Editing Caloric theory (section)

=== Igneous fluid ===
On 28 June and 13 July 1783, Lavoisier read his two-part manuscript ''Reflections on phlogiston'' ({{Lang|fr|Réflexions sur le phlogistique}}){{refn|Full title:
Reflections on phlogiston, to serve as a continuation of the theory of combustion and calcination, published in 1777 (French: ''Réflexions sur le phlogistique, pour servir de suite à la théorie de la combustion et de la calcination, publiée en 1777'').|group=lower-alpha}} at the [[French Academy of Sciences|Royal Academy of Sciences]] in Paris.{{Snf|Best|2015}} 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''.{{Snf|Best|2015|p=[641]}} Lavoisier argued that this “igneous fluid” is the cause of heat, and that its existence is necessary to explain thermal expansion and contraction.
{{Blockquote|text=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.{{Snf|Best|2015|p=[640-41]}}}}