AskDefine | Define phlogiston

Dictionary Definition

phlogiston n : a hypothetical substance once believed to be present in all combustible materials and to be released during burning

User Contributed Dictionary



Coined by Stahl in 1702, from , neuter of ‘inflammable’, from ‘to set fire to’, from ‘flame’.




  1. In the context of "chemistry|historical": The hypothetical fiery principle formerly assumed to be a necessary constituent of combustible bodies and to be given up by them in burning.


Translations to be checked

Extensive Definition

The phlogiston theory (from the Ancient Greek φλογιστόν phlŏgistón "burning up," from φλόξ phlóx "fire"), first stated in 1667 by Johann Joachim Becher, is an obsolete scientific theory that posited the existence of, in addition to the classical four elements of the Greeks, an additional fire-like element called “phlogiston” that was contained within combustible bodies, and released during combustion. The theory was an attempt to explain oxidation processes such as combustion and the rusting of metals.


In 1667, Johann Joachim Becher, published his Physical Education, which was the first mention of what would become the phlogiston theory. Traditionally, alchemists considered that there were four classical elements: fire, water, air, and earth. In his book, Becher eliminated fire and air from the classical element model and replaced them with three forms of earth: terra lapidea, terra fluida, and terra pinguis.
In Becher's theory, presence of terra lapidea, represented the degree of fusibility. Terra fluida, indicated the degree of fluidity, subtility, volatility, and metallicity. Terra pinguis was the element which imparted oily, sulphurous, or combustible properties. Becher believed that terra pinguis was a key feature of combustion and was released when combustible substances were burned. Thus, phlogiston as first conceived was a sort of anti-oxygen.
Joseph Black's 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 oxygen was first discovered it was thought to be "dephlogisticated air", capable of combining with more phlogiston and thus supporting combustion for longer than ordinary air.

Challenge and demise

Eventually, quantitative experiments revealed problems, including the fact that some metals, such as magnesium, gained weight when they burned, even though they were supposed to have lost phlogiston. Mikhail Lomonosov attempted to repeat Robert Boyle's celebrated experiment in 1753 and concluded that the phlogiston theory was false. He wrote in his diary: "Today I made an experiment in hermetic glass vessels in order to determine whether the mass of metals increases from the action of pure heat. The experiment demonstrated that the famous Robert Boyle was deluded, for without access of air from outside, the mass of the burnt metal remains the same."
Some phlogiston proponents explained this by concluding that phlogiston had negative weight; others, such as Louis-Bernard Guyton de Morveau, gave the more conventional argument that it was lighter than air. However, a more detailed analysis based on the Archimedean principle and the densities of magnesium and its combustion product shows that just being lighter than air cannot account for the increase in mass.
Still, phlogiston remained the dominant theory until Antoine-Laurent Lavoisier showed that combustion requires a gas which has weight (oxygen), which could be measured by means of weighing closed vessels. The use of closed vessels also negated the buoyancy which had disguised the weight of the gasses of combustion. These observations solved the weight paradox and set the stage for the new caloric theory of combustion. In some respects, the phlogiston theory can be seen as the opposite of the modern "oxygen theory". The phlogiston theory states that all flammable materials contain phlogiston that is liberated in burning, leaving the "dephlogisticated" substance in its "true" calx form. In the modern theory, on the other hand, flammable materials (and unrusted metals) are "deoxygenated" when in their pure form and become oxygenated when burned. However, the first part of the old theory requires that phlogiston has weight (since ashes weigh less), but the second requires that it have no weight or negative weight, since corroded metals weigh the same or more, depending on whether or not they are allowed to corrode in sealed chambers.

Enduring aspects

Phlogiston theory allowed chemists to bring explanation of apparently different phenomena into a coherent structure: combustion, metabolism, and formation of rust. The recognition of the relation between combustion and metabolism was a forerunner of the recognition that the metabolism of living creatures and combustion can be understood in terms of fundamentally related chemical processes. The nearest comparable contemporary concept is entropy, whereby the amount of phlogiston in a system would be inversely proportional to its entropy.

In popular culture

Dinosaur Comics discussed phlogiston in its July 5, 2005 edition of the comic. T-Rex concluded that the theory is close to the current combustion theory, but reversed. Phlogiston is also explored in chapter 2 of Colin Bruce's The Einstein Paradox and Other Science Mysteries Solved by Sherlock Holmes (Helix Books, 1997). The focus is on explaining phlogiston as a predecessor to conservation of energy.
Phlogiston features in the science fiction short story "...The World, As We Know'T" by Howard Waldrop. In the story, a post-American Revolution scientist proves that phlogiston is real, with catastrophic results.
The 1991 computer game Worlds of Ultima Martian Dreams involved a "space cannon" that used phlogistonite to send a capsule to Mars.
Briefly referred to in the final chapter of Michael Crichton's "The Lost World".
Bonobo Conspiracy mentions phlogiston in Episode #907.
In the Dungeons & Dragons Spelljammer setting, Phlogiston was given as the name of the mysterious substance in which the crystal spheres which contained the planets bobbed around. It was highly flammable, a considerable problem for ships attempting to traverse the Phlogiston.
In World of Warcraft Phlogiston is a source of fuel for various inventions
Within Issue 6 of the Tom Strong comic book series, antagonist Paul Saveen attempts to burn Tom to death using "liquid phlogiston". Later in the same issue, the scene is revisited in the future with Paul Saveen acknowledging that phlogiston never existed and that it's a curious thing that it functioned as it did when in the past.
Kurt Vonnegut, Jr, briefly mentions phlogiston in his novel Jailbird.


phlogiston in Catalan: Teoria del flogist
phlogiston in Czech: Flogistonová teorie
phlogiston in German: Phlogiston
phlogiston in Spanish: Teoría del flogisto
phlogiston in French: Phlogistique
phlogiston in Korean: 플로지스톤설
phlogiston in Croatian: Flogistonska kemija
phlogiston in Italian: Teoria del flogisto
phlogiston in Hebrew: פלוגיסטון
phlogiston in Hungarian: Flogiszton-elmélet
phlogiston in Dutch: Phlogiston
phlogiston in Japanese: フロギストン説
phlogiston in Polish: Teoria flogistonu
phlogiston in Portuguese: Teoria do flogisto
phlogiston in Romanian: Teoria flogisticului
phlogiston in Russian: Флогистон
phlogiston in Slovak: Flogistónová teória
phlogiston in Finnish: Flogiston-teoria
phlogiston in Swedish: Flogiston
phlogiston in Vietnamese: Thuyết phlogiston
phlogiston in Ukrainian: Флогістон
phlogiston in Chinese: 燃素说
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