THE DISCOVERY OF THE ELEMENTS. XIII. SOME SPECTROSCOPIC DISCOVERIES* MARYELVIRA WEEKS.THEUNIVERSITY OF KANSAS, LAWRENCE, KANSAS
Many elements are present i n the earth's crust i n such minute amounts that they could never have been discovered by ordinary methods of mineral analysis. I n 1860, however, Bunsen and Kirchhoff invented the spectroscope, an optical instrument consisting of a collimator, or metal tubefitted at one end with a lens, and closed at the other except for a slit at the focus of the lens, to admit light ,from the incandescent substance to be examined; a turntable containing a prism mounted to receive and separate the parallel rays from the lens; and a telescope to observe the spectrum produced by the prism. With this instrument they soon discovered two new metals, cesium and rubidium, which they classified m'th sodium, potassium, and lithium, which had been previously discovered by Davy and Arfwedson. The spectroscopic discovery of thallium by Sir William Crookes and its prompt confirmation by C. A. Lamy soon followed. I n 1863 F. Reich and H. T. Richbr of the Freiberg School of Mines discovered a very rare element in zinc blende, and named i t indium because of its brilliant line in the indigo region of the spectrum.
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Nnr immer zu! wir wollen es ergrainden, In deinem Nichts hoff' ich das All zu finden (1). Thus there was for him nothing small or great in Nature. Every phenomenon embraced for him a n endless diversity of factors, and in the yellow flame of a n ordinary alcohol lamp whose wick was sprinkled with salt, he saw the possibility of accomplishing the chemical Rnalysis of the most distant stars (2).** As early as 1758 Marggraf had noticed the yellow color imparted to a flameby sodiumsalts and thelavender color imparted by potassium salts (3). In 1802 Dr. Wollaston examined the spectrum of a candle flame through a prism, and saw the discontinuous band spectrum ( 4 ) , (22). He said (22)s When a very narrow line of the blue light a t the lower part of the flame is examined alone, in the same manner, through a prism, the spectrum, instead of appearing a series of lights of different hues contiguous, may be seen divided into five images, a t a distance from each other. The 1st is broad red, terminated by a bright line of yellow; the 2nd and 3rd are both green; the 4th and 5th are blue, the last of which appears to correspond with the division of blue and violet in the solar spectrum. . . * Illustrations collected by I?. B. Dains of The University of Kansas.
** So gab es jiir ihn nithts Kleines ode? Grosses in der Natur. Jade Erschcinung umfasste ihm einc udegrenete Mannigjaltigkeit von Faktoren, und in d n gelben Flamme einer gewiihnlichen Weingeisllampe, deren Docht mit Sale bestreut war, soh er die Moglichkeit, die chemisckc Analyse der fernsten Gestirne ouseuftihren. 1413
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(li8iP182fi) E x l r r n i ~ l r nTlrs Sriwiis SPaclnuscope IN 1x18 J ~ E PFRAUSLIOFEK COUNSELOR ~ S C H N B I D E KAND A ~ R . RRICHENBACA, HIS I'ARISEKS I N THE GLASSWORKS AND OPTICAL ESTABLISHMENTAT BENEDICTREUERN He discussed with them his latest researches on the diffraction of light which had led him to the discovery of gating spectra, the exdct measurement of wave-lengths, and a brilliant confirmation of the undulatory theory of light. (The ohowe illustration i s from a painting Dy Karla Fischer. 190.9.) BEFORE
In 1814 Josef Fraunhofer, a young German physicist who had had thorough training in the art of glassmaking, made an unusually fine prism, saw for the first time the dark lines in the sun's spectrum, and designated eight of the most prominent ones by letters ( 3 ) , (23). Henry Fox Talbot (24), an English scientist, found that, with the aid of a prism, he could distinguish lithium from strontium,* even though the salts of both give red flames ( 4 ) , (26), (32). He stated that the dark lines previously observed by Sir David Brewster (33) in the spectrum of light which had passed through vapors of nitrous acid were caused by absorption of light ( 5 ) , ( 2 5 ) . Important as these contributions undoubtedly were, none of these men founded the science of spectroscopic analysis. That achievement required the genius of a Bunsen and the skill and sagacity of a Kirchhoff. Robert Bunsen was the son of a professor of modem languages a t
* Strontium salts were very rare a t that time, and Talbot was indebted to Faraday for the specimen he used.
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THE DISCOVERY OF THE ELEMENTS.
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English antiquarian, physicist, and pioneer in optics and photography. One of the first to decipher the Assyrian inscriptions at Ninevah. In 1839 he made negative prints on silver chloride paper, and two years later he invented the d o type process for making positives.
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Auousr. 1932
Gcttingen, and was born in that city in the springof 1811.* After attending the academy a t Holzminden he. entered the University of Gottingen, and studied chemistry under Professor Stromeyer. At the age of nineteen years he received his degree of doctor of philosophy. This does not mean that Bnnsen was precocious, for, as Wilhelm Ostwald explains, students graduated a t a much earlier age then than they do now. Aided by a grant from the Hanoverian the youthful Bunsen broadened his scientific education by traveling, mostly on foot, SIR DAVIDRnrrwsrrrx
1781-1868 Scottish physicist famous for his researches on the absorption, reflection. refraction, and polarization of light, and a n doubly refracting crystals. One of the founders of the British Association for the Advancement of Science. He invented the kaleidoscope and improved the stereoscope. His optical researches led t o great improvement in the construction of lighthouses.
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through Germany, France, Austria, and Switzerland, and meeting the scientists of those countries. For three years he went about studying geological formations, visiting factories and mines, and meeting technical men and professors (2). I n 1836 he succeeded Wohler a t the higher technical school a t Cassel. After serving in similar positions a t Marburg and a t Breslau, he finally became Leopold Gmelin's successor at ~ ~ i d ~ where l b ~he ~ taught for thirty-eight years, finally retiring at the venerable age of seventy-eight years (2), (50).
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