Thiosulphates

Thiosulphates are the salts of a thiosulphuric acid (H₂S₂O₃). The most important, both chemically and commercially, is the sodium salt, which is commonly known as "hyposulphite of soda." It is a colourless crystalline salt of composition Na₂S₂O₃5OH₂, readily soluble in water. It is prepared by boiling a solution of sulphlte of sodium with powdered sulphur, and is also obtained from the waste liquors of the soda manufacture. It is used in chemistry especially as a reagent for numerous volumetric analyses. It is employed to a large extent in photography as a fixing agent [PH0TOGRAPHY], as its solution dissolves the iodide or chloride of silver. It is also employed as an antichlore, i.e. to remove the last traces of chlorine from materials which have been bleached by that gas.