Platinum Sesquisulphide, Pt₂S₃

Platinum Sesquisulphide, Pt₂S₃, is stated to result on oxidising - by exposure to air - thioplatinic acid, H₂Pt₄S₆, obtained by the action of dilute hydrochloric acid upon potassium thioplatinate. Upon desiccation at 120° C. it is converted into a grey powder, of density 5.52. It is readily reduced on warming in hydrogen, and when ignited in air the sulphur burns, leaving a residue of metallic platinum. Mineral acids do not attack the sulphide, and even aqua regia reacts but slowly upon it.