D2386_1 (15e1)
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Collar assemble the collar
(5.2 of the written standard),
thermometer (5.5 of
the written standard)
and stirrer (5.3 of the written
standard) into the cork.
To prevent the ingress of
water into the test portion,
it is important that an
effective moisture-proof collar
as prepared in accordance
with 8.1.1 or 8.1.2
of the written standard is used.
Collar type A,
flush with nitrogen
or dry air before fitting
to the jacketed sample tube
and throughout the
entire determination.
The air can be effectively
dried by passing
through absorbent tubes
filled with dehydrating
agents (6.8.1 and 6.8.2
of the written standard).
Collar type B, fill
with fiberglass
(6.7 of the written standard)
and a suitable dehydrating
agent (6.8.1 and 6.8.2
of the written standard)
as shown in Figure 2 of
the written standard.
The fiberglass shall be
replaced every fourth test.
The dehydrating agent
should be renewed
at intervals of not
more than three months
or when a color change
shows it to be ineffective.
Measure out 25
milliliters, plus or minus
1 millimeter of the
fuel, and transfer it
to the clean, dry,
jacketed sample tube.
Close the tube
tightly with the cork,
holding the stirrer,
thermometer,
and moisture-proof collar and
adjust the thermometer position
so that it's bulb does not touch
the walls of the tube flask
and is approximately
in the center.
The bulb of the
thermometer should
be 10 millimeters to 15
millimeters from the bottom
of the sample tube.
(Warning do not add solid carbon
dioxide to liquid nitrogen.)
Performance of this test
method can be difficult,
since the specimen
tube is immersed
in a coolant medium that evolves
gas bubbles during the test.
This can interfere with
visual observations.
In addition, the crystals that
are formed in the specimen
can be difficult to
recognize, And they can appear
in a variety of manifestations.
It is strongly suggested
that operators seek guidance
from experienced operators
of this test method
to assist them in the correct
recognition of these crystals.
This test method
should be performed
under laboratory
conditions where there
is an ample supply of light.
Some crystals can be
very faint in appearance
and difficult to observe under
inadequate lighting conditions.
Clamp the jacketed
sample tube so
that it extends as far as
possible into the vacuum flask
(Warning implosion
hazard) containing
the cooling medium (Note 7
of the written standard).
The surface of the sample should
be approximately 15 millimeters
to 20 millimeters below
the level of the coolant.
Unless the medium is cooled
by mechanical refrigeration,
add solid carbon dioxide as
necessary throughout the test
to maintain the coolant
level in the vacuum flask.
Acetone and either methyl,
ethyl, or isopropyl alcohols
are suitable.
All of these require
cautious handling.
Liquid nitrogen may also be used
as a coolant instead of liquids
cooled with solid carbon
dioxide for fuel samples
which have a freezing point
below -65 degrees Celsius.
Mechanical refrigeration
is permitted.
Where used, the
refrigerant temperature
should be -70 degrees Celsius
to 80 degrees Celsius.
Stir the fuel continuously,
moving the stirrer up and down
at the rate of 1
cycle per second
to 1.5 cycles per
second, taking care
that the stirrer loops approach
the bottom of the flask
on the downstroke and remain
below the specimen surface
on the upstroke.
It is permissible for
momentary interruption
of stirring while
performing some operations
of the procedure (see Note
8 of the written standard).
Observe the specimen
continuously
for the appearance of
hydrocarbon crystals.
Disregard any cloud that appears
at approximately -10 degrees
Celsius and does not
increase in intensity
as the temperature decreases,
because this cloud is
due to water.
Record the temperature at which
hydrocarbon crystals appear.
Remove the jacketed sample
tube from the coolant
and allow the specimen
to warm by ambient air,
stirring it continuously at
1 cycles per second to 1.5
cycles per second.
Continue to observe this
specimen continuously
for the disappearance
of hydrocarbon crystals.
Record the temperature at
which the hydrocarbon crystals
completely disappear.
Because the gases
released by the coolant
can obscure observations,
the sample tube
can be removed from the
coolant for observations.
The tube can be removed
for periods no longer
than 10 seconds.
If crystals are observed
to have already formed,
the specimen temperature
should be noted
and the specimen allowed to
be warmed by ambient air,
with continued stirring
to at least 5 degrees
Celsius above the temperature at
which the crystals disappeared.
The specimen should then be
re-immersed in the coolant
and allowed to cool.
Remove the specimen
from the coolant
slightly above the
noted temperature,
and observe for appearance
of the crystals.
It is recommended to compare
the crystal appearance
temperature with the crystal
disappearance temperature.
The appearance
temperature should
be colder than the
disappearance temperature.
If this is not the case,
this is an indication
that the crystals were
not correctly recognized.
Also, the difference
between these temperatures
should typically be no greater
than 6 degrees Celsius.