Three methods are adopted in calorimetry, as it is called, to distin guish it from thermometry, or the measuring of sensible or apparent heat. First, by measuring the heat by the quantity of ice which the body in question liquefies ; Secondly, by calculating it by the method of mixtures ; Thirdly, by observing the rate at which heated bodies cool.
By the first method the calorimeter of Messrs. Lavoiaier and Laplace is used. It consists of two similar metallic vessels, one smaller than For further details on this subject, and for the method of deter mining the specific gravity of vapours, we must refer to Professor Miller's ' Elements of Chemistry,' Part I. 2nd edition, 1860. In the appendix to the third part of that work will be found tables of specific gravities corresponding to degrees of Bourne's hydrometer, and also of Twaddell's hydrometer, the latter being converted into their corres ponding specific gravities by multiplying them by 5 and adding 1000. The specific gravities of the various solids, liquids and gases are given under their respective heads in this Cycloptedia, also in works on Chemistry. Copious tables are also published in a separate form. As a sample of such tables, a list of the specific gravities of the metals is given at the end of this article. A number of instruments on the principle of the HYDROMETER are sold in the shops, such as the Are meter, the Lactomcter for testing the quality of milk, the Saccharometer for enabling the brewer to form an estimate of the quality of his sweet-wort, and some others. The
Barometrical Mriometer consists of a tall siphon tube, inverted and mounted on a pedestal with a graduated scale between the two limbs. It was intended to compare the specific gravities of immiscible liquids ; thus 1 inch of mercury in one limb will balance about 131 inches in the other limb. Brewster's Staktometer or Drop-measurer is an instru ment for measuring specific gravities by the size of the drops which exude from a small orifice. The instrument is formed like a pipette, and is filled by the action of the mouth with distilled water, and the number of drops which escape between an upper and a lower level are counted, and serve as a standard. The instrument may now be filled, say with proof spirit, and the drops similarly counted. In one instru ment the number of drops of water was 724, while the number with proof spirit was 2117, thus indicating that the drop of water was about three times the size of the drop of proof spirit. What are called specific gravity beads or hollow beads of different sizes' with projecting tails, and marked with certain numbers, are used to show roughly the density of a liquid. A number of these beads being thrown into it, those which sink or swim are of no account, but those which remain just suspended indicate the specific gravity.