Spectral analysis 1859
Robert Bunsen (1811-1899) and Gustav Robert Kirchhoff (1824 - 1887)
Robert Wilhelm Bunsen was born in Göttingen on March 30, 1811 as the youngest of four sons of the professor and librarian Christian Bunsen and his wife Auguste Friederike.
After attending elementary school and grammar school, Robert, who was gifted with an extraordinary gift for observation, began studying chemistry at the University of Göttingen at the age of just 17. The young student with an interest in science also attended lectures in physics and mathematics, mineralogy and geology. Just three years later, Bunsen completed his doctorate with a thesis on hygrometers (air humidity meters). Thanks to a scholarship, he then undertook a one-year educational trip to Austria, Switzerland and France, where he met many important chemists, such as Justus Liebig.
After returning from his study trip, he habilitated at the University of Göttingen in 1834 and began experimental research into the solubility of metal salts of arsenic acid. Together with the physician Adolph Arnold Berthold, he discovered the effectiveness of iron hydroxide as an antidote for arsenic poisoning.
In 1836, Bunsen became a teacher at the Higher Trade School in Kassel, where he researched the organic arsenic compound known as "cacodyl", which was highly flammable in the air due to its disgusting smell. His right eye is injured in an explosion in the laboratory, permanently impairing his eyesight.
In Kassel, Bunsen also studies the thermal efficiency of blast furnaces and realizes that the analysis of the gases produced during smelting provides information about the chemical processes taking place. He discovers that only a small proportion of the calorific value of coal is utilized and is thus able to improve firing technology.
In the fall of 1839, the University of Marburg appoints him Professor of Chemistry. The students enjoy attending his lectures, not only because of his teaching methods, but also because he is friendly towards them.
In order to equip his laboratory with an inexpensive yet powerful power source, Bunsen further developed a simple fuel cell already constructed by Christian Friedrich Schönbein and improved by Sir William Grove by replacing the expensive platinum electrode with a considerably cheaper carbon electrode. This nitric acid-containing zinc-carbon battery, known as the "Bunsen element", supplies an electrical voltage of around 1.9 V and is the most widely used power source until Werner von Siemens discovers the electrodynamic principle.
In 1850, Bunsen was appointed to the University of Breslau, where he met the physicist Gustav Robert Kirchhoff, 13 years his junior.
Born on March 12, 1824, 200 years ago, in Königsberg, then East Prussia, now Kaliningrad, Gustav was the youngest of the three sons of the councillor of justice Carl Friedrich Kirchhoff and his wife Johanna. He attended the Kneiphöfische Gymnasium and studied mathematics and physics at Königsberg University after graduating in 1842. He was particularly interested in the theory of electricity.
After Carl Friedrich Gauss discovered in 1833 during experiments that there are relationships between currents, voltages and resistances in electrical circuits, Kirchhoff was able to formulate the laws of current branching (and voltages) in electrical networks 12 years later as a 21-year-old student and publish them in the Annalen für Physik und Chemie in 1845. Kirchhoff's rules can be used to calculate currents, voltages and resistances in electrical circuits.
In 1848, just one year after completing his doctorate at the Albertus University in Königsberg, Kirchhoff qualified as a professor in Berlin and just two years later, at the age of just 26, was appointed associate professor at the University of Breslau, where he lectured on experimental physics. When Robert Wilhelm Bunsen also came to Wroclaw a short time later, a lifelong friendship began between the two researchers.
But after just three semesters, Bunsen accepted a position at the Ruprecht Karls University in Heidelberg. Here he was not only offered a high salary and a modern chemical laboratory in the new chemical institute in Akademiestrasse, but also an official residence just around the corner. Two years later, Kirchhoff also moved to Heidelberg when he was offered a professorship in physics on Bunsen's recommendation.
In the following years, Kirchhoff and Bunsen conducted research together and wrote many scientific papers. Bunsen's research into exact gas analysis, which he had already begun twenty years earlier in Kassel, was of great importance. He continued this research in Heidelberg and published it in 1857 in his book "Gasometric Methods". In it he describes, among other things, methods for determining the constituents of gases. Based on the gas analysis he developed, volcanic eruptions can still be predicted today.
In their free time, the two friends went on walks together and went to the theater. While Bunsen remained single for the rest of his life, Kirchhoff married Clara Richelot, the daughter of his former Königsberg professor Friedrich Julius Richelot, with whom he had five children, in August 1857.
A colorful fireworks display at Heidelberg Castle is said to have inspired Bunsen to analyze the chemical composition of the salts that produce different luminous colors in fireworks.
Visible light is produced in the electron shells of atoms when the electrons are temporarily put into a state of higher energy by the supply of energy. When they leave this excited state again, they emit the absorbed energy in precisely defined portions as photons, i.e. light quanta of a very specific wavelength characteristic of the type of atom in question. We perceive the different wavelengths of light as different colors. Sodium, which we know as a component of the sodium chloride or common salt molecule, emits yellow light with a wavelength of 590 nm; barium salts glow green, potassium salts violet and strontium salts red.
Bunsen needed a gas burner with the highest possible temperature for his investigations. However, Michael Faraday's burner, which was operated with a mixture of town gas and oxygen, could not be precisely regulated. After several experiments, Bunsen therefore constructed a valve (Bunsen valve) with which the air supply to the gas burner could be regulated and a soot-free flame could be produced even at high temperatures.
The "Bunsen burner", which is still used in every chemical laboratory today, produces a flame with a low intrinsic brightness but at such a high temperature that Bunsen can use it to vaporize the salts and observe their different flame colors. Nevertheless, he was unable to identify the individual chemical elements by the color of the flame alone. Kirchhoff therefore suggested splitting the light of the flame into its colored components with the help of a prism.
In the city palace "Haus zum Riesen" in Heidelberg's Hauptstraße, they both developed the first spectral apparatus: a trapezoidal box A resting on three legs carried the two telescopes B and C. The ocular lenses of tube B were replaced by a plate with a slit placed in the focal point of the objective lens. The eyepiece lenses of tube B are replaced by a plate with a slit placed in the focal point of the objective lens. The salt sample attached to the bent end of a very fine platinum wire is heated to glow by the flame of the Bunsen burner and the light is directed through the slit onto a prism arranged between the objectives of telescopes B and C. The light is then reflected through the slit onto the prism. The light emitted by the atoms of the gas is broken down into its individual colors like a rainbow. The prism resting on a brass plate can be rotated around a vertical axis. Underneath is a mirror G. Through a telescope pointed at the mirror, the mirror image of a horizontal scale set up at a short distance can be seen. By rotating the prism, the spectrum of the flame can be guided past the telescope C and the lines contained in the spectra can be measured.
In their experiments, they also recognize bright lines in the spectra against a dark background and observe that the dark absorption lines in the solar spectrum discovered by Joseph Fraunhofer in 1814 become either brighter or darker depending on the intensity of the respective light. They discovered that each chemical element in the gaseous state emits light of a very specific wavelength and that characteristic spectral lines appear in a few narrow color ranges. However, when light penetrates colder gas masses, the atoms there swallow up their characteristic glow and the dark Fraunhofer lines appear.
Kirchhoff's investigations led him to the realization that the temperature of a radiation-absorbing body increases and thus its emission also increases until a radiation equilibrium is reached, and in 1859 he formulated the radiation law named after him. According to this law, the relationship between the absorption and emission capacity of all bodies depends only on the temperature and wavelength, but not on the material properties. According to this law, every luminous body absorbs the spectral lines that it also emits.
Kirchhoff not only found the explanation for the Fraunhofer lines, but also recognized that their wavelengths coincide with the emission lines of known chemical elements, which now makes it possible to analyze the matter of even celestial bodies millions of light years away using only the light they emit.
With spectral analysis, Kirchhoff and Bunsen created one of the most important instruments in astronomy to this day. Astronomy, which had previously been limited to observing the stars, developed into astrophysics with spectral analysis. Bunsen immediately recognized its far-reaching significance when he wrote "These investigations caused us sleepless nights, for the method can reveal the composition of the sun and the stars with the same reliability as chemical methods did for earthly substances." Spectral analysis later formed the basis of atomic and molecular theory and led to the development of quantum physics.
In 1860, Kirchhoff and Bunsen published the basics of spectral analysis in their book "Chemical Analysis by Spectral Observations". It also shows the spectrometer they developed and the first recorded spectra. Above is the solar spectrum with the Fraunhofer lines, below are the spectra of potassium, sodium, lithium, strontium, calcium and barium.
In the same year, Kirchhoff began a detailed analysis of the solar spectrum and concluded from his knowledge of the radiation of bodies that the sun was a fireball with an extremely dense core at a temperature of around 20 million degrees. His eyes were badly damaged during these investigations.
In the same year, Kirchhoff began an in-depth analysis of the solar spectrum and concluded from his knowledge of the radiation of bodies that the sun is a fireball with an extremely dense core that is around 20 million degrees hot. His eyes were badly damaged during these investigations.
But Bunsen and Kirchhoff soon discovered two new chemical elements by means of spectral analysis in the mineral water of the newly tapped Bad Dürkheim Max Spring: caesium in 1860 and rubidium the following year. Bunsen can now add caesium and rubidium in pencil to the periodic table of 60 elements and Kirchhoff can also publish their spectra (above the solar spectrum, below the spectra of potassium and the new elements rubidium and caesium).
Spectral analysis not only made it possible to discover new elements in the laboratory, but also in the gaseous envelopes of stars, such as helium in the sun, which Kirchhoff was able to detect in the solar spectrum in 1868. Even today, analyzing the spectra of cosmic objects can provide information about their chemical composition, temperature and pressure. The displacement of the lines contained in the spectra can even be used to calculate the speed at which the objects are moving towards or away from us.
In 1863, Kirchhoff moved with his family to the newly built Institute of Natural Sciences at the University of Heidelberg and spent a happy time there until 1868, when he injured his foot so badly falling down a flight of stairs that he needed a wheelchair for a while and crutches for another five years afterwards. He was no longer able to give his popular and always well-attended experimental lectures or conduct experiments. He therefore devoted himself entirely to theoretical physics.
A year later, his wife Clara dies of pneumonia at the age of just 35. His two sons are able to stay with him. His two young daughters went to live with his mother-in-law in Königsberg. In December 1872, Kirchhoff marries Luise Brömmel, a matron working at the Heidelberg Eye Clinic, who takes loving care of him.
After 21 years, Kirchhoff's fruitful time in Heidelberg came to an end. Having already turned down offers from other universities three times, he decided to move to Berlin at the end of 1874 and became the first full professor of theoretical physics at the university. He moved to Berlin in April 1875 and immediately began lecturing. His students included Heinrich Hertz and Max Planck. But he and his wife found it difficult to get used to life in the big city and often thought of Heidelberg.
Although his foot injury finally heals in Berlin, his health soon deteriorates, which he covers up with his characteristic cheerfulness. Even though he continued to enjoy his lectures, they were associated with increasing physical exertion. After bouts of weakness, Kirchhoff interrupted his lecturing activities on medical advice in 1884, but resumed them for a short time in the winter semester of 1885/86, until attacks of dizziness and fever caused by a brain tumor forced him to end his teaching activities.
After patiently enduring suffering, Gustav Robert Kirchhoff died on the morning of October 17, 1887 at the age of 63 and was buried in St. Matthew's Cemetery in Berlin-Schöneberg. His grave is still there today.
Bunsen remained in Heidelberg and continued to teach many students, whose practical training was close to his heart. They greatly appreciated their professor's vivid lectures. Bunsen offered a lecture on "General Experimental Chemistry" every semester and was one of the first to combine teaching and research. The manuscript prepared by an assistant for the lecture "Experimental Chemistry" from the winter semester of 1879/1880 deals with different types of flames and their composition as well as gas analysis.
Bunsen only retired at the age of 78 at Easter 1889 and moved to Luisenstraße 12, which was renamed "Bunsenstraße" in 1893. He was now able to travel, take long walks in the countryside and devote himself to his hobby of geology.
He outlived his friend Kirchhoff by 12 years. Robert Bunsen died on August 16, 1899 at the age of 88 and was buried in Heidelberg's Bergfriedhof cemetery. The monument in front of the Friedrichsbau in Heidelberg's Hauptstraße, inaugurated in 1908, still commemorates the important chemist today.
The interdisciplinary approach of the physicist Kirchhoff and the chemist Bunsen laid the foundation for Heidelberg to develop into one of the most important centers for the natural sciences, especially astronomy, with a large number of research facilities.
The Max Planck Institute for Astronomy, the House of Astronomy, the Astronomical Computing Center, the State Observatory on the Königsstuhl, as well as the European Molecular Biology Laboratory (EMBL), the German Cancer Research Center and the Center for Molecular Biology at Heidelberg University attract scientists from all over the world.
