Phlogiston theory

The idea of a phlogistic substance was first proposed in 1667 by Johann Joachim Becher and later put together more formally in 1703 by Georg Ernst Stahl.

Phlogiston theory attempted to explain chemical processes such as combustion and rusting, now collectively known as oxidation.

The theory was challenged by the concomitant weight increase and was abandoned before the end of the 18th century following experiments by Antoine Lavoisier in the 1770s and by other scientists.

Phlogiston theory led to experiments that ultimately resulted in the identification (c. 1771), and naming (1777), of oxygen by Joseph Priestley and Antoine Lavoisier, respectively.

[3]Joseph Black's Scottish student Daniel Rutherford discovered nitrogen in 1772, and the pair used the theory to explain his results.

[4] Empedocles had formulated the classical theory that there were four elements—water, earth, fire, and air—and Aristotle reinforced this idea by characterising them as moist, dry, hot, and cold.

[5] In 1667, Johann Joachim Becher published his book Physica subterranea, which contained the first instance of what would become the phlogiston theory.

He compared phlogiston to light or fire, saying that all three were substances whose natures were widely understood but not easily defined.

Giobert won a prize competition from the Academy of Letters and Sciences of Mantua in 1792 for his work refuting phlogiston theory.

[14] Eventually, quantitative experiments revealed problems, including the fact that some metals gained weight after they burned, even though they were supposed to have lost phlogiston.

However, a more detailed analysis based on Archimedes' principle, the densities of magnesium and its combustion product showed that just being lighter than air could not account for the increase in weight.

[9] During the eighteenth century, as it became clear that metals gained weight after they were oxidized, phlogiston was increasingly regarded as a principle rather than a material substance.

[18] Phlogiston remained the dominant theory until the 1770s when Antoine-Laurent de Lavoisier showed that combustion requires a gas that has weight (specifically, oxygen) and could be measured by means of weighing closed vessels.

[19] The use of closed vessels by Lavoisier and earlier by the Russian scientist Mikhail Lomonosov also negated the buoyancy that had disguised the weight of the gases of combustion, and culminated in the principle of mass conservation.

Her book on the subject appeared in print soon after Lavoisier's execution for Farm-General membership during the French Revolution.