The bones, having been carbonised, are ground in a mill, and the resulting coarse powder, sorted by sieves into two kinds, one, granular, somewhat resembling gunpowder, for decolorising liquids, and the other, quite fine, to be used as a pigment. The first is sold under the name of animal charcoal; the second as bone or ivory black. The latter and other fine varieties of animal charcoal are fully described under the head of Black pigments.
Uses, &c. This crude animal charcoal possesses
the valuable property of taking lime and other saline matter from syrups and other aqueous solutions, especially organic ones, at the same time that it decolours them. Its power as a decoloriser may be tested by adding it to a solution of brown sugar or of molasses, or to water containing 1⁄1000 part of indigo dissolved in sulphuric acid. The test should be made in a small glass tube. By well washing and carefully reburning it, this charcoal may be used any number of times. As a decoloriser and deodoriser, animal charcoal is vastly superior to vegetable charcoal.
Dr Stenhouse has invented a charcoal respirator to cover over the mouth and nostrils of a person going into an infected atmosphere. Charcoal is also used with excellent effect to prevent the escape of noxious vapours and offensive effluvia from the ventilating openings of sewers. The charcoal condenses and oxidises the escaping sewer gas in its pores. Dr Garrod has proposed animal charcoal as a general antidote in cases of poisoning.
Prepared Animal Charcoal. Hydrochloric acid, 1 lb.; water, 1 pint; mix, add bone black, 7 lbs.; make a paste; in 2 or 3 days stir in boiling water, 1 quart; and the next day wash it with fresh water until the washings cease to affect litmus paper or a solution of carbonate of sodium; then collect it in a cloth, and drain, press, and dry it; lastly, heat it to redness, as before. Used to decolour syrups, &c.; and occasionally by the distillers and rectifiers.
The most powerful charcoal is prepared by calcining blood, and well washing the residue, and which is the method of the last ‘London Pharmacopœia.’ The B. P. directs it to be made by burning bones in a closed vessel.
Concluding Remarks. Animal charcoal, however prepared, if intended to be used as a deodoriser or decoloriser, should be kept thoroughly excluded from the air, as by exposure it loses all its valuable properties, and becomes absolutely inert. Freshly burnt charcoal is therefore to be employed whenever it can be obtained.
Charcoal, Wood. Syn. Veg′etable charcoal; Car′bo lig′ni, L. The residue obtained after heating wood without access of air to about 572° Fahr. It is extremely porous, and retains the structure of the wood from which it is derived. It consists essentially of carbon and of the fixed or inorganic matter which exists in wood; but if carbonisation be imperfectly effected, it may contain a sensible amount of hydrogen.
Charcoal burning is effected in the open air in piles or stacks provided with a yielding cover, in pits, in closed chambers of brick or stone, and in iron retorts heated externally like common gas retorts. The latter method is only practised by the manufacturers of pyroligneous acid and gunpowder.
Charcoal for Fuel, &c. The method of pile burning is that which is most extensively practised. Pieces of wood of equal length are piled concentrically round a sort of chimney formed by driving 3 stakes in the ground; those nearest the centre are almost vertical, and the surrounding pieces have a slight but gradually increasing inclination; a second row, and in the case of very large piles even a third, may be stacked in a similar manner one above the other. The pile is covered with turf and soil, and kindled by filling the space within the 3 central stakes with easily inflammable wood, which is ignited. The character of the smoke which issues from vents made in the piles indicates exactly the degrees of carbonisation in different parts. When the charcoal is drawn from the pile it is extinguished by cold water, or if that is not at hand, by charcoal dust or dry soil. In some parts of Sweden the wood is charred in large rectangular stacks, and in China the method of charring in pits is practised.