The electrode equilibrium of the standard cell

Abstract

Some experiments described by Hulett 2 indicatingthe existence of a state of unstable equilibrium in the Weston cell have, on account of the importance of the subject, led to a further study of the question at the Bureau of Standards. The equilibrium between cadmium amalgam and cadmium sul phate was first studied. Saturated solutions of the latter were shaken up in air, nitrogen, hydrogen, and in vacuo with cadmium amalgam, but in no case did the electromotive force of cells set up with the treated and untreated solutions differ more than 10 microvolts, even though the samples shaken in the presence of air had become cloudy from the formation of an excess of basic cadmium sulphate. The equilibrium of the system mercury, mercurous sulphate, cad mium sulphate, and of the corresponding system of the Clark cell was then studied in special cells, so constructed that the above materials could be rotated and the effect determined without open ing the cell. This consisted of a tube about 2 cm in diameter and 1 2 cm long, provided at the lower end with a small bulb into which a platinum wire was sealed. The bulb was connected to the main tube by a narrow neck, so that, with sufficient mercury in the cell, the plati num terminal was not in contact with the solution, even during rotation.