French aristocrat and chemist Antoine Laurent Lavoisier was an incredibly important figure in the history of chemistry, whose findings were equivalent in stature to the impact of Isaac Newton鈥榮 discoveries on physics. His new structure of chemistry, which understood the constituent parts of air and the process of combustion more clearly, set chemistry on a modern road and laid the groundwork for Dmitri Mendeleev鈥榮 work and the creation of the periodic table.听Lavoisier鈥檚 work overturned centuries of incorrect thinking about the nature of elements and compounds.
Lavoisier鈥檚 most notable book听,听published in 1789 by the elite French Academy of Sciences, could be considered the first modern chemistry textbook and contained theories about the nature of elements which replaced the听鈥減hlogiston theory,鈥� the belief that there was a 鈥渇ire element鈥� was contained within all combustible objects which was released in the form of fire, heat and light when an object burned.
At the time, the development of chemistry was being held back by this widespread and erroneous belief.听The theory, and the name phlogiston, was coined in 1718 by Georg Stahl, a Bavarian professor of medicine. The essence of it was that combustible substances contain a curious substance called phlogiston, which they lose when they burn. Because balances were inaccurate, the fact that substances often gained weight when they burnt was often missed. And so firm was the belief in phlogiston that when a gain in weight was recorded, it was explained away 鈥� for example, by saying that the phlogiston was an incorporeal, ethereal fire that was lighter than any other known substance and buoyed up heavier ones, or even a substance with negative weight.
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Before Lavoisier published his听罢谤补颈迟茅, aided by his wife Marie-Anne-Pierette who learned English to help him translate the growing body of scientific research, helped him with experiments and drew all the diagrams,听phlogiston theory was accepted as fact by the leading chemists of 18th Century Europe and听the 鈥渇our element鈥� theory of the elements was mostly accepted (or not denied) by most chemists.
Building off the work of听Anglo-Irish natural philosopher听Robert Boyle who in the 17th Century defined an element as 鈥渁 substance that cannot be decomposed into any simpler substance,鈥� Lavoisier revived this definition and proved its accuracy through extensive and rigorous experimentation.
Lavoisier was concerned with improving the lives of the public, and the origin of his discoveries about elements began with a project in听1768 to improve the supply of good drinking water in French cities. At the time, there was no effective method for measuring the quality of water chemically, so he had to rely on measuring the density, a physical measure. Since听the most widely accepted theories of the time said that when water was heated some of it turned into 鈥渆arth鈥�, measuring its density would clearly be confusing and the results questionable.
To better understand the process, he created an experiment to learn more. By heating an amount of distilled water in a sealed container over 100 days, he found that the weight of the container had not changed. Even more interestingly, he found particles of 鈥渆arth鈥� floating in the water and that the weight of this 鈥渆arth鈥� matched the decline in weight of the container after it was emptied, meaning that it must have come from erosive actions of the water on the container, and not through the conversion of water into earth.
This was a huge discovery which ultimately would overturn the dominant thinking of two centuries of chemistry.
Later, in experiments with phosphorus and sulphur he found that the substances absorbed air on burning, and increased in weight. He wrote and left a sealed note to the Secretary of the Academy on 1 November 1772 proposing that this effect might occur in all substances. Further extensive experiments showed that 鈥渆lastic fluids鈥� 鈥� what we would now call gas 鈥� absorbed different amounts when burned with different types of air. When powdered metals, or calcinates, were burned in听an enclosed space they absorbed different proportions of the weight of the air in the containers, ultimately suggesting that air, once considered an element, was in fact a mixture or a compound.
During the winter of 1782-83 he collaborated with his friend and mathematician Pierre-Simon de Lapace and published a paper in the Academy attacking phlogiston theory as 鈥渋maginary鈥�, saying that it did not exist within metals or any other substance, and that the process of combustion and calcination of metals was听easier to explain without it.
Later, Lavoisier learned about experiments by English scientist Henry Cavendish, who had obtained water from the burning of 鈥渋nflammable air鈥� (hydrogen). Lavoisier replicated this and explained that water must not be an element, but instead was comprised of a compound of hydrogen and 鈥渄ephlogisticated air鈥� (oxygen).
His greatest and lasting achievement was to impose order on the language and symbolism that have shaped the thoughts of chemists. The 罢谤补颈迟茅 was intended as a beginner鈥檚 guide to chemistry, and included a table that recognised 55 elements with the old and new names. Metals were now shown to be compounds of metals with oxygen, hence 鈥淰itriol of Venus鈥� became 鈥渃opper sulphate鈥�.
When the French Revolution began in 1789, Lavoisier was working on the process of respiration and transpiration 鈥� his earlier work suggested that these processes were a form of combustion and that the heat an animal gives out is due to the conversion of inhaled oxygen into 鈥渇ixed air鈥� or carbon dioxide. After the Academy was suppressed in 1793 by the Revolutionary Committee, he was arrested, convicted and executed without trial on听8 May 1794. As Douglas McKie wrote in the introduction to the 1960s edition of the 罢谤补颈迟茅, 鈥渢hus perished the most illustrious victim of the Revolution.鈥澨�Conrad Quilty-Harper
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