THE BELGIAN-SILESIAN SYSTEM OF EXTRACTING

ZINC.

The furnaces used in this method are so constructed as to conduct the flame round the muffles, and then beneath the furnace into a flue which communicates with a chimney. This arrangement does not allow the use of the escaping flame for calcining and other purposes, but it effects a more uniform. heating of the muffles, and their lower part is especially better heated than in the old Silesian furnaces; the smoke which is so very troublesome to the workmen in the Silesian furnaces, is also avoided, and the fuel is considerably economised. Bituminous flaming coal must be employed; if the muffles of these furnaces become defective they usually cause a larger loss of zinc than defective muffles in common Silesian furnaces. These furnaces also differ from the old Silesian furnaces in allowing the liquid zinc to run direct from the adapters into moulds.

In order to increase the production and economise the fuel, the muffles have been enlarged and increased in number, namely, from 20 to 24, 28, 32, 36, or even 40. Furnaces with 32 muffles are the most common. One muffle requires about I cwt. of ore in 24 hours.

Experiments have been made at Valentin Cocq and Flone-a, with furnaces having 24 muffles, 1°30 metres long, 0'55 metre high, and o'22 metre broad; b, with furnaces of 28 muffles of the same dimensions; c, with furnaces of 32 muffles and the same dimensions; and d, with furnaces having 32 muffles, each 14 metres long, o'6 metre high, and o 22 metre broad, and in 24 hours the following results were obtained from one furnace :

The furnaces, a, c, and d, consumed respectively 796, 656, and 614 lbs. of fuel per 100 lbs. of zinc, and the wages amounted respectively to Is. 116d., Is. 5'7d., and Is. 3'3d.

The adapters rest, as in the Silesian furnaces, upon a support which at the same time divides the front of the muffle into two parts, the lower of which serves for removing the residues. The adapters are of different constructions at Valentin Cocq.* They consist of a tube (v) (Fig. 122), fur

FIG. 122.

m

nished with a swelling on its lower side; its aperture in the front is closed by a clay plug (s).

At the zinc works in Moriston,† near Swansea, the adapters (Fig. 123) are provided with apertures above their lowest

points which are closed with clay plugs, so as to allow the zinc to be tapped off from different levels; it is therefore of varying purity. If the ores contain an amount of lead which becomes volatilised, it will condense and remain in the swelling of the adapter, and thus a purer zinc results.

The same result is obtained by the arrangement at Borbeck (Fig. 124). The adapter (a) resting upon an iron supFIG. 124.

port (b) is hermetically closed by a luted clay plate (c), behind which the zinc collects. Zinc can be made to run out by a tapping hole. On its upper part the clay plate has an opening two inches wide for the escape of the gases, and this aperture is surrounded by a circular projection (d), to which the vessel for receiving the zinc dust may be fixed.

The construction of a Belgian-Silesian furnace with 32 muffles is shown in Figs. 125, 126, 127, 128, and 129. a, a, are FIG. 125.

partition walls forming niches, each for the reception of two muffles; they also support the arched roof of the furnace, and allow the muffles to be fixed by their front, and keep off any cold air which may enter; b, b, are channels conducting the flame near to the mouths of the muffles by means of the flues (d). These flues are larger the farther they are from the fire-place (Moriston, near Swansea), in order to induce a more uniform distribution of the flame. The channels (b, b) either communicate with the clay tubes (f) (Valentin Cocq), 8.6 metres high, o'45 metre upper and o°35 metre lower diameter, which are formed in moulds,* or the flame of all the furnaces is conducted into one chimney; c, c, are channels for receiving residues, which fall into the vaulted space (i), which crosses the chief vault (k); k is used for working under the grate, for collecting and removing the ash, &c. ; e, an opening for charging fuel; g, flue for letting the flame escape, as in the old Silesian process; h, the bridge or support in the muffles for the adapters to rest upon; l, space between two furnaces, formerly used for calcining calamine, and now for re-melting zinc, except in larger furnaces where it is now done away with; m, muffles standing with their backs somewhat higher, and two inches distant from the partition walls (a). As the fire-place becomes enlarged, the muffles are moved to the front, often up to the channel c; n, are niches ; o (Fig. 129), is a door or frame for the niches, constructed of strong band-iron, and coated with loam. The mouths of the adapters (p) project from the upper part of that frame, whilst its lower open part (q) may be closed with a door (r), coated with loam if the temperature of the adapters requires it. If adapters are employed, like a in Fig. 124, the whole frame (o) is not required, but only the door (r), and the upper part may be walled up with bricks; u is a receiver fixed to the adapter (v); t is the fire-place constructed of the best firebricks of the form shown. The walls (a), the hearth sole, and the places where the channels (b) join, also require bricks composed of the materials used in the manufacture of the muffles.

B. u. h. Ztg., 1860, p. 31.

A good furnace lasts on an average two years, and consumes about eight muffles per month.

At the zinc works at Birkengang,* near Stolberg, furnaces are constructed with two rows of muffles one above the other, as shown by Fig. 130. The upper muffles (a) are longer than FIG. 130.

the lower muffles (b) by 10 centim.; both are 0'21 metre broad. Their front is placed upon an inclined iron plate (c), and their back on the wall (d), which is constructed of fire-bricks, and rests upon pillars standing between the niches. One of these furnaces has 60 muffles, 3 in each niche, o'84 metre wide. The partition walls are o'1 metre thick. The flame rises from the fire-place (e) to the arched roof, plays completely round the upper muffles, and passing the spaces between the upper and lower muffles, enters the channel (f), which communicates with the chimney. As the upper muffles are exposed to a higher heat, they are somewhat larger, and

B. u. h. Ztg., 1861, p. 407; 1862, p. 140.