268 
DR. HAROLD A. WILSON ON THE 
waiting, whereas when it lias just lieen lowered the leak rises on waiting. In spite 
of this, however, the numbers at each temperature keep fairly concordant towards the 
end of the experiment, which shows that they must approximately represent the 
variation of the leak with the temperature for a constant state of the wire with regard 
to the hydrogen. This means that the time between the observations was so short 
that very little change in the amount of hydrogen in the wire occurred during the 
latter measurements, in spite of the changes made in the temperature. This may be 
due to the amount of hydrogen absorbed by the wire varying very slowly with the 
temperature at the temperatures used in this experiment. It is stated in Eoscoe and 
Schorlemmer’s ‘Chemistry’ (vol. 1, p. 139) that platinum at a red-heat absorbs 
3-8 times its volume of hydrogen, and at 100° C. only 076 times its volume. ^ If the 
volume absorbed were proportional to the absolute temperature, then platinum in 
equilibrium with hydrogen at any particular temperature would be in equilibrium at 
any other temperature. According to Eoscoe and Schorlemmer, the volume absorbed 
increases more rapidly than the absolute temperature up to a red heat, hut on the 
other hand platinum certainly loses some of its hydrogen when heated to near its 
melting-point; consequently there must he a region of temperature between a red heat 
and the melting-point where the actual amount of hydrogen absorbed is nearly 
independent of the temperature at constant pressure. The very small variations with 
time in the latter of the above experiments seem to show that the range of 
temperature used in this experiment lies in this region. The latter numbers m the 
above experiment have been reduced to amperes per square centim. The results are 
o-iven in the following table. The pressure in this experiment was 0T12 millim. 
Temperature. 
Current per 
square centimetre. 
° C. 
amperes. 
1520 
7-55 xlO-s 
1459 
3-02 xlO-5 
1400 
1-15 X10“^ 
1341 
0-442 X 10 -5 
1284 
0-145 X10-5 
1 
The formula ? I when these numbers are substituted in it, 
gives Q = 85,900. A similar series of experiments done at a pressure of 0‘0013 millim. 
of hydrogen gave the following results :— 
