AT FREIBERG. 



41:5 



This raw speiss is subjected to two or three meltings with various reagents, such as litharge, oupellation hearth, 

 highly silicious slags and heavy spar, and Anally becomes a speiss with about 0.0:! per cent, of silver, 15 per cent, of 

 copper, and 15 to 18 per cent, of nickel and cobalt. This operation is culled (lie desilverizing of the speiss, or the 

 separation of silver from it. The thus desilverized speiss is placed in a small rcverbcratory furnace with 50 to 00 per 

 cent, heavy spar, and 20 to 25 per cent, quartz, and refined. The result is a copper matt, and a natural speiss, 

 almost free from iron, with ahout 40 to 50 per cent, of nickel and cobalt, and 10 per cent, of copper. This product, 

 winch is an educt in so far as it is not furthor treated at the Freiberg Smelting Works, commands a good price at 

 the cobalt blue manufactories. 



Recently, the refining and desilvering of the speiss have been accomplished at one time. The speiss is refined 

 with heavy spar and quartz, and after the slag is drawn oil', ahout one or one and a half times the amount by weight 

 of lead poor in silver, is added to the molten mass, and stirred well, the fire being increased. After this, the mass 

 is drawn off into some convenient receptacle ; and the products are, raw load, copper matt, and a speiss much richer 

 in cobalt and nickel, and containing 0.01 to 0.02 per cent, of silver. 



REFINING Raw Lead. — This consists in gradually raising the heat to the melting point, and scraping off tlu 

 less fusible impurities which float, as scum, on the surface of the metal bath. The lead is kept at a low red heat, 

 and air is freely admitted to its surface. 



Lead Slag, ok Raw Pkocess. — These two names really designate the same prooess, and they exist because, at 

 the Muldncr Works, the lead slag, besides the ores, is subjected to it, while at the Halsbruokner Works only the Piirr 

 ores and reagent ores having less than 0.1 per cent, of silver, are treated in this way, the lead slag from the Pils 

 furnace being thrown away as worthless. Such ores, of course, are also treated at the Muldncr Works. 



The, object hero is to collect the small percentage of silver in an iron matt, which is afterwards roasted at the 

 sulphuric acid works, and provides the latter, to a great extent, with sulphurous acid gas, while the argentiferous 

 iron oxide which is the other product, forms the most valuable base for the composition of the slag in the lead 

 process, and exchanges its associated percentage of silver for the sulphur of the Galena,, in the evolution of the raw 

 lead. In the following remarks, the lead slag process will bo considered, but it is to be understood that it differs 

 from the raw prooess only in admitting to the same treatment the product from which it derives its name. 



Tina Pattinson Pkocess, ok tub Concentration op Silveb in the Raw Lead. 



This process was invented in the year is:!:! by Mr. Pattinson, of Northumberland, originally with the design of 

 desilverizing loads so poor in silver that they could not bo economically cupelled. More recently, this process has 

 also been applied with advantage to loads rich in silver. The plan is to make a lead richer in silver, which diminishes, 

 firstly, the volume of lead to be subjected to oupellation ; and secondly, the loss of lead. The plain explanation of 

 the principle underlying this process is as follows : — 



A lead containing some silver is melted up in one of a row of large iron kettles, capable of containing 

 from 200 to 250 centners (20,000 pounds, or 10 tons), and then allowed slowly to cool, the fire being withdrawn. While 

 the molten lead is slowly cooling, it is carefully stirred by means of a, large perforated iron ladle. In cooling, numbers 

 of crystals are continually being formed and deposited in the bottom, the mother-liquor, or that part which remains 

 molten, containing more silver than that which crystallizes out. The ladle is run down the sides, and scraped over 

 the bottom of the kettle, and then drawn up slowly, and struck once or twice to permit the mother-liquor to run out 

 through the perforations. The crystals are then transferred to the next kettle to the right hand. The consequence 

 is, that at one end of the battery or row of kettles, almost pure lead is obtained, while at the other the required 

 richness, 1.4 to 1.5 p. c. is reached. 



The purity of the lead lias especial influence on the working of the process itself, so thai the lead which is subjected 

 to Pattinsoning must first bo refined, in order to remove the arsenic, antimony and sulphur which it contains. The 

 latter substance especially must be guarded against, as it not only interferes with the proper course of the work, but 

 destroys the kettle itself, as a refining experiment with one of these kettles in Freiberg, and the fate of a whole 

 battery of them, under the charge of an incompetent man in the West, abundantly prove. 



AMEUI. PHILOSO. SOU. — VOL. XIV. — 104 



