On 05 July 1826, Joseph-Louis Proust (1754–1826) passed away in Angers, France.
From the Encyclopædia Britannica (2016):
“The essence of Proust’s law is that chemical substances only truly combine to form a small number of compounds, each of which is characterized by components that combine in fixed proportions by weight… Although the statements of the law that attracted the attention of European chemists first appeared in French journals starting in 1797, Proust had formulated the law by 1793 and published it by 1795 in Spanish journals. Proust’s law of definite proportion had precursors in 18th-century chemistry and a parallel in 18th-century French mineralogy. Contemporary with Proust’s formulation was the doctrine of fixed mineral species in French mineralogy, which was defined in terms of fixed crystal form and constant chemical composition.
“What eventually settled the dispute in Proust’s favour was the impact of the chemical atomic theory (1801) of the English chemist John Dalton (1766–1844). Dalton’s atomic theory provided a simple theoretical underpinning for the law of definite proportions, especially after the Swedish chemist Jöns Jacob Berzelius established the conceptual relationship between Proust’s law and Dalton’s theory in 1811.”
Quote from Joseph Proust (Annales of Chimie, Vol.32, 1799, p.26): “We must recognize an invisible hand which holds the balance in the formation of compounds. A compound is a substance to which Nature assigns fixed ratios, it is, in short, a being which Nature never creates other than balance in hand, pondere et mensura.”
Referenced: — Mauskopf, Seymour H. “Joseph-Louis Proust.” Encyclopædia Britannica, 2016. — “Law of multiple proportions.” Wikipedia.— “Law of reciprocal proportions.” Wikipedia. —Gaither, Carl C. Gaither’s Dictionary of Scientific Quotations. (New York, NY: Springer, 2012), 276. Image: © Grupo Editorial Raf.