How Did Joseph Priestley Discover Oxygen?

English chemist Joseph Priestley discovered oxygen by reacting mercury oxide with heat through the use of a burning lens. Although the element was isolated by Swedish pharmacist Carl Wilhelm Scheele prior to Priestley’s discovery, Scheele failed to publish his findings. However, it was French chemist Antoine Lavoisier who gave oxygen its modern name.

Priestley identified oxygen as a distinct element in 1774. In one of his experiments, Priestley used a large magnifying glass, which was 1 foot in diameter, to concentrate sunlight on a compound of mercury oxide to elevate its temperature. The heated substance produced a gas that enabled a candle to burn at a much faster rate compared to burning in normal air. Priestley further noted that the blaze was incredibly brighter and stronger than usual. He meticulously recorded his observations, which he later published within the same year he performed his initial experiments.