HYDROGEN AND OXYGEN. 



297 



have already noticed the remarkable fact that water 

 deprived of air is explosive at a comparatively low tem- 

 perature, less than 300 ; gunpowder requiring a tem- 

 perature of nearly 1000 F. 



If we place in a globe, oxygen and hydrogen gases, 

 in the exact proportions in which they combine to form 

 water, they remain without change of state. They 

 appear to mix intimately; and, notwithstanding the 

 difference in the specific gravities of the two gases, the 

 lighter one is diffused through the heavier in a curious 

 manner, agreeably to a law which has an important 

 bearing on the conditions of atmospheric phenomena.* 

 The moment, however, that an incandescent body, or 



* Dr. Priestley appears to have been the first to observe the 

 peculiar property of the diffusion of gases. Dr. Dalton, however, 

 first drew attention to the important bearing of this fact on natural 

 phenomena^ -and he published his views on The Miscibility of 

 Gases in the Manchester Memoirs, vol. v. The following extract 

 from his memoir On the Constitution of the Atmosphere will exhibit 

 its bearings : 



ft may be worth while to contrast this view of the constitution 

 of the atmosphere with the only other one, as far as I know, that 

 has been entertained. 



According to one view, 

 1. The volumes of each gas 

 found at the surface of the earth 

 are proportional to the whole 

 weights of the respective atmos- 

 pheres. 



Azote . . . 

 Oxygen . . . 

 Aqueous vapour 

 Carbonic acid . 



101-43 



According to one view, 

 2. The altitude of each at- 

 mosphere differs from that of 

 very other, and the proportions 



According to the other view, 



1. The volume of each gas 

 found at the surface of the 

 earth, multiplied by its specific 

 gravity, is proportional to the 

 whole weight of the respective 

 atmospheres. 



Azote .... 76'6 

 Oxygen .... 23*4 

 Aqueous vapour . 0'83 

 Carbonic acid . . 0'15 



100-88 

 According to the other view, 



2. The altitude of each at- 

 mosphere is the same, and the 

 proportion of each in the com- 



