THE BROWN-DUVEL MOISTURE TESTER 
21 
tests showed not only too much moisture but were more irregular 
than when the tests were made at a slower heating time. Moreover, 
careful investigations in this field showed that for certain moisture 
contents, particularly low-moisture contents, 20 minutes was too long 
to heat the sample, whereas the reverse was true if the moisture con- 
tent was high. 
It therefore became a necessity in order to obtain accuracy and 
uniformity of results, to standardize the heating time of each in- 
dividual burner. The standard chosen was 20 minutes, the same as 
in the earlier method. In these experiments, however, the standard 
heating time was made specific for only one moisture content; 
namely, 18 per cent, and the grain was specified as corn. This per- 
centage of moisture was chosen because it was known that at this 
figure the moisture in corn is uniformly distributed, and this figure 
is halfway between the maximum and minimum grade requirements 
for the Federal grades for corn. 
„.,,.. /2 Minutes 
SERIES /5.8Z> Moisture 
ONE 
'"/// '/////, 17 Minutes '///A 
TWO 
(/////, '■'//'//, 20 Minutes'//////////////////, 
THREE 
FOUR 
\ >>///> > *>,>' j >>/>>>>>>>, y >>/>>>> > >>,,,,,,,,,>> >>>>>>>>>> >>//// >>>>> >>>>>>> >>> >> >)>>,,j>y/ h 
("""■ ,//t,////'///t//*/t',/'t//*/r,,/f ,,/,/*/ t /*////,,/////,, t ss* ,,,///, //,,/////*r/*,/A. 
E///~) Heating Time g Mo isture Test Result 
Fig. 17 — Effect of heating time on the moisture test result on a sample of wheat 
It is apparent that grain that is drier than this (18 per cent) will 
take less than 20 minutes to reach 190° C, the proper cut-off temper- 
ature for corn, and likewise that grain having moisture in excess of 
18 per cent will take a somewhat longer time than 20 minutes, 
roughly one-half minute for every 1 per cent of moisture over and 
above 18 per cent. In other words, in place of the earlier method of 
trying to manipulate the burners to make them consume 20 minutes 
of time to reach a specified temperature, regardless of the moisture 
content of the material being tested, a standard of heat has been de- 
fined equivalent to that which will drive the moisture out of 18 per 
cent corn in exactly 20 minutes. Realizing that one would have to 
know accurately beforehand whether he had 18 per cent corn in 
order to standardize his tester; and, knowing that this type of corn 
is not always easy to obtain, a simple method for standardizing the 
gas flame has been developed that gives equivalent results and at the 
same time is easy of application. This method is generally referred 
to as the " oil test." 
60637°— 26 4 
