Parr Instrument 6300 - Manual (Page 77)

S
TANDARDIZATION
6300
C
w w w . p a r r i n s t . c o m 77
A
PPENDIX
C
S
TANDARDIZATION
S
TANDARDIZING THE
C
ALORIMETER
The Energy Equivalent Factor.
The term “standardization”, as used here, denotes the
operation of the calorimeter on a standard sample from
which the energy equivalent or effective heat capacity of
the system can be determined. The energy equivalent,
W or EE of the calorimeter is the energy required to
raise the temperature one degree, usually expressed as
calories per degree Celsius. Standardization tests should
be repeated after changing any parts of the calorimeter,
and occasionally as a check on both the calorimeter and
operating technique.
Standardization Procedure.
The procedure for a standardization test is exactly
the same as for testing a fuel sample. Use a pellet of
calorific grade benzoic acid weighing not less than 0.9
nor more than 1.1 grams. The corrected temperature
rise, T, is determined from the observed test data and
the bomb washings are titrated to determine the nitric
acid correction. The energy equivalent is computed by
substituting the following equation:
W =
Hm + e
1
+ e
2
+ e
3
T
Where:
W = Energy equivalent of the
calorimeter in calories per °C.
H = Heat of combustion of the
standard benzoic acid sample in
calories per gram.
m = Mass of the standard benzoic acid
sample in grams.
T = Temperature rise in °C.
e
1
= Correction for heat of formation of
nitric acid in calories.
e
2
= Correction for sulfur which is
usually 0.
e
3
= Correction for heating wire and
combustion of cotton thread.
S
TANDARD
M
ATERIALS
A bottle of 100 one-gram benzoic acid pellets (Part
No. 3415) is furnished with each calorimeter for
standardizing purposes. The Parr benzoic acid has
been calibrated against NIST benzoic acid. Additional
benzoic acid pellets can be obtained from Parr.
For very high precision measurements, a primary
standard benzoic acid powder can be purchased from
the National Institute of Standards & Technology,
Washington, D.C.
It is not common to have sulfur in standard materials,
or to use spikes in standardizations, but the capabilities
have been included in this calorimeter.
Users should take great care to ensure that the
conditions during standardization runs and
determinations are as identical as possible.
Caution:
Benzoic acid must always be compressed into
a pellet before it is burned in an oxygen bomb
to avoid possible damage from rapid combustion of the
loose powder. This is best accomplished by using a Parr
2811 Pellet Press.
A
UTOMATIC
S
TATISTICAL
C
ALCULATIONS
The 6300 Calorimeter includes a provision for
calculating and using a mean energy equivalent for each
of up to 4 separate bomb and bucket combinations.
ASTM procedures recommend that the energy
equivalent be determined by averaging ten tests. The
6300 Calorimeter automatically determines and uses up
to ten tests in its memory and will update the EE Value
as additional standardizations are run. Only Final Tests
will be used in determining and updating EE values.
These values, the number of tests, and the relative
standard deviation for the tests used in determining the
EE value are stored in the Calibration Data Page under
the EE Value for each bomb.
The user can chose to turn off the automatic averaging
and updating procedure and protect the EE Values by
turning ON the protection feature for the appropriate
bomb on the Calibration Data and Control Page using
Protected EE Value.