The Air of Revolution: How a Scientific Rivalry Changed Chemistry Forever
The story of how Priestley and Lavoisier's clash over oxygen discovery transformed science through facts, ideas, and language
The Rivalry That Breathed New Life into Science
Imagine a world where scientists believed that objects burned because they contained a mysterious, invisible substance called "phlogiston" that was released during combustion. This was the scientific consensus in the 18th century, until two brilliant chemists with clashing worldviews embarked on a race to understand the true nature of air.
Their story is not merely about the discovery of oxygen but about how facts, ideas, and language interact to create scientific revolutions.
Joseph Priestley, the dissenting minister who discovered "dephlogisticated air," and Antoine Lavoisier, the meticulous French aristocrat who named it "oxygen," represent one of science's most compelling rivalries. Their conflict demonstrates that scientific advancement requires not just new discoveries, but new ways of thinking and speaking about those discoveries.
Through their experiments on the composition of air, they overthrew centuries-old beliefs and established the foundations of modern chemistry, proving that the language we use to describe nature can be as revolutionary as the facts we uncover.
Joseph Priestley
English theologian and natural philosopher who discovered oxygen but remained committed to phlogiston theory
Antoine Lavoisier
French nobleman and chemist who established the modern system of chemistry and named oxygen
The Clash of Worldviews: Facts Versus Systems
At the heart of the Priestley-Lavoisier story lies a fundamental philosophical divide about how to approach scientific inquiry. Both were master experimentalists, but they held strikingly different views about what their experiments meant.
Priestley: Empirical Observation
Priestley, a British polymath and dissenting minister, was a champion of empirical observation and was deeply suspicious of overarching theoretical systems. He preferred to accumulate facts through experiments, believing that "more is owing to what we call chance—that is, philosophically speaking, to the observation of events rising from unknown causes than to any proper design or preconceived theory in this business" 4 .
His approach was modest, open-ended, and grounded in what he could directly observe. He was content with the phlogiston theory because it seemed to explain his experimental results reasonably well.
Lavoisier: Cohesive Systems
In contrast, Lavoisier sought to create a cohesive, rational system for chemistry. He believed that for chemistry to advance, it needed precise language, strict quantification, and a theoretical framework that could accommodate new facts 2 9 .
He famously wrote that he was "destined to bring about a revolution in...chemistry" 9 . For Lavoisier, the phlogiston theory was not just incorrect; it was an obstacle to progress—"a veritable Proteus that changes its form every instant" that needed to be replaced with a "stricter way of thinking" 9 .
Key Insight
This philosophical clash shaped their entire approach to the same experimental facts. Priestley saw a new gas that supported combustion exceptionally well; Lavoisier saw the key to a new chemical system.
Priestley's Pivotal Experiment: Isolating "Dephlogisticated Air"
The summer of 1774 witnessed one of the most celebrated experiments in the history of chemistry. Using relatively simple apparatus, Joseph Priestley made a discovery that would ultimately transform the field.
The Experimental Setup
Priestley's equipment was elegant in its simplicity. His key apparatus included:
- A 12-inch-wide burning lens: Used to focus sunlight intensely onto chemical samples 1 .
- Mercurius calcinatus: A reddish powder we now know as mercuric oxide (HgO) 1 .
- An inverted glass container: Placed in a pool of liquid mercury, which created a sealed environment that could capture gases 1 .
The Step-by-Step Discovery
- Heating the Substance: Priestley placed a sample of mercurius calcinatus in the glass container and used his powerful burning lens to focus sunlight onto the powder, heating it intensely 1 .
- Gas Collection: As the powder heated, it released a colorless gas, which was trapped in the inverted glass container over the mercury 1 .
- Initial Observations: He noted that the gas did not dissolve in water, unlike the "fixed air" (carbon dioxide) he was familiar with from his earlier work on carbonated water 1 .
Diagram of Priestley's experiment with the burning lens and mercury trough
Remarkable Properties and a Personal Test
Driven by curiosity, Priestley conducted follow-up tests that revealed the gas's extraordinary properties:
Combustion Test
A candle burned in this new air with "a remarkably vigorous flame" far more intense than in ordinary air 1 .
Respiration Test
A mouse placed in a container of the gas lived about four times longer than a mouse in a similar quantity of common air 1 .
The Human Test
Ever the intrepid investigator, Priestley breathed the gas himself, reporting, "The feeling of it in my lungs was not sensibly different from that of common air, but I fancied that my breast felt peculiarly light and easy for some time afterwards" 1 .
Priestley's Interpretation
True to his philosophical leanings, Priestley interpreted these results within the existing phlogiston framework. He reasoned that since the gas supported combustion so well, it must be exceptionally hungry to absorb phlogiston. Therefore, it must contain very little phlogiston to begin with. He logically named it "dephlogisticated air" 1 7 .
The Scientist's Toolkit: Key Materials in the Race to Understand Air
Essential research materials used in 18th-century pneumatic chemistry
| Material/Apparatus | Function in Experiments |
|---|---|
| Pneumatic Trough | A fundamental setup for collecting gases over water or mercury, enabling their isolation and study 1 4 . |
| Mercury (Hg) | Used in pneumatic troughs to capture gases that dissolve in water. Also, mercuric oxide was the key source of oxygen in Priestley's experiment 1 . |
| Burning Lens | Concentrated sunlight to achieve the high temperatures needed to decompose metal compounds and release gases 1 . |
| Nitrous Air (Nitric Oxide) | Used in the "nitrous air test" (eudiometry) to measure the "goodness" or oxygen content of air samples 4 . |
| Mice | Served as living sensors to test the breathability of different airs by measuring how long they survived in a confined volume 1 . |
Pneumatic Trough
Essential apparatus for collecting and studying gases in the 18th century
Burning Lens
Used to focus sunlight to achieve high temperatures for chemical experiments
Lavoisier's Revolutionary Insight: From Fact to Framework
Unlike Priestley, Lavoisier was not content with simply adding a new "air" to the growing list. He was determined to rebuild chemistry around it.
The Demise of Phlogiston
Lavoisier repeated Priestley's experiment but added his signature rigor: precision measurement. He carefully weighed the mercuric oxide before heating and the mercury that remained afterward, demonstrating that the weight of the gas released plus the mercury equaled the weight of the original substance 9 .
This adherence to the Law of Conservation of Mass was fatal to the phlogiston theory, which struggled to explain why some metals gained weight when burned (supposedly by losing phlogiston).
The Naming of Oxygen
In a move of profound scientific consequence, Lavoisier gave Priestley's gas a new name: oxygen, from the Greek for "acid producer" because he initially (and incorrectly) believed it was a component of all acids 9 .
More important than the name itself was its placement within a new systematic nomenclature he developed with colleagues. This new language eliminated confusing terms like "calx" in favor of descriptive names like "oxide" 9 .
The New System of Chemistry
Lavoisier's 1789 textbook, Elements of Chemistry, presented a complete package: a new theory of combustion, a revised list of elements, and a logical nomenclature 9 . He correctly identified oxygen's role in both combustion and respiration, recognizing them as similar processes of oxidation. His systematic approach ultimately convinced the next generation of chemists, leading to a paradigm shift known as the Chemical Revolution 7 9 .
Chemical Revolution in a Nutshell
OLD SYSTEM
Phlogiston Theory
Qualitative descriptions
Confusing terminology
NEW SYSTEM
Oxygen Theory
Quantitative measurements
Systematic nomenclature
Quantifying a Revolution: Data from the Birth of Modern Chemistry
Experimental Observations and Interpretations
| Observation | Priestley's Phlogiston Interpretation | Lavoisier's Oxygen Interpretation |
|---|---|---|
| A candle burns out in a closed jar. | The air is saturated with phlogiston and can absorb no more 1 . | The oxygen in the air has been consumed 9 . |
| A metal calx (oxide) forms when a metal is heated. | The metal loses phlogiston 9 . | The metal combines with oxygen from the air 9 . |
| A candle burns brighter in Priestley's new gas. | The gas is "dephlogisticated" and readily absorbs phlogiston 7 . | The gas is pure oxygen, which supports combustion 9 . |
| Air is "refreshed" by a green plant. | The plant absorbs phlogiston from the air 1 . | The plant produces oxygen 1 . |
Timeline of Key Discoveries
~1772
Carl Wilhelm Scheele - Isolated oxygen (called "fire air") but delayed publication 1 .
August 1774
Joseph Priestley - Isolated oxygen using a burning lens and mercuric oxide, calling it "dephlogisticated air" 1 4 .
Fall 1774
Priestley & Lavoisier - Priestley demonstrated his experiment for Lavoisier in Paris 4 9 .
1775-1777
Antoine Lavoisier - Repeated experiments, identified oxygen as a component of air, and named it 9 .
1783
Henry Cavendish/Lavoisier - Lavoisier interpreted Cavendish's experiment showing water is formed from hydrogen and oxygen, dealing a final blow to phlogiston 9 .
1789
Antoine Lavoisier - Published Traité Élémentaire de Chimie, outlining the new oxygen-based chemistry 9 .
Impact of the Chemical Revolution
The chart below illustrates the paradigm shift from phlogiston theory to oxygen theory in scientific publications:
Hypothetical data showing the decline of phlogiston theory and rise of oxygen theory in scientific literature
The Lingering Air of the Past: Why the Revolution Wasn't Instant
Despite the overwhelming evidence for Lavoisier's new system, Joseph Priestley never accepted it. He remained a staunch defender of the phlogiston theory until his death in 1804 7 .
This was not merely stubbornness; from his perspective, phlogiston theory was a useful and coherent system that explained a wide range of phenomena. His adherence illustrates a profound truth about scientific progress: data alone does not change minds. Scientists interpret facts through their conceptual frameworks, and when those frameworks are deeply held, they are remarkably resistant to change 2 7 .
The "Chemical Revolution" was not a single event but a process of persuasion that took place over decades, ultimately succeeding because Lavoisier's system provided a more powerful, predictive, and teachable framework for the next generation 9 .
Lessons on the Nature of Scientific Progress
The story of Priestley and Lavoisier is more than a historical curiosity; it is a case study in how science truly advances. It demonstrates that discovery and interpretation are two different things. Priestley, the brilliant experimentalist, discovered the fact—oxygen gas. But Lavoisier, the systematic theorist, discovered its meaning and wove it into a new conceptual fabric for chemistry.
Their work reminds us that scientific revolutions require three interconnected elements:
New Facts
From careful experimentation
New Ideas
That provide better explanations
New Language
To articulate ideas with clarity
The very air we breathe became the battleground where old ideas gave way to new, teaching us that understanding our world requires not just looking at it, but learning to see it through new eyes and describe it with new words.