936 Research Staff of: the Gr. E. C, London, on the 



the power of decolorizing tungsten subsequently deposited on 

 them. They attribute the action to the formation of large mole- 

 cular aggregations of the metal which cover but a small part 

 of the surface, but they produce little evidence for their view 

 except a proof that the action cannot be due to the formations 

 of chemical compounds, as had been imagined previously. 

 Now, the decolorizing of tungsten might be effected merely 

 by the binding of the free electron and the transference of 

 absorption to a definite region in the ultra-violet, similar to 

 that of most chemical compounds in which the electrons are 

 " bound " ; and it is known that films of tungsten too thin 

 to show appreciable absorption in visible light show strong 

 absorption of ultra-violet light. We suggest tentatively 

 that this decolorization of tungsten is physically the same 

 process as the absorption of gas ; both represent the 

 binding of a negative charge on an electrically polar layer. 

 Whether such binding is to be called " chemical combina- 

 tion " is a question of words ; we prefer (cf. I., p. 586) to 

 confine the term " chemical " to cases where separable 

 compounds of fixed constitution are found, obeying the 

 law of constant proportions. But the action would, in our 

 view, be " chemical" in the sense employed by Langmuir 

 in his theory of surface actions associated with mono- 

 molecular films. 



Perhaps we may proceed further. In II., p. 703, we 

 suggested that there is only one reason for believing that 

 the action of phosphorus in promoting absorption is 

 " chemical," namely that the absorption of gas decolo- 

 rized the yellow film of phosphorus on the walls. If the 

 colour is associated with the positively charged portion of 

 the phosphorus molecule, the binding of negative charges 

 on the layer might well decolorize it. Once more, if 

 this explanation of the matter is correct, absorption by 

 phosphorus is closely related to chemical action ; but it is 

 not chemical in the sense that any compound of phosphorus 

 and the gas in definite proportions is ever free from atoms of 

 those elements in the " uncombined " state. 



20. We have so far discussed actions in which salt and 

 phosphorus can be mutual substitutes. But the salts do not 

 possess all the properties of phosphorus in the promotion of 

 absorption. With phosphorus, but not without it, pressures 

 well below the glow potential can be reached starting from 

 pressures well above it. On this matter we have nothing to 

 add to the explanation offered in II., p. 697, based on the 



