Cluster in a Gas under Influence of an Electric Field. 941 



field assists in breaking up .the clusters, after which it 

 decreases. When the period of life is constant it is the same 

 as that of a cluster not under the action of an electric field 

 and in equilibrium with free ions. In that case t 3 is given 



by t 3 = ti= -, where y denotes the fraction of clusters 



becoming free ions per second of a number of clusters and 

 free ions in equilibrium with one another. The mean free 

 path of disintegration of a cluster under the action of an 

 electric field is then also given by the equation 



vp 



or L=-2lvr 7 ) 



since rj = £>M 3 , where M 3 depends only on the nature of the 

 gas. 



Summary. 



1. Experimental evidence was obtained that the negative 

 ion clusters in a gas nre gradually disintegrated through 

 bombardment by neutral molecules, and consequently a con- 

 dition of equilibrium is that the free negative ions should 

 gradually form clusters. The average period of life of a 

 negative ion cluster in air not specially dried at atmospheric 

 pressure was calculated to be 4*2 x 10 ~ 7 sec. and that of an 

 elementary negative ion 1*1 x 10" 8 sec. The corresponding- 

 periods of life in C0 2 were shown to be of the same order of 

 magnitude. 



2. Evidence was also obtained that the velocity of a 

 negative ion cluster is greater than proportional to the 

 electric field whose order of magnitude is the same as that 

 producing readily ionization by collision. This is the case 



in air not specially dried for values of - equal to 173 and 



higher values, where X denotes the electric field per cm. and 

 p the pressure of the gas in mm. of mercury. 



3. The negative ion clusters in a gas are disintegrated by 

 an electric field if of sufficient strength through the velocity 

 given to the clusters, the field being of the same order of 

 magnitude as that producing ionization by collision. The 

 magnitude of the effect, like ionization by collision, gradually 

 increases with increase of electric field, which is best shown 

 by curves. It may be stated, however, that the clusters are 



disintegrated in the case of air, C0 2 and H 2 when - has 



