Robert Bunsen, observation

With the benefit of hindsight, it seems obvious that geology should have become a field of application for physical chemistry. As early as 1851, Robert Bunsen had observed that magmas were solutions and might be treated by the same principles that governed the behavior of aqueous solutions. Minerals did not simply crystallize out of magmas in the reverse order of their fusibilities, but might show the same complex solubility patterns as were exhibited by mixtures of salts in water (20, 21). 

In 1861 Robert Bunsen and G. R. Kirchhoff separated the alkalies from some lepidolite from Saxony and precipitated the potassium with platmic chloride. After they had washed this precipitate, they examined it with the spectroscope and observed two new hnes which proved to be those of an unknown element, which they named rubidium. The report runs as follows ... 

Figure 15 Gustav Kirchhoff and Robert Bunsen s spectrocope, from Chemical analysis by Observation of Spectra, (1860).

Scientists had observed that sodium and potassium salts produce characteristic colours in a flame. ROBERT BUNSEN (1811 -1899) and GUSTAV ROBERT... 

Cesium is an alkali metal that reacts explosively with water and melts just above room temperature. The word cesium is derived from caesium (Latin for sky blue ). The name was chosen because of the blue lines observed by Robert Bunsen and Gustav Kirchhoff during their analysis of springwater with a spectroscope in 1860. Currently, cesium metal is generated via thermal decomposition of the azide, electrolysis of molten CsCN, or reduction of molten CsCl with calcium vapor followed by fractional distillation. 

Each element has its own distinctive line spectrum—a kind of atomic fingerprint. Robert Bunsen (1811-1899) and Gustav Kirchhoff (1824-1887) developed the first spectroscope and used it to identify elements. In 1860, they discovered a new element and named it cesium (Latin, caesius, sky blue) because of the distinctive blue lines in its spectrum. They discovered rubidium in 1861 in a similar way (Latin, rubidius, deepest red). Still another element characterized by its unique spectrum is helium (Greek, helios, the sun). Its spectrum was observed during the solar eclipse of 1868, but helium was not isolated on Earth for another 27 years. 

A solvothermal process is one in which a material is either recrystallized or chemically synthesized from solution in a sealed container above ambient temperature and pressure. The recrystallization process was discussed in Section 1.5.1. In the present chapter we consider synthesis. The first solvothermal syntheses were carried out by Robert Wilhelm Bunsen (1811-1899) in 1839 at the University of Marburg. Bunsen grew barium carbonate and strontium carbonate at temperatures above 200°C and pressures above 100 bar (Laudise, 1987). In 1845, C. E. Shafhautl observed tiny quartz crystals upon transformation of freshly precipitated silicic acid in a Papin s digester or pressure cooker (Rabenau, 1985). Often, the name solvothermal is replaced with a term to more closely refer to the solvent used. For example, solvothermal becomes hydrothermal if an aqueous solution is used as the solvent, or ammothermal if ammonia is used. In extreme cases, solvothermal synthesis takes place at or over the supercritical point of the solvent. But in most cases, the pressures and temperatures are in the subcritical realm, where the physical properties of the solvent (e.g., density, viscosity, dielectric constant) can be controlled as a function of temperature and pressure. By far, most syntheses have taken place in the subcritical realm of water. Therefore, we focus our discussion of the materials synthesis on the hydrothermal process. 

It remained, however, for Gustav Kirchhoff and Robert Wilhelm Bunsen in 1859 and 1860 to explain the origin of the Fraunhofer lines. Bunsen had invented his famous burner (Figure 24F-2) a few years earlier, which made possible spectral observations of emission and absorption phenomena in a nearly transparent flame. Kirchhoff con-... 

Robert Wilhelm Bunsen, 1911-1899. ProfessorofChemistry at the University of Heidelberg, Germany. He observed in 1859 that each element emits light of a characteristic wavelength. These studies of spectral analysis led Bunsen to his discovery of cesium and rubidium. 

Bohr s theory was received with a certain amount of scepticism by Rutherford, but it did have the advantage of explaining various features of atomic spectra. There had been numerous attempts to rationalise the lines observed in atomic emission spectra since the invention of the spectroscope by Bunsen and Kirchhoff in 1859 (Chapter 9). Little progress was made until 1885 when Johann Jacob Balmer (1825-1898), a Swiss school teacher, showed that the wavelengths of the four lines then known in the hydrogen spectrum could be expressed in terms of a simple equation. In 1890 Balmer s formula was rearranged by Johannes Robert Rydberg (1854-1919) to the form... 

C. Remigius Fresenius once again deserves credit for noting, toward the middle of the nineteenth century, that new analytical techniques invariably lead to fresh sets of discoveries. Whereas the element germanium was found on the basis of "classical methods (Clemens Winkler, 1886), Fresenius observation clearly applies to the discovery of the alkali metals rubidium and cesium (by Robert W. Bunsen after he and G. R. Kirch-HOFF first developed emission spectroscopy in 1861). Other relevant examples include the discoveries of radium and polonium (by Madame Curie), hafnium (Hevesy and Coster, 1922), and rhenium (1. Tacke and W. Noddack, 1925), all with the aid of newly introduced X-ray spec-trometric techniques. This is also an appropriate point to mention the discovery of nuclear fission by Otto Hahn and Fritz Strassmann (19. 8), another accomplishment with strongly analytical characteristics 110]. 

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