Parr Instrument 1122 - Manual

1121 & 1122 Oxygen Combustion Vessel
Operating Instructions
210M
An Oversized Special Purpose Combustion Vessel
1121 Oxygen Combustion Vessel
The 1121 Oxygen Combustion
Vessel has been developed spe-
cifically to burn large samples
of slow burning materials such
as grain, wood fiber, paper and
other vegetable matter. Vola-
tile liquids can also be burned
in this bomb provided special
techniques are used to retard
the burning rate. The ability of
the 1121 vessel to handle large
samples with complete recov-
ery of all liquid and gaseous
combustion products makes it
particularly effective for deter-
mining trace elements in com-
bustible materials and for pre-
paring samples for tritium and
carbon-14 measurements.
1122 Oxygen Combustion Vessel
The 1122 Oxygen Combustion Vessel has been developed
specifically to burn samples liberating up to 0.1 MJ. This
bomb can safely accommodate sample sizes that are
significantly larger than the 350 ml 1108 vessel (33 kJ)
but less than the 1850 ml 1121 vessel (0.26 MJ). The 1122
style vessel is especially useful for preparing samples for
C-14 measurements where the volume of residual post-
combustion gas must be minimized.
Allowable Sample Size
1121 Oxygen Combustion Vessel
Slow burning, combustible samples weighing up to 10
grams and releasing up to 0.26 MJ can be burned in the
1121 vessel using oxygen charging pressures up to 300
psig (20 atm), but these limits vary and must be checked
experimentally for each sample. The sample size must be
adjusted to an amount which will give complete combus-
tion with peak pressures held in the range from 1000 to
1200 psig. The pressure should never exceed 1500 psig as
an absolute maximum. After a safe procedure has been
established for a specific material, the entrance to the
gage can be closed at the underside of the bomb head
using the 440A plug which is furnished for this purpose.
This will prevent repeated stress on the gage and keep
combustion products out of the gage passage.
1122 Oxygen Combustion Vessel
Slow burning, combustible samples weighing typically up
to 4 grams can be burned in the 1122 Oxygen Combustion
Vessel using oxygen charging pressures up to 300 psig
(20 atm). This filling pressure and the volume of the cyl-
inder yields ~0.8 moles of 0
2
. Using more than half of the
available oxygen during a sample preparation increases
the risk of incomplete combustion. Larger samples can be
prepared in this bomb as long as the total energy released
in the bomb doesn’t exceed 0.1 MJ. For example, each
mole of cellulose [(C
5
H
10
O
5
)
n
(mwt 150), where n =1500 to
>6000] burned requires 10 moles of 0
2
. The heat of com-
bustion of cellulose is ~17kJ/g. Preparing 6 grams of cel-
lulose in the 1122 vessel results in a total energy release of
0.1 MJ and uses (10*6/150) moles, or half of the available
oxygen.
Sample Preparation
Finely divided samples to be burned in this bomb must
be compressed into pellets or, if this is not convenient,
powdered samples must be packed firmly in the bottom
of the combustion cup. Cellulosic materials should be rea-
sonably dry, but some moisture may be desirable since
bone-dry samples usually burn too fast, resulting in in-
complete combustion. It may be necessary, therefore, to
add moisture to cellulosic materials to slow the burning
rate. The amount of water added will have to be deter-
mined experimentally, with some materials such as paper
accepting up to 40% water by weight to obtain good com-
bustions. In all cases, compress the sample into the cup
as firmly as possible.
Preparing the Charge
When loading the bomb, set the head in the tripod sup-
port ring and adjust the capsule support so that the top of
the cup is positioned 6 to 7 inches from the underside of
the bomb head. Fasten a 10 cm length of 45C10 fuse wire
to the electrode hooks and bend the wire so that it touches
the sample but not the capsule. If the wire does not reach
the sample, its length can be increased to 14 or 15 cm, but
longer lengths should not be used because the wire will
not get hot enough to ignite the sample. If the wire does
not reach the sample, add an auxiliary fuse made from a
strip of filter paper or a length of cotton or nylon thread.
It is always well to place from 25 to 50 ml of water in the
bottom of the cylinder before closing this bomb. This is
not absolutely necessary, but it is an excellent safeguard
against damage which might be caused if any of the metal
parts should ignite and drop to the bottom of the bomb.
Note: The bottom of the A445A Cup Support Bracket in
the 1122 vessel must be 5 mm from the end of the dip
tube. This positions the combustion cup a safe distance
from the head of the bomb. Attach 15 cm of the 45C10
fuse wire between the two electrode hooks. Refer to
the assembly drawing on page 4.
Note About Nomenclature:
Historically, burning a sample enclosed in a high
pressure oxygen environment is known as Oxygen
Bomb Calorimetry and the vessel containing the
sample is known as an Oxygen Bomb. The terms
bomb and vessel are used interchangeably.