Parr Instrument 6725 - Manual (Page 20)

6725
Semi-micro Calorimeter Instruction Manual
3-2
9. At the conclusion of the test, the calorimeter will signal the user.
10. Open the cover and remove the bomb and Dewar flask. Remove the bomb from the
flask and 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
left on the card. (Alternatively a fixed correction of 1.5 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.