216 THE CHEMISTRY OF CREATION. 



barometric pressure 30 inches, one hundred 

 cubic inches of air weigh 30 grains, under 

 similar circumstances one hundred cubic inches 

 of carbonic acid will weigh more than 47 grains. 

 Its tendency, therefore, is to collect and accu- 

 mulate near the surface of the ground. This 

 may be seen by any one who will pay a visit to 

 a large brewery. Standing by the side of one of 

 the large fermenting vats, and in such a position 

 that it may be seen against the light, he will 

 perceive trembling transparent floods of this 

 gas pouring over the top and down the sides of 

 the vessel. The same appearance is also fre- 

 quently visible in a glass of soda-water, which 

 is charged with carbonic acid. This gas, as has 

 before been noticed, is poured into the air in 

 enormous quantities. Why does it not obey the 

 laws of gravity, and remain near the ground? 

 What is there to hinder its falling down and 

 overwhelming the human race and the whole 

 animal world with its deadly floods ? The 

 answer is, the power of diffusion. What, then, 

 is the "power of diffusion?" This question 

 must be answered by an experiment. 



If a glass jar or bottle were filled with car- 

 bonic acid, and the mouth stopped by a plug 

 of plaster of Paris, and left, in a little time the 

 vessel would be found only to contain com- 

 mon air. The heavy carbonic acid would have 



