400 Dr . priestley’s Experiments relating to Phlogiflon , 
The arguments in favour of this opinion, efpecially thoff? 
which are drawn .from the experiments of Mr. lavoisier 
made on mercury, are fo fpecious, that I own I was myfelf 
much inclined to adopt it. My friend Mr. kirwan, indeed, 
always held that phlogiflon was the fame thing with inflam- 
mable air; and he has fufflciently proved this from many expe- 
riments and obfervations, my own as well as thofe of others. 
I did not, however, accede to it till I difcovered it by direct 
experiments, made with general and indeterminate views, in 
order to afcertain fomething concerning a fubjedt which had 
given myfelf and others fo much trouble. 
I began with repeating the experiments in which I had found 
that inflammable air, made red-hot in flint glafs tubes, gave 
them a black tinge, and was in a great meafure abforbed, 
which I had difcovered to be owing to the calx of lead in the 
glafs attracting phlogiflon from the inflammable air. As the 
quantity of air in thefe tubes was very fmall, though I gave it 
as my opinion, that the refiduum in one of the procefies was ‘ 
phlogifticated air, becaufe I perceived no marks of afcenflon on 
prefenting to it the flame of a fmall candle ; I was not, on 
recolledtion, fatisfied with this conclufion, and was defirous of 
repeating the experiment with more care, efpecially as, in one 
of the above-mentioned experiments, I found only a very 
fmall bubble of the inflammable air in the tube in which it had 
been heated. / 
I 
I found, however, great difficulties in repeating thefe expe- 
riments ; and the quantity of inflammable air operated upon 
in them is neceflarily fo fmall, that the refult is always liable 
to much uncertainty. I thought, therefore, that throwing 
the focus of a burning lens upon a quantity of pounded 
flint glafs, furrounded with inflammable air, or rather 
on 
