Parr Instrument 6200 - Manual (Page 26)

5
Operating Instructions
P a r r I n s t r u m e n t C o m p a n y 24
Foodstuffs and Cellulosic Materials
Fibrous and fluffy materials generally require one
of three modes of controlling the burn rate. Fibrous
materials do not pelletize readily and generally
require either moisture content or a combustion aid
such as mineral oil to retard the burn rate and avoid
development of high pressures.
Partial drying may be necessary if the moisture con-
tent is too high to obtain ignition, but if the sample
is heat sensitive and cannot be dried, a water
soluble combustion aid such as ethylene glycol can
be added to promote ignition.
Coarse Samples
In most cases it may be necessary to burn coarse
samples without size reduction since grinding or
drying may introduce unwanted changes. There
is no objection to this if the coarse sample will
ignite and burn completely. Whole wheat grains
and coarse charcoal chunks are typical of materials
which will burn satisfactorily without grinding and
without additives or a special procedure.
Corrosive Samples
The 1108P Oxygen Combustion Vessel is made of a
corrosion resistant alloy designed to withstand the
corrosive mixture of sulfuric and nitric acids pro-
duced in normal fuel testing operations. Samples
containing chlorine and particular samples contain-
ing more than 20 mg of chlorine samples with high
sulfur contents will greatly accelerate corrosion of
the bomb. An alternate 1108PCL is available con-
structed of an alloy selected to specifically resist the
corrosive effects of samples with high chlorine or
chloride.
While no material will offer complete corrosion
resistance to these samples, the 1108PCL offers
significantly enhanced corrosion resistance for this
service.
Explosives and High Energy Fuels
The 1108P and 1108PCL used in the 6200 Calorimeter
have been designed to provide highly automated
testing of routine samples. Materials which release
large volumes of gas which detonate with explosive
force or burn with unusually high energy levels
should not be tested with these bombs. Rather,
they should be tested in a model 1104 High Pressure
Oxygen Combustion Vessel designed specifically for
these types of samples.
Volatile Sample Holders
Volatile samples can be handled in a Parr 43A6
platinum capsule with a spun rim, or in a Parr 43AS
stainless steel capsule which has a sturdy wall with
a flat top rim. These holders can be sealed with a
disc of plastic adhesive tape prepared by stretching
tape across the top of the cup and trimming the
excess with a sharp knife. The seal obtained after
pressing this disc firmly against the rim of the cup
with a flat blade will be adequate for most volatile
samples.
The tape used for this purpose should be free of
chlorine and as low in sulfur as possible. Borden
Mystic Tape, No. M-169-C or 3M Transparent Tape,
No. 610, are recommended for this purpose. The 3M
Transparent Tape can be ordered through Parr, Part
No. 517A.
The weight of the tape disc must be determined
separately and a correction applied for any elements
in the tape which might interfere with the deter-
mination. The approximate Heat of Combustion of
the tape is 6300 cal/g. An actual amount should be
determined by running a blank test with tape alone
using a sample weighing 1.0 gram. The compensa-
tion for heat of tape may be done through the spike
option; see Spike Controls, Line 2 - Heat of Combus-
tion of Spike.
Note: Tape should always be stored in a
sealed container to minimize changes in its
moisture and solvent content.