Joseph Proust

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

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Life

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.

Under Carlos IV's influence Proust went to Spain. There he taught at the Chemistry School in Segovia and at the University of Salamanca.

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.

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)

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 Berthollides, 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.