THEORIES OF ELECTROLYSIS. 295 



Moreover, he showed that the velocity of any one ion — 

 sodium suppose — was independent of the nature of the solu- 

 tion containing it — the same, for example, in a dilute solution 

 of sodium chloride as in one of sodium nitrate. In this way 

 he was able to assign to many ions specific ionic velocities 

 -numbers representing the speeds with which they move 

 through a very dilute solution, when driven by a potential 

 gradient of one volt per centimetre. These results were 

 confirmed in two ways. Kohlrausch calculated the con- 

 ductivities of various solutions from the velocities of their 

 ions as found by observations on other solutions containing 

 them, and showed that the values thus obtained agreed 

 with those given by direct measurements, and Oliver Lodge 

 and the present writer have directly observed the velocities 

 of various ions, by tracking them through the liquid by 

 means of indicators or changes in colour, and again con- 

 firmed Kohlrausch's numbers. 



Passing to solutions of greater concentration, Kohlrausch 

 showed that the conductivitv increased more slowlv than 

 the concentration. If we call the number obtained by 

 dividing the value of the conductivity by the concentration 

 (expressed in gram- equivalents per litre) the molecular con- 

 ductivity, we can express Kohlrausch's results by saying 

 that, as the concentration of an electrolytic solution de- 

 creases, the molecular conductivity gradually rises and tends 

 to a constant limiting value as the dilution becomes infinite. 

 The decrease in the molecular conductivity indicates a 

 corresponding decrease in the velocities of the ions. It is 

 much greater than can be explained by changes in the ionic 

 viscosity, and must be due to some other cause. We must 

 suppose that, in such solutions, the ions are electrolytically 

 active only for a part of their time, and, during the rest of 

 their existence, they are incapable of moving forward. We 

 shall find other indications, both from chemical and from 

 osmotic pressure phenomena, that, at any instant, a certain 

 number of the molecules differs from the rest in con- 

 dition, and the same number as we deduce from the 

 conductivitv is indicated by these two effects. Various 

 hypotheses might be framed in order to explain the 



