\Slag\, n. (Metal.)
A product of smelting, containing, mostly as silicates, the
substances not sought to be produced as matte or metal, and
having a lower specific gravity than the latter; -- called
also, esp. in iron smelting, {cinder}. The slag of iron blast
furnaces is essentially silicate of calcium, magnesium, and
aluminium; that of lead and copper smelting furnaces contains
iron.

\Slag\, v. i. & t. [imp. & p. p. {Slagged}; p. pr. & vb. n.
{Slagging}.] (Metal.)
To form, or form into, a slag; to agglomerate when heated
below the fusion point.

\Slag\, n. [Sw. slagg, or LG. slacke, whence G. schlacke;
originally, perhaps, the splinters struck off from the metal
by hammering. See {Slay}, v. t.]
1. The dross, or recrement, of a metal; also, vitrified
   cinders.
2. The scoria of a volcano.
{Slag furnace}, or {Slag hearth} (Metal.), a furnace, or
   hearth, for extracting lead from slags or poor ore.
{Slag wool}, mineral wool. See under {Mineral}.