Note 530 — Chapter XIV · OXIDATION AND REDUCTION REACTIONS. I
Reading edition
For elements that form negative ions, e.g. for chlorine, bromine, oxygen, etc., the equation reads (see pp. 273, 275 and the table at the end of Chapter XV):
εElem., Electrolyte = −(0.0575 / v) log(C / K).
Note the changed sign of the expression on the right. The difference in sign expresses the fact that, when negative ions discharge on an electrode, they render it negative, and when they are formed by an electrode, they leave the latter positive; for positive ions, it will be recalled, the conditions are just the reverse (see above).
Where a soluble element (e.g. chlorine) or a solution of a metal (e.g. sodium amalgam) is used as an electrode, its concentration, in general, is not constant, as in the case of a pure, solid metal like copper (p. 258). In such cases, the quantity in the denominator of the ratio in the logarithm cannot be expressed by a constant K, but is expressed by K × CElement, CElement being used to indicate the concentration of the element in the experiment in question.