PRODUCED BY HOT PLATINUM IN DIFFERENT GASES. 



59 



account of the electrostatic attraction the charged atoms might be expected to have 

 greater difficulty in escaping from the metal. This would especially be the case at 

 low temperatures, and may account for the hydrogen set free from palladium not 

 being ionised. These considerations are also in agreement with the fact that 

 electrolytic hydrogen, which is positively charged, is capable of diffusing into some 

 metals for instance iron at ordinary temperatures. 



Experiments were also made to see how the positive ionisation in air varied with 

 the temperature, (1) when the tube had been heated for a long time in air and there 

 was no hydrogen inside the tube, (2) with a constant pressure (atmospheric) ot 

 hydrogen inside. The results, which extend from 973 C. to 1331 C., are exhibited in 

 fig. 17 ; the numbers in brackets denote the order in which the observations were 



700 

 600 

 500 



,400 



I 



;300 



200 



100 



m 



/" 



950 1050 1150 1250 1350 



Temperature: Degrees Centigrade 



Fig. 17. 



taken. The upper curve represents the ionisation with hydrogen inside the tube, the 

 lower one that without. The difference between corresponding ordinates represents 

 the part of the ionisation which is due to the hydrogen diffusing through at any 

 temperature. The values of the hydrogen part of the current (1 = 1*8 x 10~ u ampere 

 per square centimetre) at various temperatures are given in the following table : 



These numbers increase much more rapidly with the temperature than the 

 quantities of hydrogen diffusing as given by RICHARDSON, NICOL, and PARNELL'S 

 experiments. Hence the efficiency for producing positive ionisation of a given 

 amount of hydrogen diffusing out of platinum increases rapidly with increasing 

 temperature. 



I 2 



