Joseph Louis Proust (1754-1826)

French chemist who was born in Angers, France, in September 26th 1754, and died in 1826. Became known by his research work on the steadiness of composition of chemical compounds.

He studied Chemistry with his father who was a pharmaceutic. In Paris was chief- pharmaceutic in Salpetrière by the time he became interested in ascension balloons. After that he went to Spain to teach at the Chemistry School in Segovia and at the University of Salamanca. By influence of Carlos IV was appointed to the Royal Laboratory, in Madrid. However, the fall of Carlos IV, in 1808, forced him to return to France.

Proust played a major role as chemical annalist, establishing the steadiness of the composition of chemical compounds. For this contributed the prestige of Berthellot, who admitted that the composition of different substances depended on the concentration of reagents used in the reactions. 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.