The various experiments which may be made with the calorimeter do not afford absolute conclusions, but only give us the measure of relative quantities; we have therefore to fix a unit, or standard point, from 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.
CHAP. IV.
Of Mechanical Operations for Division of Bodies.
SECT. I.
Of Trituration, Levigation, and Pulverization.
These are, properly speaking, only preliminary mechanical operations for dividing and separating the particles of bodies, and reducing them into very fine powder. These operations can never reduce substances into their primary, or elementary and ultimate particles; they do not even destroy the aggregation of bodies; for every particle, after the most accurate trituration, forms a small whole, resembling the original mass from which it was divided. The real chemical operations, on the contrary, such as solution, destroy the aggregation of bodies, and separate their constituent and integrant particles from each other.