Berthollet was engaged in a long-term battle with another French chemist, Joseph Proust, on the validity of the law of definite proportions. While Proust believed that chemical compounds are composed of a fixed ratio of their constituent elements irrespective of the methods of production, Berthollet believed that this ratio can change according to the ratio of the reactants initially taken. Although Proust proved his theory by accurate measurements, his theory was not immediately accepted partially due to Berthollet's authority. His law was finally accepted when Berzelius confirmed it in 1811, but it was found later that Berthollet was not completely wrong because there exists a class of compounds that do not obey the law of definite proportions. These non-stoichiometric compounds are also named "berthollides" in his honor.