One, to which chemists not unreasonably attached great importance, was this:--If a certain quantity of chloride of sodium is dissociated into chlorine and sodium, it should be possible, by diffusion, for example, which brings out plainly the phenomena of dissociation in gases, to extract from the solution a part either of the chlorine or of the sodium, while the corresponding part of the other compound would remain.

This result would be in flagrant contradiction with the fact that, everywhere and always, a solution of salt contains strictly the same proportions of its component elements.
M.Arrhenius answers to this that the electrical forces in ordinary conditions prevent separation by diffusion or by any other process.
Professor Nernst goes further, and has shown that the concentration currents which are produced when two electrodes of the same substance are plunged into two unequally concentrated solutions may be interpreted by the hypothesis that, in these particular conditions, the diffusion does bring about a separation of the ions.

Thus the argument is turned round, and the proof supposed to be given of the incorrectness of the theory becomes a further reason in its favour.
It is possible, no doubt, to adduce a few other experiments which are not very favourable to M.Arrhenius's point of view, but they are isolated cases; and, on the whole, his theory has enabled many isolated facts, till then scattered, to be co-ordinated, and has allowed very varied phenomena to be linked together.

It has also suggested--and, moreover, still daily suggests--researches of the highest order.
In the first place, the theory of Arrhenius explains electrolysis very simply.

The ions which, so to speak, wander about haphazard, and are uniformly distributed throughout the liquid, steer a regular course as soon as we dip in the trough containing the electrolyte the two electrodes connected with the poles of the dynamo or generator of electricity.