How Bunsen and Kirchhoff’s Pioneering Spectroscopy Transformed Science

A few weeks ago, I was fortunate enough to visit the picturesque town of Heidelberg, home to the oldest university in Germany and a very special part of scientific history. I was inspired to write about the revolutionary collaboration that happened within a laboratory on the university grounds. To specify,  it was the laboratory of Robert Busen, famed inventor of the Bunsen Burner that frequents student labs, and Gustav Kirchhoff, a renowned physicist that has his name marked down in electric circuit work, radiation and the discovery of new elements. Seeing the plaque on the stone walls amidst the busy street inspired me to dig deeper into their collaboration, the technology created and how it changed our world.

Robert Bunsen was born on March 30, 1811 in Göttingen, Germany. His father was a professor of modern languages at Göttingen University and Bunsen himself would later receive his doctorate in 1830 from the university as well at the mere age of 19. He received a travelling scholarship to visit various laboratories in Europe, including Gay-Lussac’s and after his tenure abroad, Bunsen returned back to Göttingen to work as a lecturer at the university. In 1834, after collaboration with a physician, he discovered an antidote to arsenic poisoning and pioneered safety protocols when working with the element. It involved adding iron oxide hydrate to a solution, where the arsenic compounds would react to produce a harmless ferrous arsenate while also wearing a mask that connected to a source of fresh air.However, one day in 1843 the arsenic compound(cacodyl cyanide) Bunsen was working with suddenly reacted, shattering his mask and blinding him in one eye. Luckily, his antidote from nearly ten years ago saved him.

Gustav Kirchhoff was a physicist born on March 12 1824 in Königsberg, he excelled academically in school hence his parents suggested a career at a university. It was during his years of higher education, Kirchhoff developed his understanding of electrical circuits after being influenced by Franz Neumann, who researched electrical induction and mathematical physics. This laid the foundation to Kirchoff’s two laws on electrical currents that are still used by students around the world today.

In 1852, Bunsen met and collaborated with Kirchhoff at the University of Breslau. Two years later, Bunsen received a position at the University of Heidelberg and used his influence to have Kirchhoff appointed in the physics department so they could continue to collaborate. 

The main project at hand was spectroscopy, which studied different material’s absorption and emission of electromagnetic waves. Using their self-built spectroscope made with a Bunsen Burner, telescopes and a prism. They subjected metals to flame tests and using the light produced, they concentrated it through a narrow slit and then through a prism. It showed lines of colour, instead of the full spectrum, leading to the use of the term ‘spectral lines’. Each combination of lines is unique to each element (like a fingerprint for every individual) because materials absorb and emit wavelengths differently, scientists used this to identify elements. 

Through this, they discovered caesium in 1860 through processing mineral water. Caesium’s name originates from the Latin word ‘caesius’ meaning sky blue, which refers to the blue colour spectral lines seen through the spectroscope by the pair. In 1861, they were able to discover rubidium using the flame of the mineral lepidolite, the spectral lines produced were dark red, hence they derived the Latin name ‘rubidus’, meaning deep red. With the new technology, various other metals were discovered such as Indium, Gallium and Europium, filling up the periodic table. 

Kirchhoff took the research further and compared the pattern of lines when burning sodium and with the spectral lines of the Sun. The light from the sun was analysed by Fraunhofer before, he discovered dark strips on the ‘rainbow’ using a spectroscope to analyse sun rays. These lines were due to the absorption and emission of radiation by elements in the sun existing as gases in an environment primarily made out of plasma. These cooler spots on the sun absorb more radiation than they emit leaving shadows on the spectrum. Kirchhoff used the various other patterns or ‘fingerprints of different elements’ and compared them with the Fraunhofer lines to determine the composition of the sun. The lines which coincided with Fraunhofer lines, meant that the element was in the sun.

This inspired Kirchhoff to formulate theories about radiation, particularly the spectrum of light emitted by black bodies. According to Quantum Physics for Dummies, it is a material that radiates corresponding to its temperature. Most black objects we have in our daily life absorb and reflect light, hence physics hypotheses that a black body is material that reflects no light but absorbs all the light falling on it. This would allow the object to appear perfectly black since all the light would be absorbed. If all energy was absorbed, the black body would have infinite energy but experimental evidence disagreed, leaving physicists with a problem called the ‘ultraviolet paradox’. Max Planck suggested that instead of a black body taking on any level of energy like in classical physics allowed, it could only take on specific discrete values of energies. This revelation led to the birth of quantum physics.

In modern times, spectroscopy, particularly infrared spectroscopy, is still used to analyse chemical compounds. Other forms of it include mass spectroscopy that looks at relative abundances of elements to find molecular weight. In forensics, UV based spectroscopy is common for analysing evidence unseen to the naked eye such as bodily fluids, fingerprints and bite marks. The technology reveals chemical makeup of blood, intoxicants in the body and even cortisol levels, important for crime scene investigators to get the information they need. This also works hand in hand with law enforcement to test seized drugs and possible linkages to other crimes.

In the pharmaceutical and food industry, there are stringent examinations on quality and composition of products. Scientists use spectroscopy which allows the quality to be monitored over the entire production process, offers instantaneous results as well as simultaneous  tests for the different compounds, faster and more efficiently than traditional separation methods.

The fruitful collaboration between Bunsen and Kirchhoff has continued to influence and change our world today. The spectroscope pioneered by them opened many scientific doors for the potential of discovery and paved the way for new fields to emerge. If you’re ever in Heidelberg, feel free to see the plaques that commemorate their work at the Haus zum Reise, near the Anatomiegarten. 

References

Black-body Radiation. (n.d.). Las Cumbres Observatory. Retrieved July 8, 2024, from https://lco.global/spacebook/light/black-body-radiation/

Boissoneault, L. (2018, August 17). How Scientists Discovered Helium, the First Alien Element, 150 Years Ago. Smithsonian Magazine. Retrieved July 10, 2024, from https://www.smithsonianmag.com/history/how-scientists-discovered-helium-first-alien-element-1868-180970057/

Cesium | Cs (Element). (n.d.). PubChem. Retrieved July 9, 2024, from https://pubchem.ncbi.nlm.nih.gov/element/Cesium#section=History

Gustav Kirchhoff (1824–1887) | High Altitude Observatory. (n.d.). High Altitude Observatory. Retrieved July 9, 2024, from https://www2.hao.ucar.edu/education/scientists/gustav-kirchhoff-1824-1887

Gustav Kirchhoff – a physicist who liked staring at the Sun. (2024, March 12). TME.eu. Retrieved July 9, 2024, from https://www.tme.eu/en/news/library-articles/page/57776/gustav-kirchhoff-a-physicist-who-liked-staring-at-the-sun/

Gustav Kirchhoff - Biography, Facts and Pictures. (n.d.). Famous Scientists. Retrieved July 8, 2024, from https://www.famousscientists.org/gustav-kirchoff/

Holzner, S. (2016, March 26). How Quantum Physicists Describe a Black Body - dummies. Dummies.com. Retrieved July 9, 2024, from https://www.dummies.com/article/academics-the-arts/science/quantum-physics/how-quantum-physicists-describe-a-black-body-161524/

Kirchhoff — Beautiful Chemistry. (n.d.). Beautiful Chemistry. Retrieved July 9, 2024, from https://www.beautifulchemistry.net/kichhoff

May 10, 1860: Discovery of Cesium. (n.d.). American Physical Society. Retrieved July 9, 2024, from https://www.aps.org/archives/publications/apsnews/201805/history.cfm

O'Connor, J., & Robertson, E. (n.d.). Gustav Kirchhoff (1824 - 1887) - Biography - MacTutor History of Mathematics. MacTutor History of Mathematics. Retrieved July 8, 2024, from https://mathshistory.st-andrews.ac.uk/Biographies/Kirchhoff/

Robert Bunsen and Gustav Kirchhoff. (n.d.). Science History Institute. Retrieved July 10, 2024, from https://www.sciencehistory.org/education/scientific-biographies/robert-bunsen-and-gustav-kirchhoff/

Robert Bunsen - Biography, Facts and Pictures. (2014, September 23). Famous Scientists. Retrieved July 9, 2024, from https://www.famousscientists.org/robert-bunsen/

Sella, A., Kidd, H., Pewsey, E., Hoda, G., Brazil, R., Seifert, V., Newton, J., McGlone, T., Robinson, P., Lowe, D., & Ball, P. (2013, September 2). Kirchhoff's spectroscope | Opinion. Chemistry World. Retrieved July 10, 2024, from https://www.chemistryworld.com/opinion/kirchhoffs-spectroscope/6547.article

Spectroscopy 101 – How Absorption and Emission Spectra Work. (2022, July 7). Webb Space Telescope. Retrieved July 9, 2024, from https://webbtelescope.org/contents/articles/spectroscopy-101--how-absorption-and-emission-spectra-work

Spectroscopy 101 – Introduction | Webb. (2022, July 7). Webb Space Telescope. Retrieved July 9, 2024, from https://webbtelescope.org/contents/articles/spectroscopy-101--introduction

Spectroscopy 101 – Types of Spectra and Spectroscopy | Webb. (2022, July 7). Webb Space Telescope. Retrieved July 9, 2024, from https://webbtelescope.org/contents/articles/spectroscopy-101--types-of-spectra-and-spectroscopy

Spectroscopy Applications in Industry and Research. (n.d.). Bionity. Retrieved July 10, 2024, from https://www.bionity.com/en/topics/spectroscopy/5/19/spectroscopy-applications-in-industry-and-research.html

Spectroscopy Matters. (n.d.). HORIBA. Retrieved July 10, 2024, from https://www.horiba.com/int/scientific/resources/spectroscopy-matters/