Calcium Thiocyanate, Ca(CNS)₂

Calcium Thiocyanate, Ca(CNS)₂, may be prepared synthetically by heating a 20-per-cent. ammonia solution in an autoclave with carbon disulphide and lime,

2NH₃ + 2CS₂ + 2Ca(OH)₂ = Ca(CNS)₂ + CaSO₄.

The sulphuretted hydrogen may be removed by carbon dioxide and the carbonate by filtration. It can also be prepared by the action of thiocyanic acid on calcium carbonate, or by boiling cuprous or ammonium thiocyanate with lime and passing carbon dioxide through the solution to remove excess of lime. The salt crystallises from aqueous solution with difficulty. The formula of the crystals is Ca(CNS)₂.3H₂O, and they are very deliquescent and soluble. The saturated solution boils at 143° C., and has an action on paper similar to that produced by caustic soda solution.

It forms a series of double salts with the heavy metal thiocyanates, and with mercuric cyanide it gives crystals of the compound Ca(CNS)₂.2Hg(CN)₂.8H₂O.