A mathematical theory of thick emulsions, based upon a previously published theorem, is developed. All important properties of the H and D curve and the Kaiser function are deduced and physical interpretations of the parameters of both functions are given. Deviations from Beer's law by a photographic emulsion are seen to be responsible for the occurrence of reciprocity failure phenomena. The occurrence of a reverse primary process is shown to be capable of invalidating the Poisson distribution of exposure.
Arno Arrak, "Theory of Thick Emulsions and the Kaiser Function," Appl. Spectrosc. 13, 143-149 (1959)