STANNIC SULPHIDE 271PREPARATION 43
STANNIC SULPHIDE (MOSAIC GOLD), SnS 2
Stannic sulphide, SnS 2 , is the higher sulphide of tin, and can
be prepared by direct combination of the metal or, still better, of
the lower sulphide, SnS, with sulphur. Under ordinary conditions
these two substances will not react at a temperature below that
which will decompose stannic sulphide. If, however, they are
mixed with ammonium chloride the presence of this substance
makes possible the combination at a lower temperature. The
stannic sulphide formed in this way appears as soft, glistening,
yellow crystals. It is used as a bronzing powder, and is known
under the name of mosaic gold. In physical properties it is very
different from the stannic sulphide which can be precipitated by
hydrogen sulphide from a solution of stannic chloride.
Stannous chloride, the raw material, if it is fresh, is completely
soluble in a very little water; with much water it hydrolyzes
somewhat with precipitation of basic stannous chloride, Sn(OH)Cl.
If the stannous chloride is old, it has probably become partially
oxidized to stannic chloride, and the latter extensively hydrolyzed
to insoluble stannic acid H 2 Sn0 3. A clear solution is therefore not
obtained when the stannous chloride is treated with a large amount
of water. Nevertheless the addition of ammonium sulphide con-
verts all the tin to sulphide, the sulphides being very much less
soluble than the products of the hydrolysis.
Materials: stannous chloride, SnCl 2 -2H 2 0,45 grams = 0.2 F.W.
hydrogen sulphide (Note 13 (c), page 20).
powdered sulphur,
ammonium chloride.Apparatus: 2-liter common bottle.
hydrogen sulphide generator.
250-cc. beaker.
5-inch filter.
mortar and pestle.
8-inch test tube, stopper, and glass tube.
6-inch sand bath and sand.
iron ring and ring stand.
Bunsen burner.