In 1833, Bunsen became a lecturer at Göttingen and began experimental studies of the (in)solubility of metal salts of
arsenous acid. His discovery of the use of
iron oxide hydrate as a
precipitating agent led to what is still today the most effective
antidote against
arsenic poisoning. This interdisciplinary research was carried on and published in conjunction with the physician Arnold Adolph Berthold. In 1836, Bunsen succeeded
Friedrich Wöhler at the
Polytechnic School of Kassel (). Bunsen taught there for three years, and then accepted an associate professorship at the
University of Marburg, where he continued his studies on
cacodyl derivatives. He was promoted to full professorship in 1841. While at University of Marburg, Bunsen participated in the 1846 expedition for the investigation of Iceland's volcanoes. Bunsen's work brought him quick and wide acclaim, partly because cacodyl, which is extremely toxic and undergoes spontaneous combustion in dry air, is so difficult to work with. Bunsen almost died from
arsenic poisoning, and an explosion with cacodyl cost him sight in his right eye. His work with
Cadet's fuming liquid was an important step in the development of the
radical theory of
organic compounds. In 1841, Bunsen created the
Bunsen cell battery, using a
carbon electrode instead of the expensive platinum electrode used in
William Robert Grove's electrochemical cell. Early in 1851 he accepted a professorship at the
University of Breslau, where he taught for three semesters. (left) and Robert Bunsen (right)|alt=Black-and-white image of two middle-aged men, either one leaning with one elbow on a wooden column in the middle. Both wear long jackets, and the shorter man on the left has a beard. In late 1852, Bunsen became the successor of
Leopold Gmelin at the
University of Heidelberg. There he used
electrolysis to produce pure
metals, such as
chromium,
magnesium,
aluminium,
manganese,
sodium,
barium,
calcium, and
lithium. A long collaboration with
Henry Enfield Roscoe began in 1852, in which they studied the photochemical formation of
hydrogen chloride (HCl) from
hydrogen and
chlorine. From this work, the
reciprocity law of Bunsen and Roscoe originated. He discontinued his work with Roscoe in 1859 and joined
Gustav Kirchhoff to study emission spectra of heated elements, a research area called
spectrum analysis. For this work, Bunsen and his laboratory assistant,
Peter Desaga, had perfected a special gas burner by 1855, which was influenced by earlier models. The newer design of Bunsen and Desaga, which provided a very hot and clean flame, is now called simply the "
Bunsen burner", a common item of laboratory equipment. There had been earlier studies of the characteristic colors of heated elements, but nothing systematic. In the summer of 1859, Kirchhoff suggested to Bunsen that he should try to form prismatic spectra of these colors. By October of that year, the two scientists had invented an appropriate instrument, a prototype spectroscope, an improvement of
Joseph von Fraunhofer's 1814 spectroscope. Using it, they were able to identify the characteristic spectra of
sodium,
lithium, and
potassium. After numerous laborious purifications, Bunsen proved that highly pure samples gave unique spectra. In the course of this work, Bunsen detected previously unknown new blue spectral emission lines in samples of mineral water from
Dürkheim. He guessed that these lines indicated the existence of an undiscovered chemical element. After careful distillation of forty tons of this water, in the spring of 1860 he was able to isolate 17 grams of a new element. He named the element "
caesium", after the Latin word for deep blue. The following year he discovered
rubidium, by a similar process. He was elected to Honorary membership of the
Manchester Literary and Philosophical Society on 17 April 1860 In 1860, Bunsen was elected a foreign member of the
Royal Swedish Academy of Sciences. He was elected as a member of the
American Philosophical Society in 1862. In 1877, Robert Bunsen together with
Gustav Robert Kirchhoff were the first recipients of the prestigious
Davy Medal "for their researches and discoveries in spectrum analysis". ==Personality==