State Agricultural Society. 293 



of the tube. The retorts are sometimes made so that they can be 

 changed from the outside of the furnace, and thus be kept at work con- 

 tinuously. A larger percentage of the metal is obtained than by the 

 process of roasting; but the cost of apparatus, labor, and extra fuel, 

 more than compensate for the gain, under ordinary conditions. 



THE OLDEST CINNABAR ROASTING FURNACE 



Still, or until recently, in use, is the Bustamenti furnace. In this appa- 

 ratus the ore and fuel are charged together in a short vertical shaft, and 

 air is admitted from below and from the side. When the shaft is incan- 

 descent, the air decomposes the cinnabar, and the volatile products, sul- 

 phurous acid, mercurial vapor, and carbonic acid, pass off through flues 

 into two large, square chambers, where the gases are somewhat cooled. 

 At some distance there is a second pair of chambers, and the two sets 

 are connected by several tubes. These tubes are formed of short joints, 

 and each joint is an earthen vessel swelling at the middle, and with one 

 end larger than the other, so that the small end of one "aludel." as 

 these vessels are called, may be thrust into the large end of the next. 

 The point is made with clay. These composite tubes slope from each 

 enfl toward the center, and rest on a foundation of masonry. The mer- 

 curial vapors passing through these tubes are cooled down and the metal 

 deposited in drops, which, on account of the inclined position of the 

 tubes, run down to the central point. A small hole in the under side of 

 the aludel occupying that position, allows the metal to escape and col- 

 lect in vessels set to receive it. So much of the vapor as escapes con- 

 densation in the aludels, passes into the second set of chambers, where 

 another portion is liquified, and the remainder passes out into the air 

 and is lost. 



Besides the metallic quicksilver, another product is condensed, called 

 soot. Its composition varies, but it contains flour of mercuiy, i. e., quick- 

 silver, in minute globules; undecomposed sulphur of mercuiy, for cin- 

 nabar is itself volatile, and, when air is not brought in contact with it, 

 may be distilled unaltered; calomel, when there has been any salt in the 

 ore, and soot proper, formed by the imperfect combustion of the fuel. 

 This product is collected and worked over by hand with lye, to cleanse 

 the minute globules of the metal from impurities, whereupon a large 

 portion of them unite to drops and are thus recovered. The remaining 

 matter is added to the ore at the next charge. 



The mixing of fuel and ore, as practiced in this furnace, has one great 

 disadvantage. If at any time there is more fuel than there should be, 

 too great a heat is produced, and if there are easily fusible compounds 

 in the ore, such as silioite of iron, a glaze is produced, which in this, as 

 in all roasting, interferes very much with the proper action of the air 

 upon the ore. 



THE ALUDELS, 



Too, are somewhat difficult of manipulation, and it is very hard to make 

 the joints between them tight, and no one would now build a furnace on 

 this plan. 



The New Almaden furnace consists, in the first place, of a large square 

 shaft, two opposite sides of which are broken through with numerous 

 openings. This shaft is filled with lumps of ore so arranged as to leave 

 passages through the mass, but no fuel is mixed with it. The fireplace 

 is placed on the outside of one of the perforated walls; the flame 



