Intensification of the latent image on photographic plates and films: II. The decomposition of hydrogen peroxide and the mechanism of latent image intensification

Abstract

1. (1) It has been shown that, just as with pure alkaline and acid solutions of hydrogen peroxide and a metal catalyst, alkaline hydrogen peroxide in the presence of gelatin-silver or gelatin-silver sulphide sol, with or without the presence of soluble bromide, is much more easily decomposed than acid hydrogen peroxide under similar conditions. 2. (2) It has also been shown that both acid and alkaline solutions of hydrogen peroxide in the presence of soluble bromide react with silver sulphide, in bulk, to give sulphuric acid or a sulphate and colloidal silver bromide. 3. (3) Colloidal silver was found to dissolve to a greater or less extent in gelatin-hydrogen peroxide solution with a pII of 5.5 or less, giving rise to silver ions which when soluble bromide is also present form colloidal silver bromide. 4. (4) These facts indicate that intensification of latent image, and probably also the effect of hydrogen peroxide on sensitivity or the production of latent fog, is chemical in nature as Clark has contended and that a chemiluminescence mechanism while it has not been disproved is not necessary in order to explain the phenomenon. 5. (5) A chemical mechanism is proposed based on Hickman's recent theory of the formation of latent image by light. 6. (6) It is proposed that the bromine set free by the action of acid peroxide on the soluble bromide in the plate being very limited in quantity acts on the silver sulphide speck to form metallic silver, which in turn may be partly converted by the acid hydrogen peroxide into silver ions, and if any soluble bromide is left in the vicinity some colloidal silver bromide is formed containing on its surfaces adsorbed silver ions. It is believed that any one or all of these, metallic silver, silver ions, or colloidal silver bromide with silver ions adsorbed, produces a greater degree of developability of the grain than the original silver sulphide speck. 7. (7) This view is supported by the experimental fact that if soluble bromide is largely removed from a plate by action of silver nitrate (less than an excess), hydrogen peroxide produces very little if any intensification of latent image.