n6 4y*>tg of Ores. [Book Vf/ 



tartar with one of nitre. The alkali of this compound 

 increafes the fufibility of the (tony matter mixed with 

 the ore, and confequently affords the metal an oppor-' 

 tunity of fcparating from it ; while the charcoal con- 

 tained in it, and which proceeds from the impurity of 

 the tartar, abftracts the oxygen of the ore, and reduces 

 the metal to a reguline form. 



When the operation has been properly performed, 

 the metal, or regulus, is found in the form of a button 

 at the bottom of the mafs, and being weighed mews 

 the proportion of metal contained in the ore. 



This method is ufed in reducing fmall quantities, as 

 in afTaying of ores, but would be too expenfive in large 

 operations. In this latter cafe it is cuftomary to mix the 

 ores or calces with the fuel, but to let as little air as 

 pofllble pals through k, as this would tend to re-calcine 

 ihe*metal. To prevent this effect, a particular fort of 

 furnace is employed, in which charcoal is chiefly ufed. 



It frequently happens that the fame minerals contain 

 the perfect metals mixed with the imperfect; thefe are 

 feparated both in the fmall and large way by heating 

 the mixed mafs in contact with air. By this operation 

 the imperfect metal is reduced to a calx, and leaves 

 the perfect metal in a ft ate of purity. If the remain- 

 ing metallic matter is ftill a compound, and contains 

 two of the perfect metals, thefe are feparated by ex- 

 pofing them, with as large a furface as poffibie, to the 

 action of a menftnium, which has the property of dif- 

 folving one of them without the other. 



There is alfo a method of aflaying in the humid 

 way,, by fubmitting the ores to the action of different 

 icidsj but this is not fo practicable as the other. 



In the extraction of metals in the large way, the ore 

 is pounded, wafhed, roafted, imelted, and refined. By 

 pounding, the deny matters are feparated from the 

 metallic, and the whole being then walhed on inclined 



planes' 



