Three distinct melting point and solubility relations discovered during the last century concern the effects of (1) simultaneous variations of pressure in the fluid and on the surface of the solid in contact with it (equal pressure), (2) independent variations of pressures (unequal presures), and (3) variations only of the elastic strain within the solid. Respectively, these are called the Thomson 1849 principle, the Poynting principle, and the Riecke principle (sensu stricto).

The differences between these theories have not always been fully appreciated. In particular, the intuitive geological hypotheses of Sorby, Van Hise, Becke, and Wagner on pressure solution and related phenomena find theoretical support (in principle at least), not in the first and third principles, but in the Poynting principle. This conclusion was initially recognized by Le Chatelier and is embodied in recent thermodynamic treatments of stress-induced mass-transfer processes.

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