The Chemical Revolution

The chemical heritage of Antoine-Laurent Lavoisier

When the 17-year-old Lavoisier left Mazarin College in Paris in 1761, chemistry hardly could be called a true science. Unlike physics, which had come of age through the work of Isaac Newton a century earlier, chemistry was still mired in the legacy of the Greek philosophers. The four elements of Aristotle — earth, air, fire, and water — had been slowly modified by the medieval alchemists, who added their own arcane language and symbolism. Thrown into this mix was the concept of phlogiston. Developed by the German scientist Georg Ernst Stahl early in the 18th century, phlogiston was a dominant chemical concept of the time because it seemed to explain so much in a simple fashion. Stahl believed that every combustible substance contained a universal component of fire, which he named phlogiston, from the Greek word for inflammable. Because a combustible substance such as charcoal lost weight when it burned, Stahl reasoned that this change was due to the loss of its phlogiston component to the air:

charcoal + heat --> ash + phlogiston

It followed that the less residue a substance left on burning, the greater its phlogiston content. Turning from organic substances to metals, Stahl knew that a metal calx heated with charcoal formed the original metal. He proposed that the phlogiston of the charcoal had united with the calx:

phlogiston + calx --> metal

Therefore, metals, which were thought to contain phlogiston, were also classified as combustibles. The difficulty with this scheme was the reverse reaction. When metals were strongly heated in air, the resulting calx weighed more than the original metal, not less, as would be expected if the lead had lost the phlogiston component. This inconsistency caused some phlogistonists to suggest that phlogiston might even have a negative weight. Lavoisier was introduced to phlogiston by Guillaume François Rouelle, whose lectures he attended while pursuing a law degree. By 1772, having abandoned law to pursue a career in science, Lavoisier turned his curiosity to the study of combustion.

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The chemical heritage of Antoine-Laurent Lavoisier | Combustion and the attack on phlogiston
A new chemistry emerges | Lavoisier's American legacy
The life of Antoine-Laurent Lavoisier (1743-1794) | Landmark designation