When vegetable substances are subjected to a strong heat in the apparatus for distillation, the fixed residue is called charcoal. Charcoal is made in various ways. For general use it is obtained by building up pieces of wood in a pyramidal form, then covering the pile with earth or clay, leaving a few air-holes, which are closed when the mass is lighted, in order that combustion may proceed in a slow and imperfect manner. Charcoal of a very superior kind is made in the forest of Benon, near Rochelle, where great attention is paid to its manufacture. Black oak from ten to fifteen years old is cut into billets of about four feet in length, which are built up as above described, and, before being inclosed in the clay or earth, covered over to the depth of four inches with dry grass or fern. When the mass is charred, great care is taken to extinguish ignition, because if exposed too soon to the atmosphere, combustion goes on, and this is not put a stop to without difficulty. Accordingly, to obviate this, a barrel of water is thrown over the pile, and earth to the thickness of five or six inches is spread on it, after which it is left for twenty-four hours to cool. Charcoal is also made on a great scale in the following manner. A series of cast-iron cylinders, about four feet in diameter and six feet in length, are built horizontally into brick work, so that the flame of one furnace may play round about two cylinders. The ends are made to project from the brick work, and both are closed with discs of iron. From the centre of one of these an iron tube proceeds, and enters at a right angle the main tube of refrigeration. The vapour which is condensed in this vessel is a strong vinegar called pyrolignous acid. The tubes, of course, are filled with wood cut up into billets. Fire is applied during the day; all night they are allowed to cool, and next morning the charge is drawn. Care is taken to prevent the access of air, both while the wood is charring and after it has begun to cool. When charcoal is wanted for the manufacture of gunpowder, it is necessary that the whole of the vinegar and tar should be allowed to escape, and that the re-absorption of the vapours should be prevented, by cutting off the communication between the interior of the cylinder and the apparatus for condensing the pyrolignous acid, after the fire has been withdrawn from the furnace. Unless this precaution be taken, the gunpowder manufactured with the charcoal will be of inferior quality. Mr Mushet has made a number of valuable experiments respecting charcoal. The following is his table of results, reduced to 100 parts, from experiments on one pound avoirdupois of various kinds of wood:

| Wood | Volatile Matter | Charcoal | Ashes | Chard | |---------------|----------------|----------|-------|-------| | Oak | 76-895 | 22-682 | 0-423 | | | Ash | 81-260 | 17-972 | 0-768 | | | Birch | 80-717 | 17-491 | 1-792 | | | Norway Pine | 80-441 | 19-204 | 0-355 | | | Mahogany | 73-528 | 25-492 | 0-980 | | | Sycamore | 79-20 | 19-734 | 1-066 | | | Holly | 78-92 | 19-918 | 1-162 | | | Scotch Pine | 83-095 | 16-456 | 0-449 | | | Beech | 79-104 | 19-941 | 0-955 | | | Elm | 79-655 | 19-574 | 0-761 | | | Walnut | 78-521 | 20-663 | 0-816 | | | American Maple| 79-331 | 19-901 | 0-768 | | | American Black Beech | 77-512 | 21-445 | 1-033 | | | Laburnum | 74-234 | 24-586 | 1-180 | | | Lignum Vitae | 72-613 | 26-857 | 0-500 | | | Sallow | 80-371 | 18-497 | 1-132 | | | Chestnut | 76-304 | 23-280 | 0-416 | |

MM. Clement and Desormes state that wood contains one half its weight of charcoal. We are informed by M. Proust that good pit-coals afford 70, 75, or 80 per cent. of charcoal, which leaves of ashes after combustion only two or three parts in the hundred. This species is much used in Great Britain under the name of coke. Turf or peat has been lately charred in France by a peculiar process. It is considered as superior to that obtained from wood. It kindles more slowly, but emits more flame, and burns longer than the other. Gold fused by it retains its malleability; and this property is increased in iron heated red hot by it in a forge.

Charcoal is black, sonorous, and brittle, and generally retains the figure of the vegetable from which it was obtained. The charcoal produced from oily or bituminous substances is of a light pulverulent form, and rises in the form of soot. This charcoal of oils is well known in the arts under the name of lamp black. For an account of the chemical and other properties of charcoal, see Chemistry, where it will be found treated of under the scientific appellation Carbon. (Ure's Dictionary of Chemistry; Tillock's Magazine, vols. iii. and viii.)