II. Some Potential-Current Relations in Galvanic Corrosion^★

A graphic method of expressing the electrical characteristics of a galvanic couple was developed by the application of Kirchoff's laws to a couple consisting of separate electrodes, each with an ammeter in series. When an external emf was impressed between the couple and a third electrode, also with an ammeter in series, a definite current pattern was established, depending on the relative directions and magnitudes of the impressed emf and the potential of the couple. These relations were demonstrated with the iron-magnetite couple. Under the conditions used, a discontinuity in the potential-current relation was observed, when the couple was cathodically polarized over a sufficient range of current. This discontinuity or "break" coincided with reduction of current, circulating within the couple, to zero. The rise in potential at this point is the logical result to be expected from the hydrogen overvoltage.