the Conductivity of Mixtures of Electrolytes. 287 



their own electrolyte only. In the case of dilute solutions 

 the difference will be small, in sufficiently dilute solutions 

 inappreciable ; but in the case of the stronger solutions it 

 may account in large part for the discrepancy observed above # 

 We have, however, so far as I am aware, no data for calcu- 

 lating the effect of mixture on the ionic velocities, or the 

 extent to which the discrepancy is due to this effect. 



To obtain some rough conception of its magnitude, I have 

 calculated the conductivity of the mixture No. 18 on two 

 assumptions, which seemed more or less probable, — viz. (1) 

 that the velocities of the ions of each electrolyte in the mix- 

 ture were the same as they would be in a simple solution of 

 their own electrolyte of a concentration (in gramme-molecules 

 per litre) equal to the mean concentration of the mixture ; 

 and (2) that the velocities of the ions of each electrolyte, 

 when passing through a region occupied by the other electro- 

 lyte, were the same as they would be in a simple solution of 

 the former of a dilution equal to that of the latter. The 

 expression used for the conductivity was 



where w, and u 2 are the sums of the velocities of the ions of 

 electrolytes 1 and 2 respectively in simple solutions of the 

 dilutions which they have in the mixture, while u/ and u 2 f 

 are the values these ionic velocities would have according to 

 the particular assumption employed, the velocities in all cases 

 being those corresponding to the same potential gradient. 

 As the graphical process above gave the dilution of each elec- 

 trolyte in the mixture, the values of u and u' were readily 

 determined by the aid of Kohirausch's table of ionic velo- 

 cities*. I found that according to assumption (1) the con- 

 ductivity would be greater than Bender's reduced value by 

 1*6 per cent., and that according to assumption (2) it would 

 be greater by 1*3 per cent. Similar calculations could not be 

 carried out in the case of solutions stronger than No. 18 

 owing to lack of data. Such calculations are of course of 

 little value ; but they strengthen the suspicion that the excess 

 of the observed values of the conductivity of mixtures over 

 the calculated values is due to the impossibility of taking into 

 account the effect of mixing on the velocities of the ions. 



* Wiedemann's Annalen, 1. p. 385 (1893). 



X2 



