to produce ferric oxide and hydrogen peroxide. In the combination of these three substances rust is produced, and also the initial portion of hydrogen peroxide which attacks a new particle of iron, and thus, as under the preceding theory, the process is continuous, or cyclic.

The weakness of this theory lies in the impossibility of detecting hydrogen peroxide during rusting under experimental conditions. It has few advocates.

The electrolytic theory, which no doubt has the strongest support, is based upon. the recognized tendency of metals to go into solution, even in pure water. The act is accompanied by the release of hydrogen positively charged with electricity, leaving on the metal a corresponding charge of negative electricity. If oxygen is at hand to combine with  the hydrogen,  the electrical