cent of suboxide of copper, 8'92 per cent of alumina, 7.83 per cent lime, 0'53 per cent magnesia, and 0.7 per cent oxide of antimony. Slag from Pontgibaud, according to an analysis by Berthier, consisted of 22'0 per cent of silica, 35'6 per cent of oxide of lead, 4°2 per cent of oxide of iron, 5'2 per cent of alumina, 30°2 per cent of lime, and 1'0 per cent of magnesia. The resulting dross is reduced in 18 hours in quantities of about 12 tons in one operation, with 18 cwts. of slags from the reducing process, and 2,480 lbs. of charcoal, producing 184 pigs of lead, and 26 cwts. of slags. On refining these 184 pigs, there are produced in 15 hours 12 tons of dross lead, containing o'0035 per cent of silver, and about I ton of cupriferous refining dross, which is worked in the last lead matt smelting. The total yield of lead from the reducing process of the litharge and dross amounts to go per cent, and the loss of lead to 2 per cent. The dross lead is composed as follows: = Lead from Clausthal, analysed by Streng: 98.30 per cent of lead, o'16 per cent of copper, 1'20 per cent of antimony, O'10 per cent of tin; its specific gravity. 11*383. Lead from Altenau, by Ulffers: 99'60 per cent of lead, o'016 per cent of copper, o'370 per cent of antimony, o'006 per cent of iron, o'oor per cent of tin; its specific gravity = II*350. The litharge of the smelting works at the Lower Hartz* is more or less cupriferous, contains from 86 to 90 lbs. of lead and 0.03 oz. of silver per cwt., and is reduced in low cupola furnaces six feet high, constructed like channel furnaces with a closed eye. It is mixed with of its weight of slags from the same process, and smelted with the mouth of the furnace kept dark and the tuyere bright. In operations of from 16 to 20 days, about 7 or 7 tons of litharge are reduced with charcoal, producing about 4 tons of lead and from 4 to 6 per cent of slags. At the Freiberg smelting works, † double furnaces, eight KERL, die Rammelsberger Hüttenprocesse, 2 Aufl, 1861, p. 65. + KARSTEN'S Archiv., 1 R., ix., 232. PLATTNER'S Vorlesungen, herausgegeben von Richter, ii. 129. feet high, are employed, and about 45 tons of litharge from unrefined raw lead are reduced in 24 hours, yielding 4 tons of lead per 5 tons of litharge; only 25 tons of litharge can be reduced in 24 hours if it is derived from the rich lead which had been treated by Pattinson's process; and only 15 tons of this rich litharge if obtained at the latter part of the cupelling process. This is worked with an addition of 10 per cent of slags, as it contains a certain amount of the hearth bottom. The resulting slag contains from 25 to 30 per cent of lead, and, at the end of the operation, is worked in admixture with 3 per cent of iron pyrites. From this smelting there results, first, slag lead, which is refined by Pattinson's process; second, matt and slags (modified slags), containing 5 per cent of lead; these are worked up again in the lead smelting process. If they are black and vitreous in appearance, they are either a mixture of mono- and bi-silicates (a, from the Muldner smelting works), or a bi-silicate (b, from the Halsbrück smelting works). According to Richter, their composition is as follows: SiO3. Al2O3. CaO. MgO. FeO. PbO. Cu2O. S. a. 36.66 6.12 5'76 I'43 30.42 8.38 1'07 3.21 b. 52.00 7'40 8.63 0.81 25 11 3.10 0.18 0'51 * Coke mechanically intermixed. 7'32 2.10 The application of turf and hot blast and also the construction of the furnace like channel furnaces with a closed eyet have given no good results. In order to diminish the loss of lead, lumps of coke are arranged over the mouth of the furnace; the escaping gases and flame ignite the coke, and the oxide of lead passing through it becomes reduced, and the metal drops back into the furnace. At Przibram, 10 tons of litharge are reduced in 24 hours without any addition of flux, in low furnaces five feet high. The lead is not tapped off, but runs continually out of the tap-hole on to the hearth as the reduction proceeds rapidly. * Freiberger Jahrb., 1834, 1840. + Ibid., 1839. Oesterr. Ztschft., 1856, p. 350. One operation lasts 10 or 12 days. From 57 tons there are produced 2 cwts. of litharge, containing 90 per cent of lead, 43 tons, 15 cwts., 16 lbs. of soft lead; 8 tons, 19 cwts. of slags, containing 60 per cent; I ton, 2 cwts., 71 lbs. of pot dross, containing 80 per cent; and 10 cwts. of furnace residues, containing 80 per cent of lead. The loss of lead is 1.85 per cent. At Tarnowitz, litharge is reduced in ore smelting furnaces with coal and a flaming furnace mouth. Five tons of litharge, consuming I ton of coal, reduce in 7 hours 4 tons, 9 cwts. of soft lead containing o'06 oz. of silver, and 15 cwts. of slags, dross, and residues. Reduction of Litharge in Hearth Furnaces. Scotch hearths and Siberian reducing furnaces are used for this purpose. The process is conducted in the Siberian reducing furnace as follows:-The furnace, which is of very small dimensions, is filled with glowing coals and put before the cupelling furnaces, and the litharge as it flows off is made to run direct into the small reducing furnace, causing the reduction to take place at a low temperature, and consuming a comparatively small quantity of fuel. Whilst skimming off the first dross the reducing furnace is either not brought close up or is closed with an iron plate covered with marl. If the process of forming litharge is interrupted by an after-charge of lead, the reducing furnace is likewise covered with the iron plate. Although very simple and inexpensive, this plan has the following disadvantages: 1. In the cupelling process a highly argentiferous litharge is likely to be produced, as the workman is prevented observing whether any lead runs out with the litharge, whilst in the usual process the metal is clearly visible on the solidifying litharge. When the lead produced from litharge is to be desilverised, this disadvantage is of no consequence (Hungarian smelting works). 2. The workmen are more exposed to heat and lead fume. 3. The manipulations in the cupelling furnace have to be conducted at a greater distance, interfering with an exact observation of the process; this is chiefly occasioned by the lead fume escaping from the reducing furnace. These disadvantages have prevented a general introduction of the process, although it has often been tried at Freiberg,* Tarnowitz, † Upper Hartz,‡ Schemnitz,|| &c. At Barnaul,§ in Siberia, the reducing furnace is two feet high and 12 inches broad and deep. It is composed of cast iron plates, three of them cast into one piece, resting upon an iron bottom plate. The fourth plate, which is fixed against the three plates, is furnished with an opening forming the front of the furnace. The sole of the furnace has a sump from which the lead is conducted, by means of a moveable spout, into pans which are placed round the furnace. At Fernezely¶ (Hungary), the litharge is reduced in small cast iron furnaces, 30 inches high, 16 inches broad, and 18 inches wide; the front wall is pierced with circular holes, and placed about two inches deep against a sloping channel, which conducts the lead to a crucible situated in the sole of the smelting house. The crucible is kept filled with charcoal; the air required for combustion enters through the lower part of the furnace, and by the holes in the front wall. This furnace produces about 70 per cent of the cupelled lead, and a variable quantity of dross and residues. 9cwts. of lead require about 12 cubic feet of charcoal. The process of reducing litharge in Scotch furnaces is very simple, consuming little fuel, but causing a great loss of lead if not furnished with ample condensation chambers. At the smelting works at Bottino, in Tuscany, from about 6 tons 6 cwts. of second litharge, 5 tons 6 cwts. of marketable lead, and 12 cwts. of poor slags were produced. *KARST. Arch., 2 R., xi., 232. + Polyt. Centrlbl., 1836, No. 50. KERL, Oberh. Hüttenpr., 1860, p. 605. || KARST. Arch., 2 R., ix., 228. § KARST. Arch., 2 R., ix. Polyt. Centrlbl., 1836, No. 50. ¶ Jahrb. d. K. K. geol. Reichsanst., 1853, No. 3, p. 610, 612. In the same operation about 4 cwts. of third litharge, and 10 cwts. of dross were reduced, giving 12 cwts. of lead for the cupelling process, and 2 cwts. of rich slags; the total consumption of coal amounted to about 34 cwts. The slags are re-smelted in cupola furnaces. At Pezey and Pontgibaud the Scotch furnaces yielded 89 per cent of lead from litharge. REDUCTION OF THE DROSS. When smelting very impure raw lead in cupelling furnaces, even before starting the blast engine, a dark crust is produced on the bath of metal, consisting chiefly of sulphuretted and oxidised metals and earthy substances, as well as some raw lead mechanically intermixed. If this crust is formed in considerable quantity, it is skimmed off from the metal bath, and goes by the name of abzug (Lower Hartz). When smelting purer lead, the crust is not skimmed off, but changes into an oxidised slag-like mass (black litharge), chiefly containing those substances which have a greater affinity for oxygen than is possessed by lead, such as antimony, arsenic, iron, zinc, &c. A small quantity of sulphur, which always retains copper and silver, causes the dark colouration of the black litharge at the beginning of the period; as the foreign substances are removed, the litharge becomes richer in oxide of lead, and assumes a more yellowish green colour. This black litharge will give, when submitted to a reducing smelting, a more or less antimonial hard lead, which is chiefly used for the manufacture of printing type, shot, &c. To separate the raw lead which is mechanically intermixed with the dross, and to reduce part of the oxide of lead in order to concentrate the antimony into the remaining part, the dross is sometimes submitted to a refining process in a cupelling furnace before it undergoes reduction; in this case the hearth of the cupelling furnace is made of small coal mixed with loam, and some marl or sand. The dross is mostly reduced in the furnaces which were |