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gen Sulphide.

ALL METALS OF THE SIXTH GROUP FROM THOSE OF THE
FIRST FOUR GROUPS.

Conduct into the acid* solution hydrogen sulphide in 166
excess, and filter off the precipitated sulphides (correspond-
ing to the oxides of the sixth group).

The points mentioned 127, a-, ft, and y, must also be
attended to here. As regards 7, antimony and tin are to be
inserted between cadmium and mercury, in the order of
i net als there given. With respect to the particular conditions
required to secure the proper precipitation of certain metals
of the sixth group, I refer to Section IY. I have to remark
in addition :

* Hydrochloric acid answers best as acidifying agent.



164.] * METALS OF GROUP VI, 701

a. That hydrogen sulphide fails to separate arsenic acid
from zinc, as, even in presence of a large excess of acid,
the whole or at least a portion of the zinc precipitates with
the arsenic (WOHLER). To secure the separation of the two
bodies in a solution, the arsenic acid must first be converted
into arsenous acid, by heating with sulphurous acid, before
the hydrogen sulphide is conducted into the fluid.

/3. That in presence of antimony, tartaric acid should be
added, as otherwise the sulphide of antimony will contain
chloride ; and that sulphide of antimony, when thrown down
from a boiling solution by hydrogen sulphide, becomes black
after a time, and so dense that it is deposited like sand,
whereby the filtration and washing are much facilitated (S. P.

SCHAFELER*).

2. Method based upon the Solubility of the Sulphides
of the Metals of the Sixth Group in Sulphides of the
Alkali Metals.

a. THE METALS OF GROUP YI. (with the exception of Gold
and Platinum) FROM THOSE OF GROUP Y.

Precipitate the acid solution with hydrogen sulphide, pay- 167'
ing due attention to the directions given in Section IY. under
the heads of the several metals, and also to the remarks in
166. The precipitate consists of the sulphides of the metals
of Groups Y. and YI. "Wash, and treat at once with yellow
ammonium sulphide in excess. (It is usually best to spread
out the filter in a porcelain dish, add the ammonium sulphide,
cover with a large watch-glass, and place on a heated water-
bath. Unnecessary exposure to air should be avoided.) Add
some water, filter off the clear fluid, treat the residue again
with ammonium sulphide, digest a short time, repeat the same
operation, if necessary, a third and fourth time, filter, and
wash the residuary sulphides of Group Y. with water contain-
ing ammonium sulphide. If stannous sulphide is present,
some flowers of sulphur must be added to the ammonium sul-
phide, unless the latter be very yellow. In presence of copper,

* Berichte der deutschen chem. Gesellsch., 1871, 279. I have myself confirmed
these observations.



702 SEPARATION. [ 164.

the sulphide of which is a little soluble in ammonium sulphide,
sodium sulphide should be used instead. However, this sub-
stitution can be made only in the absence of mercury, since
the sulphide of that metal is soluble in sodium sulphide.

Add to the alkaline nitrate, gradually, hydrochloric acid in
small portions, until the acid predominates ; allow to subside,
and then filter off the sulphides of the metals of the sixth
group, which are mixed with sulphur.

SCHNEIDER* states that he was unsuccessful in effecting
complete separation of bismuth disulphide and stannic sulphide
by digestion with potassium sulphide, but did succeed by con-
ducting hydrogen sulphide into the potassium-hydroxide solu-
tion of bismuthic tartrate and stannous oxide (which decom-
pose into bismuthous oxide and stannic oxide).

If a solution contains much arsenic acid in presence of
small quantities of copper, bismuth, &c., it is convenient to
precipitate these metals (together with a very small amount of
arsenous sulphide) by a brief treatment with hydrogen sul-
phide. Filter, extract the precipitate with ammonium sulphide
(or potassium sulphide), acidify the solution obtained, mix it
with the former filtrate containing the principal quantity of
the arsenic, and proceed to treat further with hydrogen sul-
phide ( 127, 4, b).

1>. THE METALS OF GROUP VI. (with the exception of Gold
and Platinum) FROM THOSE OF GROUPS IY. AND Y.

a. Neutralize the solution with ammonia, add ammonium 168
chloride, if necessary, and then yellow ammonium sulphide in
excess ; digest in a closed flask, for some time at a moderate
heat, and then proceed as in 167. Repeated digestion with
fresh quantities of ammonium sulphide is indispensable. On
the filter, you have the sulphides of the metals of Groups IY
and Y. Wash with water containing ammonium sulphide.
In presence of nickel, this method offers peculiar difficul-
ties; traces of mercuric sulphide, too, arc liable to pass into
the filtrate. In presence of copper (and absence of mer-
cury), soda and sodium sulphide are substituted for ammonia
and ammonium sulphide, f

* Annnl. d. Chem. u. Pharm., ci, 64.

f The accuracy of this method has been called in question by BLOXAM (Quart.
Journ. Cfwm. Soc., v, 119). That chrmisi found thai ammonium sulphide fails



164.] METALS OF GROUP VI. 703

ft. In the analysis of solid compounds (oxides or salts), it
is in most cases preferable to fuse the substance with 3 parts
of dry sodium carbonate and 3 of sulphur, in a covered porce-
lain crucible. When the contents are completely fused, and
the excess of sulphur is volatilized, the mass is allowed to cool,
and then treated with water, which dissolves the sulphosalts
of the metals of the sixth group, leaving the sulphides of
Groups IY. and Y. undissolved. By this means, even ignited
stannic oxide may be readily tested for iron, &c., and the
amount of the admixture determined (H. ROSE). The solu-
tion of the sulphosalts is treated as in 167. In the presence
of copper, traces of the sulphide may be dissolved with the
sulphides of Group YI. Occasionally a little ferrous sulphide
dissolves, coloring the solution green. In that case add some
ammonium chloride, and digest till the solution has turned
yellow. Instead of the mixture of sodium carbonate and sul-
phur you may also use already prepared hepar sulphuris, or,
as FROHDE* says, you may fuse the substance with 4 or 5 parts
of sodium thiosulphate.

E. Special Methods.

1. Methods based upon the Insolubility of some
Metals of the Sixth Group in Acids.

a. GOLD FKOM METALS OF GROUPS IY. AND Y. IN ALLOYS.

a. Boil the alloy with pure nitric acid (not too concen- 169
trated), or, according to circumstances, with hydrochloric acid.
The other metals dissolve, the gold is left. The alloy must
be reduced to filings, or rolled out into a thin sheet. If the
alloy were treated with concentrated nitric acid, and at a tem-
perature below boiling, a little gold might dissolve in conse-
quence of the co-operation of nitrous acid. In the presence
of silver and lead, this method is only applicable when they

to separate small quantities of stannic sulphide from large quantities of mercuric
sulphide or cadmium sulphide (1 : 100); and that more especially the separation
of copper from tin and antimony (also from arsenic) by this method is a failure,
as nearly the whole of the tin remains with the copper. The latter statement I
cannot confirm, for Mr. Lucius, in my laboratory, has succeeded in separating
copper from tin by means of yellowish sodium sulphide completely; but it is
indispensable to digest three or four times with sufficiently large quantities of
the solvent, as stated in the text.
*Zeilschr.f. analyt. Chem., v, 405.



704 SEPARATION. [ 164

amount to more than 80 per cent., since otherwise they are
not completely dissolved. Alloys of silver and gold contain-
ing less than 80 per cent, of silver are therefore fused with 3
parts of lead, before they are treated with nitric acid. The
residuary gold is weighed ; but its purity must be ascertained,
by dissolving in cold dilute nitrohydrochloric acid, not in con-
centrated hot acid, as silver chloride also is soluble in the latter.
In the presence of silver, a small quantity of its chloride is
usually obtained here. If it can be weighed, it should be
reduced and deducted.

At the Mint Conference held at Vienna in 1857, the fol-
lowing process was agreed upon for the mints in the several
states of Germany. Add to 1 part of gold, supposed to be
present, 2^- parts of pure silver ; wrap both the alloy and the
silver in a paper together, and introduce into a cupel in which
the requisite amount of lead is just fusing.* After the lead
has been absorbed,! the button is flattened by hammering or
rolling, then ignited and rolled. The rolls are treated first
with nitric acid of 1*2 sp. gr., afterwards with nitric acid of
1*3 sp. gr., rinsed, ignited, and weighed.^ Even after boiling
again with nitric acid of 1-3 sp. gr., they retain 0-75 to O'OOl
of silver which will remain as chloride if the rolls are treated
with cold dilute aqua regia (II. ROSSLER, loc. cit.).

ft. Heat the alloy (previously filed or rolled) in a capacious
platinum dish with a mixture of 2 parts pure concentrated
sulphuric acid and 1 part water, until the evolution of gas has
ceased and the sulphuric acid begins to volatilize ; or fuse the
alloy with potassium disulphate (II. ROSE). Separate the gold
from the sulphates of the other metals, by treating the mass
with water which' should finally be boiling. It is advisable to
repeat the operation with the separated gold, and ultimately

* If the weighed sample, say 0'25 grm., contains 98-92# gold, 3 grm. of lead
are required; if 92-87 '5, 4 grm.; if 87-5-75, 5 grm.; if 75-60, 6 grm.; if 60-35,
7 grm. ; if less than 35, 8 grm.

f A small quantity of gold from one to three, thousandths is always lost
in cupellation. The loss increases with the amount of lead, and is also depend-
ent on the proportion of silver to gold. The more silver present the less is the
loss of gold. In large buttons the loss is less than in small ones (H. ROSSLER,
Ding, polyt. Journ., ccvi, 185; Zeitachr. /. analyt. Chem., xm, 87).

\Kunst- und Oewerbeblatt f. Baiern, 1857, 151; Chem. CentralbL, 1857, 307;
Polyt. CentralbL, 1857, 1151, 1471, 1639.



164.] METALS OF GKOUP VI. 706

test the purity of the latter. In presence of lead this method
is not good.

y. The methods given in a and J3 may be united, i.e., the
cupelled and thinly-rolled metal may be first warmed with
nitric acid of 1-2 sp. gr., then thoroughly washed, the gold
boiled 5 minutes with concentrated sulphuric acid, washed
again, and ignited (MASCAZZINI, BUGATTI).

I). PLATINUM FROM METALS OF GROUPS IY. AND V. IN
ALLOYS.

The separation is effected by heating the alloy in filings 170
or foil with pure concentrated sulphuric acid, with addition of
a little water, or by fusing with potassium disulphate (169, /?);
but not with nitric acid, as platinum in alloys will, under cer-
tain circumstances, dissolve in that acid.

2. Method based upon the Separation of Gold in
the metallic state.

GOLD FROM ALL METALS OF GROUPS I. Y., with the excep-
tion of LEAD, MERCURY, AND SILVER.

Precipitate the hydrochloric acid solution with oxalic acid 171
as directed 123 &, y, or with ferrous sulphate, 123, &, a,
and filter off the gold when it has completely separated. Take
care to add a sufficient quantity of hydrochloric acid after the
reduction to insure solution of any oxalates. In the presence
of copper the addition of hydrochloric acid does not suffice,
since the coprecipitated cupric oxalate will dissolve with diffi-
culty in this acid. E. PURGOTTI* recommends in this case,
after precipitation, adding potash cautiously to the boiling hot
fluid till it is neutral, and then if necessary some normal
potassium oxalate. Double oxalate of copper and potash will
be formed which dissolves with a blue color. The gold after
washing will now be pure.

3. Method based upon the Precipitation of Pla-
tinum as Potassium Platinic, or Ammonium Platinic
Chloride.

PLATINUM FROM THE METALS OF GROUPS IY. AND Y. 9
with the exception of MERCURY IN MERCUROUS COMPOUNDS,
LEAD, AND SILVER.

Precipitate the platinum with potassium chloride or 172

* Zeitschr. /. analyt. Chem., ix, 128.



706 SEPARATION. [ 164

ammonium chloride as directed 124, and wash the precipi-
tate thoroughly with alcohol. The platinum prepared from
the precipitated ammonium or potassium salt is to be tested
after being weighed, to see whether it yields any metal
(especially iron) to fusing potassium disulphate.

4. Methods based upon the Separation of Oxides
insoluble in Nitric Acid.

a. TIN FROM METALS OF GROUPS IY. AND Y. (not from
Bismuth, Iron, or Manganese*) IN ALLOYS.

Treat the finely divided alloy, or the metallic powder 173
obtained by reducing the oxides in a stream of hydrogen with
nitric acid, as directed 126, 1, a. The filtrate contains the
other metals as nitrates. As stannic oxide is liable to retain
traces of copper and lead and iron, you must, in an accurate
analysis, test an aliquot part of it for these bodies, and determine
their amount as directed 168, /?.

BKUNNER recommends the following course of proceeding,
by which the presence of copper in the tin may be effectually
guarded against. Dissolve the alloy in a mixture of 1 part of
nitric acid, 4 parts of hydrochloric acid, and 5 parts of water ;
dilute the solution largely with water, and heat gently. Add
crystals of sodium carbonate until a distinct precipitate has
formed, and boil. (In presence of copper, the precipitate
must, in this operation, change from its original bluish-green
to a brown or black tint.) When the fluid has been in ebulli-
tion some 10 or 15 minutes, allow it to cool, and then add
nitric acid, drop by drop, until the reaction is distinctly acid;
digest vhe precipitate for several hours, when it should havr
acquired a pure white color. The stannic oxide thus obtained
is free from copper ; but it may contain some iron, which can
be removed as directed in 168, ft.

Before the stannic oxide can be considered pure, it must
be tested also for silicic acid, as it frequently contains traces of
this substance. To this end, an aliquot part is fused in plati-



* If the alloy of tin contains bismuth or manganese, there remains with the
stannic oxide, bismuth trioxide or manganese sesquioxide, which cannot be
extracted by ritric acid; if it contains iron, on the contrary, some stannic oxide
always dissolves with the iron, and cannot be separated even by repeated evapo-
ration (II. HOSE, Pogg. Annul., cxn, 169, 170, 172)



164.] METALS OF GROUP VI. 707

num with 3 4 parts of sodium and potassium carbonate, the
fused mass boiled with water, and the solution filtered ; hydro-
chloric acid is then added to the filtrate, and, should silicic acid
separate, the fluid is filtered off from this substance. The tin
is then precipitated by hydrogen sulphide, and the silicic acid
still remaining in the filtrate is determined in the usual way
( 140). If hydrochloric acid has produced a precipitate of
silicic acid, the last filtration is effected on the same filter
(KHITTEL*).

l>. ANTIMONY FROM THE METALS OF GROUPS IV. AND V. IN
ALLOYS (not from Bismuth, Iron and Manganese).

Proceed as in 173? filter off tlu precipitate, and convert it 174
by ignition into antimony tetroxide according to 125, 2.
Results only approximate, as a little antimony dissolves.
Alloys of antimony and lead, containing the former metal in
excess, should be previously fused with a weighed quantity of
pure lead (VARRENTRAPP|).

5. Methods based on the Precipitation of Tin in
Stannic Salts by Normal Salts (e.g., Sodium Sulphate)
or by Sulphuric Acid.

TIN FROM THE METALS OF GROUPS I., II., Ill, ; ALSO FROM
MANGANESE, ZINC, NICKEL AND COBALT, COPPER, CADMIUM

(GOLD).

Precipitate the hydrochloric acid solution, which must 175
contain the tin entirely as stannic chloride, according to 126,
1, , by ammonium nitrate or sodium sulphate (LOWENTHAL),
or by sulphuric acid, which, H. ROSE says, answers equally
well. Alloys are always treated as follows : First, oxidize by
digestion with nitric acid ; when no more action takes place,
evaporate the greater portion of the nitric acid in a porcelain
dish, moisten the mass with strong hydrochloric acid, and after
half an hour add water, in which the metastannic chloride and
the other chlorides dissolve. Alloys of tin and gold are dis-
solved in aqua regia, the excess of acid evaporated, and the
solution diluted with much water, before precipitating with
sulphuric acid.

It must be remembered that in this process any phosphoric

* Chem. CentralbL, 1857, 929. \ Dingier' s poly t. Journ., CLVIII, 316.



708 SEPARATION. [ 164.

acid that may be present is precipitated entirely or partially
with the tin. After the precipitate has been well washed by
decantation, LOWENTHAL recommends to boil with a mixture
of 1 part nitric acid (sp. gr. 1-2) and 9 parts water, then to
transfer to the filter, and wash thoroughly. Results very
satisfactory. If the fluid contains a ferric salt, a portion of
the iron always falls down with the tin. Hence the stannic
oxide must be tested for iron according to 168, /?, which, if
present, must be determined and deducted.

6. Method based on the Insolubility of Mercuric
Sulphide in Hydrochloric Acid.

MERCURY FROM ANTIMONY.

Digest the precipitated sulphides with moderately strong 176
hydrochloric acid in a distilling apparatus. The sulphide of
antimony dissolves, while the mercuric sulphide remains
behind. Expel all the hydrogen sulphide, then add tartaric
acid, dilute, filter, mix the filtrate with the distillate which
contains a little antimony, and precipitate with hydrogen
sulphide. The mercuric sulphide may be weighed as such (Fn.
FIELD*).

7. Methods based upon the Conversion of Arsenic
and Antimony into Alkali Arsenate and Antimonate.

a. ARSENIC FROM THE METALS OF GROUPS II., IV., AND Y.

If you have to do with arsenites or arsenates, fuse with 3 177
parts of sodium and potassium carbonates and 1 part of potas-
sium nitrate ; if an alloy has to be analyzed it is fused with 3
parts of sodium carbonate and 3 parts of potassium nitrate.
In either case the residue is boiled with water, and the solution,
which contains the arsenates of the alkalies, filtered from the
undissolved oxides or carbonates. The arsenic acid is deter-
mined in the filtrate as directed 127, 2. If the quantity of
arsenic is only small, a platinum rrurihle may be used, other-
wise a porcelain crucible must be used, as platinum would be
seriously injured. In the latter case, bear in mind that the
fused mass is contaminated with silicic acid and alumina. If
the alloy contains much arsenic a small quantity may be readily
lost by volatilization, even though the operation be cautiously

. Jonrn. Chan. Soc., xu, 32.



164.] METALS OF GTCOUP VI. 709

conducted. In such a case, therefore, it is better first to oxidize
with nitric acid, then to evaporate, and to fuse the residue as
above directed with sodium carbonate and potassium nitrate.

b. ARSENIC AND ANTIMONY FROM COPPER AND IKON,
especially in ores containing sulphur.

Diffuse the very finely pulverized mineral through pure 178
solution of potassa, and conduct chlorine into the fluid (comp.
p. 467). The iron and copper separate as oxides, the solution
contains sulphate, arsenate, and antimonate of potassium
(RivoT, BEUDANT, and DAGUIN*).

c. ARSENIC AND ANTIMONY FKOM COBALT AND NICKEL.
Dilute the nitric acid solution, add a large excess of potassa, 179

heat gently, and conduct chlorine into the fluid until the pre-
cipitate is black. The solution contains the whole of the
arsenic and antimony, the precipitate the nickel and cobalt as
sesquioxides (HivoT, BEUDANT, and DAGUIN, loc. cit.)

8. Methods based upon the Volatility of certain
Chlorides or Metals.

a. TIN, ANTIMONY, ARSENIC FROM COPPER, SILVER, LEAD,
COBALT, NICKEL.

Treat the sulphides with a stream of perfectly dry chlorine, 180
proceeding exactly as directed in 160. In presence of anti-
mony, fill E and F (Fig. 116) with a solution of tartaric
acid in water, mixed with hydrochloric acid. The metals may
be also separated by this method in alloys. The alloy must
be very finely divided. Arsenical alloys are only very slowly
decomposed in this way. In separating arsenic and copper
the temperature must not exceed 200, and chlorine water
should be put into the receiver (PARNELL-J-). If tin and copper
are separated in this manner, according to the experience of
H. ROSE,^ a small trace of tin remains with the copper chloride.

b. STANNIC OXDDE, ANTLMONIOUS OXIDE (AND ALSO
ANTIMONIC ACID). ARSENOUS AND ARSENIC ACIDS, FROM
ALKALIES AND ALKALINE EARTHS.

Mix the solid compound with 5 parts of pure ammonium 181
chloride in powder, in a porcelain crucible, cover this with a

* Compt. rend., 1853, 835; Journ. f. prakt. C7iem.,i J xi, 133.
f Chem. News, xxi, 133. \Pogg. Annal, cxn, 169.



710 SEPARATION. [ 164,

concave platinum lid, on which some ammonium chloride is
sprinkled, and ignite gently until all ammonium chloride is
driven off ; mix the contents of the crucible with a fresh por-
tion of that salt, and repeat the operation until the weight
remains constant. In this process, the chlorides of tin, anti-
mony, and arsenic escape, leaving the chlorides of the alkalies
and alkali-earth metals. The decomposition proceeds most
rapidly with alkali salts. With regard to salts of alkali-earth
metals it is to be observed that those which contain antimonic
acid or stannic oxide are generally decomposed completely by
a double ignition with ammonium chloride (magnesium alone
cannot be separated perfectly from antimonic acid by this
method). The arsenates of the alkali-earth metals are the
most troublesome to decompose ; barium, stronium, and cal-
cium salts usually require to be subjected 5 times to the opera-
tion, before they are free from arsenic, and magnesium arsenate
it is impossible thoroughly to decompose in this way (H.
ROSE*). According to SALKOWSKT)- barium arsenate may be
converted into chloride quite free from arsenic by one ignition
with ammonium chloride ; however calcium arsenate was found
to leave a residue containing arsenic acid even after six igni-
tions with ammonium chloride.

c. MERCURY FROM GOLD (SILVER, AND GENERALLY FROM
THE NON-VOLATILE METALS).

Heat the weighed alloy in a porcelain crucible, ignite till 182
the weight is constant, and determine the mercury from the
loss. If it is desired to estimate it directly, the apparatus
(Fig. 88) may be used. In cases where the separation of mer-
cury from metals that oxidize on ignition in the air is to be
effected by this method, the operation must be conducted in
an atmosphere of hydrogen (Fig. 83). 50).

9. Methods based on the Volatility of Arsenous
Sulphide.

ARSENIC ACID FROM THE OXIDES OF MANGANESE, IRON,
Zi^c, COPPER, NICKEL, COBALT (NOT so WKI.I. KK<>M Oxmi. 03

1 . 1 A I), AND NOT FROM OxiDES OF SlLVER, ALUMINIUM, OR MAG-
NESIUM).

Mix the arsenic-acid compound (no matter whether it has 183

* Pogg. Annal., TAXIII, r>sO; TA-.XIV, 578; cxn, 173.
\ Journ. f. prakt. Cfiem., civ, 138.



164.] METALS OF GROUP VI. 711

been air-dried or gently ignited) with sulphur, and ignite
under a good draught in an atmosphere of hydrogen (Fig.
83) ; the perforated lid must in this case be of porcelain ;
platinum would not answer). The whole of the arsenic vola-
tilizes, the sulphides of manganese, iron, zinc, lead, and copper
remain behind ; they may be weighed directly. After weigh-
ing, add a fresh quantity of sulphur to the residue, ignite as
before, and weigh again ; repeat this operation until the weight
remains constant. Usually, if the compound was intimately
mixed with the sulphur, the conversion of the arsenate into
sulphide is complete after the first ignition. Results very good.
In separating nickel the analyst will remember that the
residue cannot be weighed directly, since it does not possess a
constant composition ; hence the ignition in hydrogen may be
saved ; nickel arsenate loses all its arsenic on being simply
mixed with sulphur and heated. The heat should be moderate
and continued till no more red sulphide of arsenic is visible
on the inside of the porcelain crucible. It is advisable to repeat
the operation. The separation of arsenic from cobalt cannot
be completely effected in this manner even by repeated treat-
ment with sulphur, but it can be effected by oxidizing the resi-
due with nitric acid, evaporating to dryness, mixing with sul-
phur, and reigniting. Smaltine and cobaltine must be treated
in the same manner (H. ROSE*). 1 should not forget to men-



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