Professor Van t' Hoff, like other chemists, would certainly have rejected--in fact, he did so at first-- such a conception, if, about the same time, an illustrious Swedish scholar, M.Arrhenius, had not been brought to the same idea by another road, and, had not by stating it precisely and modifying it, presented it in an acceptable form.
A brief examination will easily show that all the substances which are exceptions to the laws of Van t'Hoff are precisely those which are capable of conducting electricity when undergoing decomposition--that is to say, are electrolytes.

The coincidence is absolute, and cannot be simply due to chance.
Now, the phenomena of electrolysis have, for a long time, forced upon us an almost necessary image.

The saline molecule is always decomposed, as we know, in the primary phenomenon of electrolysis into two elements which Faraday termed ions.

Secondary reactions, no doubt, often come to complicate the question, but these are chemical reactions belonging to the general order of things, and have nothing to do with the electric action working on the solution.

The simple phenomenon is always the same--decomposition into two ions, followed by the appearance of one of these ions at the positive and of the other at the negative electrode.