Seeing the Light

Abstract This chapter shows how Roscoe’s stay in Heidelberg, Germany, between 1853 and 1856 had a profound effect on his subsequent career. Drawn to Heidelberg in the small liberal German state of Baden by the allure of working with Robert Bunsen, Roscoe quickly established a good working relationship with the great chemist. He helped Bunsen to develop the Bunsen burner and translated his treatise on gasometry. Having taken his PhD, Roscoe was instructed by Bunsen to explore the new field of photochemistry. Roscoe worked on the photochemical reaction between chlorine and hydrogen, and quickly established the Bunsen-Roscoe Law. The chlorine-hydrogen actinometer was used to discover which part of the spectrum was most chemically active and to investigate the nature of sunlight. This work laid the basis for Bunsen and Kirchhoff’s development of spectroscopy, which Roscoe publicized. Bunsen and Roscoe maintained their relationship through correspondence until Bunsen’s death in 1899.