01 August - Joseph Priestley discovered oxygen by isolating it in its gaseous state.

 

Joseph Priestley was an English theologian, chemist, and natural philosopher. He is best known for his contributions to the field of chemistry and his discovery of several gases, including oxygen. Priestley's experiments with the "dephlogisticated air" (what he called oxygen) were groundbreaking and had a profound impact on the understanding of chemistry.

In August 1774, Priestley conducted an experiment in which he isolated a colorless, odorless gas by heating mercuric oxide with a magnifying glass. He noticed that a candle burned more brightly and a mouse placed in this gas could breathe more easily and for a longer time compared to ordinary air. He referred to this gas as "dephlogisticated air," believing it to be the essence of air that supported combustion and respiration.

Priestley's discovery of oxygen was one of the critical milestones in the history of chemistry and laid the foundation for our modern understanding of gases and combustion. His work was later built upon by Antoine Lavoisier, who recognized the true nature of oxygen and coined its name. As a result, Priestley is often credited as one of the pioneers of modern chemistry.