Page:Transactions of the Natural History Society of Northumberland, Durham, and Newcastle-upon-Tyne 1838 Vol.2.djvu/171

Rh A pipestone g, Figs. 1 and 3, being a prism 10 inches square, and 28 inches long, with an opening to admit the bellows-pipe, as in Fig. 6, where it is shewn separate, and lying upon what is its upper part when properly placed in the hearth.

An upper backstone a, Figs. 1 and 3, a parallelopiped 28 inches long, 4 inches deep, and 5 inches wide, which completes the back part of the hearth.

A forestone c, Figs. 1 and 3, 26 inches long, 6A inches deep, and 5 inches broad, and Four keystones being exact 10-inch cubes of iron b, b, b, b, Fig 1. The two cubes nearest the back of the hearth, are placed upon the bearers d, d, so as to correspond with them on the inside, and are thus 22 inches apart; but the two cubes in front are made to lie against the ends of the forestone, and are consequently 26 inches distant from each other.

The forestone itself is moveable to a certain extent. It can be placed at the distance of 10 inches from the backstone, by being put in contact with the two keys nearest the back, and it can be lowered down so as to rest upon the two bearers d, d, if necessary, and in that case would be only 6 inches above the upper edge of the workstone. In Figs. 1 and 3, it is represented 12 inches from the back of the hearth, and supported by a fire brick at each end, placed upon the bearers; its under edge being thus 11 or 12 inches above the workstone, which is its usual position. The various castings are secured in their places by brick-work, and the top of the hearth is finished level with masonry, to receive any particles of ore, called hearth ends, that may be expelled by the blast. Each hearth is placed under a chimney supported by an arch (as shewn in Figure 1), and communicating with the horizontal flues already referred to, by passages through which the fume and smoke are conveyed away.

In Figure 3, the pipe of the bellows is represented to enter the hearth 6½ inches above the level of the upper edge of the workstone, which regulates the surface of the lead when the hearth is in a working state, but it more frequently happens, that by the bearers and hearth-bottom