1903.] 



and the Mechanical Friction of the Solvent. 



349 



"between the ion and the outer portion of the solvent diminishes as the 

 atmosphere becomes of greater thickness. 



Conclusion*. — (a.) The electrical resistance of an ion, expressed in 

 mechanical units, must be of the same order of magnitude as the 

 mechanical f rictional resistance of a molecule of the solvent ; a law 

 whose assumption, as I some time ago showed, " leads to an expression 

 for the distance between the molecules which is comparable with the 

 usually accepted views in regard to this quantity."* 



(b.) The empirically discovered law that the temperature change of 

 the resistance of the most sluggish ions is very like the temperature 

 change of the viscosity of water, becomes now understandable. For 

 ions of large resistance we must assume that the atmosphere is of 

 considerable thickness, and hence the action of the ion itself on the 

 •outer portion of the solvent will be small. As a limiting case, for a 

 very sluggish ion there will be only the friction of water against water, 

 and the electrolytic resistance will have the same temperature coeftV 

 'dent as the viscosity of water, provided that the atmosphere itself 

 does not change its dimensions with the temperature. If, however, 

 the atmosphere become, for example, smaller with increasing tem- 

 perature, the temperature gradient of the conductivity might be 

 greater than that of the fluidity. According to the observations now 

 at hand, this would seem to be the case for the slowest moving 

 univalent ion Li. Even here, however, the differences scarcely exceed 

 the errors of observation. 



(c.) I now come to the remarkable relationship between the mobility 

 of the ions and their temperature coefficients, which was mentioned in 

 Section 8. This first led me to seek a general explanation for the 

 electrolytic resistance in the idea of a water atmosphere, in order to 

 ■escape being compelled to explain this otherwise unreconcilable funda- 

 mental characteristic of the ions as a deus ex machina. 



Assuming as the single fundamental characteristic of each univalent 

 monatomic ion the formation of a water atmosphere which varies 

 -according to the nature of the ion, the mobility of this complex on 

 the one side, and its temperature coefficient on the other, will be 

 functions of these atmospheric formations, and therefore both 

 • quantities must hold functional relations to each other. We know 

 too little of the molecular forces at present to attempt to describe this 

 ■ connection more exactly. But for the case in which the water shell is 

 so thick that the ion exerts no force beyond it, the resistance to motion 

 becomes simply a matter of water friction, which explains the fact 

 that the most sluggish ions have nearly the same temperature 

 coefficients as the viscosity. In the case of smaller aggregations, 

 we must remain content with the fact that we have at least the 

 possibility of a fundamental explanation. 



# ' Gottinger Xach rich ten,' 1879, p. 1. 



