In more than 50 years since its publication, a paper in the Transactions of the Faraday Society by Prout and Tompkins has been extensively cited in the literature. The paper dealt with the kinetics of the thermal decomposition of crystals of potassium permanganate, and suggested a rate equation, which has become known within the field as the Prout-Tompkins equation, for use in the kinetic analysis of solid-state reactions. This equation and its applications in a variety of different fields, including general kinetics of solid-state reactions; continuing work on KMnO4; irradiation effects; pharmaceutical stability studies, and colloid and interfacial chemistry, are discussed.