Johannes Nicolaus Broensted (1879-1947), the Danish physical chemist. Broensted qualified in chemical engineering in 1897, and then in chemistry in 1902 in Copenhagen. He taught there from 1905. He worked mainly in electro-chemistry and reaction kinetics, applying thermodynamics to chemical problems. He is best known for a definition of acids and bases, due to him (and independently and concurrently in 1923 to T.M. Lowry of Cambridge). This, the Broensted-Lowry definition, defines an acid as a substance with a tendency to lose a proton, and a base as a substance that tends to gain a proton.