Wednesday, 31 July 2013

Battle of the Sciences: Chemistry

First in a series of articles in which writers debate which scientific discipline was responsible for the most important scientific discovery. Daniel Rollins argues for Chemistry

Antoine Lavoisier (1743 –1794) was a French aristocrat who has been called the “father of modern chemistry”. As well as helping develop the metric system naming both hydrogen and oxygen and first identifying sulphur as an element, he is responsible for many of Chemistry’s basic theories. He proved, for example, that oxygen combined with other elements upon combustion disproving earlier theories about burning. His most significant contribution, however, was his careful quantitative method of experimentation, the weighing out and measuring of chemicals with accurate balances using sealed glass containers to prevent gases escaping. It was through this method that he discovered one of chemistry’s most fundamental laws: the Law of Conservation of Mass.

In his book, Elements of Chemistry (1785), Lavoisier wrote:
"Nothing is created, either in the operations of art or in those of nature, and it may be considered as a general principle that in every operation there exists an equal quantity of matter before and after the operation; that the quality and quantity of the constituents is the same, and that what happens is only changes, modifications. It is on this principle that is founded all the art of performing chemical experiments; in all such must be assumed a true equality or equation between constituents of the substances examined, and those resulting from their analysis."

He proved this by burning several compounds and elements in sealed containers and discovering that the total weight of the container did not change from before the substance was burned to after it had been burnt. In one of his experiments, he burnt sulphur in a sealed container and found that, while the total content of the container kept the same mass, the piece of sulphur he had burnt had increased in mass, showing that that sulphur was reacting with a gas in the air later identified as oxygen. He repeated this experiment with phosphorous and other elements such as tin and lead and found the same result. He also decomposed lead calx (lead oxide) and mercury clax (mercury oxide) and, while the compounds seemed to lose mass as they were burnt, the total mass of the container still remained constant, suggesting that the compounds decomposed and gave off a gas: oxygen.

In yet another experiment Lavoisier proved this was not only true in inorganic reactions but in natural biological processes as well. He placed fruit into one of his sealed glass containers and left it in a warm place for several days to decompose into a putrid pile of rotten matter. After this, he observed that, while the colour, shape and texture of the fruit had changed and water had condensed onto the sides of the glass, the total mass of the container remained unchanged, yet again proving that in any chemical reaction, while the state and combination of elements change, the mass of the matter does not.

Lavoisier, unfortunately, came to an untimely and gruesome end; during the French Revolution, because of his membership of the Ferme Générale, an unpopular group of tax collectors and because of his protection of foreign scientists, he was branded a traitor and executed. He was later exonerated by the French government; the Italian scientist, Lagrange, said of Lavoisier’s death, “It took them only an instant to cut off his head, but France may not produce another such head in a century.” His contribution to Chemistry, although cut short, has remained significant to this day, as he made many of the discoveries that we take for granted now, including the existence of oxygen and hydrogen, the fact that the diamond is a form of carbon and that burning and rusting are reactions with oxygen. His Law of the Conservation of Mass and his methodology, however, are probably his most significant contributions to Chemistry. The entire field of Stoichiometry, in which the relative quantities of reactants and products are predicted and measured, is based almost entirely upon these principles.

The use of closed containers also revolutionised chemistry, moving it from its vague alchemistic past into the modern age. While it may seem obvious now that lost gases affect the results of experiments, it was Lavoisier who insisted on keeping his experiments in “closed systems”, a concept that has now been applied to many areas of Chemistry and even Physics, ensuring that any changes in a reaction are able to be measured accurately and to be reliably understood. 

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