Cupric Cobalti-cyanide, Cu₃[Co(CN)₆]₂

Cupric Cobalti-cyanide, Cu₃[Co(CN)₆]₂, is obtained as a blue precipitate when potassium cobalti-cyanide is added in sufficient quantity to completely precipitate a copper sulphate solution. It is insoluble in acids, but readily soluble in ammonia. It is decomposed by hydrogen sulphide, copper sulphide being precipitated and hydrogen cobalti-cyanide remaining in solution, from which it can be obtained by concentration. The ammoniacal solution of this salt yields, on evaporation, small blue crystals of a diammoniate, Cu₃[Co(CN)₆]₂.2NH₃.5H₂O.