290 THE CHEMISTRY OF CREATION. 



form, it would otherwise have been little valu- 

 able. 



Carbonic acid gas is also largely soluble in 

 water. At the ordinary temperature and baro- 

 metric pressure, water will take up about its 

 own volume ; a cubic foot will dissolve a cubic 

 foot of the gas. Carbonic acid exists in air in 

 still larger and less variable proportions than 

 ammonia. If the rain dissolves the one, it must 

 dissolve the other gas. There cannot be a 

 doubt, therefore, that the descending drops all 

 contain, in addition to a solution of ammonia, a 

 notable amount of dissolved carbonic acid. This 

 solution, coming in contact with the roots of 

 plants, is absorbed by them, conveyed into the 

 digestive organs of the vegetable economy, and 

 being decomposed there, contributes toward the 

 formation of the solid portions of the vegetable 

 structure. It appears, from some experiments 

 by Mr. Mallet, that rain-water, when fresh 

 fallen, frequently also contains one-fifth of its 

 volume of oxygen. 



The beneficial duties of rain to vegetation 

 do not end here. When the emigrants of a 

 new colony set about clearing whole forest 

 districts, and destroy, by burning, the timber 

 they cannot store or transport, there are found, 

 in the ashes, large quantities of alkalies and 

 other mineral ingredients. These once existed 



