Parr Instrument 6400 - Manual (Page 57)

6400
Calorimeter Instruction Manual
6-2
This factor is added to the calculations when Spike Controls, Use Spiking is set to ON.
The Heat of Combustion of the spiking material is entered as calories per gram. The
calorimeter will prompt the user to enter the weight of spiking material. Fixed spikes can
also be used. To do this, set Use Fixed Spike to ON and enter the mass of the spike
(Weight of Fixed Spike key).
Nitric Acid Correction
In the high pressure oxygen environment within the oxygen bomb, nitrogen that was
present as part of the air trapped in the bomb is burned to nitric oxide which combines
with water vapor to form nitric acid. All of this heat is artificial since it is not a result of
the sample burning. The nitric acid correction removes this excess heat from the
calculation. Users may find it convenient to enter a fixed value for the acid correction
and avoid the need to determine this correction for each test. Use of a fixed value for
the acid correction is highly recommended. Fixed acid corrections can be entered when
Fixed Acid - Thermochemical Corrections, is set to ON. A correction of 8 calories is a
good number for the fixed nitric acid value. For most work, it is recommended to set
“Acid Value is Nitric Acid Only”, in Calculation Factors to ON. Total errors of more than
3 calories will seldom occur when using fixed nitric acid corrections.
Sulfur Correction
In the oxygen rich atmosphere within the bomb, sulfur in the sample is oxidized to
sulfur trioxide which combines with water vapor to form sulfuric acid. This liberates
additional heat over the normal combustion process which converts sulfur to sulfur
dioxide. The sulfur correction removes this excess heat from the calculation.
Fixed sulfur corrections can be entered if a series of samples contain a constant
amount of sulfur. Fixed sulfur corrections can be entered when Fixed Sulfur -
Thermochemical Corrections, is set to ON. Enter percent sulfur as indicated on
this line. Any errors will be proportional to the difference between the actual and
assumed value for sulfur.
Note:
For ordinary work where benzoic acid is used for standardizing the
calorimeter, the Fixed Sulfur Correction for Standardizations should be
ON applying a fixed value of 0.0 to all standardization tests. Benzoic acid
contains no sulfur.
Manual vs. Fixed Corrections
If fixed values for fuse, acid and sulfur are turned OFF on the Thermochemical
Corrections Menu, then the user must manually enter the values at the prompt. Final
reports for each test can be obtained whenever the operator is prepared to enter any
required corrections for fuse, acid and sulfur. When entering corrections, the user can
choose either of two methods. These are:
• Manual
Entry
• Fixed
Corrections