sodium thiosulphate is familiar as sodium hyposulphite, the hypo of the photographers.
The second bath of the two-bath chrome tannage consists of a solution of sodium thiosulphate acidified with hydrochloric acid.
This is done by immersing the plate in a solution of sodium thiosulphate (hypo).
Direct titration with sodium thiosulphate solution indicated the presence of 1.68 per cent.
In order to make them permanent the unchanged silver chloride must be dissolved off with sodium thiosulphate.