78
INFLAMMABLE
AIR
HENRY CAVENDISH (1731–1810)
I
n 1754, Joseph Black had
described what we now call
carbon dioxide (CO 2 ) as “fixed
air.” He was not only the first
scientist to identify a gas, but also
demonstrated that there were
various kinds of “air,” or gases.
Twelve years later, an English
scientist named Henry Cavendish
reported to the Royal Society in
London that the metals zinc, iron,
and tin “generate inflammable air
by solution in acids.” He called his
new gas “inflammable air” because
it burned easily, unlike ordinary
or “fixed air.” Today we call it
hydrogen (H 2 ). This was the second
gas to be identified and the first
gaseous element to be isolated.Cavendish set out to measure the
weight of a sample of the gas, by
measuring the loss of weight of
the zinc-acid mixture during the
reaction, and by collecting all
the gas produced in a bladder and
weighing it—first full of the gas,
then empty. Knowing the volume,
he could calculate its density. He
found that inflammable air was 11
times less dense than ordinary air.
The discovery of low-density
gas led to aeronautical balloons
that were lighter than air. In France
in 1783, inventor Jacques Charles
launched the first hydrogen balloon,
less than two weeks after the
Montgolfier brothers launched
their first manned hot-air balloon.IN CONTEXT
BRANCH
ChemistryBEFORE
1661 Robert Boyle defines an
element, laying the foundations
for modern chemistry.1754 Joseph Black identifies
a gas, carbon dioxide, which
he calls “fixed air.”AFTER
1772–75 Joseph Priestley
and (independently) Sweden’s
Carl Scheele isolate oxygen,
followed by Antoine Lavoisier,
who names the gas. Priestley
also discovers nitric oxide,
nitrous oxide, and hydrogen
chloride, and experiments with
inhaling oxygen and making
soda water.1799 Humphry Davy suggests
nitrous oxide could be useful
as an anesthetic in surgery.1844 Nitrous oxide is first used
for anesthesia by American
dentist Horace Wells.This must be an
inflammable air.They burn rapidly
when ignited.When a metal such as zinc
reacts with dilute acid,
it produces bubbles.These bubbles
may be a new air.