Illustrations of the Precipitation Process.

In the Upper Hartz,* at Clausthal, Altenau, Lautenthal,+ and Andreasberg, dressed galena containing silver‡ in the form of schlich, and from 40 to 70 lbs. of lead and o'05 to 0'33 lb. of silver per cwt., is chiefly worked. These ores contain earthy minerals in large quantities (calc spar, quartz, baryta, clay, &c.), and less, but still enough to be influential, of metallic minerals (copper and iron pyrites, zinc blende, bournonite, &c.). At Andreasberg the galena is worked together with real silver ores (red silver ore, &c.). The processes at Clausthal and Altenau are very similar. At Lautenthal there are some modifications, as the ores worked there contain zinc blende, and the difference in the process at Andreasberg is caused by the silver ores.

The schlich are so mixed that those principally containing sparry iron ore as their associated minerals are worked together with those having difficultly fusible matrices. They are mixed in such a proportion that the average yield in Clausthal and Altenau amounts to from 54 to 56 lbs. of lead and o'i lb. of silver per cwt., and in Lautenthal from 62 to 64 lbs of lead and from o'og to o'1 lb. of silver. The schlich is smelted with an addition of iron, schlich slags, matt slags, and plumbiferous products.

The iron is used in the form of grains, scraps, and turnings.

Basic lead matt slags absorb silica, and prevent lead from

* Annales des Mines, I sér., vii., 159. Bergmännisches Journal, 1790, 8. stck, p. 97. LAMPADIUS, Hüttenkunde, ii., Thl. 2 Bd., p. 7, u. 229. Suppl. i., 31, ii., 192. ZIMMERMANN'S Harzgebirge, i., 481, ii., 432. JARS, metallurg., Reise, iii., 514. HERON DE VILLEFOSSE, Mineralreichthum nach Hartmann Bd. iii., 4 Abthl., Cap., 2. KARSTEN'S Metallurgie, v., 162. WEHRLE'S Hüttenkunde, ii., 246. HARTMANN, Repertor, der Bergbau und Hüttenkunde, 1840, i., 265. RUSSERGER'S Reisen, iv., 688. KERL, Oberharzer Hüttenprocesse, 1860, 2 Aufl. KERL, Dèr Oberharz, 1852, p. 40. Geschichtliches : B. u. h. Ztg., 1859, No. 2.

+ RIVOT, Métallurgie du Plomb et de l'Argent, p. 450

KERL, Oberharzer Hüttenprocesse, 1860, p. 16. COTTA, Erzlagerstätten ii. 90. V. DECHEN, Statistic des zollv. and nördlichen Dèutchl., i., 756. NOLTE, Uber die Grösse des Eisenzuschlages: Berg und hüttenmännische Zeitung, 1860, p 165. KARSTEN'S Archiv., 2 R., x., 131. KERL, Oberharzer Hüttenprocesse, 1860, p. 362. ZIMMERMANN, Harzgebirge, i., 450. Bergwerksfreund, ii., 265.

scorifying ; they also render the process in the furnaces hotter, and cause a quicker smelting, but not an invariably better yield. Acid schlich slags have a contrary effect upon the process; otherwise the slags serve to prevent any movement of the schlich, and to protect the molten metallic products from oxidation and volatilisation. The blende in the ore at Lautenthal, and the gangue in the silver ores at Andreasberg, necessitate a greater addition of basic slags.

The fluxes, consisting chiefly of oxide of lead, are added to the mixture partly to extract the metal contained in them, and partly to assist the extraction of the silver from the ore (Andreasberg). In these last works the fluxes are given in such quantity that in poor mixtures o'o1 lb. of silver is contained in every 4 to 5 lbs. of lead, and in rich mixtures o'or lb. of silver in every 2 to 3 lbs. of lead.

The following table will show the composition and yield of a mixture containing 36 cwts. of mixed schlich :At the smelting works of Clausthal

Mixture.

36 cwts. schlich with o'10 p. c. of silver and 54 to 56 p.c. of lead.

6 cwts. fluxes with o'008 to o‘0175 p. c. of silver and 57 to 80 p. c. of lead.

12 cwts. schlich slags with o'008 p. c. of silver and 3 p. c. of lead.

34 cwts. matt slags with o'006 p. c. of silver and 1'5 p.c. of lead.

92 cwts., containing 3.6 to 3.7 lbs. of silver and 27 cwts. of lead.

Yield.

19 to 20 cwts. of raw lead with 0.13 to 0.16 p. c. of silver. 16 cwts. of matt with o'07 p. c. of silver and 29 p. c. of lead. 48 cwts. of slags with o'008 p. c. of silver and 3 p. c. of lead. 3 cwts. of fume with o'05 p. c. of silver, and 45 p. c. of lead.

210 cubic feet of charcoal = 14'7 cwts.

10 hours' time for smelting.

£3 cost for smelting. Operations of 8 to 10 weeks.

IO to II hours' time. Operations of 10 to 14 weeks.
At the smelting works in Lautenthal-

36

Mixture.

cwts. of schlich with o'09624 p. c. of silver and 60*55 p. c. of lead.

243 cwts. of hearth with o'0125 p. c. of silver and 68 p. c. of lead.

122 cwts. of fluxes with o'or p. c. of silver and 88 p.c.

of lead.

o'61 cwts. of scum with 0.0025 p. c. of silver and 82 p. c.

of lead.

25.98 cwts. of schlich slags with o'0009 p. c. of silver and 5 p. c. of lead.

32'79 cwts. of matt slags with o'0009 p. c. of silver and 4°5 p. c. of lead.

4'50 cwts. of iron.

103°53 cwts., containing 3'562 lbs. silver and 27'73 lbs. lead. Yield.

15'45 cwts. of raw lead with o'13 per cent of silver.

17.15 cwts. of lead matt with 0'07 p. c. of silver and 41 lbs. of lead.

46 32 cwts. of pure slags with 0.0049 p. c. of silver and 5 lbs. lead.

14'086 cwts. of impure slags with o'0037 p. c. of silver

and 56 lbs. of lead.

o'922 cwts. of soot with o'062 p. c. of silver and 50 lbs. of lead.

Requiring 200 to 210 cubic feet of charcoal.

12 hours' time for smelting. Operations of 4 to 5 weeks.

The consumption of charcoal amounts to about 380 cubic feet. In the smelting works of the Upper Hartz charcoal only was formerly used, but coke is now almost exclusively employed, and with good results. The process is more uniformly carried on, on account of the higher temperature on the hearth given by the coke; the gases escaping from the furnace are also cooler, as less combustion takes place in the upper parts of the furnace. At Lautenthal, where ores associated with blende are worked, a greater formation of fume in the upper part of the furnaces was observed. The furnaces in use are represented by Figs. 32, 33, 34, 35, and 36.

a is the mantle; b, the back wall; c, counters; d, front wall; e, opening of the front wall; f, breast; g, an opening for removing soot, &c.; h, an opening showing the flame of FIG. 33. FIG. 38.

the furnace, so that if anything escapes from the furnace mouth, it may be observed by the smelter working before the hearth of the furnace; i, tuyere arch; k, opening for the tuyere; m, chimney hood; n, channel leading to the smoke chambers; p, mouth of the furnace; q, platform for charging the furnace; r, smoke chambers or boxes; s, openings for removing the smoke; t, foundation; u, sole stone; y, is formed out of loam; z, bottom composed of a mixture of coke-dust and fire-clay.