I originally learned something about Joseph Priestley’s theory of phlogiston in secondary school, but needed to refresh my memory when I wrote this clerihew. To be scrupulously fair, the theory had been around for about a hundred years when Priestley – a Dissenting minister and amateur chemist – took it up; but he took it up in a big way.
The basic idea is that all flammable materials contain a mysterious substance called phlogiston, which is released when those materials are burned, leaving behind a ‘de-phlogisticated’ residue. The main problem with the phlogiston theory was that phlogiston itself was invisible and unmeasurable – phlogiston was supposed to have no colour, odour, taste or mass.
In 1774 Priestley took his phlogiston roadshow to Paris, where he demonstrated what he thought was the existence of air from which phlogiston had been removed. What he was actually demonstrating was the existence of the gas that we know today as oxygen.
The Frenchman Antoine Lavoisier was at one of Priestley’s demonstrations, but he was not impressed with Priestley’s conclusions. He knew that experiments had shown that some materials actually gained weight when burned, which led to a conclusion that Lavoisier could not accept – that phlogiston, if it existed, had to have negative mass. He and his contemporaries went looking for alternative explanations, and modern chemistry is based on the work they did, while Priestley’s ideas are now one with the dodo.
It was politics and not chemistry that brought both Priestly and Lavoisier undone.
Joseph Priestley’s Dissenting principles – and his support for the American and French revolutions – contributed to the Birmingham riots in 1791 that saw his home burned and forced him and his family to flee, ultimately, to the United States. Lavoisier fared even worse. Falsely branded a traitor during the French Reign of Terror, he was sent to the guillotine in 1794.
“Dissent is the native activity of the scientist, and it has got him into a good deal of trouble in the last years. But if that is cut off, what is left will not be a scientist.”
– Jacob Bronowski (1908-1974)