CARBONIC ACID 141 



constituent is probably a necessary adjuvant 

 in the most far-reaching geological phenom- 

 ena. Indeed, it is the united action of water 

 and carbonic acid, aided in lesser degree by 

 nitric acid, which has been formed in the atmos- 

 phere by electrical action, and by acid prod- 

 ucts of vegetation, which sets free the in- 

 organic constituents of the earth's crust and 

 turns them into the stream of metabolism. 



But apart from the solvent action of car- 

 bonic acid, there is another group of phenomena 

 which depend upon its acid character. These 

 must now be explained. They are the neu- 

 trality or faint alkalinity of the ocean, and of 

 protoplasm. 



According to the modern theory of solution, 

 water itself, like the dissolved electrolytes, 

 is dissociated into ions, though only to a very 

 slight degree. 1 The reaction is expressed as 

 follows: — 



H 2 0==H+OH 



and the deposit of the material so removed in stalactites and 

 stalagmites, likewise the rapid effacement of marble epi- 

 taphs in our church yards, are instances of this solution. . . . 

 Among the sulphates, gypsum is the most important example 

 of solution. It is dissolved in the proportion of about 1 

 part in 400 parts of water. Even silica is abstracted from 

 rocks by natural waters." — Geikie, "Geology," pp. 451-452. 

 1 For a discussion of this subject the textbook of Mellor, 

 "Chemical Statics and Dynamics," p. 205, may be consulted. 



