but the English process is used on the coasts, as cheap coal from England and Asturia is to be obtained there.

The reverberatory furnaces in use are similar in construction to those of Flintshire (page 39).

4 charges of about 20 cwts. each are worked every 24 hours with 42 cwts. of coal; the average product is 56 cwts. of crude lead, equal to 58 to 62 per cent. In consequence of the addition of lime, the resulting slags are poorer than those from Spanish furnaces, but, on the other hand, the resulting lead is also more impure than that from Spanish furnaces, on account of the higher temperature used; the production is, however, greater. The slags contain from 16 to 20 per cent of lead, and yield from 12 to 15 per cent in small cupola furnaces.

The loss of lead by volatilisation (5 or 6 per cent) is lessened by extensive condensation flues. The deposited fume, after being mixed with lime and pressed into the form of bricks, and containing from 30 to 40 per cent of lead, is also smelted in cupola furnaces.

The residues are worked in low cupola furnaces. From 120 to 150 cwts. of residues, mixed with from 25 to 30 cwts. of old slags, are smelted every 24 hours, with the consumption of 20 to 24 cwts. of coke, or 35 to 40 cwts. of charcoal; yielding from 17 to 20 cwts. of somewhat hard lead. The yield, therefore, amounts to from 15 to 18 per cent, and the consumption of coke is 1 parts to I of metal. The smeltings in succession in one furnace occupy about 6 weeks.

The total smelting expenses for ore and residues in Spanish furnaces amount, for every 2 cwts. of ore, to 3s., and and for 2 cwts. of reduced metal, to 13s. In English furnaces these expenses are respectively 3s. 6d. and 13s. The residues are sometimes also worked in air cupola furnaces.

The increasing scarcity of charcoal in the Hartz led to determined attempts being made to import the English. method of smelting lead ores, as practised in Flintshire. But, as a slight admixture of quartz prevents the complete extraction of lead, and as the ores of the Hartz often con

tain as much as 17 per cent of silica and alumina, all these trials were unsuccessful.

C. THE FRENCH REVERBERATORY PROCESS.

The theory of this process is as follows:

Galena, when calcined at a long continued and gradually raised temperature, is for the greater part transformed into sulphate of lead and a little oxide of lead. If the roasting is interrupted at that period at which some undecomposed galena is present along with the sulphate of lead, and the temperature then raised to near the fusing point, the constituents of the mass will decompose each other in such a way that oxide of lead is formed, together with sulphurous acid and a small quantity of metallic lead. The resulting oxide of lead is then reduced by treatment with coal. The following equations represent the reactions:

PbS+3PbOSO3=4PbO+4SO2.

4PbO+4C=4Pb+4CO.

The remaining sulphate of lead is also decomposed by the coal. According to Gay Lussact an excess of coal transforms it into sulphide of lead with evolution of carbonic acid. If equal equivalents of carbon and sulphate of lead act upon each other at a low red heat, carbonic acid is evolved, and only half the sulphate of lead is transformed into sulphide.

2PbOSO3+2C=PbOSO ̧+PbS+2CO2.

At a higher temperature the sulphate of lead reacts upon sulphide of lead, forming metallic lead and sulphuric acid. If for 2 equivalents of sulphate of lead only 1 equivalent of coal is used at a lower temperature, an equivalent of sulphide of lead is formed in the first instance, thus

4PbOSO3+2C=3PbOSO3+PbS+2CO2, which at an increased temperature becomes changed by the I equivalents of sulphate of lead into sulphurous acid and oxide of lead, thus

3PbOSO3+PbS=4PbO+4SO,

* ERDM. J., f. p. Ch., xi., 68.

These chemical facts are the foundation of the French reduction process in reverberatory furnaces.

More impure and siliceous lead ores may be worked by this method than by the English process, as the temperature may be kept so low as not to cause scorification. With regard to the yield of metal, the process is more unfavourable when the quartz is above 5 per cent, on account of a scorification which then takes place at the lower temperature employed. A certain amount of pyrites, on the one hand, augments the residue, but, on the other hand, it assists the formation of sulphate of lead; zinc blende has a favourable influence, as the oxide of zinc formed during the roasting enters into combination with the silica. Blende also acts mechanically by stiffening the mass and facilitating the roasting. The production in French furnaces is smaller than in English furnaces, and the dimensions are less. The form is also somewhat modified, and the hearth furnished with a sump.

At Poullaouen a mixture is worked consisting of galena poor in silver, raised in that neighbourhood, t and ores from Huelgoet rich in silver, containing on the average 54 per cent of lead and 2 ounces of silver in a cwt. These are also accompanied by pyrites, argentiferous zinc blende," and quartz.

The reverberatory furnaces represented by Figs. 17 and 18 are either heated with coal or with wood; in the former case the grate is raised higher, and the fire-bridge is made smaller. The furnace is first furnished with a clay hearth, and after this has been gradually dried for about 2 months, and carefully warmed, a charge of 10 cwts. is given for the purpose of saturating the hearth with sulphide of lead. After

BEAUMIER ET GALLOIS, Journ. des Mines, xvi., 193; KARST. Arch., 1. R., vi., 161. Journal des Mines, xiii., 272 ; xx., 419. Ann. d. Min., 1 sér., iii., 549; vii., 21; 3 sér., xviii., 161; 4 sér., iv., 331. ERD., J., f. ök. u. techn. Ch., xiii., 197. KERL, B. u. h. Ztg., 1854, p. 178. KUTCHER, ibid, 1859, p. 341. RIVOT, c. i., 611, 620, 630.

+ BERTHIER, Analyt. met. Ch., ii., 629. COTTA, Erzlagerstätten, ii., 429, 685, 687.

429.

DAMOUR, in Ann. d. Min., 3 sér., xvii., 19. COTTA, Erzlagerstätten, ii.,

B. u. h. Ztg., 1862, p. 9.

24 hours that which has not been soaked into the hearth is removed, and higher charges are added, which yield more and more lead, until with the 9th charge the furnace has obtained the full quantity, amounting to 26 cwt. With the 13th to the 15th charge the yield of crude lead begins to be regular, and the furnace is now in the proper state for production. Each charging takes about half an hour, two-thirds of the ore being put before the fire-bridge and one-third at the back. In about 1 hours a crust of sulphate of lead, 1 to 2 inches in thickness, is formed, indicating the beginning of the first period of the roasting. On lowering the temperature to dull redness, the second period, which is the real roasting, begins; when this takes place the crust is broken up and mixed with the mass beneath, which is now continually turned over.

After a crust has again been formed and mixed up with the mass, to facilitate the formation of sulphate of lead, the charge commences to cake together, and drops of lead

appear, formed, as in the Carinthian process, by the reaction of the sulphide of lead upon the sulphate. This completes the second or roasting period, which occupies about 4 hours. The third period, the production of crude lead, is now commenced by throwing in pieces of wood, reducing the oxide to metallic lead, which flows into the sump. If necessary, the roasting mass may be previously rendered. more pasty by mixing it up with coal slack. The contents of the furnace are now thoroughly worked up with wood by the different working doors, till after a lapse of from 4 to 5 hours the sump is filled up with lead. The latter is then tapped off, and before running it into moulds is purified by stirring it up with pieces of wood. The temperature is now raised again, and the mass is stirred up and mixed with wood, until after a lapse of hours the crude lead is tapped a second time. The operation is then repeated a third time. Lastly, the ore which had been put at the back is drawn to the front of the fire-bridge; the temperature is then raised, and the last yield of lead results. In 16 hours from the beginning of the operation, those residues which are not required for the repair of the hearth are removed; they contain from 20 to 30 per cent of lead and th oz. of silver, and are smelted in a small cupola furnace 5 feet in height, or in a reverberatory furnace, together with other lead products, 10 per cent of iron, and argentiferous iron ore and quartz from Huëlgoet, producing crude lead with about 8 ounces of silver. 84 cwts. of such mixture are worked in a reverberatory furnace in 24 hours. The cupola furnace produces less lead, but gives poorer slags, and occasions less loss by volatilisation.

The lead fume containing from 38 to 40 per cent of lead and oz. of silver, is treated in reverberatory furnaces of the ordinary construction; the 4 hours' roasting period is, however, not required. 16 cwts. of fume are worked in 12 hours. From 15,000 cwts. of ore, which are usually treated in a reverberatory furnace, there are obtained on an average 225 cwts., or 1 to 2 per cent of fume.

The hearth of the reverberatory furnace is removed every 1 years, and added in mixture to the ore smelting in cupola furnaces.