XII. Chromate of Iron.

Chrome ore, or chromated iron ore, is infusible before the blowpipe; acts upon the magnet after being roasted; of difficult smelting with borax.

Its composition, in 100 parts, is

43.00 oxide of chrome

34.70 protoxide of iron

20.30 alumina

2.00 silica

100.00 chromedron.

Chrome ore is found in serpentine and cotemporaneous rocks, in irregular veins and beds. It is found in Europe; but in largest quantity within the United States; at the Bare Hills, near Baltimore; at Hoboken, New Jersey, and at Milford and West Haven, Conn. Europe derives its supply from these places.

XIII. Franklinite.

Dodecahedral Iron Ore.-Color black, and behaves before the blowpipe like the black magnetic ore: but with alkalies in the reduction fire, it emits fumes of white oxide of zinc, and becomes green. It is composed of

66.00 peroxide of iron.

16.00 red oxide of manganese

17.00 oxide of zinc.

Franklinite is found near Franklin furnace, in Hamburg, New Jersey, accompanied by another variety of zinc ore, in large veins and masses; it is a species belonging to North America alone.

XIV. General Remarks.

The ores of iron are distributed over the whole globe in great profusion. They are found in every latitude and in every climate. But every mineral which contains iron does not constitute an iron The consideration of quality and quantity determines the application of a mineral species to the manufacture of iron. The basis upon which our arguments in this case rest, is the general theory of reducing metals, and the experience of old establishments.

ore.

We will proceed to define the general theory, and to illustrate that theory by facts.

a. Theory of Reducing Ores to Metals.-The metals, with the exception of gold, silver, and copper, are seldom found in their native state. They are combined with other matter in their native beds, and it is the study of the metallurgist, by dissolving this combination, to reduce them to their simple condition. The matters thus combined, are oxygen, sulphur, carbon, chlorine, and phosphorus; and combinations of the oxides of metals with the acids of the above metalloids.

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b. Metals and Oxygen.—Metals, particularly iron, combine very readily with oxygen, and form oxides. In the combinations of iron with oxygen, there are four distinct grades; the first is one atom of iron with one atom of oxygen, or FO,* the protoxide. The second, two atoms of iron with three atoms of oxygen, F,O,, or the peroxide. The third is a combination of one atom of the protoxide with one atom of the peroxide, FO+F2O,, the magnetic oxide; and the fourth, one atom of iron with three atoms of oxygen, or the ferric acid. The latter is a production of the chemical laboratory, and is beyond the limits of our labors.

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The affinity of the metals for oxygen is different in different metals, and varies with the temperatures under which the combinations are formed. Some are oxidized by a temperature below freezing, as potassium or manganium: others by the medium temperature, as zinc, tin, lead, iron, &c. Some cannot be oxidized by the atmosphere at all, as gold, platina, silver. Most of the metals can be combined with oxygen by being dissolved in nitric acid, or nitromuriatic acid (aqua regia). Some metals decompose water readily; such are potassium, sodium, and the metals of the alkalies generally; but iron and zinc decompose water slowly. If, however, an acid be added to the water which dissolves the oxide formed, the decomposition of water goes on rapidly. In all these instances the oxygen of the water is absorbed by the metal, and the hydrogen liberated. Some metals cannot be oxidized by means of acids, nor directly by the atmosphere, as rhodium and iridium, but oxidize very easily by being previously melted together with potash or saltpetre. Chrome, and a few others, are of this kind.

Noble metals are those which are not oxidized by heat and access of oxygen. To this class belong gold, platina, silver, iridium. Another class of metals are oxidized in the heat of a flame, but lose their oxygen in higher temperatures; such as palladium

*F for ferrum (iron), and O for oxygen.

rhodium, quicksilver, nickel, and lead. All other metals, when heated with access of the atmosphere, absorb oxygen and retain it. When a metal combines with oxygen, it loses its metallic, and assumes an earthy appearance, sometimes of a white, or black color. For this reason the old chemists applied to the oxides of metals the term calc-that is, resembling alkaline earth. This idea is worthy of notice, for most of the oxides of the metals are electro-positive, while but few are electro-negative. This subject is of great importance in metallurgy, and deserves attention. Metals whose oxides are mainly electro-positive are gold, osmium, iridium, platinum, rhodium, silver, mercury, uranium, copper, bismuth, tin, lead, cadmium, zinc, nickel, cobalt, iron, manganese, and cerium. These are at least four times heavier than water; very few are oxidized at common temperatures of the atmosphere, but all can be deoxidized by means of carbon.

Metals whose oxides are mainly electro-negative, are selenium, tellurium, arsenic, chrome, vanadium, molybdenum, wolfram, antimony, and titanium. The oxides of these metals take the place of acids, and form, with the above oxides and the alkalies proper, salts of definite proportions.

Metals which form with oxygen the alkalies proper, are potassium, sodium, lithium, barium, strontium, calcium, magnesium, aluminum, beryllium, yttrium, zirconium, and thorium.

We should be cautious not to conclude that this classification of the oxides of metals into electro-negative and electro-positive, is absolutely or literally true, for most metals have oxides of different composition; combine with one, two, three, five, or seven atoms of oxygen, and are in that proportion more or less alkaline or acid. The oxides of potassium and zinc are always electro-positive to those oxides whose metals are negative to potassium and zinc. Sometimes, in fact, the first oxide of a metal is an alkali, and the second an acid; this is the case with the oxides of tin and manganese, and also with iron. The protoxide of iron is a strong alkali, and its peroxide so much of an acid, that both combine and form a distinct salt, with all the characters of neutralization, the magnetic oxide. We intend to refer to this subject in the theory of fluxes.

c. Hydrates.-Oxides of metals form definite compounds with water, and are then called hydrates. The water in the hydrates of potash and clay is so strongly combined with its base, that the

strongest heat is hardly sufficient to separate them. Other hydrates are easily decomposed, as the hydrate of iron; while a few are decomposed in boiling water. Hydrates always decompose and combine more readily than the oxides.

d. Reduction of Oxides.-Most of the oxides of metals can be decomposed, that is, the metal revived by means of carbon, under various conditions; which conditions we will explain more particularly in the chapter on reviving iron. There is a great difference, however, in the affinity of oxygen for metals, and that may be assigned as a cause of their different behavior with carbon; but the main cause is, undoubtedly, the aggregate form of the oxide for carbon is strong enough to separate potassium and oxygen, and why not silicon and oxygen, or aluminum and oxygen? The cohesion of the atoms of these oxides is so strong, that the particles, or congregation of atoms, which the oxides form, resist in a body the affinity of carbon for oxygen. We find this general law of the difficult decomposition of particles, particularly applicable to the oxides of iron. The solutions of the peroxide salts of iron are very easily reduced to protoxide salts, but with great difficulty to metal. It appears, therefore, that the oxygen is more firmly connected to the metal in the protoxide than in the peroxide, or, that the atoms of the protoxide are more inclined to crystallization. Most of the other oxides follow the same law, and very few the reverse. To the latter belong mercury and tin. According to this general theory, the more oxygen the metal absorbs, that is, the higher the state of oxidation, the more readily will oxides be reduced to metals. This theory is confirmed by experience at the blast furnace, for we know by practice that magnetic oxide is disadvantageous in its raw state, and that it is far better after being roasted or oxidized. The most favorable condition of iron ore for the blast furnace is the peroxide of iron, the reason of which we will explain hereafter; and if we cannot find native peroxides, we must produce such by art-that is, by roasting and calcining-in the cheapest and most practicable manner.

e. Reviving of Metals. To illustrate the foregoing principle more fully, it will be best to explain the reviving of metals in each particular case. This will furnish practical proof that the reduction of the oxides is the more complete, the higher the state of oxidation; it will also prove that oxides are the material from which metals can be most conveniently derived.

Potassium is produced by mixing the oxides with carbon and heat, or, more imperfectly, by heating the hydrated oxide of potassium along with metallic iron.

Sodium is revived by the same means as potassium, but it is not so easily evaporated as potassium, and requires more heat. It revives more readily if the oxide of sodium is mixed with hydrated oxide of potassium.

The metals of the alkaline earths, barium, strontium, calcium, cannot be reduced by means of carbon, because the metals are more permanent, and resist evaporation. The oxides of these metals are reduced by means of electricity.

Magnesium, Aluminum, Beryllium, Glucinum, Yttrium, cannot be revived by direct application of carbon. The best way of producing these metals is by melting their chlorides together with potassium.

Tellurium and Arsenic can be made by exposing their hyperoxides, mixed with carbon, to ignition.

Chrome and Vanadium are revived from their oxides and hyperoxides by mixing the oxides with carbon and igniting the mass. Molybdenum, Wolfram or Tungsten, may be easily revived from their oxides by means of carbon.

Antimony and Zirconium are not so easily revived from their combinations; they require some skilful manipulations.

Titanium can be revived from titanic acid by means of carbon. It requires a high heat to melt it.

Gold can be revived from its oxide by mere heat; of course more readily by adding carbon.

Osmium, Iridium, Platinum, Palladium, Rhodium, have very little affinity for oxygen, and of course are easily revived.

Silver, Mercury, Uranium, Bismuth, are very easily revived from their oxides by means of carbon.

Copper, Tin, Lead, Zinc, are produced by exposing their oxides, mixed with carbon, to a red heat.

Nickel, Cobalt, Iron, Manganese, Cerium, are easily revived from their oxides, but require a somewhat strong heat.

We here observe that experience proves the oxides are the most available for the production of metals from their combinations, and of this fact we must not lose sight, for it not only justifies the roasting of ores, but shows that to be both necessary and economical. The perfect oxides alone, that is, the red oxides of iron, should be sent to the furnace in their raw state. We will describe the most common