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Abstract
The reasons for the validity of Elvegard’s equation governing the relation between contrast and time of development are examined and explained in terms of a first order reaction. The Elvegard constant is found to approximate to contrast at infinite time of development and to be independent of rate of reaction. By combining the Sheppard-Mees and Elvegard equations together a simple equation can be obtained which may be plotted as an alternative to the Elvegard equation. The experimental data indicate that colour development follows first order kinetics.