ON THE

MANUFACTURE OF IRON.

CHAPTER I.

IRON ORE.

A GEOLOGICAL classification of the ores of iron is, in our case, not the proper way to divide the subject before us: it would not include that clear, comprehensive, practical demonstration needed for our purpose; and we choose, therefore, a division based upon the composition of the material, or a chemical classification. According to this, we shall divide the iron ores proper into Native Iron; Oxides, Carburets, Sulphurets, Arseniurets, and Phosphurets of Iron; Chlorides, Sulphates, Phosphates, Carbonates, and Titanates of Iron.

I. Native Iron.

The deposits of native iron are very limited, and the insufficient quantity of material it affords, precludes it from being ranged, for our purpose, among the iron ores. We notice it as a matter of curiosity, merely to complete the class. Native iron has been found in Canaan, Conn., in a vein or plate two inches thick; it is sufficiently ductile to be wrought into nails by a blacksmith. It was found in a mica slate rock, upon a primitive mountain, and very much intermixed with plumbago. In France and Germany native iron has also been found; but there are serious doubts whether it is formed by nature; and its existence may probably be assigned to the previous burnings of stone coal in its vicinity.

II. Oxides of Iron.

These constitute the most important class for the manufacture of iron. They may be considered under four distinct subdivisions, namely, Protoxide, Magnetic Oxide, Peroxide, and Hydrated Oxide of Iron.

a. Protoxide of Iron has never been found as a natural deposit, and it is difficult even in the chemical laboratory, to make it. It can be made by precipitating salts of the protoxide by caustic soda; but it is very apt to oxidize in being washed and strained, whereby a part of it is converted into oxide. The best way to produce it, is to oxidize iron heated to redness by means of steam. It is of a black color, attracted by the magnet, and very hard. It is composed of

77.23 iron

22.77 oxygen

100.00 peroxide of iron.

Should, therefore, an iron ore exist of this composition, it could not contain more than 77 parts of iron in 100 parts of ore.

b. The next degree of the oxidation of iron is the Magnetic Black Oxide of Iron, Loadstone. Its color is a grayish-black; and when rubbed, it gives a black powder. It is strongly attracted by the magnet, and is magnetic itself. It is altered neither by nitric acid nor the blowpipe. It dissolves slowly in hydrochloric and diluted sulphuric acids, the former of which dissolves the protoxide, and leaves a red powder, peroxide, undissolved. This circumstance is evidence of its being no particular oxide of iron, but a mixture of the protoxide and the peroxide. Its composition is, in 100 parts, 71.79 iron

28.21 oxygen

100.00 magnetic oxide of iron;

or, it consists of 31 parts of the protoxide and 69 parts of the peroxide of iron; and in 100 parts of ore there cannot be more than 71 per cent. of iron.

This species of iron ore constitutes a large body of the native deposits. It is found in Sweden, Norway, Siberia, China, Siam, the Philippine Islands, Germany, France, and very little in England. There is a large deposit at lake Champlain, N. Y., of the best quality. It is also found in Bridgewater, Vt., Marlborough, Vt., and Franconia, N. H.; and New Jersey and the State of New York contain it in large quantities. The exploration of the northwest of the United States promises an addition to the already known valuable deposits, for the iron mountain in Missouri appears to belong to this class. This is one of the most valuable ores, furnishing, by proper treatment, the best quality of iron. From it the main body of the superior iron from Sweden, Russia, and Germany

is manufactured; but the modern improvements in manufacturing, particularly the hot blast, appear to impair its good disposition, and furnish inferior qualities of iron. We will, in the following chapters, explain the reasons why this ore requires particular treatment and attention.

Magnetic iron occurs in primitive rocks, commonly in gneiss, sometimes in clay hornblende or chlorite slate, greenstone, and limestone, and is mixed with epidote, pyroxene, and garnet. We never find it in more recent geological deposits. Its crystalline form is an octahedron, and it varies in size from an inch to the finest sand. It is seldom found in solid masses.

Oxide of Iron, Peroxide of Iron, Iron-glance, Specular Iron, and Red Iron Ore.-These subdivisions of the oxides form a very extensively distributed ore. This ore This ore is very hard, sometimes the color of polished steel, and crystals of this kind transmit light through the edges, and appear to be beautifully red. When coarse, the oxide is of a brown color; but its powder is always red, thus distinguishing it from the magnetic oxide. It is infusible before the blowpipe, but melts with borax, and forms a green or yellow glass. Heated hydrochloric acid is the only acid able to dissolve it. By high temperatures, without the addition of any other matter, it is reduced to the magnetic ore. The magnet does not attract it, nor is the magnet attracted by the iron.

Oxide of iron is composed, in 100 parts, of

69.34 iron

30.66 oxygen

100.00 protoxide of iron.

This oxide of iron is used for various purposes besides the manufacture of iron; as calcined hydrate, it forms a red-brown paint, Spanish or Indian brown, which is the most durable of all paints for preserving wood and iron. In northern Europe the houses of the peasantry are mostly painted with it. It serves for polishing silver and gold, and for that purpose is manufactured from copperas, which is calcined along with common salt. The red color of the common brick is oxide of iron.

Those varieties of specular iron ore which have lost their metallic appearance, are called red iron ore; they are either fibrous or solid, compact or ochry; sometimes they form a firmly connected mass of a red impalpable powder. The scaly red iron and the red iron foam belong to this class; in masses they are but slightly coherent. The

whole variety is in close connection with the micaceous specular iron, between which and the crystallized oxide of iron is an uninterrupted transition. If this variety of ore is mixed with foreign matter, its red color is sometimes altered-and, mixed with silica, lime, &c., turns into hydrates of iron; but an admixture of clay does not alter its red color, and the ore is called clay ore. Reddle, jaspery clay ore, columnar, and lenticular iron ore, are of this kind: the first of which is compact, friable; the second very hard, of conchoidal fracture; the third, distinguished by its columnar forms; and the latter by its granular composition.

This variety of ore yields very unequal amounts of iron; it ranges from the red clay of hardly 12 per cent. of iron, to the rich micaceous ore, which is pure oxide of iron. In this case, the evidence of sense is no safe dependence, for a very poor clay appears sometimes as red as the richest ore-though by drying the specimens, a difference in color may be perceived: still, it would be premature to infer from this, what amount of iron a given specimen contains. The only way to ascertain the quantity of iron is by chemical analysis, and the humid is the only test we can depend upon. But this variety of ore yields always good and strong iron, and is, perhaps, on that account, the most valuable; for the iron manufactured from it is the most tenacious of all known kinds. It improves, even in small quantities, all inferior ores, and forms a most excellent flux in the blast furnace. The damask iron of Persia and the woots of India are manufactured from specular iron ore. Red iron ore occurs most commonly in ancient rocks, and transition clay slate is generally its locality, where the best and richest beds are deposited. The Island of Elba is justly celebrated for an inexhaustible abundance of specular iron, which has been worked since immemorial antiquity. The total height of the metalliferous mountain is more than 600 feet, and never will be exhausted. Specular iron ore is found throughout Asia, Corsica, Germany, France, Sweden, and in almost every country. The United States of America have yet afforded no amount worth noticing of the better qualities; but immense beds of inferior quality, for instance, the Pittsburg coal field, are loaded with some very valuable red clay ores, interspersed with nodules of the specular kind. Massachusetts, Ohio, and the western part of New York, contain similar deposits. Specular iron ore is found in crystals in the craters of volcanoes, the result of the evaporation of chlorides of iron in the fissures of lava. It forms heavy beds in transition mountains, and is frequently found imbedded in clay in the shape