Determination of Oil Content of Pecans New Sulfuric Acid Digestion Method RULOND. LEWIS,Bureau of Chemistry and Soils, Shreveport, La.
T
HE gravimetric+&her extraction methods now used for the quantita&% determination of the oil or fat content of pecans have several disadvantages. First, they are time-consuming, a factor to be considered when many tests are to be made; second, ether solvents extract other materials besides oil; and third, it is practically impossible to drive off all moisture without oxidizing some oil. A new method for extracting oil from pecans has been developed which overcomes the foregoing disadvantages, at least in part. It is based upon the same procedure as is applied in the Babcock cream test. Pecan oil in a pure state is liberated from the nut meats by dilute sulfuric acid a t a certain temperature. With the ether extraction method, from 21 to 22 hours are necessary for making the test, as compared with 30 minutes with the new method. Aside from the considerable time saved by the new method, some progress has been made in overcoming error. Preliminary tests indicate that the method gives promise of equal value in the determination of oil in nuts and seeds of other plants, such as peanuts, walnuts, coconuts, cotton seed, flax seed, etc.
EQUIPMENT AND MATERIALS 1. Fifty per cent, 9-gram, so-called "6-inch cream-test" bottles, used in the Babcock cream test, They have a bulb capacity of approximately 45 cc. 2. A centrifugal machine equipped with a Babcock-test attachment and geared to a speed of 800 to 1000 revolutions per minute. 3. A constant-temperature bath, large enough to hold all the bottles used in one run, deep enough to come within 0.5 inch (1.27 cm.) of the top of the test bottle, and capable of maintaining temperatures of 55" and 65' C. 4. Sulfuric acid, with a specific gravity of approximately 1.84, diluted 1.5 to 1 part of water.
balanced, and after the proper speed (800 to 1000 r. p. m.) had been attained, whirled 5 minutes. The bottle was filled to the neck with dilute sulfuric acid and whirled 3 minutes. More acid was added until the liquid column approached near the top graduations of the scale, and the bottle whirled 1minute, The bottle was transferred back to the water bath for 10 minutes a t 55" C. With the aid of dividers or calipers, the spaces occupied by the oil column from its lower surface to the top of the upper meniscus were measured. The per cent oil can quickly be calculated using the formula: Spaces oil occupied in test bottle ' oil Spaces 1 gram oil occupied X wt. of sample X 100 = %
As the cream-test bottles used are graduated to read in terms of butter fat and not pecan oil, it was necessary to determine the spaces occupied by 1 gram of oil and calculate the per cent of oil from the factor found. The spaces occupied by 1 gram of oil were determined as follows: a creamtest bottle was filled to the neck with sulfuric acid (1 to 1.5) and pecan oil was added to the first graduation of the bottle, then the bottle was placed in the water bath for 10 minutes at 55" C., transferred to the centrifuge, and whirled 3 minutes. The bottle was again placed in the water bath at 55" C. for 10 minutes and the space occupied by the upper meniscus of the oil read. Now the test bottle was placed on the analytical balance and 3 grams of oil accurately weighed into it; then it was placed in the water bath for 10 minutes at 55' C., transferred to the centrifuge, and whirled for 1 minute after the proper speed had been attained, and again placed in the water bath for 10 minutes at 55" C. With the aid of calipers, the spaces occupied by the 3 grams of oil were measured from its lower surface to the top of the upper meniscus. The spaces occupied by the 3 grams of oil divided by 3 equals the space occupied by 1gram of oil. By using the factor thus obtained, the per cent oil is readily calculated.
EXPERIMENTAL PROCEDURE TABLE I. SPACES OCCVPIEDBY OIL FROM DIFFERENT VARIETIJJIS OF PECANS The pecans used for this work were collected from orchards (1 gram of oil at 6 6 O C.) in Texas and Louisiana and consisted of several of the more V A R I ~ TOF Y PECAN SPACESOCCUPIED common varieties. These nuts were cracked and stored in Sohley 11.16 tightly sealed bottles; then, as needed for experimental Moneymaker 11.16 Pabst 11.17 purposes, were very finely ground with the nubbutter cutter Success 11.22 Stuart 11.23 in a Russwin food chopper, and used immediately. Moisture determinations were made on all samples of nuts RESULTS BY PETROLEUM ETHER TABLE11. COMPARATIVE by placing a 10-gram sample of finely ground nut meats in the EXTRACTION AND NEW METHOD vacuum oven at 65" C. for 5 hours a t approximately 12.55 OIL BY OIL BY PBTROLWJY pounds vacuum. All calculations were based on oven-dried VARIETY OF PECANS NEW MEITHOD ETHEREXTRACTION samples. % % 77 ..io 77 ,'BO All oils used for comparison were tested for oxidation, using Schley 76.34 76.83 Kreis' test for detection of oxidation. Any oil found to be 74.36 74.10 Success oxidized was discarded. 76.04 74.20 Four grams of the finely ground nut meats were weighed 73.11 73.77 Stuart and transferred into a dry cream-test bottle (this can be 76.10 74.40 accomplished by cutting off the stem of a 4-inch (10.16-cm.) 72.89 72.62 Pabst 74.43 73.96 glass funnel and holding it in position over the test bottle). Next 35 cc. of dilute (1 to 1.5) sulfuric acid were added and 76.26 76.39 Moneymaker 77.73 77.68 the bottle placed in the water bath for 15 minutes at 65" C. (a higher temperature will give a dark color to the oil). The The space factor is not the same for all varieties of pecans. bottle was shaken occasionally to aid digestion of the nut meats, and was then transferred to the centrifuge, counter- Table I shows the spaces occupied by 1 gram of oil at 55" C. 296
July 15, 1932
INDUSTRIAL AND ENGINEERING CHEMISTRY
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for several varieties of nuts. From this table it is evident that the spaces in the cream-test bottle occupied by 1gram of oil vary slightly with each variety. The average of all the tests was 11.18 spaces occupied by 1 gram of oil. Using the factor 11.18 gives results very near to those obtained by the gravimetric method, as seen in Table 11. Greater accuracy, however, can be obtained by using the individual factor for each variety of nuts, but this does not seem necessary for most work. More work needs to be done a t this point and will be undertaken when time permits.
The percentages of oil as determined by the petroleum ether extraction and the new method are shown in Table 11. Samples of each variety were collected from two different localities and the determinations made in duplicate. The results are found to compare favorably. Table I11 shows a comparison of the physical and chemical characteristics of pecan oil extracted by expression and by the two foregoing methods. This table shows the oil from the different methods to have practically the same properties. The refractive index and specific gravity were the same with all three methods. The iodine number and saponification number were highest with the new method, indicating that a TABLE111. CHEMICAL AND PHYSICAL CHARACTERISTICS OF PECANOIL EXTRACTED BY EXPREBSIOM, PETROLEUM ETHER, purer oil was obtained by this method. AND NEW METHOD ACKNOWLEDGMENT (Stuart variety) REFRACTIVE The author wishes to express his indebtedness to A. 0. IODINE INDEX SPECIFIC Alben, Pecan Soil Fertility Laboratory, U. S. Bureau of No. (ABBB RE- SAPONI- GRAVITY M ~ T H OOF D (WIJS FRACTOME- FICATION (WESTPHAL Chemistry and Soils, Shreveport, La., for valuable suggesEXTRACTINQ METHOD) TBR) No. BALANCE) COLOR tions and kind assistance in connection with this work. Light golden 1.4670 189.89 Expressed 102.86 0.9190 Petroleum ether 103.27 New method 103.83
1.4670 1.4670
187.80 189.95
0.9190 0.9190
Light golden Colorless
RECEIVED December 23, 1931.
Graphic Calculations in Water Analyses JOHNKENNETHSELLERS, Copper Queen Laboratory, Bisbee, Ariz.
T
HE facts that the existing methods for calculating the
elements and radicals present in mineral waters into certain hypothetical combinations are many and diverse, rendering the results of such calculations confusing and not readily comparable one with the other, and that modern ahemical knowledge Eully justifies no such calculations, are diverting the general tendency toward the ionic form of stating the results of water analysis. The practice of combining the ions, however, still finds extensive application in industry] and various schemes have been evolved whereby these calculations are reduced to a routine applicable by the operator with limited chemical training. The use of milligram equivalents (or reacting values) in water analyses has long been practiced (1,4), and anelaboration on the use of equivalents has been made by graphically r e p r e s e n t i n g the results of analysis (2’8). These graphic representations have been employed for a number of years in p u b l i c a t i o n s of the U. S. Geological Survey. The use of equivalents may be further extended to thelength of integrating the hypothetical combinations by mechanical methods. I n the method herein advocated, a determination of calcium, magnesium] carbonate, sulfate, and chlorine is made. The results, stated as parts per million, are converted to the milligram equivalents per kilogram (Stabler’s reacting values, 4) by multiplying by the rec i p r o c a l s of the c o m b i n i n g weights of the respective ions. The r e s u l t s being thus conFIGURE1
verted, any ion may be combined with any other ion in numerically equal quantities. The advisability of determining the sodium and potassium is contingent upon the accuracy desired, and when sodium and potassium are not determined, such an amount of sodium is “written in” as will cause the sum of the equivalents of the acid radicals to be exactly equal to the sum for the bases. The probability of the two sums balancing when all of the ions are determined is very small, and the small difference usually existing is distributed so as to effect a balance.
FIGURE 2
The equivalents of the positive and negative radicals, being thus adjusted, are then consecutively laid out on prepared coordinate paper (calibrated in milligram equivalents) on either side of a central line (Figure 1). The length on the graph representing an ion may be called the “reacting length” of that ion. Since linear distance on the graph is quantitatively proportional to the equivalents of the ions, it is also proportional to the equivalents of the compounds. All radicals lying laterally contiguous are combined, and the compounds supposedly present in the sample may thus be instantly visualized. The failure of two radicals to lie laterally adjacent connotes the absence of the compound composed of those two radicals. The results as read from this graph are in terms of milligram equivalents and necessitate a conversion into the desired units. A series of graphic scales, one for each possible compound, are constructed for this purpose (Figure 2) and may be used indefinitely,
