Iron. Iron is only prepared on the large scale. It is obtained by smelting the ore along with coke and a flux (either limestone or clay). The crude iron thus obtained is run into moulds, and then constitutes cast iron or pig iron. By the subsequent process of refining, (puddling, welding,) it is converted into soft iron or wrought iron. The properties and uses of iron are too well known to require description. Its applications in almost every branch of human industry are almost infinite. It is remarkably ductile, and possesses great tenacity, but it is less malleable than many of the other metals. Its specific gravity is 7.788, and melts at about 2700° Fahr. It is the hardest of all of the malleable and ductile metals, and when combined with carbon or silica (steel), admits of being tempered to almost any degree of hardness or elasticity. Metallic iron is distinguished by being attracted by the magnet; by being dissolved by dilute muriatic and sulphuric acids, with solution of hydrogen gas, recognized by its inflammability; and the solution exhibits the usual reactions of protoxide of iron. (Cooley.) Iron does not alloy easily with other metals, principally on account of its high melting point. It is easily attacked by acids, and requires protection from the air, to prevent oxidization or rusting.

3259. To Estimate the Percentage of Iron in Ores

3259. To Estimate the Percentage of Iron in Ores. Prepare a crucible of refractory clay by pressing into it successive layers of moistened powdered charcoal until full and solid; clear out a cavity by removing the central portion. Take 200 grains of the powdered ore, and mix it with the same weight of dry slacked lime, and 50 grains charcoal ; if necessary a litte carbonate of soda may be used with very refractory ores; introduce this mixture into the crucible and lute it up. Expose the crucible to a moderate heat until the contents of the crucible are dry, then apply, and maintain for half an hour the full heat of a blast furnace. Then remove the crucible, tap it steadily on the edge of the furnace, so as to bring the metallic portion of its contents together at the bottom; and, when cool, break the crucible open. The iron will be found in a clean button at the bottom of the slag. Clean the iron with a scratch brush, and weigh it. Its weight, divided by 2, will give the percentage of richness of the ore under examination.

3260. To Distinguish Wrought and Cast Iron from Steel

3260.    To Distinguish Wrought and Cast Iron from Steel. Eisner produces a bright surface by polishing or filing, and applies a drop of nitric acid, which is allowed to remain there for one or two minutes, and is then washed off with water. The spot will then look a pale ashy gray on wrought iron, a brownish black on steel, a deep black on cast iron. It is the carbon present in various proportions which produces the difference in appearance.

3261. To Impart to Cast Iron the Appearance of Bronze

3261.    To Impart to Cast Iron the Appearance of Bronze. The article to be so treated is first cleaned with great care, and then coated with a uniform film of some vegetable oil; this done, it is exposed in a furnace to the action of a high temperature, which, however, must not be strong enough to carbonize the oil. In this way the cast iron absorbs oxygen at the moment the oil is decomposed, and there is formed at the surface a thin coat of brown oxide, which adheres very strongly to the metal, and will admit of a high polish, giving it quite the appearance of the finest bronze.