Clarke's father had been the European representative of US photographic pioneer company Kodak for several years, and was a personal friend of founder George Eastman.
When World War I erupted, Eastman was forced to look for other sources of the chemicals that he had been obtaining from Germany, and he turned to Hans Clarke for assistance.
At Eastman's request, Clarke moved to Rochester, New York in 1914 to assist what he assumed to be the company's considerable chemical engineering department.
[2] His administrative skills and ability to recognize talent contributed to the growth of Columbia's biochemistry department, which by the 1940s had become one of the largest and most influential in the United States.
[3] As the dark events foreshadowing World War II pushed eminent Jewish scientists out of Europe, Clarke opened his laboratory to refugee biochemists, among them E. Brand, Erwin Chargaff, Zacharias Dische, K. Meyer, David Nachmansohn, Rudolph Schoenheimer, and Heinrich Waelsch.
[4] As head of Columbia's Biochemistry Department, Clarke took a personal interest in graduate students, of whom he demanded rigorous qualifications prior to admission.
[5] Clarke's time at Kodak resulted in few publications in the chemical literature, but he aided the preparation of 26 substances to the Organic Syntheses series, and checked some 65 others.
Clarke was named Assistant Director of the Office of Scientific Research and Development in 1944, which placed him in charge of coordinating penicillin production in the United States.