Parr Instrument 6772 - Manual (Page 20)

6772
Calorimetric Thermometer Instruction Manual
3-2
ID number, sample ID number, sample weight and spike weight in accordance with the
instructions set into the operating controls page.
8. The thermometer will now take over and conduct the test. During the time it is
establishing the initial equilibrium, it will display PREPERIOD on the status bar. Just
before it fires the bomb, it will sound a series of short beeps to warn the user to move
away from the calorimeter. Once the bomb has been fired, the status bar will display
POSTPERIOD. The calorimeter will check to make certain that a temperature rise occurs
and will then look for the final equilibrium conditions to be met. If it fails to meet either the
initial or final equilibrium conditions, or if it fails to detect a temperature rise within the
allotted time, the thermometer will terminate the test and advise the user of the error.
9. At the conclusion of the test, the thermometer will signal the user.
10. Open the cover and remove the bomb and bucket. Remove the bomb from the bucket
and open the knurled valve knob on the bomb head to release the residual gas pressure
before attempting to remove the cap. This release should proceed slowly over a period
of not less than one minute to avoid entrainment losses. After all pressure has been
released, unscrew the cap; lift the head out of the cylinder and examine the interior of the
bomb for soot or other evidence of incomplete combustion. If such evidence is found, the
test will have to be discarded. Otherwise, wash all interior surfaces of the bomb,
including the head, with a jet of distilled water and collect the washings in a beaker.
11. Remove all unburned pieces of fuse wire from the bomb electrodes; straighten and
measure the combined length in centimeters. Subtract this length from the initial length
of 10 centimeters. Multiply the burned length by 2.3 calories per cm (for Parr 45C10
Fuse Wire) to obtain the fuse correction. The scale on the fuse wire card can be used to
obtain this value in calories by laying the unburned pieces from right to the left on the
card. (Alternatively a fixed correction of 15 calories may be entered into the calorimeter
in the Thermochemical Corrections menu.)
12. Titrate the bomb washings with a standard sodium carbonate solution using methyl
orange, red or purple indicator. A 0.0709N sodium carbonate solution is recommended
for this titration to simplify the calculation. This is prepared by dissolving 3.76 grams of
Na
2
CO
3
in the water and diluting to one liter. NaOH or KOH solutions of the same
normality may be used.
13. Analyze the bomb washings to determine the sulfur content of the sample if it exceeds
0.1%. Methods for determining sulfur are discussed in Operating Instructions No. 207M.
14. At the end of the testing period, turn OFF the stirrer motor and the thermometer at the
power switch.