Tarnish Studies: The Electrolytic Reduction Method for the Analysis of Films on Metal Surfaces

A method is described for analysis of tarnish films on metals by electrolytic reduction at the cathode. Its suitability is demonstrated for the rapid and accurate measurement of oxide films on copper varying in average thickness from monomolecular layers to 1,000 Aå. It is shown to be useful for reduction of mixed oxide‐sulfide films on copper and silver. The method is used to measure the oxide films on freshly reduced copper after one‐half hour's exposure to oxygen or air. Such films are shown to be 10 – 20 Aå thick. A thicker film, measuring 30–70 Aå, is found to be produced by abrasion of copper in air, water, benzene or toluene. No film is produced on silver by abrasion in air. Adaptations and modifications are discussed which give wide analytical application to the method.