Disappearance of Gas in the Electric Discharge. 699 



literature of the subject that we have discovered. Jt is 

 therefore necessary to consider that theory. 



It is doubtless based on the belief that a greater amount 

 of gas can be absorbed in the presence of phosphorus than in 

 its absence. This belief is doubtless well-founded, but it 

 must be insisted strongly that the facts described so far 

 afford no warrant for it. The important fiction which we 

 have just discussed depends only on a reduction of the lower 

 limit of pressure attainable and on a consequent increase of 

 the potential that can be applied without a discharge passing. 

 The attainment of this lower limit is not necessarily associated 

 with the absorption of more gas, for the limit is set, not by 

 the cessation of absorption if the discharge continues, but 

 fey the cessation of the discharge. 



So far, then, there is no evidence for the chemical theory. 

 We will now proceed to give the evidence that has been 

 obtained against it. 



This evidence may be summarized in three statements : — 



(1) If the gas that has disappeared is restored, it is found 

 to be in the same chemical state as it would have been if it 

 has disappeared in the absence of phosphorus. 



(2) There is no simple relation between the quantify of 

 gas that can be made to disappear and the quantity of phos- 

 phorus necessary for its disappearance. There is nothing 

 approaching to a " law of constant proportions ". 



(3) The amount of gas that will disappear depends very 

 greatly on the surface condition of the walls of the discharge 

 vessel. 



These three statements will be expanded in order. 



23. Restoration of absorbed gas. — (1) When the gas has 

 disappeared in the presence of phosphorus, part of it at least 

 can usually be restored by baking the vessel as described 

 in § 12. If sufficient phosphorus has been used to give a 

 " yellow bulb," the evolution of gas appears to accompany 

 closely the disappearance of the yellow colour. If the gas 

 that has disappeared is CO, the gas can be restored almost 

 completely as a mixture of CO and C0 2 , the proportion of 

 the latter being the greater as the total amount increases. 

 That is exactly the result obtained without phosphorus. If 

 it is argon, the gas restored is argon with some hydrogen — 

 as before. If it is hydrogen, the gas restored is hydrogen 

 (partly in the "active" condition) together with water 

 vapour. Sometimes the whole of the gas can he restored ; 

 sometimes only part; the proportion restored varies consider- 

 ably from experiment to experiment in much the same way 



