The Science of Existence (75-3) Discovery of Oxygen

Discovery of Oxygen

English theologian Joseph Priestley is often credited with discovering oxygen, though claims can be made for Antoine Lavoisier and Carl Wilhelm Scheele.

Priestley gained a scientific reputation for inventing soda water. He also wrote on electricity, and discovered several airs, including “dephlogisticated air,” now known as oxygen. Priestley was a staunch adherent of Johann Joachim Becher’s phlogiston theory: that combustible matter contained a hidden fire element, phlogiston.

Priestley’s attribution of oxygen as dephlogisticated air was confused, because, under the theory of phlogiston, oxygen would be the gaseous venue by which phlogiston can be released: a phlogisticating air, not dephlogisticated air.

Priestley’s discovery was made by heating mercury oxide by sunlight, and having mice, and later himself, breath the results (vaporous mercury and oxygen). His 1776 published description of isolated dephlogisticated air did not identify oxygen per se.

Antoine Lavoisier determined air as a mixture of gases, primarily nitrogen and oxygen. Lavoisier demonstrated oxygen as the agent of rusting metals and explained oxygen’s role in plant and animal respiration.

Lavoisier’s explanation of combustion disproved the phlogiston theory that Priestley held dear. Priestley never accepted Lavoisier’s outrageous speculations on oxygen, respiration, and rust. Instead, Priestley religiously defended phlogiston theory for the rest of his life.

Priestley, with a Presbyterian cast of mind, also maintained that humans have no free will, that instead conditions create dynamics with inevitable outcomes (predeterminism). According to Priestley, everything in Nature, including men’s minds, are subject to the law of causation, but because a benevolent God created all, perfection of man and the world would come in due time. For Priestley, evil arose only from an imperfect understanding of the world.

Swedish pharmaceutical chemist Carl Wilhelm Scheele was called “hard-luck Scheele” by American writer and biochemistry professor Isaac Asimov because Scheele made several chemical discoveries before others who are generally given the credit. Slow to publish, Scheele was scooped on oxygen, hydrogen, chlorine, barium, tungsten, and molybdenum. Scheele isolated oxygen about 2 years before Priestly, but Priestly published first.

Like Priestley, Scheele, who called oxygen “fire air,” described the gas using phlogistical terms, as he considered his discovery as confirming, not overturning, phlogiston theory.

Though Scheele did not comprehend the import of his oxygen discovery, others did. Scheele wrote Lavoisier about his findings. Lavoisier grasped the significance. Ironically, Scheele’s report was pivotal in invalidating the long-held theory of phlogiston.