STUDIES OF THE MECHANISM AND THE KINETICS OF THE PHOTOGRAPHIC BLEACH PROCESS .1. SIMULATION OF THE BLEACH PROCESS ON A ROTATED SILVER DISC AND DETERMINATION OF THE BLEACH RATE

The photographic bleach process was simulated by chemical oxidation of a rotating silver disc with both iron(III)-ethylenediamine tetraaceti c acid (EDTA) and iron(III)-propylenediamine tetraacetic acid in the p resence of halide ions. The insoluble silver salt formed on the surfac e of the disc was subsequently reduced galvanostatically in order to d etermine quantitatively the amount of silver(I) formed during the chem ical oxidation. Thus, by varying the bleach time the formation rate of silver halide was obtained and by varying the rotation speed of the s ilver disc the rate constants for the electron transfer between silver and iron(III)-EDTA could be determined. The dependence of the bleach rate on both the kind and the concentration of the iron(III)-complex a nd the halide was explained with the theory of mixed potential and mix ed current. For this purpose the current potential curves were recorde d at the silver disc for the electrochemical reduction of the iron(III )-complexes, as well as for the electrochemical formation of the silve r halides. The procedure described allows a rapid study of the efficie ncy of photographic bleach baths.