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

French French (french: français(e), link=no) may refer to: * Something of, from, or related to France ** French language, which originated in France, and its various dialects and accents ** French people, a nation and ethnic group identified with Franc ...

chemist A chemist (from Greek ''chēm(ía)'' alchemy; replacing ''chymist'' from Medieval Latin ''alchemist'') is a scientist trained in the study of chemistry. Chemists study the composition of matter and its properties. Chemists carefully describe ...

. He was best known for his discovery of the law of definite proportions in 1794, stating that chemical compounds always combine in constant proportions.

Life

Joseph L. Proust was born on September 26, 1754, in

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

France France (), officially the French Republic ( ), is a country primarily located in Western Europe. It also comprises of overseas regions and territories in the Americas and the Atlantic, Pacific and Indian Oceans. Its metropolitan ar ...

. 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 , image_flag = Bandera de España.svg , image_coat = Escudo de España (mazonado).svg , national_motto = '' Plus ultra'' ( Latin)(English: "Further Beyond") , national_anthem = (English: "Royal March") , ...

. There he taught at the Chemistry School in

Segovia Segovia ( , , ) is a city in the autonomous community of Castile and León, Spain. It is the capital and most populated municipality of the Province of Segovia. Segovia is in the Inner Plateau ('' Meseta central''), near the northern slopes o ...

and at the

University of Salamanca The University of Salamanca ( es, Universidad de Salamanca) is a Spanish higher education institution, located in the city of Salamanca, in the autonomous community of Castile and León. It was founded in 1218 by King Alfonso IX. It is ...

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

. The mineral

proustite Proustite is a sulfosalt mineral consisting of silver sulfarsenide, Ag3 As S3, known also as light red silver or ruby silver ore, and an important source of the metal. It is closely allied to the corresponding sulfantimonide, pyrargyrite, from w ...

(Ag₃AsS₃) is named in his honour.

Chemistry studies

Proust's largest accomplishment in the realm of science was disproving Berthollet with the law of definite proportions, 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 1794, but the law was not accepted until 1812, when the Swedish chemist

Jöns Jacob Berzelius Baron Jöns Jacob Berzelius (; by himself and his contemporaries named only 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 ...

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 compounds, or Berthollides, after Berthollet. The ratio of the elements present in the compound can fluctuate within certain limits, such as for example ferrous oxide. The ideal formula is FeO, but due to

crystallographic Crystallography is the experimental science of determining the arrangement of atoms in crystalline solids. Crystallography is a fundamental subject in the fields of materials science and solid-state physics (condensed matter physics). The wo ...

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 most populous city of Spain. The city has almost 3.4 million inhabitants and a metropolitan area population of approximately 6.7 million. It is the second-largest city in the European Union (EU), an ...

, how the sugar in

grapes A grape is a fruit, botanically a berry, of the deciduous woody vines of the flowering plant genus ''Vitis''. Grapes are a non- climacteric type of fruit, generally occurring in clusters. The cultivation of grapes began perhaps 8,000 years ago, ...

is identical to that found in

honey Honey is a sweet and viscous substance made by several 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 plants (primar ...

Works

* * * * * * * * * * * * * * * * **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 University of Salamanca faculty French aviation record holders 19th-century French chemists