38 



MR. O. W. RICHARDSON ON THE IONISATION 



These numbers were found to obey the formula A#*e * >/a *. 



The values of the energy changes associated with the liberation of a gram-molecule 

 of positive and negative ions respectively are found to be o> + = 7'12x 10 4 calories and 

 W- = ll'2x!0 4 calories. Thus the work required to liberate a positive ion from 

 platinum in an atmosphere of nitrogen is more than twice the value of the 

 corresponding quantity in oxygen. 



At low pressures the positive saturation current in nitrogen was found at 905 C. 

 to consist of two parts, one independent of the pressure and the other nearly 

 proportional to it. This is shown by the following numbers : 



The current did not continue increasing with the pressure at the above rate up to 

 atmospheric pressure, but at slightly higher pressures than the above the current 

 curve began to bend round towards the pressure axis. It did not, however, tend to 

 become independent of the pressure as in the case of oxygen, but it increased at 

 a rate proportional to the pressure at high pressures. The variation of saturation 

 current with pressure up to atmospheric pressure is shown in the lower curve in 

 fig. 11. The unit of current = 1:05 x 10~ 12 ampere per square centimetre. The 

 temperature was 920 C. 



The nitrogen used in the last experiment was allowed to remain all night in the 

 apparatus, whilst both the platinum wire and the copper spiral were heated in it. 

 During this time the leak with +40 volts decreased considerably, as is shown by the 

 following numbers : 



Oxygen was certainly absorbed during the above heating by the copper spiral, for 

 it was afterwards found to be blackened. It is therefore difficult to be certain that 

 the final value of the ionisation was really due to nitrogen rather than to a small 

 trace of oxygen which the copper spiral was incapable of removing. Assuming that 



