348 



Dr. Kohlrausch. The Resistance of the Ions [Feb. 17, 



that forces must exist between the ions and the water. Ciamician,* 

 twelve years ago, concluded that this must lead to the hypothesis of a 

 water-shell about the ion. The attempt was also made to measure 

 this hydration, by using a method proposed by Nernst. 



We may, therefore, look upon it as probable that the moving ion 

 carries with it a mass of adhering solvent, just as a moving immersed 

 solid carries with it a portion of the liquid, and we will endeavour on 

 this basis to construct a new representation of electrolytic resistance. 

 According to this the mechanics of electrolysis assume an appearance 

 quite different from the old hypothesis of isolated ions. The resist- 

 ance to motion takes place not directly between the solvent and the 

 ions, not between H 2 and K or CI, &c, but it is a phenomenon of 

 friction between the particles of the solvent itself, modified by the fact 

 that the accompanying shell of solvent may be thin enough to allow 

 the ion to act through it, to a certain extent, upon the outer liquid. 



It is impossible at first to make anything more than this rough 

 sketch of the hypothesis, and the more so, as the expressions " continu- 

 ous " and "discontinuous" must be especially denned if we are to apply 

 them to molecular processes. The expression "continuous" stands 

 from its very nature in contradiction to the atomic or molecular 

 hypothesis ; and in the case of solutions, and especially in electrolysis, 

 a molecular representation seems to be the only one which is scientific- 

 ally thinkable. 



I hardly need after this to say that in our hypothesis we shall not 

 claim to be able to differentiate strictly between the outer portions of 

 the solution and those parts which have separated themselves from the 

 rest as the accompanying atmosphere of the ion. A continuous change 

 in the condition of motion from the moving ion to the solvent con- 

 tradicts a strict differentiation. Fundamentally, however, the same is 

 true for all atmospheres, even for that of the earth. 



For the sake of brevity, we will retain the expression that an 

 atmosphere of the solvent takes part in the motion of the ion. In the 

 light of this hypothesis, I believe that all the phenomena which have 

 been here described become so much clearer that this fact itself 

 serves as a remarkable experimental support of the hypothesis. 



(10.) Hypotheses and Conclusions. — The hypotheses are : About every 

 on moves an atmosphere of the solvent, whose dimensions are deter- 

 mined by the individual characteristics of the ion. The atmospheres 

 of multivalent or compound ions differ from those of monatomic ions. 

 Data are at present lacking for a more detailed representation. 



The electrolytic resistance of an ion is a frictional resistance that 

 increases with the dimensions of the atmosphere. t The direct action 



* Zeitschr. f. physikal. Cheni.,' vol 6, 1890, p.' 405. 



t The resistance of a sphere is proportional to its radius. Kirchhoff, ' Vorles. 

 lib math. Physik.,' 1, 380, 1897 (berausgegeben von W. Wien). 



