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Digital Archive of Toyo Bunko Rare Books

IX. Treatment of the Filtrate from Precipitates formed by Hydrogen Sulphide in
Presence of Acid.

The filtrate from the sulphides precipitated by hydrogen sulphide in the
acidified solution from which copper had been removed as cuprous sulphocyanide
was neutralized carefully with ammonium hydroxide (no precipitation taking
place in the presence of tartaric acid) and treated with hydrogen sulphide. The
precipitate should contain the sulphides of iron, nickel, cobalt, and possibly copper
in traces, if compounds of these elements are present. The filtrate was rejected.
The precipitate was treated on the filter with dilute hydrochloric acid and the
residue washed. The filtrate was reserved for the estimation of iron. The insol-
uble precipitate was ignited with the filter and the residue dissolved in aqua regia,
the solution evaporated to dryness, the residue taken up in hydrochloric acid,
the solution treated with hydrogen sulphide, and any precipitate filtered off,
ignited, and weighed as copper oxide.

The filtrate from the copper sulphide, or the solution in which hydrogen
sulphide gave no precipitate in presence of hydrochloric acid, was carefully made
alkaline with ammonium hydroxide, and hydrogen sulphide was passed in. The
precipitate, filtered off and ignited, was weighed as nickelous oxide and cobaltic
oxide. Any considerable residue obtained at this point should be treated for
the separation of nickel and cobalt by the double nitrite process; in the case of
the very small residues actually obtained in this work, the simple test for cobalt
with the borax lead was all that could be made.

The filtrate reserved after treatment of the sulphides of iron, nickel, cobalt,
and copper with hydrochloric acid, was boiled, treated with bromine water, and
made alkaline with ammonium hydroxide. The precipitate was filtered off,
washed, ignited, and weighed as ferric oxide.

X. Special Tests for Tin.

In the special tests for tin alone, it was usual to attack the material with
nitric acid, desiccate, take up into nitric acid and water, boil, heat with ammonium
hydroxide, and then with nitric acid, filter off the insoluble material, ignite and
weigh. By this treatment all the tin originally present was gathered in the residue.
The residue was fused with a mixture of sodium carbonate and sulphur, the melt
extracted with water. The extract was acidified, and the precipitate thus obtained
collected, washed with ammonium nitrate, ignited and weighed. In the ignition
any arsenic present would be volatilized, so that the residue should consist only
of stannic oxide and possibly antimony oxide. If the residue was considerable,
the separation of antimony and tin was effected by the method previously
described in section IV. If the residue was inconsiderable and no indication of
antimony had been noted in the color of the sulphide, the qualitative confirmatory
test for tin was made at once.

In the main, the procedure outlined above was followed closely; but great
care was taken in the scrutiny of final products, which were often subjected to
special analysis to make sure that the separations had been as nearly complete
as possible. The analyses were made, almost entirely, by Dr. Martha Austin
Phelps and Dr. Charles Paxson Flora.