OF GASEOUS BODIES. 117 



city, except in the case of the binoxide, which is 

 composed of equal volumes of each. Besides, it 

 would seem to be a general law, that, whenever 

 unequal volumes of gases unite chemically, there 

 is a diminution of their aggregate volume. This 

 view is supported by the facts presented in Table 

 III. page 63 ; while it is evident from the fore- 

 going details, that all such chemical combina- 

 tions are attended with a reduction of elasticity. 

 But the volume and elastic force of oxygen and 

 nitrogen, as they exist in atmospheric air, are the 

 same as when in a separate state, which would 

 seem to demonstrate, that air is a mechanical 

 mixture, and not a chemical combination. 



The elastic force of light carburetted hydrogen 

 is less than that of simple hydrogen. When Mr. 

 Perkins submitted it to mechanical pressure, he 

 found that it began to liquefy under a force equal 

 to the weight of 40 atmospheres ; and that under 

 a pressure of 1200 atmospheres it was perfectly 

 condensed into the liquid form. Being composed 

 of 2 atoms hydrogen to 1 of carbon, its specific 

 gravity and atomic weight are to hydrogen in the 

 ratio of 8 to 1 . 



When 2 atoms or volumes of carbon unite with 

 2 of hydrogen, they form bicarburetted hydro- 

 gen (olefiant gas), a compound, the specific gra- 

 vity and atomic weight of which are 14, compared 

 with hydrogen as unity. During this combina- 

 tion, the 4 volumes of hydrogen and carbon con- 

 tract into 1 volume, the elastic force of which 



