254 
PROFESSOR H. A. WILSON ON THE EFFECT OF HYDROGEN ON THE 
from the same sets of observations as were used in getting the values of A and Q. 
It is interesting to find that observations by other observers over a very wide range 
also agree with the calculated values of x fx. 
The following table gives some values of x jx calculated from the formula when 
p = 1 millim. 
Temperature. 
x'/x. 
X. 
°C. 
amperes per sq. centim. 
800 
3-4 x10 s 
l-8x 10“ n 
1000 
3-4x10 s 
6'8x 10~ 9 
1200 
1-1 x10 5 
5-1x10“ 7 
1400 
0■9 x10 4 
1 • 4 x 10~ 5 
1600 
1 • 2 x 10 3 
2-0 x10~ 4 
1800 
2-4 x10 2 
1•6 x10~ 3 
It will be seen that xfx diminishes rapidly as the temperature rises. 
Without making any assumption as to whether the hydrogen changes II or D, or 
both, we may draw an important inference from the results so far considered if we 
assume that the effect of the hydrogen is due to its presence in the platinum. Since 
the effect varies continuously with the pressure at constant temperature, we may 
conclude that the amount of hydrogen in the surface layer of the platinum varies 
continuously with the pressure. It follows from this that the hydrogen is in the 
platinum in a state of solution and not in a state of definite chemical combination. 
If a definite compound were formed, then the amount of combined hydrogen would be 
zero when the pressure was below its dissociation pressure, and constant when the 
pressure was above this. The results obtained with new wires indicate therefore that 
the hydrogen is in solution in the platinum. 
2. Variation of the Current with the Pressure at Constant Temperature. 
A wire, which had been heated for several hours in hydrogen at pressures up to one 
atmosphere, was kept at a constant temperature, and the leak observed at a series of 
pressures from one atmosphere downwards. At each pressure the leak was observed 
until it became nearly constant. The resistance of the wire at 0° C. was determined 
from time to time, and its resistance when hot was kept proportional to its resistance 
at 0° Cl, so that its temperature was kept nearly constant. The difference of 
potential used was proportional to the pressure, except at low pressures. The 
following table contains the results obtained in this way :— 
