in the fact that his general studies were along lines leading
away from the accepted doctrines of the time, and that they gave
the impetus to the investigation of the properties of gases by
such chemists as Black, Priestley, Cavendish, and Lavoisier,
whose specific discoveries are the foundation-stones of modern
chemistry.


JOSEPH BLACK

The careful studies of Hales were continued by his younger
confrere, Dr. Joseph Black (1728-1799), whose experiments in the
weights of gases and other chemicals were first steps in
quantitative chemistry. But even more important than his
discoveries of chemical properties in general was his discovery
of the properties of carbonic-acid gas.

Black had been educated for the medical profession in the
University of Glasgow, being a friend and pupil of the famous Dr.
William Cullen. But his liking was for the chemical laboratory
rather than for the practice of medicine. Within three years
after completing his medical course, and when only twenty-three
years of age, he made the discovery of the properties of carbonic
acid, which he called by the name of "fixed air." After
discovering this gas, Black made a long series of experiments, by
which he was able to show how widely it was distributed
throughout nature. Thus, in 1757, be discovered that the bubbles
given off in the process of brewing, where there was vegetable
fermentation, were composed of it. To prove this, he collected
the contents of these bubbles in a bottle containing lime-water.