MR. J. S. TOWNSF.NP ON THE DIFFUSION OF IONS INTO OASES. 153 



where e is the charge on the ion of the gas in electrostatic units, n the number of 

 ions per cub. centim., and p their partial pressure, we see that when dp/dx = 0, the 



velocity u due to the electric force X is - . If the potential gradient is 1 volt 

 per centim., X = jJ 5 in electrostatic units, and the corresponding value of u is 



Ke n 

 "'=300 X p' 



Let N be the number of molecules in a cub. centim. of a gas at pressure P, equal to 

 the atmospheric pressure, and temperature 1 5 Centigrade, the temperature at which 

 MI and K are determined. 



The quotient N/P may be substituted for n/p in the above equation, and since the 

 .itmospheric pressure P in C.G.S. units is 10', we obtain 



3 x 10X 

 ~ -' 



If we take the values of MI from the table of mean velocities given by RUTHER- 

 FORD,* and the mean values of K obtained for dry gases, we get the following values 

 of Ne : 



Air ..... Ne A = 1'35 X 10', 



Oxygen . . . . Ne = 1'25 X 10', 



Carbonic acid . . N? c = T30 X 10', 



Hydrogen . . . Ne H = TOO X 10', 



Experiments on electrolysis show that 1 electrodynamic unit of electricity in passing 

 through an electrolyte gives off 1/23 cub. centims. of hydrogen at temperature 

 15 Centigrade and pressure = 10 s C.G.S. units. The number of atoms in this volume 

 is 2'46 N, so that if E is the charge on a hydrogen atom in the liquid electrolyte, 



2 '4 6 NE = 1 electromagnetic unit, 



= 3 X 10' electrostatic units. 

 Hence 



NE = 1-22 X 10', 



the charge E being expressed in electrostatic units. 



Since N is a constant, we conclude that the charges on the ions produced by 

 Rtintgen rays in air, oxygen, carbonic acid, and hydrogen are all the same, and equal 

 to the charge on the hydrogen ion in a liquid electrolyte. 



Professor THOMSON! has shown that the charge on the ions in hydrogen and 

 oxygen, which have been made conductors by Rontgen rays, is 6 X 10~ 10 electro- 

 static unit, and is the same for both gases. 



* E. RUTHERFORD, ' Phil. Mag.,' November, 1897. 

 t J. J. THOMSON, ' Phil. Mag.,' December, 1898. 

 VOL. CXCIII. A. X 



