Phlogiston (Greek phlogistós - burned) or Caloricum is a hypothetical substance, of which one in late 17. and 18. Century believed that it escapes from all inflammable bodies with the burn as well as penetrates when heating up into it. The Phlogistontheorie is an outdated theory.

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the Phlogistontheorie

Robert Boyles Chemie war ein früher Konkurrent der Phlogistontheorie
Robert Boyles chemistry was in former times a competitor of the Phlogistontheorie

the Phlogiston theory became, based on work of the chemist Johann Joachim cup, in particularby the chemist Georg Ernst Stahl at the beginning 18. Century prepared. You to consequence were Phlogiston a component of subject, from which with transformations such as burn or rusting escapes, ash or the rust leave and no or a negative mass have.

If a body, penetrated allegedly Phlogiston was warmed up into it, whereby the body expanded. If one it pressed together (z. B. Air in a pump), was squeezed out the Phlogiston according to the theory and penetrated into surrounding subject. It became thereby warmth at a neighbouring body noticeably. Withthe time withdrew the material the body, which cooled off thereby.

Phlogiston was not invisible a substance, but a principle and as such. Beside Phlogiston (also phlogistische earth) there was still metallic and glassable earth. These principles are to be understood as descriptors, those thatto examining materials are too own. Thus a material, consisting of metallic earth, was characterised by it, to be ductile with hammer and anvil metallically to shine etc. Phlogiston lent the descriptor to materials to be inflammable.

The Phlogistontheorie differentiated, contrary to the cartesisch coined/shapedChemistry Robert Boyles, between mechanically producible mixtures and so-called Mixts (chemical compounds). The characteristics of the Mixts were not simple the sum of their components: Metals contained Phlogiston (see below), were not not inflammable however even, since they contained still the principle of the metallic earth.

strengths and borders of the theory

the Phlogistontheorie could some phenomena of the burn quite well explain. After it wood burned, because trees took up Phlogiston from air, and a candle expired in an final container, because air - a sponge similarly - only onecertain quantity of the Phlogiston to take up could, which was delivered by the burning candle. Thus Joseph Priestley explained itself at the beginning of also the reaction-joyful characteristic of oxygen. Oxygen was for Priestley “dephlogestierte air”, i.e. air, which less Phlogiston than normal air exhibited. “Dephlogestierte air” favoured burns,since it more Phlogiston, which escaped from the burned material, could take up.

During smelting became, which according to Phlogistontheorie, ore with the burn with activated charcoal Phlogiston caused, which was contained in the latter. Thus developed metals, which, when understood mixture, contained Phlogiston and metallic earth (i.e.Ore was materially simpler than metal).

according to the Phlogistontheorie:

Ore = metal   −   Phlogiston

according to the today's view:

Ore = metal   +   oxygen

Antoine Laurent de Lavoisiers Oxidationstheorie löste die Phlogistontheorie ab.
Antoine Laurent de Lavoisiers oxidation theory replaced the Phlogistontheorie.

The theory had their borders however, where z. B. Metals with the burn (oxidation) onWeight increased, if they should deliver Phlogiston nevertheless. To explain but also this tried the trailers of the Phlogistontheorie, by assigning a negative mass to the Phlogiston. If now with the burn of a metal Phlogiston escapes, the mass of the metal increases therefore. Rust (after thattoday's understanding oxidized metal) is to be regarded therefore as dephlogistiertes metal. Also the burn of hydrocarbons can be explained by this theory.

However Benjamin Thompson could disprove 1798 through a simple attempt this thesis in favor of the theory of the movement of the particles: It left in cannon pipesblunt steel drills run. The pipes were exhausted again and again on the new hot and the allegedly existing Phlogiston by water. The warmth could not have been caused thus by an exhaustible material existing in the pipes. After the discovery of the hydrogen by Henry Cavendish and of theOxygen by Joseph Priestley and Carl William cross-eyed one, one stated besides that these two substances became with the burn water and set free no Phlogiston, which shifted the theory the first heavy impact.

separation by the oxidation theory

the Phlogiston theory becameEnd 18. Century by the chemist Antoine Lavoisier by the oxidation theory replaced. It examined the weight change of different materials with oxidation and/or. Reduction and discovered that the straight discovered element oxygen plays thereby the crucial role.

He knows after that

  • when burning metals orSulfur so much oxygen is not used, as is contained in the developed oxides,
  • thereby these elements with burning with oxygen to unite,
  • one, in order to recover metals from the oxides, Phlogiston to add, but the oxygen to remove must.


  • Gilman McCann: Chemistry Transformed:The paradigm TIC SHIFT from Phlogiston ton of Oxygen, Ablex Pub, 1998, ISBN: 089391004X
  • Peter Laupheimer: Phlogiston or oxygen, scientific VG, 1998, ISBN: 3804712126

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