i*8 A SYSTEM OF 



tjmony to advantage ; and the antimony 

 likewife in a great meafure hinders the 

 extracting of the filver. 



SECT. CXCL 

 Observations on Lead Ores. 



I know of no native lead •, and all which has 

 been faid on that fubjecfc is liable to remarkable 

 reftrictions. 



Such of the potters ores as do not contain any 

 filver are very fcarce •, yet they are often found 

 fo poor in lilver, that it does not anfwer the ex- 

 pences of extracting, Thefe, when they are free 

 from mixtures of the rqck, are, without any pre- 

 vious fufion, employed to glaze earthen -ware ; 

 ^nd a great trade is carried on in the Mediterra- 

 nean with fucK ores, from the lead-mines of Sar- 

 dinia and France, 



SECT. CXCIL 



& Copper, Cuprum, Venus, A$< 

 This metal is, 



a. Of a red colour. 



b. The fpecific gravity of the Japan copper 

 is 9000, and of the Swedifh 8784 or 8843, 

 to 1000. 



if. It is pretty foft and tough. 



d. The calx of copper being diflblved by 

 acids becomes green, and by alcalies blue. 



e. It is eafily calcined in the fire into a 

 blackifh blue fubftance, which, when 

 rubbed to a fine powder, is red •, when 

 melted together with glafs, it tinges it full 



rcddifh 



