As the materials are measured instead of weighed, the data of the smelting results are not quite exact. According to the "Preuss. Ztschr." (vii. 226), 5 tons of lead ores, previously roasted with an addition of 10 per cent of lime, are smelted in admixture with 25 cwts. of calcareous oolitic red iron ore, 4 tons of old lead slags, and 3 cwts. of iron. 10 tons of ore yield about 5 tons of lead in 24 hours. The red iron ore gives better results than the refinery cinders formerly used; the addition of metallic iron is intended to lessen the production of matt.

The raw lead with the 0'2 oz. of silver per cwt. is treated by Pattinson's process, which concentrates the amount of silver to 12 or 13 ozs. The lead matt contains as much as 23 per cent of lead. The slags are so poor that they may be thrown away. The metallic fume is added to the mixture of the next operation, and is previously heated till it cakes. The smoke of 2 furnaces produces in 6 weeks about 25 or 30 cwts. of lead. The reduction of the red iron ore causes deposits in the hearth. In the year 1860, 625 lbs. of silver and 1,883 tons of lead were produced.

At Münsterbusch, near Stolberg (Aix-la-Chapelle), the lead ore (Dieplinchen) is associated with calamine, zinc blende, a little iron pyrites, calc spar, and quartz; some galena from Commern, containing 50 per cent of lead and 30 per cent of quartz, is worked; white lead ore is also used in small quantity. The ores are delivered to the smelting works in the form of grains and schlich, and the ores from Stolberg yield when worked alone, a raw lead containing about 1 oz. of silver, whilst from the ores of the Eifel a raw lead is produced containing about oz. in 100 lbs.; the ores contain no copper. The mixture used contains 55 per cent of lead and o'375 oz.

of silver per cwt.

The ores from Dieplinchen are roasted as at Binsfeldhammerhütte (page 63), and those from Commern as described at page 157. From 8 to 10 tons of ore are roasted in 24 hours, consuming 39 cubic feet of small coal and 4 cwts. of coal in lumps, costing about 19s. 6d. The roasting mass contains from 60 to 70 per cent of oxide of lead, and has a vitreous fracture, a greasy lustre, and a completely homo

geneous appearance. According to Eich, it consists of 18.18 per cent of silica, 3.87 per cent of alumina, 2'56 per cent of peroxide of iron, 71.80 per cent of oxide of lead, 1*12 per cent of lime, o 37 per cent of magnesia, and o'49 per cent of sulphur. 5 tons of ore are mixed with 4 tons of iron refinery cinders, and 4 to 5 cwts. of limestone, and are smelted with 24 or 25 cwts. of coke in crucible furnaces with 2 tuyeres; the operation in 1 furnace lasts 2 or 3 weeks; 8 furnaces consume about 55 tons of ore and 15 tons of coke in 24 hours, producing on an average 30 tons of lead; 400 tons of ore yielded 200 tons of lead. The lead is tapped off every 4 hours.

When the process goes on well, the production of lead matt only amounts to about 1 per cent, which is roasted and added to the mixture; if it contains from 3 to 4 per cent of copper it is kept for the purpose of extracting the copper from it. These works, like all the smelting works near Stolberg, have extensive flues for condensing the smoke, which is much poorer in silver than ore with the same amount of lead; the production of smoke is about 1 or 2 per cent; the slags are assayed daily, and if they contain more than per cent of lead they are returned and resmelted. The slag is run into cast iron pots, 14 inches wide and 20 inches deep, which are suspended in two-wheeled barrows; when the slag is sufficiently liquid, the lead and matt, which may be mechanically mixed up with it, will deposit in the pots.

According to F. Osann, these slags are composed as follows: 33°57 per cent of silica, 6·64 per cent of alumina, 54°93 per cent of protoxide of iron, 3°41 per cent of lime, o 28 per cent of magnesia, 2'04 per cent of oxide of lead, o'II per cent of oxide of zinc, and 1'53 per cent of sulphur.

In 1860, the smelting works at Münsterbusch produced 2,683 lbs. of silver and 6,955 tons of lead.

A similar process is carried on at the smelting works in Ramsbeck (Westphalia), which produced in 1860, 2,755 lbs. of silver, 1,957 tons of lead, and 144 tons of litharge.

At the smelting works at Ems,* argentiferous galena is

* COTTA, Erzlagerstätten, ii., 142. ERDMANN'S Journ. f. ök. u. techn. Chem. xiii., 204.

used in the form of schlich, grains, and fragments, associated with blende, sparry iron ore, and a little quartz; the metal contained in the ore varies between 40 per cent of lead and o'35 oz. of silver per cwt., and 65 to 70 per cent of lead and 14 oz. of silver; most of the ores contain on an average about 50 per cent of lead, and o'g oz. of silver per cwt.

The ores are converted into the form of schlich, in order to admit of a better roasting, and the process is carried on in double furnaces, with one hearth lying at the side of the other, and capable of receiving 3 tons in six lots. One lot is brought to the caking state on the fire-bridge, and removed every 4 hours, and a new charge is added on the back of the hearth; from 3 to 3 tons of ores are roasted in 24 hours, consuming 11'5 cwts. of coal, and each furnace is attended to by two workmen, working in shifts of 12 hours; 6 per cent of lead is lost in the roasting.

The roasting mass is mixed with 25 per cent of slags from the puddling and re-heating furnaces, from 75 to 100 per cent of lead ore slags, from 8 to 10 per cent of limestone, and as much metallic iron. More or less sparry iron ore, containing from 5 to 15 per cent of lead, may be substituted for the metallic iron or the ferruginous slags, if desired.

The smelting is effected in furnaces with two tuyeres according to Vogl's construction.

The raw lead from the ore and matt smelting processes is cupelled in quantities of 17 tons, containing about 1.7 oz. of silver per cwt.; 5 tons of raw lead produced in 1861

Scum 6.59 per cent, containing 5.89 per cent of lead. Hearth. 13'41

8.72 81.99

The resulting silver is refined in a small furnace holding 30 lbs. The lead matt is roasted in Hungarian reverberatory furnaces, in order to conduct the gases into a common chimney by means of a flue 500 feet long; the second lead matt, with about 12 per cent of lead, is roasted and re-smelted; its amount of lead is thus reduced to 3 per cent, when it may be thrown aside, for though it contains from 1 to 2 per cent of copper this cannot be profitably extracted.

DIVISION II.

TREATMENT of Oxidised ORES AND PRODUCTS.

Oxidised Ores.

Carbonate of Lead (white lead ore) is usually treated by metallurgical processes differing from those employed for the sulphate. Oxidised ores generally occur together with galena, and are worked with them, either by the common lead process (Ruszberg, Holzappel), or by a modified process (scorification roasting at Commern and Stolberg). In rare cases only is white lead ore worked by itself, either in reverberatory furnaces or in cupola furnaces, according to the richness of the ore, the earthy and metallic gangue, or the price of materials.

REDUCTION OF WHITE LEAD ORE IN REVERBERATORY FURNACES.

Rich ores only are treated in these furnaces, and when the price of coal is not too high; furnaces with a sump or an inclined hearth are used, and a reducing reaction is to be performed; the grate of the furnaces is low down, and the working door is put under the flue to prevent the access of air to the hearth.

The crushed ore is mixed with 7 or 8 per cent of charcoal or coke rubbish, or with 13 or 14 per cent of non-caking coal or brown coal; when charcoal or coke rubbish is used, a finer division of the ore is requisite, as they chiefly act by direct contact with the roasting mass, necessitating a more intimate mixture. Raw fuel developes reducing gases abundantly; these gases permeate the particles of ore, and therefore raw fuel allows the treatment of ores of coarser grain; the reduction takes place quicker and at a lower temperature, and less loss occurs from the escape of ore dust owing to the coarser state of the ore. The coal should be in such large pieces as to evolve gases during the whole period of reduction. Anthracite reacts less upon oxide of lead, and requires a higher temperature.

The ore is then spread out upon the hearth of the furnace,

M

and treated by a reducing flame at a gradually increasing temperature; it is repeatedly turned as long as any lead is extracted; the porous residues are then moved towards the fire-bridge and heated till they cake; this is done in order to avoid a reduction and volatilisation of lead in the upper parts of the cupola furnace in which they are worked up again. Very little lead is extracted during this period. Lime will prevent the caking if no silica is present, and in this case easily fusible slags must be added to replace the silica. Sulphates of baryta and lime are reduced, partly by the caking process and partly by the smelting of the residues in cupola furnaces; the metallic sulphides formed react advantageously in the reduction of oxide of lead, and the oxides of calcium and barium facilitate the formation of slags. Sparry iron ore reacts in the first process like lime, but facilitates the formation of slags; calamine occasions a loss of metal by volatilisation, counteracts the caking, and causes in the smelting process in cupola furnaces the formation of soot and difficultly fusible slags; it also renders the raw lead impure.

The products of the smelting process are-

1. Lead, with more or less silver;

2. Smoke, consisting mostly of fine ore dust;

3. Residues. These are mixed with other lead products (impure litharge, scum, metallic fume, &c.), and ferruginous substances, and smelted in low cupola furnaces.

TREATMENT OF WHITE LEAD ORE IN CUPOLA

FURNACES.

Ore in the form of grains and coarse sand is best worked in cupola furnaces; the schlich is previously mixed with lime and moulded into shape, and the ores are usually mixed with lead products, impure slags, and ferruginous substances. The porosity of the ore and its easy reducibility cause the formation of metallic lead in the upper part of the furnace, and to avoid as far as possible this disadvantage, the smelting process is carried on in low sump or crucible furnaces, in which a suitable pressure of blast produces a high temperature round the tuyere. The mixture then passes quickly before the tuyere, smelts rapidly, and the reduced lead is not