The Rusting of Iron ¹

Abstract

IN the October issue of the Chemical Society's Journal, Mr. Bertram Lambert describes a second series of experiments on the rusting of iron. In these experiments it is shown by spectroscopic examination that carbon dioxide was actually present under the conditions used previously. Elaborate care was there fore taken to remove this, by heating as much as possible of the apparatus, whilst maintaining a high vacuum, and (during some of the successive heatings) cooling an attached tube in liquid air. The spectro scopic indications of carbon dioxide disappeared after the first of eight successive heatings, but no change was noticed in the readiness with which commercial iron rusted in the apparatus when purified oxygen and purified water were admitted. The author maintains, therefore, that these substances are capable of bring ing about rusting in the absence of any trace of carbonic or other acid. The contrast between these results and those observed by Moody and by Friend is attributed to “passivity” induced in the metal in the one case by treatment with _chromic acid (as suggested by Tilden), and in the other case by treatment with caustic soda (as suggested recently by Dunstan and Hill). This passivity must evidently be supposed to be permanent during many months of contact with air and water, but to be destroyed immediately by the merest trace of carbonic acid or by contact with glass.