Prevention Of Iron-rust

A very important paper has lately been remi before the Society of Arts by Mr. Barff, Professor of Cliemistry to the Koyal Academy, upon a method of preserving irou from rust by coating it with its own mognetic oxide. The facts which Prof. Barff has brought forward, and the specimens which he has exhibited, are sueh as to justify the belief that his discovery will prove to be one of enormous value, and that it will, indeed, render all all kinds of iron-work, however much exposed to weather or to coiTosive vapors or liqnids, practically indestructible and everlasting. When au iron surfaee is exposed to the actioü of water, or of moist air, it speedily becomes covered by a film of protoxide, or ferrous oxide, which consists of 56 parts by weight of the metal to 16 parts of oxygen. The ferrous oxide continúes to attract oxygen from the atmosphere, and is gradually converted into another compoimd, the sesquioxide, or ferric oxide, which is composed of twice 56 parts by weight of iron, and three times 16 parts by weight of oxygen. The ferric oxide, in its turn, gives up some of its oxygen to the as yet unoxidizediron beneath it,and the ferrous oxide thus formed is gradually converted into ferric oxide by the access of air through the spongy layer of superficial rust which covers it. In this way tiie first formed film of rust exposes to the atmosphere the surface which lies below it ; and henee the rust becomes a carrier of oxygen to the deeper parts of the iron, until the latter is completely corroded and worn through. Many attempts have been made to protect iron surfaces by the application of some kind of paint or varnish ; and these attempts have, of course, been to some partial extent successful. Sttch coatings, however, have no real adhesión to the metal on which they ai-e placed, and are Hable to scale off or to perish in a variety of way s. Even when the coating is generally sound, the smallest flaw in its continuity will give entrance to the enemy ; for the rust from the exposed spot will spread laterally under the coating, and may be all the more dangerous and destructiye from being partially concealed fíom view It is manifest that the evils incidental to rusting are entirely due to the unstable character of the two oxides alruidy nlentioned, which are formed spontaneously under of dinary clisiatic conditions. There is, however, a third oxide wliieh possesses characteristics of a totally different kind, and which is uninfluenced, not only by moist air, but even by aeids and other corrosive substances. This is the magnetic or black oxide, which consists of three times fifty-six parts by weight of iron, and four times sixteen parts by weight of oxygen. Prof. Barff has discovered that if any iron article is exposed, at a liigh temperature, to the action of supei-heated steam,-it will become covered by a film of this black oxide, of a thickness which is determined by the degree of tenrperature and by the length of exposure. The oxide is harder than the original iron, and adheres to it even more firmly than the partióles of iron adliere to each other, so that there is a gain not only in chemical, but also in mechanical resistance. If the operating chamber is heated only to 500 degrees Fahrenheit, ■ aild the expoBttre is continued for only five hours, a surface is obtained which will resist emery-paper for a considerable time, and which will not rust within doors, or after any moderate degree of exposure to moisture. If the oxidizing process is conducted at 1,200 degrees Fahrenheit, and continued for six or seven hours, the surface will resist a rasp and will bear any amount of exposure to weather. The oxidation doen not affect the appe'arance of the &iir= face in any other way than by turning it black. Aroughforging retains its roughness, ancí a turned or polished surface its snioothness. If there should be any flaw in the coating, or if the black oxide is designedly removed from part of the surface, the common oxidation will occur where the iron is thus left uuprotected. But such oxidation is strictly limited to the unprotected portion, and has not the smallest tendency either to spread laterally tillder the black oxide or to detach this from the sitbiacent parts. Among the most valuable anti important of the probable applications of the invention will be the protection of steam boilers and of the plates of iron ships ; and Prof. Barff hopes that by certain arrangements it will be possible to opérate upon very large mamüactured articles withoiit its being necessary to provide a heating-chamber large enough to contain tliem. The applications seem almost without number. The process will be conducted at very small cotst, and it will pi'obably be employed, at no distant time, for" iron goods of every description. Not only o, but it will extend the applications of iron itself to several purposes for which its liubility to rust hitherto rendered it unsuitable. Copper vessels will no longer possess any advantages for cooking, and iron saucepans will no longer need to be tinned. Leaden pipes for the conveyance of water will in all probability be entirely superseded ; and there can be no doubt that new uses for incorrodible iron will every day suggest theinselves.