Barff Process.

Scribners monthly 6, 1880

The so-called "Barff process" for coating iron articles with a film of magnetic oxide, described at the time of its announcement in this department, is now carried on upon a large scale, but the objection has always been raised that, while the film prevents rust, it has a disagreeable appearance and color. Other experimenters used air instead of steam, in applying the magnetic oxide coating, and secured a better color, but at the expense of stability. By a new process, the chamber in which the iron to be coated is placed is filled with carbonic oxide, and, on introducing heated air, combustion begins, and continues till all the carboic oxide is converted into carbonic acid, when the surplus oxygen in the air attacks the iron, converting the surface first into a magnetic oxide and then into common rust. A second supply of carbonic oxide is admitted, and burned as before, but the supply of air being with-held, combustion is maintained in part by extracting oxygen from the rust, which is again converted to a magnetic oxide, which is the film desired. Repeating the operation tends to thicken the film and make it secure, and, at the same time, retain an agreeable color and surface.