12 Messrs. Richardson, Nicol, and Parnell on the 
We come now to the theoretical interpretation of the 
results which have been obtained. Winkelmann showed that 
Pressure in cms. 
his results could be explained by supposing that the hydrogen 
dissociated outside the platinum and that only the atoms could 
get through On this supposition, he was able to obtain the 
dissociation constant of the hydrogen. In the units used in 
his paper (and in the present one), he gives the value of this 
as 0°64 in two experiments and ("81 in the other. He points 
out, however, that there is a considerable choice in the value 
of this constant which may be taken to fit his results. This 
might be due to the fact that he takes only three observations 
to test a formula with two undetermined constants, but as a 
matter of fact any value of K which does not make the 
dissociation too big over the comparatively limited range of 
pressure in his experiments wil] give the values found. We 
consider that our experiments demonstrate clearly that a 
value for the dissociation constant as high as 0°64 is quite 
inadmissible, and that the external dissociation, for the 
existence even of which we have no definite experimental 
evidence, must be much smaller than Winkelmann supposed. 
