Page:Text-book of Electrochemistry.djvu/161

 146 CONDUCTIVITY OF ELECTROLYTES. chap.

current is divided between the two dissolved electrolytes in the ratio of their conductivities. He regarded the separation of the chlorine, as well as the iodine, at the anode as the result of a primary action, but it immediately reacts with the potassium iodide, producing potassium chloride and free iodine. Hittorf's explanation has recently been confirmed by Schrader {16) for mixtures of potassium chloride and iodide, and copper sulphate and sulphuric acid, and further by Hopfgartner (6),

Complex Ions. — In his investigation of the so-called double salts, such as potassium argentocyanide (KAg(CN')2), potassium ferrocyanide (K4Fe(CN)6), sodium platinichloride (NaaPtCle), and sodium aurichloride (NaAuCl4), Hittorf observed that the alkali metal always formed the positive ion, whilst the negative ion consisted of the rest of the molecule (termed a complex ion, on account of its composition). This observation was diametrically opposed to the chemical views then held, according to which, in consonance with the doctrine of valency, the formula AgCN + KCN" was given to potassium argentocyanide, indicating that there is no close connection between the radicle ON of the potassium cyanide and the AgCK

Ionic Migration and the Theory of Dissociation. — If we assume that the ions are perfectly free and transport the electricity quite independently of each other, it is quite natural to suppose that under the influence of the same force they will not pass through the solution with the same velocity ; but rather a different friction against the liquid is a priori to be expected. Even if we suppose that the molecules are not dissociated in the solution, but that the ions influence each other in their migrations, it would be natural to imagine that they would travel with different veloci- ties. To us at the present time, therefore, it seems incredible that Hittorf's doctrine of the unequal migrations of the ions was not at once accepted. As a matter of fact, however, the leaders in the science opposed Hittorf's views, and it was only after thirty years that these were adopted.

�� �