POTENTIALS AT PHASE BOUNDARIES 197 



within two definite limiting values. The one limiting value is 



that E.M.F. which would be jdelded by an ordinary concentration 



chain containing a metal for the common ion species involved, 



Ci • 



or = RT In — , with the sign depending on the positive or negative 

 C2 



charge of the ion. The other limiting value of the E.M.F. is zero. 

 Between these two fall all the observed values. 



The necessary condition for the maximal concentration effect is 

 that the concentration of the cormnon ion-species in the entire mxiss of 

 the oil phase should be constant, although the concentration of this 

 common ion in the two adjacent aqueous phases is different. For 

 when in the equation given on page 193 



''i ^iii 

 E = RT In -!- X -^ 



Cm becomes = Cjv, and we actually obtain 



E = RT In - 



C2 



K this condition is incompletely or not at all fulfilled, as when 

 the concentration of the common ion is weaker on the boundary of 

 the oil phase with the weaker aqueous solution than it is on the 

 boundary of the oil with the stronger solution, or when, in other 



words, Ci < Cjy and Cu < Cm, then E < RT In — . 



C2 



Let us see just when this condition for the maximal concentration 

 effect is fulfilled. 



1. The first example of the maximal concentration effect is the 

 so-called glass-chain, which has been first used by Cremer.^ This 

 author was the first to conceive the idea of imitating a physiological 

 membrane by means of an extremely thin walled glass sheath, 

 which can be easily blown out at the end of a test tube. In this 

 way glass bulbs are obtained whose walls are a few hundredths of 

 a millimeter in thickness, and which show at room temperatures, 

 or better at 40-50"", a distinct^ demonstrable electric conductivity. 

 In accord with aheady estabhshed ideas concerning the conductivity 

 of glass, Cremer had to assume that he was dealing with true elec- 



6 M. Cremer, Zeitschr. f. Biol. 47, 1 (1906). 



