Parr Instrument 6400 - Manual (Page 57)

Calculations
6400 7
w w w . p a r r i n s t . c o m 55
Using the default acid and sulfur multipliers as well as
a heat of formation of nitric acid of 14.1 cal/milliequiv-
alent a 1 gram sample with 25 ml of washings and 2
% sulfur would result in the following calculation:
e1 = [((25)(.0709)) – (2)(1)(.6238)] 14.1
e1 = [(1.7725) – (1.2476)] 14.1
e1 = [.5249] 14.1
e1 = 7.40
When the Acid Correction is set to Fixed Total the
value is considered a final value and the operator is
not prompted for an acid value when reporting the
results.
Entered Total: The Acid Correction represents the
total base required to titrate the bomb washings
(in milliliters). This includes both nitric and sulfuric
acid. The correction is entered by the operator when
reporting the results.
The calculation is the same as the Fixed Total above.
The value listed on the Acid Correction button is
used for preliminary calculations. When finalizing
the report the operator will be prompted for the acid
value.
Calculated HNO
3
: In ASTM D5865 there are provi-
sions for calculating the nitric acid contribution.
For test samples that contain no nitrogen, the
quantity of nitric acid formed during the combustion
process is a function of the volume of the bomb, the
oxygen filling pressure, and the quantity of energy
released.
For the calculated nitric acid method:
e1 = (nitric acid factor/1000) x (Energy Equiva-
lent) x (corrected temperature rise)
Example: For a test run with energy equivalent of
927.40 and a corrected temperature rise of 6.892
would result:
e1 = (1.58/1000)(927.4022)(6.892)
e1 = 10.10 calories
The calculated nitric acid method can be applied
to samples containing up to 2% nitrogen without
introducing a significant error in the resulting heat
of combustion value.
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 recom-
mended. Fixed acid corrections can be entered
when Acid Correction - Thermochemical Corrections,
is set to Fixed HNO
3
. 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.
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 and then
enter percent sulfur as indicated on this line. Any
errors will be proportional to the difference between
the actual and assumed value for sulfur.
For ordinary work where benzoic acid is used, for
standardizing the calorimeter, the Fixed Sulfur Cor-
rection, for Standardizations should be ON applying
a fixed value of 0.0 to all standardization tests.
Benzoic acid contains no sulfur.
Please note that the values entered into the test
report appear as entered in the report. Values for e1,
e2 and e3 are calculated and used as energy correc-
tions in accordance with the formulas and settings
given above. The formulas used above to arrive at
e1 or e2 are not the same as the formulas used for
e1 and e2 which appear in most ASTM bomb calori-
metric procedures. However, the sum of e1 and e2,
above, is equal to the sum of the ASTM treatment of
e1 and e2.