Page:The American Cyclopædia (1879) Volume XI.djvu/414

 402 MERCURY are then passed into condensers. By the sec- ond system the ore is burned in furnaces, where the sulphur is converted into sulphurous acid gas by the admission of air, and the quicksilver is set free as a vapor. All the vapors and gases from this combustion pass into condensing chambers, where the quicksilver is condensed, while the gases escape to the chimney. The retort system, although less wasteful in quick- silver, involves so much additional expense that it is not advantageous in practice. The roasting of cinnabar in furnaces is now uni- versal. The furnaces used are of two gene- ral classes, intermittent and perpetual. In the former, a large charge is introduced, burned, and withdrawn when it has become cool, leav- ing the furnace ready for another. In a per- petual furnace small charges are continually introduced at stated intervals, and the burned ore is withdrawn without interrupting the pro- cess. Intermittent furnaces of different varie- ties are used at Almaden, Idria, and some points in California. A Spanish furnace at Almaden is peculiar in its system of condensation, by which the quicksilver is distilled in large num- bers of clay crucibles joined together like pipes. The condensing chambers contain 528 of these in 12 rows of 44 each. Each Aludel, so called, is about 18 in. long, 10 in. wide in the middle, and 6 in. wide at each end, where it fits into the next. A small hole in each allows the con- densed quicksilver to flow out into a gutter leading to a central channel. The furnace con- sists of a cylindrical shaft about 6 ft. in diame- ter and 25 ft. high, divided by perforated arches, 9 or 10 ft. from the top, into two compart- ments, the upper being for ore and the lower for fuel. The process of burning and distilling quicksilver lasts three days. On the fourth day the furnace is recharged, and the Aludeln are taken up, emptied, and rearranged. The furnace used at Idria has a series of brick chambers separated by partition walls for con- densing the quicksilver. The intermittent fur- naces of California are also provided with brick condensers. The power which bricks have of retaining heat is one of the greatest objections to their use ; another is the inevitable loss of quicksilver, which forces its way even through the best made bottoms of condensing cham- bers, and through imperceptible cracks in the walls. The furnaces of California are built upon arches, and near the bottom of these arches pieces of sheet iron are placed in the masonry, which catch the quicksilver as it filters through, and conduct it to a basin. The merit of brick condensers as compared with iron lies in their ease of construction and re- pair, and in their indifference to the sulphuric acid which is formed with the sulphurous acid gases in contact with steam and oxygen. The intermittent furnaces at New Almaden are 40 ft. long, 8 ft. wide, and 10 ft. high, each being divided into compartments, the fire oc- cupying one at the end, and the heat passing through the ores into flues. A charge of 15,000 Ibs. is worked in 60 hours with wood fuel. A flue from the furnace passes upward to the first condensation chamber, which is 8 ft. long, 4 ft. broad, and 5 ft. high. The chambers are covered with cast-iron plates luted down. After passing through eight chambers the remaining vapors are conducted into a tank, where they are sprinkled with water, and thence escape by wooden chimneys. The ore is usually so mixed for treatment as to present a uniform low per- centage. The finer fragments are worked up with the soft loamy portion, and the mass is kneaded with water and moulded into bricks, which being dried in the sun are worked like the rest. A great saving of fuel may be effect- ed by the use of perpetual furnaces, or of kilns such as are employed for roasting iron ore or lime. Of this class are the Alberti furnace, which is a reverberatory, and hence suitable for small-sized pieces only ; the Hahner, Pult, and Vail' Alta, which are shaft furnaces em- ployed in Europe ; and the furnaces of Riotte, Knox, and Pershbacker, which are California improvements. Cast-iron, wooden, or wooden and sheet-iron tanks, or iron tubes, are em- ployed as condensers. Draft is obtained by means of suction fans. From 20 to 24 tons of ore is passed through a perpetual furnace daily, every ton remaining in the furnace nine hours above the fire bridge, and an additional time of three to four hours below the fire bridge in the hottest portion of the furnace, where the last particles of quicksilver are ex- pelled. The great subtilty with which the vapors of this metal penetrate through the minutest openings is well known to workmen at quicksilver furnaces. Beneath the old fur- naces at New Almaden 2,000 flasks were re- covered by washing out the ground to a depth of 30 ft. The men and animals employed about the smelting works are subject to salivation and other injurious effects ; and the same is true of mines where, as at Idria, native mercury occurs in the ores, and the atmosphere is contaminated with mercurial fumes. At New Almaden there has been little or no complaint among the miners. Metallic mercury in its usual form has no action upon the human system ; it has been taken with impunity in quantities of a pound weight ; but in vapor it acts energetically, producing its constitutional effects. Poisoning occasionally results from exposure to the vapor of mercury, as from the breaking of packages in the hold of a ship, or in various processes in the arts, as in gilding, in silvering mirrors, &c. Mercury is used in medicine in many forms, all of which may give rise to its constitutional effects, varying in the time required for the pro- duction of their action and in the nature of the local disturbance they produce. Mercury with chalk, or hydrargyrum cum creta, prepared by rubbing up 3 oz. of mercury with 5 oz. of prepared chalk, and blue pill made from a mass composed of 1 oz. of mercury rubbed up with 1 oz. of confection of roses, and then beaten with oz. of powdered liquorice root, are