showed that it could not sustain a flame or keep an animal alive; however,
plants thrived in the presence of fixed air.
Joseph Black’s findings led directly to other foundational studies by the
legends of chemistry over the next few decades, and it has been argued
that his thesis was “a brilliant model, perhaps the first successful model,
of quantitative chemical investigation, as well as a classic exemplar of
experimental science worthy of comparison with Newton’s Opticks.”^11
And it started with the young Scotsman leaning over a small flask of acid,
questioning why champagne-like bubbles would be emitted from a stone
submerged in liquid acid.
Thinking back on Jan van Helmont: is it possible that a tree gains
weight not from water, but from the air?
The notion that air was made of molecular building blocks was
appealing, but the monumental challenge of untangling the enigma was
daunting. Other British chemists produced hydrogen gas (Henry
Cavendish, 1766) and nitrogen gas (Daniel Rutherford, 1772) using the
bell jar. Those early chemists collected information about the constituent
gases in air principally by heating or burning objects trapped in a jar, or by
observing how plants and animals responded to each other in the chamber,
or by burning objects in the compartment. The explosion in the interest in
gases was no doubt fueled by the invention of the steam engine and the
burgeoning understanding in combustion. The mounting inquest among
the curious was, what fuels combustion?
Joseph Priestley was rising in prestige among the learned English, and
as British authority was crumbling in the American colonies, he accepted a
position as a tutor and savant at Bowood House, the estate of the Earl of
Shelburne, one hundred miles due west of London. In 1773, Priestley
became the librarian and intellectual companion to the Earl and his family,
and more important, became caretaker of experimental equipment that
would lead to one of the most important discoveries in the history of
thought.
In the late summer of 1774, Joseph Priestley focused his considerable
attention on a curious red material called mercury calx, a crimson powder
that resembles paprika. When heated, mercury calx turns into liquid
mercury, the legendary quicksilver that had intrigued alchemists for
centuries. But even savants like Isaac Newton had squandered the