IRON.

533

Clay iron ore (technically called mine) is burned with coal in largeheaps, by which it loses carbonic acid, water, and sulphur. It is thensmelted with a flux (in South Wales this is limestone ; in the forest ofDean, clay ;) and coke. The smelted iron is run into moulds, and is thencalled cast iron (ferrum fusum), or pig iron. This contains carbon,oxygen, silicon, and often sulphur and phosphorus. To separate these,it is submitted to several processes (called refining, puddling, and weld-ing,) by which it is converted into wrought iron {ferrum cusurn ), ( Manu-facture of Iron , in the Library of Useful Knowledge; also, Treatise onIron and Steel, in Lardner’s Cyclopedia).

Properties. —The primary form of the crystals of native iron is theregular octahedron. Pure iron has a whitish grey colour, or, according toBerzelius , is almost silver white. When polished it has much brilliancy:its taste is peculiar and styptic; when rubbed it becomes odorous. Itsductility and tenacity are great; its malleability comparatively small. Itssp. gr. is 7'788, but diminishes by rolling or drawing. It is attracted bythe magnet, and several of its compounds are capable of becoming per-manent magnets; but pure iron retains its magnetic property for a shorttime only. It requires a very intense heat to fuse it; and it is not volatileat any known temperature; while in the softened state, previous to melting,it is capable of being welded. Its equivalent or atomic weight is 28.

Characteristics. —Iron readily dissolves in diluted sulphuric acid,with the evolution of hydrogen gas. The solution contains the proto-sulphate of iron, and produces, on the addition of caustic potash or soda,a greenisli-white precipitate (the hydrated protoxide): this precipitate,by exposure to the air, attracts oxygen, and is converted into the red orsesquioxide. Auro-chloride of sodium forms a purple precipitate withthe protosalts of iron. By boiling the solution with a little nitric acid,we obtain a persulphate of iron, recognized by ferrocyanide of potassiumcausing a blue precipitate; sulphocyanic or meconic acid, a red colour ;gallic or tannic acid, or infusion of galls, a purple or bluish black ; andsuccinate, or benzoate of ammonia, a yellowish precipitate.

Physiological Effects, {a.) Of the metallic iron. —Iron is probablyinert so long as it retains its metallic form, but it readily oxidizes in thealimentary canal, and thereby acquires medicinal power. As acidspromote this chemical change, acid wines and fruits assist in renderingthe metal active, while alkalies and their carbonates have an opposite effect.The oxidizement of the iron is attended with the evolution of hydrogengas, which gives rise to unpleasant eructations. If sulphur be takenalong with iron, hydrosulphuric acid is developed. Like the ferru-ginous preparations generally, the internal employment of iron causesblackening of the stools. The nature of the effects produced by oxideof iron formed in the alimentary canal will be best examined hereafter,under the head of ferruginous preparations. I may, however, remarkhere, that it is one of the few metals which by oxidizement is notrendered more or less poisonous.

{b.) Of the ferruginous compounds, a. On vegetables. —Most of thecompounds of iron do not appear to be hurtful to plants : at least thisis the case with the oxides (Decandolle, Phys. Veg. 1337.) The sulphate,however, is said to be injurious {vide p. 551.)

On animals. —The effects of the ferruginous compounds on animalsgenerally are similar to those on man. It is stated that in animals to