On the Continent and in America, the Huntingdon-Heberlein process has been extensively adopted, with lessened incidence of poisoning, the result of mechanical methods of working, obviating hand labour, and the low temperature (diminishing risk from lead fume) at which the roasting is carried on. In this process the crushed ore is desulphurized by first mixing with lime and heating in presence of air in a revolving furnace, provided with automatic rabble, at moderate temperature (about 700° C.). Subsequently the roasted material is conveyed from closed bins, into which it falls automatically, by dust-proof elevators to a converter, in which atmospheric air at slight pressure is forced through it. The agglomerated mass so formed, when tipped out of the converter (in doing which there is risk from dust), is well damped, broken by hand, and charged with coke in the usual way into the blast furnace. In some lead-smelting works the material arrives on the premises in the form of ingots of base bullion--_i.e._, impure lead rich in silver--the product of previous smelting of the ore where it is mined in Australia or Spain. And one of the main objects of the blast-furnace smelting of galena in the factory is to produce a base bullion rich in precious metals. The lead so obtained requires further softening or refining to get rid of copper, antimony, arsenic, and tin. This is effected in a reverberatory furnace, first at a low temperature to allow of formation of furnace dross, which is removed through the working doors, and secondly with increase of heat and access of air to oxidize, in the order named, the tin, arsenic, and antimony. Finally the lead is tapped into kettles or pots. If free from silver, such lead, when poured into moulds, is ready for the market; but if rich in silver, it is treated for the recovery of that metal either by (_a_) Pattinson’s process, depending on the higher temperature of crystallization of lead than of an alloy of lead and silver, which enables a separation of one from the other to be made by a process of ladling the crystalline from the liquid portion; or, much more commonly, by (_b_) Parkes’s process, depending on the formation, on addition of zinc to a pot of molten lead, of crusts consisting of an alloy of silver, lead, and zinc. The crusts obtained in the latter process, after cooling, are broken up, placed in a crucible, and the zinc driven off at a temperature of 1,000° C. in a dezincing Faber du Faur retort. The rich bullion, retained either in the last kettle by the Pattinson process, or remaining in the crucible after dezincing, next undergoes cupellation--_i.e._, exposure to a blast of air in a furnace. The lead is oxidized into litharge, which drops into a receptacle below the furnace, leaving the silver behind. In all lead-smelting works the draught from the furnace carries much dust of ore and fuel, and fume, consisting of sulphide, sulphate, and oxides of lead, into the flues.