Calcium Oxycyanide, Ca(CN)₂.3CaO.15H₂O

Calcium Oxycyanide, Ca(CN)₂.3CaO.15H₂O, can be obtained by evaporating a solution of calcium cyanide in vacuo over sulphuric acid. The undissolved portion left when hydrocyanic acid is allowed to act upon an excess of milk of lime is the same product. It crystallises in small needles which are decomposed by water and alcohol.

At atmospheric temperature gaseous hydrocyanic acid reacts with solid calcium hydroxide, producing the compound 3Ca(OH)₂. 2Ca(CN)₂.13H₂O.