Physical and Chemical Behavior of Solids. 215 



pie, — namely, that non-uniform pressure does cause a lowering 

 of melting point, — which follows either from Riecke's formula 

 or from the equations of the present paper. Equation III can, 

 however, be applied much more generally, for it holds for crys- 

 talline aggregates and is not subject to any limitations as 

 regards the magnitude of the effective stress. Hence the 

 general principle has a much wider significance in the co-ordi- 

 nation of geological observations than has hitherto been 

 attributed to it. 



The Phenomenon of Regelation. 



This type of compression accounts easily for regelation, a 

 phenomenon which cannot in general be produced by uniform 

 pressure, because uniform pressure raises the melting point of 

 most substances. 



Consider a block of ice at 0° supporting a loaded wire. The 

 pressure exerted by the wire depresses the melting point of the 

 ice by the amount At ; immediately beneath the wire, there- 

 fore, we have at any instant a thin layer of ice at —At in equi- 

 librium with water at —At. The water escapes round the 

 wire and so comes in contact with ice at 0° ; such a system 

 is, however, unstable, for under these conditions water cannot 

 remain subcooled. Consequently the water freezes, thus form- 

 ing again a solid block above the wire. 



The process by which a mass of loose snow is compacted into 

 a block of ice is identical with this. The pressure, due to the 

 superincumbent material, lowers the melting point at the sur- 

 face of contact of adjacent grains ; the water at —At flows into 

 the interstices where the pressure is smaller and freezes again. 

 This process continues until the interstices are all filled up, that 

 is, until a solid block of ice is formed. 



According to Le Chatelier* : " This is a type of consoli- 

 dation which is in every respect comparable with that which I 

 have given for the setting of cement. In either case we have 

 a solid substance, which is not in equilibrium — either because 

 of its chemical condition or because it is compressed — in con- 

 tact with a supersaturated solution or vapor, the temporary 

 formation of which renders possible the return to equilibrium 

 conditions." 



Influence of Unequal Pressure upon the Solubility of 

 /Solid Substances. 



Considerations in every respect analogous are applicable to 

 systems of a solid in contact with water or other solvent : in 

 such cases pressure acting in excess on the solid increases its 

 * Zs. phys. Chem., ix, 838, 1892. 



