[ 2 9 7 ] 



SECT, XXIX. 



All that has been faid hitherto of experiment* 

 upon mineral bodies, is only concerning the ftones 

 and earths. I am now proceeding to the metals 

 and ores, in order to defcribe the manner of ex- 

 amining thefe bodies, and particularly the manage- 

 ment of th£ Blow-pipe in thefe experiments. An 

 exadt knowledge, and nice proceeding are fo much 

 the more neceffary here, as the metals are often fo 

 difguifed in their ores, as to be very difficultly 

 known by their external appearance, and liable 

 fometimes to be miftaken one for the other : Some 

 of the cobalt ores for inftance, refemble much a 

 Pyrites Arfenicalis ; there are alfo fome iron an4 

 lead ores, which are nearly like one another, &c # 



SECT. XXX. 



As the ores generally confift of metals minera- 

 lifed with fulphur or arfenic, or fometimes both 

 together •, they ought firft to be expofed to thp 

 fire by themfelyes, in order, not only to deter* 

 mine with which of thefe they are mineralifed, but 

 alfo to fet them free from thefe volatile minera- 

 lifing bpdies : Thus this ferves inflead of calcina^ 

 tion, by which they are prepared for further 

 e flays. 



SECT. XXXT. 



Here it mnfr. be obferved, that, whenever any 

 metal, or fufible ore is to be tried, a little con- 



rity muft be made in that place of the charcoal 



■ the matter is to be put • becaufe, as foon 



$s it is melted, it forms ftfetf into a globular figure, 



mi 



