Parr Instrument 6772 User Manual
Page 50
6772
Calorimetric Thermometer Instruction Manual
6-3
Fixed Corrections
In many cases, fixed values for fuse and acid can be used without introducing a significant
error since the corrections are both relatively small and constant. Fixed sulfur corrections
can also be used whenever a series of samples will be tested with a reasonably constant
sulfur content. Any value set-up as a fixed correction will be automatically applied and the
controller will not prompt the user for this value.
Definitions
Total acid is the amount of base required to titrate the bomb washings (milliliters).
Nitric acid is that portion of the total acid in the bomb washings that result when the
nitrogen in the air that is trapped in the bomb is burned at high pressure.
Since this nitric acid does not result from the sample, and the combustion
conditions are reasonably constant from test to test, the amount of nitric
acid formed is also constant.
Acid multiplier is multiplied by the user entered acid value to arrive at the number of
milliequivalents of acid. This value is normally the concentration
(normality) of the base in equivalents per liter (N).
Percent sulfur is the concentration of sulfur in the sample (weight %).
Molecular weight of sulfur is 32.06.
Equivalent weight of sulfur in H
2
SO
4
is 16.03 (one half of the molecular weight).
Heat of formation of nitric acid is 14.1 calories / milliequivalent.
Heat of formation of sulfuric acid (from SO
2
) is 36.1 calories / milliequivalent.
Sample mass is the mass of sample burned in the bomb (grams).
Sulfur multiplier is multiplied by the product of the user entered sulfur value and
the sample mass to arrive at the number of milliequivalents of sulfuric
acid in the bomb washings.
Example:
Where:
16.03 is equal to the equivalent weight of sulfur in H
2
SO
4
e
1
is the nitric acid portion of the total acid correction
e
2
is the sulfuric acid portion of the total acid correction
e
1
+e
2
is the total bomb acid correction
Sulfur Multiplier Calculation:
6238
0
10
.
4
SO
2
H
in
sulfur
of
weight
equivalent
4
SO
2
H
of
alents
milliequiv
4
SO
2
H
in
sulfur
of
weight
equivalent
(mg)
Sulfur
(mg)
Sulfur
10
mass
Sample
%Sulfur
=
=
=
Ч
Ч