C 298 ] 
and might then roll from the charcoal, if its fur- 
face was plain ; but when borax is put to it, this 
inconveniency is not fo much to be feared. 
SECT. XXXIL 
Whenever an ore is to be tried, a fmall bit is 
broke off for that purpofe, of fiich a fize as is di» 
redled in Sefl. xvi. this bit is laid upon the char- 
coal, and the flame blown on it flowly : I'hen the 
fulphuT or arfenic begins to part from it in form 
of fmoke ; thefe are eafily diftinguifhed from one 
another by their fmell, that of fulphur being fuf- 
liciently known, and the arfenic fmelling like gar- 
lick. The flame ought to be blown very foftly, 
as long as any fmoke is feen to part from the ore ; 
but, after that, the heat rnufl be augmented by 
degrees, in order to make the calcination as per- 
fedt as pofTible. If the heat is applied very flrong 
from the beginning upon an ore, that contains 
much of the fulphur, or arfenic, this ore wall pre- 
fen tly melt, and yet lofe very little of its mine- 
talifing bodies, and by that means render the cal- 
cination very iniperfeA. It is however, impofllble 
to calcine the ores in this manner to the utmofl; 
'perfeftion, which is eafily feen in the following 
inftancc, viz. in melting down a calcined Potter’s 
ore with borax, it will be found to bubble upon 
the coal, which depends on the fulphur, which is 
fl-ill left, the vitriolic acid of this uniting with the 
borax, and caufing this motion. However, lead 
in its metallic form, melted in this manner, bub- 
bles alone upon the charcoal, if any fulphur re- 
mains in it. But, as the lead, as well as fome of 
^he other metals, may raife bubbles upon the 
charcoal, although they are quite free from the 
fulphur, only by the flames being forced too vio- 
lently 
