An electrical resistance method for the rapid determination of the moisture content of grain


Material Information

An electrical resistance method for the rapid determination of the moisture content of grain
Physical Description:
Briggs, Lyman J ( Lyman James ), 1874-1963
United States -- Bureau of Plant Industry
U.S. Dept. of Agriculture, Bureau of Plant Industry : ( Washington D.C. )
Publication Date:

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aleph - 29726052
oclc - 48872586
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Full Text

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I I A N I N I ) I I Y

AN ]E'l\ 1 I. IIESISTIO I IF h I 1) 1" 4tI
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l'hysioloy/;' aid P'itho'hoif, ain d ('hif f f Bureau, Bvorl v I. Ialloa'v.
Physioloqist and Paliolof/isi. and .A sistant thofif f Bureau., AlbXrl YF. Woods.
Laboratory of Pla nt 1'alhaologqi Er win I. Smith, Pathologist in Charg,.
Fruit Disiuasv Insaiuaatioits. Metrton B. Wait(,. Pathologist in ('Chargo.
Laboratory itf founest P'lthology, lHaven Matcall, IP'alhologist in (C'hargm.
(Cotton and T,'iick Disiauses and Plant Disuasa \Villinm A. (Ortio, Pal'tahologist in Charge.
Pathiologicai" 0/hc/lions and inspiclion Wiork, I'lora W. PIal , Plant Lief History Infasfiiatiaons, V alto'r T. Sw'inglh, P'hysiolovist in Charg(a.
('niton 1riri diin liiiat aigutian, Archiblal t I). SthanM l and DanicI N. Shomaak'r, I'lysiologists in (haorgp.
Tobaccoii li as/iyiuatins. Archlialhl 1). Shaintl. WiXh!tnian W. garner. andl Ernast II. MaIt h'wson, ill Chargo.
Corn Ia'uaiii/iiiins. Charlos I1'. llartlxy, Plhyiioloagist in Chargi.
Alkali and Droughlt e/aistant Plant Itraeding Iitiiiiatiiins. Thomas 1. Kearncy, Pllysiologist in Cliargv'.
Soiil / ',... anid Water airitfication ii ii sliiatiaotna Karl F. K ollnr aii. in li .... 1 in ( 1i 1-.
Bionomnic a Iniat uiiions of Tropical and Stbtropical Plants, Orator F. Cook. Bioiiomist in C'harg'.
Dritt, and Poisontt Pl a'hnit and T'ia ('a0,1ira lnris.tigiations, todi wy II. Trio,, IP'hysiologist in Charga.
r' Laboratory, I.,yaiian J. Iritggs. Phyli'ist in Chargc.
Cropji Tchnology andl Fibtr Plant int stiiatiains, Natthan A. Cobbl. ('rop i-,I 1..l.. in Charge.
Twoaaaoi atiend a ang( Inrfestiga'tiin.s, Frederi(k V. Coville, Botanit in Ch('argv.
F'iarim Managt mtnt. William .1. Spillman, Agricilturist in Chargo.
Grain Inrisiaitioiins. Mark Alfri'l ('arliton, Ci'ralist in Charge.
Arlington Exprrimiental Farin and Hoirticull/ural li t nslignaions. Leo C. Corill,. I Forliailli urist in Charge.
Vegetable Tas tint Gardin.a, William W. Tracy. sr., Siporintanditdnt.
Sugar-Bet lniritigations, Char'is 0. TIow nsondii Pathologist in ('harg'.
'starn Agricunilturaii le ''nsion. Carl S SScofild.I Agriiltlarist in ('Chargo.
Dry-Laind Agriculture liiyia atioin s, E. Channing Chilcott, Atricultnrist itn i r-_
Poamulo/ical Colletalions, (aistava's B. Blrackett, Pomologist in C'har r.
Field Jlnt'estig;;ions in Pamolongy, William .\. Taylor anl CG. lHarol l'owelld i ..,t.i... in t. r.
Eperimental Gardinsa aind Grounds, Edward I M. Ityrrws, Suaparintanh'lnt.
F r, a1 Sed ad n Plant Intraduclion, IDavii Fairchild, .Agricultural Exploro'r in Chliargm.
Foraqe ('Crop Inrestigations, Charles V'. l'ip'r, -\arostologist 'l Charge.
Seed Laboratory. Edgar Brown,Botlanis in Charge.
Grain Stalndardization, John D. Shnahanaa. Crop 'r'Tehnologist in 'Charg'.
Subtropical Garden. Miami. Fla., 1' . Wcslvr. in Clhargo.
Plant Introducltion Garden, 'hico, Cal., W. W. Tra(,y. jr.. Assistant Botanist in C'ha i.
South T"ras Garden, Browsu'sriae, u. E.i ldward C. I r'in 'i' Poinologist in C'hargo.
Farmers' ('ooperatie l) tnolt.tratiotn 'Work, SfaItla A. Kt aptj) StWpcial A9nl ii n a ,r .
Scad Distribution ((tirete'd by Chief of Buranau i. Lsl Morrisou, Assistant in (;''nral ('Charo.

E"'ifor, J. 1E. Rockwpli.
('Chif Cl/rk, JTami's K. Joi's.



The shipping a.1d stori. lalities ot1 grtin are so dependent upon
its mo tis ture co)[ntetli thit ;>n ac luraIte k ,,,,oldh-I d,' (i( moisttu. 1re
in ,,ill ill storaL''e a d in (ralln'it is diehl, (Iesiralhle. This -..; 1 ,,ject
has leenl -iy(n special sitet'tiot 1) Brown all d Duuvel", w0'o have
described :i rapid method l of makitll'- tiwistlre dtert mlinlationst4.
Their, method consi.--ts Ill b~oilin Ille -r'aIII Ill all oil liavill" a1 llas-hiilw'
]ioint tnnlich ;1hio' l| o the \lailcnr l llt (,I* ",, ter il l r
xvhic'h distill, off, ;ill c',lcctiiii+ and mlcisitll wri it in ;i -'.ttilald
_i..duat(1. Mois-.tu dcm' tht miiie t tio cal l h nn In (h lllsld he made il
lJout onle-half houtr, whereas hlelrmnati lls in te, water oven+
'e<|nre ++several davs. This mlethod is.. however, suitable for labora-
to(W V s ll nlv40 Y. nevcossitaliiiw the collect iill" ) ol' samples efore (lhe
detorlinltlio.s ca ell h d, he ade 11, d doe", no4t i ippealr t) be adatiled to
sulh 1"ii"in produlictsi ;is, 1i-al and tllo r.
At the reu([est ()f thie 1ice ol' rainn S(atilhihtizatilon, tilte ', it1
tundertook illie developImen1 t, all ;I locirical re'i'tiilce metloiod for
uu1 hsrt ).ii l lie moistulre content o ito (il adi]pt>(ed ioimeas tmen)s
iill a (I'll' ()I' elevatolr o, well at it i a la lbor tory, :111dnd e i rii l
oldls" two or tln'ee minlutes; for a heeiin lin le m aue e t
so) far hIa-ve beell cmitilled t(o wh 'tll. Tl te ri lt l o t ild ore "f)
|' ,inil-i,,_* thiit I brieh f pi'elitin1:1rv, de-.e i|)li,, -f the me o i si l
sk-vie ('iorrvpwl diili 11)( u-e0e4t1 ,ill be talde lo1 other _'T s,
well as; I'or flo11 and cown meal., A portable ai arllsl suit abl e
tor mlleas rell enillts ill a:1rs and eleva1t or, s i ~ .. !o eili^ coI-lruclted.
I'l!, Il lhe t developed o siss esse tialll i the me1aslrit lieme t of
tit resistlance offered l to +liepa -,_', o all lhc!i+Ic ('1irrlent tlirt)oln li
tlhe i1+iii lll o )oll0 e mleallic rod orhW .trode to another. The clec-
*' II, uth ltiii ''), lihn-. m ,,' I kl~inl II init r I t l I )It7+

11. I. 1:


tric'al resistance decreases rapidly as the moisture content of tilhe
grain increases. The electrical resistance of wheat ,',l:ilinlL 13
per cent of moisture is seven times that of wheat it;Iliiiig, 14 per
cent and fifty times that of wheat containing 15 per cent of moisture.
This method, therefore, gives a very open scale, and a considerable
variation in resistance can take place without seriously aflfectiii,
the accuracy of the moisture determinations.
The relation between the electrical resistance and the moisture
content of wheat is shown graphically in figure 1. The moisture
percentages in this figure are plotted as ordinates and the natural
logarithms of the corresponding resistances are plotted as abscissas.
Five widely differing types of wheat soft red winter, hard red winter,
No. 1 hard ;-irI.,
durumn, and a badly
6 ________mixed wheat con-
trainingg many weed
,. ___ _________ seeds-were used in
-% t h e s e determina-
"_ _-- --- tions. The close-
ness with which the
-,-- -,,,,,, different points on
the diagram ap-
^ -- proacli the straight
line drawn thr,,ii,"t
them illustrates tlhe
/o___- accuracy with which
,+- moisture determi-
z 067 -nations can be made
I'l. 1 .I-Chart showing I h( relation between L ln moisture content and
the electrical resistance of w\hcat. Misiurarnnts maiiile ia t 7 ; F. )V this m ethod.
For dIrscription of electrodes, see texl. or'sisnancs a expressed in Tle logarithmi s of
imegolims. Moisltur' percentage based on weight of moist grain.t
the resistances in-
stead (f tile resistances themselves are plotted in order to condense
tlie diagram and to bring out the straight line relation between the
two variables as shown.

Thlie electrical resistance of wheat is'also dependlent upon thile tem-
)perature of the grain. In fact, the rapidity with which the resist-
ance decreases as the temperature increases is quite remarkable and
greatly exceeds that occurring in most substances. Thie manner in
which the electrical resistance of wheat varies with tlie temperature
is shown graphically in figure 2, in which temperatures are plotted
as ordinates and electrical resistances as abscissas. The resistance
at . 0. (.;*'- F.) is seen to be IS times the resistance at 240C. (75 F.).
I Cir. 21)J

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mixt'tdI XX ClI P. l)',iils- o the di a iiJg rel er tii lo e s, -rse- ti-
lIh ,sisn er I I i r ,. I t i rI Is h Is ro ts po d i I IrI I i i rr l e li nt I ii-I
i- I (I'xiii' all I i e o I t( I I hIi) n r Iii I I 1o e i [)fii

tI i ine Ift lie rIatIsI I I I i r It e it o I I Ie I I I Ie Irre (0- 1 l ii 1 r11 -i- I
Is ol ore curve take n z t a I sta dardI. In C( )d1,- *hi these 1e 1 i+
In ttilti. tlt 1 \ieit, alt k ,'i t Ioz I l iD al ice niet., X\\ -- asI, ;IIdo
t ;ii )|)r) aci li h l lIIi I"l II'e ti Iif I., )Ii I a ; i :-,a ies i l'l e istaIs I -I

L ~ - ---.-- I-T ,-- --

11 C I ,1 .' I I I I, I I I : I I _I I_ r( I_4 ... I .' (1

2 : 0 i i- i' f- 7 "
i t "
NV I ti zc l W c'" I I I I I rI. I I I I I I I I In I rI

buti Ion as ssI e I i, l eoth l t 4 eiach set a IlIIt I I/Iasu III ts III T"lIlt ilm'pe Ia ntl
:1l1i) Iliat oI tf It IUl Xen)' oll ii\ere (d l in I a siit r it1 :[1tn tcr v l It ItIat W,
tlhe riin anti : Id measuringi tlih re'.i-it(ui a. it : t h li. It I I hill lIlt
t del l'II T' 1 1 illI t wli t lr e I oIiperat l c X) hu tIi 'rel \ li I II I Iliil 1 X it li] 'ii w a, I,'r)I-
Ir )' cooIled inI this \Iva,. vIw* I 1 acco )'IunIts f Ito( lh rahe1 \1 eide depa [ rt1 ure
ol s IoIIe otII t oe I n()IIIts frn m ) I l ll I Ie l me I eI'\ I.
By o} i Nitr r thlie d",ata l hiown itI I lit '-' I and 2t we ca, ci'll co struct
i "itt ii"w i 'e'titlLie otllei t n (i tt a :Isa Iple <' d wXl cal it oti l
l ii a hivi i telecricai re'-islaillce al at y X emper'at e it'I 11111


llthe niange of the experiments. Such a chart is presentetl as fi',i,, 3.
This chart is similar to that shown as figure 1, except that we have
here lines showing the relation between moiisture content and resist-
ance not only ftor a single temperature, as in figure 1, but fir tempera-
lure intervals of 5 [egrees from SO' to 40 F. In this chart the
moisture contents are lottt'edl as odinatles and lthe l._.11,ithins o(f the
electrical resistances as abscissas. To facilitate thle use of the chart,
resistances aire written ini place of the corresponding 1 *.i ithills.
T() Iillustrate tile utse ()f thle chart, suppose that a resistance oIf .)5
imegohims was observed inl a given sample of' wheat at a temperature
Of 7"-0 F. Referlrii. 1 to thle chart, it will be seen that thle iii.iini;iy
line co(Irresp(ondin t) 55 me(gohims crosses tle 75 F. line at a point
corresponding to 13.95 per cent of moisture. This statement
assulliles, o)f course, that tlie measurements were made with elec-
trodes ()f standard size, to which this chart is onlyl applicable.


Winless tile ._11%i1, is very wet, its specific electrical resistance is
very high. The resistance, While electrolytic in character, is so
rentt that polarization is not trou)lesomile and mneasurem ents can
'e I made within direct currents. Tlihe electrical apparatus required
fo, such mleasurelimenits is therefore similar to that used or f .-lii
hle insulation ()f cables. Tlihe mieasuremlients described were made
principally withi a Wheatstone bridge, using a fairly sensitive gal-
vanlolleteir an1d aln electromnotive force of 17 volts. In thlie driest
samliples belloww 12 per cent) tile resistance was so hiil that it ciuld
not be measured b1y this method. For these saml)les t'le direct
deflecti(n methotI was uised, thle galvanometler c nd a grain resistance
1eing cm Inect ed in series wit i a )at It'ry havin'og an elect r()m)otive
force o(f 10 v(olts.
In all li'he metasl urements described, ithe electro)dles uIsed c, insisted
of t'w () parallel tM -i)nc rtlld i'ss rods, I. inches betwee'l centers
anid 12 inches loi,_. These rods we're kept parallel and insulated
from each other bv being supported in a haird-rubber lohk at their
upper endsIs. ('Coniecting wires witli extraa heav rubber insula-
ti,)n welle soldered to the Iwo) upper ('end-s )f (he electrodehs. The
1'rain during measurements was held in dlass batt.rv jars 5 inches
ill diameter and 11 inches hi1g,. Tile height ()f the 'grain. inside
1101asii,.r,,,.,,l, was 10 inches. Tile hower ends (f tile electtro)des
rested upln ile b()lottm ()f tile jar. Tlie temperature was measured
\6i1h a mercuial thermoleter having a cylind'ical bulb, which could
be readilv forced into thle grain.
I (Air. 2o I




1)1'tIIT I/M N AI'IDN O .<1IM,-1t ('()NTIF: IO1N 61(. 1UN'.

0 o 3 o 0

---. .. ... ..1 ", ,l 000
-.. .. -'P --- 000
-- -- - - ** > t l ... .. .. ... t i ... .. "i 7fO0
- ,- ,., $-.I, -,-i -(70-

--- I--. --- r ------ r-- .. .. ... -- I ... y- .... --- -I ,5"0

....V- ................ "----! '--- _--!-- QO0

--* ----- i-- -'--- I-- *--.-- -+"* -^-f- -- -+"-+-f r- ---- 00

r -^ -'--*-- -- ,u900
1 I'4 6'00
- -. # f- 600
+ +- oo
-** - - ----- 700
_1 - --,
, ': / . - o
. ..-- -- + 4 4--"- ------ -C -+ -00C'
':--'--,<" .. .. o i i~ / f i

I ,
-*-* -' -'- -. i f f f < ** 4-------\ o
4." / // y i

--- I --- l-- r- f f f --f f I f -- -- -- --- -- l -- l ------- '
--- /0 0 t f 90
~~ 700
V~tI!V 1 1

/ f
- / I/ 1 v / v 1/ - -- 1i 1-1- 1

II /y I /0
--i- ^ ^-- -^ --- -' ---- 9o

-4 . 7'
, I I I :

/// -Y-4 --- ---'---1---~---- /."'*"----; ; -
/ / .. 1/ --- ^-- i
! I [,/----- ^- -- ----^

/6" /~ /f /_r /l?
1m/4 < A/ 7--" Am'O/,4'" T](-44PE

|t+>utdurr /rtr kixiwn. 1 b'*: l<'tri h's Itt\V 1tK I In" >Ltiiir ilinr L-.mlll -, ;>'. Ifhn).' il.'-t
|* ulS! lit lI < ("oini lr u it Is tlh s ruh rf,
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Before each measurement the electrodes were removed and the -_
grain was packed by jaring' the bottom of the container against some 2
solid( object. It is important that this precaution in 1,i king be o
observed if satisfactory results are to be obtained. This will not be
necessary in measurements made in cars, since thle settling of the q
grain in transit will have reduced it to a stable condition. ___
Other types of electrodes and containers designed for using smaller ,---
quantities of grain have been tried, but the most satisfactory results --
hiave been obtained with the apparatus described.
Portable cable-testing sets can lbe used for the resistance measure-
ments necessary for moisture determinations, provided the grain is
not too dry. A special testing set is now being constructed in which
a resistance coil for determining the temperature of the grain is
placed within one of the electrodes. A shunt box for use in connec-
tion with the direct deflection method is also being constructed.
This method is similar in principle to that developed some years
ago in the Division of Soils for the measurement of the moisture con-
tent of soils. The difficulties that developed in connection with that
method, namely, the translocation of salts and the cracking away of
the soil from thle electrodes, are not encountered in the measurement
of the moisture content of grain. There is a possibility that wheat
grown in different localities will show a sufficient variation in salt
content to affect the moisture determinations, but such variation has
not been indicated in the samples so far examined.

This paper deals with an electrical resistance method for the rapid
determination of the moisture content of grain. The experiments
have so far been confined to wheat. The electrical resistance of
wheat cointiitini 13 per cent of moisture is fifty times that of wheat
containing 15 per cent. The temperature of the grain must be
determined. The results of the experiments indicate that the
moisture content can be determined by this method with a probable
error not exceeding 0.3 per cent. Measurements can be made
rapidly, requiring only two or three minutes. The apparatus is
portable in character, so that measurements can be carried on in cars
or elevators as well as in the laboratory. The use of this method
in connection with other grains and grain products is now being
Secretary of Agriculture.

WAsmxINGTON, D). C., October 1), 19ti..
1 'ir. 21)1