INTRODUCTION 



44. All solutions of electrolytes contain equal amounts of posi- 

 tively and negatively charged ions. Deviations from this proposition 

 are possible only to so slight an extent that it is beyond the scope of 

 analytical chemical methods to detect the inequalities between the 

 two ionic species. But, nevertheless, because of the large amounts 

 of free electricity which arise in such cases, this inequality is demon- 

 strable by physical methods, and it is the cause of a number of 

 electric phenomena. It is not our purpose to treat of these as 

 extensively as of ionic equilibria. But since the methods for measur- 

 ing hydrion concentration are based upon these phenomena they 

 must be discussed here insofar as our understanding of these methods 

 requires it. Furthermore, our explanations in general will be made 

 in the direction in which they are to have a probable physiological 

 bearing. 



Among the potential differences brought about by the unequal 

 partition of ions, several groups may be differentiated; such as: 

 1. electrode potentials, or those which are located on the surface of a 

 metal in contact with a solution; 2. diffusion -potentials, or those which 

 ensue at the contact of two different electrolyte solutions or of two 

 solutions of unequal concentration; 3. phase boundary potentials 

 which are generally located on the boundary surface between two 

 phases, in such a manner that one phase shows a potential towards 

 the other phase; 4. membrane potentials, which are based upon the 

 impermeabihty of certain membranes for certain ions; 5. adsorption 

 potentials which also develop on a phase boundary surface, but in 

 such a way that the boundary layer of a phase exhibits a potential 

 difference towards the rest of the same phase. 



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