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RESEARCH COMMITTEES. 
Free Energy and Polarisation. 
In an interesting memoir, Jahn and Schinrock* have investi- 
gated the polarisation set up during the electrolysis of a solution 
between platinum electrodes, from the point of view of changes 
of free energy. They write down the terms which include the 
changes of intrinsic energy and entropy due to every transforma- 
tion which goes on, both at the anode and at the kathode, and 
also in the body of the solution—owing to ionisation—and thus 
obtain, in the simplest and most direct manner possible, an 
expression for the change of the free energy of the system, in 
terms of the changes both of its intrinsic energy and of the 
entropies of its constituents. As the first attempt to apply the 
laws of thermodynamics to the modern theory of electrolysis the 
paper has great value ; the theoretical conclusions advanced in it 
are, moreover, confirmed by experiment. The results may be 
summed up as follows :— 
(1.) The maximum polarisation for all salts formed from 
heavy metals and the radicles of strong oxyacids is the 
same. 
(2.) The polarisation of a cell containing a dilute oxyacid 
must be increased by increasing the external pressure ; 
moreover it has the same value for all oxyacids, whether 
strong or weak, at the same pressure. 
(3.) The maximum polarisation in an oxyacid cell is inde- 
pendent of the concentration of the acid solution. 
(4.) The maximum polarisation in an alkaline solution is 
identical with that in an oxyacid solution. 
(5.) The maximum polarisation in a dilute salt solution will 
always exceed that in the corresponding acid; the 
difference between the two being equal to the change of 
free energy brought about by the dissociation of water 
into hydrogen and hydroxyl ions. 
10. Relation between Electromotive Force and External Pressure. 
Let the action of a cell result in the performance of external 
work, not only in the circuit in accordance with Joule’s Law, but 
also in changing its own volume against external pressure during 
the passage “of the current. If no other work is done we may 
write equation (2)—of eae a eae 
iL fi 6U 8U 
d dT ——.dv-+H.d dv 
o=nisy +98 ots +E.dg+p 
where p and v denote the ale pressure} and the volume of 
the cell respectively. 
¥* Zeitsch. ftir phys. Chem., xvi, p. 45. 
+ Whether it be due to electrolytic gas or anything else. 
