THEORY OF DISSOCIATION. 85 



This theory is firmly placed in the text-books. No opinion is expressed 

 by me as to its correctness. Indeed, I have no right to any opinion on the 

 subject. As already pointed out, this theory has been vigorously opposed 

 by Kahlenberg, but as yet that author has offered no constructive theory 

 to take its place. I therefore follow the theory of the standard text-books 

 so far as necessary to show how it would apply to the work of ground solu- 

 tions if it prove to be true; but so far as practicable I make the statements 

 in such form that they will be correct even if the theory of free ions and 

 reactions between such ions is finally abandoned. 



Under the theory of dissociation the superiority of water as a solvent 

 for chemical interchanges is regarded as largety due to the fact that the 

 dissolved substances are separated into their ions to a greater degree than 

 in any other solvent. To the fact of active reactions in water, whatever 

 their cause, are very largely due the profound changes which occur in rocks 

 through the medium of water solutions. 



Under the theory of dissociation water solutions, acids, bases, and salts 

 separate into their ions. For instance, HC1 separates into the free ions H 

 and CI; NaOH separates into the free ions Na and OH; and NaCI into the 

 free ions Na and CI. However, in solutions the dibasic acids are supposed 

 to separate into free ions somewhat differently from what might be expected. 

 For instance, it might be expected that H 2 C0 3 would separate into the free 

 ions H 2 and C0 3 , but it is supposed to separate thus : 



H 2 C0 3 = H + HC0 3 . 



Other dibasic acids are thought to dissociate in a similar manner. However, 

 if the dibasic acid be very strong the compound ion may again break up. 

 Thus, H 2 S0 4 is thought to first break up into the free ions H and HS0 4 , 

 and the latter to break up into the free ions H and S0 4 , so that these would 

 be the ions present in the water. But iD the case of the weak acid, carbonic, 

 it is thought that the last change does not take place, and that the free ions 

 remain H and HC0 3 . 



Ostwald regards the absence of the second stage of dissociation as the 

 explanation of the peculiar characteristics of carbonic acid. a Since carbonic 

 acid is, next to silica, the most important rock-making acid, the manner in 

 which it breaks up is of great consequence in metamorphism. 



a Ostwald, W., Grundlinien der anorgamschen Chemie, Engelmann, Leipzig, 1900, pp. 276-278, 

 397-398. 



