Parr Instrument 6300 - Manual (Page 71)

C
ALCULATIONS
6300
B
w w w . p a r r i n s t . c o m 71
A
PPENDIX
B
C
ALCULATIONS
C
ALCULATING THE
H
EAT OF
C
OMBUSTION
The 6300 Calorimeter will automatically make all of
the calculations necessary to produce a gross heat of
combustion for the sample. However, it is important
that the user understand these calculations to ensure
the instrument is set up so the calculations match the
procedures and the units are consistent throughout the
process.
G
ENERAL
C
ALCULATIONS
The calculation for the gross heat of combustion is
done by:
H
c
=
WT-e
1
- e
2
- e
3
m
Where:
H
c
= Gross heat of combustion.
T = Observed temperature rise.
W = Energy equivalent of the
calorimeter being used.
e
1
= Heat produced by burning the
nitrogen portion of the air trapped
in the bomb to form nitric acid.
e
2
= The heat produced by the
formation of sulfuric acid from the
reaction of sulfur dioxide, water
and oxygen.
e
3
= Heat produced by the heating wire
and cotton thread.
m = Mass of the sample.
These calculations are made in calories, grams, and
degrees Celsius and then converted to other units if
required.
Temperature Rise.
The 6300 Calorimeter produces a corrected temperature
rise reading automatically. Corrections for heat leaks
during the test are applied. (For a complete discussion
of this process see Introduction to Bomb Calorimetry,
Manual No. 483M).
Energy Equivalent.
The energy equivalent (represented by W in the
formula, or abbreviated as EE) is determined by
standardizing the calorimeter as described in Appendix
C - Standardization. It is an expression of the amount
of energy required to raise the temperature of the
calorimeter one degree. It is commonly expressed in
calories per degree Celsius. Since it is directly related to
the mass of the calorimeter, it will change whenever any
of the components of the calorimeter (i.e. the bomb,
bucket or amount of water) is changed.
T
HERMOCHEMICAL
C
ORRECTIONS
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.
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.
Fuse Correction.
The fuse correction in the 6300 Calorimeter is
significantly different than the correction used in earlier
model Parr calorimeters where the correction was made
to compensate for the amount of fuse wire burned
in the test. There are two components to the fuse
correction in the 6300 Calorimeter:
The heat introduced by heating the wire used to •
ignite the cotton thread.
The heat of combustion of the cotton thread used to •
ignite the sample.
The semi-permanent heating wire is heated by
dissipating an electrical charge from a capacitor. Since
this charge is controlled by the size of the capacitor and
the charging voltage, and because the capacitor is fully
discharged for each test, the energy released can