Page:Transactions of the Natural History Society of Northumberland, Durham, and Newcastle-upon-Tyne 1838 Vol.2.djvu/166

156 Mr. H.L. Pattinson on Smelting Lead Ore, &c. particles, the fume from the roasting furnace is conveyed into this flue, where the heavy metallic portion is deposited.

SMELTING IN THE ORE HEARTH.
The furnace in which the roasted ore is reduced into Lead is called an Ore Hearth. Its construction is almost exactly the same in all smelting houses in the north of England, and seems to have undergone but little alteration from a very remote period. It may be briefly described as a square furnace, close on three of its sides, and open towards the bottom of the fourth. Immediately in front of this opening is placed a sloping cast-iron plate, the upper edge of which is four and a half inches above the bottom of the furnace, forming a reservoir of that depth, in which the reduced lead accumulates, and out of which it flows, through a channel in the plate, into a pot below, after the reservoir becomes full.

To construct an ore hearth, twelve pieces of cast iron are necessary, (exclusive of the melting pot, f, Plate II., Figs. 1 and 3), viz.:— A hearth bottom, Fig. 5 and i, Figs. 1 and 3, 22 inches square, inside measure, the bottom 3 inches thick, and the sides 3 inches thick and 4½ deep. In building an ore hearth, it is usual to place the hearth bottom upon a layer of sand a few inches deep above the brick or stone bed.

A workstone e, Figs. 1 and 3. This is a plate 3 feet long, by 1½ broad, and 2½ inches thick, having a raised border an inch high on its two ends and front side, with a channel o, Figs. 1 and 3, 2 inches wide, and 1 deep, running diagonally across it. It is placed at a slope of three or four inches from its upper to its under edge.

Two bearers d, d, Fig. 1, being square prisms of cast iron of 6 inches a side, by 26 or 28 inches in length. There is an advantage in making these long, as they can be turned when worn at one end, and, as they project over and rest upon the workstone, they tend to keep it firm in its place.

A backstone h, Fig. 3, upon which the bellows-pipe rests, as in the figure. It is a parallelopiped 28 inches long, 6½ in height, and 5 inches broad.