CHARCOAL. This is a well known black substance, which possesses many singular chemical properties, the details of which will be given under the article Cn EMS TR Y. In the present article we shall confine ours•Ives to the modes of preparation employed in Britain and in France, and to its economical uses.
Charcoal which is employed as fuel, is obtained rene rally from wood of different kinds ; the most dense and hard being preferred. The white and resinous woods are commonly reject d. Large timber is seldom em ployed for this purpose, both because it is too expensive, and because it does not yield charcoal equal in qua'itv to that procured from coppice wood. Pieces of three or four inches thick must be cloven into four pieces.
It is an object of some moment to ascertain the most productive wood in the preparation of charcoal ; and al thougo accurate results are not to be expected on the great scale, yet experiments mad( by Mr \lushet afford very good general proportions, which may be the rule by which the products may be estimated.
The following Table exhibits very satisfactorily the resuits of these experiments.
In Scotland very large quantities of charcoal are pre pared for the iron works, in the following way :—A plat form, having a diameter of from twenty to thirty feet, i formed on the ground, by laying strata of earth upon it, and giving it a slightly convex surface. On the centri of this circular area, a circle of sticks are so placed as to cross each other a little below the top, and thus to form a cavity resembling an inverted cone, around which successive concentric layers of truncheons, having a dia meter of from one to ten inches, are placed ; cat e being taken, that the truncheons in the same circle are of the same size, and as few interstices as possible left. The exterior circle is composed entirely of brushwood. When the platform is nearly covered, a coating of turf is laid on the pile, the grassy side being next to the wood ; dry earth is then heaped up around the lower part, and well rammed down, so as to exclude all air. The pile is then lighted, by placing a few inflamed chips of wood in the interior cavity; and when these are consumed, others are added during the first three or four days. When the upper part of the pile is completely inflamed, a row of holes, each of which has a diameter of two inches, is made around it at a few inches below the top, and the opening at that part is closed up. The flame
then gradually descends to the circle of holes, and its arrival there is announced by a very perceptible diminu tion of smoke and vapour. Another row of air holes is then made at a distance of six or eight inches below the first row, which are closed up, and the same operation is repeated until the flame has been conducted to the low est part of the pile, which generally happens in about a fortnight ; when the whole is carefully covered until the fire is extinguished. Such pieces as are not completely charred, are separated, and reserved as fuel for the next pile.
The charcoal produced from the truncheons is laid aside for particular uses ; and that obtained from the brushwood is sold, under the name of small coal, as fuel.
In France there is some difference in the mode of preparing the charcoal : it therefore is worth while to give an outline of the various processes there adopted.
The wood is cut down in large faggots, and after hav ing been well dried for some months, it is divided int•. brushwood, small and large fag;;;cits. The last are cut into truncheons of three or four feet in length. The turf is then taken off a square or circular space. having a dia meter of about fifteen feet, and the earth beaten until the surface becomes dry and solid. A stake is next fixed in the middle of the area, and some brushwood laid on the surf ice as a foundation for the remainder. A stra tum of truncheons is then laid on the brushwood, and the same alternatives are repeated, until the pile is com plet:d to tie height of about six feet, in the form of a truncated cone a pyramid. As soot) as this is done, the whole surface of the pile is covered to the thickness of about two inches with dry earth, over which sods are ve ry compactly laid, except at the base, where considera ble spaces are left between them. The central stake is now withdrawn, and the cavity is filled with chips, which are lighted at the top ; the whole of the chips become inflamed, and after a considerable quantity of smoke has been poured out, a light flame rushes from the chimney in the centre of the pile ; the aperture of which is im mediately closed by laying a piece of turf over it.