Joseph Priestley

Birth: March 13, 1733
Death: February 6, 1804
Nationality: English
Occupations: Theologian, clergyman, natural philosopher, educator, and political theorist.How the element oxygen was discovered: Priestleyput a sprig of mint into a transparent closed space with a candle that burned out the air until it soon went out. After 27 days, he relit the extinguished candle again and it burned perfectly well in the air that previously would not support it. And how did Priestley light the candle if it was placed in a closed space? He focused sun light beams with a mirror onto the candle wick (Priestley had no bright source of light, and had to rely on the sun). Today, of course, we can use more sophisticated methods to light the candle like focusing light from a flood light through converging lens, or by an electrical spark.So priestly proved that plants somehow change the composition of the air. In another celebrated Experiment from 1772, Priestley kept a mouse in a jar of air until it collapsed. He found that a mouse kept with a plant would survive. These kinds of observations led Priestley to offer an interesting hypothesis that plants restore to the air whatever breathing animals and burning candles remove - what was later coined by Lavoisier "oxygen".
Other accomplishments: Many other gasses and he invented carbonated beverages (soda water) and the pencil eraser. He also had a great impact on the Unitartian movemement. He wrote over 150 works. His influence may be why most credit only Priestley for discovering oxygen.