PRODUCED BY HOT PLATINUM IN DIFFERENT OASKs. 



15 



available in the laboratory. By means of the tube E, which, like D, was filled with 

 mercury, both being connected to separate reservoirs, the volume above the mercury 

 at E could be regulated, and so any desired variation could be made in the pressure 

 driving the gas through the tube F. Finally the glass tap E allowed the time 

 during which the flow took place to be varied in any desired manner. By suitably 

 \:trving the two controlling factors it was found that the pressure in the main 

 apparatus could be increased by any amount from O'OOl millim. to several centimetres 

 at will. This apparatus works very well and will probably be found to be very 

 convenient for work of this kind. It permits of a much greater range of variation of 

 pressure than a regulator which it has been found convenient to employ in previous 

 experiments, which is practically a tube like E sealed directly on to the apparatus. 

 With this the pressure is regulated by the change of volume produced when the 

 height of the mercury column is altered. 



Using the apparatus just described, a series of measurements of the leak was now 

 made, with the pressure of the oxygen gradually increasing. The temperature was 

 826 C. and the potential on the filament = + 40 volts. The numbers obtained were 

 as follows : 



30 



20 



13 



C 

 d 



It will be observed that these numbers are very similar to those previously obtained 

 with decreasing pressure, showing that the time effects do not play a very important 

 part under the specified experimental con- 

 ilitions. In order to have a more exact 

 test, two consecutive series of readings 

 were taken, one with decreasing and the 

 other with increasing pressure. The re- 

 sulting observations are plotted in fig. 5. 

 The temperature was 828 C. and the 

 potential 4- 38 '2 volts. The points marked 

 thus x were taken with the pressure 

 (U'civasmi;. those marked thus Q with the 

 pressure increasing. 



It will be seen that the two sets of 

 points fall very nearly on the same curve, 

 but that those with the pressure increasing tend to be lower than -those with the 

 pressure decreasing, in agreement with the time-lag effects previously described. 



The experiments were now pushed to higher pressures, atmospheric pressure being 



10 



33 



67 1-0 



FVeaaure : mma. 



Fig. 6. 



t-83 



