﻿Ionization of Metals by Cathode Rays. 373 



The discharge in petrol vapour for 10 inin. reduced R to 

 1*115 : a further 15 min. increased R to 1*216 ; a further 

 15 min. reduced it to 1*187. Leaving the plate standing in 

 a mixture of petrol vapour and air for 72 hours increased It 

 to 1*209. A discharge in oxygen changed R to T369 ; a 

 further discharge to 1*097 and so on. Then the copper was 

 taken out and heated in a bunsen flame ; R became 2*39 ; 

 finally the surface was polished as at the start, and R returned 

 to 2*45. 



These experiments and many others of the same kind lead 

 to the following conclusions with regard to platinum, copper, 

 and nickel. They are very similar to those announced 

 previously. There are two states of the metal, A and B, 

 which can always be reproduced. A is that produced by 

 polishing the surface with emery and (though with less 

 certainty) by heating it in a bunsen flame. In state A the 

 ionization is nearly the same for all three metals ; I found 



Pt2*38; Ni2*46; Cu 2*44. 



State B is that produced by reducing the ionization by 

 means of the discharge, and then restoring it as far as 

 possible by means of the bombardment of cathode rays in a 

 high vacuum. The ionization in state B varies notably 

 between the different metals ; I found 



Pt 1*98 ; Ni 2*22 ; Cu 1*62. 



The ionization can be reduced below that corresponding to 

 state B by heat or by the discharge. The lowest values I 

 have found are 



Pt 1*203; Ni 1*201; Cu 0*888. 



But I have not been able to find a method of reproducing 

 these values certainly, and it is not, therefore, by any means 

 sure that these are the lowest values which can be produced 

 or that there is a real difference between the three metals. It 

 will be noted that since in order to measure R it is necessary 

 to bombard the metal with cathode rays, it is quite im- 

 possible to measure accurately the lowest values of R. 

 Long-continued standing of the metal, whether in the most 

 complete vacuum that can be produced or in any mixture of 

 gases and vapours, produces a slight increase in R ; but the 

 variation in R which I have been able to produce by this 

 means is never so great as that which exists between the 

 actions of different discharges which are as similar as it is 

 possible to make them. 



In aluminium the ionization in state A is much the same 

 as in the other metals; R = 2*G0. But by no action o£ the 



