Strontium Thiosulphate, SrS₂O₃

Strontium Thiosulphate, SrS₂O₃, may be formed by boiling sulphur with strontium hydroxide and precipitating with alcohol, by the action of sulphur dioxide on a hot solution of strontium sulphide, or, finally, by precipitating a hot solution of strontium nitrate with sodium thiosulphate. The thiosulphate crystallises out on cooling or on adding alcohol. It forms large hexagonal crystals of composition SrS₂O₃.5H₂O, more stable than the corresponding calcium salt. It is soluble in 4 parts of water at 13° C., and in 1.75 parts at 100° C. It loses 4 molecules of water at 100° C. Dried at 200° C., it has the composition 2SrS₂O₃.H₂O. Further dehydration is accompanied by decomposition, and, on strongly heating, the salt forms a phosphorescent mixture of sulphide, sulphate, and sulphur according to the equation -

4SrS₂O₃ = SrS + 3SrSO₄ + 4S.

Clarke gives the density of a hexahydrate as 2.1566 and 2.1991 at 17° C.