234 



MERCURY 



the less bulky fragments are arranged, which are covered with the shivers and pieces 

 of less dimension. On the middle vaults, the small ore is placed, distributed in 

 cylindrical pipkins of earthenware, of 10 inches diameter and 5 inches depth. The 

 upper vaults receive likewise pipkins filled with the sands and pastes called schlich. 



In 3 hours, by the labours of 40 men, the two double sets of apparatus are charged, 

 and all the apertures are closed. A quick fire of beech-wood is then kindled, and 

 when the whole mass has become sufficiently heated, the sulphuret of mercury 

 begins to vaporise ; coming into contact with the portion of oxygen which had not 

 been carbonised by combustion, its sulphur burns into sulphurous acid, while the 

 mercury becomes free, passes with the other vapours into the chambers for condensing 

 it, and precipitates in the liquid form at a greater or less distance from the fire-place. 

 The walls of the chambers and the floors, with which their lower portion is covered, 

 are soon coated over with a black mercurial soot, which, being treated anew, furnishes 

 50 per cent, of mercury. The distillation lasts from 10 to 12 hours ; during which 

 time the whole furnace is kept at a cherry-red heat. A complete charge for the two 

 double apparatus consists of from 1,000 to 1,300 quintals of ore, which produce from 

 80 to 90 quintals of running mercury. The furnace takes from 5 to 6 days to cool, 

 according to the state of the weather ; and if to that period be added the time re- 

 quisite for withdrawing the residuums, and attending to such repairs as the furnace 

 may need, it is obvious that only one distillation can be performed in the course of a 

 week. 



It has been long well known, that quicksilver may be most readily extracted from 

 cinnabar, by heating it in contact with quicklime. The sulphur of the cinnabar com- 

 bines, by virtue of a superior affinity with the lime, to the exclusion of the quicksilver, 

 to form sulphide of calcium, which being fixed, remains in the retort, while the mer- 

 cury is volatilised by the heat. In a few places, Hammerschlag, or the iron cinder 

 driven off from the blooms by the tilting hammer, has been used instead of lime in 

 the reduction of this mercurial ore, whereby sulphurous acid and sulphide of iron 

 are formed. 



The modes practised at Almaden and Idria are far from economical ; the ores 

 being heated upon open arches, and the vapours attempted to be condensed by enclosing 

 them within brick or stone and mortar walls, which can never be rendered either 

 sufficiently tight or cool. 



To obviate all these inconveniences and sources of loss, the proper chemical arrange- 

 ments suited to the present improved state of the arts ought to be adopted, by which 

 labour, fuel, and mercury might all be economised to the utmost extent. The only 

 apparatus fit to be employed is a series of cast-iron cylinder retorts, somewhat like 

 those employed in the coal-gas works, but with peculiarities suited to the condensation 

 of the mercurial vapour. Into each of these retorts, supposed to be at least one foot 

 square in area, and 7 feet long, 6 or 7 cwts. of a mixture of the ground ore with the 

 quicklime may be easily produced from a measured heap by means of a shovel. The 

 specific gravity of the cinnabar being more than 6 times that of water, a cubic foot of 

 it will weigh more than 3 cwts. ; but supposing the mixture of it with quicklime 

 (when the ore does not contain the calcareous matter itself) to be only thrice the 

 density of water, then 4 cubic feet might be put into each of the above retorts, and 

 still leave 1 cubic foot of empty space for the expansion of volume which may take 



place in the decomposition. The ore should certainly be ground to a moderately fine 

 powder, by stamps, iron cylinders, or an edge-wheel, so that wheii mixed with quick- 



