GEOPHYSICAL LABORATORY. 125 



ment, to reach positive conclusions upon separate portions of this 

 compHcated problem. 



First of all, the classical work of Spring and of his contemporaries, 

 which covers the widest range of application of pressure (at ordinary 

 temperature) to solid substances hitherto undertaken, and which 

 has led to a number of contradictory conclusions, was examined with 

 great care and portions of it were repeated in this Laboratory'. It 

 has proved to be possible to throw considerable light upon this 

 confused situation. It was discovered, for example, that many of 

 Spring's experiments were conducted in a bomb with a loose-fitting 

 piston (witness the frequent squeezing out of his materials past the 

 piston), while that of his contemporaries was carried out for the 

 most part in bombs with tight-fitting pistons. The distinction is 

 vital. After the first crushing together, the former method gives 

 a non-uniform compression which produces deformation of the mate- 

 rial, the latter a nearly uniform or hydrostatic pressure, with very 

 little or no permanent deformation of the material. When viewed 

 in the light of this distinction in the character of the compression 

 (a distinction which appears to have passed unnoticed at the time), 

 many of the contradictory conclusions which have cast a shadow- 

 over this great mass of experimental data are happily removed and 

 definite and tangible results have taken their places. 



Still further uncertainty was removed from the problem of the 

 interpretation of those experiments which were offered in support 

 of the contention that chemical reaction between solid salts is pro- 

 moted by pressure. With uniform pressure the reaction takes place 

 only at the surface of contact, and reaction velocity at ordinary 

 temperatures is practically nil. With non-uniform pressure, which 

 always produces deformation of the material, new surfaces are con- 

 tinually brought into contact and a greater total of surface reaction 

 results, but the cases are in other respects identical. From this it 

 follows that pressure, of itself, is without direct effect in producing 

 chemical reaction in solid systems, nor does it affect appreciably the 

 reaction velocity. 



These studies have interest not alone to the geophysicist, for their 

 value in helping to elucidate problems of earth formation, but also 

 to the physicist as a contribution to our knowledge of the properties 

 of matter. In fact, as a result of the investigation a tentative 

 theory of general application has been offered of which the physicist 

 may find frequent occasion to test the validity in future work in this 

 domain. It is in effect that ''every permanent deformation of a 

 crystaUine aggregate is conditioned by a real local melting of those 

 particles which at any instant bear the brunt of the load.'' 



In addition to the analysis of the effects of pressure upon crystal- 

 line aggregates, the study of systems, one component of which was 



