GEOPHYSICAL LABORATORY. 133 



(6) On the effect of high pressures on the physical and chemical behavior of solids. John 



Johnston and L. H. Adams. Am. Jom-. Sci. (4), 35, 205-253. 1913. 



This paper is an endeavor to review and define the present status of our 

 knowledge of the effect of high pressures on the behavior of sohds, to recon- 

 cile some of the conflicting statements to be found in the literature pertain- 

 ing to the subject, and to indicate the conclusions which may justifiably be 

 drawn from the available evidence, especially with regard to their aj)plica- 

 tion to the discussion of geological phenomena. Some of this confusion 

 results from the emjjHjyment of indefensible criteria in ascertaining the 

 character and magnitude of the change produced by pressure, as, for 

 example, in determining the effect of pressure in promoting chemical reac- 

 tion between solids; but in the main it is due to failure to take into account 

 the fact that the effects produced depend upon the character, or mode of 

 action, of the compression. The effects are different, namely, according as 

 we are dealing with pressure uniform in all directions (true hydrostatic 

 pressure) or with a mode of compression which does not satisfy this condi- 

 tion; in other words, the effects vary — as indeed is almost obvious — accord- 

 ing as the solid retains its original form or undergoes deformation. 



Uniform pressure has a comparatively slight effect on the melting-point; 

 it usually raises it, and by an amount which, in the systems hitherto inves- 

 tigated, is seldom greater than 10°, and never greater than 40°, per 1,000 

 atmospheres. Its effect on solubility is slight, and for practical purposes 

 negligible as compared with the influence of temperature upon solubility. 

 Uniform pressure tends to further those reactions which are accompanied 

 by a decrease of volume ; but it by no means follows that it will cause these 

 (or other) reactions to occur; for whether a reaction takes place or not is 

 determined by its velocity under the particular conditions, and such evi- 

 dence as there is tends to show that reaction velocity is not. much affected 

 by uniform pressure. 



The effects of non-uniform pressure greatly outweigh those of uniform 

 pressure. It always lowers the melting-point and raises the solubility, and 

 by amounts which are many times greater than the corresponding changes 

 with uniform pressure. Indeed, if we make the plausible assumption that 

 permanent deformation of a crystalline aggregate is conditioned by a real 

 local melting (of those parts which at any moment bear the brunt of the 

 load), we find the amount of pressure required to cause melting at ordinary 

 temperature to be well within the bounds of probability. Such we believe 

 to be the efficient cause in producing most of the phenomena recorded as 

 occurring when solid systems were submitted to compression. This view, 

 while it coordinates satisfactorily the whole of the experimental work 

 hitherto done, conflicts Avith none of the available direct evidence. It 

 follows, therefore, that we can determine the effect of pressure on a solid 

 system only if we can define the character of the compression (with reference 

 to its approach to uniformity or otherwise) as well as its magnitude; and 

 even then only when the requisite thermal and other data, characteristic of 

 the system, are available. 



(7) ijber den Einfluss hoher Druckc auf das physikaUsche luul chcmischc Verhalten 



fester Stoffe. John Johnston und L. H. Adams. Z. anorg. Chcm. SO, 281- 

 334. 1913. 



A German translation of ''On the effect of high pressures on the physical 

 and chemical behavior of solids" (Am. Jour. Sci. (4) 35, 205-253, 1913). 

 Reviewed under No. G above. 



