506 



Mr. W. B. Haines on Ionic Mobilities 



entirely got rid of. Even when the chamber had been 

 thoroughly desiccated by many days' use, this contamination 

 would make itself felt on letting the gas stagnate for a short 

 time. The greatest care was exercised in assembling the 

 parts to have clean interior surfaces, the ebonite parts being 

 covered with paraffin-wax. When the arrangements were 

 complete, the mean value obtained for the mobility was 

 w = 367 cm./sec. per volt/cm. This value is the mean of 

 nine independent readings varying between 337 and 378 

 (d=8'45 cm.; n = 50 alternations per sec). This value re- 

 presents the practical limit reached to the purity of the gas. 

 In one series of experiments, where the conditions were 

 exceptionally favourable, the values w = 438 and w = 509 

 were obtained, but these were not repeated. Fig. 4 shows 

 some specimen curves. 



Fig. 4. 



1- 



! 

 i 











■ I A: , 





1 



n: 



a! 



3 



1-4 

 1-2 



1-0 

 ■8 

 •6 











/!/ 





/! 





l 







I V 



/ 















i/i/ 



Y / 





/ 















A A . 



/ 



















v r / 









y 



X 











A A 



















/ 



/ V 



/ / 



v\ 

















/ 



/ V 





y 











20 



40 



50 60 

 VOLTS 



80 



90 



In testing the effect of impurities it was not practicable to 

 carry the purification beyond the point corresponding to a 

 value of u about 200, owing to the time required to remove 

 the very last traces of a foreign gas from the chamber. The 

 results show that almost all *gases and vapours when added 

 to the nitrogen in small proportions, reduce both the number 

 of electrons and also their mobility. Some gases are much 

 more effective than others, and in all cases the effect of the 

 first addition is greater in proportion to its amount than 

 are subsequent additions. 



