These metals are not found to any great extent in the pure metallic state, but chiefly in the form of oxides, carbonates, or sulphides, called "ores."
The ores are broken up, and separated from the earthy matters adhering to them, by stamping or crushing in mills, and by washing in a stream, which carries away the lighter impurities, leaving the ore, which is then said to be "dressed."
The next step is, as a rule, to roast the ore in heaps or in kilns, in order to drive off the moisture and carbonic acid, and to fit it for smelting.
The ore is mixed with a substance called a "flux," selected in consequence of its tendency to combine with the particular impurities of the ore. The mixture is then thrown into a furnace and subjected to intense heat, upon which the metal sinks down in a fluid state, while the impurities combine with the flux, and run off in a light and fusible slag.