IS 6212 : 1992 Determination of thiosulphate and other residual chemicals in processed photographic films, plates and papers

1 Scope

1.1 This standard specifies two methods for determination ofresidual thiosulphate in processed films, plates and papers, namelya methylene blue photometric method and a silver sulphidedensitometric method. The methods are not applicable to stabilizedblack -and -white products.

1.2 The methylene blue method measures only thiosulphate.Procedures are specified to cover the range 0.1 to 45 �g of thiosulphate ion per square centimetre. The samplemust be tested within two weeks of processing.

1.3 The silver sulphide method measures thiosulphate,polythionates and all other residual chemicals that react with thesilver ion to give silver sulphide under the conditions of thetest. The results are reported as optical densities, and thedensity increase due to the residual chemicals should be at least0.03, this value corresponding approximately to 0.7 �g/cm₂. Test results from this methodmay be converted to thiosulphate concentration if a correlationgraph is first established for the particular type of materialbeing tested.