100 A TREATISE ON METAMORPHISM. 



burial. And it is certain that the temperature can be very materially 

 increased, and therefore that the chemical activity is enormously increased. 



NATURE OF THE CHEMICAL REACTIONS. 



Pressure influences chemical reactions under the following law: If a 

 chemical system be compressed at a constant temperature, there follows a 

 displacement of the equilibrium in that direction, which is associated with 

 a diminution of volume. This law in relation to pressure and chemical 

 activity may be stated in a more general form, as follows: "Those chemical 

 forces are strengthened by compression which condition a diminution of 

 volume; and those chemical forces are weakened by compression which 

 condition an increase in volume.'' ° In other words, so far as pressure 

 influences chemical reactions, changes go on in directions which produce 

 smaller volumes. Therefore pressure at all times and places is influencing 

 chemical reactions in the direction of the production of more condensed 

 sVstems. It has been seen (Chapter II, pp. 48-49) that pressure alone, 

 without the presence of solutions, may produce reactions under this law. 

 However, in nature, the vast majority of reactions under the law are 

 accomplished through the agency of water. The importance of water in 

 this connection is well illustrated by Spring's experiments upon the con- 

 solidation of clay when dry and wet. By pressure upon moist clay 

 confined in a cylinder he was able to consolidate the clay into a body as 

 compact as a piece of shale — indeed, so compact that it was difficult to 

 scratch it with the finger nail. But using the same pressure upon dry clay 

 he produced a substance so little consolidated that it was easily scratched 

 with the finger nail. In the case of the moist clay, he attributed the consoli- 

 dation to the escape of the plastic material about the piston, and to the 

 precipitation of material from solution at the moment of escape. 6 Spring's 

 explanation therefore does not introduce chemical readjustment of the com- 

 pounds. However, it will be seen that pressure does promote chemical 

 interchange, producing compounds which are, on the average, denser than 

 the original ones. This, as will be shown on the following pages, is 

 believed to be a dominant process for a great many chemical reactions 



"Nernst, W., Theoretical chemistry, translated by C. S. Palmer, Macmillan Co., Ne^- York, 1895, 

 p. 567. 



6Tolman, C. F., jr., Professor Spring on the physics and chemistry of solids: Jour. Geol., vol. 6, 

 1898, p. 323. 



