WATER 79 



in which water plays so large a part. In the 

 first place the chemical reactions in which it 

 is concerned during the process of geological 

 evolution, though they are no doubt in the 

 total of great magnitude, are both slow and 

 far from violent. Long since any very active 

 changes of this sort, so far as the superficial 

 part of the crust is concerned, have run their 

 course. In the second place water is really, 

 at the temperature of the earth and in com- 

 parison with most other chemical substances, 

 an extremely inert body, for the union of hydro- 

 gen with oxygen is so firm that it is not readily 

 dissolved. 



Thus water exists as a singularly inert con- 

 stituent of the atmosphere, as a liquid nearly 

 inactive in chemical processes on the surface 

 and in the soil, and everywhere as a mild sol- 

 vent which does not easily attack the sub- 

 stances which in great variety dissolve in it. 

 The chemical changes which do follow upon 

 solution are not such as to produce substan- 

 tial chemical transformations, and most sub- 

 stances can pass through water unscathed. 

 The nature of water, then, is a great factor in 

 the chemical stability, which, no less than the 

 physical stability of the environment, is es- 

 sential to the living mechanism. But it may 

 be questioned if such stability would not 



