Many years ago, Messrs. Hill and Co. of the Plymouth works near Merthyr, took out a patent for the use of the " cinder " produced in the refining and puddling operations, as a substitute for a portion of mine in the smelting pro cess. This cinder or scoria' is an oxide of iron combined with but little foreign matter, and usually contains from 50 to 70 per cent. of metal. All previous attempts to smelt it economically had failed. , Messrs. Hill and Co. mixed with it such a portion of argillaceous matter as to assimilate it to the natural ore of their district, and by this combination succeeded in its perfect reduction. The patent was soon after invaded; and, upon an action being brought for infringe ment of right, the defendants proved a prior application of the process. The patent was thereby quashed, and the iron masters, in consequence, generally adopted the process; but, from injudicious management, much bad iron was made, which got it into disrepute. With proper care, and in small proportion, the cinder is now used advantageously at most of the iron works, in the making of forge-pigs, under the subsequent process of puddling. It is usual, in most furnaces, to make the coke always a fixed quantity, and to proportion the iron stone and the lime or other flux, to the quantity of iron to be made, and the working order of the furnace; and in proportion to the latter additions, the furnace is said to carry a greater or less burthen. Some furnaces carry se little burthen as to produce only about 13 tons per week, while there are others which yield as much as 70 tons per week. In these latter, the ore is in much greater proportion to the coke than the former, but the product is inferior. The burthen is varied according as the iron is required to possess more or less carbon ; thus in making No. 1, or best iron, (which contains the greatest pro portion of carbon, the burthen must be considerably less than that required to make less carburetted iron, or what is called white-iron, or forge-pig. A general idea of the proportions of the materials from an argillaceous ore, con taining about 27 per cent. of iron, with a strong carbonaceous coal, and a good limestone, consisting of shells, is afforded by the operation of a furnace under Mr. Mushet's direction. The furnace works with a bright to ere, and receives from the blast about 2500 cubic feet of air per minute, through a circular aperture 2t inches in diameter. The quantity of calcined ore for the manu facture of good melting iron is upon a par with the coke; and forge-pig, or the least carburetted variety, six of coke to seven of ore. The lime-stone, unburnt, under the same circumstances, is to coke as 4 to 11 ; and for melting metal, retains a similar ratio.
Smelting external figure of a blast furnace is that of a trim cated pyramid, while its interior form has been very aptly compared to that of a decanter, supported upon a funnel In the subordinate details of their con struction, there is much variation by different iron masters, which, however, probably does not essentially affect the results. In the annexed sectional representation of one of these great laboratories, we have not selected one of the latest mould, but one that was described and found to be very efficient by that great master in metallurgic operations, Mr. David Mushet ; since which, we believe there have been no improvements of essential importance, except in the blowing machinery, which we shall duly notice. a is the regulating cylinder, 8
feet in diameter, and 8 feet high ; b the floating piston, loaded with weights pro portionate to the power of the machine ; c the valve by which the air is passed from the pumping cylinder into the regulator; d the aperture by which the blast is forced into the furnace; diameter of the pipes, 18 inches ; e the blowing or pumping cylinder, six feet diameter, 9 feet high, 7 feet stroke ; f its piston, with a view of one of its several valves ; g solid masonry, on which the regu lating cylinder rests, and to which the flanch and tilts of the blowing cylinder are attached. h the safety-valve or cock, by the simple turning of which, the blast may be admitted to, or shut off from the furnace, and passed off to a collateral tube in the opposite side. i the tuyere, by which the blast enters the furnace. The end of the tapered pipe, which approaches the tuyere, receives small pipes of various diameters, from 2 to 3 inches, called nose pipes, which are applied at pleasure, according to the strength of the blast required. k is the bottom of the hearth, 2 feet square ; 1 the top of the hearth, 2 feet 6 inches square; k1 the height of the hearth, 6 feet 6 inches ; 1 is also the bottom of the bashes, which here terminate, of the same size as the top of the hearth, only the former are round and the latter are square. m the top of the boshes, 12 feet in diameter, and 8 feet high; n the top of the furnace, 3 feet diameter, at which the materials are charged; ,n n the internal cavity of the furnace of the top of the boshes upwards, 30 feet high. n k, total height of the internal parts of the furnace, 44; feet; o o the lining, which is built with fire bricks, 13 inches long by 3 thick, in the nicest manner; pp a vacancy left all round the outside of the first lining, 3 inches wide, which is rammed full of coke dust, this space being left for the expansion of the materials by heat ; q q a second lining, similar to the first; r a cast iron lintel, in which the bottom of the arch r e supported—this arch is 14 feet high on the outside, and 18 feet wide ; v o the extremes of the hearth, 10 feet square. Fig. 2 represents a plan of the foun dation of the furnace ; a a are the bottom stones of the hearth ; b stratum of bedding sand ; c c passages for the escape of vapour; d d pillars of brick ; these parts, in the dotted elevation, are indicated by similar letters of reference. The subjoined, Figs 3, affords an horizontal section of the diameter of the boshes, the linings and vacancy being indicated by similar letters of reference to those in the elevation. Fig. 4 exhibits a vertical side section of the hearth and boshes, showing the tymp and dam stones, and the tymp and dam-plates. a the tymp stone ; b the tymp-plate, wedged firmly to the stone, to hold it in case of splitting by the heat; c, dam-stone, which occupies the whole breadth of the bottom of the hearth, excepting about six inches, which, when the furnace is at work, is filled every cast with strong sand.
This stone is surmounted by an iron plate of great thickness, called the dam-plate, the top of which is about 3 inches below the tuyere hole. The space be tween the bottom of the tymp and the dotted line is rammed full of strong sand or fine clay, called the tymp stopping, which prevents any pert of the blast being wasted. The square of the base of this blast fur nace is 38 feet; the height from the false bottom to the top of the crater, 55 feet.