02.18.10
Phlogiston and Caloric Theory
Sometimes it’s easy to forget how humiliatingly invalid our theories can prove to be, even if they do seem to explain what we observe with a certain amount of reliability. Not more than 300 years ago, the common consensus to explain combustion went something like this. Everything that is capable of burning, can do so because it has been endowed with a certain amount of an invisible, massless, colorless, odorless substance called Phlogiston. As the substance burns it releases it’s phlogiston into the air. Once that happens, the air becomes saturated with this phlogiston, and can hold no more, then there is sort of an equilibrium of phlogiston between the burning object and the air, then the object stops burning.
The theory was both unique and explained a lot of our observations. As something became dephlogistinated it would lose mass, and if air could no longer hold phlogiston then the burning would cease. This worked to explain observations, until it was replaced by a new theory by Antoine Lavoisier in which he observed the masses of heated gases in closed vessels using the apparatus shown above. He deduced that what causes something to burn is a gas he called oxygen, and that this combined with hydrogen to form water. To explain heat, he proposed Caloric Theory. Heat was said to be made up of a fluid gas with no mass which flows from areas of high density to areas of low density. This was actually not to far off from our current understanding and is the basis for a lot of current mechanics such as Carnot engines, where temperature gradients determine the amount of work an engine is capable of doing as the temperature stabilizing produces energy exothermically.
It’s kind of interesting how ideas can build on a framework of what, in retrospect, can be seen as an embarrassing failure. It’s also kind of funny to think that people will look back at us a hundred years from now, and very likely laugh at something we hold as a seminal pillar to our view of the world. Something like atomic theory could be revolutionized and all that would remain of it would be a vague tribute in the nomenclature of it’s replacements.
