Parr Instrument 1108R - Manual (Page 9)

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1108R Oxygen Combustion Vessel
polished with an abrasive to remove any ash or
other surface deposits. Heating in a muffle furnace
is also a good way to destroy any trace of carbon
or combustible matter which might remain in the
capsule from a previous test. After heating, place the
capsules in a clean container and handle them only
with forceps when they are removed to be weighed
on an analytical balance.
Capsules should be monitored for wear. Do not use
the capsule if the wall or base thickness is less than
0.025”.
Foodstuffs and Cellulosic Materials
Fibrous and fluffy materials such as vegetable fibers
may have to be packed into the combustion capsule
and moistened to slow the burning rate, but food-
stuffs and cellulosic samples generally burn with
little difficulty. Partial drying may be necessary if the
moisture content 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
with no additives or special procedure.
Corrosive Samples
Although the Parr bomb is made of corrosion resis-
tant alloys, repeated use with high sulfur samples or
with samples containing over 20 mg of chlorine may
corrode the metal surfaces and produce a dull film
on the inner walls of the bomb. Materials containing
appreciable amounts of caustic; such as dried black
liquor from a pulp mill, may also damage the bomb,
with the caustic attacking the alloy capsule and
causing the metal capsule and the bomb electrodes
to ignite and burn. These corrosive attacks on the
bomb can be reduced by using smaller samples
and by increasing the amount of liquid placed in the
bottom of the bomb. If a corrosive film develops on
the bomb surfaces it should be removed by proper
polishing before it grows to a point where deep
pitting occurs.
Liquid Samples
Non-volatile samples are treated in the same
manner as solid materials. Oils and other liquids
which are not volatile at room temperature can be
weighed directly into open combustion capsules.
The cotton thread should be positioned just slightly
above the surface of the sample or just touching the
surface.
Gelatin Capsules
Volatile liquid samples to be burned in an oxygen
bomb can be handled conveniently in Parr 3601
Gelatin Capsules. These 0.9 mL capsules consist
of two cups which telescope together with a fric-
tion fit adequate to retain most liquids. Corrections
must be made for the heat of combustion of gelatin
43A6 Combustion Capsule with
Adhesive Tape Seal 3601 Gelatin Capsules 43AS Combustion Capsules