Pittsburgh became the centre of the indus try, largely because there was in that vicinity an abundance of coal, which was used as fuel in glass-making from 1796 to late in the next century. In 1875 the Rochester Tumbler Works used natural gas for heating lears and partly for furnace heat. About 1880, when wells had been drilled that promised inexhaustible quan tities, natural gas began to be very extensive used for lear heating and batch melting. provided a cheap fuel, perfectly adapted to the industry, and thereafter glass manufacturing greatly developed in western Pennsylvania and West Virginia, and later in the gas regions of Ohio, Indiana, Illinois, Missouri, Kansas and Oklahoma. When the supply of natural gas became exhausted many factories closed or moved to new gas fields, but in recent years many factories have begun to use artificial gas produced from coal• in the plants, and some are now using oil for fuel. Even in the Pittsburgh district the price of natural gas is now so high that producer gas is used to some extent in glass making. Oil or producer gas is used by all plants east of the Alleghanies. The East ern plants, at a disadvantage regarding natural gas, have the advantage of nearness to the larger markets.
The regenerative furnace, an invention of Siemens, first used for melting glass in 1861, was soon adopted in America. By this method the waste heat from the gases generated by com bustion was utilized for heating, and much fuel was saved, the melting time reduced, the out put increased and the quality of the product improved. Another revolutionary invention for batch melting was the tank. In pot furnaces the batch is melted in separate pots, which are placed around the inside furnace walls, while with tank furnaces the tank occupies the whole furnace area. There are day tanks and con tinuous tanks. The latter enable a plant to work to capacity 24 hours a day. Tanks were introduced into America in 1889, after they had been used in Belgium. During the last 30 years many pot- furnaces have been replaced by tank furnaces. The only efficient establishments that now use pots are those that make plate glass, very fine qualities of table ware and, other fine goods, or a great diversity of colored glass. Until recent times the making of glass was a handicraft, and many glass articles are still shaped by the breath of a blower. Machinery has been invented and improved chiefly for the manufacture of window glass, plate glass, bottles, table ware and lighting goods.
Crown window glass was made in Massachu setts from 1792 to 1826. A bulb was blown, opened, flared out into a disc, cut into half circles and then into panes. The cylinder proc ess for making window glass was introduced from Europe after 1830. The cylinders, blown on a blow-pipe, were cracked into lengths, split lengthwise and flattened. The great develop ment in window glass manufacture dates from about 1880, when natural gas began to be largely used. At a window glass factory which he erected at Jeanette, Pa., James Chalmers be
gan, in 1889, to use the first continuous tank in this country. The first successful machine for making window glass, constructed under the Lubbers patents, was installed by the American Window Glass Company at Alexandria, Ind., in 1903. In this machine and in other types later invented by Americans, the glass is drawn by a tbait member) from the vmetal* in the tank, and the cylinder is formed by a pressure of air in it controlled by an operator. During the blast of 1915-16 the production of 50-foot boxes by hand was 3,708,000 and by machine 5,575,000, the hand production being about 40 per cent of the total. In 1916 there were in the United States 51 plants, with 1,737 pots, in which window glass was blown by hand, and 25 plants with 296 window machines. The intro oluction of machinery led to the production of more window glass than the domestic con sumption, with the result that window glass factories are usually operated only seven or eight months a year. Census figures show that the average value of a 50-foot box was $2.51 in 1899, $2.39 in 1904, $1.70 in 1909 and $2.18 in 1914. About 1908 Irving W. Colburn invented a machine by which glass is drawn from a tank in continuous sheet form. The sheet passes between rollers, and an operator controls the thickness and width. The Colbuni patents were purchased by the Owens Bottle Machine Com pany, which, in 1917, erected at Charleston, W. Va., a factory for making sheet window glass.
Under the management of Cuthbert Dixon, a plate glass worker and manufacturer from London, England, rough plate glass was pro duced in 1852 at Williamsburg, L. I. A window glass factory erected at Cheshire, Mass., in 1850, was changed, in 1852-53, to a rough cast plate factory. A window glass factory erected at Lenox Furnace, Mass., in 1853, was con verted, in 1855, into a plate glass factory. The successful establishment of the plate glass in dustry was chiefly due to James B. Ford of Pittsburgh. In 1869 he visited the works at Lenox and learned what he could from foreign plate glass workers there. Then he started a factory at New Albany, Ind., for which he imported grinding, smoothing and polishing machinery. This factory, from which he with drew in 1872, was successfully continued by William C. De Pauw. Ford later built plate glass factories at Louisville, Ky., Jeffersonville, Ind., Creighton, Pa., and Tarentum, Pa. A plate glass plant was established, in 1872, at Crystal City, Mo. In 1917 there were nine plate glass plants in Pennsylvania, two in Missouri and one each in Michigan, Ohio, Indiana and Illinois. The 15 plants in the United States had 113 furnaces and 2,116 pots. From 1875 to 1915 the price'of plate glass decreased about 75 per cent. The first process for manufacturing wire glass suc cessfully was patented by Frank Shuman in 1892. Since 1890 there has been successful de velopment in this country in the manufacture of cathedral, opalescent and art sheet glass, and all kinds of figured, ribbed and colored glass.