Anthracite latter in two or three sizes, all three being above in (38 mm) size on round-hole screens. High grade (HG) and ultra high grade (UHG) anthracite are the highest grades of anthracite coal. They are the purest forms of coal, having the highest degree of coalification, the highest carbon count and energy content and the fewest impurities (moisture, ash and volatiles). High grade and ultra high grade anthracite are harder than standard grade anthracite, and have a higher relative density. An example of a chemical formula for high-grade anthracite would be CHONS, representing 94% carbon. UHG anthracite typically has a
Pittsburgh coal seam that was piled with coke inside iron furnaces. It has a high proportion of carbon, which accelerates combustion, and a low proportion of impurities, including ash and moisture, which retards combustion. Pittsburgh coal also has a low proportion of sulfur, which is critical to making high-quality iron. In addition, the Pittsburgh seam was located close to Pittsburgh, then the center of the growing American iron and steel industry. Coke had to be transported by water or rail to iron furnaces, and the Pittsburgh seam's proximity to iron furnaces gave the bed another competitive advantage over more distant coal seams that