How did Antoine Lavoisier interpret Joseph Priestley’s oxygen experiments?

When Joseph Priestley discovered a new gas in 1774, he identified it as "dephlogisticated air," believing it was ordinary air that had been stripped of phlogiston.1

After Priestley shared his findings with Antoine Lavoisier in Paris, Lavoisier repeated the experiments and interpreted the gas quite differently. Rather than viewing it through the lens of phlogiston theory, Lavoisier recognized the gas as a distinct chemical element—which he named oxygen—and identified it as the "active" principle in the atmosphere.21

Lavoisier used this discovery to construct a new, experimentally grounded theory of combustion, respiration, and calcination. By demonstrating that oxygen was the agent responsible for these processes, he provided a quantitative explanation for weight changes that the phlogiston theory could not account for. While Priestley remained a staunch defender of phlogiston throughout his life, Lavoisier’s interpretation ultimately superseded the older theory and revolutionized the field of chemistry.21