[ 300 ] 
’files ©ff, Vv^hen the iron fcorifies : neither can aH 
t&ofe Blendes, which contain filver or gold mi- 
oeralifed with them, be tried in this manner, 
which is particularly owing to the imperfe<51: calci- 
nation *, nor are the quickfilver ores fit for thefe 
experiments, the volatility of this femi-metal mak- 
ing it impoflible to bring it put of the poorer fort 
of ores *, and the rich ores, which fweat out the 
quickfilver, when kept clofe in the hand, not 
^vanting any of thefe affays, dec. Thofe ores 
ought to be affayCvd in larger quantities, and even 
with fuch other methods, as cannot be applied 
Upon a piece of charcoal. 
SECT. XXXIV. 
Some of the rich filver ores arc eafily tried 
for inftance. Miner a argeyiti vitrea^ commonly cal- 
led Silver-glafs, which confills only of filver and 
fulphur. When this ore is expofed to the flame, 
it melts inftantly, and the fulphur goes away in 
fume, leaving the filver pure upon the charcoal, 
in a globular form. If this filver fhouid happen 
ito be of a dirty appearance, which often is the cafe, 
then it muft be melted anew with a very little 
borax, and after it has been kept ihfuflion for a 
minute or two, fo as to be perfectly melted and red- 
hot, the proof is fuffered to cool : it may then be 
taken off the coal, and being laid upon the Heel- 
plate, (Sedl. xi. n.) the filver is feparated from the 
flag by one or two ftrokes of the hammer (Se6t. xi. 
g.). Here the ufe of the iron rkig (Seft. xh) is 
manifeft, for this ought firfl to be placed upon 
the plate, to hinder the proof from flying off by 
the violence of the ftroke, which otherwife would 
* A piece of gold being laid over the proof, to receive the 
jfumes, readily dilcoversif it contains any quick-filver. And it 
is probable, that by like procelles, we may alfo be enabled |o 
.dikover Avkh the Blow-pipe other of the volatile fubitances. 
happen. 
