A study was made on the topochemical processes of hydration-dehydration, ammonation-deammonation, disproportionation and anionic
condensation (certain of which can proceed concurrently) that occur during the production, storage and exploitation of phosphoric
salts and phosphate materials. These processes which can be accompanied by complicated structural transformations and sometimes
by melting were shown to be satisfactorily described by the known kinetic regularities. The detected deviations, that are
associated with the anomalous influence of temperature, the gaseous phase, the size and habit of the crystals and the ageing
of samples on the process rate, were explained in terms of the localization peculiarities of the reactions proceeding on the
surface or in the bulk of the reactant.