IKA C 200 - Manual (Page 18)

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Failure to observe these instructions could re-
sult in damage to the decomposition vessel.
Exploding decomposition vessels present a risk
of serious injury or death. When working with
unknown substances, select very small weighted
samples at the start in order to determine the na-
tural energy.
Normally solid materials in powder form can be
combusted directly. Materials which com-
bust quickly (e.g. benzoic acid) must not
be burnt loose. These materials tend to splash
and there is therefore no guarantee of complete
combustion.
Furthermore, this can damage the inner
wall of the decomposition vessel.
IKA ® pelleting press C 21 and IKA ® analytical mill
A 11 basic (see Accessories) are available for sam-
ple preparation.
Materials which are diffi cult to burn (materials
with a high mineral content, low caloric materi-
als) can often only be fully combusted using IKA
®
acetobutyrate capsules C 10, IKA ® combustion
bags C 12 or IKA ® combustible crucible C 14 (see
Accessories). It is also possible to use liquid bur-
ning aids such as paraffi n oil.
Before fi lling the capsule or the combustion bag
with the substance to be determined, weigh
them to calculate the extra external energy ad-
ded by the burning aid from the weight and the
calorifi c value. This must be taken into account
in QExternal2. You should keep the amount of
burning aid used to a minimum.
Most fl uid substances can weighed out directly
into the crucible. Highly volatile substances are
poured into combustion capsules (IKA
® gelatine
capsules C 9 or IKA ® acetobutyrate capsules C
10, see Accessories) and combusted together
with the capsules.
The burning aids (e.g. cotton thread) must also
fully combust. If there is any unburnt residue, the
test must be repeated.
When working with unknown substances, select
very small weighted samples at the start in order
to determine the natural energy. If you are bur-
ning unknown samples, leave the room or keep
your distance from the calorimeter.
After combustion the water produced is collec-
ted and the decomposition vessel is thoroughly
rinsed with distilled water. The water used for
rinsing and the solution produced are combined
and examined for their acidity. If the sulphur con-
tent of the fuel and the nitric acid correction are
known, it is not necessary to analyse the water.
Note: in all the automatic calculations an extra
100 J have already been included for the electric
ignition energy. This value cannot be set.
Materials which are diffi cult to ignite or combust
are combusted together with a burning aid. The
burning aid is fi rst weighed and then put into
the crucible with the sample. The additional heat
quantity can be determined from the weight of
the burning aid and its known specifi c calorifi c
value. You must correct the test result by this heat
quantity.
IKA ® - combustible crucible C 14 is a combustible
crucible, which can be used instead of a standard
crucible. The combustible crucible burns without
leaving any residue whatsoever. When using a
combustible crucible you do not need an extra
cotton thread. The crucible is placed directly on
the permanent ignition wire in the decompositi-
on vessel and ignited.
The cleanliness of the material used in the com-
bustible crucible prevents chemical contaminati-
on of the sample (no blank values).
Decomposition vessels, in which the combustible
crucible is used, must be fi tted with an extra part
(support C 5010.4, see Accessories). The sample
is weighed out into the combustible crucible as
normal. In most cases no additional burning aid
is required because the combustible crucible itself
serves as a burning aid.
Virtually all of the materials to be studied contain
sulphur and nitrogen. Under the conditions in ca-
lorimetric measurements, sulphur and nitrogen
combust to SO2, SO3 and NOx. Together with
the water from combustion and moisture, sulp-
huric and nitric acid as well as heat of solution
are produced. In order to obtain the standard ca-
lorifi c value, the infl uence of the heat of solution
on the calorifi c value is corrected. The calculation
formulae depend on the standard used. These
are not taken into account in the calculation for
C 200. Use IKA
® 's CalWin software for this.
5.3 Information about the sample
FIt is essential that the sample fully combusts
to ensure correct determination of the calorifi c
value. After each experiment check the crucible
and all the solid residue for signs of incomplete
combustion.
As a rule the weighted sample must be se-
lected in such a way that the temperature
increase during the measurement is below 4 K
and comes close to the temperature increase
of the calibration (max. extra energy: 40,000 J).
.