study of the character, causes, and prevention of the rusting of iron and steel, though of comparatively recent date, has already inspired a vast literature. Evans (5), Friend (9), Pollitt (14), and Speller (18) are the authors of handbooks on this subject.Certain metals-for example, aluminum, copper, and leadare protected from more than a very superficial corrosion in air or in water by the development of a tightly adhering, impervious film of oxide, basic sulfate, or basic carbonate (6). A similar protective film of oxide is formed on iron that has been rendered passive by immersion in chromate solution or in concentrated nitric acid ( 22). Evans has also shown that even on exposure to air a film of iron oxide forms on iron which gives temporary protection against rusting (If),The destruction of iron and steel by rust is usually more rapid in salt solutions (refrigerator brines, sea water, etc.) than in ordinary fresh water. The usual inhibitor employed in refrigerator brines is sodium or potassium chromate (20),