But the good effects of the era of experimental research, to
which the theory of Stahl had given such an impetus, were showing
in the attitude of the experimenters. The works of some of the
older writers, such as Boyle and Hooke, were again sought out in
their dusty corners and consulted, and their surmises as to the
possible mixture of various gases in the air were more carefully
considered. Still the phlogiston theory was firmly grounded in
the minds of the philosophers, who can hardly be censured for
adhering to it, at least until some satisfactory substitute was
offered. The foundation for such a theory was finally laid, as
we shall see presently, by the work of Black, Priestley,
Cavendish, and Lavoisier, in the eighteenth century, but the
phlogiston theory cannot be said to have finally succumbed until
the opening years of the nineteenth century.



II. THE BEGINNINGS OF MODERN CHEMISTRY

THE "PNEUMATIC" CHEMISTS

Modern chemistry may be said to have its beginning with the work
of Stephen Hales (1677-1761), who early in the eighteenth century
began his important study of the elasticity of air. Departing
from the point of view of most of the scientists of the time, be
considered air to be "a fine elastic fluid, with particles of
very different nature floating in it" ; and he showed that these
"particles" could be separated. He pointed out, also, that
various gases, or "airs," as he called them, were contained in
many solid substances. The importance of his work, however, lies