considerable amount of protoxide of iron they contain acts advantageously in smelting the siliceous ores. The raw matt, being rich in iron and containing valuable metals, is a useful flux in the lead smelting process.

The present mode of working up the lead slags combines the advantages of giving a better yield and of allowing the time which was formerly required for the re-smelting of the slags to be used for the working of a larger quantity of ore.

If impure slags result from the ore smelting, the amount of metal they contain is extracted by the subsequent smelting in reverberatory furnaces, and the yield of the first process may therefore be increased without disadvantage. As the slags are completely worked up, an exact calculation of the cost of the different processes is possible.

The lead slag process allows a decrease of the expensive raw smelting, and an increase of the lead smelting process, as the earthy silver ores which were formerly used in raw smelting are more extensively worked in lead smelting.

The Raw Smelting Process comprises the following manipulations:

a. Roasting the Flux Ores. As part of the flux ores contain much blende, they are roasted either in an English reverberatory furnace or in a double furnace. In the former, 30 cwts. are roasted in 8 hours, in order to avoid an impure smelting, and to produce less matt with a suitable amount of metal; the reverberatory furnaces, constructed like gas furnaces, consume 10 cwts. of coal and 9 cwts. of cinders, and the English furnaces with a direct firing, 18 cwts. of coal in 24 hours. Two workmen attend to the furnace in shifts of 8 hours. The roasted mass must not contain more than 4'5 per cent of sulphur.

b. The Smelting of Raw Matt is conducted in reverberatory furnaces, as represented by Figs. 54 and 55; a, is the foundation; b, the cast iron plates; c, the pillars; d, mantle; e, fire-place; f, grate, consisting of 13 grate bars each 2 inches square; g, opening for charging the fuel, 16 inches high; h, fire-bridge; i, channel for cooling; k, refractory coating, consisting of 3 parts quartz and 1 part clay, 12 inches high;

1, arched roof of the furnace; m, bottom made of bricks; n, bottom formed of quartz and clay; o, channels for the admission of air; p, working door, 12 inches square; q and r, side openings; s, tap opening; t, opening for charging the furnace; u, support for the tools, coated with a lubricating mixture of oil and graphite; v, support for tools used for lifting the grate; w, flue; x, chimney, 66 feet high. The slope of the hearth from the fire-bridge to the tap-hole, s, is from 5 to 6 inches. The opening in the arch for the flue is of trapezoidal section, 11 inches broad, 2 feet 8 inches long on the back, and 14 inches long on the front towards the working door.

The body of the furnace, n, consisting of a refractory mass, is covered with a mixture of 5 parts of quartz and I part of raw slag, and the hearth is formed by burning it; then the first charge only of lead slags is given, that the hearth may

attain greater solidity. By means of the movable charging funnel, charges of 20 cwts. of lead slags, 5 cwts. of raw and 5 cwts. of roasted flux ores (or sometimes instead of the roasted ore, pyrites previously burned in heaps or in the manufacture of sulphuric acid), are now added in such a way that the ore lies on the top of the slags; 1 or 2 cwts. of quartz are also added if necessary. The roasting mass is then spread out upon the hearth in such a manner that the layer is somewhat higher near the fire-bridge, and is smelted in 2 hours, when the grate is cleared and the fire stirred for about half an hour; the atmospheric air is excluded as much as possible during the whole process. The liquid mass is then stirred and again heated by a fierce fire for about a quarter of an hour, whilst the working door is kept closed; then the slag is drawn out from the working door. The slag first runs into moulds of sand upon the floor of the smelting house, and thence into moulds of cast iron, 2 feet long and I foot broad and high. By letting part of the new charge

pass over the hearth, the slags accumulate against the working door, and thus they may be more perfectly removed. After having treated two more charges in a similar manner (two or three times in 24 hours), the raw matt produced is tapped off, by s, into iron moulds 4 feet long, 18 inches broad, and 10 inches deep; the tap-hole is then closed, the firebridge and hearth repaired with a mass consisting of five parts of refractory clay, and two parts of quartz, and the smelting process is re-commenced. In operations of about twelve months, in twenty-four hours about 5 tons of slate coal are consumed for the production of

a. 2 tons of Raw Matt, containing from o'15 to 0.20 lb. of silver, 8 or 10 lbs. of lead, and 4 or 5 lbs. of copper per cwt.; if the matt contains a greater amount of zinc blende, it has a granular, laminated, black fracture of some lustre, and possesses a certain solidity and density, in consequence of which it is difficult both to roast and to fuse. Some powdered coke and fluor spar were formerly added before the tapping off of the matt, with very good effect, the coke then reducing some peroxide of iron from the roasted flux ores, and the reduced iron extracting some zinc which became volatilised; the fluor spar assisted the formation of slags. But as this treatment both prolonged the smelting process and caused a greater consumption of fuel, also, as the slag became pasty, rendering the separation of the matt more difficult, and as greater loss of lead and silver took place, it was abandoned, and the attainment of a purer reverberatory furnace matt has been attempted by a more perfect roasting of the flux ores. Sometimes the raw matt has a certain amount of slag and per- and protoxide of iron mixed up with it.

The reverberatory furnace raw matt is composed, according to an analysis by Richter, of 53.81 per cent of iron, 7.65 per cent of tin, 7'35 per cent of lead, 3'87 per cent of copper, 0.84 per cent of arsenic and antimony, 23'43 per cent of sulphur, and 2.11 per cent of silica.

These matts are compounds of FeS with more or less Fe2S and PbS, Cu2S, ZnS and AgS, and are sometimes mixed with (Fe, Ni, Co), As.

The matt must be crushed into pieces the size of the fist, and roasted in mounds before it is in a condition to be used. Well roasted raw matt has a greyish black, dull appear

ance.

b. Furnace Hearth.-This is worked up in the lead smelting process.

c. Slags containing on an average 1 lb. of lead and 0'002 lb. of silver per cwt. These are mixtures of monoand bi-silicates. They are either thrown away or are moulded into bricks of 3 cwts. each for building purposes.

Such a slag from the Halsbrückner smelting works was, according to Richter, composed of 36'04 per cent of silica, 5:38 per cent of alumina, 42'60 per cent of protoxide of iron, 6'29 per cent of lime, 171 per cent of oxides of magnesium and manganese, o°24 per cent of sub-oxide of copper, 134 per cent of oxide of lead, 4'66 per cent of oxide of tin, and 1'47 per cent of sulphur.

In the year 1859, 23,220 tons of ores (amongst them 130 tons of foreign ores), containing on an average o*1291 lb. of silver per cwt. were worked at the smelting works near Freiberg. They yielded 23°5655 lbs. of fine gold, 605460070 lbs. of fine silver, 1578 2824 cwts. of refined copper, 297 cwts. of copper vitriol, 32 cwts. of mixed vitriol, 27'475 cwts. of assay lead, 5152176 cwts. of soft lead, 4120'6 cwts. of hard lead, 4900 4 cwts. of red litharge, 7697'04 cwts. of yellow litharge, 709 58 cwts. of black litharge, and 3'15 cwts. of lead smoke. In the manufacture of sulphuric acid there were produced: 1236'72 cwts. of sulphuric acid, 887.71 cwts. of iron vitriol, 8.35 cwts. of arsenical sulphur, 255'35 cwts. of raw chamber acid, and 3'40 cwts. of lead pan acid.

At the silver smelting works in Lower Hungary the ores used are silver ores (silver glance, and more rarely red silver ore and native silver) and lead ores. The matrices consist of quartz, clay, limestone, zinc blende, manganese, spar, iron pyrites containing gold and silver, copper pyrites very seldom, and in some cases sulphide of antimony. There is more quartz than lime.