68 A TREATISE ON METAMORPHISM. 



usually regarded as oxides, although in some cases the aluminum was 

 treated as united with the chlorine." However, results of recent analyses 

 have ordinarily been given on the basis of ions. 6 



In a solution, under the law of mass action, each of the bases is to be 

 considered as divided between all acids, and under the theory of disso- 

 ciation there are also present in the solutions the free ions of both the 

 bases and the acids. For example, suppose a strong underground water 

 solution to contain three bases and three acid radicals; as, for instance, the 

 bases sodium, calcium, and magnesium, and the radicals of carbonic, 

 sulphuric, and hydrochloric acid; then the following- nine compounds are 

 present, Na 2 C0 3 , Na 3 S0 4 , NaCl, CaC0 3 , CaS0 4 , CaCh, MgC0 3 , MgS0 4 , 

 MgCl 2 , and also the six free ions, Na, Ca, Mg, C0 3 , S0 4 , and CI, making 

 altogether fifteen separate combinations of the elements. However, under 

 the theory of dissociation, if the solutions be so weak that the substances in 

 solution are wholly ionized the nine compounds first mentioned will not be 

 present. If the dissociation theory be rejected, under "the law of mass 

 action in all cases all of the nine compounds will be present, but not the 

 free ions. 



Under the principles of solutions it is necessary to consider the cases 

 of (1) the solution of gases in ground waters, (2) the solution of solids in 

 ground waters, and (3) diffusion. 



SOLUTION OF GASES IS GROUND WATERS. 



The quantity of gases which can be dissolved in underground water 

 depends upon the gases present, the pressure, the temperature, and the 

 solids in solution. 



Gases present — AH the natural gases may be dissolved in water or may 

 unite with water. In the latter case the resultant compounds are dissolved. 

 In both cases solutions are formed. 



Since below the level of the free surface of underground water it is 

 clear that the gases enter into solution either by absorption or by combina- 

 tion, it follows that the more far-reaching effects of these substances in 

 metamorphism are not as gases, but as aqueous solutions. The gases are 



« Peale, A. C, Lists and analyses of the mineral springs of the United States: Bull. U. S. Geol. 

 Survey No. 32, 1886, pp. 43, 115, 133. 



& Clarke, F. W., and Hillebrand, W. F., Analyses of rocks and analytical methods, U. S. Geol. 

 Survey, 1880-1896: Bull. TJ. S. Geol. Survey No. 148, 1897. Clarke, F. W., Analyses of rocks, 

 laboratory of the TJ. S. Geol. Survey, 1880-1899: Bull. U. S. Geol. Survey No. 168, 1900. 



