Louis Plack Hammett was an American physical chemist. He was born on April 7, 1894 in United States of America. He is known for the Hammett equation, which relates reaction rates to equilibrium constants for certain classes of organic reactions involving substituted aromatic compounds. He is also known for his research into superacids and his development of a scheme for comparing their acidities based on what is now known as the Hammett acidity function. He received the National Medal of Science from President Johnson and a number of other significant honors, including the Chandler Medal, the James Flack Norris Award (twice), the Willard Gibbs Medal, and the Lewis Medal. He was elected an honorary member of the Chemical Society (British) and in 1962 received an honorary degree from Columbia. He died on February 9, 1987 in New Jersey, United States.