Coal breaker the United States in the state of Pennsylvania (where, between 1800 and the mid-20th century, many of the world's known anthracite reserves were located). At least one source claims that, in 1873, coal breaking plants were found only at anthracite mines in Pennsylvania. The first function of a coal breaker is to break coal into pieces and sort these pieces into categories of nearly uniform size, a process known as breaking. The second function of a coal breaker is to remove impurities (such as slate or rock), and then grade the coal on the basis of the percent of impurities
Pittsburgh coal seam matter (gases expelled when coal is burned), leaving carbon and ash from the coal fused together in the form of coke. They made coke in turf-covered "mounds," in which coal burned slowly and without oxygen to drive off impurities. The adoption of beehive coke ovens in the 1830s spurred the use of Pittsburgh-seam coal in iron furnaces, and these ovens made better-quality coke than mounds. Pittsburgh-seam coal, especially the highest-quality coal found in the Connellsville district, was the best coal in America for making coke. When converted into coke, it was sufficiently strong to withstand the weight of iron ore