Wood charcoal consists of the carbonaceous residue of wood charred by exposure to a red heat without access of air, the wood of the beech, oak, poplar, hazel, dogwood, and willow being chiefly used for the purpose. It is also official in the U.S.P. The proprietary French charcoals are prepared generally from young poplar shoots. Willow charcoal is most commonly used in this country. The yield of charcoal is from 17 to 18 per cent. when the wood is simply protected from the air with earth and sods, and from 22 to 23 per cent. when charred in iron cylinders. It occurs as a black, tasteless and odourless powder, free from gritty matter. When freshly prepared it is capable of absorbing 12 to 14 per cent. of water if exposed to the air. When heated to a high temperature with free access of air, it should not leave more than 7.5 per cent. of ash, the quantity varying with the kind of wood from which it is prepared. Charcoal usually contains inorganic matter, from which it can be freed by digestion with diluted hydrochloric acid and subsequent washing with boiling water.
Action and Uses.—Dry charcoal has the power of absorbing and condensing gases, especially oxygen, but it loses this property when thoroughly wetted. It contains no combined nitrogen, and is therefore useless as a decolourising agent. It is used internally as an antiseptic and absorbent, in flatulent dyspepsia, intestinal distension, diarrhoea, and dysentery. Its action is mainly mechanical, removing mucus and stimulating the movements of the stomach and intestine. Externally, charcoal is absorbent and deodorant. It is sometimes employed as a poultice for foetid ulcers, some of the charcoal being spread on the surface of the poultice to retain its oxidising properties. The powder is usually administered in cachets, sometimes with sodium bicarbonate, bismuth carbonate, and naphthol, but it may also be administered on buttered bread in the form of sandwiches. Lozenges of charcoal and charcoal with bismuth are prepared. Charcoal biscuits are a popular form of administration. Charcoal tooth powders may contain from 25 to 75 per cent. of wood charcoal.
Dose.—4 to 8 grammes (60 to 120 grains).
The British Pharmaceutical Codex, 1911, was published by direction of the Council of the Pharmaceutical Society of Great Britain.