1. Furnace called Gallery of the Palatinate.—The construction of this furnace is disposed so as to contain four ranges, a a′, b b′, of large retorts, styled cucurbits, of cast iron, in which the ore of mercury is subjected to distillation. This arrangement is shewn in [fig. 656.], which presents a vertical section in the line a b of the ground plan, [fig. 657.] In the ground plan, the roof e e′ of the furnace ([fig. 656.]) is supposed to be lifted off, in order to shew the disposition of the four ranges of cucurbits upon the grate c f, [figs. 656], [657.], which receives the pit-coal employed as fuel. Under this grate extends an ash-pit d. [Fig. 658.], which exhibits an elevation of the furnace, points out this ash-pit, as well as one of the two doors c, by which the fuel is thrown upon the grate c f. Openings e e, ([fig. 656.]) are left over the top arch of the furnace, whereby the draught of air may receive a suitable direction. The grate of the fire-place extends over the whole length of the furnace, [fig. 657.], from the door c to the door f, situated at the opposite extremity. The furnace called gallery includes commonly 30 cucurbits, and in some establishments even 52. Into each are introduced from 56 to 70 pounds of ore, and 15 to 18 pounds of quicklime, a mixture which fills no more than two-thirds of the cucurbit; to the neck a stoneware receiver is adapted, containing water to half its height. The fire, at first moderate, is eventually pushed till the cucurbits are red hot. The operation being concluded, the contents of the receivers are poured out into a wooden bowl placed upon a plank above a bucket; the quicksilver falls to the bottom of the bowl, and the water draws over the black mercury, for so the substance that coats the inside of the receivers is called. This is considered to be a mixture of sulphuret and oxide of mercury. The black mercury, taken out of the tub and dried, is distilled anew with excess of lime; after which the residuum in the retorts is thrown away, as useless.

[Figs. 659 and 660 enlarged] (180 kB)

Aludel furnaces of Almaden.—[Figs. 659.] and [660.] represent the great furnaces with aludels in use at Almaden, and anciently in Idria; for between the two establishments there was in fact little difference before the year 1794. [Figs. 659.] and [662.] present two vertical sections; [figs. 660.] and [661.] are two plans of two similar furnaces, conjoined in one body of brickwork. In the four figures the following objects are to be remarked; a door a, by which the wood is introduced into the fire-place b. This is perforated with holes for the passage of air; the ash-pit c, is seen beneath. An upper chamber d, contains the mercurial ores distributed upon open arches, which form the perforated sole of this chamber. Immediately over these arches, there are piled up in a dome form, large blocks of a limestone, very poor in quicksilver ore; above these are laid blocks of a smaller size, then ores of rather inferior quality, and stamped ores mixed with richer minerals. Lastly, the whole is covered up with soft bricks, formed of clay kneaded with schlich, and with small pieces of sulphuret of mercury. Six ranges of aludels or stoneware tubes, f f, of a pear shape, luted together with clay, are mounted in front of each of the two furnaces, on a double sloping terrace, having in its lowest middle line two gutters t v, a little inclined towards the intermediate wall m. In each range the aludel placed at the line t m v of [fig. 660.], that is to say at the lowest point, g, [figs. 659.] [662.], is pierced with a hole. Thereby the mercury which had been volatilized in d, if it be already condensed by the cooling in the series of aludels f g, may pass into the corresponding gutter, next into the hole m, [fig. 660.], and after that into the wooden pipes h h′, [fig. 659.], which conduct it across the masonry of the terrace into cisterns filled with water; see q, [fig. 661.], which is the plan of [fig. 662.]

The portion of mercury not condensed in the range of aludels, f g, which is the most considerable, goes in the state of vapour, into a chamber k; but in passing under a partition l l, a certain portion is deposited in a cistern i, filled with water. The greater part of the vapours diffused in the chamber k′ is thereby condensed, and the mercury falls down upon the two inclined planes which form its bottom. What may still exist as vapour passes into an upper chamber k′, by a small chimney n. On one of the sides of this chamber there is a shutter which may be opened at pleasure from below upwards, and beneath this shutter, there is a gutter into which a notable quantity of mercury collects. Much of it is also found condensed in the aludels. These facts prove that this process has inconveniences, which have been tried to be remedied by the more extensive but rather unchemical grand apparatus of Idria.

Details of the aludel apparatus: 25 are set in each of the 12 ranges, seen in [fig. 661.] constituting 300 pear-shaped stoneware vessels, open at both ends, being merely thrust into one another, and luted with loam. What a multitude of joints, of which a great many must be continually giving way by the shrinkage of the luting, whereby the mercurial fumes will escape with great loss of product, to poison the air!