Sodium thiosulfate (sodium hyposulfite) is a colorless crystalline compound, stable on air up to 80 °C, in vacuum decomposes at 300 °C to sodium sulfite and sulfur. Soluble in water. Sodium thiosulfate crystallize from water solutions in temperature range 11-48 °C as pentahydrate. Good reducing agent. The thiosulfate anion reacts stoichiometrically with iodine, reducing it to iodide as it is oxidized to tetrathionate
Sodium thiosulfate is produced chiefly from liquid waste products of sodium sulfide or sulfur dye manufacture. It is also produced from the action of sodium sulfite on sulfur in aqueous solution.
Because sodium thiosulfate dissolves silver salts, its major use is in photography for dissolving silver halides from photographic emulsions. In this role it is known as a fixer and is used for both film and paper;
Sodium thiosulfate is also used in the tanning of leather;
in bacteriological water assessment;
and in treating cyanide poisoning;
for automatic hand warmers;