D189_8 (6(2014))
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Shake thoroughly the
sample to be tested,
first heating to
50 plus or minus
10 degrees Celsius for
0.5 hours when necessary
to reduce its viscosity.
Immediately following
the heating and shaking,
filter test portion
through a 100 mesh screen.
Weigh to the
nearest 5 milligrams
a 10 gram sample of
the oil to be tested,
free of moisture and
other suspended matter,
into a tared porcelain or silica
crucible containing two glass
beads about 2.5
millimeters in diameter.
Place this crucible
in the center
of the Skidmore crucible.
Level the sand in a
large sheet iron crucible
and set the Skidmore
crucible on it
in the exact center
of the iron crucible.
Apply covers to both the
Skidmore and the iron
crucible, the one on the
ladder fitting loosely
to allow free exit to
the vapors as formed.
On a suitable stand or ring,
place the bare nichrome wire
triangle and on
it, the insulator.
Next, center the
sheet iron crucible
in the insulator with its bottom
resting on top of the triangle
and cover the hole with
the sheet iron hood
in order to distribute the heat
uniformly during the process.
See Figure 1 of the
written standard.
Apply heat with a high, strong,
flame from the Meker-type gas
burner, so that the
pre-ignition period will be
10 plus or minus 1.5 minutes.
A shorter time can
start the distillation
so rapidly as to cause
foaming or too high a flame.
When smoke appears
above the chimney,
immediately move
or tilt the burner
so that the gas flame
plays on the sides
of the crucible for the
purpose of igniting the vapors.
Then remove the heat
temporarily, and before
replacing, adjust by screwing
down the pinchcock on the gas
tubing so that the ignited
vapors burn uniformly
with the flame
above the chimney,
but not above the wire bridge.
Heat can be increased,
if necessary,
when the flame does not
show above the chimney.
The period of burning
the vapors shall
be 13 plus or minus one minute.
If it is found impossible
to meet the requirements
for both flame and burning
time, the requirement
for burning time is
the more important.
When the vapors cease to burn
and no further blue smoke
can be observed,
readjust the burner
and hold the heat
as at the beginning
so as to make the bottom and
lower part of the sheet iron
crucible a cherry
red and maintain
for exactly seven minutes.
The total period of heating
shall be 30 plus or minus
two minutes, which constitutes
an additional limitation
on the tolerances for the
pre-ignition and burning
periods.
There should be no
difficulty in carrying out
the test exactly as
directed with the gas
burner of the type named using
city gas, 20 to 40 megajoules
per cubic meter, with the top of
the burner about 50 millimeters
below the bottom
of the crucible.
The time period shall be
observed with whatever
burner and gas is used.
Remove the burner and
allow the apparatus
to cool until no smoke
appears and then remove
the cover of the Skidmore
crucible, about 15 minutes.
Remove the porcelain or silica
crucible with heated tongs.
Place in the desiccator,
cool, and weigh.
Calculate the percentage
of carbon residue
on the original sample.