b. Five tons of raw lead require 10 or 12 hours' calcining for a subsequent treatment by Pattinson's process, consuming about nine cubic feet of coal. c. Lead reduced from furnace ends and dross of the different processes, being similar in quality to hard lead, requires 60 hours or more for calcination, according to the purpose for which the calcined lead is destined. The following analyses may prove interesting:— 1. Lead which has been calcined in reverberatory furnaces: Fe. Ni. Sb. As. 10'987 II 162 II*340 0'03 074 0'56 3. 97'56 0'44 0'03 These four kinds of lead are slag lead from Freiberg, analysed by Reich. 1, raw slag lead; 2, the same after having been calcined for 6 hours; 3, the same after 14 hours' calcination; 4, the same after 19 hours' calcination (soft lead).* 2. Lead produced at Altenau from intermediate products, after treatment by Pattinson's process:· Pb. Sb. Cu. Zn. Fe. Sp. gr. 1. Lead from reducing the poor scum of the 11th, 12th, and 13th crystallisation pan, by Streng; 2, lead produced from argentiferous furnace ends, taken from a crystallisation pan, by Streng; 3, lead reduced from litharge which had been produced by cupelling rich lead.† Calcination of Lead at the Smelting Works at Kremnitz.-According to Bittsansky, there is contained in the calcined marketable lead These leads may be used for common purposes, but not for the finer manufactures. Von Amon has completely purified this lead, with the exception of some traces of iron, by the following treatment : The lead resulting from the reducing process of litharge, is smelted in lots of 5 tons, 3 cwts., at a moderate temperature in a cupelling furnace furnished with a sloping hearth; the dross is skimmed off and is stirred with green wooden poles for 1 to 2 hours, till the separating dross consists merely of yellow oxide of lead. As the copper and antimony cannot be completely extracted by this operation, some air is admitted for oxidation, at a moderate temperature, until in two or three hours the litharge running out is pure yellow. The lead is then allowed to cool and is tapped off into an outer basin, and is ladled from this into warmed cast-iron moulds. The lead must be sufficiently cooled before the ladling, as otherwise a thin covering of oxide will be formed, giving a rough, ill-looking surface to the lead. The loss of lead in this calcination process amounts to 198 per cent, and the cost of calcining 1 cwt. of lead to about 2s. Baker's Method of Calcining Lead.*-According to this method, hard slag lead, whose calcination in reverberatory furnaces is both expensive and tedious, may be purified in a short time, by ladling it from the receptacle basin into a red hot iron pot, after skimming off and adding either potash or soda saltpetre, adding it in the proportion of I part saltpetre to 100 of lead, or of 2 parts of sulphate of potash to 900 of lead. It is then stirred at a temperature higher than the melting point of lead, and the dross formed is skimmed off till the lead has assumed the hues characteristic of pure lead. The resulting lead is then fit for rolling or any other technical application. Pontifex and Glassford's Method of Calcination.tAccording to this method, soft lead, or a lead rich in antimony, may be produced as follows: * B. u. h. Ztg., 1861, p. 440; 1862, p. 40. Polyt. Centrlb., 1861, p. 827. + Polyt. Centrlb., 1855, p. 618. Hard lead containing from 3 to 15 per cent of antimony is melted in a reverberatory furnace whose hearth consists of a cast iron pan; the dross formed is skimmed off, and upon the surface of the metal a mixture of 3 parts of soda saltpetre, 4 of calcined soda, and 4 of burned lime, is uniformly spread out. Then the furnace doors are closed for some time, but occasionally opened to observe whether a brownish scoria appears on the surface of the lead, which is generally the case after 10 or 20 minutes; the doors are then re-closed, fresh fuel is added, and when the smoke has disappeared so that the fire burns brightly, the covering is removed and another portion of the mixture is added; this goes on until a sample of the lead shows ductility. Nine or 10 tons of lead may be treated in 24 hours, consuming about 55 lbs. of the mixture; when the lead is poor in antimony the addition of saltpetre may be omitted. The scum of the lead is reduced in a cupola furnace; the resulting lead rich in antimony is smelted in an iron pan and cooled to the point at which highly antimonial lead crystallises, when it is ladled out as in Pattinson's process. This lead is sold as hard lead, and the remaining liquid is again treated with the mixture. The annual production of lead amounts— In Great Britain, to about 67,000 tons. 201 CHAPTER II. SILVER. PRINCIPAL ORES OF SILVER. ACCORDING to Malaguti and Durocher,* silver occurs frequently in nature, and the following are the ores to which the attention of the metallurgist will probably be directed :— 1.-ORES IN WHICH SILVER FORMS A CHIEF COMPONENT (REAL SILVER ores). Native Silver, Ag, sometimes containing as much as 3 per cent of antimony, arsenic, and iron; the native ore silver at Freiberg, containing from 97'10 to 99.8 per cent of silver, is usually associated with other silver ores, sometimes also with grey copper ores. In California, silver occurs in admixture with gold; at Lake Superior, || it is found upon native copper; at Kongsberg, § it contains about 90 per cent * MALAGUTI et DUROCHER, Ü. d. Vorkommen, etc., des Silbers, Quedlinburg and Leipzig, 1851. Neuer Schauplatz der Bergwerkskunde, xii. 57. B. u. h. Ztg., 1842, p. 3. COTTA, Gangstudien, i. 437; ii. 115, 254, 491. v. Dechen, Statis. des nördl, and zollv. Deutchlands, i. 750. + Jahrb. f. d. B. u. Hm., 1831, p. 223. LAMPADIUS, Fortschr., 1839, p. 111 ̧ B. u. h. Ztg., 1858, p. 37. HAUSMANN, norddeutche Beitrage, Stück, i. p. 127. Allg. B. u. h.Ztg., 1862, p. 405. Laur, de la production des métaux précieux en Califonrie .Paris: 1862. || Berggeist, 1862, No. 93. Allg. B. u. h. Ztg., 1863, p. 164. § B. u. h. Ztg., 1858, p. 102; 1862, p. 434. of silver. One mass from that locality in the royal collection at Copenhagen weighs upwards of 5 cwts., and later two blocks have been obtained weighing respectively 238 and 436 pounds. Much of the silver of Peru has been found in a native condition; a mass discovered at Huantaya weighed 800 pounds. But all these are surpassed by an immense mass discovered in Sonora, which, Wilson states, weighed 2,700 pounds, and was the subject of a suit brought on behalf of the King, who thought to recover it on the plea that it was a curiosity, and belonged to the Crown. Amalgam, of different composition, Ag,Hg, containing 44'8, AgHg containing 519, and Ag,Hg, containing 57'2 per cent of silver, occurs frequently in Chili.t Antimonial Silver, AgSb, and Ag,Sb containing respectively 84 and 77 per cent of silver, occurs at Andreasberg also in Dauphiné, and near Coquimbo, South America. Mixed Antimonial Silver. Its constituents are, silver 16, iron 44, arsenic 35, antimony 4; it occurs at Andreasberg in the Hartz. Telluric Silver, Ag Te, containing 61 per cent of silver, sometimes also gold and traces of iron; it occurs in Siberia in a talcose rock with pyrites and blende; specimens have been obtained a cubic foot in size. Silver Glance, AgS, containing 87 per cent of silver; it is frequently met with in the mines of the Hartz, Saxony, Bohemia, Mexico, and is also found in Cornwall and in the United States. Bismuth Silver (Sprödglaserz, Melanglance), 5AgS, SbS,, containing 68.5 per cent of silver, and sometimes small amounts of Fe, Cu, and As. Miargyrite, AgS, SbS, containing 36'9 per cent of silver. Light Red Silver Ore, 3AgS+AsS, containing 65°4 per cent of silver; sometimes part of the AsS, is replaced by SbS,; it is found in Saxony and in Bohemia, also at Guadalcanal, in Spain. * LAMBORN, a Rudimentary Treatise on the Metallurgy of Silver and Lead. London: 1861. † Allg. B. u. h. Ztg., 1863, p. 121. |