THE CONDUCTANCE OF SOLUTIONS VISCOSITIES 125 



means of transference experiments, the ions are hydrated in water. In 

 order to account for the fact that the speeds of the different ions at 

 higher temperatures approach one another, it might be assumed that the 

 hydrates break down at higher temperatures, but this assumption would 

 not be in harmony with certain facts. Since the conductance of the 

 slowly moving ions changes in direct proportion to the fluidity of the 

 solvent as the temperature increases, it is reasonable to assume that the 

 relative dimensions of the ion complex remain practically constant. If, 

 therefore, the speed of the more rapidly moving ions approaches that of 

 the more slowly moving ions at higher temperatures, it points to a slow- 

 ing up of the more rapidly moving ions as the temperature increases. 

 This corresponds to a greater relative resistance to their motion, which 

 can only be interpreted as due to an increase in the dimensions of the 

 ion-complex. In other words, as the temperature increases, the hydra- 

 tion of the more rapidly moving ions increases, which tends to reduce 

 their speed relative to that of more slowly moving ions. 



If the hydration of the ions is due primarily to electrical forces acting 

 between the ions, which are charged, and the surrounding solvent mole- 

 cules, which have an electrical moment, then we should expect that, as 

 the dielectric constant of the medium decreases, the size of the complex 

 will increase, since in a dielectric medium the force is inversely propor- 

 tional to the dielectric constant. For this reason we should expect the 

 relative speeds of ions in non-aqueous solvents of low dielectric constant 

 to approach one another much more nearly than they do in water. This 

 appears to be the case. Moreover, this is also in harmony with the fact 

 that in the case of very large ions, in other words, in the case of ions 

 which have a low conducting power, the conductance in different sol- 

 vents, as well as at different temperatures, is very nearly proportional to 

 the fluidity of the solvent. We may conclude, therefore, that the hydra- 

 tion of the ions increases, or, including non-aqueous solvents, that the 

 solvation of the ions increases with the temperature because of a decrease 

 in the dielectric constant of the medium. It is not to be assumed, how- 

 ever, that the dimensions of the ions in different solvents are controlled 

 entirely by the dielectric constant. The solvent may combine chemi- 

 cally with a given ion to form a complex, which ion in turn may have 

 associated with it additional solvent molecules, due to electrical inter- 

 action between this ion and the solvent. We should expect this to be 

 the case with silver ions which form an extremely stable complex with 

 ammonia. Even in aqueous solutions, the silver ion forms a complex 

 Ag(NH 3 ) 2 + with ammonia. This may account for the relatively low 

 conducting power of the silver ion in liquid ammonia solution. Whereas, 



