Phlogiston, AKA The Things We Used to Know


Science, as in all human ventures, has taken its fair share of wrong turns. But unlike our usual reaction to gaffes and slip-ups, those made in science can offer humanity a chance to grow and learn.

My favourite of all our mistakes is by far phlogiston. I would say that I’m not sure if it’s my favourite because of the undeniable beauty of the theory, the way it reminds me simpler times when we knew that earth was an element, or because of what happened next, except that I’m absolutely sure it’s the latter. You see, this silly mistake would go on to define what we know and how we go about knowing what we know.

For the non-scientist readers, I would like to say at this point that you should stick with me here. I’m going to explain some science for a bit, but it’s not all numbers and quantum tunnelling. I’m not sure if I’m being blinkered by a lifetime of scientific obsession, but I honestly think this is a funny story with an important lesson.

So to set the scene, imagine it’s 1667. Alchemists still think that earth, air, fire, and water are the only four elements, Dmitri Mendeleev hasn’t constructed the periodic table of elements yet (or been born, for that matter), and to make matters worse just last year in 1666 London was ravaged by the worst fire in history. Whilst boring people decided that large amounts of uncontrolled fire wasn’t conducive for comfortable living and went around making sure that there was less of it around London, the more peculiar scientific minds of the time decided to tackle what they saw as a more important matter. You see, we didn’t know much about fire in 1667 other than it being bad for buildings and good for cooking. Then came Johann Joachim Becher.

Becher was a German alchemist who first proposed the phlogiston theory in his book Physical Education in 1667. He had noticed that when wood was burned, the resulting ash weighed less than the original piece of wood. It followed that wood was made of ash and something else, which was dissipated into the air during the process of combustion. Using this information, he proposed a change to the classical theory of the four elements, replacing fire and air with ‘terra lapidea’, ‘terra fluida’, and ‘terra pinguis’. The latter, said Becher, was what caused combustibility and was released during burning, causing a drop in weight. In 1703 Georg Ernst Stahl renamed ‘terra pinguis’ as phlogiston, and although he proposed minor variants on the theory, the main characteristics remained unchanged.

Soon, we had a classification system for all substances, namely that everything was either “phlogiscated” or “dephlogisticated”. A “phlogisticated” substance became “dephlogisticated” when burned. So instead of ash, we had “dephlogisticated wood”. James Bryan Conant described phlogiston in his 1950 paper The Overthrow of Phlogiston Theory: The Chemical Revolution of 1775–1789:

“In general, substances that burned in air were said to be rich in phlogiston; the fact that combustion soon ceased in an enclosed space was taken as clear-cut evidence that air had the capacity to absorb only a finite amount of phlogiston. When air had become completely phlogisticated it would no longer serve to support combustion of any material, nor would a metal heated in it yield a calx; nor could phlogisticated air support life, for the role of air in respiration was to remove the phlogiston from the body.”

Although to us living in the future this sounds ridiculous, almost everything about the theory held up. A candle, when trapped in a bell jar, does stop burning. We know now that this is because it’s used up all the oxygen required for combustion, but we knew then it was because air only had a finite capacity for holding phlogiston. It makes so much sense! If only we could capture some of it; if only it weren’t such an ethereal substance that evades our efforts to understand it more…

This is the point in the story where phlogiston takes a major hit. Becher, Stahl and later contributors to the theory such as Robert Boyle had all missed something. Everything about phlogiston theory was hanging on one fact; that materials lost weight during combustion due to the loss of phlogiston. If this were to be disproved then the whole theory would fall to pieces. In 1753 Mikhail Lomonosov did just that. Lomonosov introduced pure heat to magnesium in an enclosed space, and noticed that the weight of the resulting ash was more than what he had started with. That was it. Phlogiston had been disproven.

After that, there were a few people who hung on to phlogiston, but their knowledge had been downgraded to belief and faith. There were suggestions that phlogiston had negative weight, or that it was lighter than air, but nothing could stop the speedy demise of this groundbreaking theory, and the corresponding rise of the modern chemistry that displaced classical alchemy.

Although the science that followed is incredibly important, I think there is a bigger lesson to be learnt here. The way science deals with mistakes can inform the way we all deal with incontrovertible evidence to the contrary of our knowledge.

Tim Minchin, I believe, describes this attitude best in his critical thinking poem Storm:

“Science adjusts its beliefs based on what’s observed, faith is the denial of observation so that Belief can be preserved. If you show me that, say, homeopathy works, then I will change my mind. I’ll spin on a fucking dime. I’ll be embarrassed as hell, but I will run through the streets yelling “It’s a miracle! Take physics and bin it! Water has memory! And while it’s memory of a long lost drop of onion juice is infinite, it somehow forgets all the poo it’s had in it!”

You show me that it works and how it works and, when I’ve recovered from the shock, I will take a compass and carve ‘fancy that’ on the side of my cock.”

Humanity, for one reason or another, has an insatiable urge to move forward. To know more today than we did yesterday, and work hard so that what we know today pales in comparison to what we’ll know tomorrow. We’re on a timeline of discovery and we’re not entirely sure what’s next, and to find out more we must be humble, and do more than merely accept the facts when they turn against us, we must actively seek out our mistakes in order to push ourselves further and be prepared to do a swift about-turn when the situation calls for it. Richard P. Feynmann once said that “we are trying to prove ourselves wrong as quickly as possible, because only in that way can we find progress”.

We mustn’t fear looking silly in the history books and we should accept failure with open arms as an opportunity to grow and learn. The only true failure, the only way we will definitely look like idiots to the eyes of future humanity, is if we dig our heels in to outdated theories and refuse to change. History is littered with big, beautiful ideas that have been proven wrong, and for all we know almost everything we know now could be headed to the same fate. We used to know the world was flat and we used to know that the sun revolved around the earth. We used to know that ash was dephlogisticated wood and we used to know who created the heavens and the earth. Imagine what we’ll know tomorrow.

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