Joseph Louis Proust (26 September 1754 – 5 July 1826) was a French

chemist A chemist (from Greek ''chēm(ía)'' alchemy; replacing ''chymist'' from Medieval Latin ''alchemist'') is a graduated scientist trained in the study of chemistry, or an officially enrolled student in the field. Chemists study the composition of ...

. He was best known for his discovery of the

law of definite proportions In chemistry, the law of definite proportions, sometimes called Proust's law or the law of constant composition, states that a given chemical compound contains its constituent elements in a fixed ratio (by mass) and does not depend on its source ...

in 1797, stating that chemical compounds always combine in constant proportions.

Life

Joseph-Louis Proust was born on 26 September 1754 in

Angers Angers (, , ;) is a city in western France, about southwest of Paris. It is the Prefectures of France, prefecture of the Maine-et-Loire department and was the capital of the province of Duchy of Anjou, Anjou until the French Revolution. The i ...

France France, officially the French Republic, is a country located primarily in Western Europe. Overseas France, Its overseas regions and territories include French Guiana in South America, Saint Pierre and Miquelon in the Atlantic Ocean#North Atlan ...

. His father served as an apothecary in Angers. Joseph studied chemistry in his father's shop and later went to Paris where he gained the appointment of apothecary in chief to the Salpêtrière. He also taught chemistry with Pilâtre de Rozier, a famous aeronaut. Under Carlos IV's influence Proust went to

Spain Spain, or the Kingdom of Spain, is a country in Southern Europe, Southern and Western Europe with territories in North Africa. Featuring the Punta de Tarifa, southernmost point of continental Europe, it is the largest country in Southern Eur ...

. There he taught at the Chemistry School in

Segovia Segovia ( , , ) is a city in the autonomous communities of Spain, autonomous community of Castile and León, Spain. It is the capital and most populated municipality of the Province of Segovia. Segovia is located in the Meseta central, Inner Pl ...

and at the

University of Salamanca The University of Salamanca () is a public university, public research university in Salamanca, Spain. Founded in 1218 by Alfonso IX of León, King Alfonso IX, it is the oldest university in the Hispanic world and the fourth oldest in the ...

. But when Napoleon invaded Spain, they burned Proust's laboratory and forced him back to France. On 5 July 1826 he died in Angers,

. The mineral proustite (Ag₃AsS₃) is named in his honour.

Chemistry studies

Proust's largest accomplishment in the realm of science was disproving Berthollet with the

, which is sometimes also known as Proust's Law. 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 compounds exist between them. Proust published this paper in 1797, but the law was not accepted until 1812, when the Swedish chemist

Jöns Jacob Berzelius Baron Jöns Jacob Berzelius (; 20 August 1779 – 7 August 1848) was a Swedish chemist. Berzelius is considered, along with Robert Boyle, John Dalton, and Antoine Lavoisier, to be one of the founders of modern chemistry. Berzelius became a memb ...

gave him credit for it. 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 compound Non-stoichiometric compounds are chemical compounds, almost always solid inorganic compounds, having elemental composition whose proportions cannot be represented by a ratio of small natural numbers (i.e. an empirical formula); most often, in s ...

s, or Berthollides, after Berthollet. The ratio of the elements present in the compound can fluctuate within certain limits, such as for example

ferrous oxide Iron(II) oxide or ferrous oxide is the inorganic compound with the formula FeO. Its mineral form is known as wüstite. One of several iron oxides, it is a black-colored powder that is sometimes confused with rust, the latter of which consists of ...

. 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 Madrid ( ; ) is the capital and List of largest cities in Spain, most populous municipality of Spain. It has almost 3.5 million inhabitants and a Madrid metropolitan area, metropolitan area population of approximately 7 million. It i ...

, how the sugar in grapes is identical to that found in

honey Honey is a sweet and viscous substance made by several species of bees, the best-known of which are honey bees. Honey is made and stored to nourish bee colonies. Bees produce honey by gathering and then refining the sugary secretions of pl ...

Works

*Joseph Louis Proust (1794 .e., 1797 "Recherches sur le Bleu de Prusse" (https://gallica.bnf.fr/ark:/12148/bpt6k9604748r/f348.image) esearches on Prussian blue ''Journal de Physique, de Chimie, et d'Histoire Naturelle'' 45 334–341. This work was actually published in 1797, as can be seen from the article published in the same issue on page 314. * * * * * * * * * * * * * * * **Translated to German i
''Journal für die Chemie und Physik'' vol. 1 (1806)
p. 249-270 * * * * *

References

External links

{{DEFAULTSORT:Proust, Joseph Louis 1754 births 1826 deaths 18th-century French chemists People from Angers Flight altitude record holders Members of the French Academy of Sciences Academic staff of the University of Salamanca French aviation record holders 19th-century French chemists