Caloric theory of heat

Thus, within the context of the Newtonian force atom and the caloric theory of heat, solids, liqitids, and gases were all viewed as organized arrays of particles produced by a static equilibrium between the attractive interparticle forces, on the one hand, and the repulsive intercaloric forces, on the other. The sole difference was that the position of eqitilibriitm became greater as one passed from the solid to the liqitid to the gas, due to the increasing size of the caloric envelopes siuToittrding the component atoms (Figures 5 and 6). 

Rumford s studies (along with those of Humphrey Davy see Section 3.4) contributed to gradual decline of the caloric theory of heat and its replacement by the modem kinetic molecular theory. By about 1840, the interconversion of heat and work was clearly understood, as well as the association of heat with molecular motion. However, there was as yet no clear statement of the conservation principle for the total heat plus work. 

The caloric theory of heat pictured heat as a fluid which permeates all materials. What experimental evidence clearly made this theory untenable, regardless of the properties assigned to the caloric fluid Why ... 

It is most amazing that scientists such as Carnot and Clausius, who laid the foundations of thermodynamics, still believed in a very naive caloric theory of heat, which held that heat is a form of fluid. The main practical question they faced was the following. Suppose there is some hot steam coming from a boiler. How much of its energy can it give away to produce useful work (Presumably, it cannot give up all its heat ) In other words. 

Experiments analogous to those just described were first performed by Joule in the 1840s [5]. Those experiments accomplished several things they fully discredited the old caloric theory of heat (a theory that considered heat to be transported by movement of a substance called caloric), they demonstrated that a temperature change can occur without heat transfer, and they provided a numerical conversion factor between equivalent amounts of heat and work. However for us. Joule s most important result leads to (2.1.27). 

The originator of thermodynamics was the Frenchman Sadi Carnot (1796-1832). Carnot was interested in the steam engines which had been developed in Great Britain by Thomas Newcomen (1663-1729) and improved by James Watt (1736-1819). It was clear to Carnot that the efficiency of the steam engine was still very low, and he tried to deduce on theoretical grounds how it might be improved. He used the caloric theory of heat, which was still in vogue in spite of Rumford s work, but this did not affect the validity of his conclusions. 

Clapeyron s paper used indicator diagrams and calculus for a rigorous proof of Carnot s conclusion that the efficiency of a reversible heat engine depends only on the temperatures of the hot and cold heat reservoirs. However, it retained the erroneous caloric theory of heat. It was not until the appearance of English and German translations of this paper that Clapeyron s analysis enabled Kelvin to define a thermodynamic temperature scale and Clausius to introduce enffopy and write the mathematical statement of the second law. 

In fact, as Beretta has shown, Lavoisier s avoidance of affinity theory is a fallacy [88]. A memoir entitled Vues Generales sur le Calorique published in 1805 by Madame Lavoisier together with other previously unpublished work shows that Lavoisier did consider affinity as of vital importance to his chemistry [89]. In this memoir he unambiguously related affinity to universal gravitation, linking it, as Parkinson had (although in a different way) to his caloric theory of heat. ... 

Figure 3.1 Illustration of the fundamental observation made > by Sadi Carnot Wherever there exists a difference of temperature, motive force can be produced [1, p. 9]. The engine absorbs heat Q from the hot reservoir, converts part of it to work W, and delivers the rest of the heat to the cold reservoir. The efficiency ri is given by W = r Q. (According to the caloric theory of heat used by Carnot, <2i —Qi)...

Though Sadi Carnot used the caloric theory of heat to reach his conclusions, his later scientific notes reveal his realization that the caloric theory was not supported by experiments. In fact, Camot understood the mechanical equivalence of heat and even estimated the conversion factor to be approximately 3.7 joules per calorie (the more accurate value being 4.18 J/cal) [1-3]. Unfortunately, Sadi Carnot s brother, Hippolyte Camot, who was in possession of Sadi s scientific notes from the time of his death in 1832, did not make them known to the scientific community until 1878 [3]. That was the year in which Joule published his last paper. By then the equivalence between heat and work and the law of conservation of energy were well known through the work of Joule, Helmholtz, Mayer and others. (It was also in 1878 that Gibbs published his famous work On the Equilibrium of Heterogeneous Substances). 

The intuitive caloric theory of heat [133] was misapprehended by scientists and historicist as it was discredited at that time by acceptance of the principles of energy conservation. It showed, however, that those who studied and made use of the caloric theory including Lavoisier, Dalton, Laplace, Poisson, Carnot, or Avogadro did so because caloric gave them a satisfactory basis for the study of heat, whether in physics or in chemistry. We should keep in mind that many foundation of thermodynamics were laid while this theory held sway, particularly between the years 1750 to 1850. 

H. L. Callendar The Caloric Theory of Heat and Carnot s Principle Proc. Phys. Soc. of London, 23(1911)153... 

Joseph Black was the first to distinguish between the quantity of heat and the intensity of heat (temperature) and to recognize latent heat absorbed or given off in phase transitions. However, Black believed in the caloric theory of heat, which incorrectly asserted that heat was an imponderable fluid called caloric. This incorrect theory was not fully discredited until several decades after Black s death. 

We come, hence,to the last quarter of the 18th century. The caloric theory of heat, whose origin lies - as we have seen - with Descartes subtle fluid, is fairly well accepted but there is some strong opposition to it. Hatsopoulos and Keenan describe the situation as follows ... 

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