Lavoisier
was a wealthy Parisian
with a flair and enthusiasm for science. In his investigations
he always looked for measurable quantities;
he was one of the first
to emphasize quantitative
methods in chemistry.
In 1772, Lavoisier became interested in combustion
for
which
the accepted explanation
at the time was the phlogiston
theory.
His experiments, along with those of Joseph
Priestley, led him to doubt this
theory. By 1777, he became convinced
that combustion was due to oxygen and
eventually he framed an oxygen
theory of combustion. In 1789, Lavoisier
published an influential book, the Traité élémentaire de
chimie that systematized chemistry in terms of the new oxygen theory. Much of
the nomenclature introduced in this book is still in use today.
Lavoisier's wealth and business connections were resposible for his
marraige to Marie-Anne Pierette (shown in the famous protrait by David
at the right) and his membership in a tax-collection firm. This membership,
among other things, led to his public execution during the Reign of Terror
following the French Revolution.
He was one of the first to emphasize the importance of weight (or
mass, as we now call it) in chemistry. In his studies, he formulated
a statement of the principle of conservation of mass.
The Phlogistion Theory
The phlogiston theory was introduced by Becher (1635-1682) and developed
by his desciple. Stahl (1660-1734). This was an important theory--one
of the first generalizations in chemistry that correlated in a simple
manner many chemical phenomena. According to the phlogiston theory,
combustion was due to a loss of phlogiston [φ]. For instance,
this theory would interpret carbon as high in phlogistron. When carbon
burns, it
loses its phlogiston.
As one example, it offered an explanation of why combustion eventually
stops in a closed container. As combustion proceeds, the air in the
container fills up with phlogistion. When the air becomes saturated
with phlogiston, combustion ceases.
Joseph Priestley (1733-1804)
Priestley was an English clergyman who "isolated and studied more
new gases than any person before or since"(3) . Among the many gases
that Priestley studied was one released when the red calx of mercury
was heated. This gas was not soluable in water and caused a candle
to burn brilliantly. Priestley, being a firm believer in the phlogiston
theory, thought that this was "dephlogisticated air"--air with all
the phlogiston removed. Lavoisier later interpreted the air to be
a new gas, oxygen, which was neccessary for combustion.
The Oxygen Theory
According to the oxygen theory, air contains a gas called "oxygen",
which is a chemical element involved in combustion. For instance,
when carbon burns it reacts with oxygen in the air. We now write this
as
C + O2 ---> CO2
The realization of the importance of oxygen was a "death blow to the
concept of air and water elements" (3).
