Hydrogen ami Nitrogen by Electron Impacts. 781 



due to electron bombardment of the gauze was measured, 

 using the same accelerating potential as before. This was 

 appreciable, especially with the higher accelerating potentials 

 and after large amounts of hydrogen had been cleaned up. 



The liquid air had to be replenished from time to time, to 

 keep its surface at the same level around the tube E. 



The clean 

 in Table I. 

 every run. 



Results. 



up with different initial pressures is shown 

 The accelerating potential was 71 volts in 



Table I. 



Electron current = 650 microamps. 

 Accelerating potential = 71 volts. 

 Pressures taken at intervals of 4 minutes. 



1 



A 



B 



C 



D 



; 5080x10-5 mm. 



2160x10-5 mm. 



942x10-5 mm. 



200x10 -5mm. 



4380 



1602 



642 



122 



4060 



1262 



482 



77 



3880 



1070 



398 



52-2 



! 3550 



926 



338 



35-6 



3380 



800 



292 



27-4 



| 3200 



730 



252 



19-2 



3060 



650 



230 



16-8 



] 2890 



592 



204 



124 



1 2740 



546 



184 



9-6 



| 2600 



512 



164 



8-8 



The absolute amount of hydrogen cleaned up decreases as 

 the initial pressure is made smaller, but the ratio of the 

 initial pressure to the final pressure increases. 



Table II. <uves the results obtained on varying the acceler- 

 ating potential, but keeping the other conditions constant. 

 It was impossible to do more than to get the initial pressure 

 approximately constant. 



A slight but definite clean up was observed at 13*3 volts, 

 a pressure decrease from 432 x 10~ 5 mm. to 408 X 10" 5 mm. 

 being observed in 60 minutes with an electron current of 

 185 microamperes. (This will be referred to as run L.) 

 No evidence of any clean up at all could be obtained when 

 the electrons were accelerated by 8'9 volts. A careful test 

 was made over a period of 90 minutes, and the very slight 



Phil. Mag. S. 6, Vol. 41. No. 245. May 1921. 3 F ' 



