Parr Instrument 6200 - Manual (Page 62)

63
6200
Calorimeter Operating Instruction Manual
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 difference between the heat of
formation of sulfuric acid (-72.2 Kcal per
mole or -36.1 calories per milliequivalent)
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, including the assumption of
a fixed nitric acid correction.
The 6200 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.
Note:
Please review the following section on
Acid and Sulfur Corrections. Different
standard test methods use different
values for the heat of formation of
sulfuric acid. These differences are
generally insignificant. The 6200
Calorimeter uses the most recent,
published 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 6200
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.
ASTM
and ISO
Methods
Differ
B-3
APPENDIX B