greater loss of lead by volatilisation, and more interruptions, than melting in cupola furnaces. The resulting lead is then either refined, and sold as such, or, if it contains a sufficient amount of silver, is treated by Pattinson's process. The following is the composition of the residues from the reverberatory furnaces at Bleiberg, analysed by Ferjent

3. Lead Fume or Smoke is formed, partly mechanically, when fine particles of ore, at the moment of their transformation into carbonate and sulphate of lead, come into contact with the hot gases during the charging of the furnaces, and during the roasting process; it is also formed by the volatilisation of metallic lead during the second period. There is less volatilisation the more the lead is extracted at the commencement of the second period, when the temperature is still low; in the later periods this loss will also be less, as the masses under treatment are then poorer in lead. The fume consists usually of oxide, carbonate, and sulphate of lead, and a little sulphide of lead, with more or less silver. Silver is volatile at very high temperatures, but most of it is carried off mechanically at the commencement of the process, together with the ore dust, and it probably becomes reduced from the sulphuretted to the metallic state when in contact with hot air.

The formation of lead fume is frequently so considerable that it is advisable and economical to collect it in proper condensation flues. It is then useful for melting up with fresh ore, for, on account of the lead-salts it contains, it considerably shortens the time of roasting. Sometimes the fume is smelted, together with the residues, in cupola fur

naces.

In this case it must be mixed with clay or lime, to

prevent too great a loss of metal from reduction and volatilisation in the upper parts of the furnace, as well as its being mechanically blown out of the furnace.

The following analyses show the composition of different kinds of lead smoke :

PbO,SO3. As03. Fe2O3. ZnO. PbO,CO2. PbS. Al2O3. SiO3. Clay.

РЬО.

1. Smoke from a roasting reverberatory furnace at Pontgibaud, by Berthier. 2. The same, by Rivot. 3. The same of Alston Moor, by Berthier. 4. Fused lead smoke of Conflans, by Berthier. 5. Caked smoke from the chimney of the reverberatory furnace at Redruth, by Berthier. In addition, No. 2 contained 2.3 per cent of ZnO,SO3, and No. 5 contained o'2 per cent of Cu. According to Rivot, the smoke of schlich melting furnaces at the Upper Hartz contains

CO2 & O As & Sb SO3 PbO,SiO3 PbO ZnO Fe2O3 SiO3 & BaO,SO3

4. Reverberatory Hearth Ends.-The hearth being made of clay is impregnated with more or less sulphuretted, oxidised, and metallic lead. It may be smelted together with the residues.

a. THE CARINTHIAN REVERBERATORY PROCESS.

In general this process produces a perfectly pure lead, a good yield, and very little slags; which are, moreover, so poor in lead that they may be thrown aside. This can only be effected by using very pure ores, and being content with a small production and a comparatively great consumption. of fuel, time, and labour. Therefore the purer the ores and the cheaper labour and fuel (wood) are to be had, the more satisfactory will be the result. The manipulation consists in roasting the galena during the first period at a gradually increasing temperature, until oxide and sulphate of lead are

produced in sufficient quantity to admit of the extraction of the greater part of the lead during the second period, by then raising the temperature and repeatedly manipulating the roasting mass. The following equations represent the reaction which takes place :

I. PbS+ 2PbO

= 3Pb + SO2.

=

II. PbS+PbOSO, = 2Pb+2SO2.

Galena also is partly transformed, during roasting, into subsulphide of lead (Pb,S), from which the lead is extracted likewise by the oxidised components.* The lead obtained at the lower temperature (virgin lead) is allowed to run at once on the inclined hearth, out of the furnace, in order to lessen the loss by volatilisation; this lead is of great purity. By continually stirring up the roasting mass, fresh portions of galena are caused to oxidise, and by the reaction of the oxides upon the sulphides the extraction of lead is continually going on. The galena thus becomes more and more decomposed until it reaches a point at which the roasting mass is chiefly composed of oxide and sulphate of lead and small quantities of oxysulphide of lead; this compound now gives no more lead by simply heating. Here commences the third period, i.e., working up of the remaining dough-like mass at a higher temperature, and mixing it with coal or wood. By this operation the free oxide of lead and the oxide contained in the oxysulphide become reduced, and the sulphide of lead liberated from the latter, as also the sulphide which has been reduced from the sulphate of lead, become transformed into metallic lead by the surplus oxide of lead; so that at last there will remain a comparatively small quantity of slag, poor in silver and not worth further working. If the galena used contained much silver, the remaining slags will retain a certain amount of it, owing to their combined sulphur. The lead (press lead) extracted at the higher temperature, is less pure than the virgin lead, as the compounds of foreign metals which may be present, get more reduced at the higher temperature of this period than in the earlier stages. A subsequent melting of this impure

* PLATTNER, in B. u. h. Ztg., 1854, p. 22.

lead in the reverberatory furnace will purify it. To carry out the process economically the following requirements are necessary:

*

1. Pure Ores, which may contain a small amount of lime, heavy spar, and blende, but must be as free as possible from silica and silicates. An amount of evento per cent of silica entails a great loss of time, fuel, and metal, by prolonging the roasting, unless neutralised by a corresponding addition of lime. It appears that a small addition of lime is advantageous to the yield even when the ores are free from silica. A greater amount of foreign substances, though it may not interfere chemically with the reaction, always prevents the lead drops upon the inclined hearth running together, and causes them to remain longer in the furnace, in consequence of which they partly volatilise or combine with the slags after becoming oxidised. The ores must be poor in silver, or the resulting slags will have to be worked up again.

2. A Perfect Control of the Temperature. This is only possible when using light charges and furnaces of small dimensions, and by having the grate at the long side of the hearth so that the flame may act equally on all parts of it. Such charges give a comparatively small production of lead, and require larger consumption of fuel, time, and labour. If the charges are increased in order to raise the production, the slags will become richer and the yield proportionately less. If the reaction is effected at a low temperature, the yield is greater, and the lead produced is of finer quality.

3. The use of Wood as Fuel.-Wood lies more loosely on the grate, and allows the passage through it of the surplus air which is essential at this period of the process, as it assists the oxidation of the galena. A coal fire has not this advantage. As a great deal of wood is burned, the process can only be profitable when it is very cheap (say to £1 worth of ore, £1 worth of wood). Brush-wood is only used in the Spanish lead works, and necessitates a particular construction of the furnace.

* Oestr. Zeitschrift, 1856, p. 254.

1

1

Illustrations of the Carinthian Process.* Ores. At Bleiberg and Raibl, in Carinthia, the galena, t poor in silver, is found in layers in Tyrolese limestone, associated with blende, calamine, some iron pyrites, sparry limestone, fluor spar, and heavy spar, together with the rarer minerals, wolfram, red lead, and vanadium lead ore. Quartz and silicates only occur in very small quantities. The zinc blende contains a larger amount of silver than the galena. After dressing, the ores contain 65 to 72 per cent of lead, and only 8 to 10 of gangue, mostly carbonate of lime with a little blende and heavy spar. The richest are those schlich obtained by buddling the ore; washed products are not so rich.

Furnaces. The smelting furnaces do not require for their construction very refractory materials (red sandstone); usually two furnaces are placed side by side, and have but one chimney. (Figs. 1 to 4), a, is the grate, having 4 inches space FIG. I. FIG. 2.

B

between the fire bars; b, the sloped hearth. The inclination increases from 8 to 40 inches, and is formed of two layers, 6 inches thick, the lower one of which is composed of pressed

* VON BORN'S, Bergbaukunde, 1789, ii. 80. KARSTEN, Metallurgische Reise, Halle, 1821, 198. Ueber die Kärnthner Bleihütten: Reisen eines Ungenannten durch einige Theile von mittägl. Deutchland, Erfurt, 1795. BOULANGER, über die Schmelz-processe in Bleiberg; Annales des Mines, 3 sér. vii. 167. LAMPADIUS, Hüttenkunde, ii. Thl. 2 Bd. 263. KARSTEN, Archiv. i. R. vi. 197, PHILLIPS, Mittheilungen über den Bergbau bei Bleiberg in Kärnthnen; Annales des Mines, iv. sér. tom. viii. 5 livr. de 1845. Bergwerksfreund, xi. 161. KARSTEN, Métallurgie, v. 95. WEHRLE, Hüttenkunde, ii. § 913-921. RIVOT, Métallurgie du Plomb et de l'Argent, 1860, p. 298. BAUER, in KRAUS' Oesterr. Jahrb. 1855, p. 364.

+ Erzvorkommen: COTTA, Erzlagerstätten, 1861, ii. 341. Alter des Raibl. Bergbaus, Bergwerksfreund, xvi. 313. Verwaltungsberichte der K. K. Berghauptmannschaften über Verhältnisse und Ergebnisse des Oester: Bergbaus in den Jahren. 1855 und 1858, Wien, 1856 und 1859.