CORROSION RESEARCH ROUND‐UP

COMBINED METHODS Rust prevention by metallic substrata and paint. Over industrial towns rain often acquires a pH 3 to 4 owing to the absorption of airborne sulphates, which pollutants may reach concentrations between 20 and 30 mg./l. Metallic coatings use zinc or aluminium, whereas organic coatings make use of varnishes, paints and similar preparations. The electrochemical potentials of Al, Zn and Fe are 1.28 V, 0.77 V and 0.34 V. Anodic metals, with reference to iron, are also chromium, magnesium and cadmium.