JULY
'
453
1947
The vari:ition in room temperatures in most laboratories is not sufficiently high to require the use of a constant-temperature bath. Should the temperature be a hove 28' C. or below 23' C. it would he advisable to use a constant-temperature bath for shaking the fuel and iodine mixture or to modify the shaking time or rate. As an esample of the variation to be expected Tahle I1 gives the results ohtained n-ith the same fuel using different temperatures during shaking. The rapid iodometric method lins herri used successfully on many differelit types of fuel. Fuels containing paraffins, naphthenes, aromlitics, olefins, and vai,ious other additives have been m a lyzed, :is shown in Tahle 111. The table lists first the fuels that did not requiye acid estraction and then those which do. Since the experience of this lahoratory with unsaturated gasoline types i h limited, it may he well to restrict the method to the usual aviation fuels unless esperinientation sIioi~-sthat, the acid est,raction method will apply. -1comparison of the results ohtained by the .I.S.T.lI. (1) and the rapid iodomet1,ic methods indicates a masimuni deviation of ==0.0t5ml. of tetrarthyllrad per gallon for the rapid iodometric
method; duplicate determinations agree ivitliiii the 0.03 ml. of tetraethyllead per gallon limit specified in the A.S.T.M. procedure (1). It has been the experience of this laboratory that the approximate tetraethyllead concentration is kriown for most of the fuels analyzed. I n addition, very few fuels contain interfering substances, so that the direct procedure is the one most frequently used. Thus the time required for most rapid iodometric method determination? is ahout 10 minute$. By use of the shaking machine, txvo Concurrent determinations on the same fuel can be made in about 15 minutes. If the acid estraction is required, the time per determination is about 20 minutes, or two concurrent determinations on the same fuel can he done in 25 minutes. LITER.ATUKE CITED
(1) A I I I . Sor. Te6ting Materials, .\.S.T.M. Standards P a r t 111. p. 219,1944. (2) Lykken, L., Tiesedei, K.S..Tueiiiiiilei, F. D., and Zahn, V.!Isu Esc. CHEM.,A N ~ LED.. . 1 7 , 3 5 3 (1945). (3) Shell Marketiiig C h . , Ltd.. London, private conimunication. (4) Vidiiiaier, O . , L r i f f f u h r f - F o r i c h . .20,181 (1943).
Rapid Method for Determining Oil Content of Tung Kernels JOSEPH H43IlLTON
4ND
SEY3IOUR G. GILBERT
Hureau of P l r m t Itidustry, Soils, and Agricultural Engineering, .4grictcltural Reseurch 4dmini.stration, z'. S . Department of Agriculture, Gainescille, Fla. In a rapid method for determining oil in tung kernels, a flaked or ground sample is dispersed in a Waring Blendor t y p e of disintegrator w ith a commercial hexane soltent. The solution of oil that resultk is separated from the kernel residue by allowing the sedinieut to settle in a bolunietric flask. The oil in an aliquot of the supernatant liquid is w eighed after elaporation of the solbent, and the percentage of oil is calculated on the basis of the total >olume occupied bj sediment and solution. On the basis of precision, accuracj, and rapidity, the method appears to hale distinct adlantages oler the iisrial percolation procedures.
A
H0L-T 2000 oil determinations are made ari~iuall>-at this station in the evaluation of experiments 011 tung culture. is thus of importance and an effort has beni made to find a procedure of sufficient accuracy and precision that would require less time thart the percolation typt. of cxtraction, using the Goldfisch apparatus heretofore in regular use at this laboratory ( 7 ) . Methods involving o t h n principles liavtr htwi developed ( 2 , 6) but have not been found suitable. The use of the \Taring Blendor for the determination of carotene with prtroleum ether ( 3 ) suggested the possibility of using this apparatus for the determination of oil in tung kernels. Preliminary experiments in 1941 showed that use of the Blendor was feasible, and in 1945 detailed n t u d i s were varried out, the results of which are reported here. Routine use of the niethod during 1945 and 1946 has given very satisfactory results. Since initiation of this work others have publiehed results o n the use of the blender for detrrmining oil in plant (4) and animal (5) material. In both of these studies the lipides were first eniulsified with water in the blendw and then freed from the emulsion bj- a sequence of manipulations. The method developed in this lahoratory for samples of low nioi?;tuw content is simpler since 110 emulsions are required. DETAILS OF RIETHOU
-1representative sample of the kernels from air-dried fruits is flaked (7'1, or ground twice in a Vniversal S o . 73 food chopper using a 16-tooth cuttPr, Thrl flaked or ground krrnrl material is
r horoughly riiisecl, a 10-gram portion of the uaniple is transferred t o a Waring Blendor, 170 ml. of Skellysolve B are added, and thr
material i.- agitated for 5 minutes. The blender disintegrates thr Haked or ground krrnel, the oil being dissolved in the solvent. Thr resulting solution of oil, with its suspension of tung meal, is transferred through a funnel into a 250-ml. volumetric flask, prefclrably a flask that is calibrated from 245 to 255 ml. in 0.5-ml. diviiicnis. The entire contents of the blender jar are carefully rinsed into thta ,flask, enough solvent is added to adjust the total volunit' t o ahout 252 nil., the contents are thoroughly mixed, and the flask is set aside t o cool and settle a t room temperature. In determinations on kernels from air-dried fruits the solutions at'e usually sufficiently clear after settling for about an hour. Smiplt~.;ext rcsmely lo\\- in moisture content, appear to require a longer time t o settle. The solution comes from the blender at B rrlnperature of 40 to 50' C. and hence will shrink several niilliLiters on wioling to room temperat,ure. Following settling, the final voluinc of the contents is read from the calibratioiis of the Hask, and a 50-nil. portion is pipetted into a thoroughly cleaned, tared 250-nil. heakrr . For routine determinations of a number of samples, only one graduatcd flask is required for each group of samples. Ordinary 250-nil. volumetric. flasks are used for the rest of the group, all ht:ing made to volunie a t the same temperature in a water bath. Subsequent volume changes during settling are corrected for by reading the graduated flask. A 1-ml. Mohr pipet can be used in d i b r a t i i i g t h r flasks above and below the 250-nil. mark. Foi precise work, the temperature of the oil solution should be within 1 of rooni temperature a t the tinir of aliquoting. The solvent is evaporated OII a steam bath, the final traces being removed in a vacuum oven a t 70" C. and I-mm. pressuw. Hoa-evrr, a skilled operator can obtain essentially the same results Iiy distilling the solvcnt on a hot platt,, prt,ferahly unticxr a hootl,
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Table I. Average Effects of Kernel Source and Blender Jars on Determinations of Oil in Tung Kernels, Dry Basis
F5 6 5 09 I 66.62 F62 70 71 I1 66.66 F88 64.12 E a c h result for blender jars is mean of 24 determinations, for source of kernel is mean of 16 determinations, ~~~
Table 11. Effect of Sample Size, Method of Preparation, and Length of Blender Run on Oil Determinations on Tung Kernels, Dry Basis Length of Blender Run
& G r a m Sample Flaked Ground Ar.
10-Gram Sample Flaked Ground Av.
Min. 66.33 5 66.84 67 09 66.96 66.93 66.84 66.88 67.21 10 66.92 66.77 Av. 66.88 66.96 Standard deviation for all 5-gram samples Standard deviation for all 10-gram samples Each initial result is mean of 6 determinations.
65.70 66.18 65.94 0.44 0.22
66.02 66.70 66.36
taking care to avoid overheating the oil (discoloration). If preferred, the beakers containing the oil may be transferred to a laboratory oven a t 7 0 ” C. a t atmospheric pressure for 15 to 30 minutes for removal of final traces of solvent. The beaker plus oil is weighed after cooling to room temperature. Exposure to the air in the balance room does not materially affect the weight. The wei h t of oil in the beaker (obtained by difference) multiplied by 1750 of the volume of the contents of the flask a t the time the aliquot is taken gives the weight of oil in the sample used. A l l results reported herein are calculated to a dry-weight basis from a separate moisture determination ( 7 ) . Under special conditions certain modifications of the above method may be advisable for obtaining maximum accuracy. EXPERIMENTAL PROCEDURE
19, N O . 7
tated. I n the factorial test the flaking and grinding methods of preparation were compared and, m seen in Table 11, although in 5-gram samples there was little difference between flaked and ground material, in 10-gram samples the flaked material gave 0.83 higher percentage of oil than ground material. On drying and sieving the residue from the two sets of materials it m’aa found that the flaked material was more thoroughly disintegrated than the ground material, thereby probably allowing for better extraction. Flaked material should be used for the most precise determinations. Length of Blending Period or Time. As one would expect, the 10-gram samples are more affected by length of run than &gram samples. The 5-gram samples are apparently fully extracted in 5 minutes, whereas the 10-gram samples take 10 minutes (Table
11). Effect of Blender Jars. The differences between readings for different blender jars (Table I) ivere without significance. The performance of the blending assembly with hydrocarbon solvents, however, is not entirely satiefact’orp. After use for a varying period, the solvent penetrates to the porous-bronze bearing surface of the blender blade assembly and dissolves the lubricant. Blank determinations shoJv the contamination of the sample by the lubricant to be negligible per run, but continued use results in overheating and reduced speed. Performance of the blenders is erratic, one new blender blade assembly having become unusable a t the end of the eighth consecutive 5-minute run, ivhile others have performed satisfactorily for several dozen runs. After the blender assembly becomes worn the solvent leaks out around the shaft or some of the fine sediment’ may lodge inside the assembly. Blade assemblies, which are supplied by the manufacturer, can be replaced in a few minutes.
Table 111. Refractive Indices, na5,as Affected by Three Experimental Factors Method
Some of the important factors affecting the accuracy and precision of the blender technique were examined in a factorial study which included all combinations of several different “factors” or sets of procedure variables. The factors studied were: source of kernel, weight of sample, method of preparing sample, length of blending period, and use of different blender jars. Additional studies were made in which the blender and Goldfisch methods Rere compared and the effect of moisture content was investigated. The data from the factorial study are given in Tables I, 11, and. 111. An analysis of variance is given in Table IV. The effects of these factors are discussed below. At the suggestion of the editor, the original experimental data have been provided (Table VII) for readers who may wish to use the data as an example in analysis of variance. Source of Kernel. T h e material, which came from three selected trees, F5, F62, and F88, covered the range of oil content from good, 64.12C;, to excellent, 70.71% (Table I). The effect of source of material is consistent for all combinations of the factors studied, as shown by the low levels of the mean squares for interactions (Table 11‘). Weight of Sample. The average of the readings for oil content of the 5-gram samples is 66.92c0, 0.56 higher in percentage of oil than the mean for the 10-gram samples (Table 111, which is a statistically significant difference. This suggests that the smaller samples were more completely extracted. However, the standard deviations, which were 0.44% for the 5-gram samples and 0.2251, for the 10-gram ones, show that more precise reading3 are obtained with the larger samples. Method of Preparing Material. As the essence of the blender method is disintegration of the kernel tissue, thus freeing the oil and allowing it to dissolve in the hexane, the sample should be prepared in such a v a y t.hat this disintegration will be most facili-
Length of Blender Refractive Run Indes Min. Flaking 1.51706 5 1.51687 1.51674 10 1.51692 Grinding Each record is mean of 24 determinations
of
Preparing Material
Refractive Indes
Weight of Sample Grams 5 LO
Refractive Index 1.51696 1.51684
Other devices which have been tried are a graphite-impregnated fiber packing inserted in a cut-out section in the upper end of the bronze bearing of the blade assembly or the use of silicone lubricant. Satisfactory operation may be obtained by cleaning the blender with fresh solvent a t the end of a series of runs, followed by blending rrith water and then oiling with two or three drops of a heat-treated oil such as Pyroil B. The oil is dropped into the shaft housing n-hile the blender jar is inverted. Before using the blender for analyses after this treatment, it should be run for 10 minutes with fresh solvent. Effect of Moisture Content of Sample. Kernels from tung fruit properly dried for milling contain about 5Yc moisture, and all tests reported above were run on such kernels. Hoivever, a special test was made to determine whether higher moisture content in the kernel affected the amount of oil extracted. Two samples were taken from a single lot of tung nuts which were unusually high in moisture (Table L-). Sample 1 was stored in an air-tight container until the kernels were shelled and oil determinations were made and calculated on a moisture-free basis. The moisture content was 15.77,, and the oil content as determined by the blender method was 62.76Y0,. Sample I1 Tvas dried 3s whole nuts with forced draft a t 70 C. before analysis. At the time the oil determinations were made the moisture content of the kernels was 4.570, and the oil content on a dry basis as determined by the blender method was 69.2670. Thus the wet sample gave 6.50 percentage units less of oil than the dry sample. Similar results were obtained by the Goldfisch method. When flaked ker-
JULY
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1947
ne1 from sample I was dried to a moisture content of 3.657, and extracted in the Goldfisch apparatus i t had an oil content of 69.747,. This shows that the oil was not completely extracted from sample I, which had the higher moisture content. Similar results have been obtained on wet samples with Goldfisch estractions in which re-extraction of the dried, reground residue produced additional oil equivalent to the oil obtained from duplicate samples of dried material.
If maximum accuracy is to be had, the blender procedure as described herein should be used only 011 kernel material dried to a moisture content of 77, or less. Oil detcrminatioris made lvith blenders \vhich heat considerably during operation usually are less affected by the moisture content of the sample than are those shun-n in Table 2'. When the tcmperature a t the end of the blending period is above 45' C., the dr,terniinatims are usually about 1 to 27, low n i t h kernel m a t w i d containing 10 to lZY0 moisture. Comparison with Goldfisch Method. For the purposes of this comparison the flaked kernel was extracted 12 or 15 hours, driod in vacuum a t 70" C.. ground to 60-mcsh, and re-extracted for 4 hours. The blender method (Table V I ) in every cast' gave a higher mcmi percentage of oil than did the Goldfisch procedurr. The oil recovered has the refractiri: indices (Tables I11 and V I ) associated x i t h tung oil. Since the actual amount of oil in the aliquot was accurately determined by n-cighing, the high values reported for neight of oil in thc sample as obtained by the blender must tie accepted :ts true within the limits of tlipir experimrnt:il errors if wultiplication of tlie weight of oil in thc aliquot by 1/30 of the fin:il volume is valid. T!lis c:ilculntion is baaed on tilt. assumption that in the volunietiic flask the proportion of oil by volume is uniform throughout both tlie supcrmtunt liquid and the sedimcmt. ThiJ assumption n-as shon-n to be valid by the data for size of samplr, which indicated that less percentage oil i; left in the enialler sample n-hen the same final volume is useti than in the larger sample. Therefore the higher yields of oil by the blender method are considered more accurate than corresponding Goldfisch r e d t s (Tahle VI). This conclusion is supported by the recovery by blending of a slight amount of additional oil (0.10 to 0.15%) from the ground, re-extracted meals obtained from these Goldfisch extractions. The refractive indices of this additional oil were characteristic of tung oil. Similar higher blender figures for so?-bean, corn, and lima bean lipides are reported by Sielsen and Boliart 14, in comparing their blendrr extraction method with the Soxh!et
Table I \ .
4nalysis of Variance of Factorial Stud! of Variations in Blender Procedures
bource of Variation ReDroducible main efferts
DE
Blender jars ( B ) Reproducible interactions M x 1'
1
0 0168
1
0 407U 2,5209 1 7101 0 (1040
.TI.
x y x 1' x
'1 1 1
T X Ti
41 If. E r r o r interactions
sx S X sx
M T
2 2 2 >
11-
S X B .I1 X B 1 X B Ti. X B Second o l d e r Third a n d fourth order Pooled error interactions (blender a n d sources) K i t h i n "duplicates" (blender effect and interactions) Pooled higher order error interactions (for testing first-order interactions) a Highly significant.
(1618 0732
1_L
0 0 0 0 0 0 0 0 0
37
0 1180
24
0.1199
26
0.1320
1
1
1 15
Total
Aleall b r j i i d i e
0043 0508 3746 1801 0002
1053 0811
47
F
3.08 19. l o a 12 5 6 Q
Table V. Effect of 5Ioisture in Sample on Recovery of Oil from Tung Keruelsa (Percentages expressed on inoisture-free basis) 13lenrii.r Goldfisch s o . of s o . of deter .\Iran deter.\lean lloisture niinaoi! n!inaoil Content tions content tions content
8an:yle
%
%
%
I (\\-et! 1.5 7 (i2 7 6 2 6 2 66 7 ii I1 ( d r y ) 4 3 fill 2 2 68 92 Roth sanil)!es dian-n f i o r n saiiie lot of t u n z n i l t ? . Sainiile I a n a l ? l e d "as is"; saiiipie I1 rlrieJ a t i o c C . with forced draft before annl>-sis. Tellgraiii saiiiples used. -
Table \ I . Comparisou of Results of Blerider and Goldfisch Procedures for Determining iniount of Oil in Tung Kernels
F48
8 1"
.i12
12
ti coinpobit(.i i n
0 2' 0 41 0 27
0.44 0.41 0.70 0.11
1 .i180 1,5179
1.5li8 1,5179
I" I? 12 duplicate 12 (1 10-grniii 5aii11,1~5of ground kernel material blended f o r 5 niinutes as di.briiheii in t e s t . b % p r a m saini:l- the blender method. The minimum elapxd time for c: mpleting a single determination by the blrnder method is about 3 hours, by tlie Goldfisch method a t least 13 hours. In routine wdrk with prepared samples a total of 21 determinations can be made by operating a 12-unit Goldf i s h apparatus 21 hours per day. The actual working time is approximately 8 hours for a chemidt and his assistant. Using two blenders and systematizing piocediire, 35 to 45 determinations can be made n-ith the same manpower in an %hour day. It is impossible to increase the output of the Goldfisch apparatus t o more than 21 determinations per day unless additional expensive units ai'e purchased. DISCUSSIOS O F STATISTICAL ANALYSIS
rested in the statistical treatment of laboratory of variance of the factorial test of Table V I has been prepared. The factors have been classed as irreprodueible (those 011 which error terms are based) and reproducible. Sources of kernel and blender jars are considered irreproducible factors. In a narrow mise, if the difference between specific selections is the question under study, source of kernel material might be viewed as reproducible. However, in the broader and more useful sense of all material to n-hich these studies might apply, the source of kernel represents the unknown. It was observed that the first blender jar used agitated the solution somewhat more violently than the second jar. Either jar may function differently from
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NO, 7
tory rather precise results with standard deviations of 0.10 to (Oil i n kernels, d r y weight basis) 0.20 in percentage of oil conSelec- Blender 5 Granisa 10 Grams tent may be had by experienced tlon Jar 5 mill., 10 Inin., 5 min., 10 min., 5 Inin., 10 min., 5 niin., 10 rnin., S
