![]() ![]() And this time Bunsen did successfully isolate the element, making his inability to isolate cesium all the more frustrating. The following year, Bunsen and Kirchhoff observed the presence of yet another alkali metal with a dark red spectrum - hence its name, rubidium (from the Latin for "dark red"). (It was more likely a colloidal mix of the metal and cesium chloride.) The result was always a kind of blue "melt." This substance "neither under the naked eye nor under the microscope" showed any trace of metallic substance, so they decided it must be a chloride. But despite his skill with the method, he failed to isolate pure metallic cesium with electrolysis. This gave him a large enough sample to determine its properties: an atomic mass of 128.4 (today we know it is 132.9). It was just a trace amount, so he hired a chemical factory to isolate the cesium by evaporating 12,000 gallons of spring water. He and Kirchhoff realized it belonged to a new element, which he dubbed cesium (Latin for "sky blue"). On May 10, 1860, while analyzing the spectral emissions from spring waters known to be rich in lithium compounds, Bunsen spotted a new sky-blue signature in the spectra in addition to the expected light from sodium, lithium, and potassium. Together they devised an instrument based on this principle: the spectroscope. ![]() Kirchhoff then suggested improving on this method by adapting the Herschel/Talbot method of passing the light through a prism. Bunsen came up with the idea of using filters to block intense colors (like the yellow of sodium compounds), to better detect less intense colors of light emitted by other elements, such as the violet hues of potassium. So there had never been a careful, systemic approach to such studies before Bunsen and Kirchhoff teamed up in 1859. But impurities in the samples available at the time made it difficult to prove, since multiple spectra would be produced simultaneously. In 1822 John Herschel noticed emission spectra lines while passing light from different colors of flame through a prism, and four years later, photographer William Fox Talbot noted, "A glance at the prismatic spectrum of a flame may show it to contain substances which it would otherwise require a laborious chemical analysis to detect." Talbot later used it to distinguish between lithium and strontium compounds, both of which emit red flames, but with different spectra. Sodium produced more yellow flame, while potassium emitted violet flames. ![]() Several years later, Andreas Sigismund Marggraf claimed he could tell the difference between sodium and potassium compounds via a similar method. Scientists had previously observed what we now know as emission spectra in the 1750s, when Thomas Melvill noticed (while observing them with a prism) that the flames from lamps burning alcohol infused with dissolved salts emitted more yellow light than the rest of the light spectrum. (Kirchhoff’s laws of electrical circuits and Kirchhoff’s law of thermodynamics are both named in his honor.)īunsen convinced Kirchhoff to move to Heidelberg with him in 1854 so they could continue to collaborate on research proving that all pure elements emit a distinct spectrum. Kirchhoff initially researched electrical circuits and thermal radiation he coined the term "black body radiation" in 1862. At just 26, he became a professor at the University of Breslau, where he first met Bunsen. Kirchoff was born in 1824 in Königsberg, Prussia (now Kalingrad) and moved to Berlin shortly after his marriage to the daughter of his mathematics professor. It proved instrumental to his studies of emission spectra from heated elements and arguably marked the beginning of spectroscopy as an invaluable tool in scientific research. But his work did produce the most effective antidote for arsenic poisoning, iron oxide hydrate, which is still used today.īunsen is best known for his invention of the Bunsen burner in 1855 with his laboratory assistant Peter Desaga, a device which has been a staple in chemistry labs ever since. Initially interested in organic chemistry, he lost an eye while working with an arsenic compound known as cacodyl cyanide, which exploded during an experiment. He held subsequent positions at the University of Marburg, Breslau (in Poland), and Heidelberg. He spent the next three years traveling across Europe before becoming a lecturer at his alma mater. Bunsen himself eventually earned his doctorate there. Born in Germany in 1811, Bunsen’s father was a professor of modern languages at the University of Göttingen. ![]()
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