1897 - 98 .] Dr John Shields on Palladium Hydrogen. 
177 
hypothetical compound Pd 3 II 2 is simply the approximation of 
the above atomic ratios to the theoretical value 1*5. 
Prom the following considerations it appeared probable that 
the electro-chemical behaviour of hydrogenised palladium would 
throw some light on the matter. 
It is well known that if a concentration cell he constructed 
containing silver, concentrated silver nitrate solution, dilute silver 
nitrate solution, silver, the current will flow in the cell from the 
dilute to the concentrated solution as long as a difference of con- 
centration remains. In the light of the modern theory of the 
osmotic production of the current, we may regard the solution of 
the silver electrode in the dilute solution, and the deposition of 
silver on the other electrode as being due to the osmotic pressure 
of the silver ions (which acts against the ‘solution pressure’ of 
the silver electrodes), being greater in the concentrated solution 
than in the dilute solution. 
The electromotive force x, in volts, of such a cell is calculable 
from the expression, 
ET _ , P ET . 
7r = — log. nat. log. nat. 
Pi 
P 
P 
where E represents the gas-constant expressed in electrical units, 
T the absolute temperature, P the solution pressure of the silver, 
p and p Y the osmotic pressures (concentrations) of the dilute and 
concentrated solutions of silver nitrate, e Q the electro-chemical 
unit of quantity of electricity — viz., 96540 coulombs, and n e the 
valency of the ions. Since the solution pressures of both electrodes 
are equal, the above expression becomes 
' Pi 
The electromotive force of the cell therefore depends only on the 
ratio of the osmotic pressures (concentrations) of the silver ions. 
In the same way we may calculate the electromotive force of a 
cell, composed of weak amalgam, a solution containing the ions of the 
metal forming the amalgam (salt of the metal), strong amalgam. 
The first to call attention to concentration cells composed of amal- 
gams was von Turin (Zeits. f. physikal. Cliem ., v. 340), in a paper 
