[ 22 6 ] 
It was not in the leaft affeCted by the magneti 
Upon the whole, the matter that forms this coating 
of the glafs feems to be a kind of charcoal, only 
white inftead of black. 
Confidering that metals refemble charcoal, in that 
they confift of an earth united to phlogifton, and 
that charcoal will not confume without burning in 
the open air (there being, probably, fomething in the 
atmofphere with which it can unite, on the principle 
of chemical affinities, the moment it is feparated 
from the metallic bafe) I imagined that metals might 
not calcine or vitrify except in the fame circum- 
ftances, and the event verified my conjecture. 
I took a certain quantity of lead, and having put 
it into an open crucible, obferved that it was all vitri- 
fied in io minutes j but the fame quantity of lead, 
covered with pipe clay, and fand, was kept feveral 
hours in a much hotter fire, and was hardly wafted 
at all, the bottom of the crucible only being flightly 
glazed ; it having been impoffible wholly to exclude 
all accefs of air, and fome being necefiarily in con- 
tact with it when the procefs began. Treating char- 
coal in the fame manner, I could never prevent fome 
lofs of weight, when the crucible was kept in a 
very hot fire, for feveral hours. 
As, by this procefs, lead will bear a much greater 
degree of heat than would calcine or vitrify it in the 
open air, I fhould think it probable, that lead thus 
prepared muft have the phlogifton more clofely 
united to its earthy bafe, and be thereby a better 
conductor than common lead ; fince this is the cafe 
with charcoal thus treated. Perhaps lead, and other 
bafe 
