412 



SMELTING PROCESSES 



(8 Raw Lead.— Which collects in the Bum p of the furnace, after the above; two processes, is a lead in which 

 various impurities, such as arsenic, antimony, and copper, exist in greater or less degree. The greater part of the 

 silver of the charge is collected in this raw lead. It contains from 0,6 to 0.8 p.c. of silver and sometimes with very 

 rich Diirr-ores reaches 1 p.c. of silver About 1(5 to 18 centners are produced daily. In order to separate the lead and 

 silver, this raw lead is either directly cupelled, or (which, is the case except with tin; very pure ores) it is refined to 

 get rid of the impurities, then submitted to Pattinson's process to concentrate the silver, and finally cupelled when it 

 reaches about 1.5 to 1.6 p.c. silver. 



LEAD Sfeiss is produced, though more rarely. It is composed of iron, copper, cobalt, nickel and arsenic. If it 

 forms in any quantity, its place is between the raw load at the bottom and the lead matt immediately above it, so that 

 the order in which these products lie is (counting from the bottom), 1st, raw lead ; 2d, lead speiss ; 3d, lead matt ; and 

 4th lead slag. It usually adheres to the matt, however, and is submitted to further treatment with the latter, until 

 a sufficient quantity is obtained to make a disc easily raised from the pot, into which the molten mass is drawn off. 



The expenditure of fuel per day is thirty to thirty-two bushels of coke. 



The force necessary to keep a, furnace in constant operation consists of six men, three by day, and three by 

 night, who have twelve hour shifts. They arc divided into smelters, assistants, and slag-runners ; of eaoh of whom 

 there is one in each shift. The smelter has the responsibility of taking charge of the furnace and conducting the 

 process. The assistant has to help him as much as possible, and especially i'<-vt\ the charge into the furnace, under 

 direction of the smelter. The slag-runner has to remove the slag to the dump heaps, and keep the part of the floor 

 over which it runs, always in order, and free from obstructions. 



Modification ok the Lead Matt. 



This is always taken up at the close of a, run of the lead process. The matt is stamped and roasted as completely 

 as possible, mixed in the slag from tin; same process, and with furnace ends from the lead process, and smelted in a, 

 cupola furnace, There is no definite relation of parts in the mixture. Generally, to about 40 ewt. of roasted malt 

 80 ewt. slag are added. It smells very rapidly, because the mixture is very fusible, and is drawn oil' six to eight times 

 in a day. 



The products are : 1st, Slag; 2d, Matt (modification) ; and 3d, Raw Lead. 



The manipulation in this process is the same as In the lead process. 



Copper Matt.— The matt which falls in the treatment of the modified matt, is called copper matt. The object 

 is to increase the percentage of copper, and the partial extraction, at least, of the silver and lead, of which this malt 

 still contains no small amount. This, and flic spur process, are undertaken at the end of a, lend matt run, in the 

 same kind of furnace as in the lead matt process. The matt is stamped or roasted, and smelted with litharge 

 reduction slag, and a small percentage of fluor-spar, lime and slag of the same process, Care must be taken with the 

 roasting, as this matt melts more easily than lead matt, on account of its higher percentage of copper. In twenty- 

 four hours, about <!0 centners of copper malt, or about 30 centners of spur matt, are produced; but besides these, raw 

 lead and some speiss, which latter goes to the lead matt process. 



Concentration Process.— By means of spuring, tin; matt has been brought up to 40 to 50 per cent, of copper ; 

 and in order to increase the percentage of if still more, it is now concentrated in the reverberatory furnace. Reagents 

 are added to it, calculated to evolve a concentration of copper matt as free as possible from iron, and suitablo for 

 vitriolizing. It is stamped and roasted, and mixed with quartz and heavy spar (or barytic slags from previous 

 runs). The use; of the baryta is to assist in slagging off the iron ; the principal object of the process being to reduce 

 the percentage of this metal to a, minimum. 



The separation of the silver and lead is really of secondary importance, because these metals arc entirely collected 

 in a residue left during the course of the next operation, or that of vit rioliza.t ion. Charges contain 18 to 20 centners of 

 matt (of which by far the greater pari; has been washed;, and 10 to 12 centners heavy spar and quartz— the latter about 

 one-half to two-thirds of the mass. As before staled, this can be replaced by barytic slags. 



Speiss Process. —The plumbiferous and pyritic material excerncd in the course of the lead and spur malt pro- 

 cesses, containing 0.4 to 0.5 per cent, of silver, anil 1 to 2 per cent, of nickel ami cobalt, is made of value by the speiss 

 process. It is mixed with tins hearth of oupcllation and barytic slag from the concentration-copper process, besides 

 some heavy spar. There result from this, speiss with 12 to 13 per cent, of nickel and cobalt, and coppor matt. 



