Page:The fundamental laws of electrolytic conduction.djvu/68

 evils. The lesser lies in the fact that the contents of each cell cannot be completely removed after the electrolysis, as some of the solution remains either in the diaphragm or comes through from the other cell. The more serious is a result of the inexplicable phenomenon, that the quantity of liquid in the negative cell increases, and in the positive cell diminishes, in these experiments. This was frequently noticed by Daniell, and has been very recently more carefully investigated by Wiedemann. The latter regards it as a motion of the liquid mass as a whole from anode to cathode, and finds it very marked in copper and zinc vitriol solutions. It seems doubly striking, therefore, that Daniell and Miller found the quantity of copper unchanged in the negative cell, since an increase should have occurred as a result of this motion.

As proof that the diaphragm offers no obstruction to the progress of the ions, the authors cite the phenomenon familiar to electrotypers, that, in a copper vitriol solution, the liquid about the negative pole becomes weaker in copper and finally exhausted, when the negative pole is placed in the upper and the positive pole in the lower layers of the solution. They tried a similar experiment by filling a long tube, provided with two upright arms, with a strong solution of copper sulphate, and connected it by means of copper strips to a battery. The liquid in the negative arm became noticeably lighter colored, while, on the other hand, that in the positive arm became darker. From this they concluded that the oxysulphur ion ( S ), which separated out at the latter place, dissolved copper from the anode, but that this copper could not migrate to the cathode so as to replace the metal precipitated there.

This same phenomenon was reported at nearly the same time by numerous physicists, and introduced into discussions on the process of electrolysis. Pouillet describes it in a gold solution which was contained in a U-shaped tube. After a current had passed a sufficiently long time, he found the solution in the negative arm almost completely deprived of its gold, while that in the positive arm still contained its original gold contents. He concludes from this "that in the decomposition of gold chloride, and therefore all metal salts, the positive pole has no