II. On the specific heats of minerals

Abstract

A number of experiments were made on minerals by the method of condensation, using the form of gravimetric calorimeter described in the beginning of the paper on calorimetry (p. 353). The con­densation of steam being in all cases employed, the values recorded are the mean specific heats between atmospheric temperatures ap­proximating to 12° C., and steam temperature, about 100° C. More exactly, the values recorded are the mean calorific capacities for a rise of one degree between the limits t 1 and t 2 , tabulated in each case. The specimens dealt with were chosen as good samples of the mineral free from visible impurities.* But before detailing the particulars of the experiments a few notes on the discriminative value and physical interest attached to this application of calorimetry may not be amiss. It seems probable that the neglect of the use of the specific heat constant is to be ascribed to the difficulties besetting its determina­tion. Certainly if its determination was as easily effected as we effect the determination of the specific gravity of a body, there are on the other hand sufficient reasons to recommend its use as in general of more physical value and interest than the much used specific gravity. There are cases indeed where specific gravity, as it is possible to obtain it, is misleading, and where specific heat gives at once valuable information on the probable chemical nature of the substance. Such eases would arise with bodies of loose vesicular or hollow structure. No misleading variations need be introduced into the thermal constant by mere conditions of volume.