Ions and .Electrons through Gases. 



51 



to a negative ion ; the most feasible hypothesis is that the 

 electron as it drifts through the vapour is for part of the 

 time in the free state, and for the remainder in attachment 

 with the molecule of the impurity. It is highly probable 

 that this attachment, occurring as it does as a result of 

 ordinary thermal motion, is of a very loose nature and is 

 liable to be broken at molecular encounters ; we would thus 

 expect continual alternations of the electron between the 

 free and combined states. 



With regard to the nature of the sink which is gradually 

 formed in the vapour of petroleum ether, nothing at all 

 definite can be said. We may imagine that polymers or 

 small aggregates of pentane or hexane are formed gradually 

 under the influence of the radiation from the polonium ; such 

 systems would probably be able to form stable negative ions^ 

 for large electron velocities and unstable ions for small 

 velocities. Initially, when the vapour is pure, the negative 

 carriers are for the most part electrons ; as the sinks appear, 

 the velocity of the electrons would be reduced through the 

 formation of unstable ions. The fact that ultimately the 

 carriers consist entirely of negative ions may be explained 

 by ascribing to a polymer the property of being able to effect 

 occasionally a union between an electron and a molecule of 

 the vapour. 



(D) Ions in Gases and Vapours. 



Gases. — The law pk = const, was verified for both the 

 positive and the negative ions in dry air over a wide range 

 of pressures. Some of the values obtained experimentally 

 for K at the lower pressures have been given in the previous 

 paper, and should be sufficient to illustrate the unchanging- 

 nature of the negative ion. A set of values obtained for the 

 mobility of the positive ion in air at low pressures is given 

 below. The first table refers to values obtained by means of 



Press, 

 mm. 



V 

 volts. 



/• 



Freq. 



K 



E x . 



8-31 



53-0 



•546 



8643 



119-5 



1-31 



1-66 



11-5 



•540 



834-2 



537-5 



1-17 



1-64 



10-2 



•540 



8509 



6180 



1-33* 



1-01 



60 



•574 



851-7 



9890 



1-31 



•563 



30 



•574 



8365 



1944 



1-44 



•416 



25 



•584 



862-1 



2363 



1-29 



•321 



1-75 



•585 



8333 



3254 



1-37 



a=S volts (v. fig. 2) 



Mean value of K x : 1-32 

 for the other determinations a^:20. 



E2 



