﻿by Elements in the Electric Discharge- Tube. 217 



discharge practically no hydrogen will be liberated from the 

 walls by bombardment with the ions. If there is any 

 absorption of the gas, this effect will not be masked by the 

 liberation of the gas from the walls or electrodes. 



The object of the present work was the study of the 

 behaviour of hydrogen in the presence of various elements in 

 a discharge-tube when a current was passing through it. 

 The pressures of the gas in these experiments were much 

 lower than those used by the author in the papers quoted 

 above, but they were much greater than those used by the 

 previous investigators — Langmuir and the General Electric 

 Campany. 



2. Description of Apparatus. 



At gas-pressures below O'l mni.Hg.it is difficult to obtain 

 a current through a discharge-tube unless very high potentials 

 are used. A valve also must be placed in the circuit to make 

 the discharge unidirectional. This entails further diminution 



Fiff. 1. 



M c LEOD GAUGE 



3=fcdl^b- 



of the current. By using a Wehnelt cathode the potential 

 required was greatly reduced. The apparatus employed is 

 shown in fig. 1. The incandescent filament was a strip of 

 platinum foil 5 mm. long and 3 mm. wide. As the 

 discharge-tube had to be thoroughly cleaned after each 

 experiment, the cathode was sealed in a glass stopper which 

 could he removed when the tube was cleaned. This 

 necessitated the use of tap-grease, but the vapour arising from 

 it did not appear to afreet the results at the pressures used. 



