Substance Index

Substance Refractive index Substance Refractive index Substance Refractive index... 

Other Substances. Several other index substances (W8), such as carotene, have been used by various workers in this field. There does not seem to be any particular advantage in these other methods. The use of one good water-soluble index substance, such as xylose, and one fat-soluble index substance, such as I131 fat or vitamin A in oil, is sufficient for diagnostic purposes. 

The refractive index is usually reported to four decimal places and has no units. Since small amounts of impurities can significantly affect the refractive index, substances must be very carefully purified in order to match the established reported refractive indices. An example of a refractive index is given as V2° = 1.4567. 

Substance Stability index Substance Stability index... 

A fiber-optic waveguide is a thin device composed of a high-refractive-index substance which is completely surrounded by a lower-refractive-index one. The situation is depicted in Fig. 16.1 la, where according to Snell s law. 

Substance Refractive index" Substance Refractive index"... 

Location of the compound within a class (or homologous series) of compounds. Reference to the literature or to tables of the physical properties of the class (or classes) of organic compounds to which the substance has been assigned, will generally locate a number of compounds which boil or melt within 6° of the value observed for the unknown. If other physical properties e.g., refractive index and density for a hquid) are available, these will assist in deciding whether the unknown is identical with one of the known compounds. In general, however, it is more convenient in practice to prepare one, but preferably two, crystalhne derivatives of the substance. 

Quite naturally there is a certain amount of arbitrariness in this system, although the lUPAC nomenclature is followed. The preferred Chemical Abstracts index names for chemical substances have been, with very few exceptions, continued unchanged (since 1972) as set forth in the Ninth Collective Index Guide and in a journal article. Any revisions appear in the updated Index Guide new editions appear at 18-month intervals. Appendix VI is of particular interest to chemists. Reprints of the Appendix may be purchased from Chemical Abstracts Service, Marketing Division, P.O. Box 3012, Columbus, Ohio 43210. 

In LC, the most common means for monitoring the eluant is to pass it through a cell connected into an ultraviolet spectrometer. As substances elute from the column, their ultraviolet absorption is measured and recorded. Alternatively, the refractive index of the eluant is monitored since it varies from the value for a pure solvent when it contains organics from the column. 

The index of refraction of most polymers is greater parallel to the chain than normal to the molecular axis. Substances showing this anisotropy of refractive index are said to be birefringent. 

Equations (10.17) and (10.18) show that both the relative dielectric constant and the refractive index of a substance are measurable properties of matter that quantify the interaction between matter and electric fields of whatever origin. The polarizability is the molecular parameter which is pertinent to this interaction. We shall see in the next section that a also plays an important role in the theory of light scattering. The following example illustrates the use of Eq. (10.17) to evaluate a and considers one aspect of the applicability of this quantity to light scattering. 

There are variations in representation of rings in different disciplines. The dye industry does not designate aromaticity or double bonds in rings. AH double bonds and aromaticity are shown in the Encyclopedia as a matter of course. For example, tetralin has an aromatic ring and a saturated ring and its stmcture appears in the Encyclopedia with its common name. Registry Number enclosed in brackets, and parenthetical CA index name, ie, tetralin [119-64-2] (1,2,3,4-tetrahydronaphthalene). With names and stmctural formulas, and especiaHy with CAS Registry Numbers, the aim is to help the reader have a concise means of substance identification. 

Refra.ctive Index. The relative amount of light reflected by a surface is dependent on both components of the iaterface, ie, filler and air. The refractive iadex is a measure of a substance s tendency to reflect light according to Fresnel s equation ... 

Dispersion staining is useful for rapid deterrnination of refractive index and dispersion. It is appHed most often, however, for needle-in-a-haystack detection of any particular substance in a mixture such as chrysotile in insulation, cocaine in dust samples, quartz in mine samples, or any particular mineral, eg, tourmaline, in a forensic soil sample. 

Naming and Indexing of Chemical Substances for Chemical Abstracts, Chemical Abstracts Service, American Chemical Society, Washington, D.C., 1992. Nomenclature of Organic Chemist, lUPAC, Pergamon Press, New York, 1979. 

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