Physical constants, determination

The electrophoretic mobility usually found in standard reference tables is a physical constant determined for complete dissociation extrapolated to infinite dilution. However, the mobility of ionic species measured under practical conditions often depends on protonation/deprotonation equilibria... 

Phthalic anhydride, 681, 753, 984, 985 purification of, 507 Phthalide, 753, 772 Phthalimide, 753, 754, 771 Phthalimides, N-substituted, 423 Phthalonitrile, 983 Phthalylacetic acid, 995 Physical constants, determination of, 1028-1037... 

Moreover, based on stability relations in architecture it can be proven that the critical fragility of a hollow spherical body depends on the modulus of elasticity of the shell material (a physical constant determined by the nature and molecular weight of the polymer used) and the quotient of shell thickness over size. This means that... 

Derivatives. The precise identification of a compound normally depends upon the preparation of a derivative and the determination of physical constants such as m.p. in the case of a solid. Many simple compounds can, however, be identified with a fair degree of certainty by intelligently-selected qualitative tests alone, e.g., formates, oxalates, succinates, lactates, tartrates, chloral hydrate. 

Determination of the physical constants and the establishment of the purity of the compound. For a solid, the melting point is of great importance if recrystalhsation does not alter it, the compound may be regarded as pure. For a hquid, the boiling point is first determined if most of it distils over a narrow range (say, 1-2°), it is reasonably pure. (Constant boUing point mixtures, compare Section 1,4, are, however known.) The refractive index and the density, from which the molecular refractivity may be calculated, are also valuable constants for liquids. 

Physical Properties. An overview of the metallurgy (qv) and soUd-state physics of the rare earths is available (6). The rare earths form aUoys with most metals. They can be present interstitiaUy, in soUd solutions, or as intermetaUic compounds in a second phase. Alloying with other elements can make the rare earths either pyrophoric or corrosion resistant. It is extremely important, when determining physical constants, that the materials are very pure and weU characteri2ed. AU impurity levels in the sample should be known. Some properties of the lanthanides are Usted in Table 3. 

PiOMde yourself with a yood book of leference, or chemist s pocket book which contains tables of physical constants. Homogeneity.—Determine if thesubstanceishomogeneous A Liquid.—If it is a hciuid, distil a few c.c. from a miniature distilling flask with a long side-tube, but no condenser, or with... 

Physical properties of the contaminants. Physical properties, particularly Henry s constant, determine the ease of air stripping. The higher the value of Henry s constant, the higher is the removal efficiency. 

Webster, G.R.B., Friesen, K.J., Sarna, L.P., Muir, D.C.G. (1985) Environmental fate modelling of chlorodioxins Determination of physical constants. Chemosphere 14, 609-622. 

It has also been possible, in various ways which cannot be detailed here, to prepare both the keto- and enol-forms of ethyl acetoacetate in the pure state (Knorr, K. H. Meyer). Their physical constants are altogether different. The refractive index, for example, is 1-4225 (D10 ) for the keto-form and 1-4480 for the enol-form. From determinations of the refractive indices of equilibrium mixtures the content of both forms can be calculated by interpolation (Knorr, 1911), and these results have been confirmed spectroscopically (Hantzsch, 1910). 

The movement of the analyte is an essential feature of separation techniques and it is possible to define in general terms the forces that cause such movement (Figure 3.1). If a force is applied to a molecule, its movement will be impeded by a retarding force of some sort. This may be as simple as the frictional effect of moving past the solvent molecules or it may be the effect of adsorption to a solid phase. In many methods the strength of the force used is not important but the variations in the resulting net force for different molecules provide the basis for the separation. In some cases, however, the intensity of the force applied is important and in ultracentrifugal techniques not only can separation be achieved but various physical constants for the molecule can also be determined, e.g. relative molecular mass or diffusion coefficient. 

Although conductimetry is useful in determining various physical constants, e.g. dissociation and solubility constants, its major analytical application is for monitoring titrations. 

Taylor reviews the use of least-squares methods to determine the best values of the fundamental physical constants (3). 

Finally, it behaves like a liquid provided the chain length is not too long. Just around T some physical properties change distinctively such as the specific volume, the expansion coefficient, the specific heat, the elastic modulus, and the dielectric constant. Determination of the temperature dependence of these quantities can thus be used to determine Tg. 

Measurements of the common physical constants such as boiling point or refractive index are not sufficiently sensitive to determine the trace amounts of impurities in question. Besides the common spectroscopic methods, techniques like gas chromatography (GC), high-pressure liquid chromatography (HPLC), or thin-layer chromatography (TLC) are useful. The surest criterion for the absence of interfering foreign compounds lies in the polymerization itself the purification is repeated until test polymerizations on the course of the reaction under standard conditions are reproducible (conversion-time curve, viscosity number of the polymers). 

The foregoing pages have shown a number of ways in which physical constants vary with molecular structure. Petroleum chemists and automotive engineers have come to recognize that the performance of a motor fuel in an internal combustion engine is also dependent upon the structure of the hydrocarbon molecules which the fuel contains. This does not mean that engine performance is a function of the physical constants, but rather that the features of molecular structure which determine the one also determine the other. 

One of the most fundamental elements of molecular structure is chain length. It serves to fix the hydrocarbon s position on its own subseries curve and thus becomes a factor in determining its physical constants. It also is a major factor in determining the hydrocarbon s rate of combustion and hence its octane number and critical compression ratio. 

Much has been accomplished in the synthesis, separation, purification, and careful determination of both physical constants and engine characteristics. Much still remains to be done but the work is progressing. 

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