POTENTIALS AT PHASE BOUNDARIES 



199 



tenfold change in h2 a difference of 58 millivolts. All other ionic 

 species which may be present in the solutions are without effect, 

 as was recently stated by Freundlich and Rona.^ 



The glass chain may be used as well as the gas chain for pH 

 measurements, and especially for electrometric titration for which 

 Haber gives beautiful examples. The glass chain represents a chain 

 reversible for H-ions only, in distinction from Beutner's oil-chains 

 which, as we saw above, can be arranged to be reversible for any 

 given anion or cation. The only possible explanation, in Haber's 

 sense, is that the H-ion constitutes the common ion for the two 

 aqueous phases and for the glass phase, and that the concentration 

 of H-ions in the glass is constant and is independent of the adjacent 



TABLE 30 



* Ci:c2 ratio in all of these cases is 1:5. 

 effect is TT = 0.058 X log 5 = 0.0406 volts. 



Hence the calculated maximal 



media. Haber assumes that the glass contains traces of water of 

 imbibition (swelHng), and that this factor determines the H-ions 

 in the glass. 



2. As we saw above, Beutner succeeded in obtaining more or less 

 complete concentration effects by employing oily liquids as the 

 middle phase. The first used by him were chains with salicyhc 

 aldehyde as the oil phase: 



KCl 

 in water 



Cl 



Salicylic 

 aldehyde 



KCl 

 in water 



Cs 



with these he found the E.M.F. values given in table 30. 



' H. Freundlich and P. Rona, Sitzungsber. d. Preuss. Akad. d. Wissensch. 

 (1920), 397. 



