240 



Mr GRAHAM on the Law of 



ference on the velocity with which hydrogen entered under a 

 certain pressure. Hydrogen entered as rapidly against hydro- 

 gen in the receiver of a certain tension, as against air of the same 

 tension. Thus, 



It is evident from this, that the air does not diffuse out against 

 so strong a pressure and the inward current of hydrogen. 



When this jar, of which the capacity was 65 cubic inches, was 

 used as a diffusion-instrument, and filled over water with hydrogen, 

 one-fourth of the hydrogen which it contained escaped by diffu- 

 sion into air in the first hour. Now, we find by the Table, (p. 

 18.), that hydrogen penetrates the plug with greater velocity 

 when passing into a vacuum or into the exhausted receiver. The 

 exhausted receiver was filled one-fourth in about fifteen minutes ; 

 hence a certain quantity of hydrogen passed through the same 

 porous plug, by the pressure of the atmosphere, into a vacuum 

 in fifteen minutes ; by spontaneous diffusion into air in sixty 

 minutes ; or the velocity of diffusion was one-fourth the velocity 

 of mechanical pressure. 



This was a dense and excellent plug ; and in others of a looser 

 texture, the velocity of diffusion was much less than a fourth. 



Dried bladder answers for shewing the diffusion of hydrogen 

 when stretched over the open end of the tube receiver. The 

 diffusion, however, through a single thickness of bladder, is ef- 



