Answer:
Lavoisier disproved the phlogiston theory. He demonstrated that there was an element called oxygen that played a major role in combustion. He also showed that the mass of products in a reaction are equal to the mass of the reactants. The phlogiston theory did not account for the weight changes found in fire. Lavoisier hypothesized that it was probably the fixation and release of air, rather than fire, that caused the observed gains and losses in weight.