There are more than five hundred and eighteen thousand coke-ovens in the United States, of which eighty per cent. are in use. Most of them are in the region about the upper Ohio River, and nearly half the total number is in the vicinity of Connellsville. The region around Birmingham, Ala., ranks next in number. The coke product of the United States is more than twenty million short tons a year. This is considerably less than the product of Great Britain, which is upward of twenty-five million tons. Most of the "scientific" ovens are near or in large cities where the gas, after purification, is used for illuminating purposes. In some instances the coke, and not the gas, is a by-product. The coal-tar is used in part for fuel, but a portion of it goes to the chemical laboratory, where it is made to yield ammonia, benzine, carbolic acid, and aniline dyes to the value of nearly seven million dollars. =Graphite.=--Graphite, plumbago, or "black lead," as it is popularly named, is found in many parts of the United States, but only a few localities produce a good commercial article; these are Ticonderoga, N.Y., which yields from six hundred to two thousand tons a year, and Chester County, Pa., which yields a small but increasing amount; a good quality is mined near Ottawa, Canada. It is extensively mined in Ceylon, and this island produces the chief bulk of the world's ordinary product. The finest grade comes from the Alibert mine in Siberia. A good article is manufactured artificially at Niagara Falls. Graphite is used as a stove polish and for crucibles; in the main, however, it is employed in the manufacture of lead[41] pencils; for this purpose only a very soft mineral, absolutely free from grit, is employed, and the Siberian output is used almost wholly. One German firm and two American firms supply most of the pencils used. =Petroleum.=--Petroleum is the name given to a natural liquid mineral from which the well-known illuminating oil "kerosene" is derived, and to obtain which it is mined. Petroleum is a mixture of various compounds known as hydrocarbons. Some of these compounds are gaseous, some are liquid, and some are solid; all of them are articles of commercial value. The petroleum from different localities differs greatly in appearance and composition. The pitch that coated Noah's ark, the slime of the builders of the Tower of Babel, and the slime-pits of the Vale of Siddim all refer to mineral products associated with petroleum. Under the name of "naphtha" it has been known in Persia for thirty centuries, and for more than half as long a flowing oil spring has existed in the Ionian Islands. The Seneca Indians knew of a petroleum spring near the village of Cuba, N.Y., and used it as a medicine long before the advent of the white man.