58 WORK OF J. N. PEARCE. 



That this relation will hold, in case there is hydration or alcoholation, is highly prob- 

 able, since the resistance offered to the ionic complex will be the same in each case. 



As stated by Jahn, 1 "recent measurements have made it probable that the mobility 

 of the ions is not independent of their concentration, that they have greater mobility 

 in more concentrated than in more dilute solutions. " Reference to the work of Jones 

 and Bassett 2 shows that this is just what we should expect. They found, by freezing- 

 point measurements, that the hydration per gram-molecule of the electrolyte decreases 

 with increasing concentration to a certain concentration corresponding to the mini- 

 mum in the molecular lowering of the freezing-point, and then decreases very slowly 

 with increasing concentration. In the more concentrated solutions, then, we have 

 smaller changes in hydration; therefore, smaller changes in the ionic volumes; hence 

 we should have smaller changes in the mobility of the ions. 



That the conductivity depends, in no small degree, upon the viscosity of the solu- 

 tion has been known for a long time; yet the simultaneous action of the two conditions, 

 dissociation and viscosity, renders it impossible to separate their effects. No simple 

 relation exists other than that the conductivity decreases with increase in viscosity. 



G. Wiedemann 3 first called attention to the fact that the friction which the ions 

 produce in their motion changes in the sense that the fluidity changes. Accordingly, 

 the mobility of the ions should be a function of the fluidity of the solution. 



That the conductivity does not depend exclusively upon the fluidity can be seen in 

 the following case : A 1 per cent (by volume) solution of cane-sugar and a 2.2 per cent 

 solution of methyl alcohol have the same internal friction, viz, 1.046, but the conduc- 

 tivity of potassium chloride in a 1 per cent sugar solution is decreased 3 per cent, 

 while in 2.2 per cent methyl alcohol it is decreased 3.85 per cent. 



Pissarjewski and Lemcke 4 made the simple assumption that the conductivity is 

 direct]}' proportional to the dissociation, and inversely proportional to the viscosity, 



e. g., n = K- . At maximum dissociation K = ju^ rj^. Therefore the dissociation is 



a - and not a = 



Moo ^oo M, 



In the dilutions which they used the K, calculated from a = , vanes, while K, 



"oo 



calculated from a = , is a constant. 



Meo^c 



OBJECT OF THE INVESTIGATION. 



It was our plan in this work to study the relation between the dissociation as meas- 

 ured by the freezing-point and conductivity methods; to determine to just what ex- 

 tent the conductivity of a solution is influenced by the hydration of the ions ; and to 

 study the effect of hydration upon the relative velocities of different ions. 



Moreover, it was desired to test the reliability of the conductivity method as a 

 means of measuring the dissociation of strong electrolytes. 



In order to do this it was found necessary to redetermine as accurately as possible 

 the freezing-point lowerings produced by various solutions of a large number of salts. 



'Grundriss der Electrochemie, p. 143. 8 Pog. Ann., 99, 228 (1856). 



s Amer. Chem. Journ.. 33, 534 (1905). 'Zeit. phys. Chem., 52, 479 (1905). 



