WORK OF J. N. PEARCE. 



INTRODUCTION. 



The conductivity of a solution of an electrolyte is a function of several conditions : 

 the nature of the electrolyte and the degree of its dissociation, the speed of its com- 

 ponent ions, and the viscosity of the solvent. The degree of dissociation, in turn, 

 depends upon the concentration of the electrolyte and the nature of the solvent. 



As was pointed out by Dutoit and Aston, that solvent whose molecules are asso- 

 ciated to the greatest extent has the greatest dissociating power. 



Weak acids, weak bases, and salts of weak acids and bases show constantly increas- 

 ing dissociation with increasing dilution; but, within the limits of accuracy of our 

 present methods, no maximum of conductivity is directly obtainable. On the other 

 hand, strong electrolytes show rapidly increasing dissociation with slight increase in 

 dilution a maximum conductivity being reached at moderate dilution. 



It is stated by Ostwald 1 that the anions of the halogen acids move more rapidly 



than do those of the oxyhalogen acids, c. g., C10 3 , Br0 3 , I0 3 ; that C10 4 has a greater 



migration velocity than I0 4 . In general, the more complex the ion, the slower its 

 migration velocity. Especially is this the case with the anions of organic acids. 

 With isomeric anions, however, the velocities are approximately equal. With increas- 

 ing increments of CH 2 the velocity decreases regularly. The same may be said with 

 regard to the organic cations. 



It has been proved by Jones and Getman and by Loomis 2 that organic acids are not 

 hydrated. It is clear that increase in ionic volume is accompanied by decrease in 

 ionic speed, doubtless due to increase in friction between ion and solvent. 



With this idea in mind, and with the evidence from the freezing-point measurements 

 that the ions form more and more complex hydrates with increasing dilution, we are 

 forced to believe that the conductivities of solutions of strong electrolytes are less 

 than they would be, theoretically, if there were no hydration, by an amount which is a 

 function of the volume of the ionic complex. 



Vollmer 3 determined the values of n> for solutions of potassium acetate, sodium 



acetate, potassium iodide, lithium iodide, lithium chloride, and silver nitrate, in water 



w 



and alcohol. He found the relation. a '- =K= 0.33 to hold in every case. 



^ M water 



Kawalki 4 found the same relation to exist between the speeds of diffusion of the 

 same electrolytes in water and alcohol. It is of especial interest to note that the value 



which he obtained for his constant n " - =K' = 0.33 is the same as that found by 



*-* water 



Vollmer for conductivity. From their results we obtain the relation 



x' : X^ : : D' : D 



00 00 



Lehrbuch, 2, 679. J Wied. Ann., 60, 523 (1897). 'Ibid., 52, 328 (1894). 'Wied. Ann., 52, 300 (1894). 



57 



