<Dl> <Dd> 2 S O + AgBr → (Ag (S O)) + Br </Dd> </Dl> <Dd> 2 S O + AgBr → (Ag (S O)) + Br </Dd> <P> This application as a photographic fixer was discovered by John Herschel . It is used for both film and photographic paper processing; the sodium thiosulfate is known as a photographic fixer, and is often referred to as' hypo', from the original chemical name, hyposulphite of soda . </P> <P> Sodium thiosulfate is a component of an alternative lixiviant to cyanide for extraction of gold . However, it forms a strong soluble complex with gold (I) ions, (Au (S O)). The advantage of this approach is that thiosulfate is essentially not toxic and that ore types that are refractory to gold cyanidation (e.g. carbonaceous or Carlin - type ores) can be leached by thiosulfate . Some problems with this alternative process include the high consumption of thiosulfate, and the lack of a suitable recovery technique, since (Au (S O)) does not adsorb to activated carbon, which is the standard technique used in gold cyanidation to separate the gold complex from the ore slurry . </P>

Why sodium thiosulphate is known as hypo solution