CHARCOAL, an impure variety of carbon, prepared from vegetable substances or bones. Wood charcoal consists of wood burned with but little access of air. Billets of wood are built into a heap, which is covered with earth or sand. The heap is fired at openings left near the bottom of the pile, and the gases escape at small openings above. For making fine charcoal, such as that of willow, used in the manufacture of gunpowder, the wood is burned in iron cylinders, or rather retorts, in which a process of destructive distillation removes the volatile hydrocarbons, pyroligneous acid, etc. By this more perfect means the process is ac curately regulated. Charcoal is used in the arts as a fuel; as a polishing powder; a table on which pieces of metal are secured in position to be soldered by the blowpipe; a filter; a defecator and decolorizer of solutions and water; an absorbent of gases and aqueous vapors; a non-conducting packing in icehouses, safes and refrigerators: an ingredient in gun powder and fireworks; and in the galvanic bat tery and the electric light.
Animal charcoal, used largely in sugar refining and as a disinfectant and filtering medium, is prepared by calcining bones in closed vessels. These are either retorts, similar to those in which coal is distilled for the pro duction of illuminating-gas, or they are earth enware pots, piled up in kilns and fired. Charges of 50 pounds of bones to a pot will require 16 hours of firing. The bones are then ground between fluted rollers, the dust re moved and the granulated material used for charging the filters of the sugar-refiner. The material is used for removing color, feculences and fermenting ingredients from the syrup.
In medicine charcoal is sparingly used, hut is of service in gastric indigestion in which there is much evolution of gas. Charcoal takes up the gas and therefore prevents distention and pain. It has no curative qualities and is solely alleviative. See LAMPBLACK.