Phlogiston was believed to be the substance that was given off by a flammable object when it was burned. For example, when wood was burned, its mass would decrease so in 1669 a scientist called Johann Becher, believed this to be a colourless, odourless, weightless fire element that was lost during combustion. Only things that contained phlogiston would burn and would be dephlogisticated when all phlogiston had left the item and had become ash or residue which was known as true material or ‘calx’. If something was burned to nothing it was thought to be completely composed of phlogiston. Nowadays, phlogiston is known to be the process called oxidation in chemistry.
The idea of Phlogiston was created at this time as a form of trying to determine what caused rusting in metals. This was invented in England
Phlogiston is that theory, it was used to explain many experiments which at the time weren’t understood or could be proven by scientists. The theory at the time was very simple and was used by scientists who tested different types of materials; once the materials had been burnt the dephlogisticated remains would be left. In 1772 the Phlogiston theory was used to prove Nitrogen.
The phlogiston theory was connected with ideas to do with alchemy where it was thought the four elements earth, air, fire and water were all contained within a substance which is shown in the diagram below. Substances which burned in the air were said to be rich in phlogiston, with the fact that combustion after a while stopped in an enclosed space this was taken as evidence that air couldn’t absorb more phlogiston.
The surrounding air that was saturated in phlogiston was said to be ‘phlogisticated air’. When oxygen was discovered it was thought to be "dephlogisticated air" which was able to take in more phlogiston and supported the theory of combustion.
The theory was believed for 100 years where problems in the theory were patched up by philologists who strongly believed in the theory. It wasn’t until 1753 that it was disproved by the discovery of oxygen as a separate element. Also a Russian chemist called Mikhail Lomonsov discovered that if magnesium was weighed,placed in a sealed bottle, and burned then the overall mass would not be reduced and weighed the same. Since phlogiston was supposed to pass through glass and so forth he concluded that the theory was wrong.
Oxygen was discovered in the early 1770s by two different people One was Carl Scheele inSweden and the other Joseph Priestley in England
Oxygen was discovered in the early 1770s by two different people One was Carl Scheele in
Lavoisier's had done similar experiments to Lomonsov which involved weighing of metal before and after combustion in an enclosed bottle and finding the weight stayed the same. But he took it further and opened the bottle, noting some gas went in. After reweighing it, he found the extra weight of the gas was the same as the increase in the weight of the metal plus the burnt metal. He therefore concluded that the metal had absorbed something from the air in the bottle that turned out to be oxygen therefore going against the idea of the phlogiston theory which was later dismissed as just a hypothesis in the 18th century and better theories were made.
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