Parr Instrument 6200 - Manual (Page 68)

69
6200
Calorimeter Operating Instruction Manual
Standard
Materials
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 =
Where:
W = Energy equivalent of the
calorimeter in calories per degree
Celsius.
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 ºC.
e
1
= Correction for heat of
formation of nitric acid in calories.
e
2
= Correction for sulfur which is
usually 0.
e3 = Correction for heating wire and
combustion of cotton thread.
.
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.
Standardizing
the
Calorimeter
STANDARDIZATION APPENDIX C
Hm + e
1
+ e
2
+ e
3
T
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.
C-1