Page:A history of the theories of aether and electricity. Whittacker E.T. (1910).pdf/393

 R. Clausius, of Zurich, the basis of a theory of electrolysis. According to it, the electromotive force emanating from the electrodes does not effect the dissociation of the electrolyte into ions, since a degree of dissociation sufficient for the purpose already exists in consequence of the perpetual mutability of the molecules of the electrolyte. Clausius assumed that these ions are in opposite electric conditions; the applied electric force therefore causes a general drift of all the ions of one kind towards the anode, and of all the ions of the other kind towards the cathode. These opposite motions of the two kinds of ions constitute the galvanic current in the liquid.

The merits of the Williamson-Clausius hypothesis were not fully recognized for many years; but it became the foundation of that theory of electrolysis which was generally accepted at the end of the century.

Meanwhile another aspect of electrolysis was receiving attention. It had long been known that the passage of a current through an electrolytic solution is attended not only by the appearance of the products of decomposition at the electrodes, but also by changes of relative strength in different parts of the solution itself. Thus in the electrolysis of a solution of copper sulphate, with copper electrodes, in which copper is dissolved off the anode and deposited on the cathode, it is found that the concentration of the solution diminishes near the cathode, and increases near the anode. Some experiments on the subject were made by Faraday in 1835; and in 1844 it was further investigated by Frederic Daniell and W. A. Miller, who explained it by asserting that the cation and anion have not (as had previously been supposed) the same facility of moving to their respective electrodes; but that in many cases, the cation appears to move but little, while the transport is effected chiefly by the anion.