Cyanide is a compound containing the –CN group. Organic cyanides are called nitriles. Inorganic cyanides are salts or esters of hydrocyanic acid (HCN), a volatile weak acid; both are highly toxic. Sodium cyanide (NaCN) is made by the Castner process: ammonia is passed through a mixture of carbon and fused sodium. Both sodium cyanide and potassium cyanide (KCN) are both deadly poisonous and have a characteristic smell of almonds. The cyanide ion (CN-) is a pseudohalogen, and forms many complexes. Cyanides are used in the extraction of gold and silver, electroplating, and casehardening.