Membrane Equilibria in Photographic Emulsions

Much confusion exists concerning the basic physico-chemical principles involved in "photographic emulsion" processes, not because these principles are particularly difficult to comprehend, but because of their obscurity due to the complexity of the system. The object of the present investigation has been to ascertain to what extent the "membrane equilibrium" theory presented by F.G. Donnan in 1911 may be used as a complete or partial explanation for certain phenomena. The suggestion that membrane equilibrium was playing any appreciable part in photographic emulsion processes cam as the result of recent investigations into the mechanisms of "hyper-sensitization" of color sensitized silver halide photographic materials. In order to make this connection clear it becomes necessary to review very briefly the effect known as hypersensitization.