manufacture of charcoal. Another great objection to peat charcoal, is its loose brittle character which soon causes it to fall to pieces, and become useless; in smelting furnaces the pressure of the layers of ore suffices to crush it to powder, in which state it so materially obstructs the blast as to derange the entire process; its application is, therefore, confined to boilers, evaporating pans, forge fires, and domestic purposes, while even for such it is inferior to kiln-dried peat. The want of firmness has been found to render this charcoal quite incapable of bearing carriage, and the carbonization must, therefore, be effected on the spot where the charcoal is to be used.

Stones has patented a process for compressing peat in boxes, between rollers in such a manner as to afford hard, square bricks, which are afterwards heated in retorts of wrought-iron, similar, in size and shape to those used in the manufacture of illuminating gas, with an apparatus for condensing the products of the distillation in a series of receivers so as to separate them to a certain extent without a second distillation; the combustible gases being employed as fuel for heating the retorts.*

Vignoles employs steam, heated to 450° or 460° F., which is between the melting-point of tin and lead, for charring peat in upright cylinders; the peat having been previously dried, either by a current of hot air produced by a fan driven by the waste steam from the apparatus, or by a hydro-extracter in which centrifugal force is employed to expel the moisture.

Fig. 30 represents a vertical section and partial elevation of the apparatus. a represents a section of the large cylindrical steam boiler set over a furnace, the flues from which pass round the cylindrical carbonizing vessels, two of which are shown in the drawing to the left of the boiler, and of which there are six on

each side, arranged round a central coil of pipes H, in which the steam from the boiler a can be heated to the required temperature before its admission to the carbonizing vessels. The steam having passed from the boiler through one department of the red-hot coil, is conveyed into one of the carbonizing vessels; whence, having sufficiently charred the peat, it passes through another part of the coil into the next, and so on, until having passed through all six it is employed to work a low-pressure engine, which drives a fan, the current of air from which is heated, by passing through pipes, to 250° F., before it is admitted into chambers where the moist peat is exposed to dry.

The cylindrical carbonizing vessels are composed of boiler-plate, conical at bottom, where they are furnished with a steam-tight man-lid or door for the emission of the charred peat, a similar door being fixed in the dome-shaped upper part for its introduction. The charred peat if exposed to the air would be liable to spontaneous combustion, it is discharged, therefore, into iron cooling-boxes p placed below the carbonizing cylinders, and low-pressure steam is blown once or twice through it.

Rogers has carried out a system of drying and charring peat in Ireland, the principle of which will be seen by reference to Fig. 31.

A long shed, shown in longitudinal section EE, is constructed over a sunk channel or ash-pit, traversing its entire length and built with bricks, on the margin of which a railway is laid down to enable small travelling chambers or kilns A to travel easily through the shed and over the ash-pit.

The kilns A are made of sheet-iron on a framework of iron with

wheels, the bottoms being constructed of bars which serve as a

FIG. 32.

grate. They are filled with the peat to be charred by inverting them, and then inserting the grate. The interior part of the shed through which these travelling ovens pass is formed into a kind of chamber by sheet-iron plates BB, through which, at regular intervals, are pipes D D leading to the top of the shed. Within these vertical pipes are placed other moveable pipes which fit on to the tops of the kilns and perform the part of chimneys; they can be moved up and

down sufficiently to admit the upper part of the kilns to pass below them. The sides of the shed are filled up with lattice-work shelves for the reception of the air-dried turf-bricks, and the slanting sides are protected from the rain by moveable louvres HH, which can be opened or closed at pleasure, and when supported by a few sods of turf below, serve as stepping-places for the workmen when employed in filling or emptying the shed. When the shed is packed, and the kilns are filled with turf and arranged under their respective chimneys, these latter are opened at d by the rod e, and the turf is ignited from below by the ash-pit. The charring is then carried on as in other furnaces of similar construction, a portion of the turf being consumed in charring the remainder and the draught is regulated by the flue-door at d and the ash-pit door below. The heat from the kilns is thus made to dry the turf in the shed, and its action is sometimes augmented by a current of air forced through the house by a fan.

Green produces a hot draught of air through a drying-house by means of chimneys and fires, and then distils the dried peat in wrought-iron cylinders placed two over a furnace, and similar to those employed in making illuminating gas, the gases from the turf being consumed as part of the fuel below the retorts.

LIGNITE CHARCOAL.

Of all kinds of fuel, brown coal, or lignite, is least adapted for carbonization, although it is decomposed with as much case as wood, and the charcoal which it produces is not so easily inflam

mable. The previous remarks on the ash of peat apply with equal force to brown coal, but even the best kinds of brown coal are not easily charred, for during the action of the heat, the single layers, concentric rings, &c., which are scarcely perceptible in the fresh specimens, split off, and a compact piece of brown coal becomes thus completely broken up into small fragments, or so fissured as not to bear carriage. Roschers states that lignite, if thoroughly air-dried when fresh from the pit and very slowly charred, is not subject to this disintegration; and, according to Mayer, very firm charcoal is obtained by charring the freshlydug lignite without previously exposing it to the air. In experiments with lignite from the Hessenbrücker Hammer (in the Wetterau), 15 per cent by weight, and 32 per cent by volume were obtained by meiler carbonization. This quantity is too small to pay for the cost of manufacture.* In the neighbourhood of Cassel, where circumstances are more favourable, the carbonization in mounds is actually carried out, but only upon a small scale.

Experiments made with brown coal upon a small scale, in which the coal was heated in close crucibles, until all vapours ceased to be evolved, gave the following results:

* A cwt. of coal costs 54d., one cwt. of charred coal about 38. 11d.

CARBONIZATION OF PIT COAL.

General Principles.-The products resulting from the charring of coal, although similar in kind, differ considerably from those obtained under the same circumstances from wood. This might reasonably be anticipated, from the different elementary composition of the two substances, the dissimilar arrangement of their elements, with the addition of nitrogen and sulphur (contained in pyrites), and the higher temperature required to complete the carbonization. The nature of the products very much depends upon this latter circumstance, or the degree of temperature employed. In addition to the solid coke as residue, both liquid and gaseous compounds are produced; the former being distinguished into an aqueous and oily portion, the latter containing many of the compounds found in wood-tar, but also numerous other bodies, which we shall notice in another place. As a general example of the products of the dry distillation of coal and their relative quantities, the following analysis, in which a slow distillation was pursued in a close vessel, may be adduced:

The relative quantities of these products, as well as the nature of the tar and water, vary with the temperature employed. When the charring goes on with the access of air, a portion of the coke as well as of the gaseous products of distillation is consumed in carbonizing the remainder.

The residue, after the action of heat upon pit coal, is commonly called coke. Coals may be subdivided with reference to the production of coke into two classes, the coking and non-coking; the