488 Dr. S. Brodetsky and Dr. B. Hodgson on the 



interest in this connexion. Many of the apparently con- 

 tradictory results obtained by different experimenters can 

 be reconciled by means of the dual explanation here 

 suggested. 



Willows x concluded that the absorption was chemical in 

 origin, because he found its rate to vary according to the 

 particular nature of the glass from which the tube was 

 made. The absorption was biggest in soda glass, less in 

 lead glass, and least in Jena glass. If the glass is electrolysed 

 this is exactly what one would expect. During the passage 

 of a discharge the glass becomes highly charged, as was 

 shown by Riecke u , and may easily be electrolysed, especially 

 if heated by the cathode rays. Warburg, in fact^ used this 

 to obtain a film of metallic sodium on the inside of vacuum- 

 tubes for the purpose of purifying gases li . Mey's 2 results 

 show that when sodium and potassium amalgams are used 

 as electrodes, compounds of these metals with hydrogen and 

 nitrogen can be formed, suggesting that the same compounds 

 can be formed with the alkali metals in the glass. The fact 

 that Hill obtained an absorption with the electrodeless 

 discharge 6 can similarly be explained on the hypothesis 

 that the glass is electrolysed, the metal liberated causing the 

 absorption observed. 



Hill found that if successive absorption experiments are 

 performed, the absorption gradually decreases. This is 

 again in agreement with the theory that part of the absorption 

 is due to the electrolysis of the glass, for as the soda glass 

 used by him became more and more electrolysed, the 

 sodium was gradually used up, and the absorption naturally 

 diminished. 



It was also found by Hill that an experiment in oxygen 

 followed up by one in hydrogen gave an accelerated rate of 

 absorption in the latter. He offers as an explanation of 

 this fact the suggestion that the cause of absorption in the 

 oxygen experiment was oxidation, and then if we use 

 hydrogen immediately afterwards, there is a reduction, and 

 consequently a rapid absorption. This may be the case. 

 But in fig. 6 the authors show the typical absorption curve 

 for hydrogen, there being a rapid absorption at once, 

 whether a previous experiment has been performed in oxygen 



1 See par. 1, note 1. 



4 Wied. Ann. iii. p. 414 (1899). ~ See par. 1, note 2. 



5 Ann. d. Phys. xl. p. 2 (1890). 6 See par. 1, note 6. 



