262 
DR. HAROLD A WILSOX OX THE 
Temperature. 
Xegative leak per 
square centimetre of 
platinum. 
° C. 
amperes. 
1686 
4x lO-s 
! 1651 
2 X 10-8 
1616 
1 X 10-s 
'riiiis tlie more thorougli treatment of tlie wire with HNOy rednced tlie negative leak 
to about of that previously obtained, but the rate of variation of the leak with 
tlie temperature remained almost unchanged. These numbers give Q = 155,000 and 
A - 6 X lOh 
If A = 6 X loh then, on liiCHAUDSON’s tlieory, the number of corpuscles (n) in a 
cubic centimetre of the platinum would be 8 X lO^h Pattersox {Ioc. cit.) obtained 
u 10”^ by experiments on the variation of the resistance of platinum in a magnetic 
held. It appears, therefore, that n cannot really be deduced from the constant A. 
On one occasion some phosphorus pentoxide accidentally got into the tube 
containing the hot wire, and the negative leak was increased enormously by its 
presence. The current at 1490° C. was about 4 X 10“^ ampO'e, or IQ-^ ampm-e per 
scpiare centimetre. TTie negative leak was therefore increased about one million 
times by the presence of the phosphorus pentoxide. Now ordmary phosphorus 
pentoxide usually contains phosphorus acid and other impurities, and may give oh 
some vapoiii's when kept in a vacuum. If any such vapours were present in the tube 
containing the hot wire, this result shows tliat they would produce a leak of negative 
electricity from it. 
It is clear, therefore, that minute traces of various substances such as hydrogen, 
phosphorus pentoxide, and alkali salts produce a large increase in the negative leak 
from liot platinum, and that the nioi'e thorough the precautions taken to remove 
traces of such sul)stances the smaller the leak becomes. I have not succeeded in 
reducing the leak to less than 1 part in 250,000 of that okserved by IIiCHARDSOX, 
V)ut I have little doubt that, if all traces of impurities could be got rid ot, the negative 
leak in air would be reduced to a still smaller value. 
There is con.siderable evidence in favour of the view that the negative leak in air 
is due to tire presence of traces of hydrogen in the platinum.'^ It will be shown in 
the next section that the negative leak in hydrogen is enormous compared with that 
in air, and that at low pressures it is proportional to the pressure ot the hydrogen. 
When the pressure of the hydrogen is very small, the value ot Q in the formula 
X = Ad-e~^ ~^ is nearly equal to its value in aii’, which makes it very probable that 
the small negative leak in air or a ^'acuum is due to the presence ot traces ot 
This view was suggested long ago by Berlivek, ‘ AVied. Ann.,’ vol. 33, p. 289 (1888). 
