256 
PROFESSOR H. A. WILSON ON THE EFFECT OF HYDROGEN ON THE 
and small quantities of pure hydrogen were successively admitted. The current was 
measured at each pressure, keeping the temperature constant. The following table 
contains the results obtained. 
Temperature 1564° C. 
Pressure. 
Current. 
millim. 
amperes 
0-006 
2-5 x10~ 7 
0-028 
4-5 xIO - 7 
0-056 
1 -8 x10~ 5 
0-337 
5•2 x10 -5 
0-169 
1-2 x10~ 5 
0-090 
2-4 x10- 6 
0-003 
5-0 x 10 -8 
The last three pressures were obtained by pumping out the hydrogen. 
These results show that with a new wire the leak rises with the pressure and falls 
when it is reduced. The experiment was repeated immediately, and similar results 
were obtained. Next day, after the wire had been all night in hydrogen at a low 
pressure, the following results were obtained :— 
Pressure. 
Current. 
millim. 
amperes 
o-ooi 
5 x 10“ 8 
0-017 
5 x 10~ 8 
0-146 
2 x 10-7 
0-297 
9 x 10-7 
0-618 
11 x10-7 
0-281 
11 xlO' 8 
0-146 
6 x 10 -8 
0-073 
5 x 10 -8 
It appears, therefore, that with a new wire the results are very different from those 
obtained with an old wire. 
If a wire which has been heated in hydrogen at high pressures and is giving a large 
leak nearly independent of the pressure is heated in air, the leak falls at once to a 
small value. If the air is pumped out and a little hydrogen admitted, the leak at 
high temperatures is not affected at first, hut after heating in the hydrogen for some 
time it usually develops rather quickly. The leak then rises when the pressure is 
increased, and has about the same value as with a new wire. On pumping out the 
hydrogen the leak only falls very slowly with the time. 
The following table gives the currents at several pressures with a wire treated in 
the way just described. This wire, after heating in air, was heated to 1490° C. in 
