L IS* 3 



The principal consumption of the carbonic acid 

 in the atmosphere, seems to be in affording nourish- 

 ment to plants ; and some of them appear to be sup- 

 plied with carbon chiefly from this source. 



Carbonic acid gas is formed during fermentation, 

 combustion, putrefaction, respiration, and a number 

 of operations taking place upon the surface of the 

 earth -, and there is no other process known in nature 

 by which it can be destroyed but by vegetation. 



After a given portion of air has been deprived of 

 aqueous vapour and carbonic acid gas, it appears little 

 altered in its properties ; it supports combustion and 

 animal life. There are many modes of separating its 

 principal constituents, oxygene and azote, from each 

 other. A simple one is by burning phosphorus in a 

 confined volume of air : this absorbs the oxygene and 

 leaves the azote ; and 100 parts in volume of air, in 

 which phosphorus has been burnt, yield 79 parts of 

 azote; and by mixing this azote with 21 parts of 

 fresh oxygene gas artifically procured, a substance 

 having the original characters of air is produced. To 

 procure pure oxygene from air, quicksilver may be 

 kept heated in it, at about 600% till it becomes a red 

 powder ; this powder, when ignited, will be restored 

 to the state of quicksilver by giving off oxygene. 



Oxygene is necessary to some functions of vege- 

 tables ; but its great importance in nature is in its rela- 

 tion to the ceconomy of animals. It is absolutely ne- 

 cessary to their life. " Atmospheric air taken into the 

 lungs of animals, or passed in solution in water 

 through the gills of fishes, loses oxygene \ and for 



