Calculations – Parr Instrument 6400 User Manual
Page 56
6400
Calorimeter Instruction Manual
6-1
CALCULATIONS
Corrections
Fuse Correction
There are two components to the fuse correction in the 6400 Calorimeter:
The heat introduced by heating the wire used to ignite the cotton thread.
The heat of combustion of the cotton thread used to ignite the sample.
e
3
= (fuse value) (fuse multiplier)
The semi-permanent heating wire is heated by dissipating an electrical charge from a
capacitor. Since this charge is controlled by the size of the capacitor and the charging
voltage, and because the capacitor is fully discharged for each test, the energy released
can be calculated. In the 6400 Calorimeter this is a correction of 10 calories per test.
Cotton has a heat of combustion of 4000 calories per gram. The actual thread being
used should be weighed to see how much is being burned. Ten centimeters of a fine
thread will weigh approximately 0.003 grams which would release 12 calories as it
burns. Heavier threads weigh up to 0.010 grams per 10 centimeters and increase this
correction to 40 calories per test. The finer the thread, the smaller errors will be if the
thread is not exactly ten centimeters in length. Polyester thread is not recommended for
use in the bomb because it has a tendency to melt and fall away from the heating wire
before it ignites.
Using the fine thread mentioned above, the fuse correction for the calorimeter would be
the 10 calories from electrical heating plus 12 calories from the burning thread for a total
of 22 calories per test. The thread supplied by Parr has a mass of approximately 1
milligram per centimeter. This results in a total fuse correction of 50 calories. Fuse
corrections can be entered when Fixed Fuse in the Thermochemical Corrections menu,
is set to OFF. Total errors of more than 5 calories will seldom occur when using a fixed
fuse correction and the fuse wire and cotton thread supplied by Parr.
Spiking Correction
It is sometimes necessary to add a spiking material to samples which are very small,
have a low heat of combustion, or have a high moisture content to add sufficient heat to
drive the combustion to completion. Benzoic acid is an excellent material for spiking for
all of the same reasons it is a good standard material. White oil is also an excellent
material. The 6400 calorimeter can automatically compensate for the addition of spiking
materials to these samples. The calculations are modified in these cases as follows:
m
m
H
e
e
e
WT
H
s
cs
c
)
)(
(
3
2
1
−
−
−
−
=
Where:
H
cs
is equal to the Heat of combustion of the spiking material in calories per
gram
m
s
is equal to the mass of the spiking material