.( 575 ) 
Charcoal, which is cominonly niaic uie of, is indeed 
a very proper fubftaace ^ but it is impodibk with it to 
vitrify any one of the Metals : 1 he Particles ot the Me- 
tal, when held any long time in fufion in the Focus of 
the Glafs, dihipate and fly away in Fume or fmali Parti- 
cles ^ and as long as any part remains, that little that does 
remain, is always Metaliick, until the whole be quite 
evaporated. 
The reafon of which I take to be this. Charcoal is a 
fubftance deeply impregnated with Oily or Sulphurous 
Parts (if I may fo call them.) The hrft Effea that Fire 
has upon Metals is to feparate the fulphurous Parts : now, 
if in proportion as the Sulphur is feparated from the- 
Metal, the Body that fupports the Metal furnidies it anew 
with other fulphurous Parts, the other Principles will ne- 
_ver feparate, and -the Metal will alv\ ays remain Metal. 
And nothing but the greateft degree of Fire is able to 
raife and feparate the Sulphur, and that but by little and 
little, and in very (mail Particles. 
I had then recourfe to an other Matter, that could 
not any ways be fufpeffed of containing any Oily Parts. 
Mr^Tfehirnbaus, to whom we are obliged for Making -of 
thefe large Glafles, and the firftExperiments that have been 
made with them, fays, he has vitri%d Metals by holding 
them in China ware, ft is true, this/ncceeds pretty well, 
provided the Pic^s be very thick, and the Glazing taken 
off: But the difficulty I had to find a fufficient quantity 
of thick and proper China ware to make all thefe Ex- 
periments, forced me to have recourfe to more common 
fubjefts, as well as fuch, if poffible, as v;ere lefs capa- 
ble of melting- 
Of all the different forts of Matter that I made Tryal 
©f, what feem befc were the Cpmmon Coppels and Plates 
of ^ gray Fire-ftone. The Coppels hold the Metal a long 
time in fufion in the Focus ot the Glafs without melting^ 
excepting. Lead, which eafily runs thro’ them as foonas 
it 
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