b74 ABSTRACTS OF PAPERS 



not be dissolved. They contain the same minerals as the rest of the granite. 

 but with a larger amount of ferromagnesian minerals, and have a granitoid 

 structure They might better be regarded, therefore, as basic segregations 

 which took place within the magma during its crystallization. 



EFFECT OF HIGH PRESSURES ON THE PHYSICAL AXD CHEMICAL BEHAVIOR 

 OF SOLID SUBSTAXCES 



BY JOHN JOHNSTON AND L. H. ADAMS 1 



(Abstract) 



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 solids, to reconcile 

 some of the conflicting statements to be found in the literature pertaining to 

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

 from the available evidence, especially with regard to their application to the 

 discussion of geological phenomena. Some of this confusion results from the 

 employment of indefensible criteria in ascertaining the character and magni- 

 tude of the change produced by pressure, as. for example, in determining the 

 effect of pressure in promoting chemical reaction between solids ; but in the 

 main it is due to failure to take into account the fact that the effects produced 

 depend on 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 condition : in other words, the effects vjjry — as. indeed, is 

 almost obvious — according as the solid retains its original Um 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 investigated, 

 is seldom greater than 10°, and never greater than 30= per 1.000 atmospheres. 

 Its effect on solubility is slight, and for practical purposes negligible as com- 

 pared 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) reac- 

 tions to occur : for whether a reaction takes place or not is determined by its 

 velocity under the particular conditions, and such evidence 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 pres- 

 sure. 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 perma- 

 nent deformation of a crystalline aggregate is conditioned by a real local melt- 

 ing (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 

 • in producing most of the phenomena recorded as occurring when solid 

 ins were submitted to compression. This view, while it coordinates satis- 



x Introduced by A. L. Day. 



