Certain sulphides, in presence of a small amount of moisture were found to catalyse the reaction between hydrogen sulphide and sulphur dioxide. The kinetics of this reaction was studied in a closed system, using an all-glass, gas circulation pump.
The partial pressure of water in the reacting system was maintained constant with the aid of a hygrostat [mixture of a hydrated salt and its anhydrous form (or lower hydrate)]. The higher the partial pressure of water, the greater was the velocity of reaction, for a given catalyst.
Of the sulphides employed, cobalt thiomolybdate was found to be the best catalyst. Cobalt sulphide and molybdenum sulphide were less efficient. Next in order of efficiency, was silver sulphide.
Boron trifluoride and anhydrous aluminium chloride were found to have no catalytic effect on the union between hydrogen sulphide and sulphur dioxide.
The mechanism of the reaction could be explained on the basis of the formation of thiosulphurous acid, as the primary product.