The carbon and nitrogen present in the organic compound of fusion with sodium metal give sodium cyanide (NaCN) soluble in water. This is converted into sodium ferrocyanide by the addition of sufficient quantity of ferrous sulphate. Ferric ions generated during the process react with ferrocyanide to form the prussian blue precipitate of ferric ferrocyanide. The prussian blue colour is due to formation of ferric ferrocyanide, Fe4[Fe(CN)6]4⋅X2O. Reaction (i) Fe2++6