INDUSTRIAL A N D ENGINEERING CHEMISTRY
August, 1927
have a controlling effect on refinery practice. This is well illustrated in the case of the two gas oils. Oil 5 of 1926 was described as an asphalt-base gas oil, and (Figure 2 ) contained practically nothing of the lubricating oil fraction. Oil 12 of 1926 was described as a paraffin-base gas oil, but it contained a large amount of material ordinarily considered lubricating oil. As a consequence, though similarly named, oil 12 made an effective spray and oil 5 did not. Conclusions
The property of killing insects under the conditions of this study resides in a considerable range of lubricating oils, but is greatest in the portion that distils over between 240’ and 300’ C. at 40 mm. pressure. Toxicity of the kind studied does not appear to be related to the viscosity of the oils. The presence of significant quantities of vapor or vapor pressure is doubtful, in view of the low field temperatures and the high boiling ranges of effective oils. Oils for this purpose may be from asphalt- or paraffin-base crude without prejudice to the effects. Oils that have been subjected to processes for completely removing the color are likely to be more effective than before the decolorizing treatment.
935
Bibliography I-Quaintaince and Siegler, U.S. Degt. Agr., Farmers’ Bull. 008 (1918). 2-Ackerman, U.S. Degt. Agu., Circ. 263 (1923). a-Melander, Wash. Agr. Expt. Sta., Bull. 174 (1923). 4-Melander, Spuler, and Green, Ibid., 184 (1924). 5-Lilley, “The Oil Industry,” D. Van Nostrand Co., 1925; see also other texts on oil technology for processes coming under “refining.” 6-Melander, Spuler, and Green, Wash. Agr. Expt. Sta., Bull. 197 (1925). 7-Spuler, Ibid., 172 (1922). 8-Brooks, “Chemistry of the Non-Benzenoid Hydrocarbons,” p. 23, Chemical Catalog Co., 1922. 9-Young and Thomas, J. Chem. Soc. (London),71, 440 (1897). l@-Young, Ibid., 73,906 (1898). 11-Jackson and Young, Ibid., 73, 926 (1898). 12-De Waele, J. A m . Chem. Soc., 48, 2760 (1926). 13-Brooks, loc. cit., p. 579. 14-Stanton, Archbutt, and Southcombe, Engineering, 108 (1919). 15-Federal Specifications Board, B U Y .Mines, Tech. Papev 323 (1922). 16-Shafer, Mich. State Agr. Coll., Tech. Bull. 11 (1911). 17-Shafer, Ibid., 22 (1916). 18-Moore, J. Agr. Research, 9, 11 (1917). 19-Moore, Ibid., 10,7 (1917). 20-Moore, Ibid., 13,11 (1918). 21-Dean, Hill, Smith, and Jacobs, BUY Mines, Bull. 207 (1922). 22-Peterkin and Ferris, Ind. Eng. Chem., 17, 1248 (1925). 23-Compare Wilson and Wilkin, Ibid., 18, 486 (1926). 24-Brooks, 206. c i t . , p. 577 (citations). 25-Mabery, J. A m . Chem. Soc., 48,2663 (1926). 26-Mabery and Mathews, Ibid., SO, 992 (1908).
Crystallization of Paraffin Wax‘ By F. H. Rhodes, C. W. Mason, and W. R. Sutton CORNBLL UNIVERSITY,ITHACA, N. Y.
A sample of slack was was sweated and the melting the funnel and its contents ITHIN recent years points and the average molecular weights of the indiwere placed in a large glass a n u m b e r of i n v e s t i g e t o r s have vidual fractions thus obtained were determined. The c y l i n d e r in a themostat. fractions were also examined microscopically- During The temperature was raised studied the crystallization of paraffin wax from petroleum the crystallization of Parafin wax two types of crystals very slowly and the oil that were obtained-needles and PlatesThe relative sweated from the wax was hydrocarbons and from sevamounts of these two type5 are determined by the collected in fractions. The era1 other solvents. It has been shown that the solid conditions under which the crystallization is effected. average molecular weight of paraffins m a y c r y s t a l l i z e Comparison of the optical properties shows that the the material in each fraction either in plates or in needles, needles obtained in this way are not true single crystals, was determined by the cryothe crystal habit depending but are composed of concentric aggregates. scopic method, using naphupon the exact conditions unthalene as a solvent. der which the crystallization is effected. Similar crystals are Fractionation Data obtained when melted paraffin is allowed to cool. The exact WEIGHT Av. relationship between the plates and the needles that may be OF MELTING MOL. WT . present in ordinary paraffin wax has not, however: been defic. F. FRACT1oN Grams C. F. nitely established, nor has evidence been presented to show 1 Below 49.9 Below120 41 43.3 110.0 416 49.9t053.9 120to129 120 47.2 117.0 403 that the two types of crystals in the solid wax are distinct 53.9to57.2 129to135 114 49.9 121.8 417 135 t o 137 132 61.7 126.0 432 crystal entities formed from different chemical compounds 4 57.2 t o 58.3 6 58.3 t o 6 0 . 0 137 t o 140 60 54.0 129.2 443 or from distinct solid modifications of paraffin. 6 (Res.) Above 60 Above 140 63 56.7 134.0 445
W
Preparation of Materials
Several samples of paraffin used were prepared from slack wax from Pennsylvania crude petroleum. The original slack wax was obtained from the Conewango Refining Company. It showed a melting point of 50-51’ C. (122-124’ F.). This slack wax was separated into several fractions by sweating. A circle of fine copper screen was fitted to a 15-cm. Buchner funnel, the outlet of the funnel was closed, and cold water was run in until the water level was about 1.25 cm. above the screen. About 550 grams of the melted wax were placed on top of the water, forming a layer about 5 cm. thick. When the paraffin had solidified the water was drained and 1
Received April 7, 1927.
‘
Am. SOC. Testing Materials, Standard Method D 87-22, Standards, p. 882 (1924).
Beginning with fraction 2, the average molecular weight increases with the melting point. This is to be expected, since the paraffins of lower molecular weight have lower melting points and should concentrate in the more readily fusible fractions. The b s t fraction, however, has a molecular weight somewhat higher than that of fraction 2. This may be explained by the assumption that the original slack wax contained a small amount of paraffins of higher molecular weights than those of the compounds which constituted the major portion of the crystals. When the wax was sweated these higher hydrocarbons dissolved in the first fraction of the melt, giving an oil of rather high average molecular weight. The
INDUSTRIAL AND ENQINEERIXG CHEMISTRY
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Val. 19, s o . 8
.tnls reiiutining after the removal of the first fraction consistcd of a mixture of pitraffins of not very widely different niolecular weighthtsand on contillired sweating gave a series US fractions of oil, each of which was slightly richer in t.lie lower hydrocarboils than was the solid matrix Srom which it was derived. From fraction 2 t.o fraction 5 the iiiolecular weight increased reguiarly and rather rapidly; while between fractions 5 and 6 there was very little cbange in molecular weight although tlrr ineltirig points differed by 2.7" C . (4.8" P.). This would appear to indicate that after the removal of the first four fractions of oil the residual crystals consisted largely of a mixture of isomeric paraffins, arid that the fifth fraction had a relatively low melting point because it crmsisted of a eotect.ic rnixtorc of the various isomers.
m d were feasible, so that phot~siiierugra~ilis of growing crystals could he obtained. Under the inicroscope t,he several fractions obtained by the sweating of the original slack wax showed essentially the same behavior on solidification, although the exact t,ernperat.uresand rates at which the various changes took place varied with the individual fraction. In every c a v the waxes start to solidify as sriiall plates. With rapid cooling (greater than 0.1" C. per minute) these plates almost irriiiiediat,ely begin to undergo a change in habit, beeoiiiing polygoiial ill outline, witli shaded outlines. (Figure 1) As the change is followed under the micmscope it is seen that t,he edges of the plates are actually roiled up, and that from these rolled edge,s there develop needles tangent to the original plnt,e. On ft~rthcr crioline .~,this chanee continues and the needles eloneate and become better defined (Figure 2 ) ; the larger plates also perMicroscopic Studies sist,, mid both needles and plates grow at the expense of the The behavior of each Eractiori oil solidification was then smaller crystals. Finally, the maxs solidifies completcly to studied microscopically. T l i e observations were iriade at I& coarse-grained mixture of needles and plntes, the relative about 100 rlianieters, using a I6-mni. objective. An iris proportions of the two types of crystals being deteriiiiiied diaphragm, mounted directly above the objective, made it by the rate of cooling (Figure 3). Witli rapid cooling tlie possible to decrease the aperture and thus to increa3e the wax consisba chiefly of fine needles mixed Trittr a few small depth of focus aiid t.he contrast. The thickness of the needles plates. In some cases and t,lie fact that they did not all lie in one plane, hgether needle and a plate; one with the very low risibility of the plates, made this accessory while the opposite end exceedingly useful. The sample under examination was conIf a sample in which a tained in a small watch glass or in the depression of a "hang- by slow eooling is chilled suddenly, the mother liquor passes ing drop" slide, and was about 1 mor. thick. It %,as covered through exactly the saine cycle as described above. A new but ivas not in contact with the cover glass. crop of small plates is formed, and these plates grow, eurl, The spec:iniens were beateii and their rates of cooling regu- aiid ehnnge over iii part into needles just like tlie plates littzd by inearns of a hot, stage, the temperatun? of which was formed from the original molt.. When a partially solidified indicated by an Ansrhiits thermoiiieter. Iq'm relatively sample ii held nt constant temperature t,he larger plates and rapid clianges uf temperature the stage described by Charnot2 needles iiicrease iri size, while the srnaller crystals disappear.
F i ~ u r r l--.lnithl slasr of crystallizafion on Figure 2-Same held as Figure 1 , slmuf one Figuic &-Third stage in ciyst.staliizstion, Plate crystals hezinnini to c m t at minute later, Showing further pm8ress in chnnse almost compleiciy converted t o needles
slow cooling. edges
to needles
was satisfa.ctory, but for very carefully controlled cooling a more heavily insulated stage with greater lag was preferable. Iiy regii'.ating the current through the heating coil the temperature could be controlled to within 0.1" C. aiid, with con-
stant line voltage: could be held constant within this limit. These hot stages were used with an ordinary chemical microscope which could be equipped with Xicol prisms for observations with polarized light.. Photomicrographs of the crystals during the various stages of their development were made with the same instrument that was used in the visual examinations. The ordinary eyepiece was replaced by a Leitz "hfakain" photomierographic camma, which permitted continuous observation 8f t,he specimen even during the exposure. The observer was thus free to devote his entire attention to the sample and to pliotograph it at any stage during the cooling. With this equipment it was found that exposures as short as 0.5 sec2"Elcmentary Chemical M~CIOEFOPY;' p. 222 (1921).
Tlie effect of this "digestion" is, of course, most marked i n the case of finc-grained crystals. With the same rate of cooliitg the fractions with the higher meltiiig points yield considerably coarser crystals. The temperature range between the initial separation of crystals and t.he complete solidification of the mass is much shorber with the harder wa.xes. When the needles are formed very slowly and are grown to a relatively large size their edges become somewhat serrated and overlapping eo-axial layers are crident (Figure 8). Further growth produces a looser structure in which these layers are less distinctly parts of a well-defined needle (Figures 1fi and 17). The plates are usu~llyvery thin and are more or less rounded. Seen flatwise they arc ahiiost invisible, Their index of resraction being nearly the same as that of the melt. Further study of the opt properties of the plates is hindered by the fact that all the crystals tend to lie in the
..
..
. .-
. . .-
Figure 7-Xeedlen and large plates, showing wzinkling at surface of plater
Figure %-Largeneedles, showing co-=xis1 Payers
Fig~mli--l.eft: PlRtebeCinninproeurl. Right: n plate
Needles starting irum
Fisure l&ncginning oi several rosettes of Figuie 11-Sectioon of solid wax, shoving Figure 12-Same field as Figure 11, viewed needles gruwini. from tiir curled edges of plstrr. fiiEUIer cross sectioas oi several large needles. betweeo crossed Nicols. The cross sections of Siariacc wrinkles may be observed at the right The stristed longitudinal ~ectionoi a needle is the needles show black C ~ O Y E ~ Sthe , a m s of wliich seen in the lower icit are parallel t o tlie plnnei of vibration of the polxrizcd light
same p,nsition; frequently several deep. Crystalliziition from snivelits (kerosene, acetone, xylene) may he more easily con-
trolled, m i d the product is suitable for detailed study. The iiiilrx of rrSraction of the crystals, for vibrations in ilieir priiieipnl &ne, is approximately 1.44, while for vibrat,ions in the pcrpendicidar plane it is close to 1.54. Seen flatwise the plates are isot,ropic, bot they exhibit fairly strong double refraction wlicn inclined or edgewise, invariably giviiig parallel extiiietion and negative “elongation.” By careful search it is possible to find crystals that appear to Ire separate, and these yield distinct bi-axial interference fignres, optically positive, with 2 V about 45 degrees. Thosc obsemations indicate that the crystals may be ascribed to the orthorhombic system. By extremely slow and regular cooling (over a period of several hours) the entire mass may be caused t.o solidify in plates (Figure 4). Usually nrhen a sample of wax is cooled rapidly enough to form needlees throughout the main portion
of the melt, very large plates developed at the surfacc~ofthe liquid and approximately parallel to it (Figures 5 and 0). The shrinking during cooling may result in pronounced %winkling of the surface layer (Figures 7, 10, and 13). It is conceivable that this oriented development OS the plates may be initiated hy the oriented arrangemerit of molecules a t the surfnce of the liquid. In spite of the striking superficial differences between the needles and the plates, tliere is no indication that these reprosent t v u different allotropic modifications of paraffin. They may eo-exist at constant temperature in contact with the melt, and there is no line of demarcation between a plate apd a needle developed from it and contiguous to it; needle and plate constitute a single solid phase. End views of the needles in the melt show that t,hey are not. simply plates seen edgewise. The two types of crystals must be considered as two crystalline habits of the same solid phase. Microscopic observation of the process of formation of
INDUSTRIAL A N D ENGINEERING CHEIMISTRY
938
Figure 16
Vol. 19, No. 8
rigure> 17
the needles s h o w definitely t.hat they originate by the curling of the edges of the plates. Although they may lengthen and thicken on digestion in the melt, this fundamental structure persists; the needles are simply plates tightly rolled. Single needles are formed when a plate rolls from one edge only or from two opposite edges; when the original plate begins to roll at several places a polygonal cluster of needles is formed (Figures 9 and 10) The structure of the needles iF consistent wit,h their origin. In cross section they are round or oval and show distinct concentric layers (Figures 5 and 11). That they do not possess the same structure as ordinary needle-like crystals is shown t y their appearance between crossed h‘icols. Cross sections, instead of being isotropic or extinguishing uniformly as would nonnal single crystals, show the black crow with arms parallel to the planes of the Nicol prisms, such as is chara,cteristic.of radiating or eoncentric structures (Figures 6 and 12). As in the case of starch granules, spherulites, etc.. this effect is much more pronounced when the specimen is rotat,ed. The birefringence shown by a cross section of a needle is apparent.ly the same as that shown by an equal thickness of solid consisting of plates lying edgewise. Longitudinal seotions of the needles show fissures and laminat,ions parallel to the long axis (Figure 11). Between crossed Nicols a longitudinal section of a needle exhibits parallel extinction and negative elongat,ion but does not show a single polarization color or n decrease in the order of the polarization colors a t the edges, as would a single normal crystal. Instead, the polarization color at the edge corresponds to that of an equal thickness of a plntc crystal seen edgewise, and the “order” of the polarization color decremes toward the center of the needle, finally reaching a value corresponding to that of an equal thickness of plates seen from the flat side. The structural and optical characteristics of the needles, as seen under the microscope, completely agree with and c o n h the observations as to their origin.
Crystal behavior such as has been described here is perhaps unique, and any statement as to its causes must be based largely upon conjecture. The crystallography of the pure paraffins is almost unstudied and the possible behavior in a complex mixture is hardly to be predicted. It is possible that the plates are hemimorphic and that the surface tension between the crystal and the melt is different on the two faces of the plate, thus tending to cause the plates to curl. Any further deposition on the “needle” or curled plate might well be in layers eo-axial with the needle. The transition from plates to needles is certainly more t.han a simple alteration of habitus or a change in the relative development of the various crystallographic faces, such as is exhibited by many substances. It is probably more or less closely rek e d to t.he behavior of “plastic” or “liquid” crystals. In the melting of some of the very soft waxes under the microscope a yery novel behavior was obsemed. When these waxes were allowed to melt rather rapidly, small irregular droplets of R second distinct liquid phase gathered at the surface of the fused mass. On standing for a short time these droplets diasolved in the mother iiquor and the liquid became homogeneous.
Synthetic Nitrate Position in Great Britain The fixation of atmospheric nitrogen seems to have established itself as definitely superior to other methods of fixation, according to Sir M a x Muspratt, one of the Directors of Imperial Chemical Industries (Ltd.). recently published in the Finenrial Times. He points out t h a t the natural nitrate of soda from Chile has the greatest difficulty in competing with fined nitrogen of sprrthctic osipiss. Gmat Britain has made oonsiderabk strides in the development o i the nitrogen industry, and the output of fixed nitrogen at the nitrogen fixation plant a t Billinyham-on-Tees is now a t the rate of 1R,000 tons per annum, and this output will be greatly increased by the end of next year. This nlant is owned bv Svnthetic Ammonia & Nitrates (Ltd.1. now associated with Impehal Chemical Industries (Ltd.)
