METHODS FOR THE STUDY OF THE KINETICS OF THE CHEMISTRY OF PHOTOGRAPHIC PROCESSES .2. DETERMINATION OF THE KINETICS OF THE BLEACH PROCESS ATSMALL FILM DISKS

The kinetics of the bleach process was studied with small film discs o f 15 mm diameter. The discs were attached at a cylinder which was rota ted and inserted for a given but varying time into the bleach bath. Th e silver bromide formed during the bleaching was dissolved with ammoni a or ethylenediamine. After neutralisation with diluted nitric acid, t he silver was determined photometrically based on a redox reaction. A plot of the absorbance against the bleach time yielded the bleach rate . N-tetra-alkylated p-phenylenediamines were chosen as reducing agent because their primary oxidation products, the p-semiquinonediimines, e xhibit strong absorption in the visible part of the spectrum. The resi dual silver was determined in the same way photometrically after oxidi zing it with half concentrated nitric acid and neutralizing the soluti on with ammonia or ethylenediamine. The most suitable conditions for b oth the dissolution of the silver halide and the quasi-homogeneous red ox reaction were determined.