Antoine Lavoisier/Antoine-Laurent de Lavoisier (1743-1794)
My first (and only) encounter with Antoine-Laurent de Lavoisier at school was being told that he discovered oxygen and was guillotined during the French Revolution. Considering the real magnitude of Lavoisier's contributions to chemistry, this sells him extremely short! When I got older and was able to start digging into his legacy myself, I was astonished at how many core concepts in science have his fingerprints on. Let me explain.
Like many scientists in the 17th century, Antoine-Laurent de Lavoisier was born into a noble, wealthy family in August 1743 in Paris. Between 11 and 18, he was well-educated at the University of Paris and took a keen interest in chemistry, botany, mathematics and astronomy, before graduating with a law degree in 1763 with the intention of following in his father's footsteps. However, though he was admitted to the bar as a lawyer in 1764, he never practised law, instead choosing to begin a career in scientific research.
Collège des Quatre-Nations, University of Paris
To fund his private laboratory, Lavoisier invested a portion of his family's wealth in the ferme générale (a tax farming organisation utterly despised by the general population). If you're thinking that, given the French Revolution is going to kick-off in about twenty years, this was unwise, you'd be right on the money (so to speak). Although a large proportion of the income Lavoisier received from the ferme générale was deployed in philanthropic donations and even though he spent a great deal of time working on improving public sanitation, holding of public lectures on Chemistry and sustaining a campaign to improve hospital and prison conditions, his story, unfortunately, does not have a happy ending.
All that is far in his future though, so let's return to the chemistry.
To put his substantial accomplishments into proper context, it is necessary to describe the state of chemistry in the mid/late 18th century as he began his work. Although substantial experimental evidence had been collected about a range of substances, there were no valid theories explaining what these substances actually were. Belief in the four elements - air, earth, fire and water - was still prevalent.
For example, in 1772, Lavoisier investigated a curious phenomenon wherein sustained reflux of water in a glass vessel led to sediment collecting at the bottom. The suspicion was that the water was, somehow, being transmuted into earth by heating (Lavoisier proved that it was actually caused by the slow disintegration of the glass vessel. The mass of the sediment formed was the same as the mass lost from the vessel). This is also the era of phlogiston, of the invention of an entirely new (and imaginary) chemical substance to try to explain why combusting materials lost mass (and heated metals gained mass), rather than consider that cherished theories from alchemy might be incorrect. This was an era on the cusp of developing modern chemistry, but it wasn't there yet.
Magnesium gains mass when heated in oxygen (as it forms magnesium oxide)
So why was Lavoisier remarkable?
For one, he killed phlogiston (or, at least, was one of its most significant assassins). Phlogiston theory stated that combustible materials contained a fire-like substance - phlogiston - that was released during combustion (explaining why burning materials lost mass - 'dephlogistication'). This substance was then absorbed from the air by plants (explaining why air didn't spontaneously burst into flames and also why plants burnt well). That fact that materials would only burn for a short time in a sealed container was seen as proof that air had a limit to the phlogiston it could absorb.
Cracks had already been forming in the theory: if metals like magnesium were losing phlogiston when heated, how was it that they were gaining mass? By carefully repeating, then extending, experiments conducted by other scientists, Lavoisier widened these cracks and showed phlogiston theory to be false. By reacting metals within sealed containers and by taking precise measurements during this reaction, Lavoiser could prove that combustion required a gas with mass to be present as a reactant as there was no mass increase from phlogiston release: the total mass remained constant while the mass of the metal increased. Coupled with his extension of the w0rk done by Joseph Priestley, Laviosier concluded that the mystery gas that was involved in the reaction must be oxygen (he also concluded that oxygen was involved in both respiration and combustion). The theory of oxygen combustion was born in 1772 and neatly explained why metals gained mass when heated (as they were chemically combining with oxygen). Although this greater understanding did not immediately kill phlogiston theory, it forced it to become more and more complicated under it collapsed under its own contradications.
If this all sounds very close to the Law of the Conservation of Mass, you'd be right: Lavoisier was one of its key architects. Although his work was predated by scientists like Henry Cavendish, Lavoiseir's obsessive desire to measure everything, coupled with better technology and more accurate measurement techniques, helped to prove the validity of the theory. In years to come, Dalton and Proust would base their own seminal theories on Lavoisier's work on the conservation of mass, sparking the beginnings of the modern chemical revolution.
Finally (but by no means is this an exhaustive list), Lavoisier and his colleagues were instrumental in setting up the beginnings of modern chemical nomenclature, which he would base around his own oxygen theories: salts containing oxygen would have the suffix -ate, for example. It was determined that 55 substances existed that could not be broken down into simpler substances: these were termed elements. Although there were mistakes (the inclusion of a heat-fluid caloric as an element as one example), it was a spirited attempt at organising elements into a table which would be refined over time.
But not by Lavoisier. His priviledged position in society and his association with the ferme générale made him a marked man in Revolutionary France. He'd also made a lot of enemies with his work with the Farmers General on tobacco (he discovered adding a small amount of water improved the quality of the product, a move that immediately was misunderstood as fraudulent as the water added also increased the tobacco's bulk). When he and others were arrested and brought to trial, he argued their defence, citing the importance of his scientific work.
Killed by tobacco
He was told rather curtly by his judge: "The Republic needs neither scholars nor chemists; the course of justice cannot be delayed." And that was that. Aged just 50, Lavoisier was sentenced to death and guillotined. After it had been carried out, a friend of his - the astronomer and mathemetician Jospeh-Louis Legrange - lamented Lavoisier's untimely passing, saying "It took them only an instant to cut off this head, and one hundred years might not suffice to reproduce its like."
Magnesium burning photograph by Captain John Yossarian, Wiki Commons
Tobacco photograph by Sjschen, Wiki Commons
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