Parr Instrument 1341 - Manual (Page 10)

1341 Plain Jacket Calorimeter
P a r r I n s t r u m e n t C o m p a n y 10
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 1.25 grams. Determine the
corrected temperature rise, t, from the observed test
data, also titrate the bomb washings to determine
the nitric acid correction and measure the unburned
fuse wire. Compute the energy equivalent by
substituting in the following equation:
W =
Hm+ e
1
+ e
3
t
W = energy equivalent of the calorimeter in
calories per °C (Centigrade)
H = heat of combustion of the standard ben-
zoic acid sample in calories per gram
m = mass of the standard benzoic acid
sample in grams
t = net corrected temperature rise in °C
e
1
= correction for heat of formation of nitric
acid in calories
e
3
= correction for heat of combustion of the
firing wire in calories
Example:
Standardization with a 1.1651 gram benzoic acid
sample (6318 cal/ gm) produced a net corrected tem-
perature rise of 3.047 °C. The acid titration required
11.9 ml of standard alkali and 8 cm of fuse wire were
consumed in the firing. Substituting in the standard-
ization equation:
H = 6318 cal/ gram
m = 1.1651 gram
e
1
= (11.9 ml) (1 cal/ ml) = 11.9 cal
e
3
= (8 cm) (2.3 cal/ cm) = 18.4 cal
t = 3.047º C
W = (6318) (1.1651) + 11.9 + 18.4
3.047
= 2426 cal per °C
Standardizing the Calorimeter
The Energy Equivalent Factor
The term “standardization” as used here denotes
the operation of the calorimeter with a standard
sample from which the energy equivalent or effec-
tive heat capacity for the system can be determined.
The energy equivalent factor (W) represents the
energy required to raise the temperature of the
calorimeter one degree, usually expressed as
calories per degree Celsius. This factor for the 1341
calorimeter with an 1108 Oxygen Combustion Vessel
will usually fall within a range from 2410 to 2430
calories per degree Celsius, with the exact value for
each installation to be determined by the user. This
requires a series of at least four standardization
tests (and preferably more) from which an average
can be taken to represent the true W value for the
user’s calorimeter. This will provide a factor which
can be used with confidence in subsequent tests
with unknown materials. Standardization tests
should always be repeated after changing any parts
of the calorimeter, and occasionally as a check on
both the calorimeter and the operating technique.
Standard Samples
A vial of 100 one-gram benzoic acid pellets is fur-
nished with each calorimeter for standardization
purposes. Additional benzoic acid pellets or powder
can be obtained from Parr. For high precision mea-
surements, a primary standard benzoic acid powder
can be purchased from the National Institute of
Standards and Technology (NIST), Washington, D.C.
The NIST also offers standard 2,2,4-trimethly-pen-
tane (Isooctane) as a calorific standard for testing
volatile fuels.
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.
Compressing benzoic acid into a pellet is best
accomplished by using a Parr 2811 Pellet Press. If a
pellet press is not available, melt the powder into a
lump by heating it carefully to the melting point, but
do not overheat the powder as this will change the
calorific value.