Optical Sensitizing of Silver Halides by Dyes II. The Mechanism of Optical Sensitizing and the Quantum Equivalent

The photolysis of silver bromide sensitized with certain acid and basic dyes has been followed by chemical and photometric determination of the silver produced. It was found that in the absence of halogen acceptors the dye is progressively bleached, but in the presence of halogen acceptors it is recovered chemically unchanged. However, the dye actually combines with the bromine released but is regenerated on giving up the bromine to another less active acceptor. The maximum of sensitivity is found to occur considerably before adsorption‐saturation, and at about the same adsorption‐density for both photolysis and photographic sensitivity. The apparent desensitizing action of sensitizing dyes at higher adsorption‐densities is ascribed to the facility of rebromination by the dye:bromine addition compound.So long as the photographic yield is proportional to the adsorption‐density of the dye an initial quantum equivalent of unity is found—one quantum of light absorbed by the dye produces one silver atom. In re...