).

1. AgN0 3 precipitates white silver sulphocyanide,
AgCNS, soluble in NH 4 OH ; insoluble in dilute
HNO 3 .

2. FeCl 3 acidified with HC1 gives a deep red colora-
tion of Fe(CNS) 3 (see Iron, p. 108).

Hydrosulphuric Acid, H 2 S (salt for study, sodium sul-
phide, Na 2 S).

1. AgN0 3 precipitates black silver sulphide, Ag 2 S.

2. Na 2 FeNO(CN) 5 (sodium nitro-prusside) added to
alkaline (NaOH) solution of a sulphide gives a brilliant
red-violet tint.

3. Fused with NaOH, insoluble sulphides form Na 2 S ;
and on dissolving the mass in a little water, the solu-
tion will tarnish a bright silver coin brown.

4. HC1 sets free H 2 S from all soluble, and from many
insoluble sulphides ; recognized by its odor and by its



ACIDS OF GROUP II 145

power of blackening paper moistened with a solution of
Pb(C 2 H 3 2 ) 2 .

DETECTION OF THE ACIDS OF GROUP II

The separation and identification of the acids of this
group are accomplished by the following means :

(a) The removal of H 2 S by means of a solution of
ZnSO 4 in NaOH.

(b) Hager's method of detecting HC1, HBr, and HI
in the presence of each other ; based upon the different
degrees of solubility of AgCl, AgBr, and Agl in ammo-
nium "sesqui" carbonate and NH 4 OH.

(c) The detection of HCN in the absence of
H 4 Fe(CN) 6 , H 3 Fe(CN) 6 , and HCNS, by the precipita-
tion of Prussian blue from a solution of a cyanide by
FeSO 4 , FeCl 3 , and NaOH.

(d) The detection of HCN in the presence of
H 4 Fe(CN) 6 , H 3 Fe(CN) 6 , and HCNS, by the evolution
of HCN on distilling with HNaCO 3 .

H 2 S must first be tested for in a small portion of the
original solution, preferably by adding HC1, boiling,
and noting whether any gas is given off which causes
lead acetate paper to blacken. If found, it must be
removed from the remainder of the solution before test-
ing for the other members of the group, since its pres-
ence would hinder their detection. Therefore, treat a
sufficient portion of the solution with a solution of
ZnSO 4 in an excess of NaOH, which will precipitate
the H 2 S as ZnS. Reject the precipitate, and divide the
filtrate, or portion of the original solution if H 2 S is
absent, into three parts.



146 CHEMICAL ANALYSIS

Part I, for HCl, HBr, and JET. 1 Acidify with HNO 3
and add AgNO 3 . Filter and reject the nitrate. Boil
the residue with 100 parts of a solution of ammonium
" sesqui " carbonate. Decant the clear supernatant
liquid, add more ammonium " sesqui " carbonate, and
again boil and decant. The decanted liquid may con-
tain AgCl, which can be determined by acidifying with
HNO 3 . The residue from which the liquid has been
decanted may consist of AgBr and Agl. Treat it with
a dilute solution of NH 4 OH (5 per cent ammonia water)
and filter. The filtrate may contain AgBr, detected
by acidifying with HNO 3 . The residue may be Agl,
indicated by its yellow color. For a further confirma-
tion of the three halogens (consisting of the AgCl and
AgBr precipitates from the ammoniacal solutions and
the undissolved Agl) each can be fused with Na 2 CO 3 ,
boiled with water, and filtered :

2 AgCl + Na 2 CO 3 - 2NaCl + Ag 2 CO 3 , etc.

The filtrates can be tested for the individual halogens
as follows :

(a) Solution of NaCl. Evaporate to dryness and heat
with concentrated H 2 SO 4 and PbO 2 . The evolved chlo-
rine can be detected by its odor, its bleaching moistened
litmus paper, or its effect on starch-KI paper.

(b) Solution of NaBr. Evaporate to dryness and
heat with concentrated H 2 SO 4 and PbO 2 . The evolved
bromine can be detected by its odor or by its color.

(c) Solution of Nal. Neutralize with HNO 3 and add
some drops of starch paste and chlorine water. A blue
solution confirms presence of the iodide.






ACIDS OF GROUP II 147

Part II, for H 4 Fe(CN) 6 , H 3 Fe(CN) 6 , and HCNS.-
Neutralize with HNO 3 and divide into two small parts.
Pour one part into a test-tube and shake the tube so
that its sides will be moistened with the liquid. Hold-
ing the tube obliquely, add a few drops of dilute FeCl 3
solution so that they will run down the sides of the
tube. A red coloration indicates the presence of HCNS.
If H 4 Fe(CN) 6 is present, Prussian blue will be formed
also, but the red color can be seen commingled with the
blue. Add more FeCl 3 . The formation of Prussian
blue confirms presence of H 4 Fe(CN) 6 . To the second
smaller part add FeSO 4 . The formation of Turnbull's
blue confirms the presence of H 3 Fe(CN) 6 .

Part III, for HON. li H 4 Fe(CN) 6 , H 3 Fe(CN) 6 ,
and HCNS are absent, add NaOH, FeSO 4 , a few drops
of FeCl 3 , and HC1 in excess. Formation of Prussian
blue confirms the presence of HCN.

If H 4 Fe(CN) 6 , H 3 Fe(CN) 6 , and HCNS are present,
add some solid bicarbonate of sodium, HNaCO 3 , to the
neutral solution in a test-tube, and boil. The odor of
bitter almonds indicates the presence of HCN. Con-
firm by kindling the gas. It should burn with a rose-
tinted flame.

HCN is a deadly poison ; do not inhale.



CHAPTER XV

ACIDS OF GROUP HI : NITRIC, CHLORIC, AND ACETIC ACIDS
No group characteristic. No group reagent.

REACTIONS

Nitric Acid, HN0 3 (salt for study, potassium nitrate,
KN0 3 ).

1. Heated on charcoal, nitrates deflagrate with igni-
tion, giving off CO 2 :

2KNO 3 + C = 2KNO 2 + CO 2 .

Use small quantities of the nitrate in performing this experiment.

2. Heated with KCN in a platinum crucible or foil,
nitrates deflagrate with ignition and detonation :

KNO 3 + KCN = KNO 2 + KCNO.

3. Mixed with copper filings and heated with con-
centrated H 2 SO 4 , nitrates give red fumes of NO 2 .

4. If a concentrated solution of FeSO 4 , free of ferric
salts, be carefully added to the cold solution of a
nitrate in concentrated H 2 SO 4 , so that the two solu-
tions form distinct layers, a brown ring will be formed
at their junction, (FeSO 4 ) 2 NO :

(a) 2 HN0 3 + 6 FeS0 4 + 3 H 2 SO 4

= 3Fe 2 (SO 4 ) 3 + 4H 2 O + 2NO ;

(b) 2FeSO 4 + NO = (FeSO 4 ) a NO.






ACIDS OF GROUP III 149

5. Brucine dissolved in concentrated H 2 SO 4 gives a
deep red color with nitrates. Touch the edge of the
dissolved brucine with a glass rod moistened with
nitrate solution ; a distinct red ring will bound the rod.

6. Reduced with zinc dust and H 2 SO 4 , nitrates yield
nitrous acid, HNO 2 , detected by starch-KI paper.

7. NaOH with zinc dust and iron filings, on heating,
reduces nitrates and sets NH 3 free :



Chloric ^cid, HC10 3 (salt for study, potassium chlorate,

KC10 3 ).

1. Heated on charcoal, chlorates deflagrate with vivid
ignition, giving off CO 2 :

2KC10 3 + 30 = 2KC1 + 3CO 2 .

2. Heated with KCN in a platinum crucible, chlorates
deflagrate with ignition and detonation :

KC1O 3 -h 3 KCN = KC1 + 3 KCNO.

As HC1O 3 gives up more oxygen than HNO 3 , the chemical action
in Reactions 1 and 2 is necessarily more vigorous than in those
under HNO 3 . Therefore, use very small quantities of chlorate.

3. Concentrated I^SC^ (a few drops), added with a
pipette to a watch-glass containing a chlorate solution,
liberates chlorine peroxide :

3 KC10 3 + 2 H 2 S0 4 = KC10 4 + 2 C1O 2 + H 2 O + 2HKSO 4 .

The peroxide is characterized by a disagreeable odor and a
yellow coloration ; also by bleaching a blue solution of indigo.
Neither heat nor large quantities of reagents should be used.

4. Brucine behaves very much alike towards nitrates
and chlorates.



150 CHEMICAL ANALYSIS

Acetic Acid, HC 2 H 3 2 (salt for study, sodium acetate,


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