Parr Instrument 1108R - Manual (Page 7)

w w w . p a r r i n s t . c o m 7
1108R Oxygen Combustion Vessel
Fire the charge by pressing the firing button on the
ignition unit, keeping the circuit closed for about 2
seconds. The indicator light will come on when the
button is depressed and will remain on while the
button is depressed.
If the indicator light does not come on when the
firing button is pressed there is either a fault in the
2901 or an open circuit in the system. Check for
voltage between the 10 cm and common terminals
of the 2901. Approximately 23 VAC should be mea-
sured. If there is no voltage present, check the fuse
inside the 2901. An open circuit can usually be lo-
cated with an ohmmeter. Flex the lead wires during
any continuity check as the wires may be broken
and making only intermittent contact. If the red indi-
cator light glows during ignition but the bomb fuse
does not burn, check the system for a voltage leak
to ground, most likely in the insulated electrode on
the bomb head. Check the electrode using the high
impedance scale on an ohmmeter and replace the
electrode insulator and seal if leakage is indicated.
Recovering the Combustion Products
Let the bomb stand in the calorimeter or water bath
for at least 3 minutes, then lift it out of the water
and wipe with a clean towel. Open the valve knob
slightly to release all residual gas pressure before
attempting to remove the screw cap.
Caution!
Do NOT have any part of the body in the
exhaust path of the bomb.
Gas release should proceed slowly over a period
of not less than one minute to avoid entrainment
losses. After all pressure has been released, un-
screw the cap; lift the head out of the cylinder and
place it on the support stand. Do not twist the head
during removal. Pull it straight out to avoid sticking.
Examine the interior of the bomb for soot or other
evidence of incomplete combustion. If such is found
the test will have to be discarded. Wash all interior
surfaces of the bomb and the combustion capsule
with a jet of distilled water and collect the washings.
If any precipitate or residue is present, remove it
with a rubber policeman. Do not filter the washings
as this might remove valuable constituents. Titrate
the washings and measure the unburned fuse wire
as required for calorific tests, then analyze the wash-
ings for sulfur and other elements, if required.
An Optional Recovery Procedure
If desired, a luer fitting, 518A, can be attached to the
bomb to provide a means for washing the bomb
and recovering the combustion products with a
syringe without opening the bomb and removing
the bomb head. To use this procedure, remove the
standard A420A valve needle and replace it with
an A420A2 needle to which a syringe, 244C, can be
attached.
To recover the combustion products via a luer
fitting, let the bomb stand in a cooling bath for at
least 3 minutes after firing to allow for complete
condensation of all residual vapor. Then remove the
bomb from the water and attach only the barrel of a
244C syringe to the luer fitting. Open the valve and
release the pressure at a slow rate, using at least
a full minute to bring the bomb pressure back to
atmospheric. The attached syringe barrel will help to
retain any condensate spray that might be carried
out of the valve during the exhaust period.
Add 30 mL of distilled water to the attached syringe
barrel and use the syringe plunge to force the
water into the bomb, then close the valve while
holding the plunger down. This will develop suf-
ficient pressure within the bomb to seat the inlet
check valve and provide enough positive pressure
to help remove the washings. Agitate and rotate
the bomb in a horizontal position to wet all inner
surfaces, then turn the bomb upside down over
a 600 mL beaker and open the valve to discharge
the washings into the beaker. Tilt the bomb slightly
toward the valve to get as much of the water out as
possible. Repeat this back-flushing procedure two
times, collecting a total of 90 to 100 mL of washings,
then open the bomb and recover any liquid that
may remain in the cylinder. The three complete back
flush and rinse cycles should recover better than 99
percent of the combustion products.