Sodium Formaldehyde BisulfiteSodium thiosulfate (Na2S2O3), also spelled as Sodium thiosulphate or thio sulphate.It is a colorless crystalline compound that is more familiar as the pentahydrate, Na2S2O3•5H2O. Sodium thiosulphate is an efflorescent, monoclinic crystalline substance also called sodium hyposulfite or “hypo” Sodium Thiosulphate is manufactured from liquid waste products of sodium sulfide or sulfur dye.