Excerpt:
Joseph Priestly was a clergyman, teacher, librarian and scientist who lived from 1733 to 1804. Joseph was the oldest son of a weaver and a farmer's daughter named Mary Swift. Mary died when Joseph's was six years old, and he was adopted by his paternal aunt, Sarah Kelghley. He attended Daventry academy, and studied under tutors as he developed a strong interest in chemistry.
His most important achievement was the isolation of oxygen by heating mercuric oxide. The gas we now refer to as oxygen was originally called "dephlostigated air"! He shared credit for this discovery with a Swede named Carl Scheele. Scheele was the one who figured out that heating liquids results in a release of gas. It was Priestly who, using Scheele's information, first isolated oxygen.