How did Antoine Lavoisier show that air is a mixture of gases?

Antoine Lavoisier demonstrated that atmospheric air is a mixture of gases by meticulously tracking the weight changes of substances during chemical reactions such as combustion and calcination.1

Through his experiments, Lavoisier observed that metals and nonmetals gained weight when they reacted with air, contradicting the phlogiston theory which suggested substances lost a principle during burning. By building upon the work of other pneumatic chemists, he identified that the active component absorbed from the air during these processes was a specific gas he named oxygen.213

Lavoisier concluded that atmospheric air was not a single, indivisible substance but rather a mixture of at least two principal components: oxygen and a physiologically inert gas he called azote, now known as nitrogen. His success relied on his rigorous use of precise weighing to account for all gases entering and emerging from his experiments, effectively establishing the foundation of modern chemistry.1