Electromotive Force of Diphasic Liquid Systems . 97 
In both the above systems two such r interphasic potentials exist at 
A and B, the difference of which is equal to 
R T log 
C x ‘ oil ’ 
C 2 ‘ oil ’ * 
since the other factors cancel out; and in Beutner’s opinion this expression 
represents the total e.m.f., which is therefore determined by the relative 
concentrations of the common ion M (or X) in the layers of oil adjacent to 
the aqueous solutions. There are, however, considerable difficulties in 
accepting the conclusion that the total e.m.f. can be expressed by a 
logarithmic formula of this type. 
The derivation of expression (1) is not entirely satisfactory, since little 
is known of the ‘ solution pressure ’ of metals in liquids other than water. 
The same result can, however, be obtained by the use of Nernst’s par¬ 
tition formula: 1 
m 1 
k +/ y + 
c + 
(for positive ions) = 
-RT 
m 2 
k y~ 
(for negative ions) 
where m — valency, k partition coefficient between phases, c and y the con¬ 
centration of the ions in the two phases. 
More serious difficulties arise in its practical application. It should be 
remarked that the f oil ’ in Beutner’s experiment was not saturated with 
salt' and was in equilibrium only at the surface layer. In most cases so 
little salt penetrated the oil that the salt produced no permanent effect 
upon its properties, and if a series of salts, of which the first and last 
members were the same, were brought into contact with the ‘ oil ’ the 
difference of potential at the beginning of the experiment was found to 
be identical with that at the end. The conductivity of the ‘oil’ must 
therefore have been mainly due to other ions, and since most of these 
‘ oils ’ were acid it may be assumed that hydrogen ions played the principal 
part. Beutner’s argument rests on the assumption that this hydrogen ion 
concentration is unaffected or is equally affected by the various salt solutions 
in contact with the ‘ oil ’; which, however, can hardly be the case. Haber 
and Klemensiewicz 2 draw attention to this point in connexion with 
Riesenfeld’s experiments on phenol, and it seems probable that the dis¬ 
crepancy between theory and experimental results which the latter 
observes may be referred to this cause. In this case the discrepancy is of 
no great magnitude, but where free acid is present, as in many of Beut¬ 
ner’s experiments, the effect becomes of far greater importance. To take 
the following example, Beutner draws an analogy between the ‘ oil ’ 
system : 
1 See Riesenfeld : Ann. d. Physiol., viii. 616 (1902). 
2 Zeitsch. f. physik. Chem., lxvii. 385 (1909). 
