Auric sulphide, Au₂S₃

Gold does not combine directly with sulphur, but at -2° C. a rapid current of hydrogen sulphide transforms aurichloric acid, HAuCl₄, in dilute solution in normal hydrochloric acid, into pure auric sulphide. Lithium aurichloride, LiAuCl₄,2H₂O, at -10° C. is converted by hydrogen sulphide into a mixture of lithium chloride and impure auric sulphide, with evolution of hydrogen chloride. After extraction of the lithium chloride with alcohol, the sulphide is dried in a current of nitrogen at 70° C. It is an amorphous, black powder, at once decomposed by the action of water. At 200° to 205° C. it is converted into a mixture of gold and sulphur. It forms double sulphides with the alkali-metals; and also unites with the sulphides of elements of weak positive, or even of negative,- character, such as arsenic, tellurium, molybdenum, and carbon. The last class of compound is probably to be regarded as an auric salt of a complex acid containing sulphur and one of the elements mentioned.