Claude Louis Berthollet Biography, A Pioneer in Chemistry


Explore the life and contributions of Claude Louis Berthollet, a Savoyard-French chemist known for his advancements in chemical equilibrium theory, modern chemical nomenclature, and the development of chlorine-based bleaching agents.

Claude Louis Berthollet

Claude Louis Berthollet (December 9, 1748 – November 6, 1822) was a Savoyard-French chemist who rose to prominence, becoming the Vice President of the French Senate in 1804. He is renowned for his scientific contributions to the theory of chemical equilibrium through the mechanism of reversible chemical reactions and his contributions to modern chemical nomenclature. Practically, Berthollet was the first to demonstrate the bleaching effect of chlorine gas and develop sodium hypochlorite solution as a modern bleaching agent.


Claude Louis Berthollet was born in Talloires, near Annecy, a part of the Duchy of Savoy, in 1749.

He commenced his education in Chambéry and later graduated in medicine from Turin. Berthollet’s significant advancements in chemistry quickly led him to become an active member of the Academy of Sciences in 1780.


Alongside Antoine Lavoisier and others, he played a crucial role in naming chemical compounds or establishing a nomenclature system, laying the foundation for the naming of modern chemical compounds.

He also conducted research on dyestuffs and bleaching agents, introducing the use of chlorine gas as a commercial bleaching agent in 1785. In 1789, at his laboratory on the outskirts of Paris in Javel, France, he produced a modern bleaching liquid by passing chlorine gas into a solution of sodium carbonate. The resulting liquid, known as “Eau de Javel” (“Javel water”), is a weak solution of sodium hypochlorite. Another potent oxidant and bleaching agent he examined and first produced is potassium chlorate (KClO3), known as Berthollet’s Salt.

Berthollet was among the first chemists to determine the elemental composition of ammonia gas in 1785.

He was one of the first chemists to recognize the characteristics of a reverse reaction, thus contributing to the discovery of chemical equilibrium.

Berthollet engaged in a long-standing dispute with fellow French chemist Joseph Proust over the validity of the law of definite proportions. While Proust believed in the fixed ratio of component elements in chemical compounds independent of the methods of production, Berthollet believed this ratio could vary depending on the initially taken ratios of reactants. Although Proust eventually proved his theory with accurate measurements, it was not immediately accepted due to Berthollet’s authority. Proust’s theory was eventually accepted when confirmed by Berzelius in 1811, though later it was found that there exists a class of compounds that do not adhere to the law of definite proportions, named berthollides in his honor.

Berthollet was one of the few scientists who accompanied Napoleon to Egypt and was a member of the physics and natural history section of the Institut d’Égypte.

Awards and Honors

In April 1789, Berthollet was elected a Fellow of the Royal Society in London. In 1801, he was elected a foreign member of the Royal Swedish Academy of Sciences. In 1809, Berthollet was elected a first-class associate member of the Royal Institute of the Netherlands, which was a precursor to the Royal Netherlands Academy of Arts and Sciences. In 1820, he was elected an Honorary Fellow of the Royal Society of Edinburgh, and in 1822, he was elected a Foreign Honorary Member of the American Academy of Arts and Sciences.


Claude-Louis Berthollet’s work “Méthode de Nomenclature Chimique,” published in 1788 with colleagues such as Antoine Lavoisier, Louis Bernard Guyton de Morveau, and Antoine François, comte de Fourcroy, was honored with the Chemical Breakthrough Award by the American Chemical Society’s Division of the History of Chemistry and was presented at the Paris Academy of Sciences in 2015.

A French high school in Annecy bears his name, “Lycée Claude Louis Berthollet,” in his honor.

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