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The phlogiston theory, a superseded scientific theory, postulated the existence of a fire-like element dubbed phlogiston (Template:IPAc-en)<ref>Template:Cite LPD</ref><ref>Template:Cite journal</ref> contained within combustible bodies and released during combustion. The name comes from the Ancient Greek Template:Wikt-lang Template:Transliteration (burning up), from Template:Wikt-lang Template:Transliteration (flame). The idea of a Template:Linktext substance was first proposed in 1667 by Johann Joachim Becher and later put together more formally in 1697 by Georg Ernst Stahl. Phlogiston theory attempted to explain chemical processes such as combustion and rusting, now collectively known as oxidation. The theory was challenged by the concomitant weight increase and was abandoned before the end of the 18th century following experiments by Antoine Lavoisier in the 1770s and by other scientists. Phlogiston theory led to experiments that ultimately resulted in the identification (Template:Circa), and naming (1777), of oxygen by Joseph Priestley and Antoine Lavoisier, respectively.
TheoryEdit
Phlogiston theory states that phlogisticated substances contain phlogiston and that they dephlogisticate when burned, releasing stored phlogiston, which is absorbed by the air. Growing plants then absorb this phlogiston, which is why air does not spontaneously combust and also why plant matter burns. This method of accounting for combustion was inverse to the oxygen theory by Antoine Lavoisier.
In general, substances that burned in the air were said to be rich in phlogiston; the fact that combustion soon ceased in an enclosed space was taken as clear-cut evidence that air had the capacity to absorb only a finite amount of phlogiston. When the air had become completely phlogisticated it would no longer serve to support the combustion of any material, nor would a metal heated in it yield a calx; nor could phlogisticated air support life. Breathing was thought to take phlogiston out of the body.<ref>James Bryant Conant, ed. The Overthrow of Phlogiston Theory: The Chemical Revolution of 1775–1789. Cambridge: Harvard University Press (1950), 14. Template:OCLC.</ref>
Joseph Black's Scottish student Daniel Rutherford discovered nitrogen in 1772, and the pair used the theory to explain his results. The residue of air left after burning, in fact, a mixture of nitrogen and carbon dioxide, was sometimes referred to as phlogisticated air, having taken up all of the phlogiston. Conversely, when Joseph Priestley discovered oxygen, he believed it to be dephlogisticated air, capable of combining with more phlogiston and thus supporting combustion for longer than ordinary air.<ref>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref>
HistoryEdit
Empedocles had formulated the classical theory that there were four elements—water, earth, fire, and air—and Aristotle reinforced this idea by characterising them as moist, dry, hot, and cold. Fire was thus thought of as a substance, and burning was seen as a process of decomposition that applied only to compounds. Experience had shown that burning was not always accompanied by a loss of material, and a better theory was needed to account for this.<ref>Template:Cite book</ref>
Terra pinguisEdit
In 1667, Johann Joachim Becher published his book {{#invoke:Lang|lang}}, which contained the first instance of what would become the phlogiston theory. In his book, Becher eliminated fire and air from the classical element model and replaced them with three forms of the earth: {{#invoke:Lang|lang}}, {{#invoke:Lang|lang}}, and {{#invoke:Lang|lang}}.<ref name="morris2">Template:Cite book</ref><ref>Becher, Physica Subterranea p. 256 et seq.</ref> {{#invoke:Lang|lang}} was the element that imparted oily, sulphurous, or combustible properties.<ref name="brock2">Template:Cite book</ref> Becher believed that {{#invoke:Lang|lang}} was a key feature of combustion and was released when combustible substances were burned.<ref name="morris2" /> Becher did not have much to do with phlogiston theory as we know it now, but he had a large influence on his student Stahl. Becher's main contribution was the start of the theory itself, however much of it was changed after him.<ref name="White">Template:Cite book</ref> Becher's idea was that combustible substances contain an ignitable matter, the {{#invoke:Lang|lang}}.<ref name="Leicester">Template:Cite book</ref>
Georg Ernst StahlEdit
In 1703, Georg Ernst Stahl, a professor of medicine and chemistry at Halle, proposed a variant of the theory in which he renamed Becher's {{#invoke:Lang|lang}} to phlogiston, and it was in this form that the theory probably had its greatest influence.<ref name="Mason2">Mason, Stephen F., (1962). A History of the Sciences (revised edition). New York: Collier Books. Ch. 26.</ref> The term 'phlogiston' itself was not something that Stahl invented. There is evidence that the word was used as early as 1606, and in a way that was very similar to what Stahl was using it for.<ref name="White"/> The term was derived from a Greek word meaning inflame. The following paragraph describes Stahl's view of phlogiston:
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Stahl's first definition of phlogiston first appeared in his {{#invoke:Lang|lang}}, published in 1697. His most quoted definition was found in the treatise on chemistry entitled {{#invoke:Lang|lang}} in 1723.<ref name="White" /> According to Stahl, phlogiston was a substance that was not able to be put into a bottle but could be transferred nonetheless. To him, wood was just a combination of ash and phlogiston, and making a metal was as simple as getting a metal calx and adding phlogiston.<ref name="Leicester" /> Soot was almost pure phlogiston, which is why heating it with a metallic calx transforms the calx into the metal and Stahl attempted to prove that the phlogiston in soot and sulphur were identical by converting sulphates to liver of sulphur using charcoal. He did not account for the increase in weight on combustion of tin and lead that were known at the time.Template:Sfn
J. H. PottEdit
Johann Heinrich Pott, a student of one of Stahl's students, expanded the theory and attempted to make it much more understandable to a general audience. He compared phlogiston to light or fire, saying that all three were substances whose natures were widely understood but not easily defined. He thought that phlogiston should not be considered as a particle but as an essence that permeates substances, arguing that in a pound of any substance, one could not simply pick out the particles of phlogiston.<ref name="White"/> Pott also observed the fact that when certain substances are burned they increase in mass instead of losing the mass of the phlogiston as it escapes; according to him, phlogiston was the basic fire principle and could not be obtained by itself. Flames were considered to be a mix of phlogiston and water, while a phlogiston-and-earthy mixture could not burn properly. Phlogiston permeates everything in the universe, it could be released as heat when combined with an acid. Pott proposed the following properties:
- The form of phlogiston consists of a circular movement around its axis.
- When homogeneous it cannot be consumed or dissipated in a fire.
- The reason it causes expansion in most bodies is unknown, but not accidental. It is proportional to the compactness of the texture of the bodies or to the intimacy of their constitution.
- The increase of weight during calcination is evident only after a long time, and is due either to the fact that the particles of the body become more compact, decrease the volume and hence increase the density as in the case of lead, or those little heavy particles of air become lodged in the substance as in the case of powdered zinc oxide.
- Air attracts the phlogiston of bodies.
- When set in motion, phlogiston is the chief active principle in nature of all inanimate bodies.
- It is the basis of colours.
- It is the principal agent in fermentation.<ref name="White"/>
Pott's formulations proposed little new theory; he merely supplied further details and rendered existing theory more approachable to the common man.
OthersEdit
Johann Juncker also created a very complete picture of phlogiston. When reading Stahl's work, he assumed that phlogiston was in fact very material. He, therefore, came to the conclusion that phlogiston has the property of levity, or that it makes the compound that it is in much lighter than it would be without the phlogiston. He also showed that air was needed for combustion by putting substances in a sealed flask and trying to burn them.<ref name="White"/>
Guillaume-François Rouelle brought the theory of phlogiston to France, where he was a very influential scientist and teacher, popularizing the theory very quickly. Many of his students became very influential scientists in their own right, Lavoisier included.<ref name="Leicester" /> The French viewed phlogiston as a very subtle principle that vanishes in all analysis, yet it is in all bodies. Essentially they followed straight from Stahl's theory.<ref name="White"/>
Giovanni Antonio Giobert introduced Lavoisier's work in Italy. Giobert won a prize competition from the Academy of Letters and Sciences of Mantua in 1792 for his work refuting phlogiston theory. He presented a paper at the {{#invoke:Lang|lang}} of Turin on 18 March 1792, entitled {{#invoke:Lang|lang}} ("Chemical examination of the doctrine of phlogiston and the doctrine of pneumatists in relation to the nature of water"), which is considered the most original defence of Lavoisier's theory of water composition to appear in Italy.<ref name="Abbri">Template:Cite journal</ref>
Challenge and demiseEdit
Eventually, quantitative experiments revealed problems, including the fact that some metals gained weight after they burned, even though they were supposed to have lost phlogiston. Some phlogiston proponents, like Robert Boyle,<ref>Template:Cite book</ref> explained this by concluding that phlogiston has negative mass; others, such as Louis-Bernard Guyton de Morveau, gave the more conventional argument that it is lighter than air. However, a more detailed analysis based on Archimedes' principle, the densities of magnesium and its combustion product showed that just being lighter than air could not account for the increase in weight.Template:Cn Stahl himself did not address the problem of the metals that burn gaining weight, but those who followed his school of thought were the ones that worked on this problem.<ref name="White"/>
During the eighteenth century, as it became clear that metals gained weight after they were oxidized, phlogiston was increasingly regarded as a principle rather than a material substance.<ref>For a discussion of how the term phlogiston was understood during the eighteenth century, see: James R Partington & Douglas McKie; "Historical studies on the phlogiston theory"; Annals of Science, 1937, 2, 361–404; 1938, 3, 1–58; and 337–371; 1939, 5, 113–149. Reprinted 1981 as Template:ISBN.</ref> By the end of the eighteenth century, for the few chemists who still used the term phlogiston, the concept was linked to hydrogen. Joseph Priestley, for example, in referring to the reaction of steam on iron, while fully acknowledging that the iron gains weight after it binds with oxygen to form a calx, iron oxide, iron also loses "the basis of inflammable air (hydrogen), and this is the substance or principle, to which we give the name phlogiston".<ref>Template:Cite book</ref> Following Lavoisier's description of oxygen as the oxidizing principle (hence its name, from Ancient Greek: {{#invoke:Lang|lang}}, "sharp"; {{#invoke:Lang|lang}}, "birth" referring to oxygen's supposed role in the formation of acids), Priestley described phlogiston as the alkaline principle.<ref>Joseph Priestley (1794). Heads of lectures on a course of experimental philosophy. London: Joseph Johnson.</ref>
Phlogiston remained the dominant theory until the 1770s when Antoine-Laurent de Lavoisier showed that combustion requires a gas that has weight (specifically, oxygen) and could be measured by means of weighing closed vessels.<ref>Template:Cite journal</ref> The use of closed vessels by Lavoisier and earlier by the Russian scientist Mikhail Lomonosov also negated the buoyancy that had disguised the weight of the gases of combustion, and culminated in the principle of mass conservation. These observations solved the mass paradox and set the stage for the new oxygen theory of combustion.<ref name="Ihde"/> The British chemist Elizabeth Fulhame demonstrated through experiment that many oxidation reactions occur only in the presence of water, that they directly involve water, and that water is regenerated and is detectable at the end of the reaction. Based on her experiments, she disagreed with some of the conclusions of Lavoisier as well as with the phlogiston theorists that he critiqued. Her book on the subject appeared in print soon after Lavoisier's execution for Farm-General membership during the French Revolution.<ref name="Rayner-Canham">Template:Cite book</ref><ref name="Datta">Template:Cite book</ref>
Experienced chemists who supported Stahl's phlogiston theory attempted to respond to the challenges suggested by Lavoisier and the newer chemists. In doing so, the theory became more complicated and assumed too much, contributing to its overall demise.<ref name="Ihde">Template:Cite book</ref> Many people tried to remodel their theories on phlogiston to have the theory work with what Lavoisier was doing in his experiments. Pierre Macquer reworded his theory many times, and even though he is said to have thought the theory of phlogiston was doomed, he stood by phlogiston and tried to make the theory work.<ref>Template:Cite book</ref>
See alsoEdit
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