Sodium thiosulfate

Sodium thiosulfate (Na₂S₂O₃) is a colorless crystalline compound that is more familiar as the pentahydrate, Na₂S₂O₃5H₂O, an efflorescent, monoclinic crystalline substance also called sodium hyposulfite or “hypo.”

The thiosulfate anion is tetrahedral in shape, and is notionally derived by replacing one of the oxygen atoms by a sulfur atom.

Because Sodium thiosulfate dissolves silver salts, its major use is in photography for developing film. It is also used in the tanning of leather and in chemical manufacture. Sodium thiosulfate is produced chiefly from liquid waste products of sodium sulfide or sulfur dye manufacture. It is also produced from sodium carbonate and sulfur dioxide.

UK English - thiosulphate