988 Prof. 0. W. Richardson on the Positire 



ones. The whole pattern was also rather irregular, and part, 

 of this irregularity persisted in the absence of the magnetic 

 field. This distortion is probably due to the salt not being so 

 uniformly distributed after all this heating as it was at first. 

 The appearance presented after 44 hours heating is shown in 

 the next curve (fig. 4). Here the main part of the curve 

 consists of the two well-marked outer humps. The value of 

 ~ was not measured at this stage, but it may be taken as 

 *480 cm., which is half way between the value *477 cm. after 

 L2 hours heating and the value '4835 cm. attained after 

 70 hours heating. 



When the heating was continued further, it was found that 

 the ionization got smaller and smaller, so that increasing 

 temperatures had to be employed in making the measure- 

 ment-. In addition, a small hump gradually developed on the 

 inside of the outer one. This got larger whilst the old one 

 became -mailer and smaller. After about 70 hours heating 

 there was again practically only one hump, and the displace- 

 ment of this on reversing the magnetic Held was very little 

 bigger than thai given by tbe ions emitted from fresh plati- 

 num. The curves obtained alter heating for 70 hours are 

 shown in the next diagram (fig. 5). The breadth and irre- 

 gularity of th»' curves is probably due to there still being a 

 small amount of the lithium salt present. Two measurements 

 of z at the end of this experiment gave '484 and "483 cm. 

 respectively, the mean of which is '4835 cm. On attempting 

 to carry the experiment still further it was found necessary, 

 in order to get a measurable amount of ionization, to raise 

 the strip to a temperature so high that it melted. 



The foregoing results can be readily explained if weassume 

 that the positive ionization emitted by fresh lithium sulphate 

 i> due to the salts of the alkali metals of higher atomic weight 

 (sodium and potassium) which it contains as impurities ; that 

 the ionization which these substances produce at a low 

 temperature is so great in comparison that it completely 

 masks that due to the much larger quantity of lithium 

 sulphate present, and that the continued heating drives off the 

 sulphates of higher atomic weight, so that we then get the 

 much bigger displacements due to the lighter ions given off 

 by the lithium salt itself. Finally if the heating is continued 

 long enough the lithium salt is driven off". We then get, at 

 a much higher temperature, a small quantity of the ionization 

 characteristic of the platinum itself. 



The evidence in favour of this view has so far been, of a 

 rather qualitative nature. It receives additional support 

 when the values of e/rn and m deduced from the above 



