whence to form a scale of the several results. The quantity of caloric
necessary to melt a pound of ice has been chosen as this unit; and, as
it requires a pound of water of the temperature of 60 (167 ) to melt a
pound of ice, the quantity of caloric expressed by our unit or standard
point is what raises a pound of water from zero (32 ) to 60 (167 ).
When this unit is once determined, we have only to express the
quantities of caloric disengaged from different bodies by cooling a
certain number of degrees, in analogous values: The following is an easy
mode of calculation for this purpose, applied to one of our earliest
experiments.
We took 7 lib. 11 oz. 2 gros 36 grs. of plate-iron, cut into
narrow slips, and rolled up, or expressing the quantity in decimals,
7.7070319. These, being heated in a bath of boiling water to about 78
(207.5 ), were quickly introduced into the interior cavity of the
calorimeter: At the end of eleven hours, when the whole quantity of
water melted from the ice had thoroughly drained off, we found that
1.109795 pounds of ice were melted. Hence, the caloric disengaged from
the iron by cooling 78 (175.5 ) having melted 1.109795 pounds of ice,
how much would have been melted by cooling 60 (135 )? This question
gives the following statement in direct proportion, 78 : 1.109795 :: 60
: x = 0.85369. Dividing this quantity by the weight of the whole iron
employed, viz. 7.7070319, the quotient 0.110770 is the quantity of ice
which would have been melted by one pound of iron whilst cooling through
60 (135 ) of temperature.
Fluid substances, such as sulphuric and nitric acids, &c. are contained
in a matras, Pl. VI. Fig. 9. having a thermometer adapted to the cork,
with its bulb immersed in the liquid. The matras is placed in a bath of
boiling water, and when, from the thermometer, we judge the liquid is
raised to a proper temperature, the matras is placed in the calorimeter.
The calculation of the products, to determine the specific caloric of
these fluids, is made as above directed, taking care to deduct from the
water obtained the quantity which would have been produced by the matras
alone, which must be ascertained by a previous experiment. The table of
the results obtained by these experiments is omitted, because not yet
sufficiently complete, different circumstances having occasioned the
series to be interrupted; it is not, however, lost sight of; and we are
less or more employed upon the subject every winter.
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