A long-time member of the faculty at Johns Hopkins, the biochemist William Mansfield Clark made significant contributions to the understanding of oxidation-reduction potentials of organic systems. This collection of Clark's professional papers includes drafts of manuscripts and correspondence, especially with James B. Conant and Barnett Cohen, relating to Clark's life and research. Of particular note are Clark's Cutter lectures at Harvard in 1930 and his correspondence with Eric G. Ball, when Ball worked in Otto Warburg's lab in Berlin in 1937-1938. Clark's participation in professional organizations is reflected in correspondence with the Society of American Bacteriologists and with the Journal of Biological Chemistry, as well as with colleagues Stanley Benedict and Rudolph Anderson. There is some material relating to Clark's lectures and papers, and there are four student notebooks (physical chemistry, optics, thermodynamics/physics), and twenty-three miscellaneous scientific notebooks, 1941-1953.