[ 21 9 1 
to a greater heat, which more thoroughly burnt the 
oil with which their pores were filled. 
I put a piece of common pipe into a crucible, in 
which I was burning fome turpentine (which will be 
mentioned below); and it came out black quite 
through, like a pipe in which tobacco has been fre- 
quently fmoaked. In this ftate it would not conduct 
at all ; but, putting it into a crucible, covered with 
fand, I treated it in the fame manner as I would 
have done a piece of wood, in order to coal it, and 
it came out a very good conductor. Had it been 
burned in the open fire, the phlogifton would have 
efcaped, and the pipe would have been left white as 
at firft. 
Being convinced that the conducting power of 
charcoal depended upon the oil, or rather the phlo- 
gifton contained in the oil, and on the degree of 
heat with which it was burned, I took feveral me- 
thods to give vegetable fubftances more of this 
principle ; or at leaft endeavoured to make them re- 
tain more of it than they ufually do, in the procefs 
of coaling. But I had no apparent fuccefs in thofe 
experiments. 
I began with plunging a piece of old dry oak in 
oil; and then, pumping the air out of it, let it ftand 
In vacuo a day and night, in which time it feemed to 
difcharge a great quantity of air ; after which, I let 
into the receiver the air, and thereby forced the oil 
into its pores. But the coal from this wood was not 
fenfibly better than others. The application of heat 
may perhaps expell the phlogifton in fuch a man- 
ner, that the refiduum, being fully faturated, can 
retain no more than a certain proportion* I made 
. F f 2 coals 
