furnaces are 4°5 metres high above the tuyere; some have In 24 hours about 8 tons are treated with 6 per cent of iron borings and cast iron, producing 10 or 11 per cent of lead, at a consumption of 15 or 17 per cent of oak charcoal. Sperpieri has founded in Cagliari the first works for smelting Sardinian slags, and he produces 1,000 tons of lead per annum. This lead is richer in silver than that produced from galena in other works, and it has lately been treated according to Pattinson's process in the works near Genoa, which are capable of treating annually more than 3,000 tons of lead. In different parts of Spain, in Amadir,* near Almazaron, for instance, old Roman slags are worked. DIVISION III. PURIFICATION OF THE LEAD. The lead produced in smelting works is never chemically pure; it contains, according to the foreign substances associated with the ore, copper, silver, antimony, arsenic, zinc, iron, bismuth, nickel, and sulphur. These substances render the lead more or less hard and sonorous, and lessen its value by rendering it less applicable both for chemical manufactures and for mechanical purposes. With regard to the former disadvantage, copper, antimony, and arsenic are chiefly injurious, and in the latter, chiefly antimony and arsenic; for instance, the rolling of the lead is not prejudiced by a certain amount of copper,* and the purest lead will sometimes show itself brittle at rolling in consequence of a crystalline structure (Pattinson's lead).† A small amount of oxide is said to make lead harder, as suboxide of copper does copper.t According to the investigations of Reich || and Streng, § iron enters but little into combination with lead unless the metals are some time in contact, as, for instance, when lead is melted in iron vessels. Iron is mostly separated by oxidising the surface of the metal, so that seldom more than o'02 to 0'07 per cent of iron remains in it. The highest amount of zinc, according to Matthiessen and v. Bosse, ¶ which remains in lead is 1.5 per cent. The purer the lead the higher is its specific gravity, and the greater its softness and ductility. In English smelting works it is regarded as an infallible sign of the purity of the lead if there is an iridescent appearance when an iron rake is moved across the molten surface, beginning at the working door. The workmen sometimes take small samples, pour them upon a hot iron plate, and observe whether the lead forms round globules or not; if no globules are formed, the lead is tolerably soft. This sign is of value if the lead contains arsenic, but of little use when it contains antimony. The methods used for purifying impure raw lead (for Pattinson's process) or impure lead poor in silver, so as to make it marketable, are founded upon the principle either of separating admixtures difficult to fuse by a process of liquation, or of exposing the lead to the oxidising influence of the common air or of a blast, in a more or less high temperature, KERL. Oberharzer Hüttenpr., 1861, p. 446. + Ibid., p. 624. Dingler's Polyt. Journ., Bd. 32, p. 286. ||Freiberger, Jahrb., 1860. B. u. h. Ztg., 1860, p. 28, 284. B. u. h. Ztg., 1860, p. 127, 284. TERDMANN'S Journ. f. pr. Chemie, Bd. 84, p. 323. and for longer or shorter periods, according to the quantity and quality of the foreign admixtures. When smelting at as low a temperature as possible, iron, zinc, and copper separate almost entirely from the lead, and swim on its surface as a pasty, half-melted mass, provided the crust is repeatedly skimmed off; arsenic and antimony require a longer oxidising smelting, and sometimes the application of blast, to become partly volatilised, and partly separated as a dross-like mass on the surface of the liquid lead. The loss of lead and the expense of the process are increased by using a high temperature, by a long calcination, and by the application of a blast. Reich* states that if cupriferous dross is kept in contact with the lead for a longer time and at a high temperature, part of the copper will again enter into combination with the lead. These different kinds of dross are afterwards treated in various ways. The Modes of Purification are as follows: A. Skimming the Lead.-The lead produced by reducing litharge, and which has been tapped off into the basin, is freed by repeated skimmings from the cupriferous and antimonial dross which forms upon its surface; this goes on till the lead has attained a suitable temperature for being ladled into moulds. In England the skimming is effected by means of two wooden boards, and in Germany by an iron scraper, and is repeated till the colour of pure lead appears. This mode of purification is only effective with the purer sorts of lead containing little copper. It is sometimes assisted by mixing wood shavings and brush-wood, &c., with the molten lead, and stirring it up with them, when a development of gases will take place, causing mechanically admixed impurities to rise to the surface, and also facilitating the oxidation of the foreign substances by increasing their contact with the air. In this way the subsulphide of lead which is frequently contained in lead produced in reverberatory furnaces, rendering it pasty, may be removed, as well as the sulphide of lead, and intermixed particles of ore, &c. B. u. h. Ztg., 1860, p. 284. B. The Liquation Process, chiefly used for separating the substances difficult to fuse (copper, nickel, iron, &c.), which are present in larger quantities in lead (Lower Hartz); this process is mostly conducted on the liquation hearth, and, though very simple, is imperfect and causes great loss of metal. c. The Process of Stirring the Smelted Lead with a Birch Pole. This is done at Altenau (Upper Hartz) in the following way:-11 tons 5 cwts. of lead are melted in an iron vessel, 5 feet 6 inches in diameter, and 2 feet 10 inches deep, for 6 or 8 hours, the impurities which rise to the top (about th of the charge) are then collected together by a piece of wood, and put into moulds by means of a pierced ladle. After a lapse of half or three-quarters of an hour the surface becomes bright, and then a birch pole is moved about in the metal bath by machinery for two hours; by this manipulation the metal begins to bubble fiercely, the surface is continually renewed, and an ample separation of impurities is effected, which are removed in pierced ladles. According to Streng's investigations, the greatest part of the antimony and copper is separated by this process; this, for the not very impure argentiferous raw leads of the Upper Hartz, appears preferable to the calcination process in reverberatory furnaces, as it saves fuel, time, and labour, and also causes less loss of lead. At the smelting works in Stadtgrund and Schemnitz* (Hungary), the lead is liquated in a reverberatory furnace, with a sloping, tray-like sole, and is then treated with a pole, the liquated lead running into a kettle which stands outside the furnace. This mode is less expensive, the consumption of fuel is a little larger, the production is greater (the loss of lead being from 0'59 to 0'73 per cent), and the lead (a) is purer than from the liquation process formerly used (b). Pb. Ag. Cu. Sb. Fe. Zn. a. 98'954 0005 0456 0212 0126 trace 0'009 * Schemnitzer und Leobener Jahrbuch, 1862, Bd. xi., p. 130, p. 199. Berg. und Hüttenmannische Zeitung, 1857, p. 26; 1859, p. 67. Experiments on the application of this process for the purification of the antimonial lead of Stolberg, did not succeed. D. Pattinson's Process.-This crystallisation process can only be advantageously employed with the purer kinds, mostly calcined raw leads, and as it yields lead of great purity is chiefly adopted with lead rich in silver (Altenau, Freiberg). Baker calls attention to the fact that the small quantities of copper and antimony contained in lead, enter chiefly into the argentiferous mother liquor, whilst arsenic collects in the crystals. If the raw lead contains a larger amount of copper, the crystals also become cupriferous, and in this case a calcination of the raw lead is advisable. The following analyses of lead treated by Pattinson's process will be of interest : No. 3 Nos. 1 and 2, lead from Altenau (Upper Hartz). and 4, lead from Freiberg. No. 5, refined lead from Sheffield, by Baker, from lead containing o'0046 per cent Ag, o'0066 per cent Cu, and o'0065 per cent Fe (Berg. u. h. Ztg., 1857, p. 26). No. 6, lead from Eschweiler. No. 7, lead from Stolberg. E. Oxidising Smelting in Air Reverberatory Furnaces, applicable to impure leads either poor or rich in silver. In England, in many smelting works, cupriferous or antimonial leads are calcined in reverberatory furnaces, and afterwards treated by Pattinson's process. When calcining large quantities of less pure raw lead, the hearth of the furnace usually consists of a cast-iron pan with one fire-place, or with two, opposite each other (Panther Works at Bristol). When working purer lead, a furnace with a very low hearth |