Parr Instrument 6100 - Manual (Page 49)

Calculations
6100 B
w w w . p a r r i n s t . c o m 47
ASTM and ISO Methods Differ
Current ASTM, ISO, and British Standard Methods
differ on their treatment of the nitric and sulfuric
acid thermochemical corrections. ASTM Methods
call for titrating the bomb washings to determine
the total acid present. This is assumed to be all nitric
acid with a heat of combustion of -14.1 Kcal per
mole. The amount of sulfur is then determined and
converted to equivalents of sulfuric acid. The differ-
ence between the heat of formation of sulfuric acid
(-72.2 Kcal per mole or -36.1 calories per milliequiva-
lent) and nitric acid is then subtracted as the sulfur
correction.
Most other test methods treat nitric and sulfuric acid
corrections as entirely separate values instead of
combined values. This eliminates the requirement for
a total acid determination and permits the nitric acid
correction to be handled in a variety of ways, includ-
ing the assumption of a fixed nitric acid correction.
The 6100 Calorimeter can be set up to apply the acid
correction by either the ASTM or ISO convention, as
the user prefers. Care must be used to ensure the
proper corrections are applied, and the calculations
made are consistent with the procedure used.
Users may find it convenient to enter a fixed value
for the acid correction and avoid the need to de-
termine this correction for each test. Use of a fixed
value for the acid correction is highly recommend-
ed. Fixed acid corrections can be entered when Acid
Correction - Thermochemical Corrections is set to
Fixed HNO
3
. A correction of 10 calories is a good
number for the fixed nitric acid value. 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.
Note: Please review the following section on
Acid and Sulfur Corrections. Different stan-
dard test methods use different values for
the heat of formation of sulfuric acid. These
differences are generally insignificant. The
6100 Calorimeter uses the most recent, pub-
lished values for all thermochemical data.
Thermochemical Calculation Details
Traditionally, standard solutions and procedures
have been established to simplify the calculations
related to the thermochemical corrections. The 6100
Calorimeter has been programmed to permit the
user to use standard solutions and units which are
most convenient, since the microprocessor can
easily apply any conversion factors required.
Fuse Correction
The fuse correction applied by the calorimeter is
calculated as:
e3 = (fuse value)(fuse multiplier from
calculation factors page)
“Fuse Value” is the number entered by the user and
the value which appears in the test report.
Note: Calculation Factors - Fuse Multiplier is
normally set to 1.0 so the entered value is in
calories
Users may find it convenient to enter a fixed value
for the fuse correction and avoid the need to deter-
mine this correction for each test.
Fixed fuse corrections can be entered when Ther-
mochemical Corrections, is set to ON. By default a
fixed fuse correction of 50 calories is applied to all
tests. Total errors of more than 5 calories will seldom
occur when using a fixed fuse correction and the
cotton thread supplied by Parr.