PHILOSOPHICAL TRANSACTIONS. 



I. The Ionisation Produced by Hot Platinum in Different Gases. 



By 0. W. RICHARDSON, H.A., D.Sc., Fellow of Trinity College find Clerk Maxwell 



Student, Cambridge University. 



Communicated by Professor J. J. THOMSON, F.R.8. 



Received June 19, Read June 28, 190G. 



I. 1. INTRODUCTION. 



THK principal objects of this investigation have been to examine the part played by 

 the surrounding gas in the production of ions by hot metals and to discover, if 

 possible, the mechanism by which the positive ions originate. In what follows, 

 previous work on ionisation by hot metals will not be described, except in so far as it 

 bears directly on the questions investigated, since the historical part of the subject 

 has l>een fully treated in previous papers by the writer,* and others. 



The present communication deals -chiefly with the emission of positive ions from hot 

 platinum, as earlier work has yielded much more information concerning the negative 

 ioriisation. In 1901 the writer t showed that a great numl)er of facts in connection 

 with the negative ionisation from hot metals could be explained by supposing that 

 the electrons, of which the ions consist, were produced in the metal itself, from which 

 they escaped by virtue of their kinetic energy. This theory makes the negative 

 ionisation a function only of the metal surface and its temperature, and therefore 

 independent of the nature and pressure of .the surrounding gas, except in so 

 far as this may have the effect of modifying the nature of the metallic surface. 

 H. A. WILSON} has confirmed this part of the theory by showing that the negative 

 leak, except when ionisation by collision occurs, has the same value in air, nitrogen, 

 and water vapour over a wide range of pressures. WILSON also showed, however, 

 tliat hydrogen u-reatly modifies the negative leak. The experiments in the present 

 paper set-in to show that the effect of hydrogen is due to some change it produces in 

 the platinum surface; its abnormal behaviour is probably bound up witli its electro- 

 positive character. 



* ' Jahrbueh der Radioaktivitat u. Elektronik.' 

 t Crtinl>. Phil. Prcx-.,' vol. 11, p. 286. 

 J ' Phil. Trans.,' A, vol. 202, p. 243. 

 VOL. CCV1I. A 413. B 22.11.06 



