Page:Popular Science Monthly Volume 19.djvu/829

Rh coal is added, while the coal on the other side having been rammed down firm, ore is added, so as to fill that part of the furnace; on this is placed moistened charcoal-dust, except at the top. A good blast is then turned on, and, if the whole is in proper order, jets of blue flame at once issue from the uncovered portion of the ore.

During the whole of the process, at short intervals, greillade and charcoal are added, and well moistened with water, to prevent too rapid combustion. After about two hours from the commencement, the wall of mine,—i. e. ore in lumps—is pushed well forward under the tuyère, and more mine is thrown into the space thus made; this part of the process is also subsequently repeated at intervals, until sufficient has been added to form a lump of iron or massé of the required size. From time to time slag is removed by opening the tap-hole. At the completion of the process, a mass of metal is obtained weighing about three hundred-weight, which invariably consists partly of soft iron, and partly of steely iron and steel.

The ore on one side of the furnace being in lumps, the hot carbonic oxide generated by the action of the blast on the charcoal is able to pass freely through its mass, reducing it, after the water has been driven off by heat, to metallic iron. At the same time the ore becomes impregnated with carbon, derived from the decomposition of the gases with which it is charged. The greillade on the other side is much richer in silica than the larger pieces, and from this it results that the quantity of slag will vary with the greillade added. It is always very rich in oxide of iron. It appears that in this process, carburized iron is produced by the gradual reduction and fusion of the lumps of ore, and this, coming in contact at the bottom of the furnace with slag, very rich in oxide of iron, the carbon of the one combines with the oxygen of the other, and the result is that iron containing more or less carbon is produced, according as much or little oxide was present.

In order that steel may be produced by this process, every precaution is taken to cause as much carburization as possible; the unavoidable presence of oxide of iron in the slag, and the low temperature, effectually preventing the formation of cast-iron; the former, indeed, making it very difficult to obtain steel.

Rightly looked at, this process explains how steel was first obtained, and what the essential conditions are in its production. When, owing to the increased size of blast-furnaces, and the consequent increase of temperature, cast-iron became the only product, it naturally followed that this substance should be treated with a view to the production of steel. This was first effected in the refining hearth, and formed an important industry in Styria, Carinthia, the Tyrol, and other places, in some of which it is still carried on. The operation was conducted in a finery, similar in construction to those employed in the production of iron—in fact, iron and steel are often produced