on the Discharge of Electricity from Hot Platinum. 193 



bring down the leak in hydrogen to a small value. If the nega- 

 tive potential on the wire was now reduced it recovered its 

 ionising power, slowly at first and then more rapidly, until it 

 settled down to a steady value. Charging the wire positively 

 did not appear to reduce its ionising power. 



These results certainly seem to indicate that the hydrogen 

 acts by producing a change in the wire, which takes a long time 

 to complete itself. They appear to be capable of explanation 

 if we assume that the positively charged hydrogen forms a double 

 layer at the surface of the platinum which helps the corpuscles 

 out. Further experiments are in progress, which, it is hoped, will 

 decide whether or not this is the correct explanation. 



Experiments were also made with the platinum tube described 

 above to see whether the diffusion of hydrogen through the tube 

 had any effect on the positive ionisation produced by the outer 

 surface. The hydrogen was found to increase the positive leak at 

 all the temperatures tried, the relative increase being greater the 

 higher the temperature. At 1200° C. the ratio of the leak with 

 hydrogen at atmospheric pressure to that with air inside the tube 

 was very nearly 2 - 2. At constant temperature the increase in 

 the leak was found to be proportional to the square root of the 

 pressure of the hydrogen inside the tube, i.e. directly proportional 

 to the amount of hydrogen diffusing through. The effect of the 

 hydrogen diffusing out of the metal on the positive leak offers, 

 therefore, a very marked contrast to its effect on the negative 

 leak. 



These results tend to indicate that the hydrogen inside the 

 metal, which is known from other considerations to be in the 

 atomic state, is positively charged. Only a small fraction (10 -7 ) 

 of the hydrogen comes out in the ionic form, but we might expect 

 most of it to be discharged in escaping from the metal. In any 

 case, charged hydrogen would have much greater difficulty in 

 escaping from a metal at lower temperatures, which may account 

 for the hydrogen set free from palladium not being ionised. These 

 considerations are also in agreement with the fact that electrolytic 

 hydrogen, which is positively charged, is capable of diffusing into 

 some metals — for instance, iron — at ordinary temperatures. 



