628 C'RKATIVK CHKMISTRV " Life Would Be Rather Dull without Graphite, although the Material Itself Is One of the Dullest of All Substances." ' Graphite is widely used in "lead" pencils and as a lubricant, stove polish, and paint pigment because of its soft, greasy, chemically inert properties. It is an electrical conductor and is therefore used to make electrodes for dry cells and electric furnaces, commutator brushes for generators, and in making electrotypes for printing. Because of its inertness and resistance to high temperatures, it is used to make refractory bricks and crucibles. Graphite may be prepared by heating anthracite coal in an electric furnace. Prepared in this way, graphite is generally superior to naturally occurring graphite. The Diamond Is the Hardest Substance Known. The highly crystalline, colorless, transparent properties of pure diamonds cause them to be highly prized as gems, but it is the great hardness of diamonds that makes them of importance in industry in providing a cutting edge for core drills and for grinding purposes. Diamonds which contain impurities which discolor them, sometimes almost black, are used for industrial purposes. Artificial diamonds of small size have been made by crystallizing carbon in cast iron, but no diamonds have been produced which are large enough for use as gems. Amorphous Forms of Carbon Vary According to Their Methods of Preparation. Anthracite Coal Is Nearly Pure Carbon. Coal is produced by changes in plant matter, and anthracite coal is the product in which these changes have gone the farthest. The various stages in the decomposition of plant materials (chiefly cellulose) are represented by peat, lignite, bituminous coal (soft coal), and anthracite coal (hard coal). Anthracite is a very desirable fuel because it burns with the production of the maximum amount of heat and the minimum amount of smoke and sulfurous. fumes. Only about 0.65 per cent of the coal resources of the United States are of the anthracite variety. At the present rate of consumption our anthracite coal resources will be exhausted in about one hundred years. Coke Is Obtained by Heating Bituminous Coal in the Absence of Air. When bituminous coal is heated in the absence of air, fuel gases (artificial gas), ammonia, and coal tar are important materials which are driven ofT from the coal, leaving the mineral matter and carbon in 1 C. C. Furnas, The Storehouse of Civilization, Columbia University Press, New York, 1939, p. 144.
: OXYGEN AND SULFUR, CARBON AND SILICON 629 a porous form, called "coke." Coke is also obtained in the refining of petroleum. Coke, like anthracite coal, is an excellent fuel, but it is used chiefly as a reducing agent in the refining of metals, especially iron, and in the production of inorganic carbon compounds. The combustion of coke provides heat to decompose limestone, carbon dioxide and lime being produced in the reaction 02