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INDUSTRIAL AND ENGINEERING CHEMISTRY
hyde, i t was found to contain 2.54 per cent sulfur. This was more than the original crude had contained. This increase was due to loss of some of the lower boiling hydrocarbons while heating a t 40" C. Therefore, a small sample (about 50 cc.) of the original crude was heated to constant weight before extracting. I n this treatment the sulfur content increased to 2.76 per cent. After an extraction with an equal volume of acetaldehyde, the residue contained 2.71 per cent sulfur, and the material extracted contained 3.21 per cent. Thus
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it is shown that the higher sulfur content of the extract in this experiment was due to a slight concentration of the sulfur compounds by extraction. Owing to the viscosity of the oil, it did not seem practical to treat a large amount of the crude in this way before an extraction. But since the sulfur content of the material extracted is higher than in the residue, even though both are higher than originally, it seems certain that here also the concentration of the sulfur compounds has resulted from the extraction.
Heats of Fusion of Some Paraffin Hydrocarbons' George S. Parks and Samuel S. Todd DEPARTMENT OF CHEMISTRY, STANFORD UNIVERSITY, CALIF.
N SPITE of the great importance of the paraffin hydro-
40 cc. capacity, the entry tube of which could then he closed carbons, the heat of fusion of only one of these, methane, by a small screw plug. This capsule was suspended by a hook has been reported in the literature up to the present time. mechanism within the heater, which was a hollow aluminum I n the past few years the lack of such data has proved a serious cylinder wound on the outside with a nichrome heating coil. handicap to several investigators, who have found it necessary By proper regulation of the current through this coil, the to make rough guesses of heats of fusion of hydrocarbons, heater and capsule could be brought to any desired temperathereby introducing a factor of uncertainty into their results. ture up to 300" or 400" C. A small, two-element, copperPartly to remedy this situation the present investigation was constantan thermocouple ran down a tube in the center of undertaken a couple of years ago; and in an experimental the capsule and thereby measured the temperature of the study the heats of fusion of four compounds-vis., hexa- hydrocarbon sample to 0.1" C. A similar thermocouple, methylethane (CsHls), n-eicosane (CwHhz), n-pentacosane placed outside, served to determine the adjoining temperature (C2SH52),and n-tritriacontane (CsaH@)-have been measured. within the heater and to provide a check upon the attainment of thermal equilibrium. The results, when combined with similar data recently At the proper time in the The heats of fusion of hexamethylethane, n-eicosane, o b t a i n e d i n another recourse of a determination, n-pentacosane, and n-tritriacontane have been meassearch in this laboratory, t h e h e a t e r a n d contents ured by a method of mixtures. These results, when furnish some interesting inwere moved by a suitable combined with similar data obtained in other investiformation on the heats of m e c h a n i s m to a position gations, have furnished the basis for a general study of fusion of paraffin hydrocardirectly above the calothe heats of fusion of paraffln hydrocarbons. By means bons. rimeter, and the capsule, reof an empirical equation the fusion values of thirtyleased on the instant by an Method and Apparatus three normal paraffins have been calculated. In genautomatic dropping device, eral, branched isomers show smaller heats of fusion fell into the c a l o r i m e t e r . I n principle the method than the normal compound, but the effect cannot be T h i s c a l o r i m e t e r was a of mixtures was employed. predicted quantitatively. n i c k e l - p l a t e d copper jar A steel capsule, containing a weighed sample of the c o n t a i n i n g a b o u t 1500 grams of water, a Beckmann h y d r o c a r b o n u n d e r investigation, was first brought to a given upper temperature thermometer calibrated by the U. S. Bureau of Standards, a in an electric heater and was then dropped into a water small stirrer of the propeller type, and a receiving holder for calorimeter, initially a t 25" C. The temperature rise of the the capsule. It was suspended by three Bakelite hooks water in the calorimeter was measured, and from this result within a second jar, 3.0 em. larger in diameter. These two the decrease in the heat content of the hydrocarbon sample jars rested in a water thermostat, kept a t 25" C., and were was calculated. By the use of various upper temperaturescovered with a double-walled copper cap filled with the therfor instance, one somewhat below the melting point of the mostat water. Initially the calorimeter and thermostat sample, a second slightly above, and a third perhaps 30 or were a t practically the same temperature, but after the fall 40 degrees above the melting point-adequate data could be of the capsule there was usually a difference of 1 to 3 degrees obtained for the calculation of the heat of fusion of the sub- and, accordingly, the Regnault-Pfaundler method was used stance as well as of its interval specific heats in both the in determining the heat loss to the thermostat during this crystalline and liquid states. part of a run. The heat capacity of the empty capsule over The apparatus had been constructed for an earlier research the temperature ranges involved was measured in a separate by Wm. M. Marker (S),to whom the writers are indebted for series of determinations. Throughout the investigation the the privilege of using it in the present investigation. It had usual devices and precautions of good calorimetric procedure been built in general along the lines developed and used by were employed. numerous investigators in the past, and therefore no detailed To give the reader a concrete example of the reproducibility description is necessary here. The hydrocarbon sample was of the method with our apparatus, we present in Table I the introduced as a liquid into a cylindrical steel capsule of about results of five determinations of the specific heat of crystalline hexamethylethane over practically the same temperature 1 Presented before the Division of Petroleum Chemistry a t the 78th range. It will be observed that the greatest deviation from Meeting of the American Chemical Society, Minneapolis, Minn , September the mean value is 1.0 per cent. 9 t o 13, 1929.
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INDLSTRTAL A N D ENGINEERING CHEMISTRY
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Table I-Specific H e a t D a t a on Crystalline Hexamethylethane TEMPERATURE INTERVAL Av. TEMPERATURE SPECIFICHEAT c. c. Cal. aer eram 79.3-26.2 52.8 0 5276 80.0-26.0 53.0 0.5358 80.8-26.1 53.4 0.5277 80.8-26.2 53.5 0.5295 81.3-26.2 53.8 0.5322 Mean result 53.3 0.5306
Materials The sample of hexamethylethane (CgHlg)had been carefully synthesized under the direction of Graham Edgar, of the Ethyr Gasoline Corporation, and was undoubtedly a very pure material. It is the most branched of the isomeric octanes and is of special interest for this reason. The melting point is 104" C. (International Critical Tables). The samples of n-eicosane (CaH42),n-pentacosane (CZjHS2) , and n-tritriacontane ( C ~ S H had ~ ) been very carefully recovered from paraffin wax in the research laboratory of the Standard Oil Company of Indiana. Thcir properties as well as their preparation by fractional distillation and fractional crystallization have been fully described by Buchler and Graves (1). The respective melting points were 36.4', 53.3", and 71.1' C.
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Vol. 21, No. 32
The last line in Table I1 contains the molal entropy of fusion, 4St, which is simply the molal heat of fusion divided by the absolute temperature of the melting point, This quantity will play an important part in the subsequent discussion. Other Fusion Data
For purposes of completeness and as a basis for the succeeding discussion, some fusion data recently obtained by Parks, Huffman, and Thomas ( 4 ) in another investigation on hydrocarbons are introduced in Table 111. These results were acquired by the Nernst method with an aneroid calorimeter; they are probably accurate to within 1 per cent in all cases. The only other aliphatic hydrocarbon which has been studied is methane. For this Eucken and Karwat ( 2 ) found a fusion value of 14.50 calories per gram a t -182.6' C. The corresponding molal entropy of fusion is 2.57 E. U. Table 111-Fusion
D a t a f o r Seven Hydrocarbons Obtained by Nernst Method MELTINO HEATO F HYDROCARBON POINT FUSION AS1 c. Cal. per gram E. U . per mol 2-Methylbutane -160.5 16.94 10.84 n-Hexane 94.5 34.89 16.84 n-Heptane 90.9 33.78 18.58 2-Methylhexane -119.1 21.16 13.75 n-Octane 57.5 42.04 22.27 2,2,4-Trimethylpentane 107.8 18.92 13.06 n-Eicosane 36.4 52.0 47,42
-
+
Discussion of Data
' 0
No. of carbon a t o m s I 20
Figure I-Molal E n t r o p y of Fusion Plotted a ainst N u m b e r of C a r b o n A t o m s in C o m p o u n 8 The circles refer t o the normal hydrocarbons and the heavy dots t o branched hydrocarbons.
Experimental Results The experimental results for the heats of fusion of these four compounds, expressed in terms of the 15-degree calorie, appear in Table 11. I n the case of hexamethylethane the heat of fusion was small relative to the total quantity of heat measured, and consequently the error in this value may be as large as 2 per cent. As the melting point of the eicosane was less than 10 degrees above the final temperature of the water calorimeter, the determination of its heat of fusion was also attended with unusual difficulties, on account of the phenomenon of premelting and the uncertainties in determining the calorimeter heat losses over the long periods of time required for thermal equilibrium in this particular case. The mean result, 49.9 calories per gram, is undoubtedly low, and it is believed preferable to rely upon the value 52.0 given in Table 111. This is probably good to within 1 per cent and hence the writers' result here may be approximately 4 per cent low. On the other hand, in the cases of pentacosane and tritriacontane the experimental method was working under very advantageous conditions and the mean values are probably accurate to within 1 per cent. Table 11-Fusion D a t a f o r the F o u r Hydrocarbons Substance CsHis Cs3Hss ClaHrz CZSHSZ 53.3OC. 71.1'C. Melting point 104OC. 36.4OC. Cal. per Cal. per Cal. per Cal. per gram gram gram gram Heats of fusion: 53.93 49.78 53.37 14.58 53.77 53.70 15.13 50.65 53.32 54.42 14.97 49.44 (3) 53.93 49.63 14.82 (4) 54.0 49.9 53.5 Mean 14.9 AS/ 4.51E.U. 45.50E.U. 57.76E.U. 72.85.E.U.
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No striking regularities are manifest, when we consider directly the heats of fusion, either per gram or per mol, although it is evident that in general the fusion of a branched isomer requires less heat than that of the normal compound. However, a consideration of the entropy of fusion is much more profitable. When the molal entropies of fusion are plotted against n, the number of carbon atoms in the chain, a very regular curve (Figure 1) is obtained in the case of the normal hydrocarbons. The equation for this curve is AS! = 4
-1.43
and the average deviation of the seven experimental points is only 0.3 calorie per degree. Furthermore, no a1t)ernation apparently exists for compounds of even and odd numbers of carbon atoms, as is sometimes found in the case of physical properties in a homologous series. Hence, this equation, though purely empirical, may be used with considerable confidence in estimating the entropy of fusion and heat of fusion of the other hydrocarbons for which no experimental data now exist. Table IV-Predicted MELTING
FORMULA POINT
O C. -182.6 -172.0 -189.9 -135.0 -131.5 94.5 90.9 57.6 51 32.0 26.5 12.0 6.2 5.5 10 20 22.5
---++
Fusion Data f o r Normal ParafRns HEAT OF
MELTIWG
HEAT OF
FUSIONFORMULA POINT As/ FUSION E. U . Cal.per E. U . Cal. per AS/
permol 2.57 5.71 8.59 11.32 13.93 16.45 18.92 21.32 23.68 25.99 28.26 30.48 32.72 34.89 37.05 39.18 41.28
gram 14.5 19.2 16.2 26.9 27.4 34.1 34.4 40.3 41.0 44.1 44.6 46.8 47.4 49.0 49.4 50.8 50.8
OC. 27.0 31.4 36.4 40.8 45.7 47.1 49.4 53.3 56.4 59.1 60.3 62.3 64.7 67.5 68.9 71.1
perm02 43.38 45.45 47.51 49.54 51.58 53.58 55.58 57.52 59.52 61.47 63.40 65.34 67.26 69.17 71.07 72.96
gram 51.2 51.6 52.1 52.5 53.0 52.9 53.0 53.3 53.5 53.7 53.6 53.6 53.8 54.0 54.0 54.1
By this method Table IV has been construct.ed for the entire series of normal compounds from methane to tritriacontane. The melting points for the first seventeen members were taken from the International Critical Tables, except in the cases of methane, hexane, heptane, and octane, where the
December, 1929
INDUSTRIAL A N D ENGINEERING CHEMISTRY
temperatures noted in the preceding section have been used again. The remaining values, found by Buchler and Graves (except those for C22H46and CaHB2,which were interpolated), are in general slightly below the melting points given in the International Critical Tables. The molal entropies of fusion, as calculated by the equation, appear in the third column. These values, when multiplied by the absolute temperature of the melting point and divided by the molecular weight, give the data of column 4. The heats of fusion thus obtained, though not experimental, are probably good to about 2 per cent in most instances; and could no doubt be used for all practical purposes. When we come to consider the branched paraffin hydrocarbons, no similar quantitative regularities are evident. Qualitatively we can say that the entropy of fusion apparently decreases progressively with an increase in the amount of branching; but this fact does not enable us to predict the fusion value. This lack of quantitative regularity in the fusion entropies of branched hydrocarbons is undoubtedly due to the fact that they possess a variety of crystal structures. Hence the melting process involves the overcoming of molecular attractive forces which differ greatly in character and magnitude from
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one compound to the next. On the other hand, the x-ray evidence indicates that we are probably dealing with the same general type of crystal structure as we proceed up the series of the normal compounds. Accordingly, the fusion process is essentially the same throughout, and it is not surprising that the energy required to overcome the crystal forces varies in regular fashion with the molecular weight and the melting temperature. Acknowledgment
The writers wish to thank the Ethyl Gasoline Corporation and the Standard Oil Company of Indiana for the loan of valuable hydrocarbon samples. They also desire to acknowledge their indebtedness to Hugh M. Huffman, of this laboratory, for assistance on several occasions during the course of the investigation. Literature Cited (1) (2) (3) (4)
Buchlerand Graves, IND. ENG.CHEM.,19, 718 (1927). Eucken and Karwat, Z. phys. Chem., 112, 467 (1924). Marker, Engineer’s Thesis, Stanford University, 1926. Parks, Paper presented before the Division of Petroleum Chemistry at the 76th Meeting of the American Chemical Society, Swampscott, Mass., September 10 to 14, 1928.
Wetting of Pigments and Its Relation to Various Paint Characteristics’ Elliott L. McMillen THE N E W
JERSEY ZINC
COMPANY, PALMERTON, PA.
H E wettingofpigments This paper presents preliminary data upon one phase f o r m e d in small additions is of interest to the of a comprehensive investigation of the factors ine a c h a d d i t i o n being compaint manufacturer in fluencing the consistency of pigment-vehicle mixtures. pressed by means of a hydrauThe method of Bartell has been applied to the study of lic press a t 200 atmospheres. two respects: (1)The time of wetting of pigments by various liquids and oils. ExFrom the weight of pigment wetting dependsupon wetting forces, viscosity of vehicle, perimental data correlating wetting forces of Pure used and thevolume of the reand the amount of mechaniliquids with Plastic Properties of lithopone-liquid sulting cake, the ratio of the cal work done upon the mixmixtures shows that flocculation and Plasticity are volume of voids to the volume more pronounced the better the liquid wets the Pigof solid was calculated, thus ture; (2) the forces of wetment. These results are in accord with recent theories insuring uniform packing in t i n g between pigment and vehicle have decided influence of the plasticity of paint which are discussed. successive determinations. Liquid from the reservoir, B, u p o n s u c h properties of a was allowed to flow into the end of the compressed pigment and paint as consistency, leveling, settling, etc. By “wetting force” is meant the spontaneous force with out of capillary tube C. With the stopcock to the reservoir which a liquid tends to spread upon and wet a solid when the B closed, the movement of the liquid into the pigment could liquid is brought into contact with the solid, no external be observed in the capillary tube, C. On account of the work being supplied. The method of Bartell ( 2 ) furnishes very slow movement of the viscous liquids, a thermometer the only method of quantitatively measuring the force of tube with its graduations was found very convenient. Gasewetting or adhesion tension of a liquid toward a powdered ous pressure was applied through tube D to oppose the flow solid. Good wetting is characterized by high adhesion ten- of liquid into the pigment. By gradually increasing the pression and low angle of contact between the solid and liquid. sure a point could be reached when the flow of liquid would This investigation presents measurements of wetting forces cease. This pressure was measured by means of a calibrated upon pigments using Bartell’s method. The data so obtained Bomdon test gage. Leather packing a t E rendered the cell are correlated with consistency data obtained by means of leakproof. The surface tensions of the various liquids used a modified Bingham and Murray vacuum plastometer (6). were measured by means of the du Nouy (9) surface tension The Bartell method of studying wetting involves measur- apparatus, applying the correction given by Harkins ( 7 ) . ing the pressure developed when a liquid displaces a gas Methods of Calculating Results (or another liquid) from a compressed cake of powdered Bartell (2) has shown that the pores in a compressed powsolid. Figures 1 and 2 show the apparatus used for this purpose. In Figure 1 the pigment cake is shown held in dered solid may be considered as a bundle of small capillary position by the perforated disks, A . The pigment cake was tubes and the formula for the rise of a liquid in a capillary due to its surface may be 1 Presented before the Division of Paint and Varnish Chemistry a t
T
the 78th Meeting of the American Chemical Society, Minneapolis, Minn., September 9 to 13, 1929.
rhag
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