An excellent range of furnaces for making a superior article of coke, for the service of the locomotive engines of the London and Birmingham Railway Company, has been recently erected at the Camden Town station; consisting of 18 ovens in two lines, the whole discharging their products of combustion into a horizontal flue, which terminates in a chimney-stalk, 115 feet high. [Fig. 875.] is a ground plan of the elliptical ovens, each being 12 feet by 11 internally, and having 3 feet thickness of walls. a, a, is the mouth, 31⁄2 feet wide outside, and about 23⁄4 feet within. b, b, are the entrances into the flue; they may be shut more or less completely by horizontal slabs of fire-brick, resting on iron frames, pushed in from behind, to modify the draught of air. The grooves of these damper-slabs admit a small stream of air to complete the combustion of the volatilized particles of soot. By this means the smoke is well consumed. The flue c, c, is 21⁄2 feet high, by 21 inches wide. The chimney d, at the level of the flue, is 11 feet in diameter inside, and 17 outside; being built from an elegant design of Robert Stephenson, Esq. (See [Chimney].) d, d, are the keys of the iron hoops, which bind the brickwork of the oven. [Fig. 876.] is a vertical section in the line A, B, of [fig. 875.] showing, at b, b, and e, e, the entrances of the different ovens into the horizontal flue; the direction of the draught being indicated by the arrows. f, f, is a bed of concrete, upon which the whole furnace-range is built, the level of the ground being in the middle of that bed. g, is a stauncheon on which the crane is mounted: (see [fig. 877.]) h is a section of the chimney wall, with part of the interior to the left of the strong line. [Fig. 877.] is a front elevation of two of these elegant coke-ovens; in which the bracing hoops i, i, i, are shown; k, k, are the cast-iron doors, strengthened outside with diagonal ridges; each door being 51⁄2 feet high, by 4 feet wide, and lined internally with fire-bricks. They are raised and lowered by means of chains and counterweights, moved by the crane l.
Each alternate oven is charged, between 8 and 10 o’clock every morning, with 31⁄2 tons of good coals. A wisp of straw is thrown in on the top of the heap, which takes fire by the radiation from the dome (which is in a state of dull ignition from the preceding operation), and inflames the smoke then rising from the surface, by the re-action of the hot sides and bottom upon the body of the fuel. In this way the smoke is consumed at the very commencement of the process, when it would otherwise be most abundant. A neighbour of the above coking ovens, having lately indicted them as a nuisance, procured, secundum artem, a parcel of affidavits from sundry chemical and medical men. Two of the former, who had not entered the premises, but had espied the outside of the furnaces’ range at some distance, declared that “the coking process, as performed at the ovens, is a species of distillation of coal”! How rashly do unpractical theorists affirm what is utterly unfounded, and mislead an unscientific judge! That the said coking process is in no respect a species of distillation, but a complete combustion of the volatile principles of the coal, will be manifest from the following description of its actual progress. The mass of coals is first kindled at the surface, as above stated, where it is supplied with abundance of atmospheric oxygen; because the doors of the ovens in front, and the throat-vents behind, are then left open. The consequence is, that no more smoke is discharged from the top of the chimney, at this the most sooty period of the process, than is produced by an ordinary kitchen fire. In these circumstances, the coal gas, or other gas, supposed to be generated in the slightly heated mass beneath, cannot escape destruction in passing up through the bright open flame of the oven. As the coking of the coal advances most slowly and regularly from the top of the heap to the bottom, only one layer is affected at a time, and in succession downwards, while the surface is always covered with a stratum of redhot cinders, ready to consume every particle of carburetted or sulphuretted hydrogen gases which may escape from below. The greatest mass, when calcined in this downward order, cannot emit into the atmosphere any more of the above-mentioned gases than the smallest heap; and therefore the argument raised on account of the magnitude of the operations, is altogether fallacious.
The coke being perfectly freed from all fuliginous and volatile matters by a calcination of upwards of 40 hours, is cooled down to moderate ignition by sliding in the dampers, and sliding up the doors, which had been partially closed during the latter part of the process. It is now observed to form prismatic concretions, somewhat like a columnar mass of basalt. These are loosened by iron bars, lifted out upon shovels furnished with long iron shanks, which are poised upon swing chains with hooked ends, and the lumps are thrown upon the pavement, to be extinguished by sprinkling water upon them from the rose of a watering-can; or, they might be transferred into a large chest of sheet-iron set on wheels, and then covered up. Good coals thus treated, yield 80 per cent. of an excellent compact glistening coke; weighing about 14 cwt. per chaldron.
The loss of weight in coking in the ordinary ovens is usually reckoned at 25 per cent.; and coal, which thus loses one-fourth in weight, gains one-fourth in bulk.
Labourers who have been long employed at rightly-constructed coke ovens, seem to enjoy remarkably good health.
PITTACALL, is one of the 6 curious principles detected in wood-tar by Reichenbach. It is a dark-blue solid substance, somewhat like indigo, assumes a metallic fiery lustre on friction, and varies in tint from copper to golden. It is void of taste and smell, not volatile; carbonizes at a high heat without emitting an ammoniacal smell; is soluble or rather very diffusible in water; gives a green solution with a cast of crimson, in sulphuric acid, with a cast of red blue, in muriatic acid, and with a cast of aurora red, in acetic acid. It is insoluble in alkalis. It dyes a fast blue upon linen and cotton goods, with tin and aluminous mordants.
PLASTER; see [Mortar].
PLASTER OF PARIS; see [Gypsum].