IKA C 5000 control Package 2/12 - Manual (Page 15)

IKA  -WERKE C 5000 control/duo-control Ver. 10 04.07
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combustion aid and a specific gross calorific value that is of course already known, it
is possible to determine the amount of heat that is introduced by the combustion aid.
The result of the experiment must then be corrected by that quantity of heat.
The C 14 combustible crucible can be used instead of a more traditional crucible.
The combustible crucible is burned completely with no residue. When a combustible
crucible is used, no additional cotton thread is required. The crucible is contacted
directly by the fixed ignition wire of the decomposition vessel and is ignited.
The purity of the material of the combustible crucible prevents chemical contamina-
tion of the sample material (no blank values).
Decomposition vessel in which the combustible crucible is used must be retrofitted
with an additional part (attachment C 5010.4, see accessories). The sample is
weighed in into the combustible crucible normally. In most cases, no additional
combustion aid is required, because the combustible crucible itself serves as a
combustion aid.
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Almost all substances to be analyzed contain sulfur and nitrogen. Under the condi-
tions that prevail in calorimetric measurements, sulfur and nitrogen burn and
are reduced to SO
2
, SO
3
and NO
x
. In combination with the water from combustion
and moisture, sulfuric acid and nitric acid are produced in addition to heat of solu-
tion. In order to obtain the standard gross calorific value, the gross calorific value is
corrected by the effect of the heat of solution.
In order to obtain a defined final state and to measure all acids quantitatively, 5 ml of
distilled water is placed in the decomposition vessel before the experiment. The
gasses liberated during combustion form acids with the distilled water. After the
combustion, the decomposition vessel is rinsed thoroughly with distilled water to
collect the precipitate that has been deposited on the inner wall of the vessel as
well. The water that was placed in the decomposition vessel is combined with the
rinse water to be titrated for acid content.
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To determine the gross calorific value correctly, it is of fundamental significance for
the sample to be burned completely. After the experiment, the crucible and all solid
residues must be examined for signs of incomplete combustion.
Normally, solid combustion substances can be burned directly in powder form. Sub-
stances that burn rapidly, i.e. substances for which the combustion has the nature of
an explosion (for example benzoic acid) must not be burned in loose form. These
substances tend to spark, and complete combustion could therefore no longer be
guaranteed. In addition, the decomposition vessel could be damaged. Such sub-
stances must be pressed into tablets before combustion (see Accessories).
Substances with low inflammability (substances with a high mineral content, low-
calorific materials) often can be burned only with the aid of combustion capsules or
combustion bags (see Accessories). It is also possible to use liquid combustion aids
such as paraffin oil or hydrocarbon oil.
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