Ammonium Cobalti-cyanide, (NH₄)₃Co(CN)₆

Ammonium Cobalti-cyanide, (NH₄)₃Co(CN)₆.H₂O, results on neutralising the free acid with ammonia. A more convenient method consists in decomposing the barium salt with ammonium sulphate solution. On filtering off the insoluble barium sulphate and concentrating the liquor, ammonium cobalti-cyanide crystallises out.3 It crystallises in colourless, transparent tablets, which readily dissolve in water, but are less soluble in alcohol. At 225° C. decomposition sets in, ammonium cyanide and carbonate being evolved, leaving a blue residue. The molecule of water cannot be expelled from the salt without simultaneous decomposition.