Barium Thiosulphate, BaS₂O₃

Barium Thiosulphate, BaS₂O₃, is prepared by mixing hot concentrated solutions of barium chloride and sodium thiosulphate and allowing to cool. It forms brilliant white crystalline plates of a silvery appearance containing 1 molecule of water, which is lost at 100° C. It has a specific heat of 0.163 and a density of 3.45 at 18° C. When heated out of contact with air it is decomposed into a mixture of sulphate, sulphite, and sulphide. It is only slightly soluble in water and practically insoluble in alcohol. It may be used instead of the sodium salt for iodine titrations.

A double salt with bismuth, Ba₃[Bi(S₂O₃)₃]₂, regarded as containing a complex anion, has been described.