VI1. On the Dlscliarfje of Electricity from Hot Flatinum. 
By Harold A. Wilson, D.Sc., B.A., Felloiv of Trinity College, Camhrulge. 
Communicated hy C. T. K Wilson, F.R.S. 
Keceived June 3,—Read June 18, 1903. 
The following paper contains an account of the results obtained in a series of 
experiments on the loss of electricity from hot platinum in several gases at various 
pressures. I shall begin by giving a brief account of some of the results obtained by 
previous workers on this subject, confining myself to those results which appear to 
hear more or less directly on the present investigation. Further information on the 
results of the earlier investigations may he found in Wiedemann’s ‘ Elektrizitat,’ 
vol. 4, in J. J. Thomson’s ‘ Recent Researches,’ in Stark’s ‘ Die Elektrizitat in Gasenf 
and in the papers referred to. 
Elster and Geitel (‘ Wied. Ann.,’ vol 37, p. 315, 1889) found that hot platinum, 
in air and oxyo-en, produces positive electrification of the surrounding gas and liodies 
immersed in it, except at low pressures, when negative electrification is obtained. In 
hydrogen they found the electrification is always negative. 
J. J. Thomson (‘Phil. Mag.’ [5], vol. 29, pp. 358-441, 1890) measured the current 
due to a constant P.D. between two pai'allel platinum plates immersed in various 
gases and vapours at a bright red lieat. He found that the current depends very 
meatlv on the nature of the nas. Gases which dissociate into atoms when heated, 
O V O 
such as HCl and salt vapours, conduct very much better than gases such as air and 
ammonia, which do not dissociate into atoms. Uidess both electrodes are hot enough 
to glow, very little current can be obtained. 
Arrhenius (‘ Wied Ann.,’ vol. 42, p. 18, 1891) measured the current between two 
})arallel jilatinum plates immersed in a Bunsen fiame, hy which they were ke})t at a 
bright red heat. He found that the current with increasing P. D. inci'eases at first 
proportionately to the P.D., hut when the P.D. is more than one or two volts, the 
curve connecting the current and P.D. Ijends over, and then liecomes nea.rly parallel 
to the axis of P.D. The current is greatly increased when an alkali salt vapour is 
introduced into the flame. He investigated the relative conductivities due to various 
salts, hut it is not necessary to describe here the results he olitained, since they do 
not bear directly on the present investigation. 
The results obtained by Arrhenius were confirmed and extended in a research hy 
VOL. ccii. —A 352. 2 I 2 14.11.03 
