AT FREIBERG. 



409 



ever produced by the Royal Mining Works ; but often very rich ores are obtained from foreign countries — chiefly 

 America. 



The above three classes of ores are united under the general head of "paid ores," because their purchase is 

 regulated by the established price which the smelting works pay for each metal. 



The sulphur and arsenio in these ores are paid for when the material is furnished in lumps, and not pulverized. 

 In such ores the sulphur is paid lor when it exceeds 20 per cent., and the arsenic when it exceeds 25 per cent. In 

 contradistinction to the "paid ores" arc : 



4. The " Reagent Oees." — The purchase of such ores takes place only conditionally on the need which may 

 be felt Cor them in the different smelting processes, and on the basis of any agreement made between the smelting 

 works and the particular mines furnishing them. All those ores belong to this class, whose percentage of silver varies 

 from one to one and a half hundredths of one per cent. (0.01-0, 0.015 p. a), provided that a percentage of 15 or more 

 per cent, of lead, or 1 or more per cent, of copper, docs not place them among the copper or lead ores. 



In these ores also the sulphur and arsenic are paid for under the same conditions as in the "paid ores," 

 except that in arsonious ores the broken form is not desirable. The constituents of these ores are principally iron 

 pyrites, arsenioal pyrites, zinc blende, quartz, ealcite, etc. ; at the same time they always contain small quantities of 

 copper and lead. According to thesis constituents, these are called pyrito-blondic, silico-pyritic, and silico-blendo- 

 pyritic. To the classes of the reagent ores come those Diirr ores, which contain but little silver (up to 0.04 per cent, 

 when 15 per cent, and upwards is present). 



The furnishing of the ores is performed with them either dry (1st) dry stamped, (2d) in lumps, as is 

 the caso with tho reagent ores, or in a moist condition (jigged or washed ore). In the stamped ores, besides a 

 oareful mixing, such a size of grain is required, that when it is sifted in a sieve of 075 meshes to the square inch not 

 more than 1.5 per cent, renin ins behind. 



In wet ores it is required that they be as free as possible from hygroscopic water; that they can bo weighed with 

 certainty, and permit the obtaining of a, reliable average analysis ; and that they be neither in a viscous nor liquid 

 condition. 



I. The Lead Pbooess in Cupola Pubnaoes. 



The object of this process is, after previous roasting of tho argentiferous Diirr ores, Qalenoids, and plurnbiferous 

 ores with tho proper reagents in a roasting furnace, so to smelt them in a cupola furnace that the silver is extracted 

 by the lead (raw lead), and further that there is produced a combination of different sulphides of the metals (lead 

 matt), and when tho ores contain nickel and cobalt, also a combination of arsenides of the metals (lead speiss) ; on 

 the other hand, the earthy constituents and less easily reducible metal oxides combine to form a slag (lead slag). 



Composition of a Ohakge. 



The ores which come to the lead process are : 



1. All tho lead ores (Qalenoids and plurnbiferous) . 



2. All the Diirr ores from 0.1 per cent. Ag. upwards. 



3. Copper ores from 0.1 to 0.15 percent. Ag. upwards, when the percentage of copper does not exceed per 

 cent., because otherwise the raw lead produced would be rendered too impure by the copper, which has a powerful 

 affinity for lead. 



The above ores arc then sorted and mixed. By sorting is understood a mixing together of those ores which 

 contain, and arc treated for the purpose of extracting, one and the same metal, but whoso various percentages of 

 this metal are different, and which behave differently in the furnace. 



For example, in Freiberg all lead ores are associated together and mixed with the Durr ores, which in their turn 

 are associated together among themselves, as they possess different percentage of silver and different earthy con 

 stituents, and also behave differently when smelted. By mixing is understood a mixing of the ores which are to be 

 treated, with the reagents, such as ealcite, heavy spar, old slag, or some already existing noddle product of the 

 smelting works. 



AME1U. PHILOSO. fcSOC. — VOL. XIV. — 103 



