104 CHEMISTRY. 



tion is covered up in its wintry toinb. This is certainly 

 very wonderful when we consider the constant changes 

 which are going on in two of these ingredients, oxygen and 

 carbonic anhydride. An exact balance is maintained by the 

 Creator in the opposing chemical operations that we have 

 noticed, under circumstances in which there would appear 

 to be a liability to great and sudden variations. Leaves 

 might give out more oxygen than would be used by lungs 

 and fires, and then there would be an increase of the oxy- 

 gen of the air, rendering every thing more combustible, 

 and producing in animals fevers and inflammations. Or 

 more carbonic anhydride might issue from lungs and fires 

 and decaying matters than the leaves could absorb, and 

 then carbonic anhydride would accumulate in the air, de- 

 stroying life and extinguishing fires. But so accurately 

 does the Creator adjust these opposite chemical operations, 

 that production and consumption in the case of each sub- 

 stance exactly balance each other. World-wide are these 

 operations, and they are carried on under circumstances 

 which are not only various, but exceedingly variable ; but 

 an Almighty Power so controls them that the air, amid all 

 its changes, preserves those proportions which exactly adapt 

 it for the respiration of the myriads of animals, great and 

 small, that swarm on the earth's surface. 



132. Nitrogen in the Chemistry of the Air. Although ni- 

 trogen constitutes four fifths of the atmosphere, it is not at 

 all affected in most of the chemical changes which we have 

 noticed in the preceding paragraphs. The oxygen and car- 

 bonic anhydride of the air are continually changing, but not 

 so with the nitrogen. It goes into the lungs of the animal, 

 and comes out unchanged, though the oxygen that went in 

 with it is much lessened, and the carbonic anhydride is 

 much increased. So also in combustion, however hot may 

 be the fire, the nitrogen of the air comes out of it unchanged. 



