Which scientist discovered that plants release oxygen in 1772?

The scientist credited with discovering that plants can restore air and release oxygen in the classic 1772 experiments was Joseph Priestley.

Priestley placed a candle or a small animal under an inverted jar and observed that the enclosed air soon became unable to support burning or life. When he added a green plant, the air was gradually “restored,” allowing a flame to burn again or an animal to survive longer. These experiments provided an early demonstration of photosynthetic gas exchange.

There is an important historical nuance. Priestley did not correctly identify the gas in modern chemical terms at the time, and his interpretation remained tied to the old phlogiston theory. He later isolated what he called “dephlogisticated air,” now recognized as oxygen, in 1774.

Jan Ingenhousz expanded the work in 1779 by showing that oxygen production depended on green plant tissues and light. Jean Senebier later demonstrated the importance of carbon dioxide. Thus, Priestley is the standard answer for the initial discovery, while Ingenhousz and Senebier supplied crucial refinements to the emerging story of photosynthesis.