926 Research Staff of the G. E. C, London, on the 



sodium fluoride, the amount of phosphorus introduced being 

 always *05 mgm. : — 



KaF coated on wire (mgm.). Hydrogen absorbed (mgin.). 



-0007 



0-09 -0007 



0-2 -0007 



0-28 -0019 



0-36 -0023 



2-0 -0023 



Almost all the effect is obtained by an increase from 0*2 to 

 0*28 mgm. Similarly with silica and sodium silicate, it 

 occurred between 0*3 and 0'35, but with lithium fluoride 

 below 0*17 mgm. It is natural to inquire whether the 

 critical amount is that required to form a monomolecular 

 layer on the surface of the glass. The area of this surface 

 was about 200 cm. 2 ; the area of a molecule of NaF is about 

 4xl0~ 16 cm. 2 ; consequently to form a monomolecular 

 layer about 035 mgm. would be required. This is only 

 about one-eighth of the experimental value ; but it is clear h r 

 possible that all the salt introduced is not deposited 

 uniformly on the walls in the active condition. 



11. Inquiry was also made how the presence of the active 

 film affected the relation between gas absorbed and phosphorus 

 present, examination being confined to quantities of phos- 

 phorus below the step in fig. 1. The significant result was 

 obtained that, in the presence of salt, any of the points below 

 the step (except possibly those corresponding to less than 

 0*02 mgm. of phosphorus) might be raised to the step at 

 •0023 mgm. of hydrogen. The maximum effect was not 

 always obtained, but the maximum obtained w T ith any given 

 salt and any given amount of phosphorus appeared quite 

 independent of the nature of the salt (so long as it would 

 produce the effect at all) and almost independent of the 

 quantity of phosphorus ; rnoreovor, this maximum was the 

 same within the limit of error as the step of the phosphorus 

 line. 



Some less systematic observations will now be described 

 which provide additional evidence on which to base a 

 general discussion. 



Absorption witlwut Phosphorus. 



12. Even when no phosphorus is present, the burning of 

 the lamp and the accompanying discharge produce some 

 absorption of gas. But unless the original pressure is very 



