Sodium Thiosulphate is a colourless crystalline compound with a chemical formula of Na2S2O3. It is sometimes spelt with a letter 'f' as in Sodium Thiosulfate, both spellings referring to the same chemical.
One of the most useful characteristics of Sodium Thiosulphate is its ability to react with dilute acids to produce Sulphur, Sulphur Dioxide and Water. This reaction is sometimes referred to as a 'clock reaction'.
In analytical chemistry, Sodium Thiosulphate is used as a titrant in iodometry, as the Thiosulphate anion reacts with Iodine. Sodium Thiosulphate is used in 'iodine clock' experiments.
Sodium Thiosulphate is used in photographic processes both for processing film and photographic paper, where Sodium Thiosulphate is widely known as 'hypo' from the original chemical name 'Hyposulphite of Soda. When used in this way, Sodium Thiosulphate or 'hypo' is regarded as a photographic chemical fixer.
Sodium Thiosulphate forms a strong complex with Gold ions and, as such, is sometimes used as an alternative to Cyanide in the process of Gold extraction.
Sodium Thiosulphate has a number of medical uses including as a treatment for patients with end-stage renal disease and in chemotherapy treatments. Sodium Thiosulfate is also used as an antidote to Cyanide poisoning. It can be used in footbaths as an anti-fungal treatment and for ringworm.
Elsewhere, Sodium Thiosulfate is used in chemical heating pads and hand-warmers, in the production of bleach, in pH testing of bleach substances, to de-chlorinate tap water for aquariums and to treat effluent from waste water treatments prior to release into rivers and streams.
Sodium Thiosulphate is used to lower levels of Chlorine in swimming pools and spas and to remove Iodine stains. Sodium Thiosulphate reacts with Bromine to produce harmless products and as a result of this Sodium Thiosulfate solutions are often found in chemical laboratories where work with Bromine is being undertaken.
Sodium Thiosulphate is used in the assessment of water from a bacteriological perspective and also in leather tanning.
Sodium Thiosulphate or 'hypo' should always be stored in tightly sealed containers, away from incompatible materials such as strong acids, Iodine and Mercury. The Material Safety Data Sheet (MSDS) provided by your supplier should always be read before working with or handling hypo. Wear appropriate protective clothing and store containers away from children and animals.