obvious and palpable.

The great first step was the substitution of the one principle,
phlogiston, for the three principles, salt, sulphur, and mercury.
We have seen how the experiment of burning or calcining such a
metal as lead "destroyed" the lead as such, leaving an entirely
different substance in its place, and how the original metal
could be restored by the addition of wheat to the calcined
product. To the alchemist this was "mortification" and
"revivification" of the metal. For, as pointed out by
Paracelsus, "anything that could be killed by man could also be
revivified by him, although this was not possible to the things
killed by God." The burning of such substances as wood, wax,
oil, etc., was also looked upon as the same "killing" process,
and the fact that the alchemist was unable to revivify them was
regarded as simply the lack of skill on his part, and in no wise
affecting the theory itself.

But the iconoclastic spirit, if not the acceptance of all the
teachings, of the great Paracelsus had been gradually taking root
among the better class of alchemists, and about the middle of the
seventeenth century Robert Boyle (1626-1691) called attention to
the possibility of making a wrong deduction from the phenomenon
of the calcination of the metals, because of a very important
factor, the action of the air, which was generally overlooked.
And he urged his colleagues of the laboratories to give greater
heed to certain other phenomena that might pass unnoticed in the
ordinary calcinating process. In his work, The Sceptical Chemist,
he showed the reasons for doubting the threefold constitution of
matter; and in his General History of the Air advanced some novel