A depiction of phlogiston theory, the supposition that when wood burned, phlogiston and calx were products. |
“Every thermodynamic material does indeed have a constitutive state function, (‘phlogiston’?), which can be given a definition: ‘minus the Gibbs chemical potential of oxygen within the material.’ It has the dimensions of (free) energy per mole of oxygen, and measures its oxidation propensity. While the antiphlogistonists may have been the first inorganic chemists, Priestley’s conceptual interpretation of phlogiston was the first attempt at the physical chemistry of reactions. If phlogiston is regarded as an alternative description of ‘Gibbs free energy,’ the theory appears to be an intuitively accurate description, as could reasonably be expected at that time, and remains essentially correct today given its precise thermodynamic definition.”