Page:The New International Encyclopædia 1st ed. v. 10.djvu/874

IRON. cent. of iron, corresponding to about 9.5 per cent. of anhydrous ferric chloride. The tincture is prepared by making up 250 parts of the official aqueous solution of ferric chloride to 1000 parts with alcohol. Ferric hydroxide with magnesia is known as ‘arsenic antidote,’ being an effective remedy for poisoning with arsenic. The antidote may be best prepared by gradually adding 10 parts of magnesia in water to 50 parts of ferric hydroxide in water, and shaking the mixture vigorously. It should be prepared immediately before using, and should be given repeatedly in large doses. Iron salts should never be given together with any preparation containing tannic or gallic acid.

The minerals which are commercially important as sources of iron may be grouped in the following classes: (1) Magnetite.—This class includes ores in which the iron occurs as magnetic oxide (Fe3O4); they contain when pure 72.40 per cent. of iron. (2) Hematite.—All varieties that are sesquioxides (Fe2O3), with 70 per cent. of iron. They are variously known as red, blue, and specular hematites, also as micaceous and fossil ores, according to their color and physical structure. (3) Limonite.—The hydrated oxides (2Fe2O33H2O), including bog ores, pipe ores, etc., with 59.89 per cent. of metal. Brown hematite is a synonymous term for limonite. (4) Siderite.—Ores containing carbon dioxide and represented by the type formula (FeCO3), with 48.27 per cent. of iron. Spathic ore is another name for siderite, while clay ironstone is a term applied to the varieties containing much clay and having a concretionary structure. When the ore contains bituminous matter in addition to clay it is called blackband.

Pyrites (FeS2) and franklinite, an oxide of iron, manganese, and zinc, are utilized to a very small extent. Pyrites is first roasted for the recovery of sulphur in sulphuric acid manufacture, and the clinker is then smelted. Franklinite is employed in the production of spiegeleisen, after extracting the zinc by roasting.

The ores of iron always contain more or less foreign matter, and only approximate the metallic content required by the chemical formulæ; the discrepancy commonly amounts to 10 per cent. or more. As the costs of handling and treatment per ton of iron are indirectly proportional to the purity of the ores, the higher grades are naturally in most demand. In the United States mining is confined practically to the hematite, limonite, and magnetite deposits, which on the average carry from 50 to 60 per cent. of iron, while elsewhere ores may be worked that run as low as 30 per cent. The nature of the impurities is of great importance in determining the value of ores. The common impurities are those which enter largely into the composition of the rocks surrounding the deposits. They are silica (SiO2), alumina (Al2O3), lime (CaO), magnesia (MgO), water (H2O), and carbon dioxide (CO2). Water and carbon dioxide are objectionable only as they replace the iron, while the others exert an influence upon the fluxing properties of the ore and the course of smelting operations. Of greater importance, however, are the small quantities of phosphorus, sulphur, and titanium, these impurities being almost wholly obnoxious in their effect. Phosphorus gives a fluid pig iron that can be converted into steel only by employing special methods of treatment. As a large part of the iron produced is now converted into steel by the acid Bessemer process, which does not eliminate phosphorus, ores adapted to this treatment find a ready market at good prices. For such ores the outside limit of phosphorus relative to the iron is ; that is, an ore carrying 60 per cent. of iron is not of Bessemer grade unless the phosphorous content falls below 0.06 per cent. In the United States common practice fixes a still lower limit for phosphorus. . The relative importance of the different iron ores mined in the United States is shown by the following percentages of the total output for 1901: Hematite, 83.1; limonite, 10.4; magnetite, 6.3; siderite, 0.2 per cent. Hematite thus contributes more than four-fifths of the total production. A large part of this ore comes from the Lake Superior region, where immense deposits have been found in metamorphosed Pre-Cambrian rocks. Five productive belts, or ‘ranges,’ as they are commonly called, are known. The Marquette range, opened in 1856, is situated in Michigan, east of the Keweenaw Peninsula. The Menominee Range, first developed in 1877, lies on the border of Wisconsin and the upper peninsula of Michigan; it is succeeded farther westward by the Gogebic Range, which was opened in 1884. The Vermilion and Mesabi ranges are situated northwest of Lake Superior, in Minnesota; they were first exploited in 1884. The deposits are found near the surface, and operations are conducted on a large scale. In some cases the ore is excavated, after removing the overburden, by steam shovels, which deposit it directly in the cars. A single mine in Minnesota has produced 1,681,000 long tons of ore in a year, or more than the annual output of the entire country prior to 1854. The total production of the Lake Superior mines up to and including 1901 was 192,008,000 long tons. The bulk of the ore is forwarded by rail to ports on Lakes Superior and Michigan, and thence shipped by boat to Chicago and Lake Erie ports, a large proportion being destined for the manufacturing centres of western Pennsylvania. A great shipping industry is engaged in the transport of Lake Superior ores, and it is largely owing to this fact that the tonnage of vessels passing through the Sault Sainte Marie Canal each year exceeds the annual commerce of the Suez Canal.

Hematite ores are also mined in many of the Appalachian and Rocky Mountain States. The Clinton formation of the Silurian, which outcrops along the western slopes of the Appalachians from New York to Alabama, contains valuable deposits interstratified with shales and limestones. Some ore is obtained at Clinton, N. Y., and near Chattanooga, Tenn.; but the most productive beds are in the Birmingham district of Alabama.

The limonite or bog ores are widely distributed, although, owing to their low iron content, they are worked extensively in only a few regions. Virginia, Alabama, Tennessee, and Colorado produce the largest quantities of limonite. Magnetite occurs in the Adirondacks, the New Jersey Highlands, near Cornwall, Pa., and in many of the Western States. Siderite is