The discovery of oxygen is one of the most important milestones in the history of science. It was a breakthrough that redefined the understanding of air, combustion, and life itself, and played a foundational role in establishing modern chemistry. Prior to its discovery, scientific theories about the nature of gases and the process of burning were primitive and heavily influenced by outdated concepts such as the phlogiston theory. The identification of oxygen not only dismantled these old ideas but also set in motion a new era of experimentation and theoretical development.
This journey, however, was not the result of a single scientist’s work. The discovery of oxygen was a cumulative process involving several scientists across Europe in the 18th century, with Joseph Priestley, Carl Wilhelm Scheele, and Antoine Lavoisier as the key figures in the story.
The Air Before Oxygen: The Phlogiston Theory
To understand the impact of the discovery of oxygen, one must first appreciate the scientific context of the 17th and early 18th centuries. At the time, the dominant theory explaining combustion and rusting was the phlogiston theory, proposed by German chemist Georg Ernst Stahl. According to this theory, all combustible materials contained a substance called phlogiston, which was released during burning. What remained after combustion—like ash or a metal oxide—was thought to be the “dephlogisticated” substance.
Air, in this model, simply absorbed the phlogiston released during burning or rusting. The idea was elegant but flawed, and it couldn’t fully explain many chemical phenomena. Yet it remained widely accepted for much of the 18th century, in part because no one had yet identified the true role of air in combustion or respiration.
Carl Wilhelm Scheele: The Hidden Pioneer
Swedish chemist Carl Wilhelm Scheele was one of the first scientists to isolate what we now know as oxygen. Around 1772, Scheele conducted experiments by heating compounds such as mercuric oxide (HgO) and potassium nitrate (saltpetre). He observed that a gas was released that made candles burn brighter and allowed a mouse to live longer when enclosed in a container with it.
Scheele referred to the gas as “fire air” due to its role in combustion. Unfortunately, Scheele’s findings were not published until 1777 in his work “Chemical Treatise on Air and Fire”, by which time Joseph Priestley had already announced a similar discovery, albeit slightly later in time but earlier in publication.
Despite this, Scheele’s experiments were groundbreaking and showed his acute observational skills. His work, though overshadowed by others, remains an essential piece of the oxygen story.
Joseph Priestley: The First to Publish
The English scientist and clergyman Joseph Priestley is often credited with the discovery of oxygen, largely because he published his findings first. On August 1, 1774, Priestley used a magnifying glass to focus sunlight on a sample of mercuric oxide, a red powder. When heated, the substance released a gas that allowed a candle to burn with exceptional brightness. Priestley called this gas “dephlogisticated air,” still interpreting his discovery within the framework of the phlogiston theory.
Priestley was fascinated by the gas’s properties. He found that mice placed in a jar filled with this new air lived longer than in ordinary air, and when he breathed it in himself, he felt invigorated. In his 1775 paper “Experiments and Observations on Different Kinds of Air,” he described these experiments in detail, capturing the attention of the scientific community.
Although Priestley had discovered oxygen independently of Scheele, his failure to break from the phlogiston theory prevented him from understanding the full implications of his findings. Nonetheless, his work was vital in advancing the study of gases and air.
Antoine Lavoisier: The Father of Modern Chemistry
While Scheele and Priestley isolated oxygen, it was Antoine Lavoisier, a French chemist, who fully grasped its role in combustion and gave it its name. Lavoisier conducted rigorous quantitative experiments, often replicating and expanding on the work of Priestley and others. He realized that when substances burned, they gained weight because they were combining with something from the air—specifically, oxygen.
This observation led him to reject the phlogiston theory. Instead, Lavoisier proposed a new theory of combustion, where burning was understood as a chemical reaction with oxygen. In his 1789 book “Traité Élémentaire de Chimie” (Elements of Chemistry), he named the gas “oxygène,” derived from Greek roots meaning “acid former,” because he believed (incorrectly, as it turned out) that all acids contained oxygen.
Lavoisier’s systematic approach laid the foundations of stoichiometry, chemical nomenclature, and the law of conservation of mass. By reframing combustion and respiration as chemical processes involving oxygen, he revolutionized chemistry and turned it into a modern science.
Oxygen and Respiration
Beyond its role in combustion, the discovery of oxygen had profound implications for biology. The similarities between combustion and animal respiration had long intrigued scientists, and Lavoisier helped bridge the gap by showing that both involved the uptake of oxygen and the release of carbon dioxide.
This led to a deeper understanding of cellular respiration, the process by which organisms generate energy. Although the molecular mechanisms wouldn’t be understood until much later, the groundwork was laid for physiology, medicine, and biochemistry.
Scientific Impact and Legacy
The discovery of oxygen marked the beginning of the Chemical Revolution. It shifted scientific thinking from mystical and qualitative models of matter to empirical, quantitative, and testable theories. Several major impacts of this discovery include:
1. Demise of the Phlogiston Theory
With the realization that burning and rusting involved a gain in mass—due to oxygen—rather than the loss of an imaginary substance like phlogiston, the theory collapsed. Chemistry embraced a new empirical foundation.
2. Establishment of Modern Chemistry
Lavoisier’s work, which stemmed from understanding oxygen, helped establish the scientific method in chemistry. His approach of careful measurement and documentation became the standard.
3. Development of Chemical Nomenclature
Inspired by his work with oxygen and other elements, Lavoisier introduced a systematic way of naming substances. This was a significant step in organizing chemical knowledge.
4. New Era in Biology and Medicine
Recognizing the role of oxygen in respiration laid the foundation for the study of metabolism, blood chemistry, and aerobic processes. It influenced theories of health, disease, and nutrition.
5. Industrial and Technological Advancements
The discovery of oxygen played a critical role in metallurgy, aeronautics, and later, in rocket propulsion and life-support systems in space exploration. Its use in welding, steelmaking, and medical oxygen therapy are just a few of its practical applications.
Conclusion: A Breath of Scientific Enlightenment
The discovery of oxygen was not a single event, but a culmination of experiments, insights, and scientific discourse across Europe. Carl Wilhelm Scheele, Joseph Priestley, and Antoine Lavoisier each made pivotal contributions, with Lavoisier ultimately providing the theoretical clarity that redefined science itself.
Oxygen’s discovery dismantled the old and ushered in the new. It bridged chemistry with biology, theory with practice, and led to one of the most transformative periods in scientific history. Today, oxygen remains central to our understanding of life and energy, a testament to the enduring legacy of these 18th-century pioneers.
In the story of science, few discoveries have had such a profound impact. The breath of air that once fueled a brighter candle flame now symbolizes the light of modern knowledge.
