Parr Instrument 1341 - Manual (Page 8)

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 8
Calculating the Heat of Combustion
Assembly of Data
The following data should be available at the com-
pletion of a test in a 1341 calorimeter:
a = time of firing
b = time (to nearest 0.1 min.) when the
temperature reaches 60 per cent of the
total rise
c = time at beginning of period (after the
temperature rise) in which the rate of
temperature change has become con-
stant
t
a
= temperature at time of firing
t
c
= temperature at time c
r
1
= rate (temperature units per minute) at
which the temperature was rising during
the 5-min. period before firing
r
2
= rate (temperature units per minute) at
which the temperature was rising during
the 5-min. period after time
c. If the temperature was falling instead
of rising after time c, r is negative and
the quantity -r (c-b) becomes positive
and must be added when computing the
corrected temperature rise
c
1
= milliliters of standard alkali solution used
in the acid titration
c
2
= percentage of sulfur in the sample
c
3
= centimeters of fuse wire consumed in
firing
W = energy equivalent of the calorimeter,
determined under standardization
M = mass of sample in grams
Temperature Rise
Compute the net corrected temperature rise, t, by
substituting in the following equation:
t = t
c
- t
a
- r
1
(b-a) - r
2
(c-b)
Thermochemical Corrections
Compute the following for each test:
e
1
= correction in calories for heat of forma-
tion of nitric acid (HNO
3
)
= c
1
if 0.0709N alkali was used for the
titration
e
2
= correction in calories for heat of forma-
tion of sulfuric acid (H
2
SO
4
)
= (13.7) (c
2
) (m)
e
3
= correction in calories for heat of combus-
tion of fuse wire
= (2.3) (c
3
) when using Parr 45C10 nickel
chromium fuse wire, or
= (2.7) (c
3
) when using No. 34 B. & S. gage
iron fuse wire