Parr Instrument 6400 - Manual (Page 22)

6400
Calorimeter Instruction Manual
4-3
To re-load the user default setting, go to the Program Info and Control Page,
User/Factory Settings, Re-load User Default Settings, and YES.
Sample Preparation
Sample Size
To stay within safe limits, the bomb should never be charged with a sample which will
release more than 8000 calories when burned in oxygen. The initial oxygen pressure is
set at 30 atmospheres (450 psig). 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 grams. To avoid damage to the bomb and calorimeter, and possible injury to
the operator, it should be a standing rule in each laboratory that the bomb must never be
charged with more than 1.5 grams of combustible material.
When starting tests with new or unfamiliar materials, it is always best to use samples of
less than 0.7 grams with the possibility of increasing the amount if preliminary tests
indicate no abnormal behavior and sample will not exceed the 8000 calorie limit.
Samples containing sulfur should contain no more than 50 mg of sulfur and have a
calorific value of at least 9000 BTU/lb.
Samples containing chlorine should be spiked to insure that sample contains no more
than 100 mg of chlorine and liberates at least 5000 calories
Particle Size and Moisture Content
Solid samples burn best in an oxygen bomb when reduced to 60 mesh, or smaller, and
compressed into a pellet with a 2811 Parr 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 recommended because the pressure
developed during combustion can be reduced as much as 40% when
compared 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.
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. Moisture 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
distribution. 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.