Parr Instrument 6300 - Manual (Page 29)

O
PERATING
I
NSTRUCTIONS
6300
5
w w w . p a r r i n s t . c o m 29
A
LLOWABLE
S
AMPLE
S
IZE
To stay within safe limits, the bomb should never be
charged with a sample which will release more than
8000 calories when burned in oxygen.
The initial oxygen pressure is set at 30 atmospheres (450
psig). This generally limits the mass of the combustible
charge (sample plus benzoic acid, gelatin, firing oil or
any combustion aid) to not more than 1.1 grams.
When starting tests with new or unfamiliar materials, it
is always best to use samples of less than .7 gram with
the possibility of increasing the amount if preliminary
tests indicate no abnormal behavior and sample will not
exceed the 8000 calorie limit.
To avoid damage to the bomb and calorimeter, and pos-
sible injury to the operator, it should be a standing rule
in each laboratory that the bomb must never be charged
with more than 1.5 grams of combustible material.
Samples containing sulfur should contain no more than
50 mg of sulfur and have a calorific value of at least
9000 BTU/lb.
Samples containing chlorine should be spiked to insure
that sample contains no more than 100 mg of chlorine
and liberates at least 5000 calories.
A
TTACHING THE
C
OTTON
T
HREAD
Remove any moisture from the heating wire prior to at-
taching the cotton thread.
A cotton thread (845DD) is used as an auxiliary fuse to
ignite the sample (See Figure 5-2).
Four inches of thread is recommended for this auxiliary
thread which is looped over the heating wire, doubled
on itself, twisted to form a single strand and fed into the
sample cup to lay on the sample.
When contact is made through the heating wire, the
thread will ignite, drop into the sample cup and ignite
the sample.
One spool of thread, part number 845DD, is 563 yards.
Part number 845DD2 contains approximately 1000
pieces of thread pre-cut to 4 inches.
Figure 5-2
Cotton Thread Assembly