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PROFESSOR H. A. WILSON ON THE EFFECT OF HYDROGEN ON THE 
for the liberation of an ion to be calculated. This method of estimating this quantity 
was first used f Phil. Trans./ A, 296, 1901) by the writer to find the energy required 
to liberate one gram-molecule of ions formed at the surface of hot platinum in 
air at atmospheric pressure. The mean result then obtained was 60000 calories. 
Richardson ( loc. cit.) finds 49200 calories for the same quantity. 
It has been suggested that in my experiments the current was very small compared 
with the saturation current, and that the variation of the current with the tempera¬ 
ture was determined by the variation of the velocity of the ions with the temperature 
and not by the variation of the ionisation. But curves are given in my paper, showing 
the variation of the current with the E.M.F., which show that 220 volts produced 
very approximate saturation, and that with 40 volts the current was about one quarter 
of the saturation current and was then very nearly proportional to the E.M.F. The 
value 60000 calories was obtained from measurements of the currents due to 40 volts. 
If the saturation currents, which are also given in my paper, are used instead, the 
mean result is 50000. 
The apparatus used in the present experiments was essentially similar to that 
employed in the previous investigation. The wire was heated by passing a current 
through it, and its temperature was estimated by measuring its resistance with 
a Wheatstone bridge. The wire consisted of a loop of about 11 centims. of wire 
0'1 or 0'2 millim. in diameter. The loop was surrounded by an aluminium cylinder 
contained in a glass tube which could be exhausted. The current from the cylinder 
to the wire was measured with a galvanometer provided with suitable shunts. 
The first part of this paper contains a discussion of the former results with new 
wires. The paper is divided into the following sections :— 
(1) The effect of hydrogen on the leak from new wires. 
(2) Variation of the current with the pressure at constant temperature. 
(3) Variation of the current with the temperature. 
(4) Variation of the current with the time. 
(5) The effect of hydrogen on the resistance of the platinum. 
(6) Effects due to passing a self-luminous discharge. 
(7) A comparison of the negative leak in hydrogen with the positive leak in oxygen. 
(8) The theory of the negative leak. 
(9) A. theory of the variation of the energy necessary for the liberation of an ion 
with the temperature. 
(10) Conclusion. - 
1. The Effect of Hydrogen on the Leech from New Wires. 
The variation of the negative leak with the temperature can be represented by 
the formula x = A6 h e~ q! ' 29 , where x denotes the current per square centimetre, 6 the 
absolute temperature, and A and Q are constants. 
