re--deg. C. against Time--Hours and Minutes

Fig. 25. Graphic Method of Recording Bomb Calorimeter Results]

After the bomb is placed in the calorimeter, and before the coal is
ignited, readings of the temperature of the water should be taken at one
minute intervals for a period long enough to insure a constant rate of
change, and in this way determine the initial radiation. The coal is
then ignited by completing the circuit, the temperature at the instant
the circuit is closed being considered the temperature at the beginning
of the combustion. After ignition the readings should be taken at
one-half minute intervals, though because of the rapidity of the
mercury's rise approximate readings only may be possible for at least a
minute after the firing, such readings, however, being sufficiently
accurate for this period. The one-half minute readings should be taken
after ignition for five minutes, and for, say, five minutes longer at
minute intervals to determine accurately the final rate of radiation.

Fig. 25 shows the results of such readings, plotted in accordance with
the method suggested. It now remains to compute the results from this
plotted data.

The radiation correction is first applied. Probably the most accurate
manner of making such correction is by the use of Pfaundler's method,
which is a modification of that of Regnault. This assumes that in
starting with an initial rate of radiation, as represented by the
inclination of the line AB, Fig. 25, and ending with a final radiation
represented by the inclination of the line CD, Fig. 25, that the rate of
radiation for the intermediate temperatures between the points B and C
are proportional to the initial and final rates. That is, the rate of
radiation at a point midway between B and C will be the mean between the
initial and final rates; the rate of radiation at a point three-quarters
of the distance between B and C would be the rate at B plus
three-quarters of the difference in rates at B and C, etc. This method
differs from Regnault's in that the radiation was assumed by Regnault to
be in each case proportional to the difference in temperatures between
the water of the calorimeter and the surrounding air plus a constant
found for each experiment. Pfaundler's method is more simple than that
of Regnault, and the results by the two methods are in practical
agreement.

Expressed as a formula, Pfaundler's method is, though not in form given
by him:

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