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| title | chunk | source | category | tags | date_saved | instance |
|---|---|---|---|---|---|---|
| Caloric theory | 1/3 | https://en.wikipedia.org/wiki/Caloric_theory | reference | science, encyclopedia | 2026-05-05T16:14:11.452778+00:00 | kb-cron |
The caloric theory is a superseded scientific theory that heat consists of a self-repellent fluid called "caloric" that flows from hotter bodies to colder bodies. Caloric was also thought of as a weightless gas that could pass in and out of pores in solids and liquids. The caloric theory was superseded by the mid-19th century in favor of the mechanical theory of heat, but nevertheless persisted in some scientific literature—particularly in more popular treatments—until the end of the 19th century.
== Early history ==
=== Phlogiston theory is replaced by combustion in oxygen === In the history of thermodynamics, the initial explanations of heat were thoroughly confused with explanations of combustion. After J. J. Becher and Georg Ernst Stahl introduced the phlogiston theory of combustion in the 17th century, phlogiston was thought to be the substance of heat. There is one version of the caloric theory that was introduced by Antoine Lavoisier. Prior to Lavoisier's caloric theory, published references concerning heat and its existence, outside of being an agent for chemical reactions, were sparse only having been offered by Joseph Black in Rozier's Journal (1772) citing the melting temperature of ice. In response to Black, Lavoisier's private manuscripts revealed that he had encountered the same phenomena of a fixed melting point for ice and mentioned that he had already formulated an explanation which he had not published as of yet. Lavoisier developed the explanation of combustion in terms of oxygen in the 1770s.
=== Igneous fluid === On 28 June and 13 July 1783, Lavoisier read his two-part manuscript Reflections on phlogiston (Réflexions sur le phlogistique) at the Royal Academy of Sciences in Paris. In this paper Lavoisier argued that the phlogiston theory was inconsistent with his experimental results, and proposed a 'subtle fluid' he named “igneous fluid” as the substance of heat. Lavoisier argued that this “igneous fluid” is the cause of heat, and that its existence is necessary to explain thermal expansion and contraction.
When an ordinary body—solid or fluid—is heated, that body ... occupies a larger and larger volume. If the cause of heating ceases, the body retreats ... at the same rate as it cools. Finally, if it is returned to the same temperature that it had at the first instant, it will clearly return to the same volume as it had before. Hence the corpuscles of matter do not touch each other, there exists between them a distance that heat increases and that cold decreases. One can scarcely conceive of these phenomena except by admitting the existence of a subtle fluid, the accumulation of which is the cause of heat and the absence of which is the cause of coldness. No doubt it is this fluid that lodges between the particles of matter, which spreads them apart and which occupies the space left between them. ... I name this fluid ... igneous fluid, the matter of heat and fire. I do not deny that the existence of this fluid is ... hypothetical.
=== Caloric ===
==== Caloric vs. heat ==== The term “caloric” was not coined until 1787, when Louis-Bernard Guyton de Morveau used calorique in a work he co-edited with Lavoisier. The word “caloric” was first used in English in a 1788 translation of Guyton de Morveau's essay by James St. John. In his influential 1789 textbook Traité Élémentaire de Chimie, Lavoisier clarified the concept of caloric and introduced it to a wider audience. Lavoisier emphasized that caloric was the cause of heat and therefore could not be equated with heat, i.e. not be the cause of itself. As for a definition of heat, Lavoisier offered just a simple, dictionary-style explanation:
heat ... the sensation which we call warmth being caused by the accumulation of this substance, we cannot, in strict language, distinguish it by the term heat; because the same name would then very improperly express both cause and effect. For this reason, in the memoir which I published in 1777, I gave it the names of igneous fluid and matter of heat. In [Méthode de nomenclature chimique] we have distinguished the cause of heat, or that exquisitely elastic fluid which produces it, by the term of caloric.