Stannic Sulphide Mosaic Gold

Stannic sulphide, SnS2, 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 H2Sn03. 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 converts all the tin to sulphide, the sulphides being very much less soluble than the products of the hydrolysis. 

Materials stannous chloride, SnCl2-2H20,45 grams = 0.2 F.W. hydrogen sulphide (Note 13 (c), page 20). powdered sulphur, ammonium chloride. 

8-inch test tube, stopper, and glass tube. 

6- inch sand bath and sand, iron ring and ring stand. 

---

More rarely use is made for the same purpose of other substances such as strontium and calcium chromates, lead oxychloride (Cassel yellow), lead protoxide, arsenic sulphide (orpiment), stannic sulphide (mosaic gold), potassium cobaltinitrite (cobalt yellow), etc. 

Besides powdered metals, certain metallic compounds are sometimes used for the same purposes, e.g., stannic sulphide (mosaic gold), antimony sulphide (iron bronze) and various oxygenated compounds of tungsten (tungsten bronzes). 

---