A colourless, soluble crystalline compound, NH4NCS. It is made by the action of hydrogen cyanide on ammonium sulphide or from ammonia and carbon disulphide in ethanol. On heating, it turns into its isomer thiourea, SC(NH2)2. Its solutions give a characteristic blood-red colour with iron(III) compounds and so are employed as a test for ferric iron. Ammonium thiocyanate is used as a rapid fixative in photography and as an ingredient in making explosives.