DISCHAKGE OF ELECTRICITY FROM HOT PLATINUM. 
27.3 
negative leak in hydrogen is proportional to the pressure at low pressures with 
palladium as with platinum. 
(9.) In air and hydrogen, at pressures above several millimetres, there is a permanent 
positive leak from hot platinum which increases with the pressure. This leak is 
larger in hydrogen than in air a,t the same tempeiatiiie. 
(7.) Conclusion. 
The question ol most interest in connection witli the leak ot electricity Irom hot 
platinum is the method of production of the ions. Richardson {loc. cit.) has proposed 
the theory that the negative leak is due to the escape of the corpuscles which, on the 
ionic tlieory of metallic conduction, metals contain. These corpuscles are supposed to 
move about freely inside the metal and to have a distribution of velocities the same 
as the molecules of an ordinary gas. All corpuscles entering the siirlace layers of the 
metal with a velocity component perpendicular to the surface greater than a definite 
value are supposed to escape; and from these assumptions a formula of the type 
X = can lie deduced, as Richardson has shovui. According to this theory 
the number of corpuscles in a cubic centimetre of the meta.1 can he calculated fiom 
the value of the constant A, and according to this view the leak depends only on the 
state of the platinum and not on the surrounding gas. 
The experiments described in this paper show that the phenomena cannot be 
explained completely by such a simple theory. There seems to be no doubt that the 
negative leak from hot platinum is due to the emission of negatively charged 
corpuscles or electrons, but the number of these emitted depends on the gases and 
other substances present at the surface of the platinum. With clean platinum in air 
at a low pressure there is, comparatively speaking, very little leak of electricity either 
positive or negative. In air at high pressures there is a small leak of positive 
electricity, while in hydrogen there is a comparatively enormous negative leak. In 
Mr. Richardson’s experiments the gas present appears to have been that evolved by 
the hot metal, and so probably contained hydrogen.* This is, no doubt, the explanation 
of the comparatively very large currents which he obtained. 
When occluded hydrogen molecules are present on the surface of the platinum, we 
may suppose that each molecule or atom of hydrogen has a corpuscle associated with 
it, and that these corpuscles have an energy distribution similar to the energy 
distribution of the molecules of a gas. If those corpuscles, having more than a certain 
amount of energy, are aide to escape from the surface, these suppositions account for 
the existence of a negative leak in hydrogen, i 
* In Richardson’s experiments the gas pressure rose considerably when the temperature of the wire 
was raised, showing that gases were being evolved by the wire. 
t When a molecule of hydrogen has lost its corpuscle it may he supposed to combine with one of the 
corpuscles present in the platinum, so that on this view the hydrogen molecule serves as a sort of stepping . 
stone to enable the corpuscles to escape from the platinum. [See Appendix.] 
2 N 
VOL. CCII.-A. 
