effected, which is increased from time to time, as circumstances seem to require. For the purpose of attracting the fire all around the heap, holes are made in the sides to create draft, through which the watery elements of the wood are expelled, by the heat of the hydrogen, oxygen and carbon, which is, in turn, held in check by the exclusion of atmospheric air.. Were the air allowed to circulate, the entire mass of wood would be reduced to ashes. The whole process is extremely intricate, depending for complete success on the state of the weather, as well as the skill and watchfulness of the colliers. The burning lasts two or three days and nights, according to the nature of the wood, and the success attending the operation.

The fuel being thus prepared, the next point is in regard to ore. These are of various qualities, and need not be enumerated here. Nearly all ores have to be cleaned, that is, the earthy matter associated with them is removed, either by washing or pounding. After

this many ores are roasted, to effect which kilns are often constructed, somewhat similar to those for burning lime.

In the engraving on page 118, a is the shaft hearth, where ore and fuel are thrown in; bb 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 is placed either charcoal or coal; then a layer of coal and ore alternately, until the oven is filled, after which the fire is kindled. When the lower strata of ore are sufficiently roasted, they are taken out at the grate bars. The air-holes, d d d d are designed to admit air when necessary, as well as to observe the progress of the work. As the top of the ore sinks, it is replaced by fresh layers. This kind of furnace is used only for the hydrates, carburets, and other easily worked ores, but will not answer for carbonates, sulphurets, or even magnetic ores-for they are too soon smelted. They are generally roasted in heaps in the open air.

COAL BARROW.

To

Putting a furnace into blast is a very delicate and responsible task-requiring great prudence, watchfulness, and activity. supply the furnace with fuel, a barrow, similar to the above, is employed. A new furnace requires firing for two or three weeks before the regular charges of ore can be thrown in. After the stack and hearth-stone are sufficiently dry, the charges of ore are introduced in small quantities, and are afterwards gradually increased.

The furnace is always exposed, at the outlet, to the liability of chilling; that is, the iron clinkers in the interior, and suddenly cools near the mouth or top-hole, impairing the draft, and not unfrequently entirely choking it up, in which case the whole interior work has

sometimes to be taken out and rebuilt. Under these circumstances, introduction of the charges of ore and fuel becomes an important matter. A measure often used, similar to the above, is constructed of two half-inch round iron-bars, so connected at one end that one bar sinks into the furnace, while the other serves as a handle; b

forming the handle; e the measure, and the iron plate, a, prevents the sinking of the rod into the materials. There are various other devices to effect the same object, but these are the most common and simple.

The philosophical principles of the blast furnace, or the causes which separate the several substances with which it is charged and precipitate the metals of the ore, are by no means easily disclosed. While the effects produced are generally well understood, the nature of those chemical and mechanical changes and combinations, formed. by the decomposition of the combustible material in the blast, during the various stages of ignition through which it passes, is not easily explained. The engraving on page 121 exhibits Mr. Overman's theory of the blast, according to which it appears that, at a, (the points where the blast is received,) the first operation of ignition commences. Here the chemical composition of the material in the furnace undergoes an important change, the immediate result of which is a new combination of fiery matter, which is borne along with great force by the ascending draft. The iron ore, being less combustible, is thrown against the walls of the furnace, where it is liable to form benches or projecting arms of clinker. The fiery draft, by its peculiar chemical qualities, penetrates the

liquid, leaping along the little banks and curvatures of the canals, as if right glad to escape from the prison where

Black spirits and white,
Blue spirits and gray,
Mingle, mingle, mingle,
They that mingle may!

Thus released from the clay and rock with which it was lately associated in the "bowels of the earth," it comes forward, crackling and sparkling, to play a very important part in the progressive and varied scenes of man. To see the stubborn, cold, hard rocks thus turned into threads of molten iron, leaping and creeping submissively at our feet, is, indeed, a scene interesting alike to our sight and pride, and gratifying to contemplate. Such scenes undoubtedly raise the human family still higher in the scale of moral grandeur-for it is here where civilized man forges his thunderbolts against ignorance and oppression ;—it is here where he asserts the majesty of mind and the glory of labour;-it is here where, by the metals raised from the caverns of mountains, "he obtains strength for his hands, and subjects all nature to his use and pleasure."

After the metal leaves the furnace, it is subjected to various manipulations, depending on the use and form to which it is to be applied. The immediate object of these manipulations, is to render the metal purer and stronger, as well as to put it in size and shape for still further working. Pig iron is always converted into blooms, and this is done either in the forge-fire or the puddling furnace. The forgefire is the oldest made, as well as the most simple-there being no material difference between it and the common fire of the blacksmith, except in the heavier character of the former. A mass of metal is thus melted and carried to the forge-hammer, which is moved by machinery, and gives a tremendous blow. Whatever impurities are in the metal, will be pretty well hammered out under this huge hammer, and the metal, as it cools, is formed into rounded pieces, about a foot in length, which are called blooms. In the annexed figure, p. 123, a is the hammer, weighing from one hundred to four hundred pounds. It is strongly wedged to the helve, b, which is moved by the projecting teeth h, of the cylinder k. This cylinder is made to revolve by the water or fly-wheel, m. The hot metal is laid under the hammer, upon the platform d. The metal is temporarily connected with an