Parr Instrument 6725 - Manual (Page 53)

6725
Semi-micro Calorimeter Instruction Manual
6-5
Fixed 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 a
fixed value set by the operator.
The calculation is:
e1 = [((total acid)(acid multiplier)) – (% sulfur)(sample mass)(sulfur multiplier)](heat of
formation of nitric acid)
Using the default acid and sulfur multipliers as well as a heat of formation of nitric acid of
14.1 cal/milliequivalent a .1 gram sample with 3 ml of washings and 2 % sulfur would
result in the following calculation:
e1 = [((3)(.0709)) – (2)(.1)(.6238)] 14.1
e1 = [(.2127) – (.12476)] 14.1
e1 = [.08794] 14.1
e1 = 1.24 calories
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 HNO3: In ASTM D5865 there are provisions 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)(Energy Equivalent)(corrected temperature rise)
Example: For a test run with energy equivalent of 541.2301 and a corrected
temperature rise of 1.4385 would result:
e1 = (1.58/1000)(541.2301)(1.4385)
e1 = 1.23 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.