Parr Instrument 6772 - Manual (Page 49)

6772
Calorimetric Thermometer Instruction Manual
6-2
acid value. Total errors of more than 3 calories will seldom occur when using fixed nitric acid
corrections.
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. 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.
Note:
For ordinary work where benzoic acid is used, for standardizing the
Calorimetric Thermometer, the Fixed Sulfur Correction, for Standardizations
should be ON applying a fixed value of 0.0 to all standardization tests.
Benzoic acid contains no sulfur.
Manual vs. Fixed Corrections
If fixed values for fuse, acid and sulfur are turned OFF on the Thermochemical Corrections
Menu, then the user must manually enter the values at the prompt. Final reports for each
test can be obtained whenever the operator is prepared to enter any required corrections for
fuse, acid and sulfur. When entering corrections, the user can choose either or two methods.
These are:
• Manual
Entry
• Fixed
Corrections
Manual Entry
During the reporting process, the controller will prompt the user to enter the following values:
• Fuse
Correction Key in the Fuse/Heat Wire Correction and press the ENTER key.
The default setting for this value is to be entered in calories.
• Acid
Correction Key in the Acid Correction and press the ENTER key. The default
setting for this value is to be entered in milliliters of standard alkali
required to titrate total acid or calories.
• Sulfur Correction
Key in the Sulfur Correction and press the ENTER key. The
default setting for this value is to be entered as percent sulfur in
the sample.
Note:
If the Spiking Correction is used, a spiking correction must be entered before
obtaining a Final Report. After the last entry has been made, the Calorimetric
Thermometer will automatically produce a Final Report. If values for these
corrections are not available, the operator can use the SKIP key to bypass
any of the corrections, however, a Final Report will not be printed until an
entry is made for fuse, acid and sulfur.