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MICROCOPY RESOLUTION TEST CHART
NAllONAl BUREAU
or
STAND~RDS-1963·A
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MICROCOPY RESOLUTION TEST CHART
NATIONAL BUREAU
or
SlANDARDS-1963-A
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Evaluation of a Rapi.d Method for
Determining Oil Content
of Cottonseed
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Technical Bulletin No. 1298
UNITED .STATES DEPARTMENT OF AGRICULTURE
Preface and Acknowledgments
The ~tlldy on which this report is based is part of a comprehensive
research project of the Agricultural Marketing Service on quality evalua·
tion of farm products and development of objective measurements of
quality factors, to improve efficiency in marketing.
This bulletin presents an evaluation of a rapid method for determining
the oil content of cottonseed by use of a dielectric meter. Results of a
similar evaluation of the same dielectdc meter for measuring the oil
content of f.iOybeans are presented in another bulletin, Technical Bul·
letin No. 1296. Somewhat ditferent procedures arc used for the two
oj/seeds.
BitHlc Owen, Planters Manufacturing Co., Clarksdale, Miss., .IamesK.
Sikes, formerly with Plains Cooperative Oil Mill, Lubbock, Tex., Ben H.
Bruce, Paymaster Oil Mill Co., Abile,le, Tex., and J. W. Curtiss, Perkins
Oil Co., Memphis, Tenn., supplied data in the field study. R. T.
Doughtie, .Ir., Cotton Division, AMS, supplied data on the standard
laboratory method.
Contents
Page
SummarY and conclusions.............. .... ...... ............ .... .... .......
Introduction......... ... ...... .... ..... ................ ..... ......... ......... ...
Development of the USDA oil meter......................................
Plan of study .................................. ,.................................
Requisites for rapid oil assay method....................................
Tbeory of dielectric constant measurement.............................
Description of test equipment..............................................
Operating procedure for the dielectric meter method................
Time required for dielectric meter and standard methods.... ......
Comparisons of oil determinations by dielectric and standard method::;........................................................................
Variations in cottonseed oil determinations..... ... .....................
Standard method at different laboratories. ......... ...... ... ..... ....
Standard method within fOllr specified laboratories...... ...........
Dielectric meter method...................................................
Time and cost comparisons.................................................
Appraisal of dielectric meter method.... ......... ............ ............
Literature cited............... ..... ...... ............ .......... .................
I.sslIed DecemLer 1963
2
3
5
5
5
6
6
6
8
9
9
12 12 13 16 17 18 19 Summary and Conclusions
Field tests of an oil meter developed by the United States Department
of Agriculture (USDA) show that the test procedure and equipment
meet qualifications for a rapid method of determining the oil content
of cottonseed.
Although cottonseed is purchased lly oil mills from ginners on the
basis of ofncial grades, this system of grading is too technical, expen·
sive, and time·consuming for use on small lots sold lly farmers.
A method for grading small lots of cottonseed must be rapid, inex­
pell$ivc, and simple. Important quality factors are the seeds' contents
of free fatty ucids, oil, moisture, protcin, linlers, and foreign mattcr.
Oil accounts for 40 to 60 percent of the value of cottonseed.
Various methods of oil assay that appeared to have promise, with
respect to a small-lot grading system, were investigated. A nll'thod
based upon dielectric measurement was found to he the most practical.
This mcthod was developed, und four commerciul models of the dielectric
meter were designed and fubricated for field testing. The equipment
wus tested during a 4-year period at fin' locations in the cotton helt.
The ral)id diclc{;trie meter method is simple. Fifty grams of seed ure
placed in a grinder-extractor with 200 milliliters of solvent und u scoop
of silica gd impulpabl{' powder, and then extracted 4 minutes. The
larg(· particles arc removed by a small hand press (household ricer).
The filtrate is then removed by a pressure filter. The oil content muy
be read on a diul after 2 minutes. Totul timt' for analysis is less than
10 minutes.
The rapid mett;r method is llased upon dielectric measurement of a
solvent mixture, the t)i1 having been extracted from the seed by a solvent
that has a dielectric value conSiderably different from that of the oil.
The oil meter is essentially a substitute-tn'c radiofrequcncy cupucity
meter and a cell suitaule for meusuring liquid dielectrics. The instru­
ment is adjusted to resonance (indicated by a meter) with a fixed con­
denser in tilt' circuit. The test cell, filled with the liquid to be measured,
is substituted in the circuit for the fixed condenser, and a calibrated
variable condenser is used to retune to resonance.
Standard errors of estimatc of the variation in oil content of 995
samples of cottonseed, when tested by dielectric oil meters at 5 field
locations during 4 seasons, ranged from ±0.2369 to±O.2598 percent
when compared with results of the standard lahorutory method. At the
USDA Itthoratory in Washington, D.C., where 334 samples were tested,
thc stundard error (If estimate was ±O. 1659 percent. All the laborutories,
as a group, have a stundard error of estimate of±O.2377 percent. This
degree of precision is acceptable for a method of determining oil content
of cottonseed and compares favorably with the standard luboratory
method.
Thirty-six laborutories, using the stundard laboratory method, for the
cottonseed check series of th~' AllIcricun Oil Chemists' Society during
1961-62, reported standard (it:viations from th,,· true means of 10 samples
ranging fmm ±O.1823 to ±0.2936 percent. The pooled estimate for all
the laboratories was ±0.2494 percent. rour of these laboratories,
having better precision, had a pooled standard deviution of ±O.2033
percent of the same samples.
This difference in precision, in th,,~ check st:ries, is alll:1ll1 the SUInt' as
the difference of the 5 field laboratories and the Wushington laboratory
.
where both methods of testing were used Oil the total of 1,329 samples of
cottonseed. When the Washington laboratory tested nine samples of
~lOltOllseed with the dielectric oil meter, the within-laboratory standard
deviation was about the same (±O.1041 percent) as the within-laboratory
standard deviation (±O.1l28 percent) of the four specified laboratories
using the standard laboratory method. These standard deviations
show that precision was about equal. However, the error due to method
only for the standard laboratory method was about twice as great
(±O.1868 percent) at the four laboratories as that due to method only for
the dielectric method (±O.0979 percent) at the Washington laboratory.
4
Evaluation of a ,Rapid Method for
Determining Oil Content of Co,ttonseed
By M. E.
WHITTEN
and L. A.
BAUMANN,
research chemists, Market Qaalit.y Research
Divisioll, Agricultural Marketing Servic;e
Introduction
Cottonseed is a major source of income in the cotton-growing regions,
and products of cottonseed are important in the national economy. The
farm value of cottonseed for the lO-year period 1951-60 averaged over
$305 million annually. Efficient and equitable marketing methods and
facilities are therefore very important.
Cottonseed processors purchase seed on the basis of official grades
in most cotLon-production areas. However, this grading system is too
expensive, technical, and time-consuming for practica.l use in trans­
actions between growers and ginners. Because individual lots of cot­
tonseed may vary greatly in composition, a reliable system of grading
is necessary for evaluating their quality.
A system for grading small lots of cottonseed must be rapid, inexpen­
sive, and simple. Quality and quantity factors used in the U.S. Stand­
ards for grading cottonseed include the seeds' contents of oil, moisture,
protein, free fatty acids, linters, and foreign matter. Oil is a major
factor in any grading system because it accounts fur 40 to 60 percent
of the entire value of the products from cottonseed.
Development of the USDA Oil Meter
Because a quick oil measurement is necessary in any rapid, simple
grading system, a study ww,- made of means for making this test. A
rapid dielectric meter method of determining the oil content of cotton­
seed was developed and reported in 1955 (/4).1 Four commercial models
of the meter were designed and fabricated 2 for field testing of the
method and equipment in the cotton-growing regions. Two public
service patents were obtained on the method and equipment.
Plan of Study
Equipment for the rapid determination of oil in cottonseed was placed
in the hlboratories or plants of cottonseed processors in Clarksdale,
Miss., Memphis, Tenn., Lubbock, Tex., Waxahachie, Tex., and Abilene,
Tex. Samples of cottonseed were divided and analyzed by the official
standard chemical laboratory method, hereinafter called the standard
method, (2):1 and by the new rapid meter method. Testing was carried
\ Italic numhers in parentheses refer 10 items in l.iterature Cited, p. 19.
:!Tla' mt~ntil)n of firm nttmt·s or trade pr"duCls dol'S nol impl)' thai Ihey arp l'ndo\'scd
or reeolllmendcd III Ih(' Oeparlnwnt ,if Agri<:uhurt- OVt~r other firm~ ur similar prodllel~
nOI rnt"ntio(wd.
"This nll'lllO\I j, tilt' salll!' as til\' Oflicial .\I\,tllOli of Iht' l'.~. [)'!partllH'nl of Agric:uhlln'
and of tht' \ational Collnll~{·"d Products :\,.sociation for grading cnttollsl'ed.
5
oul at no more than three field locations at one lime during the test.
In addition, a representative number of samples were also sent to Wash­
ington for analysis by both methods_
Since the purpose of the field test was to compare results from lhe
rapid method with results from the standard method, efforts were made
to eliminate errors from sources other than method_ If the oil content
did nol check within ±O.4 percent, the sample was rennalyzed or sent
to Washington for analysis by both methods. In pr\ilctically every
instance, errors were found to result from improper sample preparation.
Requisites forftapid Oil Assay Method
Any oil determination used in a small-lot grading system must be rapid.
The equipment should be rugged and easy to operatt~, and should require
m.inimum handling of the sample. A measurement of the dielectri.c
value (If the oil-solvent solution proved to be a satisfactory means of
rapid determination of the oil content of the cottor.seed (J 4).
Theory of Dielectric Constant Measurement
When a substance is placed in an electrical lidd, the molecules tend
orient themselves in a definite pattern with respect to the direction of
the fidd. The dielectric constant of the material. can, for simplicity, be
defined as a measure of the degree [0 which (he individual particles are
oriented or the material polarized. For any substance, the dielectric
constant is a ddinite and fundamental charu<:tcristic. Theories as de­
veloped by Debye, Falkenhagen, Smyth, and others have been applied
successfully to experimental results in this fidd.
Determinations of the dielectric constant, dielectric loss, and conduc­
tivity have been used for a numher of years, with varying degrees of
success, for analyzing and studying the composition of gases, liquids, and
solids (3, .5, 6). The electrical measurement can he made in several
ways. The choice of tht' method depends on the kind of sample, the
accuracy desired in the determination, and other factors such as cost
and operational convenience of the equipment. [n recent years, interest
in h~gh-frcqueney oscillation titrators has led to the development of
several instruments useful in measuring certain dielectric properties of
liquids (/, 4, 7, II). Although, in most investigations, the instruments
have been used to indicate the end point of titrations, progress has been
made toward using the e1ectricaloscillators (and associated detectors) for
direct analysis of binary (and in some instances, tertiary) mixtures
(12, /:~). The measurement of the dielectric properties of solids and of
/,iquids has also been successful in continuous process applications (8, 9).
In using dielectric measurement for routine analyses of a binary
mixture, it is relatively unimportant whether the instrument reading is
affected by only the dielectric constant or by both the dielectric constant
and the dielectric loss of the samples tested. If the mixtures are
stable, then; with prO~ler cell and circuit design, an empirical calibration
with a high degree of accuracy can be developed. This technique has
been used with several commercial meters.
~o
Description of Test Equipment
Electronic ilJeler. - The oil meter is essentially a substitute-lype
radiofrequency capacity meter with a cell suitable for measuring liquid
6
dielectrics. The instrument is adjusted to resonance (indicated by a
.meter) with a fixed condenser in the circuit; the test cell, filled with the
liquid to be measured, is substituted in the circuit for the fixed condenser,
and a calibrated variable condenser (which is read directly in oil percent)
is used to retune the instrument to resonance (fig. 1).
Pressure Filter. - The extract is filteted in 2 to 3 minutes with an
air-pressure filter, which is made in two parts. The lower part, mounted
directly over the test cell, is the filter~ng base. The upper section of the
filter, or the air chamber, is removable and contains the inlets for the air
pressure, and a funnel device for the extract. Strong, retentive filter
paper (Whatman No.2 or equivalent) is used to retain the particles,
allowing the filtrate to flow through into the heat-exchange tube below
N-~O'60
FIGURE 1.- Th~ C.S. DeparImenl of Agriculture's dielectric uilmctcr. The grind(:r·
\·xtractor and aec\·s~"ry equipmenl are nn the table at the right.
7
the filter press.. After each analysis, the filter unit is cleaned, new filter
paper is' placed~in the press, and the operation is repeated for another
sample. Air pressure is applied with a small hand bulb.
Test Cell. - From the air-pressure filter, the extract drains into the
heat-exchange tube. This heat-exchange tube serves to bring the
extract to the desire€! temperature while conducting it from the fiher to
the cell.
The cell is basically two concentric cylinders. The inner cylinder
(with both ends sealed) is suspended in, and electrically insulated
from, the outer cylinder. The space betwt'en the two cylinders, forming
the condenser, is maintained by a rugged mounting system. The outer
cylinder is at ground potential; therefore, no special electric shielding
is needed. All surfaces of the cell are at least 45 degrees from the
horizontal; therefore, no difficulty with air drainage or bubbles is
encountered.
Constant-Temperature Oil Batiz.- The te:>,rcell and heat-exchange tube
are immersed in a temperature·controlled oil bath. A heater, thermo.
regulator, and stirrer are used to control the temperature at 500 C.
Allowable temperature variation is 0.10 C.
Grinder-Extractor. - Two types of commercially available grinder­
extractors were used in these tests. The iarger and more powerful
model prepared the sample in 4 minutes. The smaller model required 6
to 7 minutes to extract the oil from cottonseed.
Operating Procedure for the Dielectrac Meter Method
The rapid oil dielectric meter method developed by the Department is
simple. A 50-gram sample of cottonseed, 200 milliliters of solvent,
orthodichlorQbenzene 99 percent (hereinafter called ODB), and one scoop
;-':-2792:'
FI(a1R~: 2. -TIlt' large dial on the instrument panel shows the percent of oil in the cottonseed.
(approximately 12 grams) of silica gel impalpable powder are placed in a
cup and processed in the grinder-extractor.
The oil is extracted by the solvent. The desiccant, silica gel impalp­
able powder, not only removes water from the solvent and the seed but
also acts as a filter aid. Removal of all water from the sample and sol­
vent is imperative, since water has a dielectric constant of 81 compared
with a value of approximately 10 for the solvent and 3 for the cottonseed
oil.
When the grinder-extractor step is completed, the mixture is poured
into an ordinary household ricer which is placed inside a funnel situated
directly above the pressure filter. The mass is pressed, leaving most of
the linters, hulls, and larger particles in the press. This material is
discarded. The solvent mixture flows from the handpress into the
pressure filter. Pressure, applied with a rubber bulb by hand, forces the
solvent-oil filtrate through the filter paper into the heat-exchange coil and
thence into the cell. The filtrate temperature is fairly well stabilized
after passing through the heat-exchange coil and into the cell. Readings
may he made in 1 or 2 minutes. The percentage of oii is shown on a dial
on the instrument panel (fig. 2).
Time
Required
by the Dielectric and Standard
Methods
The dielectric meter method of oil determination is more direct than
the standnrd method. As previously stated, the sample uf cottonseed is
weighed and, with the solvent and silica gel, placed in the grinder cup.
The mixture is grinder-extracted, filtered, and the oil content read.
Total time required is less than 10 minutes.
In the standard method, the cottonseed is pre-dried for 2 hours and
fumed with hydrochloric acid for an additional hour before grinding.
After grinding, th(· sample is carefully mixed and 5-gram portions
weighed for the 4-hour extraction with petroleum ether. The solvent is
then evaporated and the oil is weighed. Moisture determinations must
be made on the original seed and on the dried seed in order to determine
the actuul oil content of the seed. Twelve separate weighings and 12 to
16 hours are required for a complete determination.
Comparisons of Oil Determinations by Dielectric
Meter .and Standard Methods
A total of 1,329 samples of cottonseed, tested at 6 locations, were
distributed as follows: 117 samples at Memphis, Tenn.; 322 at Clarksdale,
Miss.; 307 at Lubbock, Tex.; 193 at Waxahachie, Tex.; 56 at Abilene,
Tex.: and 334 at the Washing~on, D.C., laboratory. Tests were made
during 2 years at Lubbock and Clarksdale and during 1 year at Waxa­
hachie, Abilene, and Memphis. At all locations, single observations
were made with the meter on aU samples, and duplicate determinations
were made by the standard method.
The meter resuIts were compared with findings by the standard method
by statistical. regression analysis (tablt, 1). The degree of relationship
(correlation coefficient) between the two methods of measuring oil con­
tent is highly significant at all six locations.
9
l-'
o
TABLE 1. -
Relatioflship oj oil content in cottonseed determined by the AOCS standard laboratory method and the USDA dielectric meter at six locations I Range
LoC'ation
Season
Formula t
Observa·
tions ~
Standard
Washington .........
1958-62 Y=.4213+.9782)(............
Meter
Corre.
lation
coeffi·
cient 4
Standard Regres· Standard
error of
error of sion co·
estimate 5 efficient" estimate
of b 7
Sb
Nllmba
334
Percent
16.6-22.4
Percent
16.7-22.3
r
0.9892
±D. 1659
b
0.9782
±D.OO79
Sur
Signifi.
cance of
b&
7'
123.83
MemJlhis ............ 1958-59
Y=.9913+.9523)(............
]]7
16.9-21. 4
17.1-21. 4
.9624
.2411
.9523
.0270
35.27 Waxahachie ......... 1960-61
Y=I.2458+.9344x ...........
193
]5.3-22.0
15.5-21. 8
.9745
.2369
.9344
.0155
60.28 Clarksdale............ 1958-59
1959-60
Y=1.1585+.9362x...........
322
15.9-21. 8
16.0-21. 6
.9518
.2576
.9362
.0168
55. 72
307
14.5-20.9
14.9-20.8
. 9674
.2598
. 9232
.0138
66.90 56
14.5-20.6
14.9-20.3
.9746
.2424
.8982
.0278
32.31 Lubhock .............. 1958-59 1961--62 Y=I.4652+.9232x ........ '"
Abilene ............... 1961--62
Y=1.8469+.8982)( ...........
Oil ('onll'nt determined by Aa 4-38. Tentative & Standard Methods, AOCS (American Oil Chemists' Society). Y=oil content in percl'nt hy meter. X=oil content in pt'rcent by the standard method.
" Number llf samples tested.
4 Degree of relationship hetween the two methods.
Perfect relationship equals I.
5 The range above and below fneter readings estimated from oil determinations hy the standard method to include two·thirds of the observations.
"Chang" in oil content in pcrcent I1Y tTle meter method for every percent by the standard metllOd.
7 Tlw range above and helow t he estimated regression coefficient which includes the regression coefficient for t wo·thirds of the observations.
H T= hIs/>.
The higher the value, the greater the significance of the regression coefficient.
I
!I
Assuming that variatIOns in oil content determinations are relatively
insignificant when repeated measurements are made on the same sample
of cottonseed by the standard method, then the deviations of dielectric
meter results from the straight lines may be used to evaluate the varia­
bility of the meter results. These variations .range from ±0.1659 to
±0.2598 percent. The relationship between the two methods for the
tests made at the Washington laboratory most nearly approaches the
perfect relationship of Y=X. Also, the Washington results vary the
least around the regtession line.
A "t" test 01 applied to the regression coefficients (b) of the results at
the five field locations (excluding Washington) indicates that the five re­
gression coetlicients do not difrer significantly (at the 0.1. percent con­
fidence level). AGcordingly, the data used in the correlations at these
locations Wt!re grouped to give the relationship of the two methods of
dt,termining oil content for all locations except at Washington.
Furthermore, when a "t" test is made of the grouped data from the
nve locations and tht;> data at Washington, there is no signitlcant dif­
ference (0.1 perCt'nt confidence level) bet ween the t\vo regression co­
eHicients (t value = 3.(4).
All the data shown in table 1 can be grouped to give an overall rellltion­
ship for the 1,329 observations (fig. 3).
RELATIONSHIP BETWEEN COTTONSEED
OIL CONTENT DETERMINATIONS
By the /)Ie/ec/rlc and Standard Laboratory Methods
2/ ~-
I
20~
I
Y.
9l~7.
95jd J. N- '"lZ9 ,. 9110
s,:
s--
;U7T
OO~7
f .,66a!-
19!­
I
t8
I
~~
1
I
II,!"",
I
i
18
19
lobt'fQlor)'~O(-;ermmed
I
20
Oil Conlent
21
(Percenl)
FI(;ln~;
3.
b, -b 2
.all(I"-
2-~
s.'/
X "- -
... - }:l
I,·hert·, h'l' = rt·gn·ssion ('ot'Ili(:i"nl~ al din'c'n'nl locali("I~
S".;s = standard ('rrors of ('slimul"
.v = nUIIIIlt'r of (lb"('r\'lllion~
(Vulut's
"t" ranged frolll A9 to 1.44 al ll)(' liVt., fipld loculilll/l.• 1
or
11
Although the standard errors of estimate (table I) ranged from ± 0.16&9
to ± 0.2598 percent at the six separate locations, the variation is ± 0.2377
percent for all the laboratories as a group. This estimate should be
representative of a comparison of the two methods.
During the 10 crop years 1951-60, .(10) over 65 percent of all cotton·
seed produced in the United States ranged in oil content from 18 to 20
percent. When cottonseed in this range is tested by the dielectric
method, 18.05 percent to 19.96 percent would be indicated, with a stand­
ard error of estimate of ± 0.2377 percent.
The standard error of estimate reflects variation about the regression
line. It measures the precision with which the meter determinations
are repeatable and also indicates meter deviations from linearity. When
results deviate from the straight line (Y=X), this deviation can be attrib­
uted to some or all of the following possible causes: (a) Errors in the two
oil-content determinations are not negligible; (b) systematic error in one
or both of the two methods of measurement; (c) systematic error in the
application of one or both of the two methods at the laboratory concerned.
The preceding comparison of the two methods of analysis does not
s.how the variations that occur when the same sample is repeatedly
tested by either the standard or meter method. In order to determine
the variations around a true or most accurate analysis, a number of
determinations must he made on the same sample by several laboratories.
The average of all these determinations on the same sample should
approach a true measure of the oil content of that sample.
Data needed to establish the variation of the standard method, on the
same sample analyzed by different laboratories, are available from the
records of the American Oil Chemists' Society Check Cottonseed Series.
Variations in Cottonseed Oil Determinations
Standard Method at Different Laboratories
For a number of years, the American Oil Chemists' Society has con­
ducted annual series of check sample tests on oilseeds and related
products. Each year, representative portions of each of 10 samples of
cottonseed are tested by approximately 36 laboratories. Each labora­
tory makes two or more tests for oil content (usually three to six), on
each sample, and reports one result, usually the mean of the results.
These 36 means are averaged and this result, known as "the sample
mean," is cons~dered the true or most accurate mean oil content for
each sample. The most proficient laboratory is determined by the
least deviation of its reported means -laboratory means·- from the re­
spective sample means. A summary of these reports for the crop year
1961-62 is shown in table 2.
By means of a "pooled" estimate,5 the results can be further summar­
ized to give a standard deviation for the 10 samples by all 36 laboratories
of ± 0.2494 percent.
• Obtained by gelling the square root of the sum of the squared deviations from .the
me ails of each sample for each laboratory, divided by the sum of the numher of tests less
OIW fnr each laboratory, or
12
Through th~ cooperation of 4 of the chemists among the 36 collab­
Orators taking part in the 1961-62 series, analytical data of aU oil tests
made .in each of the 4 laboratories were obtained. These laboratories
made from 3 to II tests on each sample, from which the means for each
sample in each laboratory were reported.
Variations in oil analyses by the standard method reported
by 36 approved chemists for cottonseed check samples during 1961-62 1
TABLE 2. -
Range
Sample
mean 2
Sample number
Analyses
Percellt
1......................................... .
2......................................... .
3......................................... .
4......................................... .
5......................................... .
6................... ,..................... .
7..........................................
!\...... " ................................ ..
9........................................ ..
10..................................... ..
19.4
19.3
19. I
]9.9
19.8
19.6
19.1
23.8
19.3
19.2
Percellt
18.5-20.0
18.8-19.7
18.3-19.5
19.2-20.5
19.3-20.1
19.2-20. I
18.7-19.5
23. 0-2'k 5
18.7-19.9
18.7-20.0
Standard
devilltion
Differences from mean:l
from mean
Percellt
Percellt
0-.9
0-.5
0-.8
0-.7
0-.5
0-.5
0-.4
0-.8
0-.6
0-.8
±0.2936
.2151
.2541
.2229
.1823
.2366
.2291
.2933
.2893
.2491
1 From rI!tiults issued by the subcommiltee on oilseeds of t.he Smalley commiltee of the
American Oil Chemists' Society, Chicago, Ill.
2 Any unulysis reported grt:ater than 4 standard deviations from the uverage was not used
in determining the mean.
;1 Standard deviation is a form of average deviation f(om the meun.
In upproximately 2
out of 3 cases, the vuriation in moisture content determinations among the laboratories
would be within plus or minus the percentage pointti indicated. The formula for the
standard deviation as used here is equul to the square root of the sum of the squared
diff(·rt~nces frnm the Illelln, divided by one less than the number of analyses, ur
/'n'!' where S=~tandard
S=V1Y!:]-,
deviation, Icl'=the sum of the squares of the differences
from the mean and N=the number of the means reportcd by 1111 the laboratories.
In order to compare the variations of these laboratory means from the
sample means with the variations of all 36 of the laboratories, data
reported by these 4 laboratories are shown separately (table 3). A
pooled estimate of the standard deviations from the 4 laboratories was
±0.2033 percent, which is somewhat lower than the ±0.2494 percent for
all 36 laboratories.
The data from the 4 specified lauoratories, as a group, also indicated
better precision in this series than the data from all 361aboratori~s, as a
group. This precision is shown by the final scores and ranking tor the
1961-62 series. The four laboratories .ranked 2nd, 13th, 14th, r. nd 21st,
with scores of 56.85, 29.89, 29.61,and -10.02, or an average of 26.58,
which is around the upper third of the scores of all the laboratories.
(A verage score for all 36 laboratories is approximately zero.)
Standard Method Within the .Four Specified Laboratories
The standard deviations in tables 2 and 3 have been determined from
sample means calculated from the reported laboratory means. Because
13
two or more individual tests were made in each of the laboratories on
each of the samples, deviations from the true or sample mean must be
determined on individual tests. This deviation can be called the "root­
mean-squared-error." The root-mean-squared-error reflects not only
variations within the laboratory, but also the systematic error of the
method. This deviation becomes a part of the variation, as represented
by the standard error of estimate, when comparing the 2 methods of
testing, as previously referred to for the 1,329 samples tested at the 6
test locations.
3. - Variations in oil analyses by the standard method reported
by 4 chemists for cottonseed check samples during 1961-62 1
TABLE
Range
Sample number
Standard
deviation
from mean 3
Sample
mcan 2
Analyses Differences
from mean
,
1. ........................................ . 2........................................ .. 3........................................ .. 4.......................................... 5......................................... . 6........................................ .. 7......................................... . 8........................................ .. 9......................................... . 10........................................ . Percent
19.4
19.3
19. 1
19.9
19.8
19.6
19. 1
23.8
19.3
19.2
Percent
19.3-19.5
19.2-19.5
19.1-19.4
19.8-20.1
19.7-20.1
19.6-20.1
19.0-19.2
23.6-24.2
19.1-19.5
18.9-19.5
Percent
0-.1
0-.2
0-.3
0-.2
.1-.2
0-.5
0-.1
.1-.4
.1-.2
.1-.3
Percent
±0.1000
.1000
.1915
.1291
.1527
.3415
.0816
.2887
.2082
.2582
1 The reports of the 4 chemists are also included in table 2.
See also footnote 1 of
table 2.
2 Mean of all 36 chemists' reports as shown in table 2.
See also footnote 2 of table 2.
3 See footnote 3 of table 2.
The standard deviation from the laboratory mean and the root-mean­
squared-error for each of the 10 samples were calculated from the data
reported by each of the 4 laboratories (table 4).
Some bias or personal error can be noted under the culumn headed
"Difference between laboratory and sample mean." Whereas results
reported by laboratory No. 2 tended to be lower than average, reports
from the other three laboratories tended to be higher.
Only when the laboratory mean is the same as· the sample mean will
the root-mean-squared-error be the same as the within-laboratory de­
viation. In other words, in this instance, there is no bias, and the root­
mean-sQuared-error consists only of variation due to the method of
testing. This variation ranges from + 0.0412 to ± 0.3089 percent (last
column of table 4).
A pooled estimate can be made· of the witllin-Iaboratory standard
deviations for all the samples at the four laboratories. The value is
±0.1l28 percent. However, when the bias as well as the systematic
error of the method is taken into account (represented by the root­
mean-sQuared-error), the pooled estimate is ± 0.2335 percent.
14
Table 4. - Variations in oil analyses by the standard method, within the
4 specified laboratories, of cottonseed check samples in 1961-62 com­
pared to those for all 36 laboratories. J
Within the IhboraJory
Laboratory No.
Sample
Number
No.
of tests
I
1
2
1
3
4
5
6
7
8
9
10
2
3
4
3
3
3
3
3
3
3
3
3
3
All 36 laboratories
Range of
analyses
DifferStandard
ence
deviaJion
.between Root­
Labora- from Sample labora· mean·
tory
labora- mean 3
tory squared·
IDean 2
tory
error·
and
mean
sample
mean
Percent
19.4 -19.6
19.4 -19.5
19.2
19.8 -19.9
Percent Percent Percent Percent Percent
19.5 ~0.1000
19.4
+0.1 ±0.158
19.5
.0707
19.3
+ .2 .2121
19.2 0
.1000
19. I
+ ·1
19.9 .0707
19.9
0
.0707
•
19.8 -19.9
19.1
24.0
19.5
19.0 -19. 1
.......... ............ ........... ............ ............
.0707
19.9
19.1 0
24.0 0
19.5 0
19.1
.0707
19.6
19.1
23.8
19.3
19.2
+ .3
0
+ .2
+ .2
- .1
19.4
19.3
19. 1
19.9
19.8
19.6
19.1
23.8
19.3
19.2
0
0
0
19.38-19.49
19.23-19.34
19.06-19. 13
19.75-19.84
19.64-19.70
19.66-1.9.72
18.95-19.07
23.p-'\-23.79
19.05-19.12
1.9.06-19. 18
19.4
19.3
19. I
19.8
19.7
19.7
19.0
23. 7
19.1
19.1
.0608
10
3
3
3
3
3
3
3
3
3
3
19. 1.9-19.41
19. 10-19.24
1.9.07-19.43
20.00-20.15
19.83-20.00
20.00-20.26
18.83-19.52
23.49-23.95
18.91-19.23
19.34-19.50
19.3
19.2
" 19.4
20. 1
19.9
20. 1
19. I
23.6
19. I
19.5
.0806
.0507
.1299
.0552
19.4
19.3
19.1
19.9
19.8
19.6
19.1
23.8
19.3
19.2
19.2
19.0
19. I
19.8
19.3
. 1384
19.3
. 1915
19.2
.0577
.0816
19.9
20.0 0
.1894
" 19.6
.1291
19.2
N.2 0
19.4
.1254
18.9
.0816
19.4
19.3
19.1
19.9
19.8
19.6
19. I
23.8
19. .3
19.2
1
2
3
4
5
6
7
8
9
I
11
2
3
4
5
6
7
8
9
10
7
7
6
7
7
7
7
7
7
I
4
4
4
4
4
4
4
4
4
4
2
3
4
5
6
7
8
9
10
19.4
19. I
19.2
18.8
-19.5
-19.4
-19.2
-20.0
20.0
-19.8
-19.4
24.2
-19.5
-19.0
.0587
.0381
.1»95
.0346
.0308
.0604
.0819
.0;}54
.0693
.0688
.0520
.0898
.3068
.IMI
.1072
-
·1
.1
·1
.1
.1
.2
·1
-+
+
+
.3315
0
.2449
.2449
.1732
.0656
.0587
.1»12
.1245
.1510
.1183
. 1292
.1473
.2636
.1407
·1
·I
.3
.2
+ .1
+ .5
0
- .2
- .2
+ .3
.2840
.1465
.2494
.1866
.1648
.5246
.3089
.2473
.2020
.2845
-
.1414
.2000
.0816
.0816
.2309
.2082
.2160
.4619
.1528
.3559
.1
0
+ .1
0
+ .2
0
+ .1
+ .4
+ ·1
- .3
I From private communications.
• Mean of determinations within the laboratory. 3 Mean of all 36 laboratories = average of all laboral<)ry means. .j Calculated in a similar manner as the standard deviation (footnot(: :3 in table 2) except that d= deviation of individual laboratory determinations from sample mean.
• Apparent typographical error-report not included.
6 Laboratory mean calculated, but not reported.
15
Assuming that the 4 laboratories, as a group, have a precision in the
ratio of +0.2033 to ±0.2494 percent for all 36 laboratories (pooled esti­
mates of the standard deviations based on laboratory means from sample
mep.ns), the best estimate that can be made for the 36 laboratories for a
.
f .
.2494
pooIed estlmate 0 the root-mean-squared-error would be: .2033 X
.2335 = .2864 percent, and for the within-laboratory standard de.viation:
.2494
.2033 X .1128= .1384 percent.
Dielectric Oil Meter Method
During 1958, 1959, and 1960, the Washington laboratory obtained
samples of cottonseed from the check sample series of the American
Oil Chemists' Society (AOCS) for those years. Enough seed was avail­
able in 9 samples to make repeated meter tests (3 to 17) on each. A
summary of the variations of the meter tests (corresponding to the
standard method in table 4) is shown in table 5.
5. - Variation in oil allalyses, by the meter within the Washington
laboratory, of cottonseed check samples, compared with results from
36 laboratories using the standard method 1
TABLE
Within the laboratorr
Sample Number
numbt:r of tests
I
2
4
4­
3
4
5
6
7
B
9
5
13
5
9
17
6
;3
Range of
analrseS
Percent
16.6-16.B
17.4-17,6
IB.2-IB.4
lB. 3-IB. 5
18.7-IB.9
lB. B-19. 9
lB. 9-19. 1
19.H9.4
19.5-19.8
All 36 laboratories
Standard
Labora· deviation
torr mean 2 from
laboratorr
mean
Percellt
Percent
16.7 ±0.1000
17.5
.1155
1B.3
.1000
IB.4
.1096
IB.B
.0911
1B.B
.0548
19.0
.0830
19.2
. 1269
19.. 6
.1049
San. pie
mean 3
Percellt
16.6
17.5
IB.2
I .5
IB.8
IB.9
19.0
19. I
19.6
Difference
Rootbetween
mean·
laboratory squared·
and sam·
error'
pie mean
Percellt
+ .1
0
+ .1
- .1
0
- .1
0
+ .1
0
Percellt
±0.1l55
.1155
. 15BI
.1414
.00Il
.0866
.0866
.1561
.1183
• From the subcommittee on oil seeds of the Smalley committee of the AOCS during the
"eries from 1958-59 through 1960-61.
2 Mean of meter determinations in the Washington laboratory.
3 Mean of all 36 laboratories = average of all laboratory means as determined br the
standard method.
• Calculated in a similar manner as the standard deviation (footnote 2 of table 2) except
that ti=deviation of individual laboratl)rr determinations from sample mean.
Comparison of the columns "Difference between laboratory and
sample mean" shows that bias is less with the meter method than with
the standard method (tables 4 and 5).
A pooled estimate of the within-laboratory standard deviations, for
the 4 specified laboratories, is ± 0.1041 percent for the meter method
and ± 0.1128 percent for the standard method.
16
Likewise, for the four laboratories, a pooled estimate of the root­
mean-squared-error is + 0_1228 percent for the meter and ±0.2335 per­
cent for the standard method. Assuming that precision for the
Washington laboratory is the same as for the four specified laboratories
as a group, then the systematic error of the standard method is estimated
to be greater than that of the meter. Likewise, the difference between
the deviations of both methods within the laboratory is small. This
may also be shown by pooling the estimates of the root-mean-squared­
errors for each method in cases where there is no personal bias in
sample testing (samples for which laboratory means equal sample means).
This condition exists for samples Nos. 4 and 7 in laboratory No.1;
samples Nos. 1, 2, and 3, in laboratory No.2; sample No.7 in laboratory
No.3; and samples Nos. 2, 4, and 6 in laboratory No.4 (table 4). The
pooled estimate of the root-mean-squared-error for these samples is
±0.1868 percent.
For the meter (table 5), there is no bias for samples 2, 5, 7, and 9.
This pooled estimate is ±0.0979 percent for the root-mean-squared-error,
or about one-half that of the standard method.
This can be shown in tabular comparison as follows:
Types of ohservations
Specified Washington
laboratories laboratory
(st·andard
(meIer
method)
method)
Percent
(Al All ohservations in 5 laboratories:
Within.laboratory slandard deviation
Root-rnean-squared-error (errors due 10 method and
application)
(B) Using only observations where sample mean equals
laboratur), mean (no hias or application error):
Rool-mean-squared-error (error due 10 mel hod (Jnly)
Percent
±O. U28
±O.l04I
.2335
. 1228
.1868
.0979
Time and Cost Comparisons
As indicated previously, the oil content of cottonseed can be deter­
mined by the meter method in less than 10 minutes. It is estimated that
one man with the dielectric equipment 6 can make 55 oil-content deter­
minations in 8 hours, or in 0.14 man-hour per sample. Since the grinder­
extraction phase requires 4 to 6 minutes, two grinder-extractions could
be used for each meter in order to handle a large number of samples.
Two operators could process 100 samples in a little less than 6 hours.
One person can. operate two grinders while the other handles the fil­
tration and reads the meter. For 100 determinations, about 12 man­
hours, or 0_12 man-hour per sample, are required. The estimated cost
for the one-operator analysis is $0.57 per sample. 7
• Equipment for tht: diel<:.l,lric method includes: ~I,·tl"r-fil~er unit. and .gri'!der-extra.!:lor.
$2,250; torsi<)n halance. $/;)0; flasks llnd olher equIpment. 540. SupplIes mclud(·: FIlter
paper, % ccnt per sheet; soh'enl (OD13 purc) 200 ml., IS¥.! cenls: 12 gm. silica gel impal.
pable powdcr, :3 cent~. Crushers of bOlh ('ollonseed and soybeans can usc thl' sanw equip·
ment Oil bOlh, follllwing slightly dirrcrt~lll prllcedures.
1 Cost includcs SUPI}li('~, labor of llont"cllllical opl~ratnr (at S 1.75 pt!r hour), and. overhead
(SO pl~rCt!nt of labor co;t).
17
The standard method of analysis, on the other hand, requires con­
siderably more equipment and. also technicians with special training.
Fifty samples for oil determination (100 results since samples must be
run in duplicate) require 13 man-hours. In addition, 100 whole-seed
moist.ure determinations and 50-ground-fumed-seed moisture determina­
tions must be made. The cost is estimated at 51.45 per sample. Furthermore, no oil-test res.ults would be available in less than 12 to 16 hours.
Appraisal of Dielectric Method
The foregoing findings indicate that the USDA dielectric meter method
for determining the oil content of cottonseed is accurate, rapid, and reo
latively simple and inexpensive. The meter method should be consid­
ered as an alternate method of oil assay in the official method of grading
cottonseed as well as for use in grading of small lots at gins.
18
.•.
,. Literature Ci.ted
F. C., JR. DIELECTRIC CONSTANT METER. Electronics 18: 116. (2) AMERICAN OIL CHEMISTS' SOCIETY. OFFICIAL AND TENTATIVE METHODS OF ANALYSIS. (3) ANDERSON, K., AND REVINSON, D.
1950. USE OF HIGH ~'REQUENCY TITREMETER·VOLUMETRIC DETERMINATION OF
BERYLLIUM. Analyt. Chern. 22: 272.
(4) BLAEDEL, W. J., AND MALMSTADT, H. U.
1951. VOLUMETRIC DETERMINATION OF THORIUM BY HIGH FREQUENCY TITREM·
ETRY. Analyt. Chern. 23 :471.
(5) BLAEDEL, W. J., AND MALMSTADT, H. U.
1952. DIRECT READING AND DIFFERENTIAL FREQUENCY METER fOR IIlGH FRE·
QUENCY TITRATIONS. Analyt. Chern. 24 : 450.
(6) BLAKE, G. G.
1946. A NEW METHOD FOR RAPID COMPARISON AND MEASUREMENT OF SOLUTION
CONCENTRATIONS WHtCH ALSO PROVIDES ~'OR THE AUTOMATIC CONTROL
OF SOI.t.'TION STRENGTH. Chem. and Ind. 3: 28.
(7) FISHER, R. B.
1947. SIMPLIFIED INSTRt.'.\IENT FOR WIDE RANGE DIELECTRIC CONSTANT MEASURE·
MENT. Analyt. Chem. 19: 835.
(lj ALEXANDER,
1945.
(8) HOWE,
\r. H.
1951.. AI'I'L1CATION OF DlELE(.'TRIC MEASUREMENT OF CONTINUOUS I'ROCESSES.
Instrumcnts 24 : 1·~3~.
(9) THOMAS. B. W .. FAEGIN. F. J .. AND WILSON, G. W.
1951. DlEI.~:CTHlC CONSTANT 1\.U:ASUREMENT FOR CONTINLOUS DETERMINATION
OF TOLUENE. AnalYI. Chem. 23 :23.
!l0) C.S. DEPART1\.IE:'IT OF AGRICFLTURE.
(;O'I'TO:'lSEED QL\LITY tannual n:ports). Colton Division, Agricultural Marketing
Scrvic(:.
fill WEST. P. W .. 13l;RJ.;II,\I:n:H, T. S .. MW BHOlSS,\RD, L.
1950. IIiGIi ~'HEQl:~::'ICY OSCILI.\TOH lTII.IZI:'IG HETEHOIWNE I'HINCtI'l.E TO
!lIE,\St:R~: FHEQl ENey CIIANGES INDCCED IIY DIVERgE cm:1IotlGAt SYSTE~IS.
Analvl. Chelll. 22 : .~69.
(12) \VEST. P. W .. RO)llCHAllX. '1'.. AND BCIIKHALTEII. T. S.
1951. AN:\ISSIS OF SYSU;1\.1 WATEII·BENZENE••\IEnn·!.·ETIIYI.·KETONE. Analy!.
Cht"lIl. 23: 1625.
(13) \\E5T. P. W.. SE1\.tlSE. P., AND BURKHAI.TEII. T. S.
1952. DEn:H~lIN,\l'ION OF WATER IN AI.COHOI.S. Anal),!' ChclIl. 23: 1250.
(I'll W lIn"l'~;N • .\IAllION E...-\ND HOL,\DA Y, CII,\III.ES E.
1955. A HAI'II) ,\U:nIOD FOB DETEBMINING THE 011. CONTENT OF COTrONSEED.
Depl. Agr. A~IS-72.
r.s.
US GQVEIU..... .orHT PAINTING OffICE
1963 OL-688-12.7
19