and the composition of the slag roasted ore is given in Table XIX. (p. 125).

The roasted ore is smelted in small rectangular blast furnaces together with iron fluxes (puddle cinder and hæmatite ore) and limestone. Besides a work-lead of great purity containing only 6 ozs. silver per ton (which is afterwards recovered by the Parkes process) a small quantity of matte is formed which is roasted in stalls and added to the ore charge. The composition of the slag, matte, and work lead is given in Tables XXVI., XXIV., and XXIII. respectively.

Goslar (Lower Harz). At the Sophienhütte and Juliushütte, ores from the celebrated Rammelsberg mine are treated. The heap roasting of these ores has been described in Chapter vii., and the leaching out of zinc sulphate is referred to in Chapter xiv. The composition of raw and roasted ores is given in Tables XII. (p. 75) and XIX. (p. 125).

The ores are deficient in silica for fluxing the bases, and being so high in zinc even after leaching of the fine portion require the addition of more iron in order to form the double subsilicate ZnO.2FeO.SiO.. Both these conditions are satisfied by the use of basic ferruginous slags from the Oker copper works near by, containing 17 to 21 per cent. SiO,, 66 to 70 per cent. FeO, and 1 to 2 per cent. Cu. To every 60 tons of roasted and leached fine ore is added 40 tons of unleached lump ore, 25 tons of ferruginous copper slag, and 20 or 30 tons of foul slag from the same process. The water tuyere furnace employed is that figured and described in Chapter viii.; it is blown by five 2-inch tuyeres, supplied with air under a pressure of 10 to 13 ozs., and puts through in twenty-four hours about 10 tons of ore (14 or 15 tons of charge), with a coke consumption of 15 per cent. of the weight of charge.

The products are work-lead with 32 ozs. silver per ton, matte containing all the copper and a small part of the lead and zinc, clean slag which is thrown away, and foul slag (2 per cent. of the whole) containing 5 to 7 per cent. lead as shots of matte. The composition of the clean slag is given in Table XXVI. (p.210). A flue dust rich in zinc is also produced, the composition of which is given in Table XXXI. (p. 238); this is worked up by leaching with sulphuric acid and crystallising out the white vitriol. The matte is once roasted in heaps and re-smelted together with the foul slags from the ore smelting, and fresh copper slag from Oker, yielding a small quantity of enriched matte, work-lead, and a clean slag with only to per cent. lead which is thrown

away.

The slags produced at these works are of a most unusual composition. Schnabel quotes the following analysis of an exceptional slag produced in 1897, viz. :-SiO, 12.87, Al,O, 3.12,

2

* Handbuch der Metallhüttenkunde, vol. i., p. 389.

BaO 23:40, CaO 210, MgO 072, FeO 20-64, Zn 2025, Pb 077, Cu 0.87, Mn 148, S 6.40 92.62. It is not easy to see the mode of combination of the above slag, but probably the Mn was as MnO, and the Zn partly as ZnO, partly ZnS, while the Ba was partly as BaS, but chiefly as BaSO4.

Clausthal (Upper Harz).-At Clausthal and Lautenthal is to be seen at work the only surviving example of the old precipitation process by which raw lead ores in a fine condition are charged into a blast furnace together with iron ores and slags. By the use of a high furnace and a small quantity of low pressure blast, the temperature before the tuyeres is kept high, while the rate of smelting remains low; sufficient metallic iron is reduced to partially decompose the sulphide of lead, producing metallic lead and an iron matte which takes up the undecomposed lead sulphide. It has been already noted that this reaction generally comes into play more or less in the ordinary blast furnace reduction process when sulphide lead ores are present in the charge, but at Clausthal it is the sole reaction relied upon. By this slow rate of smelting the consumption of fuel is very high, and the labour cost per ton smelted is also much greater than in the roast and reduction process; while, allowing for the subsequent roasting of the matte, it can hardly be said that the saving of roasting on the ore is a sufficient offset to these disadvantages.

Both circular and oblong furnaces are employed in the precipitation process in the Upper Harz, the latter being a modification of the Raschette furnace, and the former from the Pilz, with a good many modifications. The circular furnace used has been already figured in Chapter viii.; the pressure of blast under which it works is from 7 to 8 ozs.

The average composition of rich dressed Clausthal ore is given in Table XII. (p. 75), somewhat poorer ores containing only 50 per cent. lead, and up to 30 per cent. of insoluble residue. The average ore mixture contains, for every 100 tons of this ore, about 200 tons of other material made up somewhat as follows::50 tons roasted ore matte, 50 tons matte slag (from the next operation), 80 tons ore slag from the same furnace, 5 tons of leady residues and drosses, and 15 tons of burnt pyrites, tap cinder, and similar iron fluxing materials. Formerly, the quantity of ferriferous slags used was much larger, but now reliance is chiefly placed on roasted matte as a means of supplying the iron required for combining with the sulphur of the ore.

The total quantity of the above mixture passed through a round furnace, of the dimensions shown in Fig. 56 (p. 143), with a blast pressure of 6 to 8 ozs., is about 10 to 11 tons, corresponding to only 3 tons of ore. The consumption of coke is about 13 per cent. on the whole charge or 40 per cent. on the ore, and three men are required on each twelve-hour shift-viz, one smelter,

one feeder, and one slag runner. The slag flows continuously, lead and matte being tapped together from time to time, the matte cake being lifted from the still melted lead as soon as set. For every 60 tons of lead set free about 65 tons of matte are produced. The composition of lead, matte, and slag are given respectively in Tables XXVIII. and XXIX.

The working up of the matte consists of a series of alternate roastings and smeltings. The roasting in heaps at Clausthal and in kilns at Lautenthal has been already referred to in Chapter x. The smelting takes place in small square masonry furnaces of antique pattern, with one or two tuyeres in the back. The roasted matte is smelted together with 140 per cent. of ore slag, and the coke consumption is 20 per cent. of the weight of matte or 8 to 9 per cent. of the weight of charge. The small quantity of work-lead produced is richer in silver than that produced direct from the ore, containing 70 ozs. silver per ton as against about 48 ozs. A second roasting and smelting produces a third lead and enriched matte; while a third roasting and re-smelting gives no more lead, but only an impure black copper with 30 per cent. of lead. The two (sometimes three) following roastings and smeltings give further quantities of purer black copper, but the matte continues about the same in percentage--viz., between 57 and 60 per cent. Cu.

The following table shows the weights of lead, matte and black copper obtained at each successive concentration smelting, beginning with 1000 tons of ore (to which are added in the ore furnace 500 tons of roasted matte and 1500 tons of fluxes and slags) :

The following tables, compiled from data quoted by Schnabel,* give the analyses of slag and matte obtained from each concentration smelting, the original matte and ore slag being added for comparison :

* Op. cit., pp. 406 to 413.

TABLE XXVIII.-MATTE ANALYSES (CLAUSTHAL).

TABLE XXIX.-SLAG ANALYSES (CLAUSTHAL).

1st or Ore 1st Matte 2nd Matte 3rd Matte 4th Matte 5th Matte

Comparing the above series of operations with the ordinary modern processes by which lead matte, in only two operations, is converted into a rich copper-silver matte and an impure silver lead, it is evident that there is unnecessary complication here, even allowing for the fact that only a small part of the original matte treated has to undergo the concentrations from No. 2 onward. While at Clausthal there may possibly be something to be said for the retention of the precipitation process in

preference to roasting the ore direct, there can be no valid reason why the treatment of matte (up to the point where silver extraction commences) should not be cut down to two or, at most, three concentrations instead of five, as above. The last of the three concentrations could be made to yield "pimple regulus," as at Freiberg, or a "black copper," if it were preferred to adhere to the Oker process of silver extraction. Altogether, the series of operations seems too complicated, and will probably ere long give place to more modern and direct methods.

AUSTRIA-HUNGARY.

Przibram (Bohemia).-This is the largest individual metallurgical centre of the Austro-Hungarian empire. An analysis of the ore treated is given in Table XII. The roasting furnaces, twelve in number, are figured and described in Chapter vii. An average sample of the ore as roasted contains 34 per cent. lead and 0.260 per cent. (85 ozs. per ton) silver, while, after roasting, the sulphur contents do not exceed 1 per cent., the proportion of copper being so small that there is no need to leave sulphur in the roasted ore to protect it from being carried away in slag.

The roasted ore is mixed with fluxes (tap-cinder, roasted pyrites, and limestone) in the proportion of 37 tons fluxes to 100 tons of ore. It is smelted in seven round water-block furnaces (described in Chapter ix.) with eight 24-inch tuyeres supplied with air at 13 ozs. pressure. In twenty-four hours 22 tons of ore are put through, or a total of 31 tons of charge, the fuel consumption being 16.4 per cent. coke and per cent. (1 bushels per ton) of charcoal.

The work-lead produced contains about 150 ozs. silver per ton. The matte is very small in quantity, and is returned to the ore furnace after roasting in the stalls described in Chapter x. The clean slags containing under 1 per cent. lead and 2 oz. silver per ton are thrown away, a large part being, however, utilised for the manufacture of slag brick. Foul slags containing more than the above-mentioned proportions of lead and silver are returned to the furnaces. Analyses of work-lead, matte, and slag are given in Tables XXIII., XXIV., and XXVI. respectively.

SPAIN.

Of late years several large establishments have been erected in this country to work fusible lead ores together with old slags, the furnaces and the work generally following the German system of large round furnaces, with re-treatment of slags in the same furnace.

Mazzarron, near Cartagena.—At this establishment, which turns out over 20,000 tons of lead annually, three large round