Wynne (1961) reported that the melting point of a zone-refined sample was 114.8 C, which may be compared with literature values of 113~114 C.
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Beynon & Saunders (1960) showed that after thirty-three zone passes the concentration of amino-dimethylanthraquinone at the top of the column was 0.5 per cent and that of diamino-methylanthraquinone was 0.20 per cent. Initially the concentration of both impurities was 0.31 per cent.
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Wolf (1957) reported that tetracene can be removed from anthracene by zone refining.
Joncich & Bailey (1960) found that Eastman White Label anthracene after zone refining showed a very sharp peak in the differential-thermal-analysis curve, indicating a considerable improvement in the specimen.
Light & Co (1959) produce zone-refined batches of 1 to 5 lb weight which are used to grow single crystals for scintillators.
Wynne (1961) reported that the melting point of a zone-refined sample was 219.10C (cf. literature values of 216~2l8 C) and that analysis of the refined material gave: C, 94.46; H, 5.78. CaIc. for C14H10: C, 94.34; H, 5.1 6.
Hoesterey (1962) reported that single crystals were grown under helium by the Bridgman method from a zone-refined specimen. The starting material was either Eastman Organic Chemical X 480 or hydrocarbon synthesized by the cyclization of o-benzoyl-benzoic acid followed by a two-stage reduction.
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Wynne (1961) reported that the melting point of a zone-refined sample was 288.90 C and compared this with literature values of 286~288 C.
Beynon & Saunders (1960) reported that anthraquinone can be purified satisfactorily by zone melting.
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Rock (1956) treated benzene in an apparatus. The purities of the original charge and of samples after treatment were determined by melting-point measurements using a Beckmann thermometer. When technical benzene containing approximately 0.2 mole per cent impurity was refined, a fraction containing less then 0.0008 mole per cent impurity was obtained.
Sue, Pauly & Nouaille (1958) reported that a sample of benzene containing .002 fraction of acetic acid contained .001 fraction of the acid after ten zone passes. The concentration of thiophene in a sample of benzene was reduced from .001 to less than .0001 by fifteen zone passes.
Schildknecht & Mannl (1957) reported that the zone refining of a crude benzene produced a fraction at the end of the sample that was liquid when the rest of the specimen was solid. It was claimed that almost 90 per cent of the benzene was free from thiophene, but unfortunately the limits of the sensitivity of the test were not given. Removal of the portion enriched with thiophen during treatment assisted purification. The work of Hudson, Hillig & Strong (1959) illustrates the care that must be taken in the manipulation of samples of the highest purity. Phillips Research Grade Benzene, initially 99.93 per cent pure, was further purified by vacuum sublimation and zone refining. Purification of the sample was carried out in a vacuum system which included two cold traps to allow successive sublimation in a degassing process, a vertical zone-refining tube and a manifold with capillaries for containing specimens. The zone-melting tube was cooled by pumping alcohol at 0 C round a jacket. Four resistance heaters in series were used to produce molten zones. The purification apparatus was evacuated before use, flamed until the residual pressure was less than 0.01 micron and then filled with dry nitrogen. The benzene, introduced through a silica-gel filter, was then frozen by means of liquid nitrogen. The opening through which the hydrocarbon had been admitted was sealed off and the system was pumped until the residual pressure was below 1 micron. Dissolved gases were removed by four sublimations between the two cold traps; the first two sublimations were made with the aid of liquid nitrogen and the other two by the use of a carbon dioxide-acetone freezing mixture. After degassing the benzene was melted and condensed into the zone-melting tube where it was again frozen. After each zone pass all residual vapor was frozen into one of the traps by means of liquid nitrogen and the condensed vapor was isolated from the rest of the system. The top inch of solid benzene was melted and a sample condensed into one of the capillaries. The specimen was frozen in liquid nitrogen and all the residual benzene was condensed into the other trap by use of the same coolant. The sample tube was then sealed off. In this manner, pyrolysis of benzene vapor during the sealing of the glass was avoided. Benzene samples with a triple point of 5.527 +/- 0.001C Were obtained after three or four zone passes; the degassed starting material had a triple point of 5.523 +/- 0.0020 C. Additional zone melting effected no further improvement.
Beynon & Saunders (1960) also reported successful zone refining of benzene.
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Handley & Herington (1956) reported that the melting point of a specimen after treatment was 121-121.5 0C; before treatment it was 119.5-121.5 0C.
Joncich & Bailey (1960) studied the removal of carbon-14-labelled naphthalene from benzoic acid. An initial concentration slightly in excess of 0.1 mg of naphthalene per gram of benzoic acid was used, and it was found that after eighteen zone passes the concentration was reduced to below the detectable limit of 0.0001 mg of naphthalene per gram of benzoic acid.
Wynne (1961) reported a melting point of 124 C for the zone-refined acid (literature values 122~123 C) and the analysis of that zone-refined material gave: C, 68.82; H, 4.85. CaIc. for C7H602: C, 68.84; H, 4.95.
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The zone refining of this material was studied by Schildknecht (1961) who presented a graph showing that after three zone passes at 3 mm/h through material with melting point 43.2~45 C, the maximum melting point of a portion of the specimen was 47.5 C. Eighteen zone passes through similar material gave colorless crystals with melting point 48.00 C and there was a large flat plateau in the curve of melting temperature plotted against distance along bar.
Schildknecht & Vetter (1961) reported the satisfactory purification of this compound on the micro-scale.
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Wynn (1961) prepared a sample with a melting point of 167.3 C (cf. literature values 165~167 C) by zone refining.
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A specimen of this compound containing a fraction of .02 of o-bromotoluene was shown by the use of 82Br-labelled o-bromotoluene to contain .0002 fraction of the ortho-compound at the beginning of the sample after the passage of nine zones (Sue, Pauly & Nouaille, 1958).
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Hesse & Schildknecht (1956) prepared a sample with a freezing point of 50 C by zone melting a specimen with freezing point 48.50 C.
Beynon & Saunders (1960) also reported the successful purification of this compound.
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A sample with melting point 181.20 C (cf. literature values 178~180 C) was prepared by zone refining (Wynne, 1961).
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Sorenson (1959) found that a rather slow speed of zone movement and many zone passes were required to purify this compound. After eighteen passes (2 cm/h) a sample of technical 4-chloro-o-cresol (m.p. 40.90 C) remained rather impure, the first fraction having a melting point of only 46.20 C. In a further experiment, however, fifty zone passes gave a pure product with melting point 48.70 C in the first 25 per cent of the column.
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Beynon & Saunders (1960) found that after two zone passes the following impurities were concentrated and were detectable, C6H3NH2CI2, C~H3NO2Cl2, C6H4NH2Cl and C6H2NH2NO2CI2. Further refinement was not attempted because concentration of explosive polynitrocompounds might have occurred.
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Handley & Herington (1956) found that a sample with a melting point of 250~250.5 C could be produced by zone melting a commercial sample with melting point 248-249.5 C.
Wolf (1957) reports that an unidentified impurity was removed from this hydrocarbon by zone melting.
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A zone-melting apparatus erected in a refrigerator has been used for zone refining this compound (Chemistry Research, 1957).
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Schildknecht & Hopf (1961) studied the purification of a material that was pale red in color but was well crystallized and had a melting point of 62.30 C. A specimen 45 cm long was treated by twenty-five passes of a zone 2 to 3 cm long, moving at the rate of 0.2 cm/h. Specimens taken at points 7.5 and 12.5 cm. from the beginning had the highest melting points, 62.60C. Specimens at points 25, 50, 150 and 25 cm from the beginning melted at 62.5 C, whilst at 27.5 cm the melting point was 62.3 0C and a specimen 31.0 cm from the beginning melted at 62.2 C.
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Colorless crystalline samples of this compound were obtained by zone refining a specimen in nitrogen (Report of the National Chemical Laboratory, 1958).
Schildknecht & Vetter (1961) have reported the successful purification of this phenol on the micro-scale.
Schildknecht (1961) has studied the zone refining of a mixture containing 88 per cent of 3,5-dimethylphenol and 12 per cent of 3,4-dimethylphenol. A sample of the more abundant phenol was separated in a yield 97 per cent of that expected from the phase diagram, but the eutectic did not separate in a pure form.
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This material was successfully purified by zone refining a specimen in dry nitrogen (National Chemical Laboratory Report, 1958).
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Schildknecht (1961) observed pale yellow transparent crystals 8 cm long at the beginning of a tube after fourteen zone passes. The end of the tube contained a brown mass of fine crystals. Infra-red analysis showed that these contained o- and p-nitrotoluene and trinitrotoluene as impurities.
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According to an unsigned report [Chem. Fngr (1959), April 20, 66, 80] water and other impurities have been removed from this heterocyclic compound by zone refining to yield a solvent of spectroscopic purity [see also Chem. Engng (1959) March 9, p.74].
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Mackle & O'Hare (1961 a) purified a sample of B.D.H. Laboratory Reagent Grade material by zone melting several times. Another sample was recrystallized eight times from pure ether. The melting point of both specimens was 124 C and the normal boiling point was 378 C, with appreciable decomposition. Analysis gave: C, 66.3; H, 4.66 compared with theoretical: C, 66.0; H, 4.62.
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Mackle & O'Hare (1961 b) prepared this compound by oxidizing diphenyl sulphide in acetic acid with one equivalent of 30 per cent hydrogen peroxide added slowly under reflux. The reaction product was evaporated to dryness under vacuum and the solid was purified by zone melting.
Analysis of the purified compound (m.p. 70.20 C) gave: C, 71.1; H, 4.92, compared with theoretical C, 7l.3; H, 4.98.
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Izergin (1958) treated ethanol in a boat made of polytetrafluro-ethylene. The alcohol was frozen by means of liquid air and the zone length was controlled by regulation of the power of the electrical heater. The alcohol initially contained 4 per cent of water, and after four zone treatments the water content was 1 per cent.
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Purification of this compound in dry nitrogen was achieved by zone melting (National Chemical Laboratory Report, 1958).
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Hesse & Schildknecht (1956) separated the alcohols C16H33OH and C18H37OH in a micro-zone-refining apparatus having three heaters and interjacent coolers. See also Hexacosanol.
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Wynne (1961) prepared a sample with m.p. 187 C by zone melting.
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McClelland, Jnr. (Pfann, 1958) showed that after fifteen zone passes through a hollow cylindrical charge of a capacitor impregnator known as Hallowax 1001, the material, a chlorinated naphthalene, exhibited variations in melting point, melting range and dielectric constant along the sample.
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Schildknecht (1961) reported a study of a mixture of 80 per cent hexacosanol (C26H53OH) and 20 per cent eicosanol (C20H41OH). These compounds form mixed crystals; separation by zone melting was followed by melting-point measurements. Segregation was found to be slow and difficult; but finally a specimen of hexacosanol with melting point 80.30 C was isolated.
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Schildknecht (1961) reported the separation of a sample of hexacosyl hexacosanate by the zone refining of an insect wax. The specimen was identified by infrared spectroscopy.
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This compound could not be purified by zone melting because the sample decomposed at a temperature only slightly higher than the melting point (Hubbard, Frow & Waddington, 1961).
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A sample of this material was zone refined by the Bureau of Mines, Laramie, Wyo., U.S.A., to 99.9 per cent purity (Ball, Helm & Ferrin, 1958, 1959).
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Wynne (1961) reported that a zone-refined sample melted at 270.80 C.
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A very pure sample of this insecticide, free from musty odor and of melting point 112.84 C, was prepared by zone refining. This melting point should be compared with the most acceptable figure (112.86 C) hitherto published (Report of the National Chemical Laboratory, 1960).
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The most abundant impurity (chloromethoxybenzanthrone) in a sample of this compound treated in a 24 in column by Beynon & Saunders (1960), had a partition coefficient greater than unity. The rate of movement of the impurity was therefore very slow. Experiments showed that it was helpful to use a much longer molten zone (e.g. 2 in) than usual so that the impurity, which could not move more than one zone length per pass, could move much further each time. The zone length was gradually reduced to a normal value of about 1 in. The original charge contained 2.0 per cent of chloro-methoxybenzanthrone, 0.12 per cent of dimethoxybenzanthrone and 0.66 per cent of chlorobenzanthrone. After forty-eight zone passes the material at the top of the column contained 3.4, 0.04 and 0.12 per cent of these impurities and the material at the bottom of the column contained 0.70, 0.17 and 0.78 per cent of the same compounds.
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This compound was zone refined to a purity of 99.9 per cent by workers at the Bureau of Mines, Laramie, Wyo., U.S.A. (Ball, Helm & Ferrin, 1958, 1959).
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Beynon & Saunders (1960) reported that this compound, which is notorious for its overpowering odor of feces, completely lost all its objectionable smell when zone refined. Presumably the odor is due to a small amount of intensely odoriferous contaminant.
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This hydrocarbon, m.p. -30.80 C, was treated in a zone-refining apparatus enclosed in a space cooled with solid carbon dioxide (Chemistry Research, 1957).
Wolf (1957) reported that anthracene can be removed from this compound by zone melting.
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Workers at the Bureau of Mines, Laramie, Wyo., U.S.A., refined samples of this base to a purity of 99.9 per cent (Ball, Helm and Ferrin, 1958, 1959).
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Wolf and Deutsch (1954) showed that two zone passes at the rate of 1 cm/h through naphthalene containing 0.1 per cent of anthracene reduced the concentration of anthracene to less than one part per million. The fluorescence spectrum was used to measure the anthracene concentration. It was suggested that in any further attempt at purification the zone refining should be carried out in vacuum or under nitrogen.
Handley (1955) and Herington, Handley & Cook (1956) showed, by studying the fluorescence under ultra-violet light, that seven zone passes reduced the anthracene concentration in a synthetic mixture of anthracene and naphthalene from 0.2 to 0.00002 per cent.
Beynon & Saunders (1960) demonstrated that it is possible to purify crude naphthalene. After nine zone passes through a sample with a melting point of 73.50 C, they obtained a specimen with melting point 80.20 C from the top portion of the sample.
Wynne (1961) reported obtaining by zone refining a specimen of naphthalene with melting point 82 C. Analysis of the purified material gave: C, 93.44; H, 6.23; CaIc. for C10H8, C, 93.71;H, 6.29.
Schildknecht (1961) reported the successful purification of this hydrocarbon.
Fryer (1962) has published a photograph of a zone-melting apparatus used in the laboratories of Hopkins and Williams Ltd, to prepare ultra-pure naphthalene.
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Colourless crystalline samples of this compound were obtained by the zone refining of a specimen in nitrogen (Report of the National Chemical Laboratory, 1958).
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This aliphatic hydrocarbon (melting point approximately - 170 C) has been zone melted in an apparatus enclosed in a space cooled by solid carbon dioxide (Chemistry Research, 1957).
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The trace impurities C6H4NO2CH3 and C6H2(CH3)3NH2 were detected after two zone passes but further treatment was not carried out for fear of concentrating explosive poly-nitro impurities (Beynon & Saunders, 1960).
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Brown & Buck (1961) zone refined a specimen of this compound before measuring the infra-red absorption spectrum.
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Joncich & Bailey (1960) reported that a sample of Eastman White Label phenanthrene purified by the method of Feldman, Pantages & Orchin (1951) showed an appreciable increase in purity after zone refining.
Beynon & Saunders (1960) also reported the successful purification of phenanthrene.
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Aftergut & Brown (1961) studied the electrical resistance of a zone-refined sample of this compound that had previously been purified by chromatography on alumina. As the zone-refined material had a higher resistivity and a lower energy gap than material purified only by chromatography or by sublimation it was considered to be purer than other specimens.
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Sorenson (1959) made an extensive study of the conditions necessary for the removal of p-nitrophenol from phenol by zone refining. With increasing impurity content it became relatively more difficult to purify the phenol.
Wolf (1957), Schildknecht (1961) and Schildknecht & Vetter (1961) have reported successful purification of this compound.
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Brown & Aftergut (1962) measured the resistivity of crystals of phenothiazine that had been chromatographed, sublimed, zone refined and resublimed. Specimens that had been sublimed only did not show ohmic resistivity, and this behaviour was attributed to the presence of impurities. Zone-refined material exhibited ohmic resistivity with an energy gap of I 6 eV and this was considered to be a good value.
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Handley & Herington (1956) reported a melting point of 152 C for a zone-refined specimen, a value which is to be compared with a melting range of 150-152 C for the starting material.
Wolf (1957), and also Beynon & Saunders (1960), reported purification of this aromatic hydrocarbon.
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Wynne (1961) compared his observed value of 161.90 C for the melting point of a zone-refined sample with literature values of 159-161 C.
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Nozaki, Tamura, Harada & Saito (1960) prepared a sample of sexiphenyl by a four-stage synthesis from p-terphenyl. The material obtained by sublimation from the crude product was yellow and contained copper and iodine. Neutron-activation analysis of products obtained in a series of zone-refining and vacuum-sublimation operations showed that iodine-containing compounds could be removed. It was considered that these compounds were probably decomposed during zone refining. However, too high a temperature decomposed sexiphenyl itself, especially when the purity was low. Temperatures between 440~ C and 450~ C were therefore used in the purification. After vacuum sublimation and recrystallization from tetralin, the carbon and hydrogen contents of the product were correct. Nevertheless the melting points rose with repeated alternate zone refining and vacuum sublimation until it reached a constant value after four repetitions of the cycle followed by a recrystallization from tetralin and a vacuum sublimation. The final sample contained less than 0.04 p.p.m. of iodine. The material was used as a scintillator and the photo-multiplier pulse obtained was higher than that from anthracene.
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Wolf (1957) reported the removal of an unidentified impurity from this acid by zone refining.
Wynne (1961) reported a melting point of 70.1 0C for a zone-refined specimen and compared it with values of 68~69.50 C from the literature.
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Hesse & Schildknecht (1956) prepared a specimen with a melting point of 58.50 C from material with melting point 57.5 C.
Schildknecht (1957) treated 180 mg of a sample of stearyl alcohol and found that after twenty-four zone passes the melting point of the material at the front of the specimen was 60.30 C and at the back was 55.90 C. The pure alcohol was in the middle portion and melted at 58.40 C.
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Light & Co (1959) treat batches of 1 to 5 lb of this hydrocarbon by zone refining as a step in the manufacture of single crystals for scintillators.
Schildknecht & Hopf (1961) zone melted a 39 g sample of stilbene with a melting point of 119-1240C in a tube 2 cm in diameter and 46 cm long. After a 2 cm long zone had been passed twelve times at the rate of 0.3 cm/h a specimen 1 cm from the beginning of the tube had a melting point of 125.4 0C. Samples between the third and eighteenth centimeters had a melting point of 125 C and a specimen near the far end had a melting point of 80 C.
Schildknecht (1961) and Schildknecht & Vetter (1961) also reported successful purification of stilbene by zone treatment.
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Wynne (1961) reported a melting point of 187.8 C for a zone-refined specimen (literature values 185~187 C). Analysis of the refined material gave: C, 40.98; H, 5.07. CaIc. for C4H604: C, 40.68; H, 5.2.
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Wynne (1961) reported a melting point of 165.2 C for a treated specimen literature values cited 164-165 C).
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Light & Co (1959) zone refined this compound as a step in the preparation of single crystals.
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Crude p-tolyl-methylsulphone was zone melted by Mackle & O'Hare (1961 a) to give a product with a melting point of 83.6~84.10 C (literature values 83~87.50 C), and a normal boiling point of 316 + 10 C. Analysis gave: C, 56.5; H, 5.90 compared with theoretical: C, 56.4; H, 5.92.
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Mackle & O'Hare (1961 a) reported that a sample from Eastman Kodak Ltd was zone refined four times and another specimen recrystallized eight times from diethyl ether was fused several times. Both batches had a melting point of 158~159 C (lit. 158 C); the normal boiling point was 403+ 10C and analysis gave: C, 68.4; H, 5.71 compared with theoretical C, 68.3; H, 5.73.
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Thirty zone passes were found by Beynon & Saunders (1960) to produce segregation of impurities, one of which, namely 1,4,5,8-tetrachloroanthraquinone, moved in the opposite direction to the zone. The color of the molten zone was found to give a sensitive indication of the presence of impurities.
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A melting point of 84.0 C for a zone-refined specimen was reported by Wynne (1961); literature values cited were 82-83.50C. Analysis of the sample gave C, 63.16; H, 5.20.
Theoretical: C, 63.15; H, 5.30.
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Various types of wax have been treated; it is reported [Chem. Engr (1959), April 20, 66, 80] that on the industrial scale low-melting waxes are improved by alternatively heating and cooling closely spaced pipes so as to cause a number of zones to pass through a bed of material over the pipes.
Hesse & Schildknecht (1956) used a micro-zone~melting apparatus to treat a wax obtained from the larva of the butterfly Attacus edwardsii and found that three zone passes were more effective than recrystallization from solvents.
Schildknecht (1961) zone refined the wax of the insect Etiopeltisfestucae and hence showed the presence of hexacosyl hexacosanate.
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This hydrocarbon, the approximate melting point of which is - 29 C, was treated in a zone-refining apparatus enclosed within a space cooled with solid carbon dioxide (Chemistry Research, 1957).
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This hydrocarbon was treated in zone-melting equipment cooled by solid carbon dioxide (Chemistry Research, 1957).
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A sample of p-xylene containing 10 per cent of o-xylene was treated by nine zone passes. Sije, Pauly & Nouaille (1958) then found by measurements of the freezing-point depression that a portion of the sample contained .005 fraction of the o-isomer.
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