Ml; .1. S. TOWNSKNI. UN TIIK I 'I! I I SIGN- OF IONS INTO GAM - 



155 



of diffusion of gases into each other, but do not differ much from the coefficients of 

 diffusion of vapours into gases. 



We give here a table of the latter coefficients, so that they may be compared with 

 the numbers given in Tables III. and IV. 



TABLE V., giving Coefficients of Diffusion of some Gases and Vapours into Air, 



C;n-lx)iiic Acid, and Hydrogen. 



The experimental results show that if K is the coefficient of interdift'usion of two 

 gases whose densities are p t and p,, K X Vp\p<t is roughly constant. The rates of 

 diffusion of the ions are roughly inversely proportional to the square roots of the 

 densities of the gases. 



Two theories have been suggested to account for the small values which have been 

 found for the rates of diffusion of the ions into a gas. 



The effect may be explained if we suppose that a number of molecules surround the 

 ion. The carriers of the charge would then diffuse slowly like a gas made up of large 

 molecules. The mass of the group could be found by comparing the rates of diffusion 

 of the ions with the rates of interdiffusion of gases. A rough calculation shows that 

 the mass of this group should be about 30 times the mass of a molecule of oxygen. 



The small values of the coefficients of diffusion may also be explained if we supjxe 

 that the carrier is as small as a molecule of the gas, and that the electric force exerted 

 on the molecules which approach it gives rise to encounters which would not have 

 taken place if the carrier were uncharged. 



If we adopt the theory that the ions are surrounded by molecules forming a sphere 

 which moves about with the ion, we can apply MAXWELL'S formula for the coefficient 

 of interdiffusion of two gases to find the radius of the sphere. 



The coefficient of iuterdiffusion of two gases, according to the theory founded on 

 the collisions of elastic spheres, is 



. 



N 



JL !.J_* 



'' 



where w t and w t are the molecular weights of the two gases, that of hydrogen 



being unity. 



* J. C. MAXWKI.I., ' Nature,' vol. 8. 

 X 2 



