CIR Rm.5: Joseph Louis Proust.

PROFILE
Louis Proust (Joseph Louis Proust)

Info

Born on September 26, 1754
Died on July 5, 1826
He was a French Chemist

LIFE

He was born 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. He also taught chemistry with Pilâtre de Rozier, a famous astronaut.
Under Carlos IV's influence Proust went to Spain. There he taught at the Chemistry School in Segovia and at the University of Salamanca. But when Napoleon invaded Spain, they burned Proust's laboratory and forced him back to France. On July 5 1826 he died in Angers, France.
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 based his work on the study of copper carbonate reactions performed in the laboratory.
He analytically studied the two tin oxides and the two iron sulfides, proving that had different compositions and that there were no substances with intermediate composition.
His laboratorial tests showed that the variable composition oxides, studied by Berthellot, were hydrated products. He also performed a series of researches to characterize different types of sugars, present in vegetable products.

Brief History

The 19th century (1801–1900) was a period in history marked by the collapse of the Spanish,Portuguese, Chinese, Holy Roman and Mughal empires. This paved the way for the growing influence of the British Empire, the German Empire and the United States, spurring military conflicts but also advances in science and exploration.
The 19th century was an era of invention and discovery, with significant developments in the fields of mathematics, physics, chemistry, biology, electricity, and metallurgy that lay the groundwork for the technological advances of the 20th century.

What is The Law of Definite Proportions?

The Law of Definite Proportions is a scientific law discovered by Joseph Proust. It states that the composition of chemical compounds is proportionate regardless of the size of the sample. Though the principle has been found to be non-universal in the past 50 years due to increased testing capabilities, it still stands as a basic foundation of chemical composition.

It is also called Proust's Law, states that a chemical compound has a set proportion of elements by volume regardless of the amount of the compound. For example, not matter what amount of water (H2O) you have, there will always be a ratio of 1/9 hydrogen to 8/9 oxygen, whether the sample size is a drop of water or a lake.

Joseph Proust, a French chemist, declared the law of definite proportions in 1806 after studying the principle for almost 10 years. It was a revolutionary concept among the scientific community and was opposed at first by other chemists. The adversaries of Proust's find believed that compounds could combine in any amount. It wasn't until John Dalton unveiled the atomic theory--that all compounds are made up of atoms--that credence was given to Proust's assertions.

Here 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.

Non-stoichiometric compounds

- also called Berthollides, after Berthollet.

- are chemical compounds with an elemental composition that cannot be represented by a ratio of well-defined natural numbers, and therefore violate the law of definite proportions.

At the end of the 18th century, however, when the concept of a chemical compound had not yet been fully developed, the law was novel. In fact, when first proposed, it was a controversial statement and was opposed by other chemists, most notably Proust's fellow Frenchman Claude Louis Berthollet, who argued that the elements could combine in any proportion.The very existence of this debate underscores that at the time, the distinction between pure chemical compounds and mixtures had not yet been fully developed.

The law of definite proportions contributed to, and was placed on a firm theoretical basis by, the atomic theory that John Dalton promoted beginning in 1803, which explained matter as consisting of discrete atoms, that there was one type of atom for each element, and that the compounds were made of combinations of different types of atoms in fixed proportions.

One of the fundamental observations of modern chemistry, the law of definite proportions states that, in a pure compound, the elements combine in definite proportions to each other.

An equivalent statement is the law of constant compostion, which states that all samples of a given chemical compound have the same elemental composition.

For example, oxygen makes up ⁸/₉ of the mass of any sample of pure water, while hydrogen makes up the remaining ¹/₉ of the mass.

Along with the law of multiple proportions, this forms the basis of stoichiometry.

This observation was first made by the French chemist Joseph Proust based on several experiments conducted between 1797 and 1804. In most of these experiments, Proust reacted several of the elements with oxygen and observed that the oxygen content of the product of these reactions was always fixed at one or two values, rather than displaying a broad range of possible values. For example, Proust measured that the product of iron and oxygen might contain 27% oxygen or 48% oxygen, but not an intermediate composition, or that the product of copper and oxygen might contain 18% oxygen or 25% oxygen, but not an intermediate composition.

He is the French chemist who proved that the relative quantities of any given pure chemical compound’s constituent elements remain invariant, regardless of the compound’s source. This is known as Proust’s law, or the law of definite proportions (1793), and it is the fundamental principle of analytical chemistry. Proust also carried out important applied research in metallurgy, explosives, and nutritional chemistry.