610 Disappearance of Gas in the Electric Discharge. 



of a cooled tube depends very greatly on the ease of access 

 to that tube. If A is cooled, the rate of disappearance in 

 given electrical conditions is much greater than if T is 

 cooled (actually T was separated from the lamp by about 

 40 cm. of tubing) ; and if the tube between the lamp and T 

 is constricted, then (with A warm) the rate of disappearance 

 is very much decreased. The rate of resultant reaction 

 depends on the rate of removal of the product. It is 

 because the rate of disappearance depends so intimately on 

 the ease of access to liquid air that it is difficult to interpret 

 at present the observations on the relation of that rate to 

 the electrical conditions and that it is useless to give them 

 in detail. In order to study this relation, conditions must 

 be found in which this complicating factor is not present. 



Summary. 



1. The research is an attempt to determine the nature and 

 cause of the disappearance of gas under the electric dis- 

 charge at low pressure. 



2. A brief summary of previous knowledge is given. It 

 is not yet known what parts are played by absorption on the 

 walls and by true chemical combination ; nor is it known 

 precisely what electrical conditions are most favourable to 

 the disappearance. 



3. Though an incandescent tungsten filament forms part 

 of the discharge vessel, the changes investigated are not 

 those studied with great care by Langmuir. 



4. The apparatus is described. 



5. Preliminary observations showed that the disappearance 

 of gas was closely connected with the appearance of the glow 

 in the vessel. The electrical conditions in which the glow- 

 appears are described briefly. In any given state of the 

 discharge vessel it appears sharply at a definite potential 

 difference between the electrodes, called the glow potential. 



6. Observations are described on the relation between the 

 glow- potential and (1) the thermionic emission, (2) the 

 pressure of the gas, (3) nature of the gas, (4) the form of 

 electrodes. 



7. Small amounts of impurities change very greatly the 

 glow- potential, especially in hydrogen. 



8. The theory of the glow is deferred for later discussion ; 

 but the general connexion between the appearance of the 

 glow and the increase of ionization in the gas is considered. 



9. The great importance of the glow potential for inter- 

 preting the rate of disappearance of gas is pointed out. 



