The Diffusion of Ions into Gases. 195 



Let N be the number of molecules in a cubic centimetre of a gas at 

 pressure P, equal to the atmospheric pressure, and temperature 15° 

 centigrade, the temperature at which u and k were determined. 



The quotient N/P may be substituted for n/p in the above equa- 

 tion, and since the atmospheric pressure P is 10 6 in C.G.S. units, we 

 obtain 



3 x 10%! 



K 



The following values of thus obtained for different gases are 



Air Ne A = 1-35 x 10 10 



Oxygen N^ = 1*25 x 10 10 



Carbonic acid Nc c = 1'30 x 10 10 



Hydrogen Ne H = 1"00 x 10 10 



The values of u were taken from the table of mean velocities given 

 by Professor Rutherford.* The values of k which were used, are the 

 mean values obtained for dry gases. 



Experiments on electrolysis show that ' one electrodynamic unit of 

 electricity in passing through an electrolyte, gives off 1'23 c.c. of 

 hydrogen at temperatures 15° and pressure 10° C.G.S. units. The 

 number of atoms in this volume is 2*46 N, so that if E is the charge 

 on an atom of hydrogen in the liquid electrolyte, 



2-46NE = 1 electrodynamic unit of quantity 

 = 3 x 10 10 electrostatic units. 

 Hence NE = 1-22 x 10 10 , 



the charge E being expressed in electrostatic units. 



Since N is a constant, we conclude that the charges on the ions pro- 

 duced by Rontgen 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 electrostatic unit, and is the same for both gases. 



Taking this value for the charge e, we obtain the number of mole- 

 cules in a cubic centimetre of a gas 



N = 2 x 10 19 . 



From this we deduce the weight of a molecule of hydrogen, p/N, 

 4*5 x 10~ 24 gram. 



* E. Rutherford, * Phil. Mag.,' NoTeruber, 1897. 

 f J. J. Thomson, ' Phil. Mag.,' December, 1898. 



