Sodium thiosulfate used in fixers, plating,, reductant, dechlorinating agent, ... 12~16-------Sodium thiosulfate (Na2S2O3), also spelled sodium thiosulphate, is a colorless crystalline compound that is more familiar as the pentahydrate, Na2S2O3 ... •5H2O, an efflorescent, monoclinic crystalline substance also called sodium hyposulfite or “hypo.”The thiosulfate ...