in. the Pyrites. 121 



constitute a clafs of filver-ores; as being not only 

 highly inconftant in filvcr-yield, but peculiarly cop- 

 pery, which can never be faid of any red-goldijb ore. 



As to the imperfeft, or rather, ignoble metals, 

 their ores are in more inftances found of a conftant 

 yield than thofe of the noble ; as in particular, we 

 learn from lead-glitter, white and green-lead ore, 

 tin-Jione, iron-pyrites, and cinnabar -, glitter, or 

 galena, commonly containing two thirds, nay fome- 

 what above, in lead ; and hitherto I have found 

 none falling much lhort of a half. The fame we 

 obferve, and that with more certainty, of no one 

 ore fo much as of the rich tin-ftone. White and 

 green lead-ore hold ordinarily above three fourths 

 in lead, and never under, only allowing for its 

 incredible volatility. 



Sulphur-iron-pyrites always yields about three 

 fourths metallic, namely, iron-earth ; and allow- 

 ing for its volatility, neither more nor lefs than 

 a fourth of fuiphur. Arfenical, or poifon pyrites, 

 which has alio conftantly an iron-earth for its 

 ground, when pure and fine, has a like yield, al- 

 lowing only for a third, or fomewhat over, of fly- 

 Jlone, or arfenic. Cinnabar-ore has often fome- 

 what foreign in its mixtion ; thus not always exhibit- 

 ing its due, beautiful, red character, but fome- 

 times appearing of a brown-red, more or lefs, al- 

 moft hke a brown-red iron-ftone-, but when arrived 

 to its true degree of perfection and purity is, like 

 the other, found in its proportion of fuiphur and 

 quickfiiver, as 1 to 6 or 7. And here it were to 

 be wifhed, afiayers were more careful in noting 

 down the feveral yields of their ores, not omitting 

 at the fame time to regifter any doubts that might 

 arife in the courfe of the procefs : as by this means 



we 



