Liquation

Liquation is used to remove HIGH-MELTING impurities from metals that themselves have a relatively LOW melting point -- the examples given are tin (Sn, mp 904 K), lead (Pb, mp 600 K), mercury (Hg, mp 234 K) and bismuth (Bi, mp 545 K). The crude metal is placed on the sloping hearth of a reverberatory furnace and heated, in the absence of air, to a temperature just above its own melting point but well below the melting point of the impurities present. At this temperature the metal itself becomes a fusible (easily flowing) liquid and flows down the sloping surface under gravity, while the higher-melting impurities remain solid and are …