Parr Instrument 6100 - Manual (Page 25)

Operating Instructions
6100 5
w w w . p a r r i n s t . c o m 23
Volatile samples are defined as one with an initial
boiling point below 180 ºC per ASTM D-2.
Low volatile samples with a 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.
Poor Combustion
Because of the difference in combustion char-
acteristics of the many different materials which
may be burned in an oxygen bomb, it is difficult to
give specific directions which will assure complete
combustions for all samples.
The following fundamental conditions should be
considered when burning samples:
• Some part of the sample must be heated to its
ignition temperature to start the combustion
and, in burning, it must liberate sufficient heat
to support its own combustion regardless of the
chilling effect of the adjacent metal parts.
• The combustion must produce sufficient tur-
bulence within the bomb to bring oxygen into
the fuel cup for burning the last traces of the
sample.
• Loose or powdery condition of the sample which
will permit unburned particles to be ejected dur-
ing a violent combustion.
• The use of a sample containing coarse particles
which will not burn readily. Coal particles which
are too large to pass a 60 mesh screen may not
burn completely.
• The use of a sample pellet which has been made
too hard or too soft. Either condition can cause
spalling and the ejection of unburned fragments.
• Insufficient space between the combustion cup
and the bottom of the bomb. The bottom of the
cup should always be at least one-half inch above
the bottom of the bomb or above the liquid level
in the bomb to prevent thermal quenching.
• Excessive moisture or non-combustible material
in the sample. If the moisture, ash and other non
combustible material in the sample amounts to
approximately 20% or more of the charge, it may
be difficult to obtain complete combustion. This
condition can be remedied by adding a small
amount of benzoic acid or other combustion aid.