INDEX 1- organic halides

Thallium is also used in low-temperature thermometers, photoelectric cells, dye pigments, and to produce various types of resistant cements. Because of the element s high refractive index it is utilized in the manufacturing of optical lenses and imitation jewelry. Thallium is included as a component of corrosion-resistant alloys, organic reaction catalysts, and fireworks. The incorporation of thallium halides into organic alkylhalides produces formation of new complexes that act as phosphors. This is the basis for using thallium in scintillation counters [Nal(Tl)]. 

The parameter k is the edge-parameter (the bond-parameter), and Estrada presented in his papers (Estrada, 1995a, 1999) the values of this parameter for most of the bonds common in organic compounds. Estrada used the edge-connectivity index to predict successfully the molecular volumes of 112 aliphatic organic compounds, including aldehydes, ketones, ethers, thioethers, tertiary amines, and alyl halides. 

Coarse or hard powders are not well served by either the compressed pellet or mull techniques mainly because of difficulties associated with grinding these materials. In such situations, the best approaches require the use of an accessory, such as diffuse reflectance or photoacoustic. Be aware that diffuse reflectance is also particle-size dependent. Mixing the sample with a potassium halide may be beneficial to reduce anomalous optical behavior at the surface of the sample. This is especially helpful with inorganic compounds or other materials that have high absorptivities or have a high index of refraction. As a rule of thumb, organic compounds can be measured in about a 10% mixture and inorganics with approximately 1 or 2 /o mixture (in KBr or KCl). 

KOV 58] Kovats E., Gas chromatographic characterization of organic compounds. I. Retention Indexes of aliphatic halides, alcohols, aldehydes, and ketones , Helvetica Chimica Acta, vol. 41, pp. 1915-1932, 1958. 

Light scattering is higher in such disks than in alkali halide disks, as the refractive index of these organic materials does not match those of minerals so well. The absorption bands of the disk material make them unsuitable for general use, but they have much to commend them in comparison with mulls, when facilities for the preparation of pressed disks are available. 

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