UKAT OF COMUl'XTION

107

1. The combustion may bo begun as far below atmospheric,
temperature as it is to end above it. By this means absorption
of heat in the first half of the experiment would appear to balance
radiation during the last half.
This is the roughest sort of approximation and it would not
serve for ordinarily accurate work,
2. The rate of change of temperature may be observed for a
certain period before firing and for another period after the
calorimeter wafer has absorbed all of the beat from the bomb.
The arcrayt- of these rates is then considered to be the? moan rate
of absorption or radiation of heat for the entire experiment and
if this is multiplied by the time elapsing between the firing and
the maximum absorption the, net gain or loss during the? entire,
observation period is given.
This method is very commonly employed and it given a very
close* approximation to the. true correction.
3. Observations are made in the, same* way as in method (2).
In addition the time, n, required for six-tenths of the? total rise? in
temperature* is observed, also the time, />, for the remaining rise.
Instead of averaging the two radiation for absorption) rates the.
preliminary rate, #,, is multiplied by a and the final rate!, /fo,
by //. The corrected rise is then
T + If in + Ay/,
where* 7'-~ total rise, and I{\ and It* are regarded an positive for
falling temperatures and negative for rising temperatures.
Tin* observation of the* time, a, is subject to some uncertainty
when the* temperature is rising rapidly ami on thin account
the method is not HO easily applioel as is method (2). It will
rarely be found that the difference between the oorroetionH
calculated by the»«» two mothoels will differ by more than 0.2
per cent and as thin in well within the* permissible variation,
mc*thod (2) is recommended for all but the mont rofinod work.
4. The llegniiult-Pfaumllor method approaches theoretical
accuracy more nearly than any of the* methenln already doHcribed.
For a eiisc.tiKsion of this method, HOO White., "(!as and Fuel Analy-
sis" (International Chemical Morion) 2nd od., page* 20K.
Time-temperature Curves......•.....-Thrcso typos of time-tempera-
turo curve's are produeod, according to whefhor the experiment is