PRODUCED BY HOT PLATINUM IN' DIFFEKKNT GASES. 



.'17 



The relation between current and E.M.F. at 2 '8 inilliina pressure and 905 C. is 

 given by the following numbers : 



At 760 millims. and 920 C. the values found were : 



Compared with oxygen under similar conditions, these numbers, which are shown 

 graphically in fig. 11, show that the ionisation in nitrogen requires a greater 'applied 



IOO 200 3OO 400 SCO 6OO 7WJ 



Fig. 11. 



E.M.F. to produce saturation. With the above wire, which was - 02 centim. in 

 iliumeter, the current in oxygen showed very little increase with voltage after 

 40 volts. The increase with 360 volts at 2 '8 millims. is due to the occurrence of 

 ionisation by collisions. 



The variation with temperature of the leak in nitrogen at a pressure of 2*8 millims. 

 \\.ia also examined. On raising the temperature the leak was too big at first and 

 usually required about 20 minutes to fall to its minimum value. The numbers 

 obtained for the positive and negative iouisation are given in the accompanying 

 table : 



