Also termed sodium hyposulfite or hypo, this inorganic salt enjoys a central role in photography because of its usefulness in dissolving silver salts during development of film emulsions. Sodium thiosulfate is also heavily employed in the tanning industry and as a chemical intermediate or reagent for the synthesis of other, more complex, chemicals.
Produced chiefly from side products generated during manufacture of sodium sulfide and sulfur dyes, sodium thiosulfate can also be synthesized from sodium carbonate, sulfur dioxide, and sulfur by a multi-step process. As a pharmaceutical agent, sodium thiosulfate is useful in the treatment of early stages of active rheumatoid arthritis and is also utilized to treat lupus erythmatosus. The most important medicinal application, however, is as an antidote to cyanide poisoning. Sodium thiosulfate has a formula weight of 248.17 and is very soluble in water, but insoluble in ethanol.
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