Initial Stages of Ionization by Collision. 



963 



Quantitative relationships between partial pressure and 

 freezing-point data may readily be obtained from equations 

 (28), (70), and (71). Thus we have 



p^L Lo - /o - 7iT °- T) j + t 



=v ]( n ^)^o 



The University, Leeds, 

 Sept. 18, 1913. 



(i = l,2). 



(74) 



CIII. Initial Stages of Ionization by Collision. 

 By S. Smith, B.A., Exeter College, Oxford*. 



WHEN negative ions are liberated from a narrow elec- 

 trode such as (fig. 1), and made to move in the elec- 

 tronic state under the influence of a uniform electric field 



Fig- 1. 



- — -ic^-o ^od^L^u. 



'# 



v 6i 



-a-t>£ ^at^Jjji 



between parallel-plate electrodes to B, there is found to be a 

 considerable spreading of the beam. The amount of this 

 spreading depends on the ratio of the applied electric force, 

 Z, to a quantity k, k being the ratio of the partial pressure 

 of the ions to that of an equal number of molecules of the 

 surrounding gas")*. When the ratio of the electric force Z 

 to the pressure p of the gas becomes sufficiently large, the 

 negative ions produce ions in the gas by collisions. The 

 positive ions thus produced possess at least atomic masses : 

 their lateral diffusion may therefore be neglected, since Z is 

 large. Hence all the positive ions produced in the spaces 

 tS l5 S 2 , and S 3 reach the portions G. 0, and D, respectively, 

 of the top electrode ; being separated from and D by 



Z 



very narrow spaces. It is assumed that — is so small that 



the positive ions do not produce any ions by collisions. The 



* Communicated by Prof. J. S. Townsend, F,R.S. 



t Prof. Townsend, Proc. Roy. Soc. A. vol. lxxxi. (1908). 



