A sepia-toned photograph depicting Theodor Curtius (1857-1928) examining a test tube in a chemistry lab. Throughout his career, Curtius was a professor of chemistry at the University of Heidelberg, the director of the analytical chemistry department at the University of Erlangen, and a chair of chemistry at the University of Kiel. He defined the Curtius rearrangement in 1890 and discovered diazoacetic acid, hydrazine, and hydrazoic acid later in his career.