Innovation and progress make the world a better place. They unlock new possibilities, correct past mistakes, and realize untapped potential. It’s not a coincidence that these words can have such positive connotations.
Yet to reap these benefits, progress must be carefully integrated into the old order. For innovators often turn their back on all that existed before, throwing away valuable past insights.
The best example I know of is the so-called Chemical Revolution at the end of the 18th century.
In most popular books and histories of science, this shift is presented as Lavoisier discovering oxygen, and with it the compositional approach to chemistry, replacing the old alchemy-imbued idea of phlogiston. The prevalent explanation of combustion at the time, phlogiston was a weightless fluid whose movement in and out of objects ruled combustion, respiration, and the properties of metals. But to the modern eye, it looks nothing like a scientific explanation — just a made-up fake substance, a fake explanation. It clearly couldn’t compete with Lavoisier’s composition of elements.
Or so we read in the modern treatment.[1]
On the other hand, a quick look at our current best models of combustion (so called oxido-reduction reactions) reveal a weightless “fluid” whose movements capture the essence of the reaction: electrons. Sure, electrons are not a fluid; but they’re not really particles either according to quantum mechanics, and the fluid/substance frame fits with the concepts available at the end of the 18th century. Properties of metals also emerge from free electrons, confirming a key prediction of phlogistonist chemistry that Lavoisierian chemistry couldn’t explain.
Gilbert Lewis, of the Lewis diagram fame, makes this point in 1926 in The Anatomy of Science:
The phlogistonists were not content with the idea alone, but must add a mechanism, the hypothetical phlogiston, so that every process of the type we are discussing was supposed to involve the gain or the loss of this almost imponderable substance. By this mechanism they fell. They had not yet recognized that the air is a chemical reagent, and thought that the process of burning was merely the loss of phlogiston. When it was found that substances in burning gain in weight they were obliged to retreat before the proponents of the oxygen theory. If they had only thought to say “The substance burning gives up its phlogiston to, and then combines with, the oxygen of the air,” the phlogiston theory would never have fallen into disrepute. Indeed, it is curious now to note that not only their new classification but even their mechanism was essentially correct. It is only in the last few years that we have realized that every process that we call reduction or oxidation is the gain or loss of an almost imponderable substance, which we do not call phlogiston but electrons.
What is more, these key aspects of the modern treatment were completely removed by the Lavoisierian approach. There everything had to be explained in terms of composition. In adding this constraint, this strand of chemistry missed not only the key role played by electrons, but also most energetic considerations.
So Phlogistonists and Lavoisierian both only held one part of modern chemistry. As chemist William Odling wrote in 1876 in The Revived Theory of Phlogiston:
For most of what has since become known mankind are indebted to the surpassing genius of Lavoisier; but the truth which he established, alike with that which he subverted, is now recognizable as a partial truth only; and the merit of his generalization is now perceived to consist in its addition to—its demerit to consist in its supercession of—the not less grand generalization established by his scarcely-remembered predecessors.
[...]
The partial truth contributed by Lavoisier was indeed more wanted, more adapted to the needs of the time, than the partial truth which it displaced. To him chemists are indebted for their present conception of material _elements;_ and especially for their knowledge of the part played by the air in the phenomena of combustion, whereby oxygenated _compounds_ are produced. The phlogistians, indeed, were not unaware of the necessity of air to combustion, but, being ignorant of the nature of air, were necessarily ignorant of the functions which it fulfilled. To burn and throw off phlogiston being with them synonymous expressions, the air was conceived to act by somehow or other enabling the combustible to throw its phlogiston off; and a current of air was conceived to promote combustion by enabling the combustible to throw its phlogiston off more easily. Moreover, contact of air was not essential to combustion, provided there was present instead some substance, such as nitre, which, equally with or even more effectively than air, could enable the combustible to discharge itself of phlogiston. But, while the phlogistians, on the one hand, were unaware that the burnt product differed from the original combustible otherwise than as ice differs from water, by loss of energy, Lavoisier, on the other hand, disregarded the notion of energy, and showed that the burnt product included not only the stuff of the combustible, but also the stuff of the oxygen it had absorbed in the burning. But, as well observed by Dr. Crum-Brown, we now know “that no compound contains the substances from which it was produced, but that it contains them _minus_ something. We now know what this something is, and can give it the more appropriate name of potential energy; but there can be no doubt that this is what the chemists of the seventeenth century meant when they spoke of phlogiston.”
Integrating the two perspectives is what modern chemistry does. Unfortunately, the Lavoisierian proved less sensible. Rather than looking for what phlogiston captured better than their new theory, they launched on of the most intense propaganda effort in the history of science, ensuring that for decades (and in most histories of chemistry to this day), no one could seriously invoke phlogistonian concepts and keep their scientific credibility.
They actually figured out a more satisfying form of modeling: where phlogiston was an unanalyzable substance, the Lavoisierian manipulated compositions whose structure and components could be investigated and amended. It’s obvious that phlogiston insights should have been integrated into the Lavoisierian model, not the other way around.
But blinded by their innovation, the Lavoisierian burned the whole history of combustion and salted the earth. In so doing they delayed the energetic and electronic understanding of chemistry by decades.
Here lies a lesson for champions of innovation: even though the point of progress comes in surpassing and replacing the past, we still must carefully integrate these new insights, or risk destroying hard won victories.
- ^
The main exception I’m aware of is Hasok Chang’s Is water H2O?, which is the initial read that made me realize this historical bias and parts of its groundlessness.
“Phlogiston Theory and Chemical Revolutions” argues that, while Lavoisier clarified the concept of a chemical element, phlogiston theory was ahead of its time as a physical theory of chemical interaction. The author’s idea is that phlogiston is now better understood as a property similar to energy (“the Gibbs chemical potential of a material with respect to its oxide”), rather than as a substance.
Joseph Priestley, the main defender of phlogiston theory against Lavoisier’s new chemistry, was a religious and economic liberal who supported the French revolution, and eventually moved to America, after being targeted by conservative mobs in Britain. A few years after Priestley’s move, at the age of 50, Lavoisier was guillotined by a French revolutionary tribunal, along with dozens of other aristocrats who had been supported by a hated royal taxation authority. The judge himself was executed three months later, and Lavoisier was posthumously rehabilitated a year after that. In his exile, Priestley outlived Lavoisier by ten years, but phlogiston theory was already considered outdated and wrong.
The entire debate surrounding phlogiston had unfolded without basic concepts that we now take for granted, like conservation of energy, or the idea that heat is “energy on the move”. That all came decades later.
My immediate response to the quoted texts, without having read the originals or the history of phlogiston, is that they are anachronistic. Identifying phlogiston with electrons is little better than identifying it with “negative oxygen”. At least there is such a thing as electrons. But when e.g. carbon burns in oxygen, there is not a flow of electrons from carbon to oxygen. Instead the carbon and oxygen both complete their electron shells by sharing electrons. None of this was known in 1876 or even 1926, but that just means that both Odling and Lewis were themselves wrong about combustion. There is nothing about electrons that can be matched to phlogiston, and even if carbon dioxide were correctly described as C++++ 2O--, well, since it isn’t, it might equally well be speculated to be C---- 2O++ with the electrons going the other way. “Dephlogisticated air” is just oxygen, nothing to do with removing electrons from the air.
I‘m afraid you’ll have to do more to convince me of the argument that Lavoisierian theory held up the development of chemistry for decades by denying the role of energy. Can you provide some evidence? Until the discovery of the atomic model, chemistry by necessity had to be an empirical science where practitioners discovered phenomena and linked them together and drew parallels, and progressed in that manner. Great progress was made without a deep underlying theory of how chemistry worked. It was well known that some reactions gave out heat, and some required heat to proceed and not much more was needed as regards the role of “energy”. Alloys and dyes and such were all first discovered without much deep understanding of chemical reaction theory.
Once quantum theory came along we understood how chemistry works and a lot of observations and linkages made sense. But for a long time quantum theory didn’t help as much as you might expect in pushing chemistry in new directions because the equations were too hard to get any real numbers out. So, much of chemical research carried on quite happily following well tried and tested paths of empirical research (and still does to quite a large extent). It was only really with the advent of computers that we started to make heavy use of calculation to help drive research.
You make the very good point that the Phlogistonists didn’t deserve to be pilloried, because they had a theory that was self consistent enough to model the real world as we know it now. But until electrons were actually discovered, it is hard to see how any Phlogistonist could seriously compete with the Lavoisierian point of view. It could scarcely be otherwise.
Sure they are. They’re a particle; the word “particle” just doesn’t mean quite what you expect it to mean. They can be a fluid: that’s why we can talk about electron gases and electron fluids; just not a classical fluid.
What they are not, though, is a “substance” in the way chemists (modern or phlogiston-era) think of the term. Identifying electrons (or heat, or free energy, or etc. etc.) with phlogiston feels akin to saying Democritus discovered the periodic table. Is there any useful insight that informed later generations working with more data and better models? Absolutely! But we have three steps (phlogiston, compositional chemistry, quantum mechanics), each of which captures more of the reality than the step before. Strictly more, I think, in terms of predictive capability. Is there any empirical question the phlogiston theorists got right that compositional chemistry did not? AFAIK, no, but it’s a real question and I’d like to know if I’m wrong here. But if I’m right, it means whatever useful model content is being added by understanding electrons has only an aesthetic connection to phlogiston at best, rather than re-introducing a once-known-but-ignored (or forgotten) truth.
Although I haven’t digged into the historical literature that much, I think there are two main candidates here: explaining the behavior of metals, and potential chemical energy.
On explaining the behavior of metal, this is Chang (Is Water H2O? p.43)
(Is Water H2O? p.21)
And on potential chemical energy, here are the quotes from Chang again
(Is Water H2O? p.46)
(Is Water H2O? p.47)
As a summary, let’s quote Chang one last time. (Is Water H2O? p.47-48)
I guess I’m confused by the assertion that phlogiston explains things about metal properties, that isn’t equally explained by “metals are calxes with the oxygen removed.” Both explanations are descriptive, not predictive, and yes that remains true until we figured out quantum mechanics. Neither will tell you how a metal will behave when burned, what color flame it’ll produce, why you can reduce iron ore with charcoal but not aluminum, what alloys you can make under what conditions and what their behavior will be, and so on.
I don’t disagree with “you can’t explain the properties of metals based on Lavoisier’s chemistry paradigm without quantum mechanics.” That’s just straightforwardly true. I remember very well one quantum mechanics lecture where my professor said, after about a week of derivations, “and that’s why metals are shiny.” What I disagree with is the assertion that phlogiston does explain this, in any sense other than just postulating the existence of a substance that tautologically, exactly matches whatever is observed in all its complexity. Understanding oxygen’s role better serves to highlight where the gaps in useful understanding already were, whether or not anyone had the tools yet to fill them.
Even if we do agree to identify phlogiston with electrons, then the phlogiston theorists were still mistaken to think of it as a substance separate from the other reactants. Electrons, and free energy too, are part of the reactant and product substances in question. “Atoms” aren’t actually atomic, or unbreakable. Neither side of this disagreement had that truth in its toolbox, and that truth is the central one that allows quantum mechanics to improve on what came before.
Are we sure the phlogistonists didn’t deserve it? Maybe they were assholes.
Nonsense. The fact that you can see some vague parallels between phlogiston and electrons or energy doesn’t make phlogiston theory any good. The fact that you can’t decide whether phlogiston represents electrons or energy should be a hint here.
Scientific theory should give useful predictions about the world and help us compress information. Phlogiston one does neither.