Also found in: Dictionary, Thesaurus, Medical, Wikipedia.
sodium thiosulfate,Na2S2O3, colorless crystalline compound that is more familiar as the pentahydrate, Na2S2O3·5H2O, an efflorescent, monoclinic crystalline substance also called sodium hyposulfite or "hypo." Sodium thiosulfate is readily soluble in water and is a mild reducing agent. Because it dissolves silver salts, its major use is in photography for developing film. It is also used in chrome-tanning 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, sulfur dioxide, and sulfur by a process that involves several steps.
(also sodium hyposulfite, N2S2O3), colorless crystals freely soluble in water (41.2 percent by weight at 20°C, 69.9 percent at 80°C). Sodium thiosulfate forms several crystal hydrates, of which only the pentahydrate Na2S2O3·5H2O is used in industry and in the laboratory.
Sodium thiosulfate is obtained by boiling a solution of sodium sulfite with sulfur in powder form: Na2SO3 + S = Na2S2O3. It is used as a fixing agent in photography and for determinations of iodine in iodometry; it also finds use in the textile industry and in other fields. In medicine, sodium thiosulfate is used as a desensitizer, an antiphlogistic, and an antitoxic agent. The antitoxic effect is based on the ability of sodium thiosulfate to form nontoxic compounds, including sulfites with arsenic, thallium, mercury, and lead and rhodanides with hydrocyanic acid. Sodium thiosulfate is usually administered intravenously (as a 10–30 percent solution) to those suffering from arthritis, dermatosis, poisoning, and illnesses related to allergies.