Parr Instrument 1341 - Manual (Page 6)

1341 Plain Jacket Calorimeter
P a r r I n s t r u m e n t C o m p a n y 6
Operating the Calorimeter
All operations required to test a sample or to stan-
dardize the 1341 Plain Jacket Calorimeter should
proceed step-wise in the following manner:
1. Prepare the sample and charge the oxygen
combustion vessel as described in Instruction
Manual No. 205M.
2. Fill the calorimeter bucket by first taring the dry
bucket on a solution or trip balance; then add
2000(+/-0.5) grams of water. Distilled water is
preferred, but demineralized or tap water con-
taining less than 250 ppm of dissolved solid is
satisfactory. The water temperature should be
approximately 1.5°C below room temperature,
but this can be varied to suit the operator’s pref-
erence. It is not necessary to use exactly 2000
grams, but the amount selected must be dupli-
cated within +/-0.5 gram for each run. Instead
of weighing the bucket it can be filled from an
automatic pipet or from any other volumetric
device if the repeatability of the filling system is
within +/-0.5 ml. and the water temperature is
held within a 1ºC range.
3. Set the bucket in the calorimeter. Attach the
lifting handle to the two holes in the side of the
screw cap and partially lower the bomb in the
water. Handle the bomb carefully during this op-
eration so that the sample will not be disturbed.
Push the two ignition lead wires into the termi-
nal sockets on the bomb head. Orient the wires
away from the stirrer shaft so they do not be-
come tangled in the stirring mechanism. Lower
the bomb completely into the water with its feet
spanning the circular boss in the bottom of the
bucket. Remove the lifting handle and shake any
drops of water into the bucket and check for gas
bubbles.
4. Set the cover on the jacket. Turn the stirrer by
hand to be sure that it runs freely; then slip the
drive belt onto the pulleys and start the motor.
Turn on the 6775 Digital Thermometer.
5. Let the stirrer run for 5 minutes to reach equilib-
rium before starting a measured run. At the end
of this period record the time on the timer of the
6775 Digital Thermometer and read the tempera-
ture.
6. Read and record temperatures at one-minute
intervals for 5 minutes. Then, at the start of the
6th minute…
7. Stand back from the calorimeter and fire the
bomb by pressing the ignition button and hold-
ing it down until the indicator light goes out.
Normally the light will glow for only about ½
second but release the button within 5 seconds
regardless of the light.
Caution!
Do not have the head, hands or any parts of
the body over the calorimeter when firing
the bomb; and continue to stand clear for 30
seconds after firing.
8. The bucket temperature will start to rise within
20 seconds after firing. This rise will be rapid
during the first few minutes; then it will become
slower as the temperature approaches a stable
maximum as shown by the typical temperature
rise curve below. It is not necessary to plot a
similar curve for each test, but accurate time and
temperature observations must be recorded to
identify certain points needed to calculate the
calorific value of the sample.
9. Measure the time required to reach 60 percent
of the total rise by estimating the temperature at
the 60% point and observing the time when the
temperature reading reaches that point. If the
60% point cannot be estimated before ignition,
take temperature readings at 45, 60, 75, 90 and
105 seconds after firing and interpolate between
these readings to identify the 60% point after the
total rise has been measured.
10. After the rapid rise period (about 4 or 5 min-
utes after ignition) record temperatures at one
minute intervals until the difference between
successive readings has been constant for five
minutes. Usually the temperature will reach a
maximum; then drop very slowly. But this is
not always true since a low starting temperature
may result in a slow continuous rise without
reaching a maximum. As stated above, the dif-
ference between successive readings must be
noted and the readings continued at one-minute
intervals until the rate of the temperature change
becomes constant over a period of 5 minutes.