192 Mr Richardson, The Effect of Hydrogen 



The Effect of Hydrogen on the Discharge of Electricity from 

 Hot Platinum. By O. W. Richardson, M.A., Trinity College. 



[Bead 27 November 1905.] 



It has been known for some time that hydrogen has a very 

 marked power of increasing the negative ionisation from hot 

 metals. The effect in the case of platinum has been investigated 

 in detail by H. A. Wilson*, who came to the conclusion that the 

 increase was due to the hydrogen dissolved in the metal. The 

 present paper is a preliminary account of experiments made to 

 shed further light on the matter. 



The method adopted was to measure the saturation current 

 from the outside of a hot platinum tube to a surrounding cylinder 

 in air, both when hydrogen was diffusing through the tube from 

 inside and when it was not. The surrounding air would of course 

 oxidise the hydrogen as fast as it came out, and thus keep, the 

 surface in a constant state, so that presumably any change in the 

 leak would be due to the hydrogen, and not to a change in the 

 platinum surface. 



Even when hydrogen was allowed to diffuse through the tube 

 at a rate equal to 2 c.c. at 76 cms. pressure per sq. cm. of surface 

 per minute, not the slightest change could be detected in the 

 value of the negative leak. This result points strongly to the 

 conclusion that the increase in the ionisation observed in an atmo- 

 sphere of hydrogen is not due to the presence of the hydrogen in 

 the metal as hydrogen, but to some alteration it produces in the 

 superficial regions of the metal. 



Two experiments which support this conclusion may be cited. 

 As is well known, a platinum wire which has been heated for 

 a long time in oxygen gives small but definite ionisations both 

 positive and negative. On replacing the oxygen round such a 

 wire by hydrogen the writer found that, though the positive 

 ionisation was increased somewhat at first, it soon began to fall, 

 whilst the negative leak increased simultaneously. Both these 

 effects seemed far too slow to be accounted for by the rate at 

 which hydrogen entered the wire (which was only '1 mm. thick), 

 though that explanation is not excluded with absolute certainty. 



The other experiment consisted in putting a big negative 

 potential on the wire just mentioned. This was found to rapidly 



* Phil. Trans. A, Vol. ecu. p. 243. 



