Platinum Disulphide, PtS₂

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.