34 PROPERTIES OF ELECTRICALLY CONDUCTING SYSTEMS 



carriers. If the current in a solution of an electrolyte is effected through 

 the motion of charged carriers within the electrolyte, then we may in- 

 quire: What fraction of the electrolyte present in the solution is con- 

 cerned in the process of conduction; that is, what fraction of the electro- 

 lyte exists in an ionic condition? 



Clausius 21 suggested that electrolytes are ionized, but he failed to 

 draw any definite conclusion as to the extent of this ionization. In his 

 time, the notion that a stable compound, such as potassium chloride, 

 could be dissociated and moreover dissociated into oppositely charged 

 constituents was contrary to accepted theories. Clausius was therefore 

 content to merely throw out the suggestion that electrolytes are to some 

 extent dissociated. 



The conclusion that an electrolyte is dissociated follows almost neces- 

 sarily from the work of Kohlrausch and Hittorf, although neither of 

 these investigators actually drew this conclusion. It was Arrhenius 22 

 who proposed the fundamental hypothesis that an electrolyte in solution 

 is dissociated and that the degree of its dissociation may be determined 

 by means of the conductance of its solutions. Moreover, he showed that 

 the dissociation as measured in this way is in agreement with many 

 other well-known properties of these solutions. 



We have seen that, as the concentration of a solution decreases, its 

 equivalent conductance increases and approaches a limiting value. We 

 have also seen that the positive and negative ions within the electrolyte 

 appear to move at definite rates under fixed conditions, provided the con- 

 centration of the solution is not too great, and that the motion of the 

 ions under these conditions takes place independently for each ion. If 

 these conclusions are correct, then it appears that a logical explanation of 

 the facts would be that, in the more concentrated solutions, a portion of 

 the electrolyte has been removed from a condition in which it is able 

 to take part in the conduction process, while the fraction of the sub- 

 stance which remains in a conducting condition is measured by the ratio 

 of the conductance at a given concentration to the conductance at very 

 low concentrations, where apparently all the electrolyte takes part in the 

 conduction process. 



Let y represent the fraction of the salt present in a conducting state; 

 then the relative amount of the salt present in this state at any con- 

 centration will be given by the ratio: 



"Clausius, Pogg. Ann. 101, 338 (1857). 



Arrhenius, Bijlumj till K. Svenska, Vet. Akad. Handl. No. 13, 1884; Sixth Circular 

 of the British Association Committee for Electrolysis, May, 1887 ; Zfschr. f. nhys. Cfiem.. 

 1, 631 (J887), 



