88 lbs. of poor lead. The cost of working 5 tons of raw lead is

When worked in cupelling and reducing furnaces the same quantity of raw lead occasions a loss of 9 per cent of lead, and costs £3 17s. 9d.; and thus the higher yield of lead by the former process (5 per cent) has to balance the extra expense of £3 3s. 8d. This is exactly effected when the market price of lead is IIS. 3d. per cwt. As in the year named the average price was 17s. 5d., Pattinson's process allowed a saving of £1 15s. 6d. upon every 5 tons treated by it. Eight workmen work during the day, and eight during the night; the 16 workmen are paid 6·24d. for each cwt. of poor lead they produce; two assistant workmen are allowed for the day and night, each receiving Is. 3d. for a shift of 12 hours. Those 16 men attend to 14 pans in 24

hours.

At Munsterbusch,* near Stolberg, the raw lead containing o'02 per cent of silver is refined in reverberatory furnaces. About 13 tons are refined in 30 hours at a low red heat, air being admitted, and some powdered lime and small coal being thrown now and then upon the surface of the lead, the dross formed is skimmed off from time to time, and the purified lead is poured into moulds. The consumption of coal in 30 hours amounts to about 27 cubic feet.

The refined lead is submitted to Pattinson's process in batteries of 13 pans, arranged like those of the Upper Hartz, and the lead is charged according to the silver it contains, either in the 5th or the 6th pan, but mostly into the 6th. The loss of lead amounts to 3 or 3 per cent, the lead is enriched up to 1 per cent, and 2 tons of coal are consumed in 24 hours, during which time from 20 to 25 pans are dipped out. The charge of each pan is from 12 to 12 tons. The cost

* B. u. h. Ztg., 1858, p. 300.

for enriching 1 ton of lead originally containing o'019 per cent of silver, up to an amount of 0.36 per cent of silver, is about IIS Iod.

At Tarnowitz,* the raw lead containing o'0986 per cent of silver is treated in a battery of 14 pans, charging 12 tons in the fourth pan. It is enriched to 12 per cent, and the poor lead then contains only o'oo1 per cent. On the 3rd of June, 1862, the single pans contained nearly the following amount of silver, in grammes per cwt. :I. 0'75 II. 0'44 III. 0.268 IV. 0151 V. 0'0745 VIII. 0.026 IX. 00145 X. 0·0076 XI. 0'0048 XII. 0'0028 XIV. 0'0010

VI. 0'05

VII. 0.035 XIII. 0'002

This condition is sustained by a continual assaying and a careful superintending of the process, and also by adding the rich third of the fifth pan to the third pan, instead of the fourth, if the room in the pan will allow it. From 5 tons of raw lead were produced

18.15 per cent of rich lead, containing 1.2 to 1'433 per cent of silver.

59°52 per cent of poor lead, containing o'oor per cent of silver, and 11'375 specific gravity at 18°.

21 27 per cent of lead skimmed off.

The loss of lead by Pattinson's process and by the reduction of the dross skimmed off is 12 per cent, and the yield of silver is 12 per cent larger than that obtained by the cupellation assay. 5 tons of raw lead consume 21'7 cwts. of coal. 21 workmen assist at one battery, and they are paid 3'48d. per cwt. of poor lead produced; out of this payment they must keep three assistants, and pay sundry items for the weighing and marking of the lead, &c. 5 tons of commercial lead cost £1 7s. 6d. for labour, 6s. 7.9d. for coal; total, £1 14s. 1'9d. The cost for I cwt. of such a lead is therefore 4'2d.

The dross from the pans, containing 88 per cent of lead and o'102 per cent of silver, is reduced in a reverberatory furnace, and the resulting raw lead again submitted to

* B. u. h. Ztg., 1864, p. 317.

Pattinson's process. 5 tons of this dross yield 90*36 cwts. of raw lead, and 9.30 cwts. of reduction slag, containing 58 to 59 per cent of lead and o'006 per cent of silver.

This slag is worked in cupola furnaces 16 feet high, mixed with 7 per cent of iron, 53 per cent of iron refinery cinders, and 12 per cent of limestone, and yields about 54'5 per cent of raw lead, containing o'015 per cent of silver, which is concentrated by cupellation.

A comparison of Pattinson's process with the process of cupelling and reducing formerly used, as far as regards the expense of producing five tons of commercial lead, may be drawn from the following table :—

B. Cost for Cupelling and Reducing, including Working up the Intermediate Products resulting from both Processes.

At some English lead works,* raw leads, sometimes not containing more than 3 ozs. of silver per ton, are treated according to the high system; they are first refined in reverberatory furnaces; the charges are from 6 to 10 tons, and the lead is

* DINGLER'S Polyt. Journ., Bd. 65, p. 386. TUNNER'S Leobener Jahrb., 1852, p. 143. B. u. h. Ztg., 1859, p. 433; 1862, p. 296. Berggeist, 1861, p. 338.

enriched up to from 160 to 600 ozs. per ton (0°48 to 18 per cent), the poor lead containing not more than from 15 to 7 dwts. of silver per ton (=0'0027 to 0'0015 per cent).

The cost of crystallising one ton of calcined Spanish lead is as follows:

Illustrations of the High System of Working with Intermediate Crystals.

In England* batteries of 9 pans are used for this system of crystallising lead containing about 10 ozs. of silver per ton. It is charged into one of the medium pans; 4 or 5-14ths of the crystals of the charge, containing about 5 ozs. of silver, are dipped out and put into the pan on the left, then 4 or 5-14ths of intermediate crystals containing 10 ozs. of silver are put on to the edge of the pan, and the last 3 or 4-14ths of liquid, containing 20 ozs. of silver, are put into the enriching pan on the right. After this the lead from the edge of the pan is put back into the charging pan, which is filled up again with fresh lead. The process is then continued in this way until the first two side pans are ready for dipping out, and in this manner the crystallisation is carried on till poor lead, containing oroz., and rich lead, containing from 200 to 400 ozs., result.

At Halsbrucke, near Freiberg, leads containing up to o'60 per cent of silver are submitted to Pattinson's process in batteries of 14 pans and charges of 10 tons. In the high system as commonly adopted, 6 tons of crystals and 3 tons of liquid are dipped out; if forming intermediate crystals, 6 tons of crystals, 2 tons of intermediate crystals, and I ton of liquid are dipped out up to the 8th pan; from the other pans 7 tons of crystals, 2 tons of intermediate crystals, and I ton

* TUNNER'S Leobener Jahrbuch, 1852, p. 143.

of liquid are taken. To prevent the state of the battery upwards from becoming too low, the intermediate crystals are not usually strained so much. The state of the battery downwards becomes poorer with intermediate crystals, the same as when adopting the common high system; this is shown by the following table :

0'0015

14

0'0029

14 99 The proportion of alloy, intermediate crystals, and liquid is, for instance, I : 1'4: 3; 2'25: 26: 72; 13'7: 19: 35'7. The rich lead contains from 1'50 to 1.68 per cent of silver; the poor lead o'003 to 0'0025 per cent.

The following experiments with 250 tons of lead containing 0'023 per cent of silver, comparing the effect of the high system with and without intermediate crystals, are of great interest :