1748-1822

French chemist who introduced chlorine into bleaching and established the composition of ammonia, prussic acid, and sulphuretted hydrogen. His masterwork, Essai de Statique Chimique (1803), contains the proposal that chemical reactivity depends on reactant masses (similar to the modern Law of Mass Action). Berthollet also proposed that compound composition can vary, contradicting Joseph Proust's now accepted Law of Constant Proportions according to which pure samples of a compound always contain the same elements in definite proportions.