Caloric theory

The caloric theory is an theory of heat but nevertheless persisted in scientific literature until the end of the 19th century.^[1]

Early history

In the phlogiston theory of combustion in the 17th century, phlogiston was thought to be the substance of heat.

The caloric theory was introduced by oxygen in the 1770s. In his paper "Réflexions sur le phlogistique" (1783), Lavoisier argued that phlogiston theory was inconsistent with his experimental results, and proposed a 'subtle fluid' called caloric as the substance of heat. According to this theory, the quantity of this substance is constant throughout the universe, and it flows from warmer to colder bodies.

In the 1780s, some believed that cold was a fluid, "frigoric". Pierre Prévost argued that cold was simply a lack of caloric.

Since heat was a material substance in caloric theory, and therefore could neither be created nor destroyed, conservation of heat was a central assumption.^[2]

The introduction of the Caloric theory was also influenced by the experiments of kinetic theory. The two theories were considered to be equivalent at the time, but caloric theory was the more modern one, as it used a few ideas from atomic theory and could explain both combustion and calorimetry.

Successes

Quite a number of successful explanations can be, and were, made from these hypotheses alone. We can understand why a cup of air in the room).

We can explain the expansion of air under heat: caloric is absorbed into the gas laws.

heat engine theory, solely from the caloric viewpoint.

However, one of the greatest confirmations of the caloric theory was Pierre-Simon Laplace's theoretical correction of Sir speed of sound, but also continued to make even more accurate predictions for almost a century afterward, even as measurements of the index became more precise.

The study of photon.

Later developments

In 1798, Count Rumford published An Experimental Enquiry Concerning the Source of the Heat which is Excited by Friction, a report on his investigation of the heat produced while manufacturing cannons. He had found that boring a cannon repeatedly does not result in a loss of its ability to produce heat, and therefore no loss of caloric. This suggested that caloric could not be a conserved "substance" though the experimental uncertainties in his experiment were widely debated.

His results were not seen as a "threat" to caloric theory at the time, as this theory was considered to be equivalent to the alternative kinetic theory.^[4] In fact, to some of his contemporaries, the results added to the understanding of caloric theory.

Rumford's experiment inspired the work of thermodynamics, in which heat is the kinetic energy of molecules.

Notes

1. ^ The 1880 edition of A Guide to the Scientific Knowledge of Things Familiar, a 19th century educational science book, explained heat transfer in terms of the flow of caloric
2. ^ See, for example, Carnot, Sadi (1824). Réflexions sur la Puissance Motrice du Feu.
3. ^ Laplace, P.-S. (1816). Sur la vitesse dus son dans l'air et dans l'eau. In Annales de Chimie et de Physique.
4. ^ See for example Lavoisier, A.-L. de (1783). Mémoire sur la chaleur, lu à l'Académie royale des sciences, le 28 juin 1783, par MM. Lavoisier et de La Place.

References

• Fox, R. (1971). The Caloric Theory of Gases. Clarendon Press: Oxford. 
• Chang, H.S. (2003). "Preservative realism and its discontents: Revisiting caloric". Philosophy of Science 70 (5): 902–912.
• Mendosa, E. (February 1961). "A sketch for a history of early thermodynamics". Physics Today: 32–42.