Phlogiston theory
The phlogiston theory, a
Theory
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.[3]
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.[4]
History
Johann Joachim Becher
In 1667,
Georg Ernst Stahl
In 1703,
To Stahl, metals were compounds containing phlogiston in combination with metallic oxides (calces); when ignited, the phlogiston was freed from the metal leaving the oxide behind. When the oxide was heated with a substance rich in phlogiston, such as charcoal, the calx again took up phlogiston and regenerated the metal. Phlogiston was a definite substance, the same in all its combinations.[10]
Stahl's first definition of phlogiston first appeared in his Zymotechnia fundamentalis, published in 1697. His most quoted definition was found in the treatise on chemistry entitled Fundamenta chymiae in 1723.
J. H. Pott
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.[9] 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.[9]
Pott's formulations proposed little new theory; he merely supplied further details and rendered existing theory more approachable to the common man.
Others
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.[9]
Guillaume-François Rouelle brought the theory of phlogiston to France, and he was a very influential scientist and teacher so it gained quite a strong foothold very quickly. Many of his students became very influential scientists in their own right, Lavoisier included.[10] 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.[9]
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 Académie royale des Sciences of Turin on 18 March 1792, entitled Examen chimique de la doctrine du phlogistique et de la doctrine des pneumatistes par rapport à la nature de l'eau ("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.[14]
Challenge and demise
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,[15] 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.[citation needed] 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.[9]
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.[16] 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".[17] Following Lavoisier's description of oxygen as the oxidizing principle (hence its name, from Ancient Greek: oksús, "sharp"; génos, "birth" referring to oxygen's supposed role in the formation of acids), Priestley described phlogiston as the alkaline principle.[18]
Phlogiston remained the dominant theory until the 1770s when
Experienced chemists who supported Stahl's phlogiston theory attempted to respond to the challenges suggested by Lavoisier and the newer chemists. In doing so, phlogiston theory became more complicated and assumed too much, contributing to the overall demise of the theory.[20] 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.[23]
See also
- Caloric theory – Obsolete scientific theory of heat flow
- Pneumatic chemistry – Very first studies of the role of gases in the air in combustion reactions
- Electronegativity – Tendency of an atom to attract a shared pair of electrons
- Energeticism – View that energy is the fundamental element in all physical change
- Antiphlogistine– Topical pain relief medicine
References
- ISBN 978-1-4058-8118-0.
- S2CID 170853908.
- OCLC 301515203.
- ^ "Priestley, Joseph". Spaceship-earth.de. Archived from the original on 2 March 2009. Retrieved 5 June 2009.
- ^ Ladenburg, Dr. A (1911). Lectures on the History of Chemistry. University of Chicago Press. p. 4. Retrieved 26 August 2016.
- ^ ISBN 9780226068602.
- ^ Becher, Physica Subterranea p. 256 et seq.
- ISBN 978-0-393-03536-0.
- ^ ISBN 978-0404069308.
- ^ a b c d Leicester, Henry M.; Klickstein, Herbert S. (1965). A Source Book in Chemistry. Cambridge, Massachusetts: Harvard University Press.
- ^ Mason, Stephen F., (1962). A History of the Sciences (revised edition). New York: Collier Books. Ch. 26.
- ^ Ladenburg 1911, pp. 6–7.
- ^ "Chemistry", Encyclopedia Britannica, 1911
- ^ Abbri, Ferdinando (2001). "GIOBERT, Giovanni Antonio". Dizionario Biografico degli Italiani [Biographical Dictionary of the Italians]. 55. Retrieved 15 September 2017.
- ^ Boyle, R. A (1673). Discovery of the Perviousness of Glass to Ponderable Parts of Flame. London: Essays of Effluvium. pp. 57–85.
- ISBN 978-0-405-13895-9.
- ^ Priestley, Joseph (1796). Experiments and Observations Relating to the Analysis of Atmospherical Air: Also, Farther Experiments Relating to the Generation of Air from Water. ... To which are Added, Considerations on the Doctrine of Phlogiston, and the Decomposition of Water. London: J. Johnson. p. 42.
- ^ Joseph Priestley (1794). Heads of lectures on a course of experimental philosophy. London: Joseph Johnson.
- S2CID 254510272.
- ^ a b Ihde, Aaron (1964). The Development of Modern Chemistry. New York: Harper & Row. p. 81.
- ISBN 978-0941901277. Retrieved 2 March 2016.
- ISBN 9788173715303. Retrieved 2 March 2016.
- ISBN 978-0405138508.
External links
- Quotations related to Phlogiston theory at Wikiquote