and as the main object is oxidation, no means should be neglected which will accomplish the end in view. The kind of fuel required is not of so much consequence as it is usually thought to be at charcoal furnaces. Wood and small charcoal (braise) are used; but where wood is scarce, stone coal, properly applied, will answer; coke or anthracite is preferable. Bad or sulphurous coal should be avoided, or at least coked before used. Turf or peat, or brown coal may be used, where they can be obtained upon advantageous terms. aa. Roasting of Iron Ore in Ovens or Furnaces.-There are many different forms of ovens, but all of them can be reduced to that of the blast furnace, or the limekiln. They are either perpetual, or work by charges. These ovens are commonly from twelve to eighteen feet high, and contain from fifty to one hundred tons of ore at once. Fig. 1 represents such an oven for perpetual work: a is the shaft or circular hearth, where ore and fuel are thrown in; b, b are the grate bars, which can be removed to let down the roasted ore; c, c are side arches, which permit access to the draft holes: d, d, d, d are four arches, including the work arch. To start operations in such an oven, the grate bars are covered with wood; upon this either small charcoal, or stone coal, coke, turf, brown coal, or any fuel fit for the purpose, is placed; then a layer of coal and ore alternately, until the oven is filled, after which the fire is kindled. When the lower portions of ore are sufficiently roasted and cool, they are taken out, and either carried to the furnace, or, in case the ore is not sufficiently roasted, returned to the top. The air holes d, d, d, d are designed to admit air when it is needed, and to enable us to observe the progress of the work. An oven of fifty tons capacity ought to yield thirty tons of well roasted ore in twenty-four hours; but this depends very much on circumstances, and especially upon the quality of ore to be roasted. As the top of the ore sinks, it is replaced by fresh charges of coal and ore. This oven is well qualified to roast the hydrates, carburets, and other easily worked ores; but will not answer for carbonates, sulphurets, or even magnetic ore, for these ores are too soon melted. In some parts of Europe, another kind of oven is in use, which affords a better product than the perpetual oven, and may be employed with great advantage. This oven is represented by Fig. 2. Its interior is a cone, wide at the base, and narrow at the top. At the bottom of this cone an arch of coarse pieces of iron ore is built, which supports the body of ore charged above it. This arch will admit enough fuel to keep up a lively fire. Where wood is plenty, it may be used in its green state, but any other fuel will answer quite as well. One great advantage which this arrangement has over the other (Fig. 1), is that it does not bring the fuel into contact with the ore; and the workmen are enabled to give just so much heat as they consider necessary. Such an oven, properly managed, may answer for any kind of ore, provided it be sufficiently coarse to admit the draft of air needed for oxidation. Though this arrangement makes manipulating more expensive than the arrangement first presented, yet the qualitative properties of the product which it furnishes-for there is no doubt that a good workman will deliver a more perfectly oxidized ore from this kiln than from the other-more than compensate for this expense. An improvement upon this principle has been made in Sweden and Norway by erecting large circular ovens, like porcelain kilns, at the base of which, in furnaces built around, or in the centre of the oven, the fire is applied. Such an arrangement will work continuously, like that of Fig. 1, but is expensive both in the first outlay, and in the operation. Reverberatory furnaces have been tried for roasting ores, but with little success; the operation proved too expensive. bb. Roasting in Mounds.-Sulphurets and carbonates, which cannot bear a high heat, and require sometimes several fires, are best roasted in mounds. Mounds are formed on a level ground, and consist of three stone or brick walls: see Fig. 3. The area or Fig. 3. a Ground plan of a roasting mound. hearth is open on one side, so as to admit the entrance of wheelbarrows or carts: the walls are about three feet high, and have at their bases fire chambers, where the fuel is applied. This is shown at a, a, a, a, Fig. 4. Through the piled ore are draft holes or chimneys, b, b, which regulate the draft; by these chimneys, the draft may be altogether stopped when the ore gets too hot. This kind of oven or mound is very useful for small ores, and those which cannot bear much heat. cc. Roasting in the Open Air in Heaps.-This mode of calcining ore is undoubtedly the most available, and that generally practiced. It affords by good management excellent results. To form a heap, or heaps, the ground must be leveled, and in many cases covered with beaten clay. The area of such a level depends entirely on the amount of ore to be roasted, and the time in which it is proposed to be done. It may be laid down as a rule, that the longer the fire remains in a pile, or the slower the roasting is carried on, the better will be the result. If the time is limited, rows of three feet high, from seven to eight feet wide at the base, and of convenient length, may be put up and fired. These rows may be finished in ten or twelve days; but though they answer well enough for hydrates, sulphurets, carburets, and all those ores which calcine easily, they do not answer for magnetic ore or carbonates. For those ores which are roasted with difficulty, round or square piles of various dimensions are used; some of these piles have a capacity of from one hundred to two thousand tons. The amount of ore in fire should depend mainly on the stock on hand, and on the quality of the ore. Magnetic ore may be roasted in the course of six or eight weeks; argillaceous ores of the blue or gray kind, require at least three months; and the sparry carbonates can scarcely be roasted in one heat, frequently require different fires, and, after all, are but seldom sufficiently calcined. In Styria, Carinthia, and other places where heavy sparry iron ore abounds, and where good iron must be delivered, the iron masters are compelled to have a stock of ore sufficient to supply the furnace for a number of years, and the compli cated manipulations by which the sparry carbonates are oxidized, often require a period of from three to five years. The operation is there mainly conducted on the principle of oxidizing by the influence of the atmosphere; for that purpose the ores are broken into small fragments of the size of walnuts, then spread upon level plains, in a thin stratum of about two inches thick, and then exposed to the action of the sun and atmosphere; in dry weather the ores are sprinkled with water once or twice every day. Ores oxidized in this way are, of course, far superior to those oxidized by means of artificial heat. The method of roasting ore in the open air by artificial heat is as follows: Billets of wood are placed, like the bars of a gridiron, upon a previously prepared level spot; sometimes they are laid parallel, and sometimes in a crosswise manner, so as to form a uniform flat bed. The crevices between the wood may be filled with chips of wood, charcoal, turf, or even stone coal, coke, or anthracite, so as to prevent the ore from falling between the other pieces of fuel, or, what is still worse, upon the ground. The ore, before it is put upon the fuel, should be broken into pieces of uniform size, of from three to four inches in diameter; the larger pieces to be used inside of the pile, the smaller ones for covering. When a foundation of fuel of about eight inches high is prepared, ore may be piled upon it to the height of from eighteen inches to two feet; upon this ore is spread a layer of small charcoal, or of turf, coke or small anthracite coal, in a uniform thickness of two inches, or one inch of fuel to one foot of ore; then alternate beds of fuel and ore, until a sufficient height is reached. The pile, thus prepared, whether of an oblong, square, or round form, should be covered with small ore, and then should be set on fire either in the centrefor which purpose one or more holes or flues are left-or around the base. After the fires are properly kindled, the piles may be covered with riddlings of ore or small coal. The combustion should proceed slowly, being somewhat suffocated, so that the whole mass may be uniformly penetrated with heat. Where the fire is too intense, it must be covered with small ore or coal dust, and where it is too imperfectly developed, holes should be pierced with an iron bar, that smoke and air may have vent. In all cases of calcining in heaps, the arrangement and manipulation are almost the same, with hardly any other variations than those arising from the difference of ore and fuel. Fig. 5 represents the cross section of an ore pile, which is so plain as to need no description. In this plan the billets of wood are raised from the |