per cent, of copper and 28 per cent, of gangue. There melting furnaces with hearths 35 ft. X 16 ft., and two or casting furnaces with hearths 23 ft. X 14 ft. When has been skimmed, the melted copper is tapped from the melting furnace into a refining furnace, where it is poled and The slag contains 40 SiOj, 16 FeO, 11 CaO, 13 AiPg, 5 cast.