May 8, 1794 - Death of Antoine Lavoisier, considered the father of modern chemistry

Antoine-Laurent de Lavoisier, better known as Antoine Lavoisier after the French Revolution, became a lawyer. However, as he was passionate about science, he attended formal courses in botany, zoology, physics, chemistry, geology, and mineralogy.

In 1765, at the age of twenty-one, he presented a project for lighting Paris, which won him the gold medal for the best study awarded by the King. In the same year, Lavoisier wrote two reports on gypsum, a mineral used in Paris to whitewash houses, and observed that the only difference between crystallised gypsum and powdered gypsum was the water of hydration and that they could be transformed into each other by simply gaining or losing water. The quantitative method used for this work would be the one he would adopt throughout his life.

In 1771, he married Marie-Anne Pierrete Paulze and her dowry enabled him to set up an equipped laboratory where he was assisted by his wife. All the illustrations in his memoirs, transcriptions of writings, and notes are due to her.

In 1777 he published ‘Memoir on Combustion’ and, in 1778, ‘General Considerations on the Nature of Acids, in which Lavoisier developed a nomenclature of technicalities for the new science, thus leaving behind the superstitious, erratic, and insecure medieval alchemy.

Lavoisier's research included some of the first chemical experiments that made him the ‘father of modern chemistry’ as he was one of the main protagonists of the scientific revolution that led to the consolidation of chemistry as a modern science.

Among his scientific achievements are:

• Law of Conservation of Mass or Lomononsov-Lavoisier Law. He carefully weighed the reactants and products of a chemical reaction in a sealed glass vessel, a crucial method in the advancement of chemistry, and demonstrated that the amount of mass of the reactants reacting is the same as the product of the reaction, i.e. mass is conserved.
• Investigations about the composition of water. He discovered two components which he named oxygen and hydrogen.
• Examining the nature of combustion. Lavoisier showed, by constant use of the balance in his experiments, that all combustion in air results from a combination with a part of it.
• Studies on the oxidation of bodies. He calcined tin in a closed vessel and found that the total weight of the vessel had not changed with calcination, that the metal, transformed into its ‘lime’ (the ‘oxide’) had increased in weight, that the weight of the air contained in the vessel had decreased, and that the increase in weight of the metal was equal to the decrease in the weight of the air.
• The air analysis. He repeated the tin experiment with other simple metals and, in 1777, with mercury, which led him to the analysis of air, whose composition he fixed at 27% of breathable air, which he later called oxygen, and 73% of non-breathable air, which he later called azoe (nitrogen). The actual composition of the air is 21% oxygen and 79% nitrogen, so he was not far off the mark in his measurements.
• The phenomenon of animal respiration. Lavoisier revealed the role of oxygen in the respiration of animals and plants as a similar process of reactions with oxygen, but on a smaller or larger scale and with a longer or shorter duration: he thus distinguished between the phenomena of oxidation, respiration, combustion, deflagration, and explosion.
• Studies on photosynthesis. In 1783, he carried out studies on plant processes related to gas exchanges when animals breathe.
• The caloric theory. Working with the mathematician Pierre Simon Laplace, Lavoisier enclosed a guinea pig for 10 hours in a glass bell containing oxygen and measured the carbon dioxide produced. He also measured the amount of oxygen consumed by a man in activity and at rest. With these experiments, he was able to show that the combustion of carbon compounds with oxygen is the real source of animal heat and that oxygen consumption increases during physical work.

Although the works of such notable experimentalists as Carl Wilhelm Scheele, Joseph Priestley, and Henry Cavendish led to numerous discoveries, their interpretations through the phlogiston theory impeded progress in knowledge and it was only Lavoisier, with his Elementary Treatise on Chemistry (1789), who definitively refuted such a theory and laid the foundations of modern chemistry.

In his publication he clarified the concept of the chemical element as a pure and simple substance that cannot be divided by any known method of chemical analysis (i.e. decomposition of the elements) and, aided by his balance, he developed the theory of the formation of chemical compounds from combinations of these simple elements, of which he described some fifty that were already known and demonstrated that a pure body did not change its properties by repeatedly distilling the same water.

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