Ionization from Heated Platinum. 



183 



relations following the positive ionization-temperature effects 

 now being discussed are shown in Curve 2, fig. 2. About 

 15 minutes' time was taken to get the readings for each 

 curve of fig. 3 ; the curves were taken seriatim, proceeding 

 in each case from low to high temperatures. Curve 1 shows 

 a rapid dropping off of the positive thermionic current from 

 786° to 800° C. ; Curve 2 shows a less decided falling off 

 from 738° C. on ; while Curve 3 indicates that the cause of 

 this decrease in the two previous curves, whatever it may be, 

 has been removed. It is to be remarked that the highest 

 current readings recorded in these curves are approximately 

 in the ratio of 1 to 200 for the currents obtained in the 

 initial stages of heating the wire. 



Y. Effects produced by Heating in Carbon dioxide. 

 When the wire was again in a condition of giving very 

 small positive ionization currents, it was heated in a dry 

 atmosphere of C0 2 and investigations carried out as described 

 under Section IV. No increase of thermionic currents was 

 obtainable in any case with this gas, although the wire 

 was heated for various periods of time and at different 

 temperatures. In fact, the positive currents were in each 

 instance lower than those obtained previous to heating in 

 this gas. The following is a simple set of data obtained 

 after heating the wire in C0 2 for 10 minutes at 750° C. 



Temperature, ° C. 



628 

 033 



654 690 732 765 786 



798 810 822 



Current (arbi- "J 

 trary units) 1 

 before heating [ 

 in 0O 2 J 



032 0-31 ... 033 (M0 



054 071 ... 



Current (arbi- ~\ 

 trary units) 1 

 after heating ( 

 inC0. 2 J 



0-27 



0-25 025 023 025 0-25 



031 0-40 0-83 



These results were not anticipated in view of Horton's * 

 work, but would be on the view that carbon dioxide has little 

 affinity for electrons. Possibly, also, referring to Curve 3, 

 fig. 2, the wire should have been heated at higher tempera- 

 tures than it was, since negative currents could not be 

 obtained in this stage of the history of the wire at a 

 temperature lower than 820° C. The latter explanation is 



* Proc. Camb. Phil. Soc. vol. xvi. pp. 89 & 318 (1911). 



