214 Johnston and Adams — High Pressures on the 



dT\ V, V 



d'l\ ~ dV ~ V s Vi ( IV ) 



or expressed in words, the ratio of the lowering of freezing 

 point of the solid phase, when this alone is subject to a given 

 pressure, to that observed with the same (given) pressure acting 

 uniformly on both phases, is equal to the ratio of the (specific) 

 volume of the solid phase to the change of (specific) volume on 

 freezing. 



This equation shows how many times greater the melting 

 point lowering is when the pressure acts only on the solid 

 phase. For example, the melting point of ice is lowered by 

 unequal pressure 12 times as much (or 0*09° per atm.) as by 

 uniform pressure (0*0075° per atm.); in general A7 r 1 /A7 2 is 

 much greater than 12, because the fractional change of volume 

 accompanying melting is usually much smaller than it is in the 

 exceptional case of ice. 



In a paper first published in 1894, E. Kiecke* discussed the 

 effect of a one-sided pressure (stress) on the melting point of 

 ice; quite recently he has re-stated his conclusions in a second 

 paperf, the general reasoning of which — apart from the mathe- 

 matical formulae — is identical with that of the paragraphs, 

 immediately subsequent to this, dealing with regelation and 

 with the influence of unequal pressure upon solubility. 

 Kiecke's formula for the lowering of melting point of ice 

 effected by the stress Z (tensile or compressive) is 



A 7\= -aZ 2 



where (for ice) a has the value 0*00036 when Z is expressed 

 in kg. per sq. cra.J ; but he appears to consider the formula 

 valid only for small values of Z. For this reason, and for the 

 reason that Riecke's formula was developed, and therefore is 

 valid only for the case of a single crystal, his formula is less 

 generally applicable than equation III (p. 213) of the present 

 paper ; moreover, within its range, it leads to much smaller 

 values of the lowering of melting point. § 



The divergence between the numerical results of the two 

 formulae is, so far at least as the arguments of the present 

 paper are concerned, of secondary importance, for in general 

 we are altogether ignorant of the nature and magnitude of the 

 stresses to which rocks have been exposed. The important 

 thing, especially from a geological standpoint, is the princi- 



* Nachr. Ges. Wiss. Gottingen, 1894, 278 ; Ann. Physik, liv, 731, 1895. 

 f Centralblatt Min. Geol., 1912, 97-103, q.v. 

 J One atmosphere = 1*033 kg. per sq. cm. 



§ With ice, the lowerings produced by 1 and 10 atmospheres are 0*00037° 

 and 0'037°, according to Eiecke ; 0"09° and 0*9°, according to equation III. 



