•272 
DR. HAROLD A. WILSON ON THE 
The palladium was found to “ splutter ” very much when hot, so that its resistance 
rose rapidly. The very large value of the positive leak from it when fiist heated is 
no doubt analogous to the positive leak from platinum not specially cleaned when it 
is first heated. 
(6.) Summary of Principal Results. 
( 1 .) The negative leak from a hot platinum wire in air, nitrogen, or water vapour 
is independent of the gas pressure, unless ionization by collisions occurs, and is the 
same as the negative leak from the same wire in a good vacuum. 
( 2 .) The variation of the negative leak in air with the P.D. and pressure at 
constant temperature can be explained on the hypothesis that the negative ions 
produce ionization by collisions with the air molecules. 
( 3 .) The number of collisions made by a negative ion probably varies in\ersely as 
the al)solute temjjerature at constant pressure. 
( 4 .) The variation of the negative leak per square centimetre with the temperatuie 
can be expressed by tlie equation x = where x is the current in ampeies, 
6 the absolute temperature, and Q and A are constants. For a wire \ery veil 
cleaned with HNO 3 , Q is 155,000 and A is about 6 X 10". 
( 5 .) The negative leak in hydrogen is much larger than that in air or in a vacuum. 
At low pressures it is nearly proportional to the pressure of the hydrogen. 
( 6 .) The presence of the hydrogen changes the value of the constants Q and A, the 
following l^eing the values obtained at different pressures ; 
00 
Pressure. 
Q. 
A. 
0 
155,000* 
6 X108 
0-0013 
120,000 
1 X 10 ' 
0-112 
85,900 
5-3 X lOi 
133-0 
36,000 
0-1 
( 7 .) It is extremely probable that the negative leak in air or in a vacuum is due 
to traces of liydrogen or other substances in the wire. The leak can be reduced to 
‘^ 5 o^ooof^^ part of its ordinary value by taking precautions to remove such traces. 
( 8 .) On first lieating a positively charged palladium wire in a vacuum it can 
dischai'ge positive electricity. The rate of discharge falls oft rapidly with time and 
idtimately becomes inappreciable. A similar eftect sometimes occurs with platinum, 
but the amount of the leak is very small and it disappears in a few seconds. The 
[* Of the three values of Q obtained at low pressures (viz. 155,000, 131,000 and 120,000) the value 
131,100 is probably nearest the truth. The value 155,000 depends on measurements of Aer^?^ small 
currents and is probably too large. See Appendix.] 
