THE BBOWX-DUVEL MOISTURE TESTER 
23 
fine brooch, used by jewelers. Trial tests should be continued until 
the required time for heating all compartments does not vary more 
than one-half minute from 20 minutes; that is, not less than 19y 2 
minutes or more than 20y 2 minutes, should be necessary to raise the 
temperature of the 450 cubic centimeters of oil to 175° C. 
The only way in which this check test differs from the making of 
an ordinary moisture test is that 450 cubic centimeters of oil are 
used instead of 150 cubic centimeters, and that the thermometer is 
adjusted so that the top of the mercury bulb is just flush with the 
surface of the oil rather than being four-fifths immersed. 
If an automatic gas-pressure regulator is used, and the correct 
heating time for each burner has been adjusted, as described on 
page 22, a uniform heating time for all compartments is assured. 
If, however, a gas governor is not available, it will be necessary for 
the operator to fix in his mind the flame necessary to heat the tester 
in the proper time, and. in case the gas pressure varies, to com- 
pensate for this by adjusting the keys and air valves at the base of 
the burner. 
VARIATIONS IN HEATING TIME CAUSED BY VARIATIONS IN GAS 
PRESSURE 
Originally it was found difficult to maintain a standard heating 
time. In making a study of the reason for this, several factors ap- 
peared. The gas pressure on the supply line of a moisture tester 
varies at different periods of the day, at different seasons of the 
year, for different cities, and with the number of burners in opera- 
tion. From Figure 18, which is a Bristol recording gauge chart of 
gas pressure on the supply line of the moisture tester installed in the 
grain chemical research laboratory at Washington. D. C, it will be 
seen that the gas pressure at this laboratory varies from 6.7 inches 
to 5 inches, or a range of 1.7 inches during the working period of 
the day. Table 1 gives the gas pressure that was found on the 
supply line of moisture testers at 13 field offices of Federal grain 
supervision : 
Table 1. 
-Variation in the gas pressure on the supply lines for moisture testers 
located at different cities 
Federal grain supervision office located 
at— 
Baltimore.- . 
Buffalo 
Chicago 
Cincinnati- . 
Duluth 
Indianapolis . 
Kansas City 
Average 
gas 
pressure 
on 
supply- 
line for 
moisture 
testers in 
inches 
head of 
water 
Minneapolis . 
Milwaukee. . 
Omaha 
Peoria 
St. Louis 
Toledo 
