Studies in photographic sensitivity VII. The action of hydrogen peroxide on single-layer silver halide plates

Abstract

1. (1) Single-grain-layer silver halide plates are only very slightly affected by hydrogen peroxide, no matter what the concentration of H 2O 2 or time of treatment, unless they have been given a previous light exposure. In this case the number of grains showing developability seems to be greater than the sum of those produced by light and hydrogen peroxide separately. 2. (2) The reason suggested for this is that not only developable latent image, but also undevelopable image is produced by light and that the hydrogen peroxide carries this over into developable latent image as well as makes its own proportion of grains developable. 3. (3) It is shown that Clark's hypotheses ( a) that the so-called sensitivity of specks consists of silver oxide or hydroxide, ( b) that the action of hydrogen peroxide is a purely chemical one on this oxide or hydroxide, reducing this to silver, which then makes the plate developable, are untenable, not being supported by experimental facts, and ( c) that reversal is due to peptization of the silver by the hydrogen peroxide, is still open to question. (4) It is further shown that while our original hypothesis that the action of H 2O 2 is one of chemiluminescence is not completely substantiated, it is at least not strongly contraverted except by one fact, namely, that acid H 2O 2 seems to be slightly more effective than alkaline H 2O 2 in producing a latent image. On the other hand, alkaline H 2O 2 may cause peptization of the sensitivity specks and hence work against the formation of developable centres.