Slag
in metallurgy, vitreous mineral matter removed in the reduction of metals; the scoria from a smelting furnace. It is used for making cement and artificial stone, in the manufacture of alum and crown glass, and is cast into slabs for pavements, garden rollers, etc.
In founding, the fused sullage and dross which accompany the metal in a furnace, and which it is the business of the skimmer to hold back from the ingate. Also the scoria of a volcano. by