Figs. 37, 38, 39, 40, and 41 represent the furnaces used at the Upper Hartz for reducing litharge, and will be referred to when that process is treated of.

A porous nose about 12 or 18 inches long is used in the precipitation process. One charge consists of 2 or 3, or alternately 2 and 3 troughs of mixture 60 lbs. and coal 25 lbs. ; the furnaces at Lautenthal are made somewhat wider on account of the blende with the ores.

The following are the smelting products :

1. Raw Lead.-This is either treated by Pattinson's process for the production of a very pure lead (Altenau), or directly cupelled for extracting the silver.

The raw lead from the Upper Hartz contains, according to analyses by Jordan, from 95'97 to 99'00 per cent of lead, 0'40 to 0.76 per cent of copper, o'28 to 2.96 per cent of iron, 0'20 to 346 per cent of antimony, and o'11 to 0.18 per cent of silver. Such lead from Pontgibaud contained 91'1 per cent of lead, o'7 per cent of copper, 6'7 per cent of arsenic, and 1'0 per cent of sulphur.

2. Lead matt.-The following analyses have been made of different lead matts from the upper Hartz.

A matt from Clausthal contained 73°346 per cent of lead, 9.814 per cent of iron, o'396 per cent of copper o°198 per cent of tin, o'397 per cent of antimony, o'116 per cent of silver, 15.338 per cent of sulphur, and a trace of carbon. A matt from Lautenthal contained 59°33 per cent of lead,

19.60 per cent of iron, 1'10 per cent of copper, o'17 per cent of tin, o'13 per cent of antimony, and 18'92 per cent of sulphur. A matt from Andreasberg contained 35.68 per cent of lead, 31′55 per cent of iron, 3'79 per cent of copper, 1'49 per cent of antimony, 23'97 per cent of sulphur, o'25 per cent of manganese, and 1'07 per cent of arsenic.

For the composition of these matts different formulæ have been suggested.*

Lead matt is roasted under cover, in heaps about 24 feet long, 16 feet broad, and 5 to 6 feet high, put upon a thick layer of pine wood laid down for the foundation, for about 3 or 4 weeks. The matt has to be broken into pieces of about the size of the fist for this purpose. After this first roasting it is put into a second fire for two weeks, then into a third for 8 or 10 days, and in two more for shorter periods, till the matt has been sufficiently freed from sulphur. 5 tons of matt require for the different roastings about 120 cubic feet of pine wood = 75 cubic feet solid wood = 1,912 lbs.

The roasting mass is then mixed with schlich slags, matt slags, products containing lead and iron (Clausthal) or lime (Altenau); at Lautenthal no iron is added to the first smelting of the roasted matt, but to the following smeltings instead; at Andreasberg no iron is added.

The reducing and purifying smelting is intended to reduce the oxide of lead contained in the roasting mass, and to decompose sulphate and sulphide of lead by the iron which has either been added, or extracted from the matt slags by the reaction of the lime, aided by the fuel. The foreign oxides, chiefly oxide of iron, become scorified by the acid ore slags; the metal must also be extracted from the furnace products containing lead.

The mixture for I charge of matt at the first smelting is composed as follows:

POGGEND., liv., 271. HAUSMANN, Beitrage zur metallurgischen Krystallkunde, 1850, p. 10, 12. LEONHARDT, Hüttenerzeugnisse, p. 383, 340. GURLT, pyrog. min., p. 22, 37. RAMMELSBERG, Mineralogie, p. 177. POGGEND. Annalen, 1858, No. 3, p. 526. Jahrbuch des Vereins fur Naturkunde in Nassau, 1851, p. 133. B. u. h. Ztg., 1860, p. 52. ERDMANN'S Journal für practische Chemie, 1859, hft. 1. Polytech. Centr., 1858, p. 1161.

Low cupola furnaces (Krummofen) are used for smelting the matt; those at Clausthal are 8 feet 7 inches high, those at Lautenthal are nearly 2 feet higher, and at Andreasberg they are only 5 feet high.

The resulting raw lead is treated by the cupelling process; the matt is again melted two or three times, being each time previously roasted. At the third or fourth smelting a copper matt is obtained, containing 20 to 36 per cent of copper and o'06 to o'1 lb. of silver. This is then worked by a separate process (Kratz copper process) for the extraction of its metals.

The resulting matt slags are more basic than the ore slags. The following analyses will show their composition :—

Proportion of Oxygen between SiO3

SiO3. CaO. Al2O3. PbO. FeO. Cu2O. MnO. KO. MgO. S. and bases.

trace o'05

I. 32:34 2:07 5'06 10'01 43'90 0'05 I'20 0'05
2. 33.58 3'57 4:46 6.19 44'44
3. 39'79 2.12 trace 917 46'44

16.80 13.89 23.09 trace 20.68 11'57

II 12

3. Lead Fume.-An analysis of this is given on page 24. From the schlich smelting at Clausthal and Altenau 7 or 8 per cent of smoke result, at Lautenthal 10 or II per cent, and at Andreasberg o'8 to 1 per cent. This smoke is smelted together with dressed scum containing o'10 to 003 lb. of

silver and from 35 to 40 per cent of lead, in schlich furnaces, when combined in the following way :—

At Clausthal, 36 cwts. of smoke, 9 cwts. of scum, 12 cwts. of roasted matt of the smoke smelting, 3 cwts. of iron, 5 cwts. of plumbiferous fluxes, 45 cwts. of schlich slags, and 6 cwts. of hard lead slags; at Altenau, 54 cwts. of smoke, 18 cwts. of scum, 13 cwts. of roasted matt of the smoke smelting, 4 cwts. of iron, 3 cwts. of plumbiferous fluxes, 28 cwts. of schlich slags, and 20 cwts. of matt slags; at Lautenthal, 30 cwts. of smoke, 6 cwts. of scum, 2 cwts. of iron, 6 cwts. of plumbiferous fluxes, 26 cwts. of schlich slags, and 29 cwts. of matt slags; at Andreasberg, 36 cwts. of smoke and scum, 2 cwts. of iron, 12 cwts. of plumbiferous products, and 73 cwts. of matt slags.

The consumption of coal at Clausthal amounts to 230 cubic feet; at Altenau, to 350 cubic feet, and Lautenthal to 186 cubic feet, and at Andreasberg to 250 cubic feet; and the yield of raw lead at Clausthal to from 16 to 20 cwts., at Altenau to 18 cwts., and at Lautenthal to from II to 12 cwts.; and that of matt at Clausthal to from 15 to 19 cwts., at Altenau to from 18 to 19 cwts., and at Lautenthal to from 12 to 13 cwts.

II per cent of the lead fume escape reduction by being again volatilised during the smelting.

4. Plumbiferous Deposits are usually roasted and smelted at the end of the schlich operation, mixed with iron slags. According to Metzger* the deposit from the furnaces at the Upper Hartz consists of

PbS 95'5

FeS ZnS
3'2 trace

SbS,

2.5

AgS trace.

5. Speiss is sometimes produced in smaller quantity, as at Andreasberg.

6. Furnace Ends are dressed and worked together with smoke or by themselves.

7. Schlich Slags are worked up again or used for the construction of cupola furnaces, and sometimes even formed into bricks and employed for building purposes.

* B. u. h. Ztg., 1853, p. 238.