222 ) 



On the Law of the Diffusion of Gases. By THOMAS GRAHAM, Esq. 



M.A. F. R.S.Ed. &c. 



(Read December 19- 1831.) 



AT is the object of this paper to establish with numerical exact- 

 ness the following law of the Diffusion of Gases : 



" The diffusion or spontaneous intermixture of two gases in 

 contact, is effected by an interchange in position of indefinitely 

 minute volumes of the gases, which volumes are not necessarily 

 of equal magnitude, being, in the case of each gas, inversely pro- 

 portional to the square root of the Density of that gas." 



These replacing volumes of the gases may be named equiva- 

 lent volumes of diffusion, and are as follows : Air, 1 ; Hydrogen, 

 3.7947; Carbureted hydrogen, 1.3414; Water-vapour, 1.2649; 

 Nitrogen, 1.0140 ; Oxygen, 0.9487 ; Carbonic acid, 0.8091 ; Chlo- 

 rine, 0.6325, &c. ; numbers which are inversely proportional to 

 the square roots of the densities of these gases, being the recip- 

 rocals of the square roots of the densities, the density of air 

 being assumed as unity. 



If the two gases are separated at the outset by a screen 

 having apertures of insensible magnitude, the interchange of 

 " equivalent volumes of diffusion " takes place through these 

 apertures, being effected by a force of the highest intensity ; 



