Diffusion of Hydrogen through Hot Platinum. 3 
results are in agreement with those which had previously 
been found by Winkelmann on the pressure variation and 
with those which we obtained later, where ithe second method 
was used, in both cases. 
Huperimental Arrangements. 
We shall now describe the apparatus used for the experi- 
ments which yielded the numbers given in this paper. It 
has been pointed out that, when the method of letting 
hydrogen out through a small platinum tube is employed, it 
is absolutely essential to have the gas as pure as possible. 
Since hydrogen takes up impurities in passing over rubber, 
it is necessary to have all joints of sealed or ground glass. 
The hydrogen was prepared by the action of caustic potash 
on aluminium. The aluminium was hung up inside a wide 
test-tube which was open at the bottom and dipped into a 
beaker containing caustic potash solution. The gas escaped 
by a tube sealed into the other end of the test-tube and passed 
through a tube containing solid potash, to absorb most of the 
moisture, to a three-way tap. This tap enabled the main part 
of the apparatus to be connected with either the hydrogen 
Pig. T. 
Cetcs &e (e) 
generator or the water-pump. The rest of the apparatus 
consisted of a Toepler pump, a mercury pressure-gauge, a 
phosphorus-pentoxide drying-bulb,and the parts shown infig. L. 
The tube B is a sulphuric-acid gauge whose movements 
B2 
