48 THE THEOEY OF IONIZATION OF GASES 



If this difference between the positive and negative 

 ions is due to the relatively large mass of the former, it 

 is to be expected that the difference would be more 

 marked in the heavier gases, assuming that the mass of 

 the positive ion is of the same order as that of a molecule 

 of the gas. It is interesting, therefore, to make similar 

 calculations for other gases and to compare them with 

 the results obtained for hydrogen. For although these 

 comparisons give no accurate information as to the ratio 

 of the masses of the positive ions in different gases, the 

 calculations afford some reason for believing that the 

 positive ions in other gases are greater than those in 

 hydrogen. 



A matter of importance that arises in making com- 

 parisons of the relative activity of positive and negative 

 ions in different gases is to decide what force to select in 

 each case, as the relative activity varies with the force. 

 The principle which is here adopted is to take in each 

 case such a force as will give a value of a in the gas at a 

 millimetre pressure that is a definite fraction of N, the 

 maximum value of a. Thus in the examples that have 

 already been given for hydrogen at 



50 volts per centimetre a='S5 = '07 N, 

 75 a= -9='18 N, 



N being equal to five for hydrogen. 



Taking the forces that give a=16 N in each case, 

 the following numbers may be obtained from the experi- 

 mental results. For air N=14'6, and the force which 

 corresponds to a=14*6x*16=2'33 is 190 volts per 

 centimetre when jp=l. The value of /3 when X=190 

 and p=*25 is obtained from the point on the curve 



corresponding to =760. This gives ='164, so 



