154 MR. J. S. TOWNSEND ON THE DIFFUSION OF IONS INTO GASES. 



Taking this value for the charge e, we obtain 



N = 2 X 10 19 . 



From this we deduce the weight of a molecule of hydrogen 



4 - 5 X 10~ 24 gramme. 



Every step in the theory by which these numbers are obtained is supported by 

 direct experimental evidence. 



Since, as we have just shown, the charge on an ion produced by Rontgen rays, 

 is equal to the charge on a hydrogen ion in a liquid electrolyte, this latter charge is 

 also 6 X 10~ 10 electrostatic unit. 



Although the value of Ne for hydrogen is 25 per cent, different from its value for 

 other gases, we are justified in including hydrogen in the above general conclusion, 

 as we would expect the value of u t for hydrogen to be too small. RUTHERFORD makes 

 no mention of having corrected for the presence of air in his apparatus, or of having 

 used perfectly dry hydrogen. If we take the mean value of K for moist hydrogen, 



we obtain 



Ne H = 1-15 X 10-'. 



In order to prove that the charge on the positive ion is equal to the charge on the 

 negative ion, the ratio of the coefficients of diffusion must be shown to be equal to the 

 ratio of the velocities. Professor ZELENY* has shown that the negative ions travel 

 faster under an electromotive force than the positive ions, the ratio of the velocities 

 being 1/24 for air and oxygen, 1'15 for hydrogen, and I/O for carbonic acid. 



The experiments on diffusion show that the ratio of the velocities would be larger 

 in dry than in moist gases, but as this point has not yet been examined by Professor 

 ZELENY, we cannot expect a very close agreement between the ratios which he gives 

 for the velocities and the ratios of the coefficients of diffusion. 



We are led to conclude that the charges on the positive and negative ions are equal 

 from another point of view. It has been proved that the mean charge is the same as 

 the charge on an ion of hydrogen in a liquid electrolyte. If the charges differed, one 

 of them would be less than the charge on the hydrogen ion, whereas experiments on 

 electrolysis show that all ionic charges are either equal to the charge on the hydrogen 

 ion, or an exact multiple of it. 



COMPARISON OF THE RATES OF DIFFUSION OF THE IONS WITH THE RATES OF 

 INTERDIFFUSION OF GASES AND VAPOURS. 



The coefficients of diffusion of ions into a gas are much smaller than the coefficients 



* J. ZELENY, ' Phil. Mag.,' July, 1898. 



