Oxygen was identified as a distinct substance during the 1770s, and three scientists share the credit in different ways: Carl Wilhelm Scheele, a Swedish-German apothecary, prepared the gas first around 1771–1772; Joseph Priestley, an English clergyman and natural philosopher, independently isolated it and published the finding first in 1774; and Antoine-Laurent de Lavoisier, a French chemist, correctly interpreted what oxygen actually was and gave it the name we use today. Which of these men “discovered” oxygen depends on what you think discovery means, and that question has fueled an argument that has lasted a quarter of a millennium.
A Polish Alchemist Had the Idea Two Centuries Early
Long before the 1770s, people had inklings that air was not a single substance and that some part of it sustained life. The most striking early figure is Michael Sendivogius (1566–1636), a Polish alchemist who called a component of air “the food of life” and connected it to the gas released by heating saltpetre (potassium nitrate).1PubMed. Eight sages over five centuries share oxygen’s discovery Sendivogius described this substance as essential to all living things, saying it was “not solid but of an intermediate nature” and likening it to a “water of life not wetting the hands,” without which nothing could grow or be generated in the world.2Chemistry-Didactics-Ecology-Metrology. Does Sendivogius’ Alchemy Cancel the Celebration of the 250th Anniversary of the Discovery of Oxygen? It was a poetic and surprisingly accurate intuition, but Sendivogius worked within the framework of alchemy rather than experimental chemistry. He never isolated oxygen as a gas, measured its properties, or communicated his ideas in a way the emerging scientific community could build on. His contribution is best understood as a conceptual ancestor rather than a discovery in the modern sense.
Scheele Made It First but Published Last
Carl Wilhelm Scheele (1742–1786) was a remarkably productive chemist who spent most of his career working in pharmacies across Sweden. By around 1771–1772, he had heated manganese dioxide and other metal oxides and collected a gas he called “fire air” because flames burned more brightly in it. He was, by all available evidence, the first person to prepare oxygen in a relatively pure form and to describe some of its properties.3PubMed. Joseph Priestley, oxygen, and the enlightenment He also noticed that mice survived longer in fire air than in ordinary air, hinting at its biological importance.
The problem was timing. Scheele was meticulous about his laboratory notebooks but slow to get his work into print. His book describing the preparation of fire air, Chemical Treatise on Air and Fire, did not appear until 1777, three years after Priestley had already announced the same gas to the world. Because scientific priority depends on publication, Scheele’s earlier lab work could not retroactively claim the credit that came with being first in print.4American Journal of Physiology-Lung Cellular and Molecular Physiology. Carl Wilhelm Scheele, the discoverer of oxygen, and a very productive chemist The delay was partly bad luck: his publisher apparently sat on the manuscript for an unusually long time.
Priestley’s Famous Experiment of 1774
Joseph Priestley (1733–1804) made his breakthrough on August 1, 1774, at Bowood House in Wiltshire, England, where he served as librarian and intellectual companion to the Earl of Shelburne. Using a large magnifying lens to focus sunlight onto a lump of mercuric oxide (then called “mercurius calcinatus per se”), Priestley heated the compound and collected the gas that bubbled off. He found that a candle burned with unusual vigor in this gas and that a mouse placed in a sealed container of it survived far longer than expected. He called the substance “dephlogisticated air,” interpreting it through the dominant theory of his era, which held that burning and rusting involved the release of a hypothetical substance called phlogiston.
Priestley published his findings relatively quickly, and in October 1774 he traveled to Paris and personally informed members of the French Academy of Sciences about his experiments. Among those who heard the news was Lavoisier.5PubMed. Fire-air and dephlogistication. Revisionisms of oxygen’s discovery That meeting would prove fateful for the history of chemistry.
Priestley continued to investigate the gas and noticed something extraordinary: a sprig of mint placed in a sealed jar could restore “spent” air, making it breathable again. This was the first experimental demonstration that plants can regenerate the breathable component of air, a process we now call photosynthesis.6PubMed Central. A paradigm of fragile Earth in Priestley’s bell jar His bell-jar experiments with mice and mint plants remain one of the classic demonstrations in biology, linking the gas he had isolated to the survival of living organisms.
Lavoisier Understood What Oxygen Actually Was
Antoine-Laurent de Lavoisier (1743–1794) did not independently discover oxygen in the way Scheele and Priestley did, but he grasped its significance more deeply than either of them. After learning of Priestley’s experiment during the 1774 visit to Paris, Lavoisier repeated it and then went much further. Through careful weighing experiments, he showed that when metals were heated in air and formed a “calx” (what we would call an oxide), they gained weight rather than losing some mysterious substance. When the calx was reduced back to a metal, it lost exactly that weight. The gain and loss corresponded to the absorption and release of a specific gas: the same gas Priestley had isolated.7ChemistryViews. Antoine-Laurent de Lavoisier
This was devastating to phlogiston theory. If burning meant releasing a weightless substance from the burning material, then the burned material should weigh less, not more. Lavoisier concluded that combustion was not a matter of shedding phlogiston but of combining with the gas he eventually named “oxygène,” from Greek words meaning “acid-former” (he mistakenly believed all acids contained it). The naming stuck, and Lavoisier’s broader reinterpretation of chemistry, sometimes called the Chemical Revolution, replaced phlogiston with the modern concept of chemical elements combining and separating in measurable proportions.
Lavoisier also extended his insight to biology. Using an ice calorimeter, he demonstrated that respiration and combustion were fundamentally the same process: both consumed oxygen and produced heat and carbon dioxide.8PubMed. Antoine-Laurent de Lavoisier (1743-1794) and the birth of respiratory physiology This was the foundation of respiratory physiology, a field that barely existed before him. While Priestley had observed that his gas kept mice alive, Lavoisier explained why: the body burns fuel, and oxygen is the substance that makes that burning possible.
The Priority Dispute and a Letter Hidden for 218 Years
Arguments over who deserves the title “discoverer of oxygen” have been shaped as much by national pride as by evidence. In the English-speaking world, especially in American education, Priestley has traditionally received primary credit for discovering oxygen in 1774 and reporting it to Lavoisier. In Scandinavia, Scheele is celebrated as the true discoverer because he prepared the gas years before Priestley. In France, Lavoisier is honored as the one who understood the gas’s nature and thereby revolutionized all of chemistry.5PubMed. Fire-air and dephlogistication. Revisionisms of oxygen’s discovery
One of the most dramatic chapters in the dispute involves a missing letter. Scheele later claimed that he had written to Lavoisier in September 1774, describing his preparation of “fire air,” before Priestley’s visit to Paris. Lavoisier denied receiving it, and without proof, Scheele’s claim remained unverified for more than two centuries. Then, in 1992, the letter was found among the papers of Madame Lavoisier, who had preserved her husband’s correspondence after his execution during the French Revolution. The letter showed that Lavoisier received Scheele’s description on October 15, 1774, and thus knew about Scheele’s work at essentially the same time he learned of Priestley’s.5PubMed. Fire-air and dephlogistication. Revisionisms of oxygen’s discovery Lavoisier, it turns out, had been informed by both men and failed on several occasions to credit either of them for their contributions.
This revelation did not settle the dispute so much as deepen it. Lavoisier’s silence about Scheele’s letter casts a shadow over his reputation, but it does not diminish the substance of his intellectual contribution: neither Scheele nor Priestley grasped that phlogiston theory was wrong, and neither replaced it with something better. Priestley, remarkably, clung to phlogiston for the rest of his life. Scheele did too. The gas they isolated was real, but their interpretation of it was not.
So Who Really Discovered Oxygen?
The honest answer is that the question does not have a single winner, and the reason is instructive. Scientific discovery is rarely a single event. It unfolds in stages: preparation (isolating the substance), publication (telling the world), and interpretation (understanding what the substance is and why it matters). Scheele achieved the first, Priestley achieved the second, and Lavoisier achieved the third. A comprehensive historical assessment describes Scheele as “undoubtedly the first person to prepare oxygen and describe some of its properties,” while acknowledging that Priestley is “rightly recognized as the first person to report” its preparation, and Lavoisier went on to describe the gas’s true nature where Priestley could not.4American Journal of Physiology-Lung Cellular and Molecular Physiology. Carl Wilhelm Scheele, the discoverer of oxygen, and a very productive chemist
If you define discovery as “first to make the stuff,” it’s Scheele. If you define it as “first to tell people about it,” it’s Priestley. If you define it as “first to understand what it is,” it’s Lavoisier. Each definition is defensible, and each leaves something out. Most historians of chemistry today treat the discovery as a collaborative achievement, even though the three men barely cooperated and one of them actively suppressed the contributions of the other two.
Why Priestley Never Let Go of Phlogiston
One of the stranger footnotes to this story is Priestley’s lifelong loyalty to phlogiston theory, even after Lavoisier’s alternative had won over most of the scientific world. Priestley was not an unintelligent man; he was a polymath who made contributions to electrical science, political philosophy, and theology in addition to chemistry. But he saw his gas through the lens of the framework he already held, and he could not bring himself to abandon it. He called oxygen “dephlogisticated air” until his death in 1804, three decades after isolating it.5PubMed. Fire-air and dephlogistication. Revisionisms of oxygen’s discovery
This is a useful reminder that making a discovery and understanding a discovery are different cognitive acts. Priestley’s hands and eyes gave science oxygen. His mind never quite caught up. It was Lavoisier who saw what Priestley’s experiment actually meant, and that interpretive leap, not the moment of isolation itself, was what allowed chemistry to move forward. The episode is a textbook case of what historians of science call “theory-ladenness of observation”: what you see depends, in part, on what you already believe.
The Personal Costs
None of the three principal figures had an easy life after their involvement with oxygen. Lavoisier, who had worked as a tax collector for the ancien régime, was arrested during the Reign of Terror and guillotined on May 8, 1794, at the age of 50. The mathematician Joseph-Louis Lagrange reportedly said, “It took them only an instant to cut off his head, and one hundred years might not suffice to reproduce its like.” Priestley, a political and religious dissenter, saw his home and laboratory in Birmingham destroyed by a mob in 1791; he eventually fled to Pennsylvania, where he spent the last decade of his life in relative obscurity. Scheele, the quietest of the three, died at just 43, likely poisoned by years of tasting and sniffing the chemicals he worked with, a common hazard of eighteenth-century laboratory practice.
Their fates reflect the turbulence of the era. The 1770s and 1780s were a time of political and intellectual revolution, and the men who reshaped chemistry were caught up in the same upheavals that reshaped governments. Oxygen’s discovery sits at the intersection of the Enlightenment’s highest ambitions and its most violent consequences.
Oxygen on Earth Long Before Anyone Identified It
While humans only recognized oxygen as a chemical element in the eighteenth century, the gas itself has been shaping the planet for billions of years. Earth’s earliest atmosphere contained almost no free oxygen. The rise of oxygen to its current concentration of about 21 percent of the atmosphere is tied to the evolution of cyanobacteria, single-celled organisms that developed oxygenic photosynthesis and began pumping the gas into the air as a waste product. This process, sometimes called the Great Oxidation Event, began roughly 2.4 billion years ago and dramatically altered the chemistry of the oceans, the atmosphere, and the rocks at Earth’s surface.9Annual Review of Earth and Planetary Sciences. THE EARLY HISTORY OF ATMOSPHERIC OXYGEN: Homage to Robert M. Garrels
The rise of atmospheric oxygen was not smooth. Evidence from ancient rocks suggests that oxygen levels fluctuated considerably over the Precambrian, with at least one period of significant decline between the initial rise and the second major increase that preceded the Cambrian explosion of animal life around 540 million years ago. The geological record, including the presence or absence of certain iron minerals and sulfur compounds in ancient sediments, provides the main constraints on what oxygen concentrations looked like through deep time.9Annual Review of Earth and Planetary Sciences. THE EARLY HISTORY OF ATMOSPHERIC OXYGEN: Homage to Robert M. Garrels
The connection to the eighteenth-century story is worth noting. When Priestley put a mint sprig in a jar with a mouse and watched the plant restore breathable air, he was observing, in miniature, the same process that made Earth habitable in the first place. The gas Scheele, Priestley, and Lavoisier identified had already been the most consequential molecule in the history of life for over two billion years. They just happened to be the first humans clever enough, and lucky enough, to trap some of it in a jar and ask what it was.