Page:Outlines of Physical Chemistry - 1899.djvu/231

 ions/ ' the electrical capacity of the ions (equal for all)/ * the transportation of the electricity by the ions/ and so on ; and scientific language gains in realism and in simplicity. But this simplicity has only an apparent existence, and when we go to the root of the matter discrepancies appear. On. this account the champions of the new theory insist on the necessity of not attributing to the free ions the properties of the elements in the massive state. The ion of potassium, for instance, is not to be confounded with the metal of that name. The ion is an isolated atom with an enormous electric charge. The massive metal on the contrary is constituted of a complex assembly of atoms and ' has no electric charge. In an electrolysis, when the potassium ion is deposited on an electrode to which it gives up its charge, metallic potassium is immediately formed and decomposes the solvent water with evolution of hydrogen.

Without admitting the whole of this theory we must confess that ArrMnius's hypothesis interprets admirably a series of phenomena of which we otherwise know neither the significance nor the raison d'Stre.

1. The law of thermo-neutrality (Hess),

When two dilute neutral solutions are mixed together no thermal effect is produced. The reason of this is that no reaction takes place.

A solution of potassium chloride, for instance, contains the ions K and CI ; in the same way a solution of sodium nitrate contains the ions Na and N0 3. When the two solutions are mixed no change takes place, for the ions remain free just as they were before.

The law only applies to sufficiently dilute solutions in which the dissociation is complete or almost so. Concen- trated solutions behave in a more or less abnormal manner.

2. Wet reactions, which are so much used in inorganic chemistry for recognising the nature of a substance, show

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