﻿by Elements in the Electric Discharge- Tube. 221 



the surface, as Langmuir suggests, these atoms will diffuse 

 slowly into the substance. The atoms arriving later will 

 have less area <>n which deposition can take place. A limit 

 to the action will be reached when the number of atoms 

 deposited is equal to the number set free by the bombard- 

 ment of the surface by the ions. 



After absorption, the proportion of the hydrogen re- 

 liberated when the tube was heated to 300° 0. varied 

 considerably in different cases, not only with different 

 elements, bat also with the same element. This is to be 

 expected when it is remembered that the thickness of the 

 substance deposited on the anode varied with different 

 substances. 



The accelerating potential affected to some extent the rate 

 of disappearance of the gas and also the final pressure 

 attained. Owing to liberation of the gas by the bombardment 

 with the ions, the final pressure reached must depend on this 

 reverse action, and the greater the accumulation of the gas on 

 the surface of the anode, the greater will be the amount of 

 gas evolved. 



With sodium on the anode a potential of 94 volts reduced 

 the gas-pressure from 743 X 10~ 3 mm. Hg. to 123 x 10 _3 mm. 

 Hg. in the course of 20 minutes. When the potential was 

 lowered to 54 volts, the pressure fell from 743 x 10 ~ 3 mm. 

 Hg. to 476 x 10" 3 mm. Hg. in the same time-interval. 

 The final pressures reached before absorption ceased were 

 96xl0" 3 mm. Hg. and 202 xlO" 3 mm. Hg. respectively. 

 The current through the discharge-tube was kept constant 

 throughout. 



The principles of the disappearance of the gas will be 

 discussed later, but there are certain features of the 

 phenomenon which can be traced to chemical actions. 



Many of the elements tested combine with hydrogen at 

 high temperatures to form chemical compounds which are 

 very stable. Any chemical action occurring in the present 

 experiments cannot be due to the heat, as the discharge-tube 

 was maintained at —40° C, and the incandescent filament 

 was always at a lower temperature than that at which 

 Langmuir found chemical action occurred with hydrogen. 

 The effect may be caused by " activation " of the gas, the 

 latter assuming some modification under the action of the 

 electric discharge. In the above experiments the amounts of 

 gas absorbed were so small that it would be extremely 

 difficult to detect the existence of any chemical compound in 

 the tube. In order to increase the amount of gas absorbed, 



