The French chemist Louis Joseph Proust, 1754-1826. Proust, son of a chemist, was a skilled and prolific analyst. His early investigations concerned the properties of sugar but the main event of his life was the discovery in 1797 of the Law of Costant Proportions, also known as Proust's law. This stated that all compounds contain elements in certain definite proportions regardless of the mass of the elements involved and the conditions of their formation. Proust's law was strongly criticised by the French chemist Berthollet (1748-1822) and they became the protagonists of a famous controversy that lasted eight years.