method for determining the acid number of fats and oils proposed by Koettstorfer in 1879 (4), which is the basis for the official methods, has been retained with slight modifications through the years.In general, organic neutralization indicators have been employed in the neutralization procedures. However, in 1931, Demarest and Rieman {2) used the potentiometric method for determining the saponification number of mixtures of asphalt and drying oils in alcohol-anisole solutions. In 1932, Caldwell and Mattiello (1) applied this procedure for the determination of the acid number of linseed oil, its free fatty acids, and bodied oils.
An ester-fractionation method, not involving acetyl values, for the analysis of natural or synthetic mixtures containing hydroxy fatty acids is illustrated by reference to a synthetic mixture containing 70 per cent. by weight of the mixed fatty acids of groundnut oil and 30 per cent. by weight of ricinoleic acid. Saturated acids are removed by the usual lead saltalcohol separation ; oleiclinoleic acid mixtures are not separated from ricinoleic acid, presumably because of the insolubility of the lead salts of ricinoleic acid in light petroleum owing to mixed salt formation, but a concentrate of oleic (containing linoleic) acid can be separated from one of ricinoleic (containing linoleic) acid by two precipitations of the urea-insoluble adducts of the oleiclinoleic mixture in methyl alcohol. The composition of the original mixture is calculated from the values of the saponification equivalents and iodine values of the fractionated methyl esters of the saturated and oleiclinoleic acid extracts and of the fractionated acetylated methyl esters of the ricinoleic acid extract. Results agree well with theory.ALTHOUGH Riley,l and Gupta, Hilditch and Riley2 have recently published a method for the component fatty acid analysis of castor oil, the method was exceptional in that it dealt with hydroxy fatty acids at concentrations of over 90 per cent.; moreover, linoleic acid was determined by the spectrophotometric technique, which is not readily accessible to many laboratories. The literature reveals that when a hydroxy fatty acid is encountered in a €at, the fat analysis is never s a t i ~f a c t o r y . ~~~~~ Consequently a method for the routine analyses of these natural fats or of any mixture containing hydroxy fatty acids was required. I n the procedure described here no acetyl values, which require large quantities of material for accurate determination in replicate, are necessary after the initial determination ; subsequent ester fractionation followed by the usual determination of saponification equivalents and iodine values of each fraction suffice, and so bring these mixtures into line with other fats, from an analytical point of view.I n the earlier stages of this work, a synthetic mixture of 70 parts by weight of the mixed fatty acids of Annona squamosa seed fat (iodine value 85.9) recently analysed in these laboratories,g with 30 parts by weight of fairly pure ricinoleic acid was used as test material; subsequently, the analysis was carried out on another synthetic mixture in which the mixed fatty acids of groundnut oil (I.V. 92.0) replaced those from A . squamosa in the same proportion by weight. Saturated acids were easily separated by the usual lead saltalcohol procedure.
1317sample and six differently stained specimens were prepared by adding from 0.1 t o 1.5 ml. of the stock sample t o 50 ml. of the specimen. The same procedure was adopted in the case of the other two samples. T h e discoloration so obtained was expressed in Lovibond tintometer units (in a l/a-inch cell). These values are given in column 2 of Table I. The procedures for the preparation of emulsions of these samples have been given.With a few exceptions (indicated in the table), emulsions were clear and the indicator end points were easily observed during the aqueous titrations. In the case of the few rather stained emulsions, difficulty in observing the indicator end point gave rise t o a slightly higher deviation from the standard results. The data obtained are shown in Figure 2, curves IIIA, IIIB, IVA, IVB, and V. Only five specimens were titrated potentiometrically and the others with indicator only.The aqueous titration curves show a striking similarity to the standard curves of Figure 1. The indicator end points in the aqueous titration occur before the zero potential of the electrode combination is reached and are consistently lower than the potentiometric end points. I n the aqueous titration curves for oleic and stearic acids, the potentiometric end points closely correspond t o the acid numbers of the turpentine solution of the fatty acids, based on the standard method (7.98 and 7.63, 8.08 and 7.73). In the other samples, except for extremely dark specimens, the per cent deviation averages 2 t o 3%. The fact that aqueous titration gives consistently lower results suggests that the hydrolysis of the soap is initiated only during the last stages of the titration. CONCLUSIONSThe method outlined above has certain limitations. It is likely t o give low results in the case of oils containing steam-vola-tile fatty acids like coconut oil, palm kernel oil, and butter fat, and in the caw of highly rancid oils which would have undergone breakdown into volatile constituents. The method is not suit-. able for materials having low acid numbers, and it also suffers by being time-consuming. Thr refluxing with water would have heen espect.ed to give riw to some h>-drolysis of the neutral fat, with a corresponding increase in the acid number, hut the results do not warrant ,such fears, as the arid number h\the emulsion method does not show higher results.The method dispenser with costly solvents like alcohol and ether, gives a definitt, cwd point trith phenolphthalein, and is particularly suit,al)le for &irk colored oils and resins.The picsent papw serves to indicatr thr possibilities of the method dwcribed, using emulsions instead of solutions, and further work may help in making it simpler and more serviceahle. Finally, while the pi'rsrnt Ivork tries to esamine the possihilities of a nc'tv mcthod, it also indirrctly d r a w attention to one of the many peculiarities of emulsif>-ing agents adsorbed a t the emulsion interface., ; attempting to evolve a simple colorimetric met'hod resins, a~ an alternative method to the u...
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