Hypo; Chlorine Control; Chlorine Cure; Declor-It; Disodium thiosulfate; Hypo (VAN); S-Hydril; Sodium hyposulfite; Sodium oxide sulfide (Na2S2O3); Sodium thiosulfate (Na2S2O3); Sodium thiosulfate anhydrous; Sodium thiosulphate (Na2S2O3); Sodothiol; Thiosulfuric acid (H2S2O3), disodium salt; Thiosulfuric acid, disodium salt; "Do not confuse synonym sodium hyposulfite with sodium hyposulfite, synonym for di-Na salt of dithionous acid." [ChemIDplus]
It is added in small quantities to ammonium thiosulfate, which is used as a photographic fixing salt. "The hydrated salt is used as an anti-chlorine in bleaching, in wastewater purification, for reduction of dichromate in chromed leather production, and as a solvent for silver chloride in the chloride roasting of silver-containing minerals." [Ullmann] Used in paper bleaching, photography (fixer), silver extraction, dyeing textiles (mordant), and leather manufacturing; Also used as an antidote for cyanide poisoning and in vet medicine for bloat and ringworm; [Merck Index]
Potential combustible dust hazard; Decomposes slowly in water with potential generation of toxic and flammable hydrogen sulfide and corrosive hydrogen sulfite and sulfuric acid; Very soluble in water; Extremely low vapor pressure; May violently decomposes at 223 deg C; [CHEMINFO] ADI = 0-0.7 mg/kg; [JECFA] May be used in food up to 0.1%; [Hawley] See "Potassium thiosulfate."