K3[Fe(CN)6] + HCl + H2O → HCN + K2[Fe(H2O)(CN)5] + KCl
Potassium hexacyanoferrate(III) react with hydrogen chloride and water to produce hydrogen cyanide, potassium pentacyanoaquaferrate(III) and potassium chloride. Hydrogen chloride - diluted solution. The reaction takes place in a boiling solution.