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separation of molecules according to shape. Maczek and Phillips in 1960 (50) used as a stationary liq uid phase tri-o-thymotide dis solved in tritolyl phosphate. The tri-o-thymotide is known to form inclusion compounds with molecules of restricted width. Relative to a non-inclusion compound forming liquid phase, the authors found straight chain molecules selectively retarded over branched chain mole cules. I t may also be noted that some success in the separation of molecules according to shape has been accomplished in gas-solid chromatography (51). Presumably in the adsorption process a molecule must "sit down" on a two-dimen sional surface. A new type of liquid phase has recently been introduced to sep arate molecules in part according to shape. I t is the characteristic of certain types of elongated, rela tively polar molecules to exhibit an isotropic behavior when first melted. Order is exhibited in the anisotropic state, and hence such systems are called liquid crystals (52), to sig nify behavior intermediate between crystalline solids and normal liq uids. Upon further heating to higher temperatures, these liquids then assume the isotropic behavior of ordinary liquids. An example of such a compound is 4,4'-di-n-heptyloxyazoxybenzene
improved for longer burner life BETHLEHEM BENCH BURNER Improvements in the design and construction of this general-purpose gas-oxygen burner offer you these distinct advantages— longer life of the burner head, by increasing the cooling area through the use of more fins and an aluminum heat sink surrounding the gear rack, for more effec tive conductivity. maintains high rate of heat dissipation, by the use of chrome plated brass body and fins. improved fuel control as a result of cooler operating needle valves. faster, easier settings with angle adjustment knobs on both sides of burner.
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BETHLEHEM APPARATUS COMPANY, INC. HELLERTOWN, PA. Circle No. 18 on Readers' Service Card
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smectic-range 75°—95° C, nematic range 95°-127° C. As seen in this example, more than one mesophase is possible for a given compound. In the nematic phase, mutual attrac tion tends to orient the polar mole cules with their long axes parallel to one another. The smectic phase, occurring at a lower temperature than the nematic phase, is the more ordered mesophase, because there is constraint not only in parallel, but also a layer structure forms. A third mesophase which sometimes occurs for other liquid crystal sys tems is the cholesteric phase, a structure similar to the smectic phase, except that rotation in the plane of the layers is possible. As noted above, it is possible for sub stances to exhibit one or more of
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HERE'S OUR OSMOMETER LINE, TODAY... What more can you expect from a leader? A l l o f these outilanding oimometer· are available from Advanced Instruments, the company which first in troduced a freezing point osmometer back in 1 9 5 5 . W e set out to become t h e l e a d e r s in osmometry . . . a n d , if sales a r e a n y i n d i c a t i o n , w e h a v e suc ceeded. A f e w of the con tributions w e have made to
t h e science o f o s m o m e t r y are: The first schools of os mometry, the first modular osmometer, the first thermo electric refrigerator, the first portable model, and the first Hot Line @ service system. N o w , in addition to the improved 1907 version of our original model w e also have: a new air-cooled refrigerator with the longest life guaran
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tee in the field, a Hi-Pre cision Research Osmometer, and a Nanoliter Osmometer for samples less than one millimicroliter. W e a r e a d d i n g others to our growing line. To us LEADERSHIP means continuing programs of prod uct improvement, outstanding service, a n d fast delivery. W e think this is the w a y a leader should act. Don't you?
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