Joseph Priestley performed the classic experiment showing that a plant could restore air that a candle had burned. In experiments reported in the 1770s, he placed a sprig of mint under a sealed bell jar after a candle had extinguished, then found that the candle could later be relit.
Priestley’s result suggested that plants could reverse at least part of the change caused by combustion. He described this as restoring the air, using the scientific language of his time rather than the modern terms oxygen and photosynthesis. His work helped establish that air was not a single unchanging substance.
The experiment did not by itself reveal the full mechanism. Jan Ingenhousz later showed that plants restore air only when exposed to light and that green plant tissues are especially important. Antoine Lavoisier’s later work clarified the role of oxygen in combustion and respiration, giving Priestley’s observation a more accurate chemical interpretation.
A common mix-up is to credit Ingenhousz with Priestley’s candle-and-mint experiment. Ingenhousz expanded and interpreted the finding, but Priestley is the standard answer for the original demonstration that a plant could restore air after combustion.