7G6
LEAD.
The quantity of small coal mixed with the litharge should be somewhat less than whatmay be necessary to effect the reduction, because if in the course of the process a defi-ciency of it is perceived in any part of the furnace, more can always he added; whereasa redundancy of coal necessarily increases the quantity of slag, which, at the end of theshift, must he removed from the furnace before a new operation is begun, whereby leais lost. In the reverberatory furnace, six fodders of lead may be revived in nine or tenhours; during the first six of which the mixture of litharge and coal is added at shorintervals. A fodder is from 21 to 24 cwts.
It deserves to be remarked that the work does not go on so well nor so quick whenthe coal and litharge are in a pulverulent form; because the reduction in this eastakes place only at the surface, the air not being able to penetrate into the body, and tkeep up its combustion, and the mutual action of the litharge and carbon in the interior-But, on the other hand, when the litharge is in porous pieces, as large as a hen’s eg»>the action pervades the whole body, and the sooty fumes of the coal effect the reducti 0even in the centre of the fragments of the litharge, penetrating into every fissure ahcarrying off the oxygen. The heat ought never to be urged so far as to melt tnlitharge. ,.
The grounds of the cupel, and the slag of the reduction furnace, being a mixture 0small coke, coal ash, and oxyde of iron, more or less impregnated with lead, are smeltupon the slag hearth, along with coke, and, by way of flux, with a certain quantity ol 1black scorirn obtained from the same furnace, prepared for this purpose, by runningout in thin plates, and breaking it into small pieces. The lead thus obtained is usual 1 ;very white, very hard, and not susceptible of refinement. ^
MM. Dufrenoy and Beaumont consider the smelting of lead ore by the reverberat ifurnace, as practised in Derbyshire, as probably preferable to that with the slag h ea1 'as carried on in Brittany; a process which seldom gives uniform products, while it ocsions a more considerable waste of lead and consumption of fuel.
The mixed process employed in Cumberland of roasting the ore, and aftenya 1 ^smelting it in a small furnace resembling that called the Scotch, apparently y' e d L,tlittle less lead than if both operations were executed in the reverberatory furnace;according to Mr. Forster (see his Treatise <m a Section of the Strata from N eV!ca t S : 0 nupon Tyne, &c.), this slight loss is more than compensated by the smaller consumP 1 iof fuel, the increased rapidity of the operation, and especially by the much SJ e %epurity of the lead obtained from the Scotch furnace. When it comes to be refined) 1loss is only about one twelfth or one thirteenth, whereas the lead revived in the re l g tberatory furnace loses frequently a ninth. Moreover, the lead furnished by the » fmethod admits of being refined with profit, when it yields only 5 ounces of silv' er *’ efodder of 20 quintals, poids de marc, while that produced by the reverberatory ihrncannot be cupelled unless it gives 10 ounces per fodder; and as in the English lation lead is constantly added anew without skimming, the litharge obtained msecond case can never be brought into the market, whereas the litharge of the l ea “ s ’ e l-the Scotch furnace is of good quality. See the new method of enriching lead for c ”lation, under Silver .
As the smelting of galena, the principal ore of lead, is not a little complex, theing tabular view of the different processes may prove acceptable to the metallurgis
I. Class.Treated in re-verberatoryfurnaces.
Treatment of
Process of
1 .
2 .
3.
A
Desulphura-tion by roast- 4.ing.
5.
B (6.
Desulphura- <tion by iron. (
Ores mixed with ) England, in gen-saline gangues. $ eral.
Ores mixed withseveral sulphu-rets.
Ores with earthy,saline, and sul-phurous gan-gues.
Combined withthe above.
Vienne, Poulla-ouen, and Tar-nowitz.