Calcium ferrocyanide, Ca₂Fe(CN)₆

Calcium ferrocyanide, Ca₂Fe(CN)₆.xH₂O (where x = 11, or 12,), may be obtained by boiling Prussian blue with the calculated quantity of milk of lime. It is also formed when hydrogen cyanide is passed into a suspension of lime and ferrous hydroxide in water. The salt crystallises in pale yellow triclinic prisms, which are more soluble in cold water than in hot.

The density of the salt is 1.68. At 500° C., in the absence of air or oxygen, it decomposes, yielding calcium cyanamide. Thus: -

Ca₂Fe(CN)₆ = 2CaCN₂ + Fe + N₂ + 4C.

The osmotic pressures of solutions of calcium ferrocyanide in water have been determined for various concentrations,5 and the results indicate that the negative radicles are associated, yielding the double ion [Fe(CN)₆]₂''''''''.