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How Furnaces Are Charged Running parallel to the long row of furnaces are the immense steel bins or trestles filled with the ore, coke, and limestone. At the bottom of this structure are small electric cars which are kept busy transferring the desired ingredients-ore, coke, and limestone-from the pockets at the bottom of the bins to the skip car. This being done, the skip, which operates upon an inclined track from the ground to the top of the furnace, is conveyed to the top, where it automatically empties its charge into the upper or receiving

gestive organs in the interior being continually at work. Encircling the lower outside portion of this tremendous test tube, so to speak, is a large pipe punctured at regular intervals by smaller ones which terminate in the interior of the furnace. As the powerful air-blast goes rushing through these nostrils into the body of this massive creature, where every atom of it is caught and utilized in some form or shape for the complicated reaction therein, it sounds like the heavy, powerful breathing of some maddened beast.

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CLOSING THE IRON NOTCH AFTER RUNNING A BLAST FROM THE FURNACE.

The large pipe circling the furnace is the bustle pipe, through which the hot blast is carried to the furnace.

bell. When filled, the bottom of this bell is lowered and the material allowed to fall into a second and larger receiver. When this has received its full quota, consisting of several such loads and known as a "charge," its bottom is lowered and the charge distributed uniformly in the furnace over the top of the previous charge. By these two bells or bottoms, the top of the furnace is at all times closed. The furnace is usually kept filled within a few feet of its top.

But this is only a portion of the operation the food, as it were-the huge di

What Happens in a Blast Furnace

There are two distinctive series of operations in the blast furnace-those which accompany the charged materials on their downward journey, and those of the ascending gases.

As before stated, the superheated airblast enters the lower portion of the furnace from all sides at a pressure of about sixteen pounds to the square inch. Immediately upon its contact, the coke or coal, whichever is used as fuel, becomes combustible, the oxygen of the blast uniting with the carbon of the fuel, forming

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RUNNING THE HOT SLAG FROM THE FURNACE INTO THE CINDER OR GRANULATING PIT.

nace. The limestone is first changed into caustic lime, which unites with the alumina and silica of the ore and ash of the fuel, with the result of a double silicate of lime and alumina. This is very fusible and does not mix with the iron.

The incombustible and solid matters are so mixed and proportioned with the combustible and fusible materials that the

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Owing to their lower specific gravity, the slags float on top of the iron, protecting the same from the influence of the blast.

What Becomes of the Gas? The gases accumulating from this conglomerate mass of liquid, semi-liquid, and heated substance, rise to the top. Not

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A MODERN BLAST FURNACE WITH ITS ARMY OF STOVES.

finding an escape through the charging bells, they dart down the two or more "downcomers" which are provided for this purpose. Here they are led through a box, where the cinders and other solid matters are extracted. A portion of the gases is now carried through pipes to feed the boilers, while another portion is utilized in the heating of the stoves.

These stoves, as before mentioned, are large, cylindrical structures whose interiors are masses of fire brick. These bricks are so arranged as to allow the greatest amount of surface to be exposed. In this manner they are thoroughly heated. Each furnace has a set of such stoves, some of which are always being heated, while others are giving their heat to the blast which is driven through them prior to entering the blast furnace proper. At intervals these stoves are changed, the cold ones heated and the hot ones employed for heating. This method of utilizing the waste gases is a comparatively new invention, but one which has almost revolutionized the iron industry.

How Hot Iron is Cast

Formerly there was but one method of casting pig iron; but, because of the rapid advance in the uses to which this material is adapted, several methods are now employed. The ultimate results of these methods are of a physical rather than a chemical nature. In any case, however, the iron is first tapped through an opening near the bottom of the furnace, at periods of four hours' duration. Leading from this opening is a long channel in the sand, through which flows the white, glittering iron.

If it is to be cast in the form of sand pig, the metal runs into a long channel in the sand, with smaller ones running at right angles to both sides. These are called "sows." Flowing from the sows, the iron is fed into smaller moulds, about three feet long and four inches wide. When solidified, these "pigs," as they are termed, are broken from the sows and loaded into cars, ready for shipment. Iron thus cast has an accumulation of adhesive sand upon its surface. It is not extensively used in any processes where sand or silica is a detriment.

Cup Moulds Sometimes Used When wanted for basic purposes and free from sand, another method is employed. Instead of permitting the iron to run into the sand moulds, it is run through the channels into specially constructed ladles or vessels which operate upon wheels. These have a capacity of 18,000 pounds each; five to six are usually filled from each blast or cast. As filled, they are drawn to the casting house, where they are tilted in such manner as to permit the molten metal to run into an

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FILLING THE SKIP CAR WITH THE NECESSARY MATERIAL TO MAKE A CHARGE.

endless chain of cups. These cups are about two feet long and eight inches wide at the base, and are attached to an endless chain that rests upon a track. By means of an engine or motor, the chain is revolved, the cups passing through a long tank of water, at the end of which is an incline, up which the chain bearing the cups passes. When it reaches an elevation of about ten feet, the chain passes over two gear wheels on its way back. The cups turn up-side-down, throwing their now solid contents into a car beneath.

During recent years the expense of casting has been greatly lessened by the invention or practice of using the iron direct in its molten condition. It is transferred in ladles direct from the blast furnace to the steel furnaces, thus avoiding a second melting in the latter operation.

What Happens to the Slag

The slag is run off at irregular intervals, in a manner similar to the iron, but through an opening above the iron line. This avoids any possible waste of iron. Channels are built in the sand to lead the slag from the furnaces to either a granulating pit or to the ladles. In the former case it falls into a large pit or well containing water. The hot, liquid

slag, coming in contact with the water, solidifies in the form of shot or sand. This is continually being lifted out by large electric scoops and loaded into cars. In this form it is utilized either for cement or ballast. If ladles are used, the molten slag is allowed to flow into several specially built ladies, which, when filled, are carried away and dumped into ravines and hollows.

There are many grades of iron, different only as to their chemical composition. The most common of these are: Foundry, gray forge, mottled, white, standard Bessemer, basic, and malleable Bessemer. The foundry irons are subdivided into Nos. 1, 2, and 3, according to the percentage of silicon.

Analysis of Pig Irons

The following table gives a rough analysis of the several grades of pig iron:

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