Phlogiston theory

A concern of chemistry in the eighteenth century on the combustion process . They argued that heating the substances to the point of incandescence produced a loss of the original substance. This loss in the combustion process was called “phlogiston”.

Summary

[ hide ]

  • 1 History
  • 2 consequences
  • 3 Writings where it appeared
  • 4 Retribution
  • 5 Sources

History

Taking the ancient Greek conceptions that everything that can burn contains within itself the element of fire, what was happening in the combustion process was a central concern for chemistry in the 18th century . When the substances were heated to the point of incandescence, the scientists saw that they emit something “in the form of vapors or smoke”, this they interpreted as a loss of the original substance. That “something” that was supposedly lost in the combustion process was called a phlogiston.

Word coined by the German chemist Georg Ernst Stahl ( 1660 – 1734 ) in 1697 as an essence contained in combustible materials, without which combustion was impossible, stated the following; Following the conceptions of his teacher Joann Joachin Becher ( 1635 – 1682 ), he believed that substances were made up of three types of “earth”, plus water and air. He renamed one of those lands, which Becher had called “fuel,” a phlogiston (which from the Greek phlogizein, means “to catch fire”, “to burn”), to which he assigned the noble and supreme purpose of being the agent and support of combustion. Combustion, according to Stahl, consisted of an exchange of phlogiston, which flowed between the materials; to burn was to let out phlogiston (which like an invisible smoke mixed with the air). What remained after combustion had no phlogiston and therefore could not continue burning. Air was indispensable for combustion, but as a mere mechanical aid and what a modern chemist would call reduction consisted of incorporating the floating phlogiston to have it ready for a new combustion.

Consequences

The phlogiston theory gave rise to some anomalies. Since it was a component of combustible materials , as it was lost during combustion, the residues had to weigh less than the substances weighed before burning, and this was the case for some, such as wood. But certain metals, when heated, turned into a soft substance called calx; in these cases, the residue weighed more than the original metal.

This anomaly was ignored by many proponents of the phlogiston theory. Others rationalized it by suggesting that the phlogiston had a negative weight, causing the residue to weigh more when the phlogiston had been consumed.

Writings where it appeared

A good example of the books that used this theory is the popular work by Joseph Macquer , Élémens de chymie-théorique.

Repercussion

Some historians claim that the phlogiston theory can be considered as the first great theory of modern chemistry.

In addition, a few years before the French Revolution, Antoine-Laurent de Lavoisier 1775 carried out certain experiments on combustion and oxidation, and using the instrument, the balance almost unknown in the quasi-alchemist laboratories of the time, carefully measured the mass before and after combustion, without forgetting the gases emitted, which it collected and also weighed. All with the aim of weighing and measuring the phlogiston formed. Result: stubbornly, the phlogiston had a negative mass; Due to this and since it could not be otherwise because when burned, the bodies gain mass, combining with some element from the atmosphere such as oxygen , finally with it Lavoisier demonstrated the nonexistence of the phlogiston.

 

Leave a Comment