Practical methods

For hydrocarbon gases, the concentration measurement tool is exclusively gas chromatography with a packed column and an FID detector, capable of precisely determining lO levels of C1-C5 in less than 5 minutes. Heavier hydrocarbons are sometimes determined using a quadrupole mass spectrometer. As these instruments and the techniques for loading gas samples onto them are described elsewhere (e.g.. Chapter 5), only field methods and, where applicable, sample pre-treatment methods for releasing gases from soils are discussed here. 

Interstitial gases in soil air are first extracted by driving a probe into the soil and sucking the soil air into a measurement device or a pre-concentration medium. A variety of procedures have been reported (Devine and Sears, 1977 Jones and Drozd, 1983 Richers and Jones, 1986). The main operational parameters are the probe depth, isolation of the soil air from the atmospheric air, the amount of negative pressure applied, the protection of the probe from blockage and the reduction of the dead volume of the tubing. These have to be optimised in terms of both cost and effectiveness. Of course it is not possible to extract interstitial soil air from waterlogged soils. 

Soil samples are usually collected at the surface proper or at depths of up to several metres below the surface. As far as possible, samples are kept in their original condition until they are prepared for analysis in the laboratory. The analytical procedures are invariably partial extraction techniques. This approach has been widely used in other branches of exploration geochemistry, but assumes particular importance in gas geochemical surveys for petroleum. 

For the extraction of hydrocarbons in carbonate minerals and microbubbles, the method widely used is acid treatment under vacuum, for which most laboratories in China use the apparatus shown in Fig. 6-5. The soil sample is heated to 40 C in the flask, then 1 6 HCl is added until its reaction with the warm sample ceases. The mixture of gases evolved is filtered through NaOH solution to remove COt (which makes up the bulk of the evolved gases) and the remaining gases are injected into a gas chromatograph. 

A selective method to flush out microbubbles is hydrogen stripping. This was first proposed by Schaefer et al. (1978) and has been developed by Ruan and Cheng (1991). Soil samples are kept in a natural wet state and an aliquot of saturated NaCI solution is added to make a slurry, through which Hi is passed. The gases stripped from the sample are condensed in a liquid N2 cold trap, which is then used as the gas sample loop in the carrier gas line to a gas chromatograph (Fig. 6-6). 

The reader is referred to more general texts for further information on general experimental techniques.7 However, it is hoped that for those not experienced 

These solvents are most conveniently dried by treatment with calcium hydride followed by distillation onto 4 A molecular sieves. 

Petroleum ether can be dried by distillation onto activated 4 A molecular sieves. 

Dichloromethane can be dried by treatment with calcium hydride in a continuous still or can be stored by distillation onto 4 A molecular sieves. Caution Never treat chlorinated solvents with sodium or strong bases—an explosion may occur. 

Stir over calcium hydride or phosphorus pentoxide for 24 h, filter under an inert atmosphere and distil (56°C at 20 mmHg) onto 3 A molecular sieves. An alternative method is to dry over three batches of 3 A molecular sieves (5% w/v, 3 x 12 h). 

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In the intervening years mueh excellent analytical work has been done by Libby, Lord, Dodd, Deeds, Palanisamy and many others which has given us a practical method of understanding eddy current behavior in many applications including nuclear inspection and aerospace where problems of safety and reliability have become so important to us all. 

Another efficient and practical method for exact 3D-reconstruction is the Grangeat algorithm [11]. First the derivative of the three-dimensional Radon transfomi is computed from the Cone-Beam projections. Afterwards the 3D-Object is reconstructed from the derivative of the Radon transform. At present time this method is not available for spiral orbits, instead two perpendicular circular trajectories are suitable to meet the above sufficiency condition. 

An alternative to obtaining 0 directly involves defining some more convenient shape-dependent function, and an early but still very practical method is the following. We define a shape-dependent quantity as S = dsldg, as indicated in Fig. 11-16, de is the equatorial diameter and ds is the diameter measured at a distance de up from the bottom of the drop. The hard-to-measure size parameter h in Eq. 11-17 is combined with 0 by defining the quantity H = -0(defb). Thus... 

Butler E P and Hale K F 1981 Practical Methods in Electron Microscopy vol 9, ed A Glauert (New York North-Holland)... 

Fletcher R 1981 Practical Methods of Optimization Vol 1—Unconstrained Optimization (New York Wley)... 

An alternative approximation scheme, also proposed by Bom and Oppenheimer [5-7], employed the straightforward perturbation method. To tell the difference between these two different BO approximation, we call the latter the crude BOA (CBOA). A main purpose of this chapter is to study the original BO approximation, which is often referred to as the crude BO approximation and to develop this approximation into a practical method for computing potential energy suifaces of molecules. 

In Chapter IX, Liang et al. present an approach, termed as the crude Bom-Oppenheimer approximation, which is based on the Born-Oppen-heimer approximation but employs the straightforward perturbation method. Within their chapter they develop this approximation to become a practical method for computing potential energy surfaces. They show that to carry out different orders of perturbation, the ability to calculate the matrix elements of the derivatives of the Coulomb interaction with respect to nuclear coordinates is essential. For this purpose, they study a diatomic molecule, and by doing that demonstrate the basic skill to compute the relevant matrix elements for the Gaussian basis sets. Finally, they apply this approach to the H2 molecule and show that the calculated equilibrium position and foree constant fit reasonable well those obtained by other approaches. 

The theory of the action of drying agents has been considered in Section 1,20. We are now concerned with the practical methods for the removal of water from organic solids and liquids and from solutions of... 

The first practical method for asymmetric epoxidation of primary and secondary allylic alcohols was developed by K.B. Sharpless in 1980 (T. Katsuki, 1980 K.B. Sharpless, 1983 A, B, 1986 see also D. Hoppe, 1982). Tartaric esters, e.g., DET and DIPT" ( = diethyl and diisopropyl ( + )- or (— )-tartrates), are applied as chiral auxiliaries, titanium tetrakis(2-pro-panolate) as a catalyst and tert-butyl hydroperoxide (= TBHP, Bu OOH) as the oxidant. If the reaction mixture is kept absolutely dry, catalytic amounts of the dialkyl tartrate-titanium(IV) complex are suflicient, which largely facilitates work-up procedures (Y. Gao, 1987). Depending on the tartrate enantiomer used, either one of the 2,3-epoxy alcohols may be obtained with high enantioselectivity. The titanium probably binds to the diol grouping of one tartrate molecule and to the hydroxy groups of the bulky hydroperoxide and of the allylic alcohol... 

Not only is pulsed FT NMR the best method for obtaining proton spectra it is the only practical method for many other nuclei including It also makes possible a large number of sophisticated techniques that have revolutionized NMR spectroscopy... 

The net effect of the sequence protect-mtrate-deprotect is the same as if the substrate had been nitrated directly Because direct nitration is impossible however the indirect route IS the only practical method... 

Fletcher, R. Practical Methods of Optimization, John Wiley Sons, New York, 1980... 

Blasters Handbook A Manual Describing Explosives and Practical Methods of Using Them, E. I. duPont de Nemours Co., Inc., Wilmington, Del., 1977. 

A considerable reduction in stress concentration could be achieved by using a cross-bore which is eUiptical in cross-section, provided the major axis of the eUipse is normal to the axis of the main cylinder. A more practical method of achieving the same effect is to have an offset radial hole whose axis is parallel to a radius but not coincident with it (97,98). Whenever possible the sharp edges at the intersection of the main bore with the cross bore are removed and smooth rounded corners produced so as to reduce the stress raising effects. 

Electrolytic Eefming. Electrolytic refining (26,27), used by Cominco Ltd. (Trad, B.C., Canada) and Cerro de Pasco Corp. (La Oroya, Pern), as weU as by several refineries in Europe and Japan, removes impurities in one step as slimes. The impurities must then be separated and purified. Before the development of the Betterton-KroU process, electrolytic refining was the only practical method of reducing bismuth to the required concentrations. 

A practical method for low level perchlorate analysis employs ion chromatography. The unsuppressed method using a conductivity detector has a lower detectable limit of about 10 ppm. A suppression technique, which suppresses the conductivity of the electrolyte but not the separated ions, can further improve sensitivity (110,111). Additionally, ion chromatography can be coupled with indirect photometric detection and appHed to the analysis of perchlorates (112). 

Practical methods for reduction of residues (by washing, peeling, cooking, etc) Proposed tolerance (in each crop and crop by-product)... 

A. M. Glauert, Practical Methods in Electron Microscopy, North-HoUand, Amsterdam, the Netherlands, 1977. 

The second approach, changing the environment, is a widely used, practical method of preventing corrosion. In aqueous systems, there are three ways to effect a change in environment to inhibit corrosion (/) form a protective film of calcium carbonate on the metal surface using the natural calcium and alkalinity in the water, (2) remove the corrosive oxygen from the water, either by mechanical or chemical deaeration, and (3) add corrosion inhibitors. 

One of the first practical methods for the manufacture of cinnamyl alcohol involved reduction of cinnamic aldehyde diacetate with iron filings in acetic acid. This approach suffered from low yields and Hberation of a significant amount of the starting aldehyde. 

Practical methods for synthesis and elucidation of the optimum physical forms were developed at Du Pont (13). The violets fill the void in the color gamut when the inorganics are inadequate. The quinacridones may be used in most resins except polymers such as nylon-6,6, polystyrene, and ABS. They are stable up to 275°C and show excellent weatherabiUty. One use is to shade phthalocyanines to match Indanthrone Blue. In carpeting, the quinacridones are recommended for polypropylene, acrylonitrile, polyester, and nylon-6 filaments. Predispersions in plastici2ers ate used in thermoset polyesters, urethanes, and epoxy resins (14). 

W. J. Diamond, Practica/ Experimenta/ Designs for Engineers and Scientists, 2nd ed.. Van Nostrand Reinhold, New York, 1989. "This book is for engineers and scientists with Httie or no statistical background who want to learn to design efficient experiments and to analyze data correctiy. .. The emphasis is on practical methods, rather than on statistical theory." The discussion is quite detailed in some areas, eg, experimental designs based on Hadamard matrices, and scanty in others. 

As a practical method, designers have employed other methods such as / -pentane conversion as a key component, kinetic severity factor (31), or molecular collision parameter (32) to represent severity. Alternatively, molecular weight of the complete product distribution has been used to define conversion (A) for Hquid feeds. 

Side-chain lithiation with lithium diisopropylamide and subsequent alkylation or acylation is a practical method for the preparation of various alkyl-, alkenyl- and acyl-methyl-pyridazines 78CPB2428, 78CPB3633, 79CPB916) (Scheme 47). 

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