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138
This will be the first Act of Parliament in which a gross calorific
power standard has been set up. My reasons for advising it are:—
(i) In determining the gross calorific power there is less liability to
variation due to experimental error or to temporary defects of the
calorimeter, and therefore less liability to dispute in case of a
deficiency being found. (2) Except technically there is no difference
in the gross calorific standard thus set up to a net calorific standard,
since the net calorific standard originally proposed has been translated
into gross value. (3) The gas referees lay no special stress
on the net calorific value, as the following extract from their "Notification
for the Year 191 " will show:—
"The heating or calorific power of any sample of gas is
represented by the number of calories produced by the combustion
of one cubic foot of such gas measured at 60 deg. Fahr.
and under a pressure of 30 inches of mercury. The maximum
calorific power which gas can thus exert is determined directly
by the calorimeter. This is a true measure of the total heating
power, and is termed the gross calorific power of the gas. But
in many cases in which gas is used as a heating agent, the
steam which is formed escapes into the air uncondensed, and
thus the heat due to the condensation of the steam and the
cooling of the water so formed is not utilised. The amount of
heat thus lost can be estimated, and if it is subtracted from the
total heat yielded by the combustion of the gas in the calorimeter
another value is obtained which is termed the net calorific
power of the gas. Since, however, when steam escapes uncondensed,
the uncondensable products of combustion also
pass away at a high temperature, and since the loss of heat thus
arising is commonly the greater of the two, the customary partial
correction from gross to net has not much significance."
Finally, I may state that the standard calorific power agreed
upon has been arrived at from a careful consideration of the tests
of calorific power of the gas which I made between October 3rd,
1911, and January 12th, 1912, which yielded an average of 135*3
gross calories (see Report dated January 24th, 1912, above referred
to). Inasmuch as tests for illuminating power were invariably
made by me at the same time, and average about I5'0 candles,
this illuminating power may be said to approximately correspond
to a calorific power of about 135 gross calories, but I shall refer to
these details later.