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SECT. XXXVI. 



Moll part of the lead ores may be brought to a 

 metallic lead upon the charcoal. The Miner* plumbi 

 cakiformes^ which are pure, are eafily melted into 

 lead : but fuch of them, as are mixed with an ocbra* 

 ferri y or any kind of earth, as Clay, Lime, &c'. 

 yield very little of lead, and even nothing at all, 

 if the heterogenea are combined therewith in ariy 

 large quantity { this happens even with the Minera 

 plumbi calciformis arfenico mixta. Thefe, therefore, 

 are not to be tried but in larger laboratories. 

 However, every mineral body fuipedted to contain 

 any metallic fubftance, may be tried by the blow- 

 pipe, fo as to give fufficient proofs, whether it 

 contains or not, by its efFe£ts being different from 

 thofe of the Hone or earths, &c* 



SECT. XXXVII. 



The Miner* plumbi miner ali fat * y leave the 

 Jlead in a metallic form, if not too large a quantity 

 of iron is mixed with it. For example, when a 

 teffellated or fteel -grained lead ore is expofed to 

 the flame, its fulphur, and even the arienic, if 

 there be any, begins to fume, and the ore itfelf 

 immediately to melt into a globular form •, the reft, 

 of the fulphur continues then to fly off, if the 

 flame is blown flowly upon the mafs, inllead of 

 that, very little of the fulphur will go off, if the 

 flame is forced violently on it : in this cafe, it ra^ 

 ther happens that the lead itfelf crackles and difli- 

 pates, throwing about very minute metallic par- 

 ticles. The fulphur being driven out, as much as 

 poffible, which is known by finding no fulphureous 

 vapour in fmelling at the proof, the whole is fuf- 



fered 



