Absorption of Gases in Vacuum- lubes. 489 



or not. Curves V., VIII., IX., X., in Hodgson's paper 4 , 

 show the rapid absorption in hydrogen after the tube has 

 rested awhile, an initial rapid absorption being obvious in 

 each case. It appears, therefore, that the initial rapid 

 absorption is due solely to the hydrogen, and does not 

 depend upon the tube having been used with oxygen 

 immediately preceding the hydrogen experiment. 



Further, the fact that the inactive gases helium and argon 

 are readily absorbed, shows that means other than chemical 

 must be at work. 



In 1907 Campbell Swinton found that gas was occluded 

 in the walls of the glass vacuum-tubes after discharge 7 . 

 This gas was found in the form of bubbles a little below the 

 surface of the glass. But in 1908 Soddy and Mackenzie 

 obtained the Campbell Swinton effect 9 , and found that the 

 gas occurring as bubbles was probably due to the electrolysis 

 of undecomposed carbonates and sulphates in the glass. The 

 gas absorbed by the discharge was found by them to be not 

 in the glass but in the film deposited from the cathode by 

 disintegration, and a large fraction of the absorbed gas 

 could be recovered. They also showed that sublimated 

 magnesium or aluminium did not absorb helium. It was, 

 however, shown b} T Heald 16 that many metals absorb 

 hydrogen on sublimation in a vacuum-tube. Heald worked 

 with hydrogen and his curves are typical absorption curves 

 for hydrogen. The absorption in a vacuum-tube is thus 

 not a mechanical occlusion, but is brought about by some 

 electrical means. 



Skinner 17 concluded that gas was evolved from the cathode 

 and absorbed by the anode. With new electrodes there is 

 often an initial evolution of gas especially in hydrogen and 

 nitrogen, or in any gas with aluminium electrodes. But if 

 the tube is used and then allowed to stand awhile, on 

 restoring the current, no initial evolution is found in most 

 cases. The evolution that Skinner speaks of must refer to 

 fresh or virgin electrodes, and is probably due to the state 

 of the surface with regard to its gas content. 



In the case of aluminium, gas is evolved for a long time 

 before absorption sets in. In Hodgson's curves XXXV., 

 XXXVI. 4 , the pressure curves for copper anode— aluminium 



4 See par. 1, note 4. 7 See par. 1, note 7. 9 See par. 1, note 9. 



16 Phys. Rev. xxiv. p. 269 (1907). 



17 Phil. Mag. xii. p. 481 (1906) ; Phys. Rev. xxi. pp. 1 & 169 (1905) ; 

 Phys. Zeit, vi. p. 610 (1905). 



4 See par. 1, note 4. 



