It was formerly believed that the reason why iron exposed to the atmosphere rusted was because it simply oxidized. Afterward it was suggested that the first stage in the rusting of this metal is the production under the influence of carbonic acid, of ferrous carbonate, which is afterward converted into rust. Five years ago, however, Professor Dunster put forward a new explanation. He thought that pure oxygen in the presence of water attacked the iron, giving rise to ferrous oxide and hydrogen peroxide, and that a portion of the latter converted the ferrous oxide into rust, while the remainder directly attacks the iron, causing a fresh quantity of ferrous oxide, when this is again oxidized in a very similar way.
Dr. G. T. Moody has shown that if very special pre-cautions are taken to exclude all traces of carbon dioxide, then iron may be left in contact with pure oxygen and water for many weeks without undergoing any change. In one of the experiments thirty times as much oxygen as is required to convert the whole of the iron into oxide was passed during the course of a few weeks, but there was absolutely no rust. But if the air were not freed from carbon dioxide rusting commenced at once, and in seventy-two hours the whole of the metal was corroded. There would seem to be no basis, therefore, for the assumtion that iron can be caused to rust by pure water and pure oxygen only.