The caloric theory is an outdated theory of heat . She postulates a caloric substance that is invisible, has no weight, stays between the molecules and thus penetrates body boundaries. The caloric substance develops a repulsive force in itself, which explains that it seeks the balance between high and low concentration. H. flows from the warmer to the colder body.
It was introduced by Lavoisier in 1783 , building on the work of Joseph Black , although Daniel Bernoulli had proposed the kinetic gas theory as early as 1738, and persisted well into the 19th century. Lavoisier, who discovered the conservation of mass in chemical reactions and had done away with the phlogiston theory, treated heat as a further element: it cannot be produced or destroyed, its quantity always remains the same in the world.
Similar to the way elements combine in different proportions, the same amount of caloric substance should cause different temperatures in different bodies . According to the theory, the loosening of the molecules by the accumulation of the caloric substance causes the transition from solid to liquid and liquid to gas. The different heat capacities of gases at constant volume or adiabatic expansion have also been treated within the framework of this theory, as has the production of work from heat by Carnot .
The theory can be refuted by a simple experiment : if you rub two bodies together, they become warmer at the contact point. Since the environment does not get colder in the process, no caloric fluid apparently flows from the outside to the body. Since the friction process can be maintained indefinitely and more and more heat is generated in the process, the liquid cannot come from 'secret stores' of the body itself, as it would eventually be exhausted. Earl Rumford was the first to become aware of this anomaly , which this process represented for the caloric theory.
However, the principle of conservation of caloric substance contained a real gist. He walked by Rudolf Clausius in the first law of thermodynamics , according to which the sum of heat and mechanical energy remains constant.
- Lars Jaeger: The natural sciences: A biography. Springer Spektrum non-fiction book, Springer-Verlag, Heidelberg / Berlin / New York 2014, ISBN 3-662-43400-8 , p. 161 f.
- Walter J. Moore, Dieter O. Hummel: Physikalische Chemie. Walter de Gruyter, Berlin 1986, ISBN 3-11-010979-4 , p. 135 f.
- Florian Wodlei, Regina Kleinhappel: Lecture series on the history and development of thermodynamics as part of the lectures Theoretical Hydrodynamics, Transport Theory . Held at the University of Graz in the field of theoretical physics in the winter semester 2007/2008, summer semester 2008. 2nd improved and revised edition.