276 Discharge of Electricity from Hot Platinum. [June 3 



enormously diminishes the negative leak, and also, to a large extent, 

 stops the evolution of gas from the wire when it is heated. The nitric- 

 acid, of course, oxidises the hydrogen. 



0. W. Richardson* has recently published two papers on the negative 

 leak from hot platinum and other substances. He obtained large 

 negative leaks from platinum, which behaved in the irregular manner 

 which I have described above as occurring when using wires not 

 specially cleaned. The results which I have obtained do not confirm 

 the theoretical conclusions to which he has been led. 



The paper also contains the results of measurements of the positive 

 leak in air and hydrogen. The results confirm the view that the 

 positive leak from clean wires is due to ionisation of the gas molecules 

 at the surface of the platinum. 



The view put forward in this paper with regard to the negative leak 

 is that it is generally due to the emission of negative ions by hydrogen 

 occluded in the platinum. Other substances, such as phosphorus 

 pentoxide and alkali salts, also give rise to a negative leak when they 

 are present. Air and nitrogen do not appear to produce any negative 

 leak appreciable on a galvanometer. 



It is probable that a pure platinum wire heated in a perfect vacuum 

 would not discharge any electricity at all, either positive or negative, 

 to an extent appreciable on a galvanometer. 



* ' Proc. Camb. Phil. Soc.,' vol. 11, Part IV; ' Eoj. Soc. Proc.,' vol. 71, 1903. 



