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Life
Joseph Louis Proust was born on 26 September 1754 in Angers, France. In Angers his father served as an apothecary. Joseph studied chemistry in his father’s shop and later came to Paris where he gained the appointment of apothecary in chief to the Salpetrire *. He also taught chemistry along with J. F. Pilfltre de Rozier, a famous aeronaut. In 1784, both went on a balloon ascent together.
After this, Proust went to Spain, because of the influence of Carlos IV, in order to teach at Chemistry School in Segovia and at the University of Salamanca. Carlos IV then appointed him to the Royal Laboratory in Madrid. But this was short-lived because in 1808 Proust was forced back to his home country due to the fall of Carlos IV *.
The best-known events in Proust’s life dealt with the controversy he had with chemist C.L. Berthollet. Berthollet strove to prove that substances do not always combine in constant and definite proportions. Proust wanted to prove Berthollet wrong. He studied many different metal-combined molecules and eventually proved his point in 1799.
Joseph Proust also took much of his time to study various sugars that are present in sweet vegetables and fruits. He published many papers in scientific periodicals and also published Indagaciones sobre ci estaada dc cobre, la vajilla de estao y el vidriado (1803); Mimoire sur Ic sucre de raisins (1808); Recueii des mmoires relatifs d la poudre h Canon (1815); and Essai sur une des causes gui peuvent amener la formation du calcul (1824) *. In 1816, he was elected to the French Academy of Sciences (Encarta 2005). Joseph Louis Proust passed away on July 5th, 1826.
Chemistry Studies
Proust’s largest improvement into the realm of science was disproving Berthollet with the law of definite proportions, which is sometimes also known as Proust’s Law (Encarta 2005). Proust studied copper carbonate, the two tin oxides, and the two iron sulfides to prove this law. He did this by making artificial copper carbonate and comparing it to natural copper carbonate. With this he showed that each had the same proportion of weights between the three elements involved (Cu, C, O). Between the two types of the other compounds, Proust showed that no intermediate indeterminate compounds exist between them. Proust published this paper in 1794, but the law was not accepted until 1811, when the Swedish chemist Jöns Jacob Berzelius gave him credit for it (Encarta 2005).
Proust then went on to show how Berthollet was incorrect in his own chemical analyses by showing that Berthollet treated some of the chemicals he used as oxides, when they were actually hydrates containing chemically-bonded water. This invalidated Berthollet’s research completely.
There are, however, exceptions to the Law of Definite Proportions. An entire class of substances does not follow this rule. The compounds are called non-stoichiometric compounds or Barthollides, after Berthollet. The ratio of the elements present in the compound can fluctuate within certain limits, such as in the example of Ferrous oxide. The ideal formula is FeO, but due to crystallographic vacancies it is reduced to about Fe0.95O.
Proust was also interested in studying the sugars that are present in sweet vegetables and fruits. In 1799, Proust demonstrated, to his class in Madrid, how the sugar in grapes is identical to that found in honey. This later became known as glucose. Overall, Proust discovered three types of sugar during his studies.
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1754 births | 1826 deaths | French chemists
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"Joseph Proust"