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(2) Burrell, G. A., and Seibert, F. M., U. S. Bur. Mines, Bull. 197 (19261, (3) Martinek, M. J., and Marti, W. C., IND.ENG.CHEM.,Anal. Ed., 3, 408-10 (1931). (4) McKee, R. H., and Burke, s. p., IND.ENG. CHEM.,15, 578-9 (1923).
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(5) Nidloux, M., and Scotti-Foglieni, L., Compt. rend. SOC. b f d , 98, 225-8 (1928). (6) Roka, K., and Fuchs, O., 2. anal. Chem., 71, 381-6 (1927). RBOEIVBD October 22, 1931. Published by permission of the Director, U. S. Bureau of Mines. (Not subject t o copyright.)
Some Titer Points of Mixed Fatty Acids 11. Mixtures of Pure Fatty Acids GEORGEW. JENNINGS,355 Marlborough Road, West Palm Beach, Fla.
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HE titer points of fatty acids and of mixtures of fatty acids is of such importance commercially, both in evaluating fats and in using them, that a better understanding of their behavior is desirable. Continuing the work reported previously (S), the titer points of mixtures of relatively-pure fatty acids were determined. It was expected that these figures would furnish indications, at least, of the causes underlying the seemingly erratic results obtained in several cases with commercial fats and oils. This was found to be true, but the behavior observed needs elucidation and consequently no explanation can be attempted until further data have been secured. The particular fatty acids predominating in the fats or oils to be mixed apparently determined the character of the resulting titer curve. The several other fatty acids usually present, although in much smaller amounts,
influence the curve somewhat, but to just how great an extent has not yet been determined. The four fatty acids selected for this work were lauric, myristic, palmitic, and oleic. The selection was determined principally by the fact that mixtures of the glycerides of these (together with that of stearic acid) in varying proportions form the majority of the commonly occurring nondrying oils and fats. The other acids, such as caproic, caprylic, capric, linoleic, etc., are present in much smaller quantity. The lauric, myristic, and palmitic acids were the specially purified grade of the Eastman Kodak Company. The oleic acid was purified in the laboratory, using a high-grade commercial red oil as the source, by the lead salt-ether method with subsequent fractionation under reduced pressure. That none of these acids was strictly chemically pure is recognized. It is a very difficult matter to effect the absolute separation of the fatty acids from one another (Z?), especially when acids close to each other in the series are under consideration, and for the present purpose strict chemical purity is not essential. The acids used were, however, of a relatively high degree of purity. The titer point is not a value of as high an order of accuracy as are some of the other physical constants. It varf certain limits according to the method employed mining it, the exact technic exerting considerable influence upon the result. The amount of fatty acid used, the method of stirring, the differential in temperature of fatty acid and surrounding bath, and the number of times the titer has been read on the same portion of fatty acid are a few only of the variables which must be standardized because no particular method can be considered the only correct one. Because of this factor of inherent variability in the titer itself, absolute purity of the fatty acids was not considered essential.
PROCEDURE The fatty acids were kept dry and, just before determining the titer point, were weighed out carefully in the desired proportions in a 50-cc. glass beaker; they were heated to about 115' C., thoroughly mixed, and, after cooling somewhat, were transferred to the titer tube. Determination of the titer from this point on was in accordance with the method of the Fat Analysis Committee of the AMERICAN CHEMICAL SOCIETY (1).
The results are reported in the form of curves which are plotted with the titer points as ordinates and the percentage composition of the mixed fatty acids as abscissas. OF LAURIC AND FIGURE1. TITERCURVEFOR MIXTURES MYRISTIC ACIDS OF LAURIC AND FIGURE2. TITERCURVE FOR MIXTURES PALMITIC ACIDS FIGURE3. TITERC
DISCUSSION OF RESULTS As it was desired to learn in the f i s t place the effect of mixing two acids adjacent to each other in the same homologous series (considering only acids with an even numberof carbou atoms), lauric and myristic were selected. The curve resulting
July 15, 1932
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44 per cent is present does the titer reach that on the mean line. At no place is the curve much above this line. As might be expected in view of the two preceding results, the addition of myristic acid (intermediate in position in the series between lauric and palmitic) to oleic, as shown in Figufe 5, gives a curve intermediate in form between that for lauric and palmitic acids. The titers of all mixtures are either on the line or above it, but there is no abrupt or great rise in any portion. That it is not possible to generalize about the behavior of the titer of mixtures of other acids until further data have been secured is apparent in view of the results obtained with these four acids. Mixtures of several other saturated acids, both with a less and with a greater number of carbon atoms, must be tried, and these acids in turn mixed with oleic. Another unsaturated acid-linoleic-present in corn oil, cottonseed oil, etc., as well as in the drying oils such as linseed, must be used before any attempt can be made to explain or predict the behavior of mixtures of naturally occurring oils and fats. LITERATURE CITED (1) American Chemical Society, Committee on Analysis of Commercial Fats and Oils. IND.EXQ.CHEM..18. 1346 (1926). (2) Francis,, Piper, and Malkin, Proc. Roy. SOL' (London), 'A128, 214-52 (1930). (3) Jennings, Q. W.,IND.ENQ.CHEM.,23, 413 (1931).
RECEIVED February 13, 1932.
FIGURE 4. TITERCURVEFOR MIXTURESOF OLEIC AND LAURICACIDS FIGURE5. TITERCURVEFOR MIXTURESOF OLEICAND MYRISTIC ACIDS (Figure 1) shows the depressing effect upon the titer of the addition of a higher titered material. This is similar to the effect upon the melting point observed in general when two materials similar chemically are mixed, but in the case of fatty acids no generalization can be made. The lowest point was reached with the mixture containing 30 per cent myristic acid. Mixtures of lauric and palmitic acids (Figure 2) give ti curve similar to Figure 1, but distinguished by the fact that palmitic acid, although having a higher titer, exerts a greater depressing effect upon the titer than does myristic acid. The low point, however, is reached at the mixture containing 30 per cent palmitic acid, just as 30 per cent myristic acid gave the low point in Figure 1. At approximately 60 per cent lauric acid the two curves cross each other and from there on the mixtures containing palmitic acid have the higher titer. At the point of greatest depression the titer of the mixture of lauric and palmitic acids is almost 15" C. below the "mean line." This is the line connecting the titers calculated arithmetically from the titers of the two pure acids involved (3). Mixtures of saturated acids with an unsaturated acid were tried next. Because its glyceride is a constituent of so many different naturally occurring oils and fats, oleic acid was selected. as the unsaturated acid. Figure 3 shows that the addition of a high titered acid (palmitic) raises the titer of the mixture even from the beginning, contrary to the effect observed in the two previous cases. The rise is abrupt and remarkable, reaching in one portion of the curve a point 16" C. above the mean line. Figure 4 shows the effect of mixing lauric acid with oleic. Instead of raising the titer of the mixtures, as did palmitic acid, it depresses it sharply a t the beginning, and not until
New Specification for Burets WITHROWMORSE,Rijhm and Haas Co., Bristol, Pa.
B
I
MARKEDBURET
Y MEANS of a few marks representing tenths of cubic centimeters below the lowest graduation of a buret, many exasperating errors of passing this mark can be obviated. Few chemists have escaped these experiences, owing to diverted attention, defective eyesight, poor light, or other cause. The added graduations should be s h o r t e r t h a n the s t a n d a r d marks to insure against mistaking them for divisions of the lowest cubic c e n t i m e t e r of t h e buret. Frequently the buret is used as a large pipet of the Mohr type. I n such a case the additional marks serve a useful function where a few tenths of a cubic centimeter are demanded beyond the decimal aliquot (10 cc., 50 cc., 100 cc.). Refilling the buret to accommodate a fraction of a cubic centimeter is obviated. The Arthur H. Thomas Company kindly prepared a buret to this specification. R B C ~ I V EMarch D 2, 1932.
