[ 220 ] 
coals of other pieces of wood, when they were 
covered with cement ; and I alfo coaled feveral pieces 
together, that they might receive phlogifton from 
one another; but, in both cafes, without any fenfible 
improvement in the quality of the coal. 
In order to prevent the efcape of the phlogifton 
belonging to the fubftance to be reduced to a coal, I 
put fome pieces of wood into a gun barrel, and 
corked it as clofe as I could, at the fame time cover- 
ing the cork with cement. In this cafe the rare- 
faction of the exhaling vapour never failed to drive 
the cork out; but it muft have been after a confi- 
derable refiftance to its efcape. However, I could 
not perceive any peculiar excellence in the charcoal 
made in this manner. 
I do not, indeed, know any method in which differ- 
ences in fubftances that condud fo well as thefe can 
be accurately tried, at leaft none that can be applied 
in this cafe. The charcoal I can make in a common 
fire, by the ufe of a pair of hand bellows, I cannot 
diftinguifh, with refped to its conducing power, 
from the moft perfect metals, gold and filver; either 
by the length of the eledric fpark, the colour of it, 
or the found of the explofion. I make no doubt 
but that wood, in the procefs of coaiing, may eafily 
have a degree of conducing power communicated 
to it, exceeding that of lead, iron, or the other 
more imperfed metals. 
We may, perhaps, be guided in our conjectures 
on this fubjed, by confidering the degree of heat 
that is neceftary, either to unite the phlogifton to its 
bafe, or to feparate them, both in the cafe of wood, 
and the different metals. Lead is very eafily calcined, 
and 
