Wellisch — Motion of Ions and Electrons through Gases. 11 



tion error in the determination of the electron mobility was of 

 necessity considerable. Moreover there was also the difficulty 

 connected with the presence of the ageing effect which, as men- 

 tioned above, occurs at the higher pressures ; it was of course 

 not feasible to attempt determinations at the lower pressures 

 where this elf ect is absent because the electron velocities become 

 excessively large. 



It was in every instance found that the effect of age (i. e. of 

 allowing the CO^ to remain for any length of time in the 

 'apparatus) was to reduce considerably the velocity of the elec- 

 trons. On this account great care was taken to exclude impuri- 

 ties, the gas being in all cases swept several times through the 

 measuring vessel, and the observations quickly made after the 

 final introduction. 



In figs. 5 and 6 there are given a few typical E curves which 

 were obtained in the determination of Y„ for the free electrons ; 

 the ions do not make their appearance until much higher poten- 

 tials are employed. Reference will be made later to the fact 

 that the experimental results rendered doubtful the assumption 

 that the velocity of the electron is proportional to the applied 

 field, so that the use of the term ' mobility ' is not certainly 

 justified ; however it was thought useful to make the calcula- 

 tions on the assumption that there exists a distinct mobility 

 for the electron just as for the ion. In the following table 

 there are given the results of the mobility determinations for 

 freshly prepared CO^ together with some of the results for CO^ 

 in various degrees of impurity ; the symbol K denotes the 

 mobility reduced to atmospheric pressure on the assumption of 

 the validity of the law pk =-- const. 



Freq. 



/ 



P 



mm. 



Vo 



k 



K 



Eemarks. 



807-9 



-545 



35-5 



1-4 



4232 



197-6 



Fresh 



820-6 



-518 



54 



2-45 



2587 



183-8 





824-5 



•527 



87 



2-8 



2233 



255-6 



$ 



796-8 



•530 



137 



4-5 



1336 



241-0 





833-3 



-540 



79 



3-0 



2056 



214-0 





830-1 



•545 



54 



8 



761-7 



54-1 



2 davs old 



834-2 



•550 



2b 



2-2 



2757 



83-4 



do. 



833-3 



-540 



79 



4-6 



1341 



139-4 



2^ hrs. old 



828-2 



•540 



81 



7-35 



834 





j 79'"'^ CO, 

 ■j 4- 2">'" air 









1 







In fig. 5 there is given an E curve for freshly-prepared hydro- 

 gen at atmospheric pressure ; the value of K deduced from 

 this curve was 1700*^"' per sec. 



