Gems Index

GLOBAL EMERGENCY MANAGEMENT SYSTEM http //fema.gov/gems/index.jsp GLOBAL EMERGING INFECTIONS SURVEILLANCE AND RESPONSE SYSTEM, DEPARTMENT OF DEFENSE ... 

Type of oil Principal fatty add components in weight % °C gem index value value... 

The hardness, index of refraction, and transparency of gemstones determine the way they are cut and polished. Since ancient times gemstones have been shaped in two main styles (1) as faceted gems, with many plane polished sides called facets, or (2) as nonfaceted, rounded, and polished gems, known as cabochons. 

Table V compares M, M and M values for two polyethylenes analyzed by SEC in TCB solution at l45°C. Sample C is a linear low density material listed in Table 1. NBS 1 476 is low density polyethylene which is stated to be a low conversion tubular reactor product with density 0.931 gem and melt index 1.2 (11). IL and are little af fected by the existence of aggregates in these two samples but values are more severely influenced.

Spinel is a colorless magnesium aluminate (MgAl204) of cubic structure. It is hard and durable, but, like white sapphire, it is not a good diamond substitute because it has a low refractive index and lacks brilliance. However, it is readily doped to produce other gems of various colors. Artificial ruby, for example, is often natural red spinel, and most synthetic blue sapphires on the market are actually blue spinel. 

P Volume 1,1991,283 pp. 109.50/ 69.50 ISBN 1-55938-180-9 CONTENTS Introduction to the Series An Editor s Foreword, Albert Padwa. Preface, Brian Halton. Strain in Organic Chemistry A Perspective, Brian Halton. Gem-Dihalocyclopropanes in Chemical Synthesis, Martin G. Banwell and Monica E. Re-um. 1-Halo- and 1, 2-Dihalocyclopropenes Useful Synthetic Intermediates, Mark S. Baird. Cyciization and Cycloaddition Reactions of Cyclopropenes, Albert Padwa and Glen E. Fryx-ell. New Synthetic Pathways From Cyclobutanones, Edward Lee-Ruff. Cyclic Alkynes, Enynes and Dienynes A Synthetic Challenge, Herbert Meier. Index. 

Recently viscosity, density and index of refraction measurements have been recorded for some liquid alkylsydnones (77MI42100). For example, for 3-methylsydnone at 40 °C the viscosity is 5.501 cP, the density is 1.3085 gem-3 and the index of refraction nD is 1.515. Measurements on the conductance of salt solutions in 3-methylsydnone are also available (80MI42111). 

Colorless zircon has been used as an imitation of diamond, since it has a very high refractive index. Zircon gems are doubly refractive, which can give them a cloudy appearance. Looking through the top of a faceted zircon, the back facet edges will appear double. Zircons come in many colors, and this gem is often heat-treated to change or enhance the color. 

Gem material Composition Colors and translucency Refractive index Hardness Specific gravity... 

Refractivity.—As is to be expected from the brilliant gem-like appearance of the crystals and drops of liquid white phosphorus, the refractive index is high. At the ordinary temperature the refractive index for the D line (A = 589-0 to 589-6 m/x) was found to be 2-144 9 or 2-14.X0 The differences between the refractive indices of the solid and the liquid are shown in the table overleaf. ... 

Clear diamonds, occasionally in coloured form, are used as gems because the high index of refraction 2.42) enhances internal reflexion and brilliance in the cut stone. Diamond powder, much now manufactured industrially, is an abrasive for arming grinding and cutting wheels larger opaque, natural diamonds are mounted in tools for cutting metal and rock. 

The exceptionally high hardness of diamond, the easy cleavage along the three main lattice planes of the crystal, its high refractive index and its optical dispersion makes diamonds a valuable raw material for brilliants. The gem diamonds utilized are still exclusively natural diamonds. 

Crytal chemitry. Cubic zirconia (CZ) is a popular simulant for diamond, and deservedly so. With a Mohs hardness of 8.25 and and a refractive index of 2.15, it closely matches the scratch resistance and brilliance of authentic diamond, and its dispersion coefficient is higher (Shigley and Moses 1998). (Fortunately for those who like their gems natural, diamond and CZ are easily distinguished by density and by thermal conductivity.) Cubic zirconia also offers important technological uses as a refractory high-temperature ceramic (Meriani and Palmonari 1989). 

Use Analysis (testing for ozone), artificial gem, optical glass of high refractive index. 

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