The charge effect in relation to the kinetics of photographic development. I. The general effect

Abstract

The view is rather widely accepted 1-:, tha t the reduction of silver ions in normal chemical (direct) development takes place at or near the interface between silver halide and silver. At the start of development, the interface is tha t between silver halide and the latent-image material (very probably silver); in the later stages of development of the individual grains, the silver involved is tha t formed by prior reduction of part of the silver halide. Once the interface is accepted as the locale of the reduction of silver ions, it remains to be decided whether or not the developing agent must be present at the interface before the reduction can occur. On the basis of what m ay be termed the catalytic hypothesis, development depends primarily upon the adsorption of silver ions to the silver and the accompanying alteration in the act ivat ion energy conditions of the reaction between the silver ions and the developing agent. An alternative view holds tha t the silver nuclei act simply as electrodes which can accept electrons from the developer at any point on the metal surface and can conduct the electrons to the interface. The per t inent experimental evidence does not allow a clear-cut decision between these views, but the trend is against the electrode hypothesis. The evidence on the adsorption of hydroquinone, in particular, seems incompatible with the electrode scheme. The kinetics of development by hydroquinone indicate tha t adsorption of the bivalent ion occurs prior to the reaction. 6 However, both direct adsorption measurements 7 and kinetic measurements 8 fall to indicate adsorption of hydroquinone to silver. The obvious implication is tha t the hydroquinone is adsorbed (as bivalent ion) to the silver bromide surface or to the interface. There is indirect evidence for the adsorption to silver bromide, 9 and it