Page:Transactions of the Natural History Society of Northumberland, Durham, and Newcastle-upon-Tyne 1838 Vol.2.djvu/172

158 sinking down a little behind, the nozzle of the bellows is not more than 3 or 4 inches above the surface of the Lead. The blast is always directed downward into the hearth, so as to cut the upper edge of the work-stone, as shewn by the dotted line leading from the bellows-pipe in Fig. 3, by which means it is more thoroughly distributed through the contents of the hearth. In Figure 3, there is a space shewn between the workstone and hearth-bottom. This is generally filled up with fire clay, or a mixture of slime ore and bone ashes, properly moistened with water; but a plan sometimes adopted, is to have the hearth-bottom and workstone cast together, which renders stopping unnecessary. Another modification of the hearth, adopted by some intelligent smelters, is making the bottom, instead of 44 inches, 10 or 12 inches deep, by this means increasing the quantity of lead retained in the hearth, and proportionally lessening its tendency to get too hot, during the process of smelting.

In proceeding to smelt by means of an ore hearth, two workmen are required to be in attendance from the beginning to the end of each smelting shift, the duration of which is from 12 to 15 hours. The first step in commencing a smelting shift, is to fill up the hearth-bottom and space bellow the workstone with peats, placing one already kindled before the nozzle of the bellows. The powerful blast very soon sets the whole in a blaze, and by the addition of small quantities of coal at intervals, a body of fire is obtained filling the hearth. Roasted ore is now put upon the surface of the fire, between the forestone and pipestone at l, Fig. 3, which immediately becomes heated red hot and reduced; the lead from it sinking down and collecting in the hearth-bottom. Other portions of ore of 10 or 12lbs. each, are introduced from time to time, and the contents of the hearth are stirred and kept open, being occasionally drawn out and examined upon the workstone, until the hearth-bottom becomes full of lead to the dotted line n, Fig. 3. The hearth may now be considered in its regular working state, having a mass of heated fuel, mixed with partly fused and semi-reduced ore, called Brouse, floating upon a stratum of melted lead. The smelting shift is then regularly proceeded with by the two workmen, as follows:—The fire being made up into the shape represented by the dotted line at l,