CARRIERS IN ELECTROLYTIC SOLUTIONS 203 



of the ionic diameter therefore passes through a minimum. In this way 

 Born accounts for the diminishing values of the ion conductance with 

 decreasing volume in the case of the simpler ions. 



The constants involved in the equation for the electro-frictional effect 

 are somewhat uncertain. In any case, these constants should depend 

 solely upon the properties of the solvent medium, assuming an ion of 

 fixed dimensions. 



The correctness of this theory appears somewhat doubtful. In the 

 first place, it is difficult to account for the fact that at higher tempera- 

 tures the ion conductances' in aqueous solutions approach the same value. 

 While it is true that the dielectric constant of the medium varies with 

 the temperature, an effect of the order of that observed in aqueous solu- 

 tions is scarcely to be expected. More convincing, perhaps, is the rela- 

 tion of the ion conductances in non-aqueous solutions. If the theory of 

 Born and Lorenz is correct, the order of the ion conductances should be 

 the same in different solvents. This is by no means the case. For exam- 

 ple, as may be seen from the values of the ion conductances in liquid 

 ammonia given in an earlier chapter, the conductance of the silver ion 

 is markedly lower than that of the sodium ion in ammonia; while in 

 water the conductance of the sodium ion is much smaller than that of the 

 silver ion. Again, the conductance of the ammonium ion in ammonia is 

 practically identical with that of the sodium ion, whereas the conduct- 

 ance of the ammonium ion in water is almost identical with that of the 

 potassium ion. While the conductance of the lithium ion in water is 

 much smaller than that of the silver ion, the conductance of the lithium 

 ion in ammonia differs but little from that of the silver ion. So, also, 

 in the case of anions, the conductance of the nitrate ion is identical with 

 that of the iodide ion in ammonia, while in water it is much smaller. 

 Similarly, the conductance of the chloride ion in ammonia is markedly 

 greater than that of the iodide ion; whereas in water the conductance of 

 the iodide ion is greater than that of the chloride ion. An examination 

 of the conductance values of electrolytes in other non-aqueous solvents 

 shows that here, too, the order of ion conductances is a characteristic 

 property of the solvent medium and of the dissolved electrolytes. For 

 example, in acetone the conductance values of the lithium, sodium and 

 potassium ions are practically identical; while the conductance of the 

 ammonium ion is markedly greater than that of the potassium ion. 

 While in water the conductance of the sulphocyanate ion is markedly 

 lower than that of the iodide ion, in acetone the conductance of this ion 

 is greater than that of the iodide ion. So, also, in pyridine the con- 



