Hot-blast heated by the flame of the furnace mouth.—This system is mounted in Staffordshire. 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 cross its interior, and open into the annular space.

The flame of the furnace passes between the intervals of the cross 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 less velocity, through the 27 cross 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, pass down within the brickwork of the furnace, and thus prevent the dissipation 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 possible 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 Derbyshire, belonging to the eminent iron-masters, Messrs. Jessop and Co., where I was kindly permitted not only to study the various processes 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 6s., whence the 6·82 tons of coals then converted into coke for smelting one ton of iron, cost fully 40s. in coking alone, in addition to their prime cost. The saving in this respect, therefore, is 40s. 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 1s. upon every ton of iron which he makes, and at the prices of 1836, he lessened his expenses by, at least, 30s. or 40s. per ton by the patent improvement.

The following tabular view of the progression 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 to613 0
—for the blowing engine10 7
Total coal per ton of iron713 7
Limestone0101⁄20
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 to46 0
—for heating the air, 5 cwt. -012 4
—for the blowing engine, 7 cwt. 4 lbs.
Total coal per ton of iron418 4
Limestone09 0
In July, 1833, with the hot blast at 612° F., raw coal alone being used for smelting,—
There were consumed,for smelting20 0
—for heating the air08 0
—for the blowing engine011 2
Total coal per ton of iron219 2
Limestone07 0