The Rusting of Iron

Abstract

IN NATURE of February 21 (p. 390) appears a letter from Prof. Wyndham R. Dunstan in which he represents me as having concluded “that carbonic acid is essential to the rusting of iron, and that rusting does not occur in its absence.” As such a general statement, without reference to the context of the paper to which Prof. Dunstan refers, may prove misleading, I shall be obliged if you will allow me to point out that the main and incontrovertible conclusion drawn from experiments extending over a prolonged period is that iron does not undergo oxidation in presence of oxygen and water. If, however, a minute quantity of acid (either carbonic acid or any other acid capable of attacking iron) be present, the metal is first converted into ferrous salt, which subsequently oxidises to rust. Samples of iron which contain such impurities as sulphur, phosphorus, and carbides may give rise to free acids when in contact with water and oxygen, and under these conditions rusting may be expected to occur, even if carbonic acid be rigorously excluded.