Volatile Sample Technique - Parr Instrument 6400 Operating Instructions Manual

6400
Volatile Sample Holders
Volatile samples are defined as one with an initial
boiling point below 180 ºC. Volatile samples can be
handled in a Parr 43AS Alloy 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.
Figure 3-1

Volatile Sample Technique

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 determi-
nation. 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, Heat of Combustion of
Spike.
Note: Tape should always be stored in a
sealed container to minimize changes in its
moisture and solvent content.
Use the following procedure when filling and han-
dling any of these tape-sealed sample holders:
1. Weigh the empty cup or capsule; then cover the
top with tape, trim with a knife and press the
trimmed edge firmly against the metal rim. Also
cut and attach a small flag to the disc (see Figure
3-1).
2. Puncture the tape at a point below the flag, then
re-weigh the empty cup with its tape cover.
3. Add the sample with a hypodermic syringe;
close the opening with the flag and re-weigh the
filled cup.
4. Set the cup in the capsule holder and arrange
the auxiliary fuse so that it touches the center of
the tape disc.
5. Just before starting the test, prick the disc with
a sharp needle to make a small opening which
is needed to prevent collapse of the disc when
pressure is applied.
6. Fill the bomb with the usual oxygen charging
pressure.
7. The calorimeter will fire the bomb and complete
the test in the usual manner.
Combustion Aids
Some samples may be difficult to ignite or they may
burn so slowly that the particles become chilled
below the ignition point before complete combus-
tion is obtained. In such cases white oil or other
suitable material of known purity can be mixed with
the sample. Ethylene glycol, butyl alcohol or decalin
may be used for this purpose.
Note: It must be remembered, that a com-
bustion aid adds to the total energy released
in the bomb and the amount of sample may
have to be reduced to compensate for the
added charge.
When benzoic acid is combusted for standardization
runs, it should be in the form of a pellet to avoid
possible damage to the bomb which might result
from rapid combustion of the loose powder.
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Operation
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