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smelting; processes 



Object of the Composition of the Obes. 



The objects of the sorting and mixing, or composition of the ores, are : 



1st. In order to obtain a quantity of the metal or product (raw lead, raw matt), which experience proves to be 

 most advantageous, and, what often depends upon this, to procure iii the product (i.e. raw lead) a certain definite 

 percentage of silver. 



'.i<\. In order to obtain a good run, in which the earthy constituents of the ore unite in a fusible slag, which 

 would not be the case if each kind of ore was smelted by itself. The weight of one of these mixtures, which are 

 kept ready in the mixing house, is from 2000 to 8000 centners, of which 80 per cent, are lead ores and 30 per 

 cent. Durr ores (including copper ores, if such are present). The amount of lead in such a mixture varies between 

 30 and 40 per cent, of lead ; that of silver, 0.15 to 0.18 per cent. 



Very rich Durr ores are excluded from this composition. They are strewed on the floor of the charge 

 room amongst the other ores, as these latter are used up, and from time to time again sorted and mixed, in order to 

 avoid as much as possible mechanical loss. The separate charges are transferred in wheelbarrows from the ore house 

 to the charge house, and dumped in alternate! thin layers of lead ore, copper ore, and Durr ore on the floor. From a 

 heap thus made the mixer takes vertical slices with a shovel, and throws them together in the form of a cone in some 

 other place. To make the mixing still more complete, this operation can be repeated. This mixed mass is pushed 

 from here in iron cars (railroad cars) over the roasting furnace, and dumped there. The dry stamped ores are 

 moistened before this mixing, in order to prevent the raising of too much dust. 



II. Roasting or Prepabatoby Wobk with the Ores and bomb A.leeadt Formed Products. 



The object of roasting is an oxidation of the metals which are combined with sulphur and arsenic, and a vola- 

 tilization of the above inflammable bodies up to a certain point. A. complete volatilization of these materials is hot 

 intended. The roasting of the lead process charge can be undertaken either, 



1st. In double roast furnaces, or in combined hearth and muffle furnaces. 



3d. Of late years principally in " forward-shoveling" roast furnaces. 



The real roasting space of the double roasting furnaces, or hearth and muffle furnaces, consists of the 

 hearth and the muffle. The hearth is alongside the fire-place, whioh latter consists of grate and ash box, and 

 the fire-place is separated from the hearth by a, bridge made of bricks. The muffle, lies over the hearth, and is 

 entirely separated from it, but is heated by the flame which passes both below and above it. The under hearth is 

 ten feet long and live; feet six inches broad (Saxon measure). The roof of the hearth consists of three strong 

 slabs of slate, which rest on three arches, which in turn abut against the longer sides of the furnaces. Those slabs 

 form at the same time the floor of the upper hearth or muffle, which, with the exception of three working doors, 

 some air holes, and an opening for the roast gases, is closed on all sides, like a, real muffle. 



The sole of such a muffle is thirteen feet long and six feet broad. The products of combustion of the stone coal, 

 mingled with the; gases arising from roasting these ores, escape from the lower hearth, anil pass through a chamber 

 above the muffle, which thus acts as a dust-condensation chamber. At the extremity of the furnace if enters a, 

 canal, which connects with a subterranean passage leading to a chimney 150 feet high. The gases from the muffle, 

 on the contrary, escape separately through a long canal to a set of terrace-built condensing chambers, which, they 

 traverse!, uniting with the other gases behind these chambers, when all go together to the 150 feet chimney. 



In these long Canals and Dust condensation chambers (which latter are erected above ground, and provided with 

 a roof of iron plates for the better cooling off of the vapors, but in other respects built of brick), the roast Cases find 

 ample opportunity to deposit all condensable ingredients, especially arsenious-acid (As 2 O.,), and I he mechanically sus- 

 pended little particles of ore dust, which otherwise would pass through the chimney and reach the open air, injuring 

 the neighboring vegetation. In the Muldner Smelting works there are 6 suoh Furnaoes in a, row, which arc to be 

 altered, as 18 already have been, into " Forward- Shoveling" Roast furnaces. 



Mode op Procedure in Roasting. 

 (The strength (the weight) of) a roasting charge for the Lead Process, amounts to ten Centners (100 lbs. Saxon). 



