MERCURY 



231 



1434 



1433 



in order to show the disposition of the four ranges of cucurbits upon the grata 



of, figs. 1432, 1434, which receives the pit-coal employed as fuel. Under thia 



grate extends an ash-pit, d, 



fig. 1434, 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 (Jig. 



1432) are left over the top arch 



of the furnace, whereby the 



draught of air may receive a 



suitable direction. The grate of the fireplace extends 



over the whole length of the furnace, ,/fy. 1433, from the 



door c to the door / situated at the opposite extremity. 



The furnace called gallery includes commonly 30 cucurbits, 



and in some establishments even 52. Into each are intro- 



diiced 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 iiicrcury, for so the substance that coats the inside of the 



receivers is called. This is considered to be a mixture of sulphide and oxide of 



mercury. The black meraury, 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. 



2. Aludcl-furnaces of Almadcn. Figs. 1435 to 1438 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. 1435 and 1438 present two 

 vertical sections ; figs. 1436 and 1437 

 are two plans of two similar fur- 

 naces, conjoined in one body of brick- 

 work. In the four figures the follow- 

 ing objects, are to be remarked : a 

 door a, by which the wood is intro- 

 duced into the fire-place /;. 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 -in- 

 ferior 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 sulphide of mercury. Six ranges of aludels or stoneware 

 tubes//, 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 tmv,jig. 1436, that is to say at the lowest point, g, figs. 1435, 

 1438, is pierced with a hole. Thereby the mercury which had been volatilised in d, 

 if it be already condensed by the cooling in the series of aludels fg, may pass into 

 the' corresponding gutter, next into the hole m, fig. 1436, and after that into the 

 wooden pipes h h', fig. 1435, which conduct it across the masonry of the terrace into 

 cisterns filled with water ; see q, fig. 1437, which is the plan of fig. 1438. 

 The portion of mercury not condensed in the range of aludels, fff, which is the most 



1436 



