[23 . ]

the bottom os its internal cavity, makes a commodiousbason for this use ; and is easily made to join to the slopingcanal in the furnace, by rasping off a little at one side,and forming a channel in the lip corresponding to thehole in the furnace : the juncture is secured by the inter-position of a little softened loam or clay.

The more sulphureous ores are commonly freed, byroasting, from great part of their sulphur, before theyare submitted to this operation : for, by this processalone, the sulphur would not be completely separated ;and the metal, after the fusion, would prove impure andbrittle, or be retained in great part among the slag.With our apparatus, the roasting is more particularlynecessary, for the fake of the furnace as well as of theore : for black lead crucibles, though they long sustainthe action of vehement fire and of metals made fluid byit, are soon preyed upon and destroyed by sulphureous bo-dies in fusion.

The pot, employed as a furnace for these uses, should,like the preceding blast furnace, be of the largest size :and its height may be increased, by inverting over it aring sawed from the upper part of another pot of thesame size. By this addition to its height, the fuelthrown on the top will be kindled, and the subjectheated, before they sink down into the body of the fur-nace ; and the convergency of the upper part of thering prevents the heat from spreading and annoying theoperator, as it does from furnaces of a diverging mouth.

As the blast furnace, designed for intense fire, is madestronger than the pots of the general construction, byhaving no other aperture than that which receives thebellows pipe ; it is in like manner expedient, for someparticular uses, to have a stronger wind-furnace, with

only