Parr Instrument 6400 - Manual (Page 58)

7
Calculations
P a r r I n s t r u m e n t C o m p a n y 56
ASTM Treatment for Acid and Sulfur
In the ASTM treatment, the correction for acid
formation assumes that all the acid titrated is nitric
acid. Obviously, if sulfur is present in the sample,
which in turn produces sulfuric acid, part of the
correction for the sulfuric acid formed is already
included in the ASTM nitric acid correction (e1). This
is adjusted by a separate computation based upon
the sulfur content of the sample. An additional cor-
rection of 1.37 kcal must be applied for each gram
of sulfur converted to sulfuric from sulfur dioxide.
This is based upon the heat of formation of sulfuric
acid, from sulfur dioxide, under bomb conditions,
which is -72.2 kcal per mole or -36.1 calories per
milliequivalent. But remember, a correction of 14.1
calories per milliequivalent of sulfuric acid is already
included in the ASTM nitric acid correction (e1).
Therefore the additional correction which must be
applied for sulfur will be the difference between 36.1
and 14.1 or 22.0 calories per milliequivalent (44.0
Kcal per mole). For convenience, this is expressed,
in the ASTM e2 formula, as 13.7 calories (44.0/32.06)
for each percentage point of sulfur per gram of
sample.
ISO Calculations
Both the ISO 1928 and BSI 1016: Part 5 methods
for testing the calorific value of coal and coke, deal
with acid and sulfur corrections in a manner which
is somewhat different than ASTM procedures.
Provision has been made in the 6400 Controller for
dealing with these different procedures.
The analysis of bomb washings in these methods
call for a titration, first using 0.1N barium hydroxide
(V
2
) followed by filtering, and a second titration
using 0.1N HCL(V
1
) after 20 mL of a 0.1N sodium
carbonate has been added to the filtrate. Table
B-1 gives the settings which allows the results of
the two titrations, V
1
and V
2
, to be entered into the
controller directly for the calculation of the total
acid correction. V
1
should be entered at the prompt
for acid and V
2
is entered at the prompt for sulfur.
The settings in Table 15-2 assume that the same
procedure is carried out for both standardization
and determination.
The offset value is the product of -1, the Heat of For-
mation of Nitric Acid, the acid multiplier, and the 20
mL of 0.1 N sodium carbonate used in the analysis.
The formula used to get the total correction in
calories is as follows: =
V
1
(Acid Multiplier)(Heat of Formation of Nitric
Acid)
V
2
(Sulfur Multiplier)(Heat of Formation of Sulfu-
ric Acid) + offset value.
The values for fixed acid and sulfur, which are used
in preliminary reports, will reflect a sulfur correction
of 0, and a nitric acid correction of 10 calories.