The Stability of Concentrated Thiosulphate Solutions at High Temperature. Part II. The Loss of the Sulphite

The decomposition of concentrated thiosulphate fixers at elevated temperatures occurs because the sulphite is converted into sulphate and thiosulphate in a reaction catalyzed by the thiosulphate. When the sulphate is gone the thiosulphate decomposes giving sulphur and sulphurous acid which latter is also lost by the above mechanism.