258 
PROFESSOR H. A. WILSON ON THE EFFECT OF HYDROGEN ON THE 
His wires, therefore, appear to have had the properties of old wires. He has described 
some experiments in which a wire giving a leak independent of the pressure was 
heated for many hours in a good vacuum and a slow evolution of gas was observed. 
The total volume of gas evolved, measured at 760 millims. pressure, was about 
30 times that of the wire. I have repeated this experiment of Richardson’s and 
have confirmed his result that the leak does not fall even after heating the wire for 
many hours in hydrogen at a low pressure. In my experiments the wire appeared to 
cease evolving an appreciable amount of gas after heating for about one hour. 
The following; table contains some numbers obtained in one series of observations 
with a wire kept between 1500° C. and 1600°C. The leak at 1600° C. was about 
10 -3 ampere. The wire had previously been heated in hydrogen and was giving 
a leak very large compared with the air leak. The volume of the apparatus was 
approximately 1000 cub. centims. 
Time. 
Pressure. 
li. in. 
millim. 
10 
55 
0-0017 
12 
7 
0-0028 
16 
48 
0-0028 
In this experiment the pressure did not rise 0'0002 millim. in the last five hours. 
It seems certain, therefore, that a wire giving' a large leak due to its having been 
heated in hydrogen can be heated to a very high temperature in hydrogen at a very 
small pressure for several hours without evolving an appreciable amount of gas. 
On another occasion a wire was kept at about 1400° C. from 5 p.m. to 10 A.M., and 
the pressure did not rise more than 0'005 millim., although the wire was giving a 
large leak, due to its having been heated in hydrogen. If we admit that a wire 
giving a large leak does not necessarily evolve gas, we may explain this in two ways. 
Either the wire contains no hydrogen, or it contains hydrogen in a state of very stable 
combination. In the section of this paper on the effect of hydrogen on the resistance 
of the wire it is shown that heating in air diminishes the resistance at the same time 
that it destroys the leak. This seems to show that the surface layers of the wire 
contain hydrogen which is burnt up by the air. The fact that platinum black absorbs 
very much more hydrogen than solid platinum also points to the conclusion that the 
absorption is mainly a surface effect. The presence of hydrogen in a wire can be 
tested by heating it in oxygen and observing the pressure before and after heating. 
If hydrogen is present it will form water which will be absorbed by the P 2 0 5 , and so 
the pressure will lie diminished. Richardson ( loc. cit., p. 45) describes an experiment 
of this kind and observed a diminution in the pressure. In this experiment of 
Richardson’s a wire at 900° C. in hydrogen at 26 millims. pressure gave a negative 
