Hot-blast heated by the flame of the furnace mouth

—This system is mounted in Staff ords hire. The heating apparatus is there set immediately upon the mouth of the furnace; and is composed of 2 large cast-iron cylinders of the same length, the one within the other, leaving a space between them. This annular interval amounts to 16 inches, and it is closed at top and bottom: but the innermost cylinder is open at both ends, and forms, indeed, the vent of the chimney or furnace. It carries nine rows of pipes, three in each row, which cro its interior, and open into the annular space. The flame of the furnace pa es between the intervals of the cro pipes, heating them, and also the two upright cylinders with which they are connected. The air of the blowing machine arrives by a vertical pipe, which is placed at the back of the furnace; it enters into the above annular space, and thence circulates, with more or le velocity, through the 27 cro tubes, upon which the flame is continually playing; lastly, it is drawn through to the bottom of the annular space; the two tubes which conduct it to the two tuyères, pa down within the brickwork of the furnace, and thus prevent the di ipation of its heat. Below this heating apparatus there is a door for putting the charges into the furnace. The above arrangement does not seem to be the best for obtaining the greatest po ible heat for the blast, nor for favouring the free action of the furnace; but it illustrates perfectly well the principle of this application. A serpentine movement in a long bent hot channel would be much better adapted for communicating heat to so bad a conductor as air is known to be. In the month of July, 1836, I paid a visit to Codner Park and Butterly works, in Derby shire, belonging to the eminent iron-masters, Me rs. Je op and Co., where I was kindly permitted not only to study the various proce es of the manufacture of cast and wrought iron, but to inspect the registers of the products of cast iron in their blast furnaces for several years back. It appeared that in the year 1829, only 29 tons of cast iron were made weekly in each of the blast furnaces at Codner Park. They were then worked with coke, and blown with cold air. Each ton of iron required for its production, at that time, 6·82 tons of coals, made into coke for smelting; with 2·64 of roasted iron ore (carbonate), called mine; and 0·87 of limestone, the castine of the French. In 1835 and 1836, the same furnaces turned out weekly, 49 tons of cast iron each; and every ton of iron required for its production only 3 tons of coal (not made into coke); 2·72 tons of mine; and 0·77 of lime. In 1829, and for many years before, as well as one or two after, each ton of coals is said to have cost for coking the sum of 6 s. , whence the 6·82 tons of coals then converted into coke for smelting one ton of iron, cost fully 40 s. in coking alone, in addition to their prime cost. The saving in this respect, therefore, is 40 s. upon each ton of iron, besides the saving of fully half the coal, and the increased produce of nearly 60 per cent. of metal per week. The iron-master pays the patentee 1 s. upon every ton of iron which he makes, and at the prices of 1836, he le ened his expenses by, at least, 30 s. or 40 s. per ton by the patent improvement. The following tabular view of the progre ion in the management and results of the hot blast, is given by M. Dufrénoy, after visiting the various iron works in this country where it had been introduced. “At the Clyde iron works, near Glasgow; in 1829, when the combustion was effected by the cold air blast ,— | Coal. | | Tons. | cwt. | lbs. | | There were consumed, | for smelting; 3 tons of coke, equivalent to | 6 | 13 | | 0 | | — | for the blowing engine | 1 | 0 | | 7 | | Total coal per ton of iron | 7 | 13 | | 7 | | Limestone | 0 | 10 | 1⁄2 | 0 | | In 1831, with the hot blast at 450° F., coke being still used in smelting,— | | | There were consumed, | for smelting; 1 ton 18 cwt. of coke, equivalent to | 4 | 6 | | 0 | | — | for heating the air, 5 cwt. | | - | 0 | 12 | | 4 | | — | for the blowing engine, 7 cwt. 4 lbs. | | Total coal per ton of iron | 4 | 18 | | 4 | | Limestone | 0 | 9 | | 0 | | In July, 1833, with the hot blast at 612° F., raw coal alone being used for smelting,— | | | There were consumed, | for smelting | 2 | 0 | | 0 | | — | for heating the air | 0 | 8 | | 0 | | — | for the blowing engine | 0 | 11 | | 2 | | Total coal per ton of iron | 2 | 19 | | 2 | | Limestone | 0 | 7 | | 0 | “At the last period the use of hot air had increased the make of the furnaces by more than one third, and had consequently produced a great saving of expense in the article of labour. The quantity of blast nece ary for the furnaces was also sensibly diminished; for a blowing engine of seventy-horse power, which, in 1829, served only for three blast furnaces, was now sufficient for the supply of four. “On comparing these several results, we find that the economy of fuel is in proportion to the temperature to which the air is raised. As for the actual saving, it varies in every work, according to the nature of the coal, and the care with which the operation is conducted. “This proce , though it has been four years in use in the works near Glasgow, (which it has rescued from certain ruin) has scarcely pa ed the borders of Scotland; the marvellous advantages, however, which it has produced, are beginning to triumph over prejudice, and gradually to extend its use into the different English iron districts. There are one-and-twenty works, containing altogether sixty-seven blast furnaces, in which hot air is used. The pig iron run out of these furnaces is generally No. 1., and is fit for making the most delicate castings. This proce is equally applicable to forge pigs for the manufacture of bar iron; since in order to obtain this quality of iron, it is only nece ary to alter the proportion of fuel and mineral. In the forges of the Tyne iron-works, near Newcastle, and of Codner Park, near Derby, pigs made in furnaces blown by hot air, are alone used in the manufacture of bar iron. “In the side of the tuyère pipe a small hole is made, by means of which the heat of the air may be ascertained at any moment. This precaution is indispensable, it being of importance to the beneficial use of hot air, that it be kept at a uniformly high temperature. With a proper apparatus the air is raised to 612 degrees Fahr., which is a greater heat, by several degrees, than is nece ary for the fusion of lead.” “At Calder works the consumption of fuel has diminished in the proportion of 7 tons 17 cwt. to 2 tons 2 cwt. There has also been a great diminution of expense in limestone, of which only 5 1 ⁄ 2 cwt. are now used, instead of 13 cwt., which were used in 1828. This decrease results, as I have already said, from the high temperature which the furnace has acquired since the introduction of hot air. “The quantity of blast has been reduced from 3500 cubic feet per minute, to 2627 cubic feet; the pre ure also has been reduced from 3 1 ⁄ 4 to 2 3 ⁄ 4 lbs.”