SECT. XXIX. 
All that has been faid hitherto of experiments 
upon mineral bodies^, is only concerning the Hones 
and earths. I am now proceeding to the metals 
^nd oreSj in order to defcribe the manner qf ex- 
amining thefe bodies, and particularly the manage- 
ment of the Blow-pipe in thefe experiments, An 
exact knowledge, and nice proceeding are fp much 
the more neceffary here, as the metals are often fo 
difgulfed in their ores, as to be very dijfiicultly 
known by their external appearance, and liable 
fometimes to be miftaken one for the other : Some 
of the cobalt orps for inftance, refemble much a 
Pyrites Arfenicalis *, , there are alfp fome iron and 
lead ores, which are nearly like pnp another, &c* 
SECT. XXX. 
As the ores generally confift of metals minera- 
iifed with fulphur or arfenic, or fometimes both 
together; they ought firft to be expofed to the 
fire by themfelves, in order, not only to deter^ 
mine with which of thefe they are mineralifed, but 
aifo to fet them free from thefe volatile minera- 
lifing bodies : Thus this ferves inftcad of 
tion, by whiph they are prepared for 
pfTays. 
SECT. XXXL 
Here it mull be obferved, that, whenever any^ 
metal, or fufible ore is to be tried, a little con- 
cavity muft be made in that place of the charcoal 
where the matter is to be put ; becaufe, as fooa 
it is mpked, it forms itfelf irito a globular figure,^ 
calcina- 
further 
