Platinic Sulphide, Platinum Disulphide, PtS2, is obtained as a dark precipitate on passing hydrogen sulphide into an aqueous solution of platinum tetrachloride. It is necessary to effect the precipitation at about 90° C., otherwise coloured precipitates are obtained consisting most probably of thioplatinic acids.
Platinic sulphide also results on heating chlor-platinic acid, decolorised by treatment with sulphur dioxide, to 200° C. in sealed tubes.
Obtained by either of these methods, platinum disulphide is a black deposit which readily oxidises in air, yielding an oxysulphide, PtOS.xH2O, and must therefore be dried in an atmosphere of an inert gas. If strongly heated in the last named it dissociates, platinum monosulphide resulting; but when ignited in air, it burns, leaving a residue of metallic platinum. Acids attack it with difficulty, and it is relatively insoluble in alkali sulphides.
A Polysulphide, of formula PtS15(NH4)2.2H2O, is described as resulting on addition of ammonium polysulphide to chlor-platinic acid. It yields large, red, rhombic crystals which, when dry, are stable. |