SMELTING OF CUPREOUS PYRITES, 37 



The mixture of quartz with the ore deserves particular ^^^ "^® °f 

 ^ . . ^^ -11 11, quartz <es5ea- 



notioe tor its importance. Many trials have been made to ^^i^ 



use other eartliy substances in its stead, but they were with- 

 out success ; and if a vein of quartz had not been discovered 

 in the neighbourhood, the working of this poor ore must 

 have been given up. 



Of the component parts of the ore, the sulphur is sepa- '^^^ sulphur 

 '?ated in great part by roasting, and the zinc subHmes at the rXTing and 

 iirst smelting : but the iron, the proportion of which in the *^^ ^^^^ sub^ 

 raetalHc state amounts to at least 40 per cent of the mass 

 to be fused, is unquestionably the most embarrassing for its trouble^oj^l 

 quantity, and because by being reduced it choaks up the 

 furnace, and stops the operation. The intention of adding 

 quartz is to carry the iron out of the furnace. In fact the ^[^ oxide corn- 

 analyses above given show, that a combination takes place siiex. 

 between the silex and oxide of iron; and that this homoge- 

 neous compound becomes sufficiently fluid in the heat of the 

 furnace, to allow the co[)per and the matts to separate from 

 the mere difference of specific gravity; so that itself can be 

 taken off the basin of the fore hearth during the fusion. 



The afiflnity between the parts of this compound must be Tlieir afTimty 

 pretty strong, to preverit the reduction of the oxide of iron, ^ *' ^ ^ ^°^*' 

 rnd to enable it to yield its sulphur to the copper, which 

 does not happen but through some particular circumstance, 

 as in this case the presence of silex. It is an established Iron here 

 fact in metallurgy, that iron takes sulphur from copper : ^^''^^pJ'JJ. j^^.^^^^ 

 here on the contrary the iron yields the sulphur to the cop- a double afli- 

 per, while itself unites with a compound in wliich it is al- "^^-'* 

 r.ady abundant to form the scoriae*, and does not appear in 



the 



taining ^.bout 21 part:^ sulphur, GG copper, and 8 metallic iron. It ap- 

 pears froDa various calcul;^tions, thai not above a hundredth of the iron 

 in the roasted ore reqiains i:i tliese two producf;, while they contain 

 iiearly half of the copper, that was in such small proportion. 



The iron therefore jnis been separated and carded off in the scoriae, Iron carried ofF 

 -ince no other product retains any considerable quantity. ' »" the scoriae. 



The sublimed matter, or cadmia of the furnaces, is nothing but oxide Zinc, 

 f'f/unc with some slight traces of copper, and free from iron- 



• Beside tlie quartz and scoria; j;resunied to retain copper, scoriie frotn 

 th'j .;.njching of I lie ore, containing aboutO-66 of , oxide of ^oa only(analysis 



^^o. 



