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Joseph Louis Proust
French chemist
Born	September 26, 1754 Angers, France
Died	July 5, 1826 Paris,France

Joseph Louis Proust (September 26, 1754 - July 5, 1826) was a French chemist.

Joseph Louis Proust was born on September 26, 1754 in Angers, France. His father served as an apothecary in Angers . Joseph studied chemistry in his father’s shop and later came to Paris where he gained the appointment of apothecary in chief to the Salpetriere [1]. He also taught chemistry along with Pilâtre de Rozier, a famous aeronaut. In 1784, both went on a balloon ascent together.

Under Carlos IV's influence Proust went to Spain. There he taught at the Chemistry School in Segovia and at the University of Salamanca. He was appointed to the Royal Laboratory in Madrid by Carlos IV, however in 1808 Calros IV fell from power and Proust was forced to return to France [2].

Proust's best known work was derived from a controversy with chemist C.L. Berthollet. Berthollet did not believe that substances always combine in constant and definite proportions as Proust did. Proust eventually was able to prove Berthollet wrong in 1799 and published his own hypothesis.

Proust spent a significant part of his career studying sugars in fruits and vegetables. He published his findings in many papers and scientific periodicals including Indagaciones sobre ci estaada dc cobre, la vajilla de estao y el vidriado (1803); Memoire sur le sucre de raisins (1808); Recueil des moines relatifs de la poudre h Canon (1815); and Essai sur une des causes gui peuvent amener la formation du calcul (1824) [3]. In 1816, he was elected to the French Academy of Sciences (Encarta 2005). Proust passed away on July 5, 1826.

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 Fe_0.95O.

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.

• Joseph Louis Proust (1754 - 1826)
  
• Encyclopedia article on him

Persondata
NAME	Proust, Joseph Louis
ALTERNATIVE NAMES
SHORT DESCRIPTION	French chemist
DATE OF BIRTH	September 26, 1754
PLACE OF BIRTH	Angers, France
DATE OF DEATH	July 5, 1826
PLACE OF DEATH	Paris,France