The refractive indices for the D-line, and the densities, of the commercialgrade paraffin waxes were determined for the liquid and solid states. The commercial paraffins show both an ordinary and extraordinary refractive index in the solid state and therefore appear to be anisotropic, uniaxial crystalline solids. These paraffins are treated as individual hydrocarbons, using molecular weight data to fix the number of carbon atoms in each. Specific refractions in the liquid state, calculated by the equation of Lorena and Lorenta, are in good agreement with theoretical values derived from Eisenlohr's atomic refraction constants for carbon and hydrogen. Refractive indices in the solid state, comparable in kind t o refractive indices of isotropic substances, were calculated from the ordinary and extraordinary values by the method of Pope. Discrepancies between liquid and solid state specific refractions were then attributed to occluded air in the solidified waxes, the occluded air causing low observed values for density. True densities are calculated, and from the two values the volume per cent of occluded air is obtained.
COMMERCIAL J. M. PAGE, JR. Standard Oil C o m p a n y (Indiana), Casper, Wyo.
agree closely with those calculated from Carpenter's data (3) on the aniline point-molecular weight relationship. TABLE I. PROPERTIES OF WAXYJS Apparent Oil
A. S. T. M,. Melting Point OF.
'
121 126 131 136 141
% 0.5 0.5 0.3 0.3 0.3
C.
O
49.4 52.2 55.0 57.8 60 6
Obsvd.
Mol. Wt.
Aniline Point
Calod. mol. Wt.
332 340 355 372 376
116.7 117.8 119.0 121.0 122.2
330 342 359 370 375
c.
Corresponding Hydrooarbon C23.61H49.1 C24.lHM.Z
Cz5.aHsz.a C26.4H64.8 CZ6.7H66.4
Determination of Refractive Index in the Solid State The Abbe type refractometer was successfully employed with little difficulty, except on high-melting waxes. These waxes were applied to the prisms in the melted state and allowed to cool to the desired temperature with the prisms closed. Other samples of lower melting point were merely pressed into thin sheets and applied to the prisms cold. About 5 minutes were sufficient to allow for thermometric lag, both in the prisms and in the wax crystals, for readings taken at the end of 16 hours did not differ from those obtained after reheating, recooling, and allowing to stand a t the same temperature for 4 or 5 minutes. The light and dark fields were not so sharply divided as is the case with wax in the molten state,
LTHOUGH considerable data are available on the refractive indices of the paraffin waxes in the liquid state (I, 5 , 7, 8, 19) with corresponding densities in some cases ( I , 7, 8), instances in which both density and index of refraction are given for the solid state appear to be lacking. Commercial paraffin waxes are composed of several, but not many, individual hydrocarbons (4). Ferris, Cowles, and Henderson (7) give evidence in the form of molecular refraction to show that narrow fractions separated by physical means from commercial paraffin wax consist only of paraffinic and isoparaffinic hydrocarbons, with the normal type in predominance. The x-ray diffraction patterns obtained by Clark and Smith (4) on the same fractions confirm these conclusions and exclude the possible presence of cyclic or unsaturated hydrocarbons. Meyer and Stegeman (1.9) show that the amount of oil (usually regarded as naphthenes and aromatics) retained by wax at the final sweating temperature is scarcely detectable; this finding is confirmed by Diggs and Buchler (5) in their work on the determination of oil in fully refined paraffin waxes.
Description of Commercial Waxes Samples of fully refined paraffin waxes were selected a t random from commercial lots, care being taken only to space the melting points about equally apart. Table I lists the properties of these waxes. Melting points are by the A. S. T. M. method; the apparent oil content, accurate t o 0.3 per cent, by the method of Diggs and Buchler ( 5 ) ; and molecular weights by the cryoscopic method, using p-dichlorobenzene as solvent. Although the molecular weights do not increase regularly with increase in melting point, the observed values
040
,
'
y!,' I&:
'
I
I$'
I$'
13
'&:' I : ; ; &' ' :1
"
1 .c1.0 ; :' ' . : :120'
130'5
INDEX OF COMMERCIAL PARAFFIN FIGCRE 1. MEANREFRACTIVE WAXESiix THB SOLIDSTATE 856
PARAFFIN WAXES Specific Refraction in Liquid and Solid States yet the readings obtained were accurate to 0.0005 scale division. Probably because of crystal growth the fields became intensified on standing for 16 hours or more; that is, the light and dark fields were much lighter and much darker, respectively, than when rapid work was being done. A second line was observed-very faint, yet unmistakable-and was recognized as the extraordinary refractive index of the crystals It therefore appears that paraffin wax is an anisotropic, uniaxial crystalline solid. The D-lie refractive indices of the solidified waxes, both ordinary (no)and extraordinary (ne),are given in Table 11. I n order that a comparison of specific refractions in the solid state may be made with those obtained on the same waxes in TABLE 11. 7
Temperature O
F.
32 41 50 59 68 77 86 95 104 113
c.
0 5 10 15 20 25 30 35 40 45
5 10 15 20 25 30 35 40 45 50
WAXES
for the purposes of this work. The liquid-state values, accurate to 0.0002 scale division, are given in Table V.
Determination of Densities Densities were determined in pycnometers a t several temperatures in both the liquid and solid states. Morris and Adkins (IS) showed that to seek an accuracy in the solid state
ORDINARY AND EXTRAORDIH-4RY D-LINE REFRACTIVE INDICES OF SOLID COMMERCIAL PARAFFINS
-
M
.
1,5490 1.5475 1 5460 1 5445 1.5422 1.5330 1,5275 1.5235 1,5190
....
--
P.,121' F. (49.4' (2.)ne
no
n
no - n e
1,5030 0,0460 1.5015 0,0460 1 5000 0 0460 1 4985 0 0460 1 4960 0.0462 1.4848 0.0482 1,4802 0,0473 1.4770 0.0465 1.4740 0.0450
....
....
1.5337 1.5321 1 5306 1 5291 1.5268 1,6169 1.5117 1.5080 1,5040
....
M.P.,136' F. (57.8' C . ) -
no
.41 50 59 68 77 86 95 104 113 122
2. DENSITY OF COMMERCIAL PARAFFIN
FIQURE
ne
1.5538 1.5520 1.5503 1.5487 1.5465 1.5442 1.5410 1.5325 1.6260 1.6200
no
- ne
n
1.5073 1.5060 1.5045 1.5022 1,5003
0.0465 0.0460 0.0458 0,0465 0,0462
1.5383 1.5366 1.5350 1.5332 1.5311
1.4930 1.4840 1.4770 1.4748
0.0480 0.0485 0.0490 0.0452
1.5250 1.5163 1.5096 1.5049
....
....
....
--
11. P..126' F. (52.2' C.)--
no
ne
.... ....
.... ....
1 5463 1 5442 1.5420 1.5398 1.5323 1.5262 1.5227 1.5173
1.5038 1.5020 1.4995 1.4972 1.4840 1.4790 1.4760 1.4715
-AM. no
ne
....
1.5523 1.5505 1.5482 1.5465 1.5452 1.5405 1.5282 1.5249
1.5062 1.5040 1.5020 1.5002 1.4960 1.4915 1.4795 1.4763
-the liquid state, the ordinary and extraordinary refractive indices were combined by the equation of Pope (16) as follows : 2%
+ ne
3
0 0422 0.0425 0.0426 0.0483 0.0472 0.0467 0.0458
ne
no
.... ....
....
1.5321 1.5301 1.5278 1,5256 1.5162 1.5104 1,5071 1,5020
1.5538 1 5513 1 5486 1.5465 1.5441 1.5384 1.9308 1.5265 1.5220
1:5033 1 5020 1 5000 1.4985 1,4950 1,4888 1.4810 1.4780 1.4743
no
- ne
....
0.0505 0 0493 0 0488 0.0490 0.0491 0.0496 0.0498 0.0485 0.0477
n
....
1.5369 1.5348 1.5324 1.5305 1.5277 1,5218 1.5142 1.5103 1.5061
no
- ne
n
....
....
.... ....
0.0461 0.0465 0,0462 0.0463 0.0492 0.0490 0.0487 0.0486
1.5369 1.5350 1,5328 1.5310 1,5288 1.5241 1.5119 1.5087
greater than 0.001 in density is unjustified, since different samples cut from the same block of wax vary by that amount because of differences in quantity of occluded air. The average accuracy for the determinations in the liquid state is approximately 0.0002. Density data are given in Table I11 and presented graphically on Figure 2.
....
r
=
....
0 0425
P.,131' F. (55.0"C . )
7-M.
n
P., 141' F. (60.8' C.)--
.I..
....
- ne ....
no
Hypothetical Liquid State Densities at 15" C. The density curves show an extrapolation from the liquid state values, which plot a straight line, through the temperature range in which the wax is normally solidified, and is taken as representing the density of the wax if it were liquid, or in solution in oil at those temperatures. At 15" C. (59" F.) the observed hypothetical values were found to be in good agreement with those calculated from the equation of Traube (9):
(1)
Values of the mean refractive index, n D , are included in Table I1 and are plotted on Figure 1. Beyond the temperature limits given, the field becomes quite hazy and indistinct, thus rendering more complete data unobtainable by the method employed. The refractive index in the liquid state was shown by Wilson and Wilkin (19) to plot a straight line against temperature. Since this was true, the refractive index of the samples in question was taken a t one temperature only as being sufficient
d =
M EA,
+ 25.9
(2)
Where d is the density a t 15" C., :M the molecular weight, I;A, the molecular volume (atomic volume of carbon = 9.9, 857
INDUSTRIAL AND ENGINEERING CHEMISTRY
838
VOL. 28, NO. 7
TABLE 111. DENSITY OF COMMERCIAL PARAFFINS M.P:, 126' F. (52.2' C.)
M. P 121' F. (49.4' C.) Dens& Temperature F. C. 0.906 34 1.1 0.903 45 7.2 0.897 57 13.9 0.893 69 20.6 0,889 70 21.1 0.872 83 28.3 0.862 95 35.0 0.849 100 37.8 0.7761 145 62.8 0.7688 165 73.9 0.7620 185 85.0
TABLEIV.
Density
0.915 0,911 0.909 0.897 0.873 0.7830 0.7753 0.7682
.. .
.... ....
121 126 131 136 141 a
49.4 52.2 55 57.8 60.6
.,.
.,.
...
., ..
....
....
Dens&
Temperature
0.917 0.914 0.910 0.902 0.877 0.859 0.791 0.7805 0.7744 0.7660
' F.
C.
34 50 59 SO
1.1 10.0 15.0 26.7 37.8 48.9 54.4 60.0 71.1 82.2
100
120 130 140 160 180
15',C.
4-Co - Vol.
ZAv
Formula
Cza.66Hre.i C24.1H60.2 Cz5.zH52.4 Czs.aHs4.8 Cza.rHa6.4
411.25 420.10 437 82 457.14 461.97
Extra o Mol. latecfd dli uid Calcd. Wt. a t 15' C. a t 15%C.a d15O 332 340 355 372 376
0.807 0.808 0.809 0.810 0.813
0.808 0.809 0.811 0.812 0.816
Density
0.807 0.809 0.811 0.814 0.814
By Bureau of Standards Petroleum Density Tables.
m
atomic volume hydrogen = 3.1), and 25.9 is a constant termed "co-volume." These hypothetical densities are given in Table IV.
Comparison of Curves for n and d in the Solid State
Temperature
F. 0.922 0.919 0.914 0.911 0.906 0.896 0.870 0.834 0.7795 0.7724 0.7653
... ....
....
M.P., 141' P. (60.6" C.)
M.P., 136' F. (57.8' C.)
M. P. 131' F. (55.0' C.)
HYPOTHETICAL LIQUIDSTATEDENSITY OF WAXES AT
h l . P. of Wax F. C.
Temperature F. C. 35 1.7 50 10.0 59 15.0 80 26.7 100 37.8 130 54.4 150 65.6 170 76.7
34 45 97 69 83 95 110 130 145 165 185
Density
C. 1.1
0.922 0.919 0.915 0.911 0.905 0.903 0.881 0.855 0.7832 0.7755 0.7690
7.2 13.9 20.6 28.3 35.0 43.3 54.4 62.8 73.9 85.0
Temperature O F. C. 34 1.1 45 7.2 57 13.9 69 20.6 83 28.3 95 35.0 110 43.3 130 54.4 145 62.8 165 73.9 185 85.0
observed value of TD for each 20" C. increase in temperature above 20' C. Application of this correction was found to be necessary in the present case, in comparing the specific refraction of the waxeg in the molten state with the theoretical value. The theoretical value is derived from the summation of t h e D-line constants of Eisenlohr (6) for the atomic refraction of carbon (2.418) and hydrogen (1.100) by dividing the resulting molecular refraction by the molecular weight. In Table V the specific refraction, uncorrected and corrected for temperature, is compared with the value as calculated from Eisenlohr's constants. The very good agreement between the corrected values for these mixtures of paraffins and the theoretical values for individual paraffins of a corresponding molecular weight appears not only to justify the treatment of such commercial fractions as individual hydrocarbons in the present case, but also to indicate that they possess a degree of purity perhaps not heretofore fully realized. The specific refraction in the solid state is calculated from the refractive index derived from the ordinary and extraorby the equation Of 'Ope: dinary Observed
As would be expected, the curves for the mean refractive index and density in the solid state have much the same temperashape. Both show a certain irregularity until ture is reached below which the points plot a straight line against temperature. 2% ne n = or n =- 3 (approx.) Carpenter (2) whose density data for a commercial wax melting a t 132.8' F. (56' C.) plot a curve similar to that for Refractive indices calculated in this manner are comparable to the wax given here which melts at 131'F. (55' C.) attributes the refractive index of isotropic or liquid substances, and are the irregular portion of the curve to a transition occurring between different crystalline forms in the solid condition, and therefore comparable to the specific refraction of the waxes in does not look upon this behavior as due to the co-existence of the liquid state. In Table VI the specific refraction is shown to be reasonboth molten and solid phases. ably constant in the solid state over that temperature range Other abnormalities at temperatures near, but below, the in which both density and refractive index are linear functions solidification point, were noted recently by Jackson (11) in connection with specific conductivity, and by Yannaquis (80), who finds a transition from TABLEV. SPECIFIC REFRACTION OF COMMERCIAL PARAFFINS IN THE orthorhombic to hexagonal crystals as the meltLIQUIDSTATE ing point is approached. Muller (14) also finds a transition from a state of lower symmetry to M , p, oi Mol. APPCOX. -FD d Temp. Wt. Formula At t o At 20° C . Calcd. hexagonal symmetry near the melting point. F. ' C. t o c.
+
+=
Specific Refraction of Commercial Paraffin Waxes According to Lorenz and Lorentz the equation for specific refraction, =
(%)($)
121 126 131 136 141
49.4 52.2 55.0 57.8 60.6
1.4349 1.4352 1.4355 1.4370 1.4294
0.7780 0.7788 0.7800 0.7815 0.7690
60 60 60 60 85
332 340 355 372 376
Cza.asH4s.i Car.iH60.z Cz6.2H~z.1 C26.4H54.8 Czs.rHaa.4
0.3353 0.3352 0.3349 0.3351 0.3353
0.3343 0.3342 0.3339 0.3341 0.3337
0.3341 0.3338 0.3340 0,3337 0.3337
~-
(3)
is independent of temperature. That the equation is likewise independent of state of aggregation is discussed in the work of Nernst (16). However, Huckel (IO)points out that variations with temperature as great as 0.01 per cent may be expected. Vlugter, Waterman, and Van Westen (18) also find that the equation is not strictly independent of temperature when applied to petroleum lubricating oils of high cold test, and a correction of 0.0005 must be subtracted from the
TABLEVI. SPECIFIC REFRACTION OF COMMERCIAL PARAFFINS IN THE SOLID STATE"
-
Temperature F. O C. 30 -1.1 40 4.4 50 10.0 60 15.6
121' F. (49.4' C.) 0.3434 0.3429 0.3430 0.3437
r~ of Wax Melting at: 126' F. 131O F. 136' E'. 141' F. (52.2O C.) (55.0' C.) (57.8' C.) (60.6" C.) 0.3405 0.3403 0.3401
....
0.3413 0.3410 0.3412 0.3410 0.3411
....
.... a
0,3400 0.3401 0.3403 0.3405 0.3405
.. .. .. ..
Caloulated from curves of n of Table I1 and d of the curves,
.,.. . ... 0.3415 0.3411 0.3413 0.3414 0.3414
INDUSTRIAL AND ENGINEERING CHEMISTRY
JULY, 1936
of temperature. Such is not the case, however, for the irregular portions of the density and index curves. It is assumed that the lack of agreement between the values of r D calculated from liquid-state data (Table V) and those of Table VI is due solely to errors in density determinations in the solid state, these errors being caused by air occluded in the samples. The fact that the specific refraction of the solid waxes fails to diminish regularly with increase in molecular weight is likewise attributed to the variable quantity of occluded air affecting the densities.
T-4BLE
859
VII. TRUEDENSITY OF, AND VOLUME P E R C E N T AIR IN, COMMERCIAL PARAFFIN WAXES
M . P. of Wax
TD
at
C.
121
49.4
0.3343
126
52.2
0.3342
131
55.0
0.3339
136
57.8
0,3341
141
60.6
0 3337
(Obsvd.)
(Obsvd.)
di
de (Calod.)
1.5306 1.5289 1.5321 1.5297 1.5348 1.5323 1.5366 1.5347 1.5366 1.6344
0.900 0.897 0.911 0.909 0.912 0.909 0.917 0.$14 0.914 0.911
0.925 0.922 0.927 0.924 0.932 0.928 0.934 0.931 0.935 0.932
n
20° C.
F.
Temp. O
F.
50 60 50 60 50 60 50 60 60 70
dz
- dl
SOLID
Vol.
% ' Air
C. 10.0 15.6 10.0 15.6 10.0 15.6 10.0 15.6 15.6 21.1
0.025 0.025 0.016 0.015 0.020 0.019 0.017 0.017
0.011
0.011
2.7 2.8
1.8 1.7 2.2 2.1 1.9 1.9 2.3 2.3
Air in Paraffins in the Solid State After the liquid-state values of r D are corrected to 20' C. (Table V), it is apparent that the equation of Loren2 and Lorents may now be employed for the purpose of calculating the true (air-free) density of the waxes at 20" C. (68" F.), using the observed refractive index a t that temperature. However, since in some cases the wax is undergoing a transition a t 20" C.,densities are calculated a t temperatures safely under the transition range. In Table VII, in addition to the true densities, the volume per cent occluded air is given, as calculated from the equation:
of many individual crystals with closed air spaces between (or evacuated pockets, if crystallization was carried out under vacuum), few of which spaces become filled with the liquid medium in which'densities are being taken. Thus, although all occluded air was removed and measured, and the apparent density was increased somewhat by virtue of the surface penetration of the liquid medium, the density so determined is not the true density.
2
The author takes pleasure in expressing his appreciation to E. W. Thiele and W. B. Kay for helpful suggestions during the preparation of this manuscript.
A = 1
-
X 100
(4)
where dr represents the density of the air-containing wax and dz the density of the air-free wax, or true density. Equation 4 gives only occluded or mechanically enveloped air, since dissolved air would have a negligible effect upon dl. Carpenter ( 2 )reports as high as 12 per cent air in an American refined wax of 132.8' F. (56' C.)melting point. The density of this wax in an air-free condition is given as 0.919 a t 60" F. (15.6"C.). On the assumption that the entire 12 per cent air was occluded, the density before deaeration must have been 0.809 a t 60' F. Since this low density is improbable and not in agreement with the values observed by the author or with the figure 0.9158given by Seyer and Inouye (17) for Parawax of 129.6"F. (54.2"C.) melting point, a large portion of the air found by Carpenter must have been held in true solution or by other means having a negligible effect upon the volume occupied by a given weight of the wax. Morris and Adkins (13) give 0.920 as the specific gravity of an air-free paraffin of 127.2' F. (52.9' C.)melting point a t 6O0/6OoF.; this figure is in good agreement with the density as found by Carpenter. However, in determining the density or specific gravity in the solid state, Carpenter and also Morris and Adkins use flotation methods. Such methods are amply accurate for many purposes, but a block of paraffin wax consists
FORDSON PLANTOF
THE
Acknowledgment
Literature Cited (1) Biichler and Graves, IND.ENG.CHEM.,19,718 (1927). (2) Carpenter, J . Inst. Petroleum Tech., 12,288 (1926). (3) Ibid., 14, 461 (1928). (4) Clark and Smith, IND.ENQ.CHEM.,23, 697 (1931). (5) Diggs and Biichler, Ibid., 19, 125 (1927). (6) Eisenlohr, 2. physik. Chem., 75, 585 (1910-11). (7) Ferris, Cowles, and Henderson, IND. ENG. CHEM.,21, 1090 (1929). \ - - - - I .
(8) Ibid., 23, 681 (1931). (9) Getman, "Outlines of Theoretical Chemistry," 3rd ed., p. 104, New York. John Wiley & Sons, 1922. (10) Hackel, "Theoretische Grundlagen der organischen Chemie," Vol. 11, p. 92,Leipzig, Akademische Verlagsgesellschaft, 1931. (11) Jackson, W., Naturwissenschuften, 22, 238 (1934). (12) Meyer and Stegeman, IND.ENG.CHEM.,20, 638 (1928). (13) Morris and Adkins, Ibid., 19, 301 (1927). (14) Miiller, Alex, Proc. Roy. SOC.(London), A138, 514 (1932). (15) Nernst, "Theoretische Chemie," 8th German ed., pp. 362-6, Stuttgart, Ferdinand Enke, 1926. (16) Pope, J . Chem. Soc., 69, 1531 (1896). (17) Seyer and Inouye, IND.ENQ.CHBM.,27, 567 (1935). (18) Vlugter, Waterman, and Van Westen, J . Inst. Petroleum Tech., 2i, 661 (1935). (19) Wilson and Wilkin, IND.EXQ.CHEM.,16, 9 (1924). (20) Yannaquis, N.,Compt. rend., 196, 784 (1933). RECEIVED April 1, 1936.
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