The excellent refinery furnace, or treibheerd, of Frederickshütte, near Tarnowitz, in Upper Silesia, is represented in [figs. 1019.] and [1020.] a, is the bottom, made of slag or cinders; b, the foundation, of fire-bricks; c, the body of the hearth proper, composed of a mixture of 7 parts of dolomite, and 1 of fire-clay, in bulk; d, the grate of the air furnace; e, the fire-bridge; f, the dome or cap, made of iron plate strengthened with bars, and lined with clay-lute, to protect the metal from burning; g, the door of the fireplace; h, the ash-pit; i, the tap-hole; k, k, the flue, which is divided by partitions into several channels; l, the chimney; m, a damper-plate for regulating the draught; n, a back valve, for admitting air to cool the furnace, and brushes to sweep the flues; o, tuyère of copper, which by means of an iron wedge may be sloped more or less towards the hearth; p, the schnepper, a round piece of sheet iron, hung before the eye of the tuyère, to break and spread the blast; q, the outlet for the glassy litharge.
Lime-marl has been found to answer well for making the body of the hearth-sole, as it absorbs the vitrified litharge freely, without combining with it. A basin-shaped hollow is formed in the centre, for receiving the silver at the end of the process; and a gutter is made across the hearth for running off the glätte or fluid litharge.
[Figs. 1021], [1022.] represent the eliquation hearth of Neustadt. [Fig. 1021.] is a cross section; [fig. 1022.] is a front view; and [fig. 1023.] a longitudinal section. It is formed by two walls a, a, 31⁄2 feet high, placed from 1⁄2 to 1 foot apart, sloped off at top with iron plates, 3 inches thick, and 18 inches broad, called saigerscharten, or refining plates, b, b, inclined 3 inches towards each other in the middle, so as to leave at the lowest point a slit 21⁄2 inches wide between them, through which the lead, as it sweats out by the heat, is allowed to fall into the space between the two walls c, called the saigergasse (sweating-gutter). The sole of this channel slopes down towards the front, so that the liquefied metal may run off into a crucible or pot. Upon one of the long sides, and each of the shorter ones, of the hearth, the walls d, d, are raised two feet high, and upon these the liquation lumps rest; upon the other long side, where there is no wall, there is an opening for admitting these lumps into the hearth. The openings are then shut with a sheet or cast iron plate e, which, by means of a chain, pulley, and counterweight, may be easily raised and lowered. f, is a passage for increasing the draught of air.
[Figs. 1024.] and [1025.] represent the refining furnaces of Frederickshütte by Tarnowitz; a, is the fire-door; b, the grate; c, the door for introducing the silver; d, the movable test, resting upon a couple of iron rods e, e, which are let at their ends into the brickwork. They lie lower than would seem to be necessary; but this is done in order to be able to place the surface of the test at any desired level, by placing tiles f, f, under it; g, the flue, leading to a chimney 18 feet high. For the refining of 100 marks of blicksilber, of the fineness of 151⁄2 loths (half ounces) per cwt., 3 cubic feet of pitcoal are required. The test or cupel must be heated before the impure silver and soft lead are put into it.
At these smelting-houses from 150 to 160 cwt. of very pure workable lead (lead containing merely a little silver) are put into the furnace at once, and from 10 to 14 cwt. run off in vitrified oxide; the remainder is then refined with some pure lead, when an alloy containing from 141⁄2 to 151⁄2 loths of blicksilber per cwt. is obtained.