d d, the ledges on each side of the hearth, 10 inches in height, and 1 foot wide. These serve to elevate the logs above the hearth, at the same time creating a draught for the air, and passage for the lead.
e, the eye of the furnace, or arch, 2 feet across at bottom, with an arch thrown in a half circle, or a flat stone laid across at the height of the ledges.
f, the iron ladle for dipping out the melted lead.
g, the iron mould. Every bar of lead cast in this, is called a pig.
h, the hole in the ground, for the reception of the lead as it runs from the furnace.
Figure 2, is a perspective view of the furnace from the back or open part. The same letters used in Figure 1 apply to the same parts of the furnace in this figure.
Figure 3. Ground Plan.
a, the eye or arch in front.
b b, the side walls.
c, the hearth.
d d, the ledges.
Log Hearth Furnace
For Smelting Lead Ore
The process of charging the furnace may be mentioned. Three large oak logs, rolled in from the back side, and resting at each end on these ledges, fill up the width of the furnace; small split logs are then set up all around on the two sides and front; the ore is then piled on until the furnace is full, and logs are then piled over it, beginning at the back, and continuing over to the front, so that the ore is completely surrounded by wood. This furnace is always built on the slope of a hill, as represented in Plate I., Fig. 1; and the hearth is laid on an angle of 45°, so that it falls four feet in a distance of eight. Two furnaces of the size here described are generally built together, by which there is a saving of the expense of one wall, and the work is rendered stronger, one serving as a support to the other. Not only so, but the same number of hands will keep a double-eyed furnace in blast, which are required at a single one. It takes three hands, one to cart wood during the day-time, and the other two to relieve each other alternately, every twelve hours, at the furnace. When a charge is melted off, the furnace is cooled, new logs and upright pieces put in, and the whole operation begun anew. Twenty-four hours is the time generally allotted for each smelting, but it often takes thirty-six; and when there is bad wood and want of attention, it requires still longer, and indeed the result is never so good.