water could not be converted into earth by repeated
distillations, as was generally advocated; and to show also that
there was no foundation to the existing belief that it was
possible to convert water into a gas so "elastic" as to pass
through the pores of a vessel. He demonstrated the fallaciousness
of both these theories in 1768-1769 by elaborate experiments, a
single investigation of this series occupying one hundred and one
days.

In 1771 he gave the first blow to the phlogiston theory by his
experiments on the calcination of metals. It will be recalled
that one basis for the belief in phlogiston was the fact that
when a metal was calcined it was converted into an ash, giving up
its "phlogiston" in the process. To restore the metal, it was
necessary to add some substance such as wheat or charcoal to the
ash. Lavoisier, in examining this process of restoration, found
that there was always evolved a great quantity of "air," which he
supposed to be "fixed air" or carbonic acid--the same that
escapes in effervescence of alkalies and calcareous earths, and
in the fermentation of liquors. He then examined the process of
calcination, whereby the phlogiston of the metal was supposed to
have been drawn off. But far from finding that phlogiston or any
other substance had been driven off, he found that something had
been taken on: that the metal "absorbed air," and that the
increased weight of the metal corresponded to the amount of air
"absorbed." Meanwhile he was within grasp of two great
discoveries, that of oxygen and of the composition of the air,
which Priestley made some two years later.

The next important inquiry of this great Frenchman was as to the