PRESSURE AND TEMPERATURE OF THE GASES. 61 



the law controlling the action of gases is applicable to the new compound, 

 and to the other gases with which it is mingled but does not unite 

 chemically. 



As to the relative importance of the gases, it might at first be thought 

 that the strong acids, such as hydrochloric and hydrofluoric, are of greater 

 consequence than the much less active compounds, carbon dioxide and 

 oxygen; but it should be remembered that carbon dioxide and oxygen are 

 everywhere at work upon the surface of the earth, whereas the presence 

 of the strongly active compounds in more than minute quantities is excep- 

 tional. It therefore follows that the action of the universally present 

 weaker agents, such as carbon dioxide and oxygen, is of immeasurably 

 greater geological importance than the action of the stronger but much less 

 abundant gases. 



The pressure. — Increase of pressure increases the chemical activity of a gas. 

 This law follows from the fact that the number of molecules which act upon 

 a given space is directly as the pressure. The varying atmospheric pressure 

 may be taken as illustrating this principle. When the pressure increases, 

 say, by .05, this means that 1.05 times as many molecules of gas are actively 

 at work upon a given area as before. 



One of the best illustrations of the increased activity of gases in accom- 

 plishing chemical work when under pressure is that of carbon dioxide. As 

 shown in another place (pp. 175-176), carbon dioxide is capable of decom- 

 posing many silicates at ordinary temperatures; but Struve and Mueller" 

 have shown that when cai'bon dioxide is under pressure its effect in decom- 

 posing silicates is very much greater than under ordinary conditions. This 

 is in accordance with the law of mass action. In proportion as the pressure 

 increases the number of active molecules increases, and therefore the 

 geological work increases in proportion. 



The temperature. — The activity of gases increases with increase of temper- 

 ature. In proportion as the temperature is high, the kinetic molar energy 

 of the molecules of gases is great. The absolute temperature of a perfect 

 gas is believed to be a direct measure of its kinetic molar energy. By 

 molar kinetic energy is meant the energy of translation of the molecule of 

 a gas, and not the vibratory or rotary motions of the moleoules themselves. 



"Mueller, Richard, Untersuchungen liber die Einwirkung des kohlensaurehaltigen Wassers auf 

 einige Mmeralien und Gesteine: Tschermaks mineral. Mittheil., vol. 7, 1877, p. 47. 



