704 Research Staff of the G. E. C. ; London, on the 



27. How does phosphorus increase absorption ? — But if the 

 action of phosphorus is not chemical, why is the amount of 

 gas that can be absorbed with phosphorus greater than that 

 which can be absorbed without ? For it is undoubtedly 

 greater — at least in hydrogen. If the supply of phosphorus 

 vapour is unlimited, then there is no limit to the amount of 

 hydrogen that can be absorbed. We suggest that the answer 

 is this. Under the discharge a limit is set to the absorption 

 of hydrogen, because absorption is balanced by evolution of 

 gas already absorbed in the walls by the bombardment of the 

 changed particles. When phosphorus is mixed with the 

 hvdrogen, it is deposited on the walls as a stable solid : this 

 solid shields from bombardment the absorbed hydrogen and 

 prevents it from being detached. If sufficient phosphorus is 

 present to form a solid layer over the hydrogen absorbed on 

 the glass, this 'layer provides a new surface on which gas 

 may once more be absorbed. If the supply is unlimited, an 

 unlimited number of layers can be found, consisting alter- 

 nately of hydrogen and phosphorus, and there is no limit to 

 the amount of gas that can be made to disappear. (Of 

 course, the layers of gas and phosphorus are not likely to be 

 completely distinct.) 



On this view, if conditions can be obtained in which 

 absorption of hydrogen takes place without evolution, then 

 the amount absorbed should not be increased by phosphorus 

 unless it is present in such quantity that it can form a layer 

 covering the hydrogen completely and providing a new sur- 

 face for absorption. For in such conditions the limit to 

 absorption will be fixed by the amount of gas which can 

 adhere, all at one time, to the surface of the walls. Now, 

 such conditions can be obtained in hvdrogen, for the gas can 

 be made to adhere to the walls in the presence of hot 

 tungsten without any discharge at all. It is strong support 

 for our view that we can discover no evidence whatever that 

 more hydrogen can be absorbed by the discharge in the 

 presence of phosphorus than can be absorbed by LangmmVs 

 method without any phosphorus at all — unless so much 

 phosphorus is supplied that a distinct yellow coloration 

 appears on the walls. In order that phosphorus may increase 

 absorption above the maximum quantity that can be absorbed 

 in its absence, so much must be used that there is definite 

 evidence of the formation of a complete layer of phosphorus 

 on the glass. It is difficult experimentally to establish that 

 proposition with perfect certainty, but we have observed 

 nothing thai cannot be reconciled with it. 



