Some of Bunsen's enthusiasm is readily apparent in a letter to Roscoe dated November 6, 1869: This name seemed to them to be justified by the beautiful blue color of the incandescent vapor of this new element (note) They proposed to give this new metal the name Caesium from cæsius (Latin), which the ancients used to designate the blue of the upper part of the firmament. Supported by unambiguous results of the spectral-analytical method, we believe we can state right now that there is a fourth metal in the alkali group besides potassium, sodium, and lithium, and it has a simple characteristic spectrum like lithium a metal that shows only two lines in our apparatus: a faint blue one, almost coinciding with Sr, and another blue one a little further to the violet end of the spectrum and as strong and as clearly defined as the lithium line." Note. We have had occasion already to convince ourselves that there are such now unknown elements. If there should be substances that are so sparingly distributed in nature that our present means of analysis fail for their recognition and separation, then we might hope to recognize and to determine many such substances in quantities not reached by our usual means, by the simple observation of their flame spectra. "Spectrum analysis should become important for the discovery of hitherto unknown elements. But after precipitating lime, strontia, magnesia, you see the lines of Sodium, Potassium, and Lithium, and in addition, two remarkable blue lines, very close together for which no known substance gives such rays. ![]() One would recognize the light of Sodium, Potassium, Lithium, Calcium, and Strontium. ![]() In the Spring of 1860 Robert Wilhelm Bunsen (1811-1899) and Gustav Robert Kirchhof (1824-1887) examined with the flame of a spectroscope a drop of Dürkheim mineral water.
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