The pig iron is shipped to different foundries, where it is melted with scrap iron (old pieces of iron parts) in a furnace called a cupola. When the heating is of long duration, or when dirty or burned (oxidized) iron is used in charging the cupola, it becomes necessary to employ a flux, that is, some mineral substance that is lighter than iron. The flux when melted floats on the liquid iron and absorbs and liquefies its non-metallic residue and the ash of the fuel, so that they may be drawn off by means of the slag holes before the heat is run off. The liquid iron is then taken from the furnace in ladles, and carried by men to different molds where it is "poured" (Fig. 186). As the hot iron flows into the mold and cools, it takes the shape of the mold.