Sodium cyanide, NaCN

The Sodium cyanide, NaCN, is formed by the action of hydrocyanic acid on sodium hydroxide; by heating sodium ferrocyanide in absence of air, or with sodium carbonate and charcoal; from atmospheric nitrogen by heating anhydrous sodium carbonate with iron-filings in air; by heating sodium in ammonia at 350° C., and converting the resulting sodamide into cyanide by heating with charcoal; and by the action of ammonia on a mixture of fused sodium cyanide, sodium, and charcoal, the sodium cyanamide, Na₂CN₂, formed being converted by the charcoal into sodium cyanide.

Sodium cyanide forms colourless crystals, very soluble in water, the weak acidic character of the hydrocyanic acid inducing hydrolytic dissociation, thus imparting to the solution a strong alkaline reaction, and an odour of hydrocyanic acid. The anhydrous salt is converted by boiling with 75 per cent, alcohol into the dihydrate, a substance converted by slow evaporation over lime into the yellow, crystalline monohydrate.

For the heat of formation of sodium cyanide from its elements, Berthelot gives 22.6 Cal., and Joannis 23.1 Cal. The heat of neutralization of hydrocyanic acid by sodium hydroxide is between 2.77 and 2.9 Cal., its low value being due to the heat absorbed by the ionization of the weak acid. At 9° C. the heat of solution of the anhydrous salt is 0.5 Cal., and of the dihydrate 4.4 Cal. It is very poisonous.