Galvanized Iron, a name given to iron coated with zinc, or zinc and tin. The process is a French invention, and was not introduced into England till 1837, when a patent was obtained by Mr. Crawfurd. The operation is not performed with a galvanic battery, as is often supposed, but by immersion in the melted metal. By Mallet's process the sheets are first cleansed by immersion in a warm bath of equal parts of sulphuric or hydrochloric acid and water, followed by scrubbing with emery and sand. They are then placed in a preparing bath of a saturated solution of hy-drochlorate of zinc and sulphate of ammonia; and from this they are removed to a metallic bath composed of 202 parts by weight of mercury and 1,292 parts of zinc. To every ton weight of the amalgam one pound of potassium, or better of sodium, is added. At the temperature of 680° F. the compound fuses, and the zinc is deposited upon the iron sheets; the iron at the same time is attacked so strongly, that in a few seconds a plate an eighth of an inch thick would be dissolved if allowed to remain. Small articles are most advantageously treated after the strength of the mixture has been somewhat spent upon larger ones.

Crawfurd's method was to plunge the cleansed sheets of iron into a bath of melted zinc covered with sal ammoniac, and stir them about for some time. Undiluted commercial acids are also used for cleaning the surface of the iron, in which case some bits of zinc are immediately added, which dissolves and is directly precipitated, forming a film upon the iron. When coated the articles may be applied to use, or they may be made still more effectually to resist the action of oxidizing agents by next dipping them in a bath of melted tin. This metal then forms the exterior coat, and adheres much more firmly than if it had been applied directly to the iron.