Barium Cobalti-cyanide, Ba₃[Co(CN)₆]₂

Barium Cobalti-cyanide, Ba₃[Co(CN)₆]₂.Aq., is a convenient starting-point for the preparation of other metallic cobalti-cyanides by double decomposition. It may be prepared by adding barium carbonate to a solution of the free acid; but a better method consists in exposing to aerial oxidation a mixture of cobalt sulphate and the cyanides of hydrogen and barium. The salt crystallises out in colourless prisms, which are readily soluble in water, but not in alcohol. They contain some 20 or 22 molecules of water.