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



Previous experiments had shown that elements such as 

 sodium and potassium are only effective in causing the 

 disappearance of gas in the electric discharge-tube if the 

 surface of the element is clean, and if it has been prepared 

 in vacuum. Accordingly the substance under test was 

 placed on the platinum foil forming the cathode, and after 

 the tube had been heated almost to the softening point of: 

 glass and exhausted, the element on the foil was vaporized 

 by passing an electric current through the latter. In this 

 way the substance was then deposited on the inner surface of 

 the anode D and an uncontaminated surface obtained. The 

 anode was of aluminium and was cylindrical in shape, fitting 

 very closely to the glass walls. Enclosing the cathode in 

 this way, the effect of the surface of the glass on the 

 absorption of the gas was minimized. A side tube B was 

 used to contain the easily volatile elements such as phosphorus, 

 sulphur, and iodine. An aperture was made in the anode 

 opposite the mouth of B so that the vapour ot the substance 

 from B could pass through and be deposited on the inner 

 surface of D. The pressures of the gas were measured with 

 a McLeod gauge. The hydrogen was prepared by the 

 electrolysis of barium hydroxide and stored in a reservoir. 

 This method of preparing the gas ensues great purity. Any 

 oxygen present was removed by passing the gas through a 

 bulb containing sodium-potassium alloy. Phosphorus pent- 

 oxide in F removed any water-vapour, and of course the alloy 

 was effective in this respect also. The gas could be admitted to 

 G, which was a known volume (0*051 c.c.) enclosed between 

 two taps. A definite volume of gas at a known pressure 

 could thus be admitted to the discharge-tube. From obser- 

 vations of the pressure in the tube before and after a discharge 

 had passed, the actual volume of gas — at atmospheric 

 pressure — which had disappeared could be calculated. 



The current through the discharge-tube was kept constant 

 by altering the filament current, and was measured with a 

 galvanometer. In previous experiments the quantity of 

 electricity passing through the tube while absorption was 

 taking place had been measured with a water voltameter, 

 but in the present work this method was not sensitive 

 enough. 



After deposition of the substance on the anode D, the 

 tube was again highly exhausted to remove any gases 

 liberated from the volatized substance. The tube was placed 

 in an enclosure maintained at —40° C. while absorption 

 of gas was in progress. 



