Page:The fundamental laws of electrolytic conduction.djvu/69

 decomposing action, that all chemical force resides in the negative pole, that this takes up the gold and sends the chlorine by a series of successive decompositions and recombinations to the positive pole, to be there set free." "If both poles acted," he adds, "the metal separated at the negative pole would be of double origin; one-half would be directly precipitated, the other would come from the positive pole; both arms of the tube would then become weaker in gold to the same extent during the whole duration of the process." Besides the physicists mentioned, Smee also discusses the phenomenon.

It is astonishing how this simple experiment has been so generally misunderstood. The dilution which the solution undergoes at the negative pole proves in no way that the metal does not migrate during electrolysis. We can convince ourselves of this at once by glancing back at Fig. 2 or 3. The cation, in the above case, is a solid body in the free state, and, as such, leaves the solvent by the separation produced by the current. Fig. 2 is drawn on the assumption that the ions move through equal distances, and shows that the cathode side is increased after electrolysis by equivalent of cations. Now as one equivalent becomes solid, the solution is thereby diminished by equivalent—that is, diluted by  equivalent of the salt. Dilution must therefore occur at the negative pole, even if the cation migrates; and it must evidently do so in all cases, as long as the cation does not migrate alone and the anion remain at rest. Only in this one case will the original concentration remain the same at the cathode.

This very dilution which the cation suffers at the negative pole where the cation leaves the solution, can be very advantageously used to determine the transference quantitatively. An exact separation of the electrolyte is easily effected without the introduction of asbestos or of a diaphragm.

Fig. 4 represents a simple apparatus which I have constructed for this purpose, and which was used in the experiments described below.

A glass cylinder, which contains the solution of the electrolyte, is composed of two parts—a larger, a, and a smaller, b. The former is cemented to a vessel, c, preferably of porcelain,