CHARCOAL. Any vegetable matter burned in a pit, or other place without free access to air, is converted into charcoal. It is usually burned as follows : Logs or billets of wood are piled either horizontally or vertically into a dome-shaped mass, a chimney being left in the centre about four or five inches square, and the rest covered close with sods and earth a foot deep, so that no smoke can escape through it; a small flue or channel for air may also be left along the ground, under the wood, on the windward side, and pass ing to the central chimney; this is the simplest construction. Sometimes a pit or walled space is used, in which the wood is laid, flues being sunk to convey air to the bottom, and a central chimney left, the top being covered with earth, ashes, or cinders. The kiln is fired by placing in the central chimney leaves, straw, or twigs well lighted, and allowing the draught to remain open until the upper logs of wood are well fired, after ward closing the under flue. As soon as the flame dies away, the wood being red-hot above, close the top of the chimney and let the fire smoulder. It requires some six to ten days to burn a kiln, and constant attention must be paid. The average yield is sixteen per cent., by weight, of coal, but
hard woods, well burned, sometimes furnish twenty-five per cent., the hard woods yielding the most. In this process, nearly all the carbon, of the wood is left, the oxygen and hydrogen uniting in combustion to form water, and the object in view is to keep out atmospheric air, which would cause the combustion of the carbon also. Charcoal pos sesses inany remarkable properties. It has thepow er of removing fetid smells from water, meats and manures; hence it is used in disinfecting. privies and manures. It removes the color of many fluids, and is used in clarifying juices and solutions, especially in refining sugar. It is re markably porous, and absorbs from the air, and other media, gases: one cubic inch of fresh coal from box-wood was found by Saussure to absorb and condense ninety of ammoniacal gas, thirty five of carbonic acid, nine and a quarter of oxy gen, and seven and a half of nitrogen; this pro-. perty gives it great value in putrescent composts, and as a manure. Charcoal is nearly unchange able in common air at the ordinary temperature, but burns when heated to redness, into carbonic acid, if abundance of air be present.