James Freeman Sellers.

An elementary treatise on qualitative chemical analysis online

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since dilute HC1 often precipitates certain members of the next
group (BiOCl and SbOCl). This source of error can be removed
by adding a sufficient excess of HC1, which redissolves the BiOCl
and SbOCl.

On the other hand, too great an excess of HC1 interferes with
the action of the next group reagent (H 2 S) ; and, furthermore, it
may redissolve the chlorides of Group I.



CHAPTER VIII

METALS OF GROUP II: MERCURY (MERCURIC SALTS,
Hg"), LEAD, BISMUTH, COPPER, CADMIUM, ARSENIC
(ARSENIOUS, As'", AND ARSENIC, As v , SALTS), ANTI-
MONY, AND TIN

CHARACTERISTIC : Insolubility of the sulphides in dilute HC1.
GROUP REAGENT : Hydrogen sulphide in the presence of hydro-
chloric acid.

REACTIONS

Mercuric Mercury, Hg" (salt for study, mercuric chloride,
HgCl 2 ).

1. H 2 S precipitates black mercuric sulphide, HgS,
soluble in aqua regia; insoluble in yellow (NH 4 ) 2 S X
and in hot HNO 3 .

When H 2 S is first added, a white precipitate is obtained
which is the salt, HgCl 2 - 2 HgS. On adding more H 2 S, it becomes
orange, brown, and then black. If insufficient H 2 S is added, it
remains orange and is often mistaken for Sb 2 S 3 (which see).

2. NH 4 OH precipitates " white precipitate," NH 2 - HgCl,
soluble in acids.

3. NaOH precipitates yellow mercuric oxide, HgO,
soluble in acids.

4. SnC^ precipitates white Hg 2 Cl 2 , changing to gray
metallic mercury by addition of an excess of reagent.
Boiling with a little HC1 causes metallic globules
to form.

5. KI precipitates scarlet mercuric iodide, Hglg, 1 solu-
ble in excess of reagent, forming 2KI-HgI 2 .

82



METALS OF GROUP II 83

6. Metallic copper deposits metallic mercury.

7. Heating in a closed tube with fusion mixture causes
separation of metallic mercury.

Lead. (See reactions for lead under Group I.)

Lead, when present in a mixture, is often found in
Group II, because PbCl 2 is somewhat soluble in acidi-
fied aqueous solutions, and is brought over with the
filtrate from Group I.

Bismuth (salt for study, bismuth nitrate, Bi(N0 3 ) 3 ).

1. I^S precipitates black bismuth sulphide, Bi 2 S 3 ,
soluble in boiling HNO 3 ; insoluble in (NH 4 ) 2 S X . The
precipitation is hastened by dilution.

2. NH 4 OH and NaOH precipitate white basic bismuth
hydroxide, (BiO)OH, soluble in acids. If made alkaline
again with NaOH, and SnCl 2 is added, black bismuth
monoxide, BiO, will be formed.

3. Water added in large excess precipitates white
bismuth oxynitrate, (BiO)NO 3 , soluble in acids. Addi-
tion of NaCl hastens the precipitation by the formation
of the less soluble (BiO)Cl by double decomposition.

In this experiment, both water arid HNO 3 (a constituent of
Bi(NO 3 ) 3 ) endeavor to react with bismuth, the one to form
insoluble basic (BiO)NO 3 and the other to maintain the soluble
nitrate Bi(NO 3 ) 3 . HNO 3 is far better ionized than water, and
with a degree of equality in the contest it would maintain the
salt Bi(NO 3 ) 3 ; but the large excess of water so handicaps the
acid that it yields to mass action. In this hydrolytic action
the positive ion, Bi, is changed to another positive ion, BiO
(bisnmthyl).



84 CHEMICAL ANALYSIS

4. Metallic iron or zinc deposits metallic bismuth.

5. Reducing flame on charcoal with fusion mixture
gives a brittle bead of metallic bismuth. The border
of the pit becomes coated with yellow bismuth trioxide,
Bi 2 3 .

Copper (salt for study, copper sulphate, CuS0 4 ).

1. HgS precipitates black copper sulphide, CuS, solu-
ble in HNO 3 and KCN ; almost insoluble in (NH 4 ) 2 S X ;
insoluble in dilute H 2 SO 4 and yellow Na 2 S x .

2. NH 4 OH precipitates a greenish basic cupric salt,
probably CuSO 4 - CuO, soluble in excess of reagent, form-
ing a blue cuprammonium compound. 1

3. NaOH precipitates blue copper hydroxide, Cu(OH) 2 ,
darkening on boiling and giving 3 CuO H 2 O.

4. Metallic iron or zinc deposits metallic copper.

5. Reducing flame on charcoal with fusion mixture
gives metallic copper. The finely divided copper is
easily detected after the reduction by triturating the
fused mass in a small mortar and then washing off the
charcoal and dissolved salts.

6. KCN precipitates greenish cupric cyanide,
Cu(CN) 2 , soluble in excess of reagent, forming the
salt CuCN-3KCN or K 3 Cu(CN) 4 . This salt is not
reprecipitated by H 2 S. This is the reverse of Reac-
tion 1.

7. K 4 Fe(CN) 6 precipitates brown cupric ferrocyanide,
Cu 2 Fe(CN) 6 , insoluble in dilute acids.



METALS OF GROUP II 85

CHEMISTRY OF CYANOGEN COMPOUNDS

As cyanogen compounds are important in many ana-
lytical reactions, it is necessary to consider their behavior
and constitution at some length.

Cyanogen, CN, is much like the halogens, in both the
constitution and behavior of its acids and salts. The
cyanogen analogues of HC1, KC1, HC10, KC10, etc., are,
respectively, HCN, KCN, HCNO, KCNO, etc.

The cyanides of the more basic metals, the alkali and
alkali-earth metals, are soluble and easily decomposed by
acids, while those of the less basic heavy metals are less
soluble and more stable in the presence of acids. Though
the cyanides of the strong basic metals are easily decom-
posed by acids, they are not readily dissociated by heat
and can be fused without decomposition. The reverse is
true of the cyanides of the weak basic metals. Many
insoluble cyanides unite with soluble cyanides to form
so-called " double cyanides " :

CuCN + 3KCN = CuCN-SKCN or K 3 Cu(CN) 4 , potassium
cuprous cyanide ;

Fe(CN) 2 + 4KCX = Fe(CN) 2 -4KCN or K 4 Fe(CN) 6 , potas-
sium ferrous cyanide ;

Fe(CN) 3 + 3KCN = Fe(CN) 3 -3KCN or K 3 Fe(CN) 6 , potas-
sium ferric cyanide;

Co(CN) 2 -f- 4KCN = Co(C]Sr) 2 -4KCK or K^CN)., potas-
sium cobaltous cyanide.

The behavior, with reagents, of the solutions of many of
these combined salts indicates that they are not mixtures of
binary cyanides but salts of ternary acids whose acid radi-
cals are cyanides of various metals. For convenience the
tern; metallo-cyanide is applied to this class of salts.



86 CHEMICAL ANALYSIS

Copper is usually precipitated as CuS by H 2 S in acid
solution, but this reaction does not occur if K 3 Cu(CN) 4 is
treated with H 2 S. This seems to indicate that there are
no free Cu ions in a solution of K 3 Cu(CN) 4 . Potassium
cyanide reacting with H 2 S liberates hydrocyanic acid,
HCN, but when K 3 Cu(CN) 4 is treated with H 2 S, HCN is
not evolved. Both examples show that the two constitu-
ents of the salt, CuCN and KCN, are so strongly united as
to destroy the identity of each, and that K 3 Cu(CN) 4 is the
preferable formula.

This view is important in analytical chemistry, as it
interprets the behavior of several substances similar to

K 3 Cu(CN) 4 .

The metallo-cyanides occurring in analytical chemistry
may be considered under three classes :

1. Metallo-cyanides decomposed by hydrogen sul-
phide :

K 2 Cd(CN) 4 + 2H 2 S = CdS + K 2 S + 4HCN ;
K 2 Hg(CN) 4 + 2H 2 S = HgS + K 2 S + 4HCN, etc.

This class is important in the separation of copper and
cadmium in Group II for metals.

2. Metallo-cyanides decomposed by dilute mineral
acids :

K 3 Cu(CN) 4 + 3HC1 = CuCN + 3KC1 + 3HCN ;
K 2 Ni(CN) 4 + 2HC1 = Ni(CN) 2 + 2KC1 + 2HCN ;
K 4 Co(CK) 6 +4HCl = Co(CN) 2 + 4KCl + 4HCN, etc.

The reaction of K 4 Co(CN) 6 is merely temporary, and the
actual product is K 3 Co(CN) 6 , showing that the cobaltous
salt is oxidized to the corresponding cobaltic salt. The
nickelous salt is not oxidized to the nickel ic salt. This
is further illustrated in the oxidation of K 2 Ni(CN) 4 and
K 4 Co(CN) 6 by a hypobromite :



METALS OF GROUP II 87

NaBrO + 5H 2 = 2Ni(OH) 3 + NaBr
+ 4KCN + 4HCN;

2K 4 Co(CN) 6 + NaBrO + H 2 O = 2K 3 Co(CN) 6 + NaBr
+ 2KOH.

This class is important in the separation of nickel and
cobalt in Group IV for metals.

3. Metallo-cyanides not decomposed by dilute mineral
acids.

The members of this class are stable chemical com-
pounds and are not decomposed except by drastic treat-
ment. They give a clearer insight into the constitution of
the metallo-cyanides. The most important are the three
reagents, potassium ferrocyanide, K 4 Fe(CN) 6 , potassium
ferricyanide, K 3 Fe(CN) 6 , and potassium sulphocyanate,
KCNS. 1 They react with many compounds and, for the
most part, form colored metallo-cyanides :

2CuS0 4 + K 4 Fe(CN) 6 = 2 K 2 SO 4 + Cu 2 Fe(CN) 6 ;
4FeCl 8 + 3K 4 Fe(CN) 6 = 12KC1 + Fe 4 (Fe(CN) 6 ) 8 ;
3FeS0 4 + 2K 3 Fe(CN) 6 = 3K 2 S0 4 + Fe 3 (Fe(CN) 6 ) 2 ;
FeCl 3 + 3 KCNS = 3 KC1 + Fe(CNS) 3 .

This class is important in the detection of copper and
ferrous and ferric iron.

Cadmium (salt for study, cadmium nitrate, Cd(NO) 3 ) 2 .

1. HgS precipitates yellow cadmium sulphide, CdS,
very soluble in boiling acids ; insoluble in cold dilute
acids, (NH 4 ) 2 S X , and KCN.

2. NH 4 OH precipitates white cadmium hydroxide,
Cd(OH) 2 , soluble in excess of reagent.

3. NaOH acts like NH 4 OH, but does not redissolve
Cd(OH) 2 in excess of reagent.



88 CHEMICAL ANALYSIS

4. Metallic zinc deposits metallic cadmium.

5. Reducing flame on charcoal with fusion mixture
gives a brown incrustation of cadmium oxide, CdO.
The salt is first reduced to metallic cadmium, which,
owing to its ready volatility, rises to a stratum of oxy-
gen and is oxidized.



Arsenious Arsenic, As'" (salt for study, sodium arsenite,

Na 3 As0 3 ).

1. H^S precipitates from acidified solutions, yellow
arsenious sulphide, As 2 S 3 , soluble in (NH 4 ) 2 S X ,(NH 4 ) 2 CO 3 ,
and aqua regia ; insoluble in concentrated boiling HC1.

2. AgN0 3 precipitates from very weak ammoniated
solutions, yellow silver arsenite, Ag 3 AsO 3 , soluble in
excess of NH 4 OH and HNO 3 .

3. CuS0 4 precipitates from ammoniated solutions,
Scheele's green, HCuAsO 3 , soluble in excess of
NH 4 OH.

4. Heating in a closed tube with Na 2 CO 3 and KCN
deposits a mirror of metallic arsenic on the cold part of
the tube.

5. Nascent hydrogen reduces arsenic compounds to
arsine, AsH 3 . If the hydrogen and the AsH 3 are

'passed through a jet tip and kindled, AsH 3 will first
be oxidized to metallic arsenic and then, on emerging
from the flame, will be further oxidized to As 2 O 3 . If
AsH- 3 is passed into a solution of AgNO 3 , metallic
silver and arsenious acid, H 3 AsO 3 , will be produced :

6 AgNO 3 + AsH 3 4- 3 H 2 O = 6 Ag + 6 HNO 3 + H 3 AsO 3 .



METALS OF GROUP II 89

These reactions constitute the principles of-
Marsh's Test 1 for Arsenic. Generate hydrogen in a
small flask with pieces of pure zinc or magnesium and
dilute H 2 SO 4 or HC1. The flask should have a funnel
tube, and the horizontal delivery tube should have a
wide, hard glass tube about 2 cm. in diameter and 3 dm.
long, drawn to a jet point, and with two constrictions
near the middle. When the zinc is put into the flask
and all connections made tight, the dilute acid is
poured through the funnel tube. After two or three
minutes, test the hydrogen by collecting by displace-
ment of water in a test-tube. If it kindles quietly
with a blue flame, the jet may now be lighted. To
insure safety a cloth should be thrown over the appa-
ratus. Test the reagents and apparatus for arsenic by
holding a cold porcelain dish at the top of the flame.
If no black spots appear, no arsenic is present.

A concentrated HC1 solution of the arsenic com-
pound is poured through the funnel. Arsenic can be
detected in four ways :

(a) The hydrogen flame assumes a pale violet color,
due to the oxidation of AsH 3 to white As 2 O 3 .

(b) Black spots of metallic arsenic are deposited on
a cold porcelain plate. The plate should not be heated
too much, as the arsenic would then be sublimed. The
black spots can be removed by a solution of sodium
hypochlorite :

lONaCIO + 4 As + 6H 2 O = lONaCl + 4H 3 AsO 4 .

(c) If the hard glass tube is heated at one of the con-
tractions, the heat will decompose the passing AsH 3



90 CHEMICAL ANALYSIS

and will cause metallic arsenic to be deposited on the
cold part of the tube. When the evolution of hydro-
gen is completed, detach the tube with the arsenic
mirror from the generator and pass H 2 S through the
slightly warmed tube. The metallic mirror will change
to yellow As 2 S 3 .

(d) Hofmanris Modification. Instead of kindling
AsH 3 , pass it through a U-tube containing glass
splinters or beads moistened with a solution of lead
acetate, in order to counteract any passing HC1 or H 2 S,
and then pass the gas into a test-tube containing a
solution of AgNO 3 . When the precipitation is com-
pleted, remove the test-tube and add very cautiously
a thin stratum of very dilute NH 4 OH. The junction
of the two liquids should show a faint yellow ring of



Arsenic Arsenic, As v (salt for study, sodium arsenate,
Na 3 As0 4 ).

1. I^S precipitates, from strong HC1 solutions (2
parts concentrated HC1 to 1 part water), yellow arsenic
sulphide, As 2 S 5 . H 2 S will precipitate As 2 S 5 from
dilute solutions of HC1 if they are warmed to about
70 and the gas is passed through for some time.
As 2 S 6 behaves much like As 2 S 3 towards (NH 4 ) 2 S X , aqua
regia, and (NH 4 ) 2 CO 3 .

As 2 S 5 is a colloidal precipitate and requires for its precipita-
tion both heat and strong acid solution. (See Washing, p. 29.)
The semi-solid often colors the solution yellow without precipi-
tation ; in which event it is necessary to add more HC1 and in-
crease the heat. Furthermore, II 2 S with cold dilute IIC1 does



METALS OF GROUP II 91

not precipitate As 2 S 5 very well, as the arsenic is reduced to the
-ous condition : Na 3 AsO 4 + H 2 S = Na 3 AsO 3 + H 2 O + S.

2. AgN0 3 precipitates from a very slightly alkaline
solution, brown silver arsenate, Ag 3 AsO 4 , soluble in
excess of NH 4 OH and HNO 3 .

3. MgS0 4 in presence of NH 4 C1 and NH 4 OH precipi-
tates ammonium magnesium arsenate, NH 4 MgAsO 4 . 1

The purpose of adding NPI 4 C1 is to avoid the formation of
the insoluble compound Mg(OH) 2 ; and the purpose of adding an
excess of NH 4 OII is to insure the insolubility of the double salt
NH 4 MgAsO 4 .

4. (NH 4 ) 2 Mo0 4 in HNO 3 solution precipitates yel-
low ammonium arseno-molybdate, (MoO 3 ) 12 (NH 4 ) 3 AsO 4 .
The precipitation does not occur in the cold, like
that from phosphoric acid (which see).

(NH 4 ) 2 MoO 4 in HNO 3 solution changes to the more com-
plex salt (NII 4 ) a Mo 4 O 13 , which, with H 3 AsO 4 , forms insoluble
(MoO 3 ) 12 -(NH 4 ) 3 AsO 4 . The reagent should be added in large
excess (about 4 : 1), as the precipitate is soluble in H 3 AsO 4 .

5. Similar to 4, under arsenious compounds.

6. Similar to 5, under arsenious compounds.

Antimony (salt for study, antimonious chloride, SbCl 3 ).

1. I^S precipitates orange antimonious sulphide,
Sb 2 S 3 , soluble in (NH 4 ) 2 S X , hot concentrated HC1,
and aqua regia; insoluble in (NH 4 ) 2 CO 3 .

2. NH 4 OH and NaOH precipitate white antimonious
hydroxide, Sb(OH) 3 , soluble in excess of NaOH.

3. AgN0 3 precipitates from alkaline solutions of anti-
monious salts a black mixture of Ag 2 O and metallic



92 CHEMICAL ANALYSIS

silver. From antimonic salts, AgNO 3 precipitates
white silver antimonate, Ag 3 SbO 4 , soluble in NH 4 OH.
These reactions are useful for detecting the -ous and
the -ic conditions of antimony.

4. Heating on charcoal with fusion mixture gives a
metallic antimony bead with white incrustation of
Sb 2 3 .

5. Water in large excess hydrolyzes soluble antimo-
nious salts and forms white insoluble basic salts :

SbCl 3 + H 2 O = SbOCl + 2 HC1.

6. Nascent hydrogen reduces antimony compounds to
stibine, SbH 3 , and deposits metallic antimony on kin-
dling, like arsenic. If SbH 3 is passed into a solution
of AgNO 3 , black silver antimonide, SbAg 3 , will be pre-
cipitated :

3 AgNO 3 + SbH 3 = SbAg 3 + 3HNO 3 .

On account of the likeness between the reactions of
arsenic and antimony with nascent hydrogen, it is well
to compare the behaviors of the two metals in Marsh's
test.

(a) The hydrogen flame is not tinted violet by
SbH 3 .

(b) The black antimony spots on cold porcelain are
blacker and less lustrous than those of arsenic. Anti-
mony spots are not removed by hypochlorite solutions.

(<?) H 2 S passed through the hard glass tube contain-
ing antimony stain produces orange Sb 2 S 3 .

(d) In Hofmann's test, SbH 3 passed into AgNO 3 solu-
tion precipitates black SbAg 3 . When the precipitation
is completed, decant the liquid and wash the residue by



METALS OF GROUP II 93

decantation. Dissolve the antimony by boiling with
a strong solution of tartaric acid to which a few drops
of HNO 3 have been added. Filter, acidify with HC1,
and pass H 2 S through the warmed solution. An
orange precipitate indicates Sb 2 S 3 .

Stannous Tin, Sn" (salt for study, stannous chloride,
SnCl 2 ).

1. B^S precipitates brown stannous sulphide, SnS,
soluble in (NH 4 ) 2 S X and hot concentrated HC1 ; insolu-
ble in dilute cold HC1 and (NH 4 ) 2 CO 3 .

2. NH 4 OH and NaOH precipitate white stannous
hydroxide, Sn(OH) 2 , soluble in excess of NaOH,
forming sodium stannite, Na 2 SnO 2 .

3. HgCLj freely added precipitates white Hg 2 Cl 2 .

4. Metallic zinc deposits metallic tin.

5. Heating on charcoal with fusion mixture gives
metallic tin and a white incrustation of SnO 2 .

Stannic Tin, Sn' v (salt for analysis, stannic chloride,
SnCl 4 ).

1. H^ precipitates yellow stannic sulphide, SnS 2 ,
soluble in (NH 4 ) 2 S X and hot concentrated HC1 ; insolu-
ble in dilute cold HC1 and (NH 4 ) 2 CO 3 .

2. NH 4 OH and NaOH precipitate white stannic hydrox-
ide, SnO(OH) 2 , soluble in excess NaOH.

3. Similar to 4, under stannous salts.

4. Similar to 5, under stannous salts.



94 ' CHEMICAL ANALYSIS

PROCESS OF SEPARATION

The group is divided into two sub-groups. Sub-
group A: arsenic, antimony, and tin, metals whose
sulphides are soluble in (NH 4 ) 2 S X . Sub-group B : mer-
cury, lead, bismuth, copper, and cadmium, metals
whose sulphides are not soluble in (NH 4 ) 2 S X .

The separation of the members of Sub-group A
depends upon the following properties :

(a) Insolubility of arsenic sulphide in boiling HC1,
or the solubility of arsenic sulphide in (NH 4 ) 2 CO 3
solution.

(b) Insolubility of metallic antimony in dilute HC1.

(c) Hofmann's separation of arsenic, antimony, and
tin.

The separation of Sub-group B depends upon the
following properties :

(a) Insolubility of HgS in boiling dilute HNO 3 ;

(b) " " PbSO 4 in acidified solution ;

(c) " (BiO) OH in NH 4 OH solution;

(d) " " CuS in dilute H 2 SO 4 , or

" CdS in KCN solution.

Into the solution 1 acidified with HC1 2 and warmed to
about 70, pass a constant stream of H 2 S for about
fifteen minutes ; then cool the diluted solution, and
before filtering pass H 2 S again till the precipitation
is completed. The precipitation of As 2 S 3 and As 2 S 5
requires heat and a strongly acid (HC1) solution, both
of which tend to dissolve the other sulphides. Hence
it is necessary to cool and dilute the solution in order
to precipitate all the sulphides. 3 Filter. The filtrate (a) 4



METALS OF GROUP II 95

may contain members of subsequent groups. The resi-
due (a) may consist of the sulphides of all the members
of the group. Thoroughly wash the residue with the
aid of the suction pump, remove it from the paper
and digest it with (NH^gS, 1 (or with Na 2 S x , 2 if the pres-
ence of copper is suspected) for about ten minutes.
Filter and wash the residue with water containing
some (NH 4 ) 2 S X , rejecting the washings. The nitrate
(b) may contain the sulpho-salts of Sub-group A. The
residue (b) may consist of the sulphides of Sub-group B.

Separation of Sub-group A. To the filtrate (b) add
dilute HC1 till acid. Filter and reject the filtrate and
washings. A yellow precipitate, residue (<?), indicates
the presence of members of the sub-group, or it may be
sulphur or a mixture of the sulphides and sulphur.
Sulphur can be dissolved by shaking the precipitate
with benzol or petroleum ether. If all the precipitate
dissolves, it is only separated sulphur. Two methods
can be used for the further separation of Sub-group A.

Method 1. Treat residue (<?), possibly consisting of
the reprecipitated sulphides, with warm concentrated
HC1 (concentrated HC1 and a little water). Filter.
The nitrate (a 1 ) may contain antimony and tin chlorides.
The residue (a 1 ) may b'e sulphur and As 2 S 5 . Divide
the residue into two parts. First part : Dry the yellow
mass and heat in a closed tube with Na 2 CO 3 and KCN.
A mirror on the sides of the tube indicates arsenic.
Second part: Fuse with Na 2 CO 3 on a platinum foil;
dissolve in HNO 3 and boil to expel carbonic acid.
Add excess of (NH 4 ) 2 MoO 4 3 solution in HNO 3 and boil.
A yellow precipitate confirms the presence of arsenic.



96 CHEMICAL ANALYSIS

Boil filtrate (a 1 ) to expel H 2 S. Transfer to a small
dish, and immerse in the solution a galvanic couple of
strips of zinc 1 and platinum. After the evolution of
gas, black antimony coats the platinum and gray tin
loosely adheres to the zinc. Wash the platinum and
boil with tartaric acid and a drop of fuming HNO 3 .
H 2 S producing an orange precipitate confirms anti-
mony. With the fingers rub off the loose tin from
the zinc 2 into a dish. Again introduce the platinum
and some HC1, and boil till all the loose tin dissolves.
(Some insoluble particles of carbon may remain.)
Filter, if necessary, and pour into a test-tube rinsed
with HgCl 2 . A white precipitate turning gray on
boiling confirms tin.



CHEMISTRY OF SULPHO-COMPOUNDS

The solution of the sulphides of arsenic, antimony, and tin by
(NH 4 ) 2 S X is due to the formation of the sulpho-salts of these ele-
ments. They occur in the periodic system about midway between
the acid-producing and base-producing elements. Hence their
oxides are generally basic with reference to strong acid oxides,
and acid with reference to strong basic oxides. In the presence
of strong bases, the oxides As 2 O 3 , As 2 O 6 , Sb 2 O 3 , Sb 2 O 5 , SnO, and
SnO 2 form classes of -ous and -ic salts :

As 2 O 3 + 6 NaOH = 3 H 2 O + 2 Na 3 AsO 3 , sodium arsenite ;

As 2 O 3 + 2NaOH = II 2 O + 2NaAsO 2 , " metarsenite ;

As 2 O 6 + 6 NaOH = 3 H 2 O + 2 Na 3 AsO 4 , arsenate ;

Sb 2 O 3 + 6 NaOH = 3 H 2 O + 2 Na 8 SbO 3 , " antimonite ;

Sb 2 O 3 + 2NaOH = H 2 O + 2NaSbO 2 , metantimonite ;

Sb 2 O 5 -f 6 NaOH = 3 H 2 O + 2 Na 3 SbO 4 , " antimonate ;

2 SnO + 2NaOII = H 2 O + Na 2 Sn 2 O 3 (?), oxystannite;

SnO 2 + 2NaOII = H 2 O + Na 2 SnO,, stannate.



METALS OF GROUP II 97

The corresponding soluble sulpho- or thio-salts are made in
two ways :

First : Reactions of H 2 S with the oxy-salts of the elements :

Na 3 AsO 3 + 3H 2 S = 3H 2 O + Na 3 AsS 3 , sodium sulpharsenite ;
NaAsO 2 -f 2H 2 S = 2H 2 O + NaAsS 2 , " metasulpharsenite;
Na 3 AsO 4 + 4 H 2 S = 4H 2 O + Na 3 AsS 4 , " sulpharsenate ; etc.

When the sulpho-salts are treated with HC1 the hypothetical
sulpho-acids are formed, but are immediately broken down to the
insoluble sulphides. This is one reason that the presence of HC1
is necessary for the precipitation of the sulphides by H 2 S.

Second: Reactions of alkali sulphides with the sulphides of
the elements :

As 2 S 3 -f 3(NH 4 ) 2 S = 2(NH 4 ) 3 AsS 3 ;

As 2 S 3 + (NH 4 ) 2 S = 2NH 4 AsS 2 ;

As 2 S 5 + 3(NH 4 ) 2 S - 2(NH 4 ) 3 AsS 4 ;

Sb 2 S 3 + 3(NH 4 ) 2 S = 2(NH 4 ) 3 SbS 3 ;

Sb 2 S 3 + (NH 4 ) 2 S - 2 NH 4 SbS 2 ;

Sb 2 S 5 + 3(NH 4 ) 2 S - 2(NH 4 ) 3 SbS 4 ;

SnS + (NTI 4 ) 2 S = no sulpho-salt formed ;

SnS 2 + (NH 4 ) 2 S = (NH 4 ) 2 SnS 3 .

All of the higher sulphides readily unite with (NH 4 ) 2 S to form
-ate salts, but the lower sulphides unite with (NH 4 ) 2 S with vary-
ing difficulty.

As 2 S 3 reacts with (NH 4 ) 2 S very readily ;
Sb 2 S 3 " " , with difficulty ;

SnS " " " not at all.

Hence, in order to change all the insoluble sulphides to solu-
ble sulpho-salts, it is necessary to add ammonium polysulphide,
(NH 4 ) 2 S X , so as to supply sufficient sulphur to convert all of the
sulphides to the -ate salts :

As 2 S 3 + 3(NII 4 ) 2 S X - 2(NH 4 ) 3 AsS 4 + (3 X- 5)S ;
As 2 S 5 + 3(NH 4 ) 2 S X = 2(NH 4 ) 3 As S 4 + 3(X - 1)S;
Sb 2 S 3 + 3(NH 4 ) 2 S X - 2(NH 4 ) 3 SbS 4 + (3X - 5)S ;
SnS + (NH 4 ) 2 S X = (NH 4 ) 2 SnS 3 + (X - 2)S ;
SnS 2 + (NH 4 ) 2 S X = (NH 4 ) 2 SnS 3 + (X-l)S.



98 . CHEMICAL ANALYSIS

As stated above, these soluble sulpho-salts are readily decom-
posed by II Cl and the sulphides reclaimed :



2(NH 4 ) 8 AsS 4 + 6 IIC1 - As 2 S 5 + G NII 4 C1 + 3 H 2 S ;
2(NH 4 ) 8 SbS 4 + 6 HC1 = Sb 2 S 5 4- 6 NII 4 C1 + 3 II 2 S, etc.


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