CHARCOAL

substance obtained by partial burning or destructive distillation of organic material. It is largely pure carbon. The most common variety, wood charcoal, was formerly prepared by piling wood into stacks, covering it with earth or turf, and setting it on fire. In this process volatile compounds in the wood (e.g., water) pass off as vapors into the air, some of the carbon is consumed as fuel, and the rest of the carbon is converted into charcoal. In the modern method, wood is raised to a high temperature in an iron retort, and industrially important byproducts, e.g., methanol (wood alcohol), acetone, and acetic acid, are saved by condensing them to their liquid form. Charcoal, being almost pure carbon, yields a larger amount of heat in proportion to its volume than is obtained from a corresponding quantity of wood; as a fuel it has the further advantage of being smokeless. Charcoal is also obtained from substances other than wood; that obtained from bones is called bone black, animal black, or animal charcoal. Because of its porous structure, finely divided charcoal is a highly efficient agent for filtering the adsorption of gases and of solids from solution. It is used in sugar refining, in water purification, in the purification of factory air, and in gas masks. By special heating or chemical processes the adsorptive property can be greatly increased; charcoal so treated is known as activated charcoal.

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