What is the Phlogiston Theorem?June 26, 2021
Lavoisier gained fame in the scientific world with his new theory about the combustion phenomenon.
However, he also had other important works in creating the alchemical revolution. In addition, the extraordinary sensitivity he showed in his experiments, especially in the measurement process, became an enviable example for the new generation researchers who followed him. chemistry language; It owes its scientific identity to Lavoisier in terms of logical order and theoretical explanation. His wife provides great support in all these works: he draws experimental shapes, makes translations from foreign languages, and prepares his articles and books for publication.
When Lavoisier began his research, the phlogiston theory of combustion was valid in chemistry, along with the Ancient Greeks’ teaching of the four elements of matter (earth, water, fire, and air). As it is known, when a piece of wood or cloth burns, smoke and flame emerge, and the burning object disappears by leaving some ash.
According to the current theory, combustion; It meant that the burning object would release a mysterious substance called phlogiston, which is unknown. Objects that left the least ash when burned, such as charcoal, were the richest in phlogiston. There were some observations that contradicted this theory, which scientists mostly found satisfactory. One of them was the necessity of air for combustion. Another was that when metals such as lead were heated to melting point, the “calx” formed on their surface was heavier than the depleted portion of the metal. In fact, one reason for the difficulty in explaining the combustion phenomenon was the lack of knowledge about gases. Air was the only gas known until 1756, when Scottish chemist Joseph Black discovered carbon dioxide, which he called the “fixed gas”. British chemist Joseph Priestley later discovered about 10 new gases experimentally. One of them is what he calls “competent gas”, which Lavoisier later calls “oxygen”.
Although Priestley discovered oxygen, he could not break with the phlogiston theory. An outstanding experimenter, this British scientist was not qualified to take on his theoretical rival, Lavoisier. Lavoisier became interested in combustion in the early 1770s. He determined that the weight of the gas did not change when phosphorus was burned in a closed container, whereas when he opened the container, the weight of the gas increased slightly as the air entered. This observation obviously did not fit the prevailing theory, but there was no more satisfactory explanation.