GEM

The term capillarity is used to designate the physical process by which a liquid penetrates into a single capillary tube or in multiple pores in a porous material. A pore does not necessarily has to be a closed tube the space between three or even two parallel rods or fibers is also considered as a pore indeed, this is the kind of pore normally found in fibrous materials. So, it is not the cross-sectional shape but the size which determines the definition of a capillary tube its radius must be smaller than the capillary length which is the length scale above which gravitational 

Consider a vertical plate partially immersed in a wetting liquid bath in Fig. 8. The liquid spreads on the solid surface and climbs through the vertical wall. The interface curves and a pressure difference which obeys Laplace law is built up across it. It can be shown that the maximum height of the liquid is h — — y/2.K when the 

This result is obtained by balancing pressures in points M and N of Fig. 8. In equilibrium the pressure in N is equal to the pressure in the outer fluid, Pq, and the pressure in M is pgh + AP + Pq where AP is the Laplace pressure difference. The order of magnitude can be obtained by assuming that the meniscus mean radius of curvature is of the order of the pressure difference is AP = — and h = 

If two vertical plates are now immersed in a wetting liquid bath, the distance d between them will define the rise height. If d is larger than the menisci do not interact and the situation is as depicted in Fig. 9(a) the curvature in point N is still zero, its pressure is Pq and the rise height is the same as before. 

Differently, if d is smaller than the interface at N will have a curvature with radius R d/2 (see Fig. 9(b)). The pressure at that point will initially be smaller than Po and in consequence, smaller than the pressure in point M. Equilibrium is only achieved by some extra pressure in point N, so, the meniscus should climb a certain height H, called Jurin s length, until the pressures in both points become equal. At that state, H must satisfy pgH = and increases as the distance between plates decreases. In fact, if k, the capillary rise between the plates is much larger than 

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This mineral, which in its transparent varieties is a most beautiful and costly gem, has been known from early times. 

A treasure-trove of over 12,000 new gems and old favourites, from Aesop and Matthew Arnold to Xenophon and Zola. 

All static studies at pressures beyond 25 GPa are done with diamond-anvil cells conceived independently by Jamieson [32] and by Weir etal [33]. In these variants of Bridgman s design, the anvils are single-crystal gem-quality diamonds, the hardest known material, truncated with small flat faces (culets) usually less than 0.5 nun in diameter. Diamond anvils with 50 pm diameter or smaller culets can generate pressures to about 500 GPa, the highest static laboratory pressures equivalent to the pressure at the centre of the Earth. 

Almost every modem spectroscopic approach can be used to study matter at high pressures. Early experiments include NMR [ ], ESR [ ] vibrational infrared [33] and Raman [ ] electronic absorption, reflection and emission [23, 24 and 25, 70] x-ray absorption [Tf] and scattering [72], Mossbauer [73] and gems analysis of products recovered from high-pressure photochemical reactions [74]. The literature contains too many studies to do justice to these fields by describing particular examples in detail, and only some general mles, appropriate to many situations, are given. 

Element Atomic number Outer electrons Density (gem ) m.p. (K) h.p. IK) Hardness 1 Brineii)... 

Fig. 7.10 Velocity autocorrelation functions for liquid argon at densities of l.i% gem and0.863gcm...

The most general synthetic route to ketones uses the reaction of carboxylic acids (or their derivatives) or nitriles with organometallic compounds (M.J. Jorgenson, 1970). Lithium car-boxylates react with organolithium compounds to give stable gem-diolates, which are decom-... 

The majority of preparative methods which have been used for obtaining cyclopropane derivatives involve carbene addition to an olefmic bond, if acetylenes are used in the reaction, cyclopropenes are obtained. Heteroatom-substituted or vinyl cydopropanes come from alkenyl bromides or enol acetates (A. de Meijere, 1979 E. J. Corey, 1975 B E. Wenkert, 1970 A). The carbenes needed for cyclopropane syntheses can be obtained in situ by a-elimination of hydrogen halides with strong bases (R. Kdstcr, 1971 E.J. Corey, 1975 B), by copper catalyzed decomposition of diazo compounds (E. Wenkert, 1970 A S.D. Burke, 1979 N.J. Turro, 1966), or by reductive elimination of iodine from gem-diiodides (J. Nishimura, 1969 D. Wen-disch, 1971 J.M. Denis, 1972 H.E. Simmons, 1973 C. Girard, 1974),... 

The benzoic acid derivative 457 is formed by the carbonylation of iodoben-zene in aqueous DMF (1 1) without using a phosphine ligand at room temperature and 1 atm[311]. As optimum conditions for the technical synthesis of the anthranilic acid derivative 458, it has been found that A-acetyl protection, which has a chelating effect, is important[312]. Phase-transfer catalysis is combined with the Pd-catalyzed carbonylation of halides[3l3]. Carbonylation of 1,1-dibromoalkenes in the presence of a phase-transfer catalyst gives the gem-inal dicarboxylic acid 459. Use of a polar solvent is important[314]. Interestingly, addition of trimethylsilyl chloride (2 equiv.) increased yield of the lactone 460 remarkabiy[3l5]. Formate esters as a CO source and NaOR are used for the carbonylation of aryl iodides under a nitrogen atmosphere without using CO[316]. Chlorobenzene coordinated by Cr(CO)j is carbonylated with ethyl formate[3l7]. 

The preparation of these [4-hydroxy-THISs, (1), X = O] by cydization of a-carboxy-N-arylthiobenzimides (5) by treatment with acetic anhydride and triethylamine has been investigated in detail, and the structure has been revised for the compound previously described as 2.3-diphenyl-4-hydroxythiazolium hydroxide inner salt (1, X = 0, R = R = Ph, R = H) (Scheme 5) (3, 10). 4-Hydroxy-THlSs also arise by condensation of gem-dicyanoepoxides with thioamides (Scheme 6) (8). 

Many of the most interesting and useful reactions of aldehydes and ketones involve trans formation of the initial product of nucleophilic addition to some other substance under the reaction conditions An example is the reaction of aldehydes with alcohols under con ditions of acid catalysis The expected product of nucleophilic addition of the alcohol to the carbonyl group is called a hemiacetal The product actually isolated however cor responds to reaction of one mole of the aldehyde with two moles of alcohol to give gem mal diethers known as acetals... 

Step 1 The peroxy acid adds to the carbonyl group of the ketone This step is a nucleophilic addition analogous to gem diol and hemiacetal formation... 

Consider a flow of argon of 0.5 L/min through an annular space of 4 x 10" cm between two concentric capillary tubes at normal ambient temperatures. If the density of argon is taken to be 1.2 X 10 gem then,... 

Diabetes mellitus Diabetic retinopathy Diabetic urine Diabmese gem-Diacetates... 

Handbook 44 defines five accuracy classes for scales in terms of the value of the scale division and the number of divisions. Class I appHes to precision laboratory weighing. Class II appHes to laboratory weighing (precious metals, gems, and grain test scales). Class III appHes to the majority of industrial and retail scales, and to all scales not specified in the other categories. Class III L appHes to vehicle, Hvestock, railway, crane, and hopper scales. Class nil appHes to portable scales used for highway weight enforcement. 

Corundum. Comndum [1302-75-5] (see Aluminum compounds) is a naturally occurring massive crystalline mineral composed of aluminum oxide. It is an impure form of the gems mby and sapphke. Prior to 1900 comndum was an important abrasive for the production of grinding wheels. Today it is mainly employed as a loose abrasive for grinding and polishing optical lenses. Almost all the world s supply of comndum now comes from Africa, primarily from Zimbabwe. 

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