Auric cyanide, Au(CN)₃

Potassium auricyanide is transformed by strong acids such as hydrofluosilicic acid into auric cyanide. The reaction is more complex than is indicated by the equation

2KAu(CN)₄+H₂SiF₆ = 2Au(CN)₃+K₂SiF₆+2HCN.

Evaporation of the solution over sulphuric acid yields the salt in large colourless leaflets of the formula Au(CN)₃,3H₂O or 2Au(CN)₃,3H₂O, which melt at 50° C., and decompose at higher temperatures. On evaporation, its solution in water decomposes.