When the furnace is finished, the bottom and sides of it for 2 feet up the square funnel, receive a lining of common bricks upon edge, to prevent the stone from shivering or mouldering when the fire comes in contact with it. On the front of the furnace is erected a temporary fire-place, about 4 feet long, into the bottom of which are laid corresponding bars. The side walls are made so high as to reach the under surface of the tymp-stone. A fire being kindled upon the bars, the whole cavity of the furnace serves as a chimney; the draught and heat is therefore considerable. la the course of three weeks, the furnace is freed from damp, and ready to receive the materials; the fire-place is then removed, but the interior brick fining remains till the operation of blowing commences. Some loose fuel is then thrown upon the bottom of the furnace, and a few baskets of coke, which are allowed to become thoroughly ignited before more are added, and the furnace is then gradually filled. The furnace represented is capable of holding 99,000 lbs. of coke, equivalent to 198,000lbs. of coal.

This quantity of materials is continually burning for several years together, without intermission ! A renewal of the total quantity occurs about every third day.

There are, nevertheless, still larger furnaces in Wales. The first charges which a furnace receives contain but a small proportion of iron-stone compared to the weight of the coke, which is afterwards increased to a full burden. The descent of the burden is facilitated by opening the furnace below, two or three times a day, throwing out the cold cinders, and admitting, for an hour at a time, a fresh body of air. This operation is repeated till the approach of the iron-stone and cinder, which is always announced by a partial fusion, and the dropping of lava through the iron bars, introduced to support the incumbent materials while those in the bottom are carried away. The filling above is regularly continued; and when the furnace at the top has acquired a considerable degree of heat, it is then judged time to introduce the blast; the preparations of which are the following: - The dam-stone is laid in its place firmly imbedded on fire-clay; the dam-plate is again imbedded in this with the same cement, and is subject to the same inclination.

On the top of this plate is a slight depression, of a curved form, towards that side farthest from the blast, for the purpose of concentrating the scoriae, and allowing it to flow off in a continued stream, as it tends to surmount the level of the dam. From this notch to the level of the floor a declivity of brick-work is erected, down which the scoriae of the furnace flows in large quantities. The opening betwixt the dam and side walls of the furnace, called the fauld, is then built up with sand, the loose bricks are removed, and the furnace bottom is covered with powdered lime or charcoal dust. The ignited cokes are now allowed to fall down, and are brought forward with iron bars, nearly to a level with the dam. The space between the surface of the cokes and the bottom of the tymp-plate is next rammed hard with strong binding sands; and those cokes, which are exposed on the outside, are covered with coke dust. These precautions being taken, the tuyere hole is then opened and lined with a soft mixture of clay and loam; the blast is commonly introduced into the furnace, at first with a small discharging pipe, which is afterwards increased as occasion may require.

In two hours after blowing, a considerable quantity of lava is accumulated; iron bars are then introduced, and perforations made in the compressed matter at the bottom of the furnace; the lava is admitted to all parts of the hearth, and soon thoroughly heats and glazes the surfaces of the fire-stone. Shortly after this it rises to a level with the notch in the dam-plate, and by its own accumulation, together with the forcible action of the blast, it flows over. Its colour is at first black; its fracture dense, and very ponderous; the form it assumes in running off is flat and branched, sometimes in long streams, and at other times less extensive. If the preparation has been well conducted, the colour of the cinder soon changes to white; and the metal, which is in the state of an oxide formerly coloured, will be left in a disengaged state in the furnace. When the metal has risen to nearly a level with the dam, it is then let out by cutting away the hardened loom of the fauld, and conveyed by a channel made in sand to its proper destination; the principal channel, or runner, is called the sow, the lateral moulds are called the pigs; hence the name of the raw commercial article, " pig-iron," of which many hundred thousands of tons are annually made.

Fig. 3.

Mode Of Working Furnace 700