Phlogiston theory

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Air & Fire Laboratory Instruments
Chemical Observations & Experiments on Air & Fire (1780)

The phlogiston theory is a superseded scientific hypothesis that postulated the existence of a fire-like element called phlogiston contained within combustible bodies and released during combustion. The name comes from the Ancient Greek φλογιστόν phlogistón (burning up), from φλόξ phlóx (flame). The idea was first proposed in 1667 by Johann Joachim Becher and later put together more formally by Georg Ernst Stahl. The phlogiston hypothesis attempted to explain processes such as combustion and rusting, now collectively known as oxidation, and was abandoned before the end of the 18th century following experiments by Antoine Lavoisier and others. The phlogiston hypothesis led to experiments which ultimately concluded with the discovery of oxygen.


  • Now Mayow, like Boyle, conceived the air as made up of minute particles, while he restricted himself to two varieties, those, namely, which are necessary to life, called by him "spiritus igno-aereus," and those incapable of supporting respiration or combustion, which are left after the removal of this "spiritus." Since a mixture of saltpetre and sulphur continued burning even under water, he assumed that his igno-aereal particles must also be contained in the salt. Acids too contained the new principle. ...Mayow died in 1679 at the age of thirty-four years; had he lived but a little longer, it can scarcely be doubted that he would have forestalled the revolutionary work of Lavoisier, and stifled the theory of phlogiston at its birth. As it was, his work, though rendered in one of the most luminous and convincing scientific publications of the period, was immediately forgotten, and so proved of little effect on the evolution of our modern chemical system.
    • Francis Paul Armitage, A History of Chemistry (1906) p.23
  • If I were giving this lecture fifty years from now, the word "gravitation" would be as old-fashioned as the word "phlogiston" is to us. Relativity has certainly demoted gravitation as a real explanation, just as Priestley's and Lavoisier's analyses and decoding of chemical reactions destroyed the word "phlogiston."
  • One of the most fundamental principles of Lavoisier's chemistry was the use of numbers, notably in relation to what we often call today the principle of conservation of mass... The principle implies that the experimenter must not only keep account of all the reacting solids and liquids, but also the gases—that is, all of the products. ...This rule led to quantitative experiments. Lavoisier was not the first person to use numbers in chemistry but he was a pioneer in using such numerical measurements as the basis of his system of chemistry. ...When Lavoisier first announced this law, chemists generally believed in... "phlogiston" which supposedly entered into chemical reactions (such as combustion) but had no weight. It was a radical step, therefore, for Lavoisier to base a system of chemistry on a balance of weights and to maintain that chemistry is not concerned with weightless "substances." ...this was indeed a chemical revolution.
    • I. Bernard Cohen, The Triumph of Numbers: How Counting Shaped Modern Life (2005)
  • Intelligent design... is not a scientific argument at all, but a religious one. It might be worth discussing in a class on the history of ideas, in a philosophy class on popular logical fallacies, or in a comparative religion class on origin myths from around the world. But it no more belongs in a biology class than alchemy belongs in a chemistry class, phlogiston in a physics class or the stork theory in a sex education class. In those cases, the demand for equal time for "both theories" would be ludicrous. Similarly, in a class on 20th-century European history, who would demand equal time for the theory that the Holocaust never happened?
  • My thesis, paradoxically, and a little provocatively, but nonetheless genuinely, is simply this:
    The abandonment of superstitious beliefs about the existence of Phlogiston, the Cosmic Ether, Absolute Space and Time, ... , or Fairies and Witches, was an essential step along the road to scientific thinking. Probability, too, if regarded as something endowed with some kind of objective existence, is no less a misleading misconception, an illusory attempt to exteriorize or materialize our true probabilistic beliefs.
  • Some hold that fundamental ideas have changed so often within science—especially within physics—that we should always expect our current views to turn out to be wrong. Sometimes this argument is called the “pessimistic meta-induction.” The prefix “meta” is misleading here, because the argument is not an induction about inductions; it’s more like an induction about explanatory inferences. So let’s call it "the pessimistic induction from the history of science." The pessimists give long lists of previously posited theoretical entities like phlogiston and caloric that we now think do not exist... Optimists reply with long lists of theoretical entities that once were questionable but which we now think definitely do exist—like atoms, germs, and genes.
  • Lacan goes wrong by relying (quite uncritically!) on Saussure's signifier-signified conception of language. It is understandable that Lacan, when he began to write in the 1930s, should learn Saussure's turn-of-the-century linguistics. But even at the end of his life he and now his followers write about signifiers and signifieds as though the Chomskyan revolution in linguistics had never happened. Contemporary literary theorists tirelessly quote Saussure. But why? Today's linguists no more use Saussure's model than today's physicists use the concept of phlogiston. ...My point is not that Chomsky is right but that Saussure and Lacan are wrong.
  • When Priestley described his discovery... he introduced... an open admission of the role of randomness in his work—even including a subtle dig at the theoretical, synthetic mode of Newton and his followers:
    More is owing to what we call chance... to the observation of events arising from
    unknown causes
    , than to any proper design, or preconceived theory in this business. ...
    ...But ...Priestley himself was trapped in a preconceived theory ...almost entirely unfounded, though he clung to it for the rest of his life. ...Priestley seared it directly into the name he gave his pure air: dephlogisticated air.
    That awkward name came from the closest thing to a dominant research paradigm in... pneumatic chemistry: the phlogiston theory, one of the all-time classics in the history of human error.
    • Steven Johnson, The Invention of Air: A Story of Science, Faith, Revolution, and the Birth of America (2008) pp. 91-92.
  • The same point can be made at least equally effectively in reverse: there is no such thing as research without counterinstances. For what is it that differentiates normal science from science in a crisis state? Not, surely, that the former confronts no counterinstances. On the contrary, what we previously called the puzzles that constitute normal science exist only because no paradigm that provides a basis for scientific research ever completely resolves all its problems. The very few that have ever seemed to do so (e.g., geometric optics) have shortly ceased to yield research problems at all and have instead become tools for engineering. Excepting those that are exclusively instrumental, every problem that normal science sees as a puzzle can be seen, from another viewpoint, as a counterinstance and thus as a source of crisis. Copernicus saw as counterinstances what most of Ptolemy’s other successors had seen as puzzles in the match between observation and theory. Lavoisier saw as a counterinstance what Priestley had seen as a successfully solved puzzle in the articulation of the phlogiston theory. And Einstein saw as counterinstances what Lorentz, Fitzgerald, and others had seen as puzzles in the articulation of Newton’s and Maxwell’s theories. Furthermore, even the existence of crisis does not by itself transform a puzzle into a counterinstance. There is no such sharp dividing line. Instead, by proliferating versions of the paradigm, crisis loosens the rules of normal puzzle-solving in ways that ultimately permit a new paradigm to emerge. There are, I think, only two alternatives: either no scientific theory ever confronts a counterinstance, or all such theories confront counterinstances at all times.
    • Thomas Kuhn, The Structure of Scientific Revolutions (1962)
  • All [Torbern Bergman's] calculation is founded on the supposition that the calcination of metals is the result of the loss of phlogiston. But what I have been saying (...well known by now) is that this loss of phlogiston, even in the presence of metals is, according to me, nothing but pure supposition. What is more real, what can be known, by the balance and direct measurements, is that in all metallic calcinations, whether made in the dry or humid way, whether... with the aid of air or water, or by means of acids, there is an augmentation of weight of the metal... due to the addition of vital air, or specifically the oxygen principle.
    • Antoine Lavoisier, "Sur la précipitation des substances métalliques les unes par les autres" (1783) Oeuvres de Lavoisier Vol. 2, pp. 529-530, DK-71, from Robert Siegfried, From Elements to Atoms: A History of Chemical Composition (2002) Ch. 10. Lavoisier and the Anti-Phlogistic Doctrine, p. 181.
  • Finding air necessary for the of fire, Scheele first turned his attention to its analysis; he found that solution of liver of sulphur, and certain other sulphureous compounds, occasioned a diminution in the bulk of air, to which they were exposed, equal to one part in about five, the flame of hydrogen and that sulphur caused a similar decrease of bulk in air standing over water, and lime-water not being rendered in either case turbid by the residuums, no fixed air was formed. He then obtains empyreal air (oxygen) by the decomposition nitric acid, and other processes; describes the method of transferring, collecting, and examining the gases, and endeavours to prove that heat is a compound of empyreal air and phlogiston; he also shows by direct experiments, that the absorption occasioned in atmospheric air by liver of sulphur, is referrible to the abstraction of its empyreal portion; that it totally absorbs empyreal air, and that, upon adding to the residuary portion of atmospheric air, a quantity of empyreal air, equal to that absorbed by the sulphureous liquor, an air is again compounded, similar in all respects to that of the atmosphere. The identity of these investigations with those of Priestley will not fail of being observed, but... although Priestley was in the field a little before him, Scheele was unacquainted with his proceedings.
  • In 1774, Scheele obtained a yellow gas by digesting marine acid with manganese (manganese dioxide). As Scheele supposed that the manganese withdrew phlogiston from the acid, he called the new gas dephlogisticated marine acid. When, at a later time, phlogiston was regarded by some chemists as identical with hydrogen, Scheele's view of the relation between the compositions of marine acid and the gas he obtained by the reaction of that acid with manganese oxide was interpreted to mean that the gas was produced by removing hydrogen from the acid. In accordance with his conception of the composition of acids, Lavoisier regarded muriatic acid to be a compound of oxygen; and in order to trace a likeness between the supposed composition of this acid and the compositions of other acids, he asserted that muriatic acid is formed by the union of oxygen with a hypothetical substance which he named radical muriatique. Lavoisier described the reaction between muriatic acid and manganese oxide as an oxidation of the acid; he said that the addition of a second dose of oxygen made the acid more volatile, but less acidic. He named Scheele's yellow gas acide muriatique oxygéné.
  • The extension of Black's method by the physicist Lavoisier led to the downfall of the purely qualitative theory of phlogiston, and gave to chemistry the true methods of investigation, and its first great quantitative law—the law of conservation of matter.
  • The results of a scrutiny of the materials of chemical science from a mathematical standpoint are pronounced in two directions. In the first we observe crude, qualitative notions, such as fire-stuff, or phlogiston, destroyed; and at the same time we perceive definite measurable quantities such as fixed air, or oxygen, taking their place. In the second direction we notice the establishment of generalizations, laws, or theories, in which a mass of quantitative data is reduced to order and made intelligible. Such are the law of conservation of matter, the laws of chemical combination, and the atomic theory.
Experiments and Observations on Different Kinds of Air
Plate I, facing Vol.1 title page
  • In the course of my inquiries I was... soon satisfied that atmospherical air is not an unalterable thing; for that, according to my first hypothesis, the phlogiston with which it becomes loaded from bodies burning in it, and animals breathing it, and various other chemical processes, so far alters and depraves it, as to render it altogether unfit for inflammation, respiration, and other purposes to which it is subservient; and I had discovered that agitation in water, the process of vegetation, and probably other natural processes, restore it to its original purity.
  • In aesthetic discourse, no interpretative-critical analysis, doctrine or programme is superseded, is erased, by any later construction. The Copernican theory did correct and supersede that of Ptolemy. The chemistry of Lavoisier makes untenable the early phlogiston theory. Aristotle on mimesis and pathos is not superseded by Lessing or Bergson. The Surrealist manifestos of Breton do not cancel out Pope's Essay on Criticism though they may well be antithetical to it.
    • George Steiner, Real Presences (1989) Ch. 3, II: The Broken Contract, p. 76.
  • [M]etals remained the alchemists' chief concern... they seemed in their own way alive, whereas the calces (oxides) from which they were manufactured crumbled to dust and looked like cinders. Theory at once suggested a natural analogy. The metal was formed from the calx by the incorporation of pneuma or spirit; and this theory of metal-formation long remained in favour, being revived around 1700 as the 'phlogiston' theory. The central problem about metals was to identify the volitile constituents which combined with the calces to form the finished metal. For a long time, the status of quicksilver was ambiguous... resembling much more the volitile reagents which corrode metallic surfaces: mercury, in fact, forms an amalgam with other metals, and is even capable of dissolving gold... So the Alchemy of Avicenna classed mercury as a 'spirit' rather than a 'body'...
  • This statement appears to us to be conclusive with respect to the insufficiency of the undulatory theory, in its present state, for explaining all the phenomena of light. But we are not therefore by any means persuaded of the perfect sufficiency of the projectile system: and all the satisfaction that we have derived from an attentive consideration of the accumulated evidence, which has been brought forward, within the last ten years, on both sides of the question, is that of being convinced that much more evidence is still wanting before it can be positively decided. In the progress of scientific investigation, we must frequently travel by rugged paths, and through valleys as well as over mountains. Doubt must necessarily succeed often to apparent certainty, and must again give place to a certainty of a higher order; such is the imperfection of our faculties, that the descent from conviction to hesitation is not uncommonly as salutary, as the more agreeable elevation from uncertainty to demonstration. An example of such alternations may easily be adduced from the history of chemistry. How universally had phlogiston once expelled the aërial acid of Hooke and Mayow. How much more completely had phlogiston given way to oxygen! And how much have some of our best chemists been lately inclined to restore the same phlogiston to its lost honours! although now again they are beginning to apprehend that they have already done too much in its favour. In the mean time, the true science of chemistry, as the most positive dogmatist will not hesitate to allow, has been very rapidly advancing towards ultimate perfection.
    • Thomas Young Miscellaneous Works: Scientific Memoirs (1855) Vol. 1, ed. George Peacock & John Leitch, p. 249

A Dictionary of Chemistry (1777)[edit]

Containing the Theory and Practice of that Science: Its Application to Natural Philosophy, Natural History, Medicine, and Animal Economy: With Full Explanations of the Qualities and Modes of Action of Chemical Remedies: And the Fundamental Principles of the Arts, Trades and Manufactures, Dependent on Chemistry. Translated from the French, with Notes, Additions, and Plates. The Second Edition. To which is Added, as an Appendix, A Treatise on the Various Kinds of Permanently, Elastic Fluids, or Gases. A translation of Dictionnaire de Chymie (1766) the dictionary attributed to Pierre-Joseph Macquer.

Calcination [Vol. 1][edit]

A Source. Note: Macquer describes calcination based upon the phlogiston theory.
  • The calcination of a body is... the exposing of it to the action of fire, to produce some change upon it.
  • The principal effects of fire in chemical operations are to carry off the volatile principles, and to separate them from the fixed, or to occasion the combustion of inflammable matters. Hence it follows that bodies are calcined either to deprive them of some volatile principle, or to destroy their inflammable principle, and sometimes for both of these purposes.
  • We have examples of the first kind of calcination, in exposing calcareous earths and stones to the fire, to convert them into quicklime, which is effected by the entire evaporation of the watery principle contained in this kind of earth.
  • The calcination of Gypsum, of Alum, of Borax, and of several other Salts, by fire, which deprives them of the water necessary for their crystallization; the roasting of minerals, by which the fire carries off the sulphur, arsenic, and other volatile contents; ought to be referred to the first kind of calcination.
  • We have an example of the second kind of calcination, by exposing imperfect metals to fire; by which they lose their inflammable principle, their form, and metallic properties, and are changed into earthy matters called Metallic Calxes.
    • Note: Pure elemental metals, capable of being oxidized, would be considered "Imperfect metals".
  • It is necessary to observe, that this second calcination differs essentially from the first, as the changes produced by it upon imperfect metals are not effected by evaporation, but by decomposition and destruction of their phlogiston. It is therefore a combustion, and not a volatilisation of their inflammable principle.
  • Hence it follows, that the first kind of calcination may succeed without the contact of air and in close vessels, although it is more quick and complete in open vessels, from a property of air, by which it greatly accelerates the evaporation of volatile bodies. ...But as the second kind of calcination is a true combustion, like that of all inflammable bodies, it requires all the conditions necessary for combustion, and particularly the free access of air.
  • There are many bodies, in the calcination of which an evaporation of volatile parts happens, and also a destruction or deprivation of their inflammable principle, although without any sensible combustion of this latter. Such particularly are all combinations of imperfect metallic matters with vitriolic and nitrous acids: when these bodies are exposed to fire, their acid evaporates, and at the same time carries off with it their inflammable principle. We have examples of this kind of calcination in exposing to fire Martial Vitriol and Bezoar Mineral.
    • Note: Bezoar Mineral is an oxide of antimony.

Chemical Observations and Experiments on Air and Fire (1780)[edit]

Carl Wilhelm Scheele, Reinold Forster's translation of Scheele's d. Königl. Schwed. Acad. d. Wissenschaft Mitgliedes, Chemische Abhandlung von der Luft und dem Feuer (1779)
d. Königl. Schwed. Acad. d. Wissenschaft Mitgliedes, Chemische Abhandlung von der Luft und dem Feuer (1777)
  • Hitherto chemists are not agreed upon the number of simple principles or elements, of which all corporeal substances are composed. ...Others believe that earth and phlogiston are those principles which are the constituent parts of all corporeal substances. The greatest number seem to admit only the peripatetic elements.
  • It appears from all these Experiments, that in each of them phlogiston, the simple inflammable principle, is present. It is well known, that Air attracts the inflammable part of bodies, and deprives them of it: not only this may be seen from the above Experiments, but it also appears that in the transition of what is inflammable principle into the Air, a considerable part of the Air is lost; but that what is inflammable principle is the sole cause of this effect, is evident...
  • It likewise appears that a given quantity of Air can be united to or saturated as it were only by a certain quantity of phlogiston...
  • Air is composed of two different fluids, the one of which attracts not the phlogiston, and the other has the quality of attracting it, and this latter fluid makes between a third and a fourth of the whole bulk of the air.
  • These experiments seem to prove, that the transition of phlogiston into the air diminishes not always its bulk; which however other experiments clearly indicate...
  • Certainly it is a remarkable circumstance to observe, that the phlogiston separated from bodies, either without or with a fiery motion, and united with air, always considerably diminishes the bulk of air.
  • It might be objected that the lost air is still contained in the residuum of air which could not farther be united with the phlogiston; for finding that kind of air lighter than common air, it might be supposed that the phlogiston when united with this air made it less ponderous, which circumstance is already known from other experiments. However, since phlogiston is a substance, (which always supposes some weight,) I very much doubt whether this hypothesis be founded on truth.

Familiar Letters on Chemistry (1843)[edit]

, In its Relations to Physiology, Dietetics, Agriculture, Commerce, and Political Economy by Justus von Liebig. Quotations are from 3rd edition (1851) ed., William Gregory, unless otherwise indicated.
  • Many chemists, even at the present day, find it impossible to do without certain collective names, analogous to the word phlogiston, for processes which they regard as belonging to the same class, or determined by the same cause. But instead of choosing for this purpose words which designate things, as was the custom till the end of the seventeenth... century, (phlogiston means, for example, fire, or light, and heat), they employ, since the time of Berthollet, terms which designate what are called "forces."
  • To investigate the essence of a natural phenomenon, three conditions are necessary. We must first study and know the phenomenon itself, from all sides; we must then determine in what relation it stands to other natural phenomena; and, lastly, when we have ascertained all these relations, we have to solve the problem of measuring these relations, and the laws of mutual dependence; that is, of expressing them in numbers. ...In the first period of chemistry, all the powers of men's minds were devoted to acquiring a knowledge of the properties of bodies; it was necessary to discover, observe, and ascertain their peculiarities. This is the alchemistical period. The second period embraces the determination of the mutual relations or connexions of these properties; and this is the period of phlogistic chemistry. In the third period, in which we now are, we ascertain by weight and measure, and express in numbers, the degree in which the properties of bodies are mutually dependent. The inductive sciences begin with the substance itself; then come just ideas; and lastly, mathematics are called in, and, with the aid of numbers, completes the work.

A History of European Thought in the Nineteenth Century (1903-1914)[edit]

John Theodore Merz, Vol.1 Chapter V. The Atomic View of Nature.
  • We are... bound to attach the greatest importance to the preliminary step taken by Lavoisier, who is even more justly called the father of modern chemistry than Kepler is called the father of modern astronomy. The exact claims of Lavoisier to this important place in the history of chemistry have been variously stated: ...since his time, and greatly through his labours, the quantitative method has been established as the ultimate test of chemical facts; the principle of this method being the rule that in all changes of combination and reaction, the total weight of the various ingredients—be they elementary bodies or compounds—remains unchanged. The science of chemistry was thus established upon an exact, a mathematical basis. By means of this method Lavoisier, utilising and analysing the results gained by himself and others before him, notably those of Priestley, Cavendish, and Black, succeeded in destroying the older theory of combustion, the so-called phlogistic theory.
  • In the time of Lavoisier, and preeminently through his exertions, this vague and unmeasurable principle phlogiston was eliminated from the laboratory and the textbooks: quantities took the place of indefinable qualities, and numerical determinations increased in frequency and accuracy. The vague phlogistic theory, which contained a germ of truth, but one which at that time could not be put into definite terms, had helped to gather up many valuable facts and observations: these were collected and restated in a new and precise language. It has been said that every science must pass through three periods of development. The first is that of presentiment, or faith; the second is that of sophistry; and the third is that of sober research.

History of Chemistry (1909)[edit]

by Sir Edward Thorpe, Volume 1. From the Earliest Times to the Middle of the Nineteenth Century.
  • Even before the appearance of The Sceptical Chemist there was a growing conviction that the old hypotheses as to the essential nature of matter were inadequate and misleading. ...[T]he four "elements" of the Peripatetics had become merged into the tria prima—the "salt," "sulphur," and "mercury"—of the Paracelsians. As the phenomena of chemical action became better known... the conception of the tria prinui, as understood by Paracelsus and his followers, was incapable of being generalised into a theory of chemistry. Becher, while clinging to the conception of three primordial substances as making up all forms of matter, changed the qualities hitherto associated with them. According to the new theory, all matter was composed of a mercurial, a vitreous, and a combustible substance or principle, in varying proportions, depending upon the nature of the particular form of matter. When a body was burnt or a metal calcined, the combustible substance—the terra pinguis of Becher—escaped.
    Georg Ernst Stahl
  • This attempt to connect the phenomena of combustion and calcination with the general phenomena of chemistry was still further developed by Stahl, and was eventually extended into a comprehensive theory of chemistry, which was fairly satisfactory so long as no effort was made to test its sufficiency by an appeal to the balance.
  • The theory of phlogiston was originally broached as a theory of combustion. According to this theory, bodies such as coal, charcoal, wood, oil, fat, etc., burn because they contain a combustible principle, which was assumed to be a material substance and uniform in character. This substance was known as phlogiston.
  • All combustible bodies were to be regarded... as compounds, one of their constituents being phlogiston: their different natures depended partly upon the proportion of phlogiston they contain, and partly upon the nature and amount of their other constituents.
  • A body, when burning, was parting with its phlogiston; and all the phenomena of combustion—the flame, heat, and light—were caused by the violence of the expulsion of that substance.
  • Certain metals—as, for example, zinc—could be caused to burn, and thereby to yield earthy substances, sometimes white in colour, at other times variously coloured. These earthy substances were called calces, from their general resemblance to lime.
  • Other metals, like lead and mercury, did not appear to burn; but on heating them they gradually lost their metallic appearance, and became converted into calces. This operation was known as calcination. In the act of burning or of calcination phlogiston was expelled. Hence metals were essentially compound: they consisted of phlogiston and a calx, the nature of which determined the character of the metal. By adding phlogiston to a calx the metal was regenerated. Thus, on heating the calx of zinc or of lead with coal, or charcoal, or wood, metallic zinc or lead was again formed. When a candle burns, its phlogiston is transferred to the air; if burned in a limited supply of air, combustion ceases, because the air becomes saturated with phlogiston.
  • Respiration is a kind of combustion whereby the temperature of the body is maintained. It consists simply in the transference of the phlogiston of the body to the air. If we attempt to breathe in a confined space, the air becomes eventually saturated with the phlogiston, and respiration stops.
  • The colour of a substance is connected with the amount of phlogiston it contains. Thus, when lead is heated, it yields a yellow substance (litharge); when still further heated, it yields a red substance (red lead). These differences in colour were supposed to depend upon the varying amount of phlogiston expelled.
  • The doctrine of phlogiston was embraced by nearly all Stahl's German contemporaries, notably by Marggraf, Neumann, Eller, and [Johann Heinrich] Pott. It spread into Sweden, and was accepted by Bergman and Scheele; into France, where it was taught by Duhamel, Rouelle, and Macquer; and into Great Britain, where its most influential supporters were Priestley and Cavendish. It continued to be the orthodox faith until the last quarter of the eighteenth century, when, after the discovery of oxygen, it was overturned by Lavoisier.
  • During the sway of phlogiston chemistry made many notable advances... in spite of it. ...[U]ntil the time of Lavoisier few if any investigations were made with the express intention of testing it, or of establishing its sufficiency. When new phenomena were observed the attempt was no doubt made to explain them by its aid, frequently with no satisfactory result. Indeed, even in the time of Stahl facts were known which it was difficult or impossible to reconcile with his doctrine; but these were either ignored, or their true import explained away.
  • It is commonly stated that the exception is a proof of the rule. The history of science can show many instances whereby the rule has been demolished by the exception. Little facts have killed big "theories, even as a pebble has slain a giant. During the reign of phlogiston a few of such facts were not unknown at least to some of the better informed of Stahl's followers.
  • Some of the alchemists had discovered that a metal gained, not lost, weight by calcination. This was known as far back as the sixteenth century. It had been pointed out by Cardan and by Libavius. Sulzbach showed that such was the case with mercury. Boyle proved it in the case of tin, and Rey in that of lead. Moreover, as knowledge increased it became certain that Stahl's original conception of the principle of combustion as a ponderable substance he imagined, with Becher, that it was of the nature of an earth was not tenable. The later phlogistians were disposed to regard it as probably identical with hydrogen. But even hydrogen has weight, and facts seemed to require that phlogiston, if it existed at all, should be devoid of weight.
  • Towards the latter half of the eighteenth century clearer views began to be held concerning the relations of atmospheric air to the phenomena of combustion and of calcination; many half-forgotten facts relating to these phenomena were recalled, and the inconsistencies and insufficiency of phlogiston as a dogma became gradually manifest. Three cardinal facts conspired to bring about its overthrow—the isolation of oxygen by Priestley; the recognition by him of the nature of atmospheric air, and of the fact that one of its constituents is oxygen; and, lastly, the discovery by Cavendish that water is a compound, and that its constituents are oxygen and hydrogen. The significance of these facts was first clearly grasped by Lavoisier, and to him is due the credit of their true interpretation. By reasoning and experiment he proved conclusively that all ordinary phenomena of burning are so many instances of the combination of the oxygen of the air with the combustible substance; that calcination is a process of combination of the oxygen in the air with the metal, which thereby increases in weight by the amount of oxygen combined. Water no longer a simple substance is formed by the union, weight for weight, of oxygen and hydrogen. ...The phlogiston myth was thus exploded.
  • Inspired by Lavoisier, a small band of French chemists Berthollet, Fourcroy, Guyton de Morveau thereupon set to work to remodel the system of chemistry and to recast its nomenclature so as to eliminate all reference to phlogiston. The very names "oxygen," "hydrogen," "nitrogen," corresponding respectively to the "dephlogisticated air," "phlogiston," and "phlogisticated air" of Priestley, were coined by the new French school.
  • For a time le principe oxygine was regarded by this school in much the same relation as phlogiston was regarded by Stahl and his followers. The one fetich was exchanged for the other. The combustible principle—phlogiston—was renounced for the acidifying principle—oxygen. The new chemistry for a time centred itself round oxygen, just as the old chemistry had centred itself round phlogiston. The views of the French school met with no immediate acceptance in Germany, the home of phlogistonism, or in Sweden or England, possibly owing, to some extent, to national prejudices. The spirit of revolution, even although it might be an intellectual revolution, had not extended to these countries. Priestley, Cavendish, and Scheele could not be induced to accept the new doctrine. It was, however, accepted by Black, and its principles taught by him in Edinburgh; and before the end of the century it had practically supplanted phlogistonism in this country. Some of those who, like Kirwan, had energetically opposed the new theory ended by enthusiastically embracing it. Its introduction into Germany was mainly due to the influence of Klaproth.

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