Page:The fundamental laws of electrolytic conduction.djvu/67

 Messrs. Daniell and A. Miller, in their beautiful investigations on the electrolysis of salts, were led to devote greater attention to the subject of transference. They effected the separation of the liquid by the introduction of a membrane. They filled the two cells into which the vessel was divided with accurately determined quantities of the aqueous solution of the electrolyte, and investigated each after the galvanic decomposition had taken place.

The results which they obtained are very striking. When, namely, copper or zinc sulphate was chosen as electrolyte, they found after electrolysis, exactly the same amount of metal in the cell containing the cathode as they had originally introduced. The quantity of reduced metal, increased by the quantity still dissolved in the liquid, amounted to exactly as much as was present before the electrolysis. According to this, copper and zinc do not migrate at all during electrolysis. Their anion S traverses the whole distance. An ammonium salt (salammoniac) gave the same result; the complex cation NH$4$ is to be classed with the two preceding. They found a transference of the cation with the salts potassium sulphate, barium nitrate, and magnesium sulphate. For potassium it amounted to, for barium , and for magnesium   equivalent. The authors conclude from their experiments that those metals which decompose water at ordinary temperature, or whose oxides are easily soluble in water, are subject to a progressive transference in the voltaic cell from anode to cathode during electrolysis, while those which do not possess so strong an affinity for oxygen retain their place. They found a transference of all anions, even the weakest ones, such as WO$1⁄3$ and CO$1⁄6$.

In the translation of their article in Poggendorff's Annalen, the direct numerical results of the individual experiments are not given completely. The accuracy of the method cannot therefore be judged. It would appear, however, that it was not satisfactory, as the results are given only in round numbers. Furthermore, it is expressly stated that the experiments are not strictly comparable, and that the figures given cannot be regarded as absolute determinations of the transferred quantity of each metal in the cell.

The introduction of the membrane entails of necessity two