IOI 
Electromotive Force of Diphasic Liquid Systems. 
It has been shown above that a simple explanation of the reaction 
exists, and that it is a necessary consequence of the establishment of 
equilibrium between dissociated and undissociated salt. How the writer of 
the above paragraph can have failed to realize that such a reaction connotes 
a change of hydrogen ion concentration is very hard to understand. He 
appears to have been led, by his experiments on the neutralization of acids 
by alkalies, to the conclusion that in solution in ‘ oils ’ all acids behave as 
weak acids, and that in consequence their dissociation is negligible com¬ 
pared with that of salts. Beutner’s strongest aoid however appears to have 
been salicylic acid, which, though highly dissociated in water, obeys the 
dilution law. Not only is it impossible for a chemist to regard the ioniza¬ 
tion of salicylic acid as throwing light upon that of hydrochloric acid, but 
very rigorous proof will be needed before chemists will be prepared to 
accept the proposition that the presence of varying quantities of any acid is 
without effect upon potential in such a system as that under discussion. In 
the case under consideration hydrochloric acid would diffuse at the boundary 
and would be present also in aqueous solution, and we have therefore the 
system exhaustively studied by Haber and Klemensiewicz in which solutions 
of different hydrogen ion concentration are separated by a phase in which 
the concentration of the ions is constant, the constancy in the present 
instance being due to the presence of a large excess of very slightly 
dissociated acid. There can be no reasonable doubt that the e.m.f. of 
systems of the type of System II is due to the same cause as that of 
the system studied by these two workers. Loeb 1 calls attention to the 
fact that the differences of potential which Beutner would attribute to the 
presence of lipoid substances can also be obtained with proteins, and he 
suggests that the difference of potential may be due to the establishment of 
the Donnan equilibrium. This explanation, however, would hardly seem to 
meet the case, since the Donnan equilibrium depends upon the concentration 
on one side of a membrane of some ion to which it is impermeable, and no 
such ion is available in Beutner’s systems. 
It is with these systems, whose potential depends upon difference 
of salt concentration, that Beutner has been able to show the most striking 
analogies between £ oils ’ and the substances which he entitles ‘ physio¬ 
logical objects ’. Uninjured apple-skin, for example, shows a concentration 
effect markedly similar to that of an ‘oil’ containing free acid. The 
parallelism of the two experiments is very striking, and the discovery may 
well be of value as a method of investigating differences in various kinds of 
cuticle, but it cannot take us very far in the interpretation of the cellular 
mechanism of the cell. Apple-skin, with its coating of wax and specialized 
nature, is very far removed from the plasma membrane of the living cell, 
and Beutner finds that tissues without cuticle do not give very definite 
1 Journ. Gen. Physiol., iv. 351 (1922). 
