206 Johnston and Adams — High Pressures on the 



Introductory. 



Anyone who has occasion to study the literature pertaining 

 to the effect of high pressures on solid substances will be 

 struck by the mass of contradictory statements to be found 

 there ; in the present paper an endeavor is made to reconcile 

 some of these contradictions, to define — as impartially as may 

 be — the present state of our knowledge of the subject, and to 

 indicate the conclusions which may justifiably be drawn from 

 the evidence at hand. Much of the existing confusion would 

 appear to be due to a neglect to observe the distinction between 

 the effects of uniform pressure and of compression which does 

 not satisfy that condition ; in other words, it is due to a misin- 

 terpretation of the results obtained. In other cases, — as, for 

 instance, in determining the effect of pressure in promoting 

 chemical reaction between solids — indefensible criteria have 

 been employed to ascertain the magnitude of the change pro- 

 duced. 



The question of the effect of high pressures on the behavior 

 of solids has been the subject of numerous isolated papers, but 

 has not been very systematically investigated hitherto, except 

 perhaps by Spring. Unfortunately for the conclusive char- 

 acter of Spring's work, some aspects of it have been seriously 

 called in question, while other parts have been, according to 

 Spring's own statement,* misinterpreted or misunderstood. 

 Now Spring's work has been quoted — and very often not at 

 first hand— by the writers of a very large number of chemical 

 and geological text-books, monographs and papers, who appar- 

 ently were unaware of the fact that many of Spring's state- 

 ments had been challenged and even disproved ; so that these 

 errors and misinterpretations seem in a fair way to be per- 

 petuated. 



Accordingly, in view of its great importance, for the science 

 of geology in particular, it seemed desirable not only to review 

 this subject but to attempt a critical discussion of it. This 

 discussion is based on the work recorded in the literature ;f 

 though with regard to a few of the doubtful points, experi- 

 ments were undertaken with the object of reaching a decisive 

 conclusion. 



* Bull. Acad. Roy. Belg. (3), xiv, 595-8, 1887 ; this Journal (3), xxxvi, 

 286-9, 1888. 



f To avoid possible misunderstanding, the authors desire to state here 

 specifically that they have endeavored to refer to all papers which appeared 

 to contain anything material to the discussion in hand and to apportion to 

 each author the credit to which he is entitled for having made some positive 

 advance or corrected some previous error. Further, it may be as well to 

 state that it is no part of the plan of the present paper to disc ass completely 

 the effect of pressure on systems containing a liquid or vapor phase, e. g. 

 solutions and their properties (electrical conductivity, etc.) ; and, therefore, 

 work along these lines is referred to only incidentally. 



