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
Coal assay in the crucible. The cross sectional profile of this coke button compared to a set of standardised profiles determines the Free Swelling Index. Several international standards classify coals by their rank, where increasing rank corresponds to coal with a higher carbon content. The rank of coal is correlated with its geologic history, as described in Hilt's law. In the ASTM system, any coal with more than 69% fixed carbon is classified by its carbon and volatiles content. Coal with less than 69% fixed carbon is classified by its heating value. Volatiles and carbon are on a dry mineral free base;