84
See also: Joseph Black 76–77 ■ Henry Cavendish 78–79 ■
Joseph Priestley 82–83 ■ Jan Ingenhousz 85 ■ John Dalton 112–13F
rench chemist Antoine
Lavoisier brought a new
level of precision to science,
not least by naming oxygen and
quantifying its role in combustion.
By taking careful measurements
of mass in the chemical reactions
that occur during combustion,
he demonstrated the conservation
of mass—the principle that, in a
reaction, the total mass of all the
substances taking part is the same
as the total mass of all its products.
Lavoisier heated various
substances in sealed containers
and found that the mass a metal
gained when it was heated was
exactly equal to the mass of air lost.
He also found that burning stopped
when the “pure” part of the air
(oxygen) had all gone. The air that
remained (mostly nitrogen) did not
support combustion. He realized
that combustion therefore involved
a combination of heat, fuel (the
burning material), and oxygen.
Published in 1778, Lavoisier’s
results not only demonstrated the
conservation of mass, but also,
by identifying oxygen’s role incombustion, demolished the theory
of a fire element called phlogiston.
For the past century, scientists had
thought inflammable substances
contained phlogiston and released
it when they burned. The theory
explained why substances such as
wood lost mass on burning, but not
why others, such as magnesium,
gained mass on burning. Lavoisier’s
careful measurements showed that
oxygen was the key, in a process
during which nothing was added or
lost, but all was transformed. ■IN NATURE, NOTHING IS
CREATED, NOTHING IS LOST,
EVERYTHING CHANGES
ANTOINE LAVOISIER (1743–1794)
IN CONTEXT
BRANCH
ChemistryBEFORE
1667 German alchemist
Johann Joachim Becher
proposes that things are made
to burn by a fire element.1703 German chemist Georg
Stahl renames it phlogiston.1772 Swedish chemist
Carl-Wilhelm Scheele discovers
“fire air” (later called oxygen)
but does not publish his
findings until 1777.1774 Joseph Priestley isolates
“dephlogisticated air” (later
called oxygen) and tells
Lavoisier about his findings.AFTER
1783 Lavoisier confirms his
ideas on combustion with
experiments on hydrogen,
oxygen, and water.1789 Lavoisier’s Elementary
Treatise on Chemistry names
33 elements.I consider nature a vast
chemical laboratory in which
all kinds of composition and
decompositions are formed.
Antoine Lavoisier