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Chemist whose Chemical Treatise on Air and Fire by Carl Wilhelm Scheele records independent investigations of oxygen.

The new chemistry prevailed because it coordinated experimental accounting, a persuasive interpretation of gases and a reproducible language of composition. Its success cannot be reduced to the isolated discovery of oxygen, to the first use of a balance, or to the claim that every part of Antoine Lavoisier's system was correct.

The crucial experimental change was to treat gases as material participants that must enter the account of a chemical reaction. In a simple version of phlogiston theory, a metal lost phlogiston when it became a calx. Yet the calx could weigh more than the original metal. This was a serious explanatory challenge, although it did not make every contemporary version of phlogiston theory logically identical or instantly untenable. The question was how to organize changes in solid material, gas volume and the properties of the surrounding air into one consistent account.

Antoine Lavoisier's sustained heating of mercury under a connected air reservoir provides a concrete example. Red calx formed while part of the confined air disappeared; the residual gas no longer supported ordinary combustion or respiration. Heating the red material more strongly released a gas that supported these processes exceptionally well, while restoring the metal. Recombining the released gas with the residual gas recovered the behaviour of ordinary air. The explanatory advantage was a connected cycle of transformations, rather than a single unexplained weighing. Importantly, his own narrative acknowledges combining results from repeated trials into its presentation: the textbook sequence should not be mistaken for one effortless, perfectly complete performance.^[ref]

The oxygen theory of combustion interpreted the increase in the mass of a calx as addition of a constituent of air. A closed material account could then relate consumed gas to the transformed solid. Conservation of mass served as a rule for experimental reasoning: one had to examine all the reactants and products, including otherwise easily missed gases. Antoine Lavoisier stated this accounting principle explicitly in his discussion of fermentation. It was not necessary to claim that he invented every earlier practice of weighing or all previous ideas about material conservation to recognize the power of making such accounting central to a system.^[ref]

The new account also supplied a language that trained its users to recognize composition. In the 1787 nomenclature collaboration, Louis-Bernard Guyton de Morveau, Claude Louis Berthollet, Antoine-François de Fourcroy and Antoine Lavoisier linked related names to related substances. The 1789 textbook organized a route from relatively simple substances to compounds and then to operations and apparatus. Thus chemical nomenclature was not merely a convenient set of labels attached after an experimental victory. It made the proposed system easier to learn, communicate and extend, while requiring a reader to adopt some of its theoretical distinctions.^[ref]

This was a collective and contested transition. Joseph Priestley and Carl Wilhelm Scheele had independently investigated the gas subsequently interpreted as oxygen. Joseph Priestley's description of unusually respirable air did not entail adopting the same explanation of it as Antoine Lavoisier. A shared experimental object could therefore support competing theoretical descriptions. The achievement was the construction and dissemination of a coherent explanatory package, not the possession of a gas inaccessible to every rival.^[ref][ref]

The limits of the victory are equally instructive. The caloric theory remained part of the system, and the table of simple substances was explicitly related to the available means of decomposition. Antoine Lavoisier's universal association of acidity with oxygen was false: hydrochloric acid, with formula $\mathrm{HCl}$, is a concrete oxygen-free counterexample. The permanence of the new chemical nomenclature did not require retaining all the assumptions embedded in its first construction.^[ref] The system triumphed through explanatory and practical advantages that survived correction. Neither its errors nor the rationality of some contemporary objections makes that achievement disappear.

The case for a Chemical Revolution is strongest if it concerns a reorganization of chemical explanation, measurement and classification. It is much weaker if it means that one isolated observation immediately overthrew a unified older theory. The production of the gas later called oxygen and the acceptance of an oxygen-based chemistry were related but distinct developments.

Carl Wilhelm Scheele and Joseph Priestley investigated an unusually combustion-supporting gas, yet interpreted their results within the resources of phlogiston theory. Priestley's term dephlogisticated air was not simply an incorrect label on an otherwise complete modern explanation: it expressed a different account of what combustion did. Scheele's preparations and Priestley's work also make a single-person priority story inadequate. Experimental preparation, publication, recognition of a material's properties and a new interpretation need not occur together.^[ref][ref]

Antoine Lavoisier's programme connected the gas with the quantitative study of combustion and metallic calces. On the oxygen account, a metal's conversion into an oxide involves incorporation of material from the surrounding gas. The increase in the solid's mass is therefore compatible with conservation of mass for the whole vessel and its contents. Simply weighing only the metal is not the same experiment as accounting for the gaseous reactant as well. This change in what must be measured helped make the explanatory alternatives testable.

The shift also concerned chemical language. A nomenclature organized around composition made new relations among substances expressible and teachable. In Elements of Chemistry by Antoine Lavoisier, the treatment of simple substances and compounds is part of a systematic programme rather than an appendix to one gas experiment. Methods, instruments, names and explanations reinforced one another.^[ref]

There are important qualifications. Older investigators were not incapable experimenters, and phlogiston accounts could be adjusted in response to new results. The newer chemistry also contained commitments subsequently rejected: caloric theory and the claim that oxygen was universally essential to acidity were not permanent truths. Hydrogen chloride provides a later counterexample to a universal oxygen-based account of acids. A theory can be a major advance without every element of its programme surviving.

Accordingly, calling the episode revolutionary need not deny continuity in apparatus, experiments or personnel. It identifies a substantial change in how chemical processes were described and coordinated. Conversely, oxygen preparation by itself does not establish a sharp boundary between rational and irrational chemistry. The explanatory achievement depended on interpreting material exchanges, connecting them to measurements and building a coherent working system. The discovery of the gas contributed to that transformation, but the historical revolution cannot be reduced to its first preparation.

Carl Wilhelm Scheele and Joseph Priestley independently prepared and investigated the gas now called oxygen; Antoine Lavoisier was central to interpreting it within a new account of combustion and chemical composition. Assigning a unique discoverer requires deciding whether discovery means first preparation, first public report, recognition of a distinct kind of gas, or a successful theoretical interpretation. The historical controversy is largely about why one of these achievements should be privileged over the others.

Carl Wilhelm Scheele's investigations, generally dated to the early 1770s, preceded publication of Chemical Treatise on Air and Fire by Carl Wilhelm Scheele in 1777. His work distinguished the component that sustained burning from the remainder of ordinary air. He obtained the active component through several chemical preparations, including heating suitable substances, and interpreted the results in terms of phlogiston. Delayed publication matters to public priority, but it does not show that the experimental work had not occurred. Equally, a publication date alone does not establish the precise date of every earlier trial.^[ref]

Joseph Priestley's 1775 account is unusually revealing because it records hesitation and revision. On 1 August 1774 he heated red mercury(II) oxide with a large burning lens and collected the released gas. A candle burned particularly strongly in it; later trials involving animals and comparison with nitric oxide helped him distinguish its properties from ordinary air. He initially lacked a settled understanding of what he had obtained. Calling the product dephlogisticated air eventually made it intelligible within his own framework: it had an unusually great capacity to accept the phlogiston supposedly released in burning and animal breathing.^[ref]

The modern chemical equation,is a useful reconstruction, but it must not be passed off as Joseph Priestley's own explanation. In modern terms, heating decomposes mercury(II) oxide into mercury and molecular oxygen. The eighteenth-century experimenter instead worked with such categories as calces and differently modified airs. The material operation can be recognized across the change in theory while the meaning of its product remains historically contested.

Antoine Lavoisier made a different contribution. His programme tracked what entered and left substances in calcination and combustion, placing gases within quantitative material balances. In the mercury experiment described in Elements of Chemistry by Antoine Lavoisier, a retort communicated with an enclosed supply of air over mercury. Prolonged heating formed a red calx and diminished the enclosed air. Stronger heating of the recovered calx released an especially combustion-supporting gas; adding it back to the residual air restored the properties of the original mixture. The persuasive feature was the linked decomposition and reconstruction, not just a single spectacular flame.^[ref]

That sequence supported the claim that air was a mixture and that calcination involved combining a metal with part of it. A metal could gain mass because material entered it from the air, without requiring an invisible substance to leave with anomalous properties. Conservation of mass made the weighing scale a constraint on the explanation. However, Antoine Lavoisier's entire system was not modern chemistry. He treated caloric as an explanatory principle and associated the newly named oxygen with the formation of all chemical acids. The latter universal claim is false: hydrochloric acid is an chemical acid whose solute, hydrogen chloride, contains hydrogen and chlorine but no oxygen. This concrete counterexample prevents us from defining discovery as possession of today's complete theory.^[ref]

There are consequently several legitimate allocations of credit. An investigator concerned with earliest preparation may emphasize Carl Wilhelm Scheele; one concerned with the well-documented 1774 experiment and its rapid communication may emphasize Joseph Priestley; one concerned with the explanatory reconstruction of combustion may emphasize Antoine Lavoisier. The last achievement depended on experimental results that the others had produced. Correct interpretation was neither a substitute for preparing the material nor an achievement wholly independent of communication between investigators.

Historians disagree because their accounts embody different pictures of scientific change. A simple accumulation story can make discovery look like identifying one additional item in a ready-made list of chemical elements. A conceptual-change story emphasizes that the list and its criteria were themselves changing: oxygen was not just another variety of modified air in the new chemistry. National priority narratives and the dramatic reputation of the Chemical Revolution can further encourage a single heroic winner. Yet replacing that winner with a collective label is insufficient unless the different experimental and theoretical contributions are explained.

The most defensible answer distributes credit while specifying the achievement. Carl Wilhelm Scheele and Joseph Priestley deserve independent experimental discovery credit; Antoine Lavoisier deserves central credit for the chemical interpretation and reorganization that gave oxygen its place in a new system. Discovery was a sequence of preparation, discrimination, communication and reinterpretation, rather than one instantaneous encounter with a theory-free fact.