MINERALOGY. 1*5 



lead could be melted from it by- 

 means of the blowpipe, as can be 

 done out of other lead fpars -, but 

 it mult be performed in a crucible, 

 and then that part of the arfenic 

 which did not fly off in fmoke, 

 during the experiment, was like- 

 wife reduced, and found in form of 

 grains difperfed, and forced into the 

 lead. Another ore of this kind, 

 which likewife was not eafily re- 

 duced by means of the blowpipe, 

 did always after being melted, and 

 during the cooling, haftily fhoot 

 into polygonal, but moftly hexago- 

 nal criftaJs, with fhining furfaces. 

 Can this criilallifation be owing to 

 falts, which are faid not to act in 

 this manner, but when they are dif- 

 folved in water ? 

 h. With a calcareous earth *. See Sect, 

 xxx viL 



* The abovementioned lead ores are very rich in lead, and 

 eafy to be tried ; becaufe moft of them, being flowly heated, 

 may be reduced to lead by means of the blowpipe on a piece 

 of charcoal. The calx of the lead in thefeores has, perhaps, 

 flrft been diflblved by fulphur and arfenic, and has afterwards, 

 when thefe two have weathered away or d-cayed, and parted 

 from it, affumed this form ; in the fame manner as we fee it 

 reaily happens during the calcination, with rich lead ores, or 

 fuch regules as contain lead. The fame, very likely, is the 

 cafe with other metals ; for which reafon their ores, when they 

 occur in form of a calx, often contain a little fulphur, an4 

 more efpecially arfenic 



SECT; 



