Studies on Oxidation Reduction IX: A Potentiometric and Spectrophotometric Study of Meriquinones on the 9-Phenylene Diamine and the Benzidine Series. By W. Mansfield Clark, Chief of the Division of Chemistry, Barnett Cohen, Chemist and H. D. Gibbs, Senior Chemist, Hygienic Laboratory, U. S. Public Health Service, Treasury Department. Being Supplement to Number 54 of the Public Health Reports