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 CHAPTER VIII. Electrol]rtes. Electrolytic Dissociation.

Deviations shown by Electroljrtes from van't Hoff's Law. — In the preceding chapters a short sketch has been given of the laws which obtain for substances in solution. Attention has been called to the fact that many substances behave in accordance with van't Hoff's law, but that salts, strong acids and bases in aqueous or alcoholic solution exhibit deviations. These substances always have an osmotic pressure which is too high, whether this be found from the depression of vapour pressure or freezing point, or from the raising of the boiling point. These substances, too, are of very great interest, both in a chemical respect on account of their applications in analytical chemistry, and in a physical respect because of their conducting the electric current and being at the same time decomposed.

Since electrical measurements are the sharpest and most exact known in physical science, it was to be expected that a complete electrical examination of these substances would tbrow some light on their nature and peculiarities. As a matter of historical fact, the electrical examination led to the same point as van't Hoff's osmotic investigations, and it was only after the two studies were considered together that the problem of the nature of solutions was satisfactorily solved.

Faraday's Experiments. — ^We have already referred to Grotthuss' views, according to which the molecules in an electrolytic (i.e. salt) solution arrange themselves into a sort of chain between two metallic plates connected with

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