1897—98.] Dr John Shields on Palladium Hydrogen. 
185 
hydrogen makes the palladium strongly positive to the platinum, 
but this characteristic gradually diminishes till, finally, when the 
palladium is fully charged with hydrogen, the electromotive force 
is less than half its original amount. 
The actual observed values are contained in the following table, 
the amount of hydrogen introduced in each case being estimated 
by the increase in weight of the palladium wire. 
Mass. 
E.M.F, 
1-0000 
1-0014 
1-0017 
1-0023 
1-0045 
1-0068 
- 0-05 
+ 0-81 
+ 0-79 
+ 0-73 
+ 0-74 
+ 0-33 
There can be little doubt that the first gradual diminution 
observed by Knott is due to partial polarisation of the palladium, 
and that, if sufficient time had been allowed for diffusion to take 
place, a constant value would have been obtained up to the point 
of supersaturation. 
The gradual fall in the electromotive force of the cell we have 
examined (see table) is undoubtedly due to the same cause, and 
therefore we are justified in accepting the last number of the series 
as a maximum value, the true electromotive force of the cell, if it 
were possible to obtain it, probably approaching more closely to 
zero. 
From the series of experiments which has just been described, 
and from others, the details of which have not been given, it 
appears, then, that the electromotive force of a cell, composed of 
palladium containing a small quantity of hydrogen, dilute sulphuric 
acid ( i.e ., an electrolyte containing H ions), palladium containing a 
large quantity of hydrogen, is either zero or very nearly so. In 
any case, the electromotive force is out of all proportion to what 
we would expect if the cell behaved like a true concentration cell, 
and therefore it remains to be seen what interpretation can be put 
on the result. If it be granted that a concentration cell is not 
formed, this would seem to preclude the idea that the hydrogen is 
YOL. XXII. 26/9/98. N 
