2. Manufacture of Iron.—The increasing use of iron is a prominent characteristic of the present age, and every day sees some new application of it in the arts of life. Although the most useful of the metals, it was not the first known. The difficulty of reducing it from its ores would naturally make it a later acquisition than gold, silver. and copper (q.v.) See also I3noxzE, and BRONZE PERIOD. The reduction of the ore known as the black oxide of iron, however, has been carried on in India from a very early time.
In Europe the rich speculdr and other ores of Spain and Elba were much used during the Roman period; in Greece, also, iron war known, though, as among the Romans, its use wassubsequent to that of bronze. We are informed, too, by the Roman historians that this metal was employed by the ancient Britons for the manufacture of spears and lances. The Romans, during their occupation of Britain, manufactured iron to a considerable extent, as is evidenced by the cinder-heaps in the forest of Dean arid other places. The rude processes then in use left so much iron in the cinders that those of Dean forest furnished the chief supply of ore to 20 furnaces for between 200 and 300 years. In those early times, the iron ores were reduced in a simple conical fur nace, called an air-bloomery, erected on the top of a bill, in order to obtain the greatest blast of wind. The furnaces were subsequently enlarged and supplied with an artificial blast. Charcoal was the only fuel used in smelting till WM when lord Dudley intro duced coal for this purpose; but the iron-masters being unanimously opposed to the change, Dudley's improvement died with himself. It was not reintroduced till Abraham Derby, in 1713, employed it in his furnace at Coalbrook Dale. But as this method was not properly understood, the production of English iron declined with the change of fuel, till, in 1740, it was only three-fourths of what it had formerly been. About 10 years after this, however, the introduction of coke gave renewed vigor to the iron-trade, and then followed in rapid succession those great improvements in the manufacture which have given to the history of iron the interest of a romance. The introduction of Watt's steam-engine in 1770, the processes of puddling and rolling invented by Henry Cort in 1784, and the employment of the hot-blast by Neilson of Glasgow in 1830, have each been of inestimable service. The greatest improvement introduced into the iron manufacture in recent times is the process of Mr. Bessemer for the production of steel, patented in 1856 (see BESSEMER PROCESS). The " Siemens-Martin" Method of making steel has also of late come into extensive use. An important new process for steel is
patented by S. T. Thomas.
Iron ores are abundantly distributed over the globe; the chief kinds being-1. Mag netic iron ore; 2. Red hematite, specular. or red iron ore; 3. Brown hematite or brown iron ore; 4. Carbonate of iron, including spathic ore, clay ironstone, and blackband ironstone. The ore richest in the metal is the magnetic (sec MAGNETISM), or black oxide of iron. When pure it contains nothing but oxygen and iron, its chemical formula being FeO,, which gives 73 per cent of iron by weight. It occurs in dark heavy masses of black crystals, and is found in the older primary rocks. Sweden is famous for this ore, and for the iron produced from it, which is esteemed the best in Europe. The celebrated mines of Dannemora, in that country, have been constantly worked since the 15th cen tury. Russia, too, has great iron workS in the Ural mountains, which arc supplied with this ore. So, also, have Canada and several of the American states, as Virginia, Penn sylvania, New Jersey, etc. The rock formations in which magnetic iron ore occurs very rarely contain coal, hence it is almost always smelted with wood-charcoal, Which, as it contains no sulphur, is one great cause of the superiority of the iron produced from it.
Red hematite differs from the last only in containing proportionally a little more oxygen, its formula being that is to say, 70 per cent of iron by weight. There are several varieties of this ore, but only two need be referred to. The first of these, specular iron, so called from its bright metallic luster, occurs in large and beautiful crystalline masses in the island of Elba, where it has been worked for more than 2,000 years, and is likewise found in many other parts of the world. It is of a steel-gray color, assunf ug a red tint in thin fragments and when scratched. The other variety is kidney ore, whose origin is still a curious problem, as its deposits occur sometimes in veins and sometimes in apparently regular beds. Its characteristic form is in large kidney-shaped nodules, with a fine radiated structure. This shape, however, is only assumed in the cavities of massive deposits. Red hematite is sometimes called blood stone. It is used for polishing metals, and yields a blood-red powder, used as a pig ment. This valuable iron ore is found in many t' countries, but in few places in greater i abundance than at.Whitehaven and Utverstone, in the n.w. of England, where splendid masses of it occur, 15, 30, and even 60 ft. in thickness. These two districts produced, in 1877, about 2,2,85,000 tons of hematite.