MR. 0. W. RICHARDSON ON THE IQNISATtON 



All the known evidence relating to the ionisation from hot solids goes to prove that 

 the positive and negative ionisations are, in the majority of cases, entirely separate 

 effects. It is true that, generally speaking, a hot metal produces ions of hoth signs 

 simultaneously, but by suitably altering the conditions the ratio of the two ionisations 

 can be made to change to almost any required extent, even at constant temperature, 

 and the one can l>e made to vary greatly whilst the other remains practically constant, 

 so that it is evident that the two ionisations are produced by the operation of at least 

 two independent causes. The leak from hot solids is, therefore, essentially unipolar. 



In the 'Philosophical Magazine' (6), vol. VI., p. 80, the writer showed that the 

 current from a fresh positively-charged hot platinum wire fell off asymptotically with 

 the time the wire was heated at constant temperature. An effect of this kind was 

 first recorded by ELSTER and GEITEL,* who noticed that an insulated plate near an 

 incandescent platinum wire received a large positive charge when the wire was new, 

 which gradually diminished, and ultimately changed sign with continued heating. 

 This initial positive ionisation is presumably independent of the pressure, since it is 

 very large in a good vacuum. Despite numerous experiments t its origin is still 

 uncertain, but it is possibly due to some gas or volatile impurity present in the purest 

 obtainable platinum. 



By using a wire in which the initial positive leak had been reduced to a small 

 value by heating in a good vacuum at a constant temperature at intervals extending 

 over a long period of time, and subsequently letting in fresh air, the writer} succeeded 

 in clearly showing that the leak, which was almost independent of the time, consisted 

 of two parts, one proportional to, and the other independent of, the pressure of the 

 air. So far as the writer is aware, this is the first experiment recorded which shows 

 that any part of the positive leak from hot metals is a function of the pressure of the 

 surrounding gas. The reasons which made such an effect difficult to detect are 

 (1) the masking of the effect by the initial positive leak, if this has not been 

 completely removed, and (2) irregularities and time effects in the part of the leak 

 produced by the gas itself. These will be discussed at some length later in the 

 paper. 



In the present investigation a much more detailed study has been made of the 

 lonisation in oxygen than in the other gases considered, for several reasons. In the 

 first place, oxygen is a simple elementary gas which is easily prepared in a state of 

 considerable purity. It has the additional advantage that small quantities of it 

 produce a large increase in the positive ionisation which is readilv measured. Finally, 

 it acts as a self-purifying agent by oxidising, and so getting rid of, hydrogen an 

 impurity winch it is of the utmost importance to avoid in experimenting on the 

 ionisation produced by hot bodies. 



* 'Winl. Ann..' vol. :!7, p. 315 (1889). 



t 0. \V. Kir iivKi.sr.x, 't'.It. C'nii-iT- Li.^f,' 1905, },. 50 



J 'Camli. Phil. Proc.,' vol. 13, p. 58 (1905). 



