﻿Thermionic Currents from Tungsten. 



817 



by the formation o£ the oxide, but above this temperature 

 they were larger, for the reason just given. The following 

 table shows how much the currents at 2040° were increased 

 by the removal of the liquid air. 



Volts. 



Total Current in Microamperes. 





Liquid Air on. 

 P = 00001 micron. 



Liquid Air off. 

 P = (>250 micron. 



20 



105 





35 



... 



18 



40 



4-1 



350 



60 



9-35 



362 



80 



17-5 



365 



100 



28-2 



... 



120 



40-4 



368 



Below 2000° K. the currents were steady, but above this 

 it was noticed that they increased with the time. The 

 following table shows one instance of this, as well as the 

 effect of replacing liquid air about the U-tube near the gauge. 



Time. 



mins 

 1 



15 

 20 

 30 

 P= 



Total Current 

 (T = 2010° K.). 



350 microamperes. 



368 



375 



388 

 410 



3-5 P=0 220 micron. 

 4-5 430 



Liquid Air replaced. 



50 



5-5 

 60 

 6-5 



7-0 



8-5 

 9 



102 

 93 



84 



84 



P=0'170 86 



86 



86 



constant. 



The increase was probably caused by the more rapid re- 

 moval of the oxide at this temperature, or to the increase in 

 temperature due to the filament burning ; while the decrease 

 was caused by the absence of ions after the condensation of 



PHI Mac,. S. 6. Vol. 29. No. 174. June 1015. 3 G 



