The Films Responsible for Oxidation Tints on Metals

Abstract

THE colours produced by heating metals in air have long attracted interest. Within the last three years it has proved possible in two cases (lead and iron) to separate from the basis metal the oxide-films responsible for these tints. In the case of lead, which is liquid at the requisite temperatures, the oxide-film is lifted off the molten metal on glass (Proc. Roy. Soc., A, 107, 228; 1925), whilst in the case of iron the method employed is that originally worked out for the isolation of the much thinner, invisible skin responsible for the passivity of iron treated with oxidising agents. This method (Jour. Chem. Soc., 1020; 1927) consists in undermining the oxide-film by dissolving away the metal below it with iodine solution, so that the film comes peeling off in curling fragments, which can be washed by decantation and examined under the microscope.