The discovery of oxygen, a gas that constitutes about one-fifth of Earth’s atmosphere, is not attributable to a single person or moment. This fundamental element, necessary for life and most forms of combustion, emerged from the work of multiple scientists during the 1770s. The full understanding of the gas—from its physical isolation to its chemical identification and naming—was a complex, multi-stage process. This scientific breakthrough involved independent experiments and theoretical insights that collectively laid the groundwork for modern chemistry.
Isolation by Scheele and Priestley
The physical isolation of oxygen was achieved independently by two chemists: Carl Wilhelm Scheele and Joseph Priestley. Scheele, a Swedish pharmacist, was likely the first to isolate the gas, performing his experiments around 1772. He produced the gas by heating substances like mercuric oxide and potassium nitrate, calling his discovery “fire air” because it vigorously supported combustion. Scheele’s findings were documented in a manuscript, but publication was delayed until 1777, several years after his English counterpart had made his work public.
Joseph Priestley conducted his own independent discovery on August 1, 1774. He focused sunlight onto mercuric calx (mercuric oxide) using a large burning glass, collecting the resulting colorless gas over mercury. He observed that a candle burned with an intensely bright flame in the substance. As a proponent of the prevailing phlogiston theory, he named his discovery “dephlogisticated air,” believing it was common air stripped of phlogiston.
Priestley published his results in 1775, meaning that although Scheele had isolated the gas earlier, Priestley was the first to widely disseminate his findings. This swift publication secured him initial recognition and introduced the isolated gas to the broader scientific community. This dual discovery highlights the simultaneous investigation that characterized the chemical revolution of the late 18th century. The two chemists had successfully produced the same substance, but neither fully grasped its true identity as a distinct chemical element.
Defining the Element: Lavoisier’s Contribution
The correct identification and naming of the gas was the contribution of the French chemist Antoine Lavoisier. Lavoisier began his investigations into combustion and calcination, utilizing the isolated gas provided by Priestley’s work. He used precise measurements to demonstrate that the increase in mass of a substance after calcination equaled the mass of the gas consumed from the air. This quantitative approach proved that air was not a simple substance, but a mixture containing a component that reacted with materials during burning.
Lavoisier used this evidence to overturn the phlogiston theory, which had dominated chemical thought for decades. He established that combustion and respiration involved the combination of a substance with this particular component of the air. This theoretical work redefined chemistry by establishing a modern framework for understanding chemical reactions.
Between 1777 and 1778, Lavoisier named the gas oxygène, derived from the Greek words meaning “acid-former.” He chose this name based on his mistaken belief that this gas was a necessary constituent of all acids. Despite this error in nomenclature, Lavoisier’s work established the gas as a unique chemical element, completing the transition from isolation to true chemical understanding. His role was not in the initial physical production, but in providing the conceptual framework that recognized the gas’s true elementary nature.
Legacy of the Discovery in Modern Science
Understanding oxygen’s role in chemical reactions was a watershed moment that ushered in the era of modern chemistry. Lavoisier’s meticulous experiments provided the empirical evidence needed to establish the Law of Conservation of Mass. This law, stating that mass is neither created nor destroyed in a chemical reaction, became a foundational principle for quantitative chemistry. The discovery shifted the focus of the science from qualitative observation to precise, measurable stoichiometry.
Beyond chemistry, the identification of oxygen had profound implications for biology and medicine. Recognizing oxygen’s function in combustion allowed scientists to interpret respiration as a slow, internal form of burning. This understanding connected the processes of breathing and metabolism, providing the first modern scientific basis for human and animal physiology. The legacy of this 18th-century work continues today, underpinning fields from atmospheric science to metabolic research.