934 Research Staff ot the G. E. C., London, on th 



the formation of a layer of red phosphorus * on the walls of 

 the vessel under the action of the discharge, and the gas 

 absorbed is held by this layer. On the other hand, the view 

 that the layer merely nets by protecting the absorbed gas 

 from further bombardment is probably too crude. For the 

 experiments with salts or tungsten evaporated from the 

 filament show that layers of these substances on the walls 

 promote absorption in a manner very closely similar to 

 that characteristic of phosphorus. Since there is no reason 

 to believe that these substances, once deposited, can be 

 removed and deposited again (as suggested in II., p. 698), 

 the gas that is held by these layers must lie above rather 

 than below the layer. The view to which we incline now is 

 that solid films deposited on the walls from ionized molecules 

 under the action of the discharge are in an electrically polar 

 condition ; they may perhaps be regarded as bearing a free 

 charge on their surface. When gaseous ions suitably 

 charged approach this polar surface, in virtue of their charges 

 they enter into a combination with it and cannot be liberated 

 again except by a considerable rise of temperature. The 

 action is similar to that which Langmuir has imagined for 

 the explanation of so many surface actions. This supposition 

 will form the basis of our discussion. 



18. First it should be noted how completely similar, up to 

 a certain point, is the action of phosphorus and of the salts 

 (a term which, for brevity, will be used to include tungsten). 

 The " first stage " of Par. 13 in absorption by phosphorus 

 (which alone will be discussed for the moment) corresponds 

 exactly to the absorption of gases in the absence of phos- 

 phorus by evaporating the salts in their presence (Par. 12). 

 The quantities absorbed in this stage depend so greatly on 

 the pressure of the gas and other factors that quantitative 

 comparison is difficult ; but the amounts absorbed in the 

 two cases under comparable conditions are not very different. 



Again, the amounts of gas that can be absorbed by a layer 

 of phosphorus and by a layer of salt are very similar. It 

 is natural to identify the step of fig. 1 with the amount that 

 can be held by a single complete layer of phosphorus, and 

 this step is very nearly, at least, the amount that can be held 



* In speaking of " red " phosphorus, we do not mean to commit our- 

 selves to the view that the element is present in the molecular condition 

 characteristic of red phosphorus in bulk. We only mean that it is 

 present in some condition differing, like that of red phosphorus, from 

 the white variety in the fact that the vapour-pressure is inappreciable at 

 room temperature. 



