CHARCOAL. The porous black brittle substance left when wood or bones are " charred," or partially burned, is called charcoal. It is an impure variety of carbon, and because of its property of absorbing enormous quantities of gases it has many uses.
Animal charcoal, or bone-black, is made by heating bones in a closed vessel or retort, thus driving off gases, water-vapor, and oil. It is seen usually in coarse grains from the size of peas to pin-heads, and is used mostly in removing colors from liquids.
Syrup of sugar, for example, is allowed to drip through a layer of bone-black; all color particles are held by the charcoal and the syrup runs through clear and colorless. Bone-black is also used to absorb dis agreeable smells. Lamp-black, made by burning oil, is an important ingredient in paints and inks.
Wood charcoal is the most important variety.
When wood, which consists chiefly of carbon, hydro gen, and oxygen, is heated in the open air, it burns away, leaving only a small quantity of white ash.
But if the air is partially cut off, only the volatile matter escapes, leaving the carbon. Most charcoal is made in "charcoal pits." Billets of wood are stood on end in rows, making a large cone-like heap ; this is covered with turf or moistened ashes, and holes are left at the bottom for air to get in. An open space for a chimney is also left at the top. The wood burns slowly from top to bottom and from center to outside.
When fully burned, the heap is covered and left to cool for two or three days. One hundred parts of wood average 24 parts by weight of charcoal. Char coal-burning is an important industry in European countries, especially in the mountains. When the burning is carried on in closed retorts, more charcoal is obtained, besides large amounts of gas, tar, and other valuable by-products.
Since charcoal burns without smoke or flame, it is much used as a fuel, especially in the arts. Charcoal fires are also far superior to any others for broiling meats. Other uses are in the manufacture of gun powder and polishing powder and as a heat-non conductor in refrigerators. Fence posts, telegraph poles, and piles driven in mud or beds of rivers for foundations are often charred on the outside to pre serve them from decay. Charcoal is also used in water filters, for tooth powder, and as a medicine.
Charcoal made from _coconut shells, as well as wood charcoal, was extensively used in making gas masks during the World War. The stones or pits of various fruits were also found useful for making charcoal for this purpose.