

Disappearance of Gas in the Electric Discharge. 687 



-•any other gas, and is so sensitive to impurities, that there is 

 no possibility of a mistake. 



It is clear then that, in accordance with the conclusion o£ 

 Langmuir, the hydrogen that disappears adheres to the 

 glass, especially to the cooler parts, and that it can be 

 liberated therefrom, at least in part, by rise of temperature. 

 In the first few moments after liberation it is still in a con- 

 dition to adhere to the glass, but it generally loses that 

 power and reverts to the normal condition of hydrogen. 

 There appears to be a definite quantity of hydrogen that can 

 adhere to a definite area of ^lass at a definite temperature ; 

 the rate of disappearance of the gas, while the filament is 

 hot, falls continuously and approaches zero asymptotically. 

 This quantity increases as the temperature of the glass 

 decreases, but it also varies with the exact condition of the 

 g'lass. Sometimes no gas will adhere to the glass until it is 

 well below room temperatures ; sometimes at room temper- 

 atures as much will adhere as corresponds to a monomole- 

 cular layer on the glass, and perhaps even more. At the 

 temperature of liquid air much more than a molecular layer 

 will adhere ; but even here the amount that will adhere is 

 definitely limited, and a state can be reached in which no 

 more hydrogen can be caused to disappear. 



According to Langmuir, the abnormal hydrogen, produced 

 by the contact with hot tungsten, which will adhere to glass, 

 is made up of monatomic molecules. This conclusion is 

 based partly on the abnormal thermal conductivity of the 

 hydrogen, partly on its abnormal chemical activity, Lang- 

 muir found that the active hydrogen, liberated by warming 

 the cooled glass, would combine with oxygen in the cold. 

 We have not been able to confirm certainly this abnormal 

 activity, but we do not pretend that our experiments are 

 conclusive. It appears to us that any theory of the dis- 

 appearance must be framed in the light of the observations 

 on other gases that will be described below. 



13. Disappearance of hydrogen in the discharge. — If the 

 temperature of the filament and the potential between 

 cathode and anode are raised so that a discharge passes 

 through the hydrogen, the phenomena are somewhat differ- 

 ent. First, the gas does not remain pure hydrogen. It 

 becomes contaminated with a substance which has a lower 

 glow potential and is condensible in liquid air. This sub- 

 stance is almost certainly water. Its identity is judged 

 partly by the temperature at which it will condense, partly 



2 Z 2 



