Closer analysis of the action shows that this interpretation of the action, from the electrical point of view, is not at all in conflict with the older definitions and conceptions of oxidation and reduction: copper is deprived of the oxygen with which it is combined in nonionized copper sulphate, O ╱ ╲ Cu SO_{2}, and by evaporation of the solution, ╲ ╱ O O ╱ ╲ zinc sulphate, Zn SO_{2}, ╲ ╱ O containing the zinc combined with oxygen, is obtained. We shall presently find, however, that it is just in the quantitative formulation of the relations, that the interpretation of the action from the point of view of the theory of ionization has proved its superiority over the older view. If a strip of copper is placed in a solution of mercuric nitrate, copper, in turn, is dissolved, being oxidized to the form of cupric-ion, and mercury is deposited: Cu ↓ + Hg^{2+} → Cu^{2+} + Hg ↓. We find, then, that cupric-ion has a tendency to give up its charges, to be reduced to the metallic condition; metallic copper, in turn, has a tendency to revert to the ionic condition, to be oxidized and to form cupric-ion. We may consider the two opposed tendencies, shown in these relations, as representing a ‹reversible› reaction: Cu ↓ ⇄ Cu^{2+}. EXP. If an electric current is passed through a copper sulphate solution, copper is ‹deposited› on the negative (platinum) electrode; if the current is reversed, the copper ‹vanishes› quite as rapidly at what is now the positive pole. [p258] «Condition of Equilibrium.»—For such a reversible reaction we might expect, if we may apply the law of equilibrium to it, that the ratio of the concentrations of copper and of the cupric-ion would be a constant for the ‹condition of equilibrium› at a given temperature.[522] We would then have: [Cu^{2+}] / [Cu ↓] = ‹k›. Since the concentration [Cu ↓] of a pure, dense[523] piece of copper may be considered a constant at a given temperature, it would follow, that the first term in our relation would also have a constant definite value for the condition of equilibrium between the metal and its ion. Consequently, ‹for the condition of equilibrium› we would have: [Cu^{2+}] = K_{Cu^{2+}}. Metallic copper would then be in equilibrium, at a given temperature, with solutions containing cupric-ion only if the latter has a perfectly definite, constant concentration. Nernst[524] discovered this and similar relations, as a result of a more rigorous analysis of the energy changes involved in the ionization and precipitation of metals, and proved the validity of the relations. The value of the constant,[525] which, according to Nernst's [p259] suggestion is called the «electrolytic solution-tension constant», is 8E−22 for copper[526]; that is, copper is directly in equilibrium with a solution containing cupric-ion only if the concentration of the latter is 8E−22 gram-ion per liter.