Carbo Ligni. Charcoal.
Preparation. — Wood, or vegetable charcoal for pharmaceutical or other purposes is made by piling billets of wood in a conical form, and then covering them with earth and sod in such a way as to exclude the access of atmospheric air ; several holes must be left at the bottom, and one at the top of the pile, in order to produce a draught to commence the combustion. The wood is to be kindled from the bottom, and when combustion has taken place and the whole pile ignited, the holes at the top and bottom are to be closed, leaving only a limited access of air. By this process, the volatile portions of the wood, consisting of oxygen and hydrogen are dissipated, while the carbon remains in the form of charcoal. From 17 to 18 per cent, of charcoal is obtained by this process; but if the wood be charred in iron cylinders, from 22 to 24 per cent, of charcoal is obtained, beside the collection of pyroligneous acid, tar, and empyreumatic oil, the volatile products of the wood.
For medical purposes, charcoal thus prepared is not sufficiently pure for exhibition, as all the volatile portions of the wood, are not wholly removed. It may be purified, according to Lowitz, by filling a crucible with ordinary charcoal finely pulverized, and luting on a perforated cover. Then expose the whole to a red heat, and continue it as long as a blue flame issues from the aperture in the cover. When this ceases, allow (he charcoal to cool, and transfer it quickly to bottles which must be well stopped.
History. — Wood charcoal is a dark-brownish-black powder, composed of shining particles, tasteless and inodorous, insoluble in water, and permanent in the air. It is easily inflammable, and readily consumed, much more so than animal charcoal. It is a good conductor of electricity, but a bad one of heat. If perfectly dry, it absorbs many times its own bulk of certain gases. It corrects the fetor from putrid animal matters, and decolorizes vegetable infusions, but not so promptly as the animal charcoal. It decomposes metallic compounds when heated with them by depriving them of their oxygen. If exposed to the air, it increases rapidly in weight, in consequence of its absorption of moisture, which takes place to the amount of from ten to fifteen per cent. Combustion disengages its carbonic acid, leaving behind an ash composed of earthy matters and carbonate of potassa.
Properties and Uses. — As a medicine, charcoal should always be purified. It is antiseptic and absorbent. Used in dyspepsia attended with fetid breath and putrid eructations ; also in dysentery, to correct the fetor of the stools. Useful in acidity of stomach, flatulency, obstinate constipation, and in the nausea and constipation attending pregnancy. Dose, from twenty grains to half an ounce, repeated according to indications. Externally, used in poultices to correct fetor of ulcers, arrest gangrene, etc., and is efficient in many cutaneous diseases. It occasionally enters into tooth-powders, and may be used with advantage to correct the fetor of the mouth, and cleanse the teeth. In such cases the charcoal prepared from bread is the best, as it contains no gritty particles.
Off. Prep. — Cataplasma Carbonis.