In science, combustion is a chemical reaction in which a substance reacts rapidly with oxygen with the production of heat and light. [1]

History
The theory of combustion was the progressive development of a number of theories, as outlined below:

Four elements four elements (s)
Three principles		Paracelsus combustion model
In 450BC, Greek philosopher Empedocles introduced the "standard model" of physics, in which everything consisted of four elements (earth, air, water, and fire) (above left), and two forces (attraction and repulsion); in 350 BC, Aristotle added to this a density model (above right), in which denser elements tend to rise; lighter elements fall; earth is the heaviest element (and the center of the universe); fire the lightest; burning (or combustion) was simply the movement of the elements to their natural inherent position. In 790, Arabian chemist Geber introduced the “three principles” model of combustion, in which metals are formed of two elements: sulphur, ‘the stone which burns’, the principle of combustibility, and mercury, the principle of metallic properties; and the third principle salt, is what gives gives solidity. In 1524, Swiss chemist Paracelsus introduced the “sulphur combustion model”, in which he adopted Aristotle’s version of the four element theory, but reasoned that they appeared in bodies as Geber’s three principles, such that mercury included the cohesive principle, so that when it left in smoke the wood fell apart; smoke represented the volatility (the mercury principle); the heat-giving flames represented flammability (sulphur); the remnant ash represented solidity (salt).



Becher combustion modelStahl combustion theory
Caloric theory model
In 1699, German chemist Johann Becher introduced the terra pinguis model of combustion, in which a fatty, oily material substance called“terra pinguis” was considered as the material of bodies that gives things the property of combustion. In 1703, German chemist Georg Stahl, Becher's student, introduced the phlogiston model of combustion, in which in which heat was viewed as a fire-like element, having mass, called “phlogiston”, contained within combustible bodies and released during combustion. In 1789, French chemist Antoine Lavoisier introduced the caloric model of combustion, in which the process of combustion was said to result in the release of weightless "caloric" particles, or rather that in every combustion there is a disengagement of the matter of heat (or igneous fluid) or of light.

The dominant theory here was the caloric theory, established in the late 18th century by French chemist Antoine Lavoisier, who between 1768 and 1787 published over sixty papers leading to his theory of combustion, in which the process of combustion resulted in the release of "caloric" particles, or rather that in every combustion there is a disengagement of the matter of heat (or igneous fluid) or of light. [2]

Bohr model (1913)
The 1913 Bohr model of the atom, in light of which combustion models became more complicated, requiring discussion of the subject of quantum electrodynamics.

Thermodynamics
Following the transformation of the notion of heat as a caloric particle to that of heat as motion (electron photon quantum electrodynamic interaction), with the invention of the the mathematical state variable entropy (Rudolf Clausius, 1865), the definition of combustion became quantified, generally, as an enthalpy quantity. [3]

Quantum electrodynamics
In 1913, Danish physicist Niels Bohr hypothesized a new quantum model of the atom in which negatively-charged electrons revolved in orbits (orbitals) about a positively-charged nucleus, at certain fixed "quantum" distances, whereby each spherical-shaped electron orbit has a specific energy associated with it and that for an electron to move down to a lower more stable orbital (closer to the nucleus) a photon, of a specific wavelength, has to be emitted and conversely for an electron to move up to a higher orbital (farther from the nucleus) a photon, of a specific wavelength, has to be absorbed; a model which as come to be known as the "Bohr model". When the electrons move up to less stable outer orbitals, the atom or molecule as a whole, tends to become more reactive, in a sense move more, and thus more likely to take place in combustion-like reactions.

Subsequently, in the years to follow, combustion models needed to take into account "quantum electrodynamics" (QED), the subject of the interaction of electrons with photons, and hence combustion models invariably became more complicated, in the sense that light and heat release involved the movement of electrons downward in orbital structure and the release of light as photons.
Love (combustion)
An artistic depiction of love, passion, or love the chemical reaction, being analogous to the process of combustion or having something to do with burning, being inflamed, fire, or heat release. [5]

Human chemical reactions
Somewhere along the line, in this historical development of the theory of combustion, such as alluded to in the works of William Fairburn (Human Chemistry, 1914) and Thomas Dreier (We Human Chemicals, 1948), the model of hydrocarbon-like chemical structures (such as wood) reacting with oxygen to produce heat and light in the process of combustion, thinkers began to scale up the burning model to explain love the chemical reaction, passion, the heat of sex, the warmth of relationships, etc.

The first extensive review of the metaphorical or analogy usages of heat, flame, or combustion as models for human relationships, love, or friction in literature (literature chemistry and literature thermodynamics), seems to have been French philosopher Gaston Bachelard’s 1938 book The Psychoanalysis of Fire in which he analyzes the existence of fire (as well as heat and light), both as a real presence throughout the history of humankind and more importantly a literary, symbolic presence. Bachelard addresses the subject of the psychoanalysis or critique of the use of thermal words (or thermal phrases), such as the fire of passion, the heat of love, the light of my life, etc., used by various famous authors throughout history. He cites, for example, German philosopher Gotthilf Schubert’s use of fire or heat as a psychoanalytic tool:

“Just as friendship prepares us for love, so by rubbing together of similar bodies, nostalgia (heat) is created and love (flame) spurts forth.”

Bachelard goes on to cite, what seems to be about two dozen or so, other various usages of heat or fire as a metaphor, analogy, or model for the intricacies of human romance, relationships, and love; one example being Bohemian–Austrian poet Rainer Rilke:

“To be loved means to be consumed in the flame; to love is to shine with an inexhaustible light.”

One of the first textbook sections on the validity and technical details of this "love as a combustion reaction" model, scaled up the the human molecular level of reactions between human molecules, in respect to smaller hydrocarbon combustion reactions, was presented by American electrochemical engineer Libb Thims in 2007 who, in a section on human chemical reaction rate variations, explained how slow combustion reactions, such as rusting may be comparable to long term diamond wedding anniversary marriages, whereas, conversely, quick combustion reactions, such as methane gas reacting with oxygen: [4]

Methane oxygen reaction

may be comparable to a very hot and intense relationship:

male female reaction

in which a male human and female human molecule, Mx and Fy, react to form an intense passionate relationship, but one that is too hot, exploding into chaos, and eventual quick to end termination; or to short-lived human reproduction reaction (double displacement reaction) wherein sparks fly, passion bubbles, and a child Bc is produced:

human reproduction reaction

but one were eventually the heat and friction of argument result in a divorce, the result of which the reaction burns out and grows cold to the state of non-existence.

See also
● Combustion theory of animal heat

References
1. Daintith, John. (2005). Oxford Dictionary of Chemistry. Oxford University Press.
2. (a) Partington, J.R. (1957). A Short History of Chemistry. Dover.
(b) Lavoisier, Antoine. (1777). “On Combustion in General”, Sept. 5th. Euvres, ii, 225.
3. Perrot, Pierre. (1998). A to Z of Thermodynamics (combustion, pg. 43). Oxford University Press.
4. (a) Thims, Libb. (2007). Human Chemistry (Volume One) (combustion, 13+ pgs; combustion reaction vs. marriage, pg. 154-160) . Morrisville, NC: LuLu.
(b) Thims, Libb. (2007). Human Chemistry (Volume Two) (combustion, 12+ pgs) . Morrisville, NC: LuLu.
5. The Brain vs. The Heart in Love – HubPages.

External links
● Combustion – Wikipedia.

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