﻿216 Dr. F. H. Newman on Absorption of Hydrogen 



as it is formed. The presence of phosphorus vapoui 

 accelerates the rate of disappearance of all gases except 

 the inert ones, and much lower final pressures are attained. 

 This, the author believes, is due to the deposition of the gas 

 on the walls of the vessel, this deposit then being covered 

 with a layer of red phosphorus formed by the electric 

 discharge passing through the phosphorus vapour. The 

 covering of red phosphorus prevents liberation of the 

 hydrogen by bombardment of the ions, and at the same 

 time provides a new surface on which further gas can be 

 deposited. 



The problem of the disappearance of the gas is a very 

 complicated one, owing to the many factors to be considered. 

 The walls of the vessel and the electrodes will certainly receive 

 some of the gas, although the latter may not disappear in its 

 original state. There will be chemical changes occurring in 

 the volume of the gas, such as the conversion of carbon 

 monoxide into carbon dioxide, and, in addition, any other 

 elements present in the discharge-tube, either in the form 

 of vapour or solid, will affect materially the rate of dis- 

 appearance of the gas and the final pressure reached. 



The author * has shown previously that various substances 

 present on the electrodes of a discharge-tube alter considerably 

 the amount of gas that can be caused to disappear when an 

 electric discharge is passing. In particular, phosphorus, 

 sulphur, and iodine cause both hydrogen and nitrogen to be 

 absorbed at a very great rate, and a high vacuum is quickly 

 produced as a result. This action of phosphorus has been 

 used for many years to obtain and maintain very low 

 pressures in valves. These three elements stand out as being- 

 very effective even at high pressures, but other substances 

 which were tested in a similar manner did not appear to 

 absorb hydrogen. On the contrary, gas appeared to be 

 liberated. This effect can be explained as follows. At 

 pressures above 1 mm. of Hg. a certain amount of the gas 

 in a discharge-tube becomes occluded within the walls. 

 This gas will be liberated when the walls are bombarded 

 by the ions produced by an electric discharge. This effect 

 will mask any disappearance. If, however, the tube is 

 heated almost to the softening point of glass and highly 

 exhausted, then on admitting hydrogen at a small pressure 

 such as O'l mm. of Hg., very little occlusion of the gas 

 within the walls will take place, and on passing the electric 



* Newman, Proc. Hoy. Soc, A. vol. xc. (1914); Proc. Ph. vs. Soc. 

 vol. xxxii. (1920) & vol. xxxiii. (1921). 



