MOLECULAR DYNAMIC ACTION. 289 
Under mass static conditions, at moderate depths, the effect of pressure 
appears subordinate to that of the chemical reactions. There may be 
increase of volume as in the case of hydration already mentioned, or 
there may be contraction as in the case of devitrification of glass, or in 
the case of recrystallization of minerals which are in a state of strain, 
and therefore have energy potentialized which is liberated in the pro- 
cess of recrystallization. 
DEVITRIFICATION OF GLASS UNDER MASS STATIC CONDITIONS 
Barus,* in experiments upon the compressibility of water in capillary 
tubes at a temperature of 185° C., found that the volume of water ap- 
parently decreased as much as 18 per cent in 42 minutes and nearly 
18 per cent in an hour. As at lower temperatures he found the com- 
pressibility of water to increase at an’ exceptionally slow rate, he con- 
cluded that there must be some other cause than real condensation for 
the apparent rapid compressibility of water when a temperature of 
180° C. to 185° C. was reached. An examination of the tubes in which the 
experiments were performed showed him that the apparent compress- 
ibility was not that of water, but was in fact due to the solution of the 
silicates of the glass by the water, the material being deposited in crys- 
tallized minerals. The change of state resulted in a more compact from. 
The natural glasses in passing into the crystalline condition’ decrease 
in volume in some cases as much as 10 per cent. ‘This decrease in vol- 
ume in the change-of the material of the glass from an amorphous to a 
crystalline condition gives more room for water, and thus its apparent 
great compressibility. Barus points out that this decrease in volume 
of the solids probably involves the evolution of heat. This reaction is 
clearly a solution and recrystallization under the first part of the law of 
chemical action and heat (see page 277), and under the law of release of 
energy by condensation. It is to be noted that the water in this process 
of recrystallization of glass is not necessarily consumed. It is consumed 
only in case the crystalline substances forming are hydrated or con- 
tain basic water. But even if water is thus consumed, it is evident that 
asmall amount of water may be a medium through which a large amount 
of work is done. It is clear from the foregoing that in ordinary glass a 
certain amount of energy is potentialized which may be liberated through 
the action of water at high temperatures. In this we evidently have an 
adequate cause for the complete and exceedingly rapid devitrification of 
old glasses (see pages 290, 291) which have been buried deep below the 
surface of the earth, and which therefore, by the rise of the temperature 
*The compressibility of liquids, by C. Barus: Bull. U.S. Geol. Survey, no. 92, 1892, pp. 78-84. 
