The Phlogiston Theory – Wonderfully wrong but fantastically fruitful

There is a type of supporter of gnu atheism and/or scientism who takes a very black and white attitude to the definition of science and also to the history of science. For these people, and there are surprisingly many of them, theories are either right, and thus scientific, and help the progress of science or wrong, and thus not scientific, and hinder that progress. Of course from the point of view of the historian this attitude or stand point is one than can only be regarded with incredulity, as our gnu atheist proponent of scientism dismisses geocentrism, the phlogiston theory and Lamarckism as false and thus to be dumped in the trash can of history whilst acclaiming Copernicus, Lavoisier and Darwin as gods of science who led as out the valley of ignorance into the sunshine of rational thought.

I have addressed this situation before on more than one occasion but as a historian of science I think that it’s a lesson that needs to be repeated at regular intervals. Because it is the American Chemical Society’s “National Chemistry Week 2015” I shall be re-examining the Phlogiston Theory whose creator Georg Ernst Stahl was born on 22 October 1659 in Ansbach, which is in Middle Franconia just down the road from where I live.

Georg_Ernst_Stahl

Georg Ernst Stahl (1660–1734) Source: Wikimedia Commons

Stahl had a fairly conventional career, studying medicine at Jena University from 1679 to 1684. 1687 he became court physician to the Duke of Sachen-Weimar and in 1694 he was appointed professor of medicine at the newly founded University of Halle, where he remained until 1715 when he became personal physician to Friedrich Wilhelm I, King of Prussia. Stahl like most chemists in the Early Modern Period was a professional physician, chemistry only existing within the academic context as a sub-discipline of medicine.

To understand the phlogiston theory we need to go back and take a brief look at the development of the theory of matter since the ancient Greeks. Empedocles introduced the famous four-element theory, Earth, Water, Air and Fire, in the fifth century BCE and this remained the basic theory in Europe until the Early Modern Period. In the ninth century CE Abu Mūsā Jābir ibn Hayyān added Sulphur and Mercury to the four-elements as principles, rather than substances, to explain the characteristics of the seven metals. In the sixteenth century CE, Paracelsus took over al- Jābir’s Sulphur and Mercury adding Salt as his tria prima to explain the characteristics of all matter. In the seventeenth century, when Paracelsus’ influence was at its height, many alchemists/chemists adopted a five-element theory – Earth, Water, Sulphur, Mercury and Salt – dropping air and fire. Robert Boyle, in his The Sceptical Chymist (1661), threw out both the Greek four-element theory and Paracelsus’ tria prima, groping towards a more modern concept of element. We now arrive at the origins of the phlogiston theory.

The German Johann Joachim Becher (1635–1682), a physician and alchemist, was a big fan of Boyle and his theories and even travelled to London to learn at the feet of the master.

Jjbecher

Johann Joachim Becher (1635-1682) Source: Wikimedia Commons

Like Boyle he rejected both the Greek four-element theory and Paracelsus’ tria prima, in his Physica Subterranea (1667) replacing them with a two-element theory Earth and Water with Air present just as a mixing agent for the two. However he basically reintroduced Paracelsus’ tria prima in the form of three different types of Earth.

  • terra fluida or mercurial Earth giving material the characteristics, fluidity, fineness, fugacity, metallic appearance
  • terra pinguis or fatty Earth giving material the characteristics oily, sulphurous and flammable
  • terra lapidea glassy Earth, giving material the characteristic fusibility

Stahl took up Becher’s scheme of elements concentrating on his terra pinguis, making it his central substance and renaming it phlogiston. In his theory all substances, which are flammable contain phlogiston, which is given up when they burn, the combustion ceasing when the phlogiston is exhausted. The classic demonstration of this was the combustion of mercury, which turns to ash, in Stahl’s terminology (mercuric oxide in ours). If this ash is reheated with charcoal the phlogiston is restored (according to Stahl) and with it the mercury. (In our view the charcoal removes the oxygen restoring the mercury). In a complex series of experiment Stahl turned sulphuric acid into sulphur and back again, explaining the changes once again through the removal and return of phlogiston. Through extension Stahl, an excellent experimental chemist, was able to explain, what we now know as the redox reactions and the acid-base reactions, with his phlogiston theory based on experiment and empirical observation. Stahl’s phlogiston theory was thus the first empirically based ‘scientific’ explanation of a large part of the foundations of chemistry. It is a classic example of what Thomas Kuhn called a paradigm and Imre Lakatos a scientific research programme.

Viewed with hindsight the phlogiston theory is gloriously, wonderfully and absolutely wrong in all of its aspects thus leading to the scorn with which it is viewed by our gnu atheist proponent of scientism, however they are wrong to do so. I prefer Lakatos’ scientific research programme to Kuhn’s paradigm exactly because it describes the success of the phlogiston theory much better. For Lakatos it’s irrelevant whether a theory is right or wrong, what matters are its heuristics. A scientific research programme that produces new facts and phenomena that fit within the descriptive scope of the programme has a positive heuristic. One that produces new facts and phenomena that don’t fit has a negative heuristic. Scientific research programmes have both positive and negative heuristics simultaneously throughout their existences, so long as the positive heuristic outweighs the negative one the programme continues to be accepted. This was exactly the case with the phlogiston theory.

Most European eighteenth-century chemist accepted and worked within the framework of the phlogiston theory and produced a great deal of new important chemical knowledge. Most notable in this sense are the, mostly British, so-called pneumatic chemists. Working within the phlogiston theory Joseph Black (1728–1799), professor for medicine in Edinburgh, isolated and identified carbon dioxide whilst his doctoral student Daniel Rutherford (1749–1819) isolated and identified nitrogen. The Swede Carl Wilhelm Scheele (1742–1786) produced, identified and studied oxygen for which he doesn’t get the credit because although he was first, he delayed in publishing his results and was beaten to the punch by Joseph Priestley (1733–1804), who had independently also discovered oxygen labelling it erroneously dephlogisticated air. Priestley by far and away the greatest of the pneumatic chemists isolated and identified at least eight other gases as well as laying the foundations for the discovery of photosynthesis, perhaps his greatest achievement.

Henry Cavendish (1731–1810) isolated and identified hydrogen, which he thought for a time might actually be phlogiston, before going on to make the most important discovery within the framework of the phlogiston theory, the structure of water. By a series of careful experiments Cavendish was able to demonstrate that water was not an element but a compound consisting of two measures of phlogiston (hydrogen) with one of dephlogisticated air (oxygen). With the same level of precision he also demonstrated that normal air consists of four parts of nitrogen to one of oxygen or better said not quite. He constantly found something he couldn’t identify present in one one-hundredth and twentieth of the volume of nitrogen. In the nineteenth century this would finally be identified as the gas argon.

All of these discoveries are to be counted to the positive heuristic of the phlogiston theory. What weighed heavily on the negative side is the fact that as the accuracy of measurement increased in the eighteenth century it was discovered that the ashes, of mercury for example, left behind on burning were heavier than the original substance being burnt. This was troubling as combustion was supposed to be the release of phlogiston. Some supporters of the theory even suggested negative phlogiston to explain this anomaly. This suggestion, which never caught on, gets particularly mocked today, something I find somewhat strange in an age that has had to accept anti-matter and is now being asked to accept dark matter and dark energy to explain known anomalies in current theories.

Ironically it was the discoveries of oxygen and the composition of water that gave Lavoisier the necessary building blocks to dismantle the phlogiston theory and build his own competing theory, which would in the end prove successful and commit the phlogiston theory to the scrap heap of the history of chemistry. However one should never forget that it was exactly this theory that delivered him the tools he needed to do so. As I wrote in my sub-title even a theory that is wonderfully wrong can be fantastically fruitful and should be treated with respect when viewed with hindsight.

 

23 Comments

Filed under History of Chemistry, History of science, Myths of Science

23 responses to “The Phlogiston Theory – Wonderfully wrong but fantastically fruitful

  1. Phillip Helbig

    “Stahl had a fairly conventional career, studying medicine at Jena University from 1679 to 1684. 1687 he became court physician to the Duke of Sachen-Weimar and in 1694 he was appointed professor of medicine at the newly founded University of Halle, where he remained until 1715 when he became personal physician to Friedrich Wilhelm I, King of Prussia.”

    For some definition of “conventional”, I suppose. 🙂

  2. Phillip Helbig

    “This suggestion, which never caught on, gets particularly mocked today, something I find somewhat strange in an age that has had to accept anti-matter and is now being asked to accept dark matter and dark energy to explain known anomalies in current theories.”

    I see your point, and it is a valid one. Similar to seeing Mach’s scepticism of atoms (“Have you ever seen one?”) in the light of the question whether quarks, or virtual particles, or whatever, are “real”. However, the analogy (which some might misinterpret) does not imply that antimatter or dark energy have negative mass. (Dark energy is essentially negative pressure, which sounds strange until you realize that it is the same thing as tension.)

  3. MarylandBill

    This is a fantastic post. Thank you very much. I love the analogy to dark matter and dark energy. I think using anti-matter is a little less useful since we know anti-matter is real. In contrast, dark matter and dark energy are very definitely very broad terms used to explain things we decidedly do not yet understand.

  4. Great article, fascinating.

    You say: “I prefer Lakatos’ scientific research programme to Kuhn’s paradigm exactly because it describes the success of the phlogiston theory much better.”

    I’m a novice on the history and philosophy of science, I’ve only read Kuhn’s The Structure of Scientific Revolutions – can you point to something readable on Lakatos?

    • The best place to start on Lakatos is his paper Falsification and the Methodology of Scientific Research Programmes in Criticism and the Growth of Knowledge a book that contains lots of other nice philosophy of science stuff, including from Kuhn

  5. John Stewart

    This is a really nice overview of phlogiston, and, more importantly, an argument for symmetry in our study of history. I think you rush the conclusion a bit though. Mi Gyung Kim has a good article on the differences between French phlogiston theories and those of Stahl (http://www.hyle.org/journal/issues/14-1/kim.pdf) and I wrote a follow up on the British phlogiston theories of Priestley, Kirwan, etc (http://www.hyle.org/journal/issues/18-2/stewart.htm). The point that both of us make is that Kuhn’s revolutions can’t be right because the later theories were so little like Stahl’s. Lakatos is closer in that the heuristic carries through while so many of the details change. It’s also interesting that phlogiston continued to be used in discussions of electricity, meteorology, and geology well into the 19th century.

  6. Phlogiston has struck me for a while as having an unfairly harsh reputation in pop science history. It does seem to me like the range of ideas about how phlogiston might behave were close enough to the way oxygen behaves. I can imagine that had a sufficiently respected figure decided that the thing we call oxygen was phlogiston cured of its major experimental problems, it would’ve been acceptable as a fuzzy hypothesis shorn of its problems and made reasonably precise and useful.

  7. Since nobody else has cited this yet, let me mention Hasok Chang’s marvelous article, “We Have Never Been Whiggish (About Phlogiston)”. More recently, he has returned to the topic with “The Hidden History of Phlogiston”.

  8. “In the ninth century CE Abu Mūsā Jābir ibn Hayyān added Sulphur and Mercury to the four-elements as principles, rather than substances, to explain the characteristics of the seven metals. In the sixteenth century CE, Paracelsus took over al- Jābir’s Sulphur and Mercury adding Salt as his tria prima to explain the characteristics of all matter.”

    Can you enlarge on the meaning of “element” and “principle” in this context? I can see at least three possible meanings of the term “elements:” 1. forces of nature, 2. primary causes, 3. basic parts (of matter). Only the last accords with our modern chemical understanding of the term. How were the principles different from the four elements?

    When you say that Abu Mūsā Jābir ibn Hayyān used the four elements and two principles, in order to explain the characteristics of seven metals, I’d very much like to comprehend how he did that, but am lost in an incommensurable universe.

    • That is probably the most difficult question you could ask and requires a somewhat longer answer. I will get back to this one later in the week, I promise!

      • I could have a go too, but it’ll take a while. It’s an area that is still unclear for me even with 58 alchemy related books on my shelves and scores of papers on my hard drive.
        From Lawrence Principe’s book “The secrets of alchemy”, it seems (page 35) that Jabir got the idea from the Book of hte secret of creation by Balinus, which is an early 9th century work. Both authors according ot principe “… states simply that all metals are compounds of two principles called Mercury (akkin to Aristotle’s moist exhalation) and Sulphur (akin to the smoky exhalation). These two principles, condensed underground, combine in different propertions and degress of purity to produce the varioufs meatls.”
        Page 36 – “Secondly, the metallic principles Mercury and sulphur were not necessarily identical with the common substances called by these names. These names were attached to the conensed exhalations by analogy with the properties of the common substances.”

        There were different qualities of ‘mercury’ and ‘sulphur’, quotes put in as scare quotes to make it clear they aren’t what we thought of as mercury and sulphur. Naturally this all caused a lot of confusion down the centuries, with some thinging it did mean real Hg and S, lots of other saying it didn’t and many alchemical texts laugh at those think it did.

        What this has to do with the elements is that they were below the principles, i.e. more like modern elements. Jabir’s theories involved correcting the qualities of the mercury and sulphur by use of proportions of the four elements based on numbers derived from numerical values of the names of the metals!

        Also important to note that when we say Jabir we mean the person who likely existed but there isn’t much evidence for him being an alchemist, and those who followed in his school of thought and probably wrote most of the Jabirian corpus decades after the original Jabir.

      • Thanks guthriestewart. You said:
        “What this has to do with the elements is that they were below the principles, i.e. more like modern elements. Jabir’s theories involved correcting the qualities of the mercury and sulphur by use of proportions of the four elements based on numbers derived from numerical values of the names of the metals!”

        Did I get ths right, the four elements were part of the two principles sulphur and mercury and these in turn somehow made metals?

      • Yes. See 74-75 of the Dover edition of “Alchemy” by E. J. Holmyard for more. It’s an old book, but still accurate enough. Sulphur provides the hot and dry natures, mercury the moist and cold. Jabir also believed in internal and external sulphur and mercury, making it all rather complicated.

  9. Reblogged this on The Interventionist Paradox and commented:
    A great explanation for why incorrect scientific theories can sometimes lead to fruitful results.

  10. If the critique of phlogiston theory is that the proponents did not make their predictions in advance, but rather conducted investigations and then used phlogiston theory to explain the results afterward, would there be historical counterexamples to this? It’s all well and good to say how their post-hoc generalizations under the banner of phlogiston were leading them towards oxygen; but there’s considerable justice, I think, in the charge that a key element of Science was missing.

  11. A very nice summary of a topic I’ve often wondered about. But i wonder are some straw men being constructed and demolished? it would heva ebeen helpful to have some refernces for those ‘gnu atheists’ or Whigsters

  12. Lavoisier’s role in this is also pivotal. Received wisdom seems to be that Priestley showed Lavoisier how he had produced oxygen, after which Lavoisier conducted the same experiments without acknowledging Priestley. But the ‘increased accuracy’ of weighing was exactly what Lavoisier was already the prince of. Looking at Lavoisier’s Oeuvres, the man was obsessed with measuring everything, even the weight of manure in his paddocks. Almost the first thing Lavoisier did once he had shown Priestley out was to repeat the experiment, weighing everything before and afterward, just like he always did. Lavoisier’s brilliant insight was to see the results not as the positive heuristic of the phlogiston theory, but as negative heuristics which required the theory’s replacement. In subsequent years, he worked with other French chemists, and also [very importantly] the Scotsman Joseph Black, to create the modern system of inorgamic chemical nomenclature which his paradigm shift then required. But he was the first to make that leap. The fact that it took hold so quickly thereafter indicates that phlogiston was already in trouble, but there needed to be something to replace it. That’s not Whiggery, I hope, but it looks and sounds like a reasonable hypothesis.

  13. In my lifetime the meaning of empiricism seems to have changed. When I was a kid, the consensus seems to have been that being an empiricist and therefore on the side of the angels meant relying on the evidence of the senses. The implication was that if you did that, it would take some time (possibly centuries) and you’d make some mistakes, but you’d eventually figure it all out because you followed an infallible and therefore virtuous method unlike the reprobates who fell back on sheer reason or intuition. In living memory, grown men believed that the best science could be was an economical summary of sense impressions. More recently, an older sense of empiricism seems to have resurfaced: the notion that to be empirical means to be willing to take risks, to try things out. That involves looking and seeing, obviously, but many other things as well including taking a chance on new theories. What’s eternally provisional isn’t just the results, but the methods; and you shouldn’t blame the gambler for his unlucky throws.

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  15. For me, the only question is: given the available data then, was the phlogiston theory reasonable?

    It was. Obviously, there’s something in combustible materials, that’s lost when they burn, and it’s hard or impossible to put it back.

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