Disappearance of Gas in the Electric Discharge. 923 



each point are not accompanied by proportional changes 

 in the hydrogen absorbed ; moreover there are some values 

 of the amount of hydrogen absorbed which seemed never to 

 occur however the amount of phosphorus was varied. 

 (5) An amount of phosphorus below the step never gives a 

 yellow coloration to the walls of the lamp after the gas has 

 been absorbed, while an amount above the step always gives 

 such a coloration. 



The points marked and joined by the dotted line were 

 obtained by a slightly different procedure. Here, before 

 the lamps were filled with gas, the filament was heated so 

 as to deposit the phosphorus as a coloured film on the walls: 

 the lamp was then filled with gas and the critical value of P 

 determined in the usual manner. The observations were 

 much less consistent than in the first series, the difference 

 being probably due to the much longer time occupied in the 

 absorption (see Par. 15), but the following features seem 

 clear: — (1) The absorption is less than in the first series, 

 especially at the higher values ; (2) the maximum vanishes 

 and is replaced by approximate " saturation " ; (3) the 

 marked step does not wholly disappear. 



8. We now pass to factor (3), the state of the surface of the 

 vessel. 



In all experiments the walls of the vessel were freed from 

 adhering gas (chiefly water and C0 2 ) by baking for five 

 minutes to 400° G. during exhaustion. It this precaution 

 is not taken, the absorption is less but results are irregular ; 

 doubtless the gas which is allowed to remain should be 

 included in the amount absorbed. But if, it is taken, the 

 absorption is independent within very wide limits of the 

 nature of the surface. Thus it is the same whether the 

 vessel is made of soda, lead or borosilicate glass, or fused 

 silica. It is unchanged by washing the surface with strong 

 acids or alkalis ; by etching it with hydrofluoric acid, liquid 

 or gaseous ; by sand-blasting it ; or by depositing on it many 

 salts by evaporation of solutions ; it is little, if at all, changed 

 by depositing silver chemically. In the examination of 

 these modes of treatment some anomalies were found that 

 have not been fully explained, but by none of them could the 

 absorption be changed consistently *. 



On the other hand, there is a method by which the absorp- 

 tion can be greatly increased with perfect consistency, if 



* In II., p. 702, it was stated that P 2 5 deposited en the walls of the 

 vessel prevented absorption. This statement is not true if the material 

 is thoroughly dried by baking and exhaustion. 



