282

CHARCOAL.

soft, dull, or without any appearance of polish in its fracture. Its specific gravity variesfrom 2*4 to 2*6. It usually contains a little silica, alumina, and oxyde of iron. Itmay be purified by trituration and elutriation. The silicious and ferruginousmatters subside first, and the finer chalky particles floating in the supernatant liquid,may be decanted, with it, and obtained by subsidence. When thus purified, it is calledwhitening and Spanish white, in England; schlemmkreide, in Germany ; blanc deTroyes, and blanc de Meudon, in France . Pure chalk should dissolve readily in dilutemuriatic acid, and the solution should afford no precipitate with water of air.

monia.

CHALK -Black. A mineral, called also drawing-slate.

CHALK -French. Steatite, or soap-stone ; a soft magnesian mineral.

CHALK-Red. A clay colored with the peroxyde of iron, of which it contains above17 per cent.

CHARCOAL. The fixed residuum of vegetables exposed to ignition out of contact ofair. In the article Carbon , I have described the general properties of charcoal and thesimplest mode of making it. I shall here detail the best systems of manufacturing thisproduct upon the continent of Europe .

To carbonize wood under a moveable covering, the plan of meiler, or heaps, is employedvery much in Germany . The wood is arranged either in horizontal layers, or in nearlyvertical ones, with a slight slope, so as to form conical rounded heaps of differ 1 .at sizes.The former are called lying meiler, fig. 272; the latter standing meiler, figs. and 274.

272 273 274

mmm

Both are distributed in much the same way.

In districts where the wood can be transported into one place by means of rivers, ormountain-slides, a dry flat space must be pitched upon, screened from storms and floods,which may be walled round, having a slight declivity made in the ground, toward thecentre. See fig. 275. Into this space the tarry acid will partially fall, and may heconducted outward, through a covered gutter beneath, into a covered tank. Themouth of the tank must be shut, during the coaking, with an iron or stone slab, lutedwith clay. A square iron plate is placed over the inner orifice of the gutter, to prevent275 ^ it being choked with coal ashes-

Fig. 275 represents a walled inri'®station ; a , the station ; b, t** egutter ; c, the tank, which is c0V ”ered with the slab d; e, a sla

-- which serves to keep the § nt * e

clear of coals. The cover of the heaps is formed of earth, sand, ashes, or such othc^matter as may be most readily found in the woods. They should be kindled in the centre. From 6 days to 4 weeks may be required for charring a heap, according to its ® ,z f ’hard wood requiring most time ; and the slower the process, the better and greater is t

product, generally speaking.

276

Charring of wood in rno11 o' 7 t,(Haufe or liegende werke), fig?- . eand 277, differs from that 111 ^

•meiler, because the wood m jhaufe is successively charred, &the charcoal is raked out byand little. The product is j g0to be greater in this way, and gbetter. Uncleft billets, 6 0feet long, being laid over ^other, are covered with asn j sthen carbonized. The sta 1sometimes horizontal, and [ntimes made to slope. The * - gmay be 24 feet, the brea .feet; and the wood is laid

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