264 
PROFESSOR H. A. WILSON ON THE EFFECT OF HYDROGEN ON THE 
2x 10~ 7 , and almost independent of the pressure. It will be seen that the leak fell 
rapidly at first and was usually greater after leaving the wire cold all night. It was 
nearly independent of the pressure below 200 millims. The variation of the leak 
with the time can usually be represented roughly by a formula of the type 
A.e~ at + Be^^ + C, in which a is much greater than /3 , and A greater than B or C. The 
term C represents the final value of the leak, which is nearly constant, but it also 
falls off very slowly. The term Ae~ at represents the large leak at first, and falls to 
half value in from a few seconds to 20 minutes, according to the temperature and 
state of the wire. The second term falls to half value in several hours. Irregular 
variations in the leak sometimes take place which make it impossible to determine a 
and /3 exactly. Moreover, these quantities are not the same on different occasions, 
but depend greatly on the previous treatment of the wire. 
I think these facts indicate that the wire absorbs hydrogen in the cold, and that 
part of this hydrogen is given off fairly rapidly on heating, part is given off very 
slowly, and part not given off at all, even in a vacuum 
If an old wire which has been heated in hydrogen for a long time is heated in air, 
and then again to a very high temperature (above 1600° C.) in hydrogen, the leak is 
nearly the same in hydrogen as in air. On reducing the temperature the leak 
remains small for a time, but then begins to increase rapidly and after a time gets to 
about the usual value for a wire in hydrogen. At first, while the leak is increasing 
with the time, it falls when the temperature is raised. After further heating 
the leak becomes more steady, and then always rises with the temperature. These 
facts seem to show that an old wire does not absorb hydrogen above a certain 
temperature, or only does so very slowly. 
The fact that while the leak is rising with time it falls on raising the temperature 
is difficult to explain. This effect was obtained on several separate occasions. The 
leak, then, has a definite maximum value at a certain temperature. The leak in these 
experiments was saturated, so that the decrease on raising the temperature was not 
due to a diminution in the velocity of the ions. The leak rose when the temperature 
was diminished. In one experiment the current was 10 -7 ampere at 1300° C., 
4 x 10~ 7 at 1400° C., and 4 x 10 -8 at 1500° C. 
An increase in the leak while heating in hydrogen at constant temperature is 
usually accompanied by a small fall in the pressure, showing that the wire has 
absorbed hydrogen. Much weight cannot be given to observations showing a small 
change in the pressure, because small quantities of gas may be evolved or absorbed by 
the glass or the electrodes, so that a small change in the pressure is not necessarily 
due to gas evolved or absorbed by the wire. 
One wire which gave a large leak in hydrogen when it was new, after heating in 
hydrogen for several days was heated in air and then gave the usual small air leak. 
On again heating in hydrogen to above 1600° C. for ten hours the leak remained 
small and showed no signs of rising with time. 
