Caesium discovery

The alkali metals form a homogeneous group of extremely reactive elements which illustrate well the similarities and trends to be expected from the periodic classification, as discussed in Chapter 2. Their physical and chemical properties are readily interpreted in terms of their simple electronic configuration, ns, and for this reason they have been extensively studied by the full range of experimental and theoretical techniques. Compounds of sodium and potassium have been known from ancient times and both elements are essential for animal life. They are also major items of trade, commerce and chemical industry. Lithium was first recognized as a separate element at the beginning of the nineteenth eentury but did not assume major industrial importance until about 40 y ago. Rubidium and caesium are of considerable academic interest but so far have few industrial applications. Francium, the elusive element 87, has only fleeting existence in nature due to its very short radioactive half-life, and this delayed its discovery until 1939. 

Rubidium was discovered as a minor constituent of lepidolite by R. W. Bunsen and G. R. Kirchhoff in 1861 only a few months after their discovery of caesium (1860) in mineral spa waters. These two elements were the first to be discovered by means of the spectroscope, which Bunsen and Kirchhoff had invented the previous year (1859) accordingly their names refer to the colour of the most prominent lines in their spectra (Latin rubidus, deepest red caesius, sky blue). 

The development of chemistry itself has progressed significantly by analytical findings over several centuries. Fundamental knowledge of general chemistry is based on analytical studies, the laws of simple and multiple proportions as well as the law of mass action. Most of the chemical elements have been discovered by the application of analytical chemistry, at first by means of chemical methods, but in the last 150 years mainly by physical methods. Especially spectacular were the spectroscopic discoveries of rubidium and caesium by Bunsen and Kirchhoff, indium by Reich and Richter, helium by Janssen, Lockyer, and Frankland, and rhenium by Noddack and Tacke. Also, nuclear fission became evident as Hahn and Strassmann carefully analyzed the products of neutron-bombarded uranium. 

After Bunsen had detected and isolated caesium, spectroscopy was taken up with great enthusiasm by William Crookes, and this led to his detection and isolation of thallium in 1861.191 Crookes letters to Charles Hanson Greville Williams, who was also working with the spectroscope, and who felt he deserved some of the credit for the discovery of thallium, have been published.192 The use of spectrochemistry in the search for hitherto unknown chemical elements in Britain over the period 1860-1869 has been described. It was perceived that, like Crookes, a scientist could make his reputation by discovering a new element. This resulted in several claims for the existence of new elements that later proved to be unfounded.193 Once Kirchhoff had established beyond doubt that the dark Fraunhofer lines were caused by the same element that caused emission lines of identical wavelengths, the way was open for the chemical analysis of the atmosphere of the sun and stars. This was a process which had been declared to be an impossibility by Auguste Comte less than 30 years previously.194... 

An interesting result reported recently by the same group of workers (70) relates to the discovery of two types of 1 1 caesium cryptates for cryptand C222. The possibility for the existence of an exclusive complex... 

For example, naturally occurring clinoptilolite is used by BNFL to remove radioactive caesium and strontium from spent pile effluent. However, the synthetic zeolites, A and P, have had the greatest impact on the home. Sodium zeolite A rapidly exchanges its sodium atoms for the divalent hard water ions calcium and magnesium at room temperature. This discovery led to the replacement of the polyphosphates previously used in washing powder, which were damaging to the environment, by zeolite A about 20 years ago. More recently, Unilever introduced MAP (maximum aluminium zeolite P) as a replacement for. zeolite A. MAP has a lower water content, and is lighter in the packet ... 

Caesium is not only of interest as being the first metal to be discovered spectroscopically. As early as 1846 Plattner had examined polluxite, then believed to be merely potassium aluminium silicate, but the analysis, on this assumption, did not work out at 100 per cent. Some alkali appeared to be missing. After the discovery of caesium, Pisanif, in 1864, re-examined the mineral and showed it to contain this new element, and not potassium, whose salts its own so closely resemble. The higher atomic weight... 

Thallium was discovered independently by Sir William Crookes in England and by the Belgian chemist M. Lamy. Crookes was the first to make the discovery. He was the founder and editor of the now defunct Chemical News which, in its day, was a valuable contribution to scientific literature. In March 1861 he was engaged in extracting selenium from a deposit obtained from a sulphuric acid factory at Tilkerode in the Harz. Bunsen and KirchhofF had just announced their discovery of caesium and rubidium with the aid of the spectroscope (p. 147), so Crookes tested his material in a similar manner. 

Armed with the empirical knowledge that each element in the periodic table has a characteristic spectmm, and that heating materials to a sufficiently high temperature dismpts all interatomic interactions, Bunsen and Kirchoff invented the spectroscope, an instrument that atomizes substances in a flame and then records their emission spectmm. Using this instmment, the elemental composition of several compounds and minerals were deduced by measuring the wavelength of radiation that they emit. In addition, this new science led to the discovery of elements, notably caesium and mbidium. 

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