Heat, theories caloric

Affinity and heat constituted the most theoretical part of chemistry. In line with the pedagogical purpose of the new school, which was to train the students in basic methods or the art of teaching, Berthollet assumed an elementary knowledge of chemistry on the part of the students and sought to provide exact notions of theories which serve as the basis of all the development of teaching and lead their spirit to general ideas. These theories for chemistry comprised affinities and the principle of heat or caloric. Chemical attraction was the principle of all chemical phenomena or the immediate cause of dissolution, combination, and composition. If the molecules of bodies obeyed only this... 

In November 1841 Joule developed this idea in a paper read to the Manchester Literary and Philosophical Society, describing experiments on heats of oxidation of metals a second communication with the same title was read to the British Association in 1842. In a paper read in 1842, on the electrolysis of water, he says that in the resistance to electrolysis accompanied by chemical changes, the heat due to its reaction is rendered latent and is thus lost by the circuit. Hence the caloric of the whole circuit is exactly accounted for by the whole of the chemical changes an appendix read in February 1844 says the names latent heat and caloric are used only for convenience, since I was then as strongly attached to the theory which regards heat as motion among the particles of matter as I am now . 

In the framework of the theory of ideal (noviscid and non>heat-conducting) calorically perfect gas (in which CpfC =s 7 is constant in the entire flow-held) the process is described in terms of six dimensionless parameters ... 

According to the caloric theory, caloric or matter of heat was an all-pervading subtle fluid which could be neither created nor destroyed. This idea was in tune with its era, which was an age of subtle fluids like electricity and phlogiston. Probably no authoritative statement of the caloric theory ever existed. A fairly complete statement is contained, however, in the following postulates of William Cleghom (1779) ... 

Joule carried out, as we mentioned in Chapter 2, a series of very careful experiments whereby he demonstrated that work was converted to heat and that there was an exact relationship between work consumed and heat produced. Caloric was thus generated, leading - eventually - to the collapse of the caloric theory. 

The prevailing theory of heat, popularized by Sinieon-Denis Poisson, Antoine Lavoisier and others, was a theory of heat as a substance, caloric. Different materials were said to contain different quantities of caloric. Fourier had been interested in the phenomenon of heat from as early as 1802. Fourier s approach was pragmatic he studied only the flow of heat and did not trouble himself with the vexing question of what the heat actually was. 

The equations of 59—61 are independent of the mechanical, theory of heat, and would apply equally well to the caloric theory. In the latter case, however, SQ is a perfect differential. They are also unchanged when T is put for 6, where T is the absolute temperature. All the twelve relations can be derived from the four in the first column, together with the equations (4). 

Lavoisier summarized his ideas developed over the previous twenty years in his seminal 1789 book Traite Elementaire de Chimie (Elements of Chemistry). This work presented his findings on gases and the role of heat in chemical reactions. He explained his oxygen theory and how this theory was superior to phlogiston theory. Lavoisier established the concept of a chemical element as a substance that could not be broken down by chemical means or made from other chemicals. Lavoisier also presented a table of thirty-three elements. The thirty-three elements mistakenly included light and caloric (heat). Lavoisier put forth the modern concept of a chemical reaction, the importance of quantitative measurement, and the principle of conservation of mass. The final part of Lavoisier s book presented chemical methods, a sort of cookbook for performing experiments. 

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). 

The phenomena of heat require explanation, however, and he expresses himself in favor of the material theory of heat—as an imponderable fluid pervading all space, which condensing in the pores of a substance accounts for the various phenomena of absorption or evolution of heat. The physicists, in fact, were divided for a long time after Lavoisier upon the nature of heat—whether it were a mode of motion or an imponderable fluid. An English writer, Metcalfe, in a two volume work on caloric, 1837, presents the material theory about as strongly as possible. 

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. 

Before about 1800, heat was widely considered to be a material substance, called caloric (listed as such by Lavoisier in his first Table of Elements ). Caloric was supposed to be a weightless, invisible fluid that could penetrate ( dissolve into ) any object, but could then be extracted ( squeezed out ) by friction. The fuzzy imagery of heat as a fluid, based on a naive but appealing analogy, presented a serious impediment to development of a rational theory of heat. 

Around 1800, experimental challenges to caloric theory were being presented by Count Rumford (cannon boring) and Humphrey Davy (melting of ice by friction). It became apparent that heat could be produced from a body in unlimited quantity by friction, further stretching its credibility as a substance. By about 1840, caloric theory was overturned by the modem kinetic molecular theory of heat (Sidebar 2.7), which identified heat with the energy of random molecular motions. 

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 ... 

Nineteenth Century Chemistry Caloric Theory and Thermodynamics Lavoisier proposed in the late 18th century that the heat generated by combustion was due to a weightless material substance called caloric that flowed from one place to another and was never destroyed. 

Sadi Carnot in the 1820s used caloric theory in developing theories for the heat engine to explain the engine already developed by Watt. Heat engines perform mechanical work by expanding and contracting a piston at two different temperatures. 

James Prescott Joule determined the equivalence of heat energy to mechanical work in the 1840s by carefully measuring the heat produced by friction. Joule attacked the caloric theory and played a major role in the acceptance of kinetic molecular theory. The SI unit of energy is named after him. 

Hermann von Helmholtz in the 1840s proposed that energy is conserved during physical and chemical processes, not heat as proposed in caloric theory... 

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