The principle of the blast furnace as shown in Fig. 6 is applied to the smelting of copper and lead ores, but the furnaces used for these ores are somewhat modified. Iron smelting furnaces vary from 50 to 100 ft. in height, but copper and lead furnaces are much smaller and are not always circular in cross section. In copper and lead furnaces the boshes and at least part of the shaft have merely inner and outer surfaces of iron, with water circulating between them. This water jacket arrangement is necessary as the oxides of these metals attack a fire brick lining. The cooling effect of the water is such that the inner surface of the iron jacket becomes covered with a solidified slag which is replaced as fast as it wears away.

The modifications of this furnace for lead and copper smelting are due to the differences of the ores of these metals from the ores of iron, and to the complexity in smelting these as compared with iron smelting.