Phlogiston (pronounced flow-GISS-tunn) is derived from the Greek language, the neuter of phlogistos, “inflammable” from phlogizein, “to set on fire”, from phlox, phlog- flame. Burning, as can be seen, is the root of this area of scientific thought.
The Old Theory
The theory of Phlogiston arose in the late 17th century, proposed by Johann Becher (who called it “inflammable earth”) and continued in the work of Georg Stahl. The theory postulates that in all flammable materials the elusive substance phlogiston is present, a substance without colour, odour, taste, or weight, which is given off when materials are burnt.
All materials could have three basic parts – phlogiston, impurities and the purest form of the material, where appropriate. Anything that could be burned to nothing would be considered to have been completely composed of phlogiston – such as charcoal or sulphur.
So, for example, wood when burnt leaves ash. It was, therefore, deemed that wood was composed of pure wood (ash) + phlogiston. Iron on the other hand was comprised of rust, the pure form of the metal, and phlogiston.
The impurities arose where the remains could not be defined as either the pure material or phlogistonated air. Gases that dissolved in water were a prime example of this kind of impurity, materials that did not meet the criteria of either pure base or phlogiston.
Antiphlogistonism
The theory maintained its position in scientific thought for a hundred years, though throughout that period loopholes were identified and then carefully patched up with new variations and terms, like the impurities of fixed and foul air. Objections were consistently countered with new information from Phlogistonists who were not keen to see their theories blown apart.
Ultimately it was the work of French scientist Antoine Laurent Lavoiser, in the late 18th century, which led to the systematic decimation of the Phlogiston Theory. His astute and systematic experimentation gave weight to gathering force of the Antiphlogistonist movement. What replaced it were theories around oxygen and the reactions experienced by materials in the presence of this life giving gas. Experiments switched from purely observational efforts to quantitative analysis that tried to qualify changes and reactions without giving in to notions of fancy expanded from what the eyes alone surveyed.
Panphlogistonism
While the somewhat dry theory of phlogiston saw its demise at the hands of science, there remain a few who believed that the whole concept had been started off on the wrong foot in the first place. The all too literal definition of the material as something that was consumed in fire meant that a narrow perception was created and a wider usage was not considered.
Boriux Praznine Florm of Iridios III hypothesized that phlogiston was part of all matter - physical, psychic, mystical or transdimensional - and was consumed in a non-corporeal fashion that supported the very weave of that materials existence. One supporter of his work described the material as something akin to a measurable source of narrative material. When wood is burnt, phlogiston is indeed consumed, but only because the story of the woods existence is unfolding and running headlong towards a bitter conclusion. Even as ash a measure of phlogiston remains - and such a material was often considered very valuable my the primitive, but wise, as a medium for story-telling by mixing it with dirty river water and daubing it liberally on cave walls in the shape of stick men, stick antelopes and stick ravening monsters.
Sentient entities, whatever level or dimension they exist on, contain a plentiful source of phlogiston, which is consumed over time at differing rates dependent on exterior stimuli, the presence of other sources of phlogiston (i.e. other entities) and whether it's a Thursday or not.