Small Crystals

When the volume of mother liquor is large and the amount of crystals small, the apparatus of Fig. II, 32, 1 may be used. The large pear-shaped receiver is supported on a metal ring attached to a stand. When the receiver is about two-thirds fuU, atmospheric pressure is restored by suitably rotating the three-way stopcock the filtrate may then be removed by opening the tap at the lower end. The apparatus is again exhausted and the filtration continued. 

Zone refining is one of a class of techniques known as fractional solidification in which a separation is brought about by crystallization of a melt without solvent being added (see also Crystallization) (1 8). SoHd—Hquid phase equiUbria are utilized, but the phenomena are much more complex than in separation processes utilizing vapor—Hquid equiHbria. In most of the fractional-solidification techniques described in the article on crystallization, small separate crystals are formed rapidly in a relatively isothermal melt. In zone refining, on the other hand, a massive soHd is formed slowly and a sizable temperature gradient is imposed at the soHd—Hquid interface. 

Since there are so few direct packing interactions between protein molecules in a crystal, small changes in, for example, the pH of the solution can cause the molecules to pack in different ways to produce different crystal forms. The structures of some protein molecules such as lysozyme and myoglobin have been determined in different crystal forms and found to be essentially similar, except for a few side chains involved in packing interactions. Because they are so few, these interactions between protein molecules in a crystal do not change the overall structure of the protein. However,... 

Spray drying can be used to crystallize small particles. Due to the short residence time amorphous material may even be obtained. 

MATERIALS Pocket watch with plastic crystal, small screw, electric wire, battery, electric blasting cap. 

Dobutamine hydrochloride generally crystallizes in a random manner usually from an oil (1). This results in a nondescript crystalline formation. In only few cases does the drug exhibit any crystalline habit of interest. Upon careful and patient crystallization small thin plates and/ or small needles are formed. 

The distillate is at once extracted with ether and the extract, after having been separated from the water, is heated on the water bath until most of the ether has distilled. The residue, which contains unchanged phenol as well as the salicylaldehyde, is now vigorously shaken in a small glass-stoppered bottle with two volumes of concentrated commercial sodium bisulphite solution. A thick paste of the bisulphite compound of the aldehyde is formed. After this paste has stood for from half an hour to one hour the bisulphite compound is separated by filtration at the pump, pressed well on the filter funnel, and washed several times, first with alcohol and finally with ether, until completely free from adherent phenol. The crystals (small plates, iridescent like mother-of-pearl) are then decomposed with dilute sulphuric acid in a small round-bottomed flask whi( h is fitted with an air condenser and gently warmed on the water bath. After the liquid thus produced has cooled, the aldehyde which separates is extracted with ether and the ethereal solution is dried with anhydrous sodium sulphate. The pure aldehyde which remains when the ether is evaporated distils at 196°. The yield amounts to 10-12 g. 

Fig. 5-8.—The structure of the PdCls crystal. Small circles represent palladium atouws and large circles chlorine atoms.

Crystallization—Small crystals (0.05 X 0.1 X 0.1 mm) were obtained using the hanging drop/vapor equilibrium method (18). 10-pl drops of 2.5 mg/ml ALBP in 0.05 M Tris, 60% ammonium sulfate, 1 mM EDTA, 1 mM dithiothreitol, 0.05% sodium azide buffer with a pH of 7.0 (crystallization buffer) were suspended over wells containing the same buffer with varying concentrations of ammonium sulfate, from 75 to 85% saturation. Small, well shaped crystals were formed within a month at an 80% saturation and 19 crystallization buffer over a well containing the same buffer. Large crystals,... 

As the name implies, this technique uses both X-rays and crystals. Small protein crystals are exposed to a beam of X-rays, whose wavelength is approximately the size of an atom. The X-rays are diffracted by the atoms in the crystal and the diffraction pattern is recorded. While there will be trillions of individual protein molecules in the crystal, this pattern can be analyzed by a computer to reveal the three-dimensional coordinates of key atoms in a stylized average protein. ... 

Zircon is native zirconium silicate (ZrSi04) that exhibits beautiful transparent crystals and a Mohs hardness of 7.5. The tetragonal crystals are usually brownish yellow in color. Also known as jargon or jargoon, zircon is a stable and durable silicate crystal. Small crystals of zircon are among the oldest mineral grains ever found on Earth. 

In the saturator process (see Figure 12.7), neutralization and crystallization are carried out in the same vessel. The sulfuric acid is delivered to the suction side and the ammonia to the pressure side of the forced circulation pump. Crystallization of the metastable solution gives particle sizes generally between 0.5 and 3 mm. The salt is continuously discharged at the lower end of the saturator. The salt is separated in centrifuges, dried, and cooled. The mother liquor is returned to the saturator. Impurities in the sulfuric acid can adversely affect crystallization. Small quantities of phosphoric acid, urea, or inorganic salts are added to promote crystal growth295. 

White or nearly white crystals, small granules, flakes, or powder. M.p. about 109°. The technical product is a waxy solid of indefinite melting point. 

Until very recently, o-ribose has been such a rare and expensive sugar that the addition of hydrocyanic acid to it and the conversion of the mixed nitriles to hexonic acids have been described only a few times. From the combined experiences of Levene and Jacobs, of Phelps and Bates, and of Steiger and Reichstein, it appears that n-altronic and D-allonic acids are produced in about equal amounts, in a total yield of 70-80% of the theoretical. To separate the two acids, they were converted to calcium salts, and most of the calcium n-altronate was recovered as the characteristic hydrate containing three and one-half molecules of water of crystallization. The mother liquor was freed from calcium ions by the addition of oxalic acid, and evaporated to a sirup from which the D-allono-7-lactone crystallized. Small additional amounts of the two compounds were obtained by further treatment of the mother liquors. 

Partial crystallization, small crystal sizes, impurity and copolymer content, and straining of molecules from the random coil conformation are the major effects to be considered. The changes of heats of transition and temperatures of transition and their use to characterize the non-equilibrium state have been given an initial critical survey (2) ... 

Impinging jets, routinely used in the plastics industry, have been used to crystallize small particles with a narrow particle size distribution [27,28].The impinging jet crystallizer is a cylindrical chamber with two spray nozzles that enter from opposite sides of the chamber. A solution of the material to be crystallized is fed into one nozzle, and the agent to induce crystallization is fed into the other nozzle. The smaller the nozzle apertures, the faster the velocity of the solutions into the chamber, and the faster the two streams mix and reach a uniform environment. In this manner a stream of finasteride (Figure 11.10) in AcOH and water was fed into one nozzle, and a stream of water (the crystallizing agent) was fed into the other nozzle. Crystallized finasteride had an average particle size of 10-15 pun. 

Properties Large, transparent crystals, small needles, or granular powder. D 1.464 (crystals), mp 33C (liquefies). Loses water of hydration at 100C. Energy storage capacity is more than seven times that of water. Soluble in water and glycerol insoluble in alcohol solutions neutral to litmus. Nonflammable. 

Ideally, a Bragg diffraction peak is a line without width as shown in Figure 2.19b. In reality, diffraction from a crystal specimen produces a peak with a certain width as shown in Figure 2.19a. The peak width can result from instrumental factors and the size effect of the crystals. Small crystals cause the peak to be widened due to incompletely destructive interference. This phenomenon can be understood by examining the case illustrated in Figure 2.20. 

The inorganic component was largely halite (NaCl), sea salt. Among the NaCl crystals, small objects of apatite were identified as the scales of small fish (Fig. 9.2). The organic compounds were monocarboxylic acids, a,(n-dicarboxylic acids, and... 

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