The name originally given to the substance known in chemistry as sodium thiosulphate, Na 2 S 2 O 3; the earlier name is still commonly used, especially by photographers, who employ this chemical as a fixer. In systematic chemistry, sodium hyposulphite is a salt of hyposulphurous acid, to which Schutzenberger gave the formula H 2 S0 2, but which Bernthsen showed to be H 2 S 2 0 4. (See SULPHUR.)