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 scientist trained in the study of chemistry. Chemists study the composition of matter and its properties. Chemists carefully describe th ...

. 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 law of constant composition states that a given chemical compound always contains its component elements in fixed ratio (by mass) and does not depend on its source an ...

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 prov ...

France France (), officially the French Republic ( ), is a country primarily located in Western Europe. It also comprises of Overseas France, overseas regions and territories in the Americas and the Atlantic Ocean, Atlantic, Pacific Ocean, Pac ...

. 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 , house = Bourbon-Anjou , father = Charles III of Spain , mother =Maria Amalia of Saxony , birth_date =11 November 1748 , birth_place =Palace of Portici, Portici, Naples , death_date = , death_place ...

'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") , i ...

. 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 of th ...

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 th ...

. 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 whi ...

(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 Copper carbonate may refer to : ;Copper (II) compounds and minerals * Copper(II) carbonate proper, (neutral copper carbonate): a rarely seen moisture-sensitive compound. * Basic copper carbonate (the "copper carbonate" of commerce), actually a cop ...

, 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 on ...

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 In chemistry, 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); m ...

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 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 w ...

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), and ...

, 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