216 Mr. H. H. Lester : Determination of Work Function 



follows : — Before sealing off, 5*799 ; immediately after seal- 

 ing off, 5*872. Succeeding values taken at various intervals 

 for two or three hours were 5*44, 5*399, 5*270, 5*116, 4*79, 

 4*85. The subsequent values oscillated around 4*8. Carbon 

 behaved similarly to the osmium and tungsten in that the 

 initial values w ere high and the later values were lower and 

 constant. A series of readings to determine the variation 

 of (f> with time was not taken ; it was noticed, however, that 

 it took carbon much longer to become " normal " than it 

 did tungsten. Usually the carbon filaments were heated 

 from twenty-four to forty-eight hours before readings were 

 recorded. 



Langmuir investigated the reduction of the residual gases 

 in the presence of a hot wire, and termed the phenomenon 

 the "clean-up effect"*. It is evident that in the progress 

 of the clean up the vacuum was cleared of all active gases 

 and successively lower pressures were produced. We have 

 seen that successively lower values of <£ were also obtained. 

 The value found for tungsten in the unsealed tube is what 

 was expected as the initial value immediately after sealing 

 off. It is noticed that the latter value was greater than the 

 former. This discrepancy was undoubtedly due to the fact 

 that certain gases were liberated from the portion of the 

 glass that was heated during the sealing-off process. It 

 was concluded from the behaviour of osmium and tungsten 

 that residual gases affect the value of <p in precisely the 

 same way that they affect the value of: b. This result was 

 expected. 



The behaviour of carbon is interesting. It may be re- 

 membered that except in one case the carbon filaments were 

 not subjected to the vacuum -furnace treatment. There 

 were no waxed or ground-glass joints, except one that con- 

 nected the glass tubing to the pump, and the pump was kept 

 running continuously. Since there could be no addition 

 of gas to the experimental chamber, it was thought that 

 after sufficient time a condition would be reached in which 

 the active gases would be consumed and the carbon would 

 be surrounded only by residual gases inert to carbon. If 

 the variation in </> is due to the influence of active gases, 

 then the elimination of these ought to produce the same con- 

 stancy of behaviour in regard to the cooling effect as the 

 elimination of gases by the clean-up effect. In fact the 

 clean-up effect removes only the active gases. The results 

 of the carbon showed practically the same behaviour as was 



* Journ. Auier. Cliem. Soc. vol. xxxiv. p. 1310 (1912). 



