V. The specific heat of water and the mechanical equivalent of the calorie at temperatures from 0° C. to 80° C

Abstract

The work described in this paper started from the researches upon the properties of aqueous solutions, which have occupied one of us for some years past. In the course of this work it had been found that the measurement of various physical properties of solutions, including density, conductivity, and viscosity, at various temperatures and various concentrations, threw considerable light, not only on the constitution of solutions, hut upon that of water itself and upon the amounts of water combined with a solute at various temperatures and concentrations. It seemed probable that similar series of observations upon the specific heat of solutions over considerable ranges of concentration and temperature would throw further light upon these matters, and the apparatus described in this paper was therefore primarily designed for the observation of the specific heat of solutions with the desired degree of accuracy, and with the facility and ease of manipulation which are essential when it is required to amass a large body of data in a reasonable time. At an early stage it became apparent that the temperature-specific heat curve of water was entirely altered in character by the introduction of a small amount of solute. With a half-normal solution of KCI the more or less parabolic curve for water becomes nearly a straight line, and even with fairly dilute solutions the water curve is greatly modified. The appreciation of this modification necessarily involved as a starting-point the consideration of the curve for pure water, as to the form of which different observers have come to widely different conclusions. A reference to fig. 10 (Section 14 post ), where the curves given by different observers are plotted, shows that the latest form of the curve, which is the result of the researches of Callendar and Barnes, differs widely from the curves given by Regnault and by Lüdin. At 80° C. the values of the specific heat of water in terms of the 15° calorie are.