 In 1958 he was further promoted to vice president, director, and member of the Executive Committee.Holbrook served on boards and committees for a number of universities, including the Carnegie Institute of Technology, University of Delaware, University of Michigan, University of Pennsylvania, University of Rochester, and Newark College.He was a member of the American Chemical Society, American Physical Society, Society of Chemical Industry, New York Academy of Sciences, Franklin Institute, American Association for the Advancement of Science, the Chemical Society (London), and honorary member of the Institute of Chemical Engineers (London), and served as president of the American Institute of Chemical Engineers in 1958.