DISCHARGE OF ELECTRICITY FROM HOT PLATINUM. 
275 
are led to the conclusion that it is only those corpuscles which are in some way 
associated with hydrogen molecules or atoms ’\\diich are able to escape from the 
platinum, at the temperatures at which it is possible to make observations. 
In a note to his paper on “The Electrical Conductivity Imparted to a Vacuum by 
Hot Conductors” (‘ Phil. Trans.,’ A, vol. 201, pp. 497-549) Mr. Richardson suggests 
that the effect of hydrogen on the negative leak which I have observed can be 
explained on his theory by supposing that the hydrogen diminishes Q while A 
remains constant. But, as we have just seen, the fact that the leak is proportional to 
p shows that Q is constant and A proportional to p. When p is greater than about 
0*02 millim. it is found that Q does diminish as p increases, but A does not remain 
constant. 
Mr. Richardson also suggests that my process of cleaning the platinum with nitric 
acid may deposit a layer of negatively charged oxygen on it which would increase Q 
and so diminish the leak. The leak can, however, be reduced without treating the 
wire with nitric acid. If the wire is simply heated in a good vacuum the leak falls 
off with time ; and if the gases evolved by the wire are removed, the leak can lie 
reduced in this w^ay to as small a value as can be obtained by treating the wire with 
nitric acid. The nitric acid process waas adopted liecause it enabled the hydrogen to 
be got rid of without long continued heating which causes the wire to disintegrate. 
[Although it appears from the experiments that the negative leak obtained from 
hot platinum at low^ pressures is due to the presence of hydrogen or other substances, 
it is, of course, possible that wdth perfectly pure platinum at a sufficiently high 
temperature some negative leak wmuld be obtained due to the emission of corpuscles 
by the platinum alone. Mr. Richardson’s results for cailion, which show that there 
is a large emission of corpuscles from hot carbon even at very low pressures, make it 
probable that there wmuld be a similar emission in the case of jiure platinum at 
sufficiently high temperatures. The author has recently made some experiments with 
carbon wffiich, as far as they have gone, confirm Mr. Richardson’s results for that 
substance.] 
18 M. 1903 
2 N 2 
