The behavior of 4,4’-bipyridine cation radical (bpyH-2.+) over mercury in the presence of iodide ions at pH 1.5 was studied by cyclic voltammetry, chronoamperometry, and capacity measurements. The results show the occurrence of three nucleation or phase-change processes below 15-degrees-C, all of which can be ascribed to the formation of the cation radical at the electrode. The surface concentration of the cation radical obtained is consistent with the occurrence over a given potential range of a mixed bpyH-2.+-I- phase over the electrode at low temperatures. At more negative potentials than those of the above-mentioned range, a new phase consisting solely of bpyH2.+ is formed that covers the electrode throughout. The molecular area obtained is intermediate between those of molecules lying parallel and normal to the electrode surface.