The use of thermal analysis for the identification of clay minerals differs from its use for the determination of phase transitions in that the latter are, in theory at least, reversible and occur at definite temperatures while the dehydration reactions utilized in the identification of clays are monotropic, irreversible decompositions proceeding at a velocity which increases continuously as the temperature is raised. There is, therefore, no definite transformation temperature and the temperature of the arrest registered on a heating curve depends on the heating rate employed.

In view of the increasing importance of thermal analysis it was decided that an attempt should be made to study the implications of this. An investigation of the kinetics of the dehydration reaction seemed the most obvious approach.