C 226 ] 
turbid, prefen tly after the heat was applied. This was 
the cafe with whatever degree of heat the charcoal had 
been made. If, however, the charcoalhad not been made 
with a very confiderable degree of heat, there neverfailed 
to be a permanent addition of inflammable air pro- 
duced ; which agrees with what I obferved before, 
that, in converting dry wood into charcoal, the greatefl 
part is changed into inflammable air. I have fome- 
times found, that charcoal which was made with the 
moft intenfe heat of a fmith’s fire, which vitrified 
part of a common crucible in which the charcoal was 
confined, and which had been continued above half 
an hour, did not diminifh the air in which the focus 
of a burning mirror was thrown upon it; a quantity 
of inflammable air equal to the diminution of the 
common air being generated in the procefs ; whereas, 
at other times, 1 have not perceived that there was 
any generation of inflammable air, but a perfedt 
diminution of common air, when the charcoal had 
been made with a much lefs degree of heat. This 
fubjedt deferves to be farther invefligated. 
To make the preceding experiment with ftill more 
accuracy, I repeated it in quickfilver ; when I perceived 
that there was a fmall increafe of the quantity of air, 
from a generation either of fixed or inflammable air, 
but I fuppofe of the former. Thus it flood without 
any alteration a whole night, and part of the following 
day; when lime-water, being admitted to it, it pre- 
fently became turbid, and, after fome time, the 
whole quantity of air, which was about four ounce 
meafures, was diminifhed one fifth, as before. In 
this cafe, I carefully weighed the piece of charcoal, 
which was exadtly two grains, and could not find 
