HYPOSULPHITE OF SODA, the name originally given to the salt, still in general use by photographers as a fixing agent, known in chemistry as sodium thiosulphate, One mole cule of the salt crystallizes with five molecules of water. In systematic chemistry sodium hyposulphite is a salt of hyposulphur ous acid, to which Schutzenberger gave the formula but which Bernthsen showed to be (See SULPHUR; and HYDROSULPHITE OF SODA.)