APPLICATION OF PHYSICO-CHEMICAL PRINCIPLES. 283 
ent conditions are very variable. One of the most important of, these 
variables is as to whether the conditions are mass static or mass dynamic.* 
However, all reactions do not reverse in the two physico-chemical zones. 
The first part of van’t Hoft’s law of heat and the law of pressure may 
work together—that is, in both zones the reaction may occur which, si- 
multaneously with the development of heat by chemical action, also 
results in development of heat by condensation. In so far as cases of 
this kind occur, it is to be presumed that such reactions are common to 
both zones. As an instance in which heat is probably evolved both by 
the chemical reactions and by the movements in both zones may be men- 
tioned the devitrification of glass (see pages 289-291). The chemical 
reaction is presumably under the first part of van’t Hoff’s law, and the 
volume is decreased. A case of condensation is the replacement of calcium 
by magnesium in limestone, thus transforming the rock into dolomite. 
‘Another illustration of reactions in the lower zone in which the first 
part of van’t Hoff’s law of chemical action and heat may coincide with 
the law of pressure and both result in the development of heat, is the 
production of the heavy compounds with complex molecules, such as gar- 
net, staurolite, etcetera; also, in the lower physico-chemical zone decar- 
bonation may take place without being replaced by silica, as in the case 
of the formation of magnetite from iron carbonate. This reaction is ac- 
companied by partial oxidation. The decarbonation results in the ab- 
sorption of heat, the oxidation develops heat to a greater degree ; there- 
fore the reaction is a case of the development of heat by chemical re- 
action and of heat by condensation, and thus the first part of the law of 
heat and the law of pressure work together. 
The reactions above summarized but illustrate the fundamental differ- 
ence between the two physico-chemical zones. In this paper other less 
important reactions, separating the outer crust of the earth into two 
zones and the upper zone into two belts, cannot be considered. 
It is thought to be certain that the total of all the changes taking place 
in the whole of the mass of rocks concerned in any given movement re- 
sult in the dissipation of energy, and it is believed that such is the fact 
for each of the physico-chemical zones separately. ‘In the upper zone 
the chemical reactions result in plus (see page 280); the average volume 
reaction results in minus. It is, however, thought certain that the resid- 
ual is plus. In the lower zone the average of the chemical reactions is 
* The verification from authorities of the heat of the chemical reactions and the volume rela- 
tions for the majority of the changes above mentioned have been very kindly made for me by Mr 
A. T. Lincoln. Mr Lincoln has found the results used either in the works of Thomson, Ostwald, 
Mendeléeff, or other standard authorities, or from the data there found has been able to caleulate 
results which answer the specific questions I gave to him. 
