Operation
6400
4
19
9. At the conclusion of the test, the calorimeter
will signal the user.
10. Open the cover and remove the head. Examine
the interior of the vessel for soot or other
evidence of incomplete combustion. If such
evidence is found, the test will have to be
discarded.
If using the optional A1050DD Rinse Container
Assembly:
11. Titrate the vessel washings with a standard
sodium carbonate solution using methyl
orange, red or purple indicator. A 0.0709 N
sodium carbonate solution is recommended for
this titration to simplify the calculation. This is
prepared by dissolving 3.76 g of Na
2
CO
3
in the
water and diluting to 1 L. NaOH or KOH solu-
tions of the same normality may be used.
12. Analyze the vessel washings to determine the
sulfur content of the sample if it exceeds 0.1 %.
Methods for determining sulfur are discussed in
Analytical Methods for Oxygen Bombs, No. 207M.
Sample Preparation
Sample Size
To stay within safe limits, the combustion vessel
should never be charged with a sample which will
release more than 33 kJ (8 kcal) when burned in
oxygen. The initial oxygen pressure is set at 3.0 MPa
(435 psig or 30 bar). This generally limits the mass
of the combustible charge (sample plus benzoic
acid, gelatin, firing oil or any combustion aid) to not
more than 1.1 g. To avoid damage to the combustion
vessel and calorimeter, and possible injury to the op-
erator, it should be a standing rule in each laboratory
that the combustion vessel must never be charged
with more than 1.5 g of combustible material.
When starting tests with new or unfamiliar materi-
als, it is always best to use samples of less than
0.7g with the possibility of increasing the amount if
preliminary tests indicate no abnormal behavior and
the sample will not exceed the 33 kJ (8 kcal) limit.
CAUTION! Do not exceed the recom-
mended energy release. Exceeding 33kJ
(8 kcal) released per test could result in
catastrophic failure.
Samples containing sulfur should contain no more
than 50 mg of sulfur and liberate at least 21 kJ (5 kcal).
Samples containing chlorine should be spiked to
ensure that sample contains no more than 100 mg
of chlorine and liberates at least
21 kJ (5 kcal).
CAUTION! Do not test samples contain-
ing metal using the 43AS Stainless Steel
sample cups. Igniting samples with metal
components could ignite the stainless steel
sample cup and interior components of the
vessel and damage the vessel. Samples
containing metal can be tested with the
43A3 Fused Silica/Quartz crucibles.
Particle Size and Moisture Content
Solid samples burn best in an oxygen combustion
vessel when reduced to 250 μm (60 mesh), or smaller,
and compressed into a pellet with a 2811 Pellet
Press. Large particles may not burn completely and
small particles are easily swept out of the capsule by
turbulent gases during rapid combustion.
Note: Particle size is important because it influences
the reaction rate. Compression into a pellet is recom-
mended because the pressure developed during com-
bustion can be reduced as much as 40 % when com-
pared to the combustion of the material in the powder
form. In addition to giving controlled burn rates, the
formation of pellets from sample material keeps the
sample in the fuel capsule during combustion.
CAUTION!
Materials, such as coal, burn
well in the as-received or air-dry condition,
but do not burn completely dry samples.
A certain amount of moisture is desirable
in order to control the burning rate. Mois-
ture content up to 20 % can be tolerated in
many cases, but the optimum moisture is
best determined by trial combustions.
If moisture is to be added to retard the combustion
rate, drop the water directly onto the loose sample
or onto a pellet after the sample has been weighed.
Then let the sample stand to obtain uniform distribu-
tion. Low volatile samples with high water content,
such as urine or blood, can be burned in an open
capsule by absorbing the liquid on filter paper pulp or
by adding a combustion aid, such as ethylene glycol.
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