When this bottle was shaken violently, so that the lime-water and
the carbonic acid became thoroughly mixed, an insoluble white
powder was precipitated from the solution, the carbonic acid
having combined chemically with the lime to form the insoluble
calcium carbonate, or chalk. This experiment suggested another.
Fixing a piece of burning charcoal in the end of a bellows, he
arranged a tube so that the gas coming from the charcoal would
pass through the lime-water, and, as in the case of the bubbles
from the brewer's vat, he found that the white precipitate was
thrown down; in short, that carbonic acid was given off in
combustion. Shortly after, Black discovered that by blowing
through a glass tube inserted into lime-water, chalk was
precipitated, thus proving that carbonic acid was being
constantly thrown off in respiration.

The effect of Black's discoveries was revolutionary, and the
attitude of mind of the chemists towards gases, or "airs," was
changed from that time forward. Most of the chemists, however,
attempted to harmonize the new facts with the older theories--to
explain all the phenomena on the basis of the phlogiston theory,
which was still dominant. But while many of Black's discoveries
could not be made to harmonize with that theory, they did not
directly overthrow it. It required the additional discoveries of
some of Black's fellow-scientists to complete its downfall, as we
shall see.


HENRY CAVENDISH

This work of Black's was followed by the equally important work