adductible fractions of the microcrystalline waxes could include methylbranched or cyclic hydrocarbons as well as n-alkanes. To compare the elution temperatures of 2- or 4-methyl substituted hydrocarbons with those of n-alkanes on the 2-foot columns, a known mixture of straight chain and branched alkanes was chromatographed. The results are presented in Table 1V. The 4-methyloctadecane and its straight chain isomer, n-nonadecane, were not resolved. The elution temperatures of the %methyl substituted alkanes did not coincide with those of either the isomeric nalkane or the normal hydrocarbon containing one less carbon atom. To obtain further information, a mixture of 2-methyltricosane, n-hexacosane, ntetratetracontane and the urea-adductible hydrocarbons of Ultraflex White was separated on the 2-foot columns. The elutions of the n-Cs2 and n-Cu alkanes coincided with those of two of the wax components. The 2-methyltricosane, however, eluted a t a temperature between those of two wax homologs, as is evident from Figure 5 which, like Figure 1, is a photographically reduced reproduction of the original chromatogram. All of the above results were limited to hydrocarbons of molecular weights much lower than those of the major components in microcrystalline waxes.
Extrapolation of those results to higher molecular weight ranges is of questionable validity. Therefore, because of the lack of Ca-Cw branched chain hydrocarbon standards, the urea-adductible hydrocarbons of microcrystalline waxes can not be identified definitely from GLC data as n-alkanes, 2-, 3-, 4-, or &methyl substituted alkanes or longchain substituted cycloalkanes. Other techniques then, such as I R and NMR spectrometry, x-ray diffraction, etc., must be employed to elucidate the structures of the urea-adductible hydrocarbons. Measurements of the methyl and methylene absorbance ratios of these fractions and of pure n-alkanes in the molten state have been made (7). These results suggest, although do not conclusively prove, that the ureaadductible hydrocarbons in the highermelting microcrystalline waxes such as (3-700 are normal alkanes, and the adductible fractions in the lower melting waxes such as Ultraflex White contain hydrocarbons with a single methyl branch near the end of a long chain of methylene groups. Definite proof, however, of the structure of these hydrocarbons may not be achieved until pure, high molecular weight-e.g., C3,,-Cso-branched-chain and cycloalkyl substituted alkanes become available for chromatographic and spectrometric studies.
ACKNOWLEDGMENT
The author thanks 0. W. GrifEn and C. W. Holyoke for technical assistance, J. A. Dixon, Director of API Research Project 42, Pennsylvania State University, for samples of pure hydrocarbons, and F. E. Mange and W. J. Heintzelman for helpful suggestions in preparing this report. LITERATURE CITED
(1) Dietz, W. A., Starnes, P. K., Brown,
R. A,, Tech. Assoc. Paper Pulp Ind., Spec. Tech. Assoc. P u b l . 2, 33 (1963). ( 2 ) Ettre, L. S., J. Chromatog. 8, 525 (1962). (3) Ferris, S. W., Tech. ASSOC., Paper P u b Ind.. Svec. Tech. Assoc. Publ. 2, i ( i 9 6 3 j . * (4) . , Hista. C.. hlesserlv. J. P.. Reschke.
R. F., Fredericks, D."H.lCooke, W. D.; ANAL.CHEM.32,880 (1960). (5) Levy, E. J., Doyle, R. R., Brown, R. A,. hfebolder, F. W., Zbid.. 33. 698 (1961 j. (6) Levy, E. J., Paul, D. G., Ninth National Instrument Society of America, Analysis Instrumentation Symosium, April 29-May 1, 1963. (7P Ludwig, F. J., AXAL.CHEM.37, 1737 I
.
(1965). (8) Njkelly, J. G., Zbid., 34, 472 (1962). (9) 0 Connor, J. G., Burrow, F. H., Norris, M. S., Zbid., 34,82 (1962). (10) Perkins, G., Jr., Laramy, R. E., Lively, L. D., Zbid., 35, 360 (1963). (11) Scott, C. G., Rowell, D. A., Nature 187, 143 (1960). (12) Terres, E., Nath Sur, S., BrennstoflChem. 38, 330 (1957). RECEIVEDfor review July 6, 1965. Accepted October 13, 1965.
Analysis of Microcrystalline and Paraffin Waxes by Means of Infrared Spectra in the Molten State F. JOHN LUDWIG Research laboratory, Pefrolife Corp., St. louis, Mo.
b The orthorhombic-hexagonal and hexagonal-liquid phase transition temperatures in paraffin waxes can be determined from the changes in intensity of the methylene chain rocking absorptions at 13.7 and 13.9 microns. Microcrystalline waxes show only a single solid-liquid transition. Microcrystalline waxes can be differentiated from paraffin waxes both from changes in the infrared spectra at increasing temperatures and from the magnitudes of the absorbance ratios of the methyl and methylene groups in the hexagonal crystalline state and/or in the molten state. Conclusions about the branching of the alkane chains in the ureaadductible fractions of microcrystalline waxes may be derived from a comparison of their adsorbance ratios with those of pure normal alkanes.
A
of different physical methods have been suggested for classifying petroleum wax as a paraffin wax or a microcrystalline wax (5). These include melting point, congealing point, boiling range, viscosity, molecular weight, index of refraction, crystal size, cooling curve, and urea reactive content. Infrared spectra of solid wax films, hob-ever, have not been included among these methods. This may be attributed to the fact that the CH2 deformation and rocking modes a t 6.8 and 13.9 microns, respectively, exist as doublets which depend upon the crystalline structure of the hydrocarbons (9, 1 6 ) . In solution or in the liquid phase, single bands are observed a t these wavelengths (1). The term molten state is used in this paper to refer to the liquid hydroNUMBER
carbon phase in order to avoid confusion with solution in a solvent. Broadhurst (2) has found that the solid phases of all n-alkanes with more than nine carbon atoms in the chain can be described in terms of four crystal structures : monoclinic, triclinic, orthorhombic, and hexagonal. In the evennumbered n-alkanes from CzZ to Car and in the odd-numbered n-alkanes from Cg to (243, the hexagonal state is stable a t temperatures just below the melting point. The orthorhombic state is the stable low temperature phase of odd n-alkanes above C9and, probably because of impurities, is the phase generally observed for all n-alkanes above about Cd0. The triclinic and monoclinic structures have been observed as stable low-temperature phases in the pure VOL. 37, NO. 13, DECEMBER 1965
1737
Table
I.
Precision of the Absorbance Ratio Measurements
Ratio
Av. value
13.9/7.25 6.8/7.25 6.8/13.9
1.18 4.11 3.49
No. of
95%
detns.
Std. dev.
11 9" 9"
0.0482 0.118 0.123
Confidence limits
0.107 0.262 0.273 Absorbances of the 6.8-micron band which fell outside of the range 0.45 to 0.85 were
not included in these calculations.
even alkanes below C24 and in the pure even alkanes above C26, respectively. Guseva, Ashkinadze, and Leifman (6) have related changes in the infrared spectra of paraffin waxes to transitions from one of these solid phases into another or into the molten state. They observed that the hexagonal phase is characterized by a single, high-intensity band a t 13.9 microns a t temperatures in the range from the solid-solid transition temperature to the melting point. I n the molten state, a single absorption of lower intensity is noted at 13.9 microns. A number of investigators ( 4 , 7, 8, 18, 16) have measured absorptivities of the bands due to the CHZ and CHa stretching and deformation modes and to the CH2rocking mode in solutions of pure normal and branched alkanes. For the homologous series of n-alkanes from hexane to hexatriacontane, Jones (8) showed that the absorptivities of CH2absorptions a t six wavelengths were a linear function of the number of methylene groups with positive slopes. The absorptivity of the CHa deformation band of the methyl group a t 7.25 microns, however, increased only very slightly in the range 8 to 34 methylene groups. Smith and Rosenberg (16) concluded that the molar absorptivity of the methylene rocking band a t 13.9 microns in CSz solution of a variety of aliphatic molecules containing up to 20
carbon atoms was sufficiently constant to use for quantitative analysis. Thus, the chain length of an alkane can be estimated, if solubility permits, by measurement of absorptivities and calculation of methyl-methylene ratios. The solubility of microcrystalline waxes in solvents which are transparent in the 3.4-, 6.8-, 7.25-, and 13.9-micron regions of the infrared spectrum is far too low for measurement of speciiic absorptivities. Therefore, we have investigated the use of infrared spectra of films of waxes in the hexagonal and/or molten phase as a method of differentiating microcrystalline waxes from paraffin waxes, either as single products or in mixtures. This type of procedure could then be used to analyze small samples-e.g., 0.1 gram or less-of wax isolated from coating materials, or by chromatographic separation. A second purpose of this study was to develop a procedure for classifying the hydrocarbons in microcrystalline wax as normal, slightly branched, or highly branched alkanes. EXPERIMENTAL
Apparatus. The Beckman IR-4 spectrophotometer with NaCl optics was operated as follows: Chart speed 0.5 micron/minute with auto out; slit schedule standard; gain 4.0%;
period 2; wavelength scale 4 inches/ micron; ordinate scale 0-100% transmittance. The disappearance of the 13.7-micron band with increasing temperature was observed more readily with the expanded wavelength scale. The temperature of the sample was controlled by means of the variable temperature chamber made by Barnes Engineering Co. The temperature of this chamber was measured by means of a Biddle-Gray potentiometer calibrated for a copper-constantan thermocouple. Procedure. The thickness of the wax film which was cast between NaCl crystals was adjusted by repetitive melting and cooling to give an absorbance of 0.6 t o 0.8 for the 6.8-micron band a t room temperature in the variable temperature chamber. The background at 15 microns was then adjusted to about 95% transmittance by means of a beam attenuator-NaC1 block in the reference beam. The transition temperatures were measured in the following manner: The chamber was heated to a temperature about 2' to 4' C. above the melting point, and then cooled a t a rate of approximately 1' C./minute. When the 13.7- and 13.9-micron doublet reappeared in the spectrum, heating was resumed a t about 0.3' to 0.5' C./ minute and the 12.0- to 15.0-micron region was scanned periodically. The temperature at which the 13.7-micron band disappeared was recorded as the orthorhombic to hexagonal phase transition. Scanning of the spectrum was repeated until the intensity of the 13.9micron absorption became constant. The temperature a t which this took place is the solid-liquid transition temperature. The latter term is used in this report rather than melting point because the melting point of a wax as reported in the literature is not a true constant but depends upon the method of measurement (6). The absorbances were calculated by
Table II. Infrared Absorbance Ratios of n-Alkanes and Paraffin Waxes in the Hexagonal Crystalline State or Molten State
Transition temp., O C. Sample
Molecular weighto
Sunoco 5512 Sunoco 4415 Sunoco 4417 Sunoco 4312 Sunoco 4414 Sunoco 3420 Sunoco 3422 Sunoco 3425 n-CWHlozc n-CuHwd n-C.dss*
444 388 375 375 354 355 365 363 703 619 451
to
Absorbance ratios in hexagonal state
orthorhombic
A6.8 __
A13.9
A6.8 A7.25
A13.9 A7.25
59.8 46.5 46.0 45.6 43.0 40.0 38.2 34.0
1.76 1.57 1.81 1.48 1.82 1.52 1.70 1.96
9.71 7.84 11.1 10.5 11.0 11.7 9.92 9.30
5.51 4.99 6.17 7.06 6.06 7.73 5.85 4.75
62.5
1.62
11.0
6.83
... ...
... ...
... ...
a
Measured in the Vapor Pressure Osmometer in toluene at 65' C.
0
Roughly 90% pure. Contains lower molecular weight n-alkane.
...
...
* Measured from changes in intensity of the 13.9-and 13.7-micron absorptions.
d e
99.9% pure.
Eastman White Label.
1738
a
ANALYTICAL CHEMISTRY
Meltitg
point, C. lit. 67.2 57.7 59.2 60.5 57.7 56.6 55.0b 52.8 90.3* 86.4 68.0b
Absorbance ratios in molten state A6.8
A13.9 2.89 2.79 2.98 3.31 3.16 3.16 3.27 2.95 3.20 3.28 3.00
A6.8 A7.25
A13.9 A7.25
4.58 3.99 4.53 4.83 4.52 4.45 4.42 4.15 5.90 5.71 4.98
1.59 1.43 1.66 1.46 1.43 1.41 1.35 1.41 1.84 1.74 1.66
100
90 80
-
-
r
70-
5 Z
8050-
Z
u
E
40-
I
ah.9
a8
40
41
80
55
60
TEMP.,
85
70
OC.
Figure 1. Intensities of the 13.7- and 13.9-micron infrared absorptions of ndotriacontane as a function of temperature
a base line procedure (14). The preparation of the urea adductible fractions is described elsewhere (11). Samples. The microcrystalline waxes are commercial products manufactured by the Petrolite Corp., Bareco Division. The waxes which melt above about 85' C. are tankbottom derived, while the others are produced from petrolatum. The Sunoco paraffin waxes were provided by the Sun Oil Co., and are commercial products which consist of mixtures of n-alkanes as major components plus small amounts of branched chain hydrocarbons. The 99.99 % pure dotriacontane and tetratetracontane were obtained from J. A. Dixon of the Pennsylvania State University and were prepared under API Research Project 42. The n-pentacontane of estimated 90% purity was obtained by K. Greenlee, Chemical Samples Company, Columbus, Ohio. Reproducibility of Absorbance Ratios. Eleven separate films of a microcrystalline wax, Be Square 170/175, were prepared and the spectra scanned as described above. The calculations (17) of the precision of the absorbance ratio measurements are summarized in Table I .
+
micron band is no longer detectible is taken as the orthorhombic-hexagonal transition temperature. The temperature a t which the intensity of the 13.9micron band decreases sharply to a relatively constant value is taken as the hexagonal-liquid transition temperature. These temperatures depend upon the rate of heating of the variable temperature chamber and upon the thermal history of the wax. To minimize these effects, the procedure which is described in the Experimental Section was adopted. Since waxes are complex mixtures of hydrocarbons of different molecular weights roughly in the range 250 to 900, phase transitions are expected to take place over a temperature range rather than at a single temperature. Consequently, the transition temperatures which are reported in Tables I1 and I11 are average values. The differences between the orthorhombic-hexagonal and hexagonal-liquid transition temperatures vary from 7.5" to 17" C. for these eight paraffin waxes, which were found by GLC to contain from 12 to 17 major components (11). Large differences in the magnitudes of
the absorbance ratios in these two states are observed. For example, the 13.9/ 7.25 ratio is four-to-five fold larger in the hexagonal crystalline state than in the molten state, reflecting the decrease in intensity of the 13.9-micron band which occurs as a result of the hexagonal-liquid transition. In contrast to the paraffin waxes, the disappearance of the 13.7-micron absorption in n-tetratetracontane and in the nine microcrystalline waxes which were analyzed is coincident with a single decrease in intensity of the 13.9micron band as shown in Figure 3. These orthorhombic-liquid transition temperatures, absorbance ratios, and molecular weights are summarized in Table 111. The absence of the orthorhombic-hexagonal, solid-solid transition in microcrystalline waxes serves as one means of distinguishing them from paraffin waxes. The absorbance ratios of the microcrystalline waxes fall into two more or less distinct groups corresponding to the higher melting waxes (85'-90" C.) and the lower melting waxes (60'-77' C.) These absorbance ratios in the molten state remain essentially constant at temperatures up to 10' C. greater than the melting point. A second infrared method of differentiating microcrystalline waxes from paraffin waxes is obtained by measurement of the absorbance ratios at temperatures about 2' to 3' C. above those a t which the 13.7-micron absorption disappears and the 13.9- and 6.8micron bands become single absorptions. Under these conditions, the paraffin waxes are in the hexagonal phase while the microcrystalline waxes are in the liquid phase. In this case, the absorbance ratios of the paraffin waxes are 2 to 5 times larger than those of the microcrystalline waxes. For example, the absorbance ratios 6.8/13.9, 6.8/7.25, and 13.9/7.25 for Sunoco 5512, m.p. 67' C., are 1.76, 9.71, and 5.51, while the corresponding ratios for Ultraflex
RESULTS AND DISCUSSION
Differentiation of Microcrystalline from Paraffin Waxes. The temperatures for the transitions between the orthorhombic, hexagonal, and liquid phases, and the infrared absorbance ratios in both the hexagonal and molten states are presented in Table I1 for eight paraffin waxes and three pure n-alkanes. The 13.7- and 13.9-micron absorptions in n-dotriacontane and Sunoco paraffin wax change in intensity with increasing temperature in the manner shown in Figures 1 and 2, respectively. The points a t which the 13.7-micron band is observed only as a shoulder to the 13.9-micron band are indicated as "sh" in these figures. The temperature at which the 13.7-
a0
-
f
i 10-
44 4 0 -
I
E
ae '00
0
I
I
I
I
-x
I
VOL. 37, NO. 13, DECEMBER 1965
1739
White, m.p. 60.5’ C., are 3.40,3.71, and 1.09. Such differences are much greater than the 95% confidence limits (Table I) of 0.107,0.262, and 0.273,respectively1 for these ratios. Composition of Urea Adductible Fractions of Microcrystalline Waxes, As shown in Table 111, the ureaadductible hydrocarbons of microcrystalline waxes have higher solidliquid transition temperatures, larger values of the 6.8/7.25 and 13.9/7.25 absorbance ratios, smaller values of the 6.8/13.9 ratios, and lower molecular weights than the nonadductible components. These data are consistent with a lower methyl content and longer continuous methylene chains in the urea-adductible substances than in the nonadductible hydrocarbons. Further deductions concerning the structure of the urea-adductible compounds may be made from a comparison of their absorbance ratios (in Table 111) with those of pure n-alkanes and paraffin waxes (in Table 11). These ratios for the C-700 urea-adductible hydrocarbons, n-tetratetracontane, and n-pentacontane are identical within the 95% confidence limits. On the other hand, the ureaadductible hydrocarbons of the Iowermelting microcrystalline waxes, which have molecular weights of 570 to 600, have ratios which are smaller than those of the lower molecular weight (451) n-dotriacontane. Two postulates are offered to explain these results. First, the urea-adductible fractions which constitute about 75% of the higher-melting microcrystalline waxes are composed of
loo
-
00
-
40-
-
z
2
70-
so-
2 aoE bp
40-
mPO 10
-
straight chain or normal hydrocarbons. Second, the urea-adductible fractions which constitute 25 to 35% of the lowermelting waxes are composed of alkanes containing a single methyl branch, probably near the end of a long chain of methylene groups. The position of the branching is assigned by analogy to the structures of the isoparaffins in a refined paraffin wax which were identified by Levy, et al. (IO). The 2- or 3methyl substituted alkanes of carbon contents from 14 to 43 atoms per molecule in a wool wax were found to form urea adducts, but were not adsorbed by molecular sieves (IS). Edwards (3) has measured the crystallinity of a laminating grade of microcrystalline wax with average carbon number 40 and maximum carbon
Table 111. Solid-Liquid Transition Temperatures and Infrared Absorbance Ratios in the Molten State of Microcrystalline Waxes and W a x Fractions
IR
Microwax sample designation Ultracera Be Square 190/195
C-1035 C-700 C-700 urea-adductibIe (75%) C-700 nonadductible (25%) Be Square 170/175 Be Square 170/175urea-adductible (37%) Be Square 170/175nonadductible (63%) Victory Amber Victory Amberurea-adductible (33%) Victory Ambernonadductible (67y0) Ceraweld Amber Ceratak Amber
nonadductible (759 1740
ANALYTICAL CHEMISTRY
measured transition Molec- temp., “C. ular solid wt. to liquid
Absorbance ratio
760 680 675 677 657 745 665
89.5 87.4 85.9 85.8 86.6 77.0 73.3
in the molten state A6.8 A6.8 A 13.9 A13.9 A7.25 A7.25 2.98 4.96 1.67 3.23 4.81 1.49 3.13 5.27 1.69 3.49 5.38 1.54 3.21 5.76 1.79 3.65 4.42 1.21 3.49 4.11 1.18
603
81.6
3.20
4.92
1.54
734 610
62.3 73.0
3.57 3.45
3.89 3.77
1.08 1.09
576
78.8
2.90
4.53
1.56
716 570 560 684
55.7 69.5 69.8 60.5
3.39 3.72 3.61 3.40
3.40 4.23 3.98 3.71
0.996 1.14 1.10 1.09
570
72.5
3.00
4.64
1.55
749
51.5
3.49
3.35
0.958
number 60 to 65 by means of x-ray diffraction. His sample probably was similar to Ultraflex White, one of the lower-melting microcrystalline waxes. The crystallinity of the air-cooled specimen was 47.7%, while that of a quenched sample was 66.6%. This amount of crystalline material was much greater than his estimated normal alkane content of 15%. He suggests that “the long side chains of non-normal hydrocarbons, provided that they are somewhat larger than the normal chains, can cocrystallize side-by-Fide with the latter in substantially the same lattice as the normal paraffins alone.” Our postulate that the lower-melting microcrystalline waxes have a single methyl branch near the end of a large chain of methylene groups seems to be in accord with Edward’s assumption. Some evidence that the ureaadductible hydrocarbons are normal or slightly branched alkanes has been obt,ained by gas-liquid chromatography on 2-foot SE-52 Chromosorb G columns (11). When a mixture of 2-methyltricosane, n-hexacosane, n-dotriacontane, and n-tetratetracontane was injected simultaneously with a urea-adductible fraction, the three n-alkane peaks coincided exactly with three peaks of the urea-adductible hydrocarbons, the intervening peaks corresponding to the correct number of homologs. For the lower melting microcrystalline waxese.g., Ultraflex White-where the carbon number range extends from about 2123 to 65, the 2-methyltricosane eluted a t a temperature between those of two wax homologs. Since it appears that a 4-methyl substituted alkane may elute on these short columns a t the same temperature as its isomeric n-alkane ( I I ) , and because of the lack of pure branched chain hydrocarbons of carbon content about 35 to 55, the conclusions concerning molecular structure which may be derived by gas-liquid chromatographic separation of microcrystalline wax fractions are limited. Also, be-
cause of the nonavailability of standard compounds, information about longchain substituted cycloalkanes, which are likely to be found in microcrystalline waxes, can not be obtained from the GLC results. However, unless the cycloalkane ring contained methyl substituents, one would expect the infrared absorbance ratios to indicate the presence of terminal groups other than methyl. Infrared Spectra of a Mixture of a Paraflin and a Microcrystalline Wax. The 13.9/7.25 infrared absorbance ratio in the molten state of five mixtures of the lower melting microcrystalline wax, Be Square 170/175, and Sunoco 5512 paraffin wax in the range 10 to 90% are given in Table IV. A rough correlation between composition and the absorbance ratio is observed. The value of the ratio for the 50-50% mixture lies outside of the 95% confidence limits of the ratios of either pure wax. For mixtures of a high-melting microcrystalline wax with various paraffin or with polyethylenes, no such correlation was evident. The erratic ratios which were obtained seem to indicate the need for a fixed path, sealed cell technique if the melting points of the components of such a mixture differ by more than 15’ to 20’ C. It appears that much additional work will be required to determine if mixtures of microcrystalline and paraffin waxes can be analyzed by means of high-temperature infrared spectra. Molecular Sieve Studies. Analyses of the composition of microcrystalline waxes by absorption of the straight chain components into Linde Type 5A Molecular Sieves have been attempted. Only 52.3% of a sample of n-pentacontane was absorbed even after 112 hours of refluxing in toluene with a weight ratio of 75 to 1 of the sieves to hydrocarbon. After a 160-hour reflux in toluene, 27Q/, of Be Square 170/175 and 15% of Ultraflex White were absorbed by the sieves. The nonabsorbed fractions of these microcrystalline waxes amounted to 66.4% and 79.4%, respectively. In contrast, the nonadsorbed fraction of (2-700 was only 38%. For this wax, which is thought to contain about 75% n-alkanes, however, only 33% of the absorbed hydrocarbons were recovered after the 30-day elution in pentane. Hence, desorption
of long-chain hydrocarbons from the sieves is also a slow process. A more important factor which limits the usefulness of molecular sieve dsorption to determine the amounts of n-alkanes in microcrystalline waxes was discovered when the above fractions were separated by gas chromatography. Lower molecular weight components were observed in the chromatograms, apparently resulting from decomposition-e.g., cracking-on the sieves. For these reasons, additional work with pure hydrocarbons must be done before molecular sieve adsorption can be used successfully in separating the normal hydrocarbons from the branched and cyclic components of microcrystalline waxes. ACKNOWLEDGMENT
Table IV. Infrared Absorbance Ratios in the Molten State of a Mixture of a Paraffin and a Microwax Absorbance ratio in Per cent molten state Be Square Per cent A13.9 170/175 Sunoco 5512 A7.25 100 88.4 69.2 48.9 30.4 10.9 0
0 11.6 30.8 51.1 69.6 89.1 100
1.18 1.21 -_
1.32 1.34 1.50 1.47 1.59
(10) Levy, E. J., Doyle, R. R., Brown,
R. A., Melpolder, F. W., ANAL.CHEM. 33, 698 (1961). (11) Ludwig, F. J., Sr., Zbid., 37, 1732 11965). (12) McMurry, H. L., Thorton, V., Zbid., 24, 318 (1952). (13) Mold, J. D., Means, R. E., Stevens, R. K., Ruth, J. M., Biochem. 3, 1293 (1964). (14) -Rae, C. N. R., “Chemical Applications of Infrared S ectroscopy,” p. 535, Academic Press, &w York, 1963. (15) Smith, H. F., Rosenberg, A. A., ANAL.CHEM.35, 1182 (1963). (16) Snyder, R. G., Schachtschneider, J. H., Spectrochim. Acta 19, 85 (1963). (17) Youden, W. J., “Statistical Methods for Chemists,” pp. 8-20, Wiley, New York, 1951. \ - - - - I
The author thanks 0. W. Griffin, W. C. Holyoke, and T. H. Glenn for technical assistance, J. A. Dixon, Director of API Research Project 42, Pennsylvania State University, for samples of pure hydrocarbon standards, and K. Greenlee, Chemical Samples Co. for other hydrocarbon samples. The author is indebted to F. E. Mange, W. J. Heintzelman, M. I. Naiman and H. H. Coffman of Petrolite Corporation, and C. D. Gutsche of Washington University for helpful suggestions in the preparation of this paper and for their interest in this work.
RECEIVEDfor review July 6, 1965. Accepted October 13, 1965.
LITERATURE CITED
(1) Bellamy, L. J., “Infrared Spectra of Complex Molecules,” 2nd ed., pp. 22, 28, Metheun and Co., London, 1958. (2) Broadhurst, M. G., J . Res. Nat. Bur. Stds. 66A. 241 (1962). ( 3 ) Edwards, R.‘T., Tech. Assoc. Pulp Paper Ind., Spec. Tech. Assoc. Publ. 2, 95 (1963). ( 4 ) Francis, S. A., J. Chem. Phvs. 18. 861 (1950). (5) Ferris, S. W., Tech. Assoc. Pulp PaDer Ind.. Svec. Tech. Assoc. Publ. 2. 1 (i963). ’ ‘ (6) Guseva, A. N., Ashkinadze, L. D., Leifman, I. Ye., Neftekhzmya 2, 662 (1962). ( 7 ) .Hastings, S. H., Watson, A. T., Williams, A. B., Anderson, J. A., Jr., ANAL.CHEM.24, 612 (1942). (8) Jones, R. N., Spectrochim. Acta 9, 235 (1957). (9) Krimm, S. Liang, C. Y., Sutherland, G. B. B. J. Chem. Phys. 25, 549 (1965).
id.,
Correction The Rotating Disk Electrode Effect of Rates of Rotation and Polarization I n this article by Ilana Fried and Philip J. Elving [ANAL.CHEM.37, 803 (1965)] on page 805, column 1, the last sentence of the fourth paragraph should read: “When the time of experiment is not sufficient for the concentration gradient to develop to the distance (a) where both convection and diffusion play equal roles in mass transport, or (b) where convection predominates over diffusion, then the current-voltage curve resembles that obtained a t stationary electrodes.’’
VOL. 37, NO. 13, DECEMBER 1965
1741
