The Jones Laboratory was built in 1928-1929 as facility and instructional space for the university's staff of research chemists and graduate students in chemistry. As part of the U.S. War Department's Manhattan Project, University of Chicago chemists began to study the newly manufactured radioactive element, plutonium. Room 405 was the site where, for the first time, a trace quantity of this new element was isolated and measured on September 10, 1942. This procedure enabled chemists to determine the new element's atomic weight. * National Historic Landmark Dedication Plaque