Proceedings of the American Academy of Arts and Sciences.

VOL. XLVIII. No. 9.-SEPTEMBER, 1912.

CONTRIBUTIONS FROM THE JEFFERSON PHYSICAL
LABORATORY, HARVARD UNIVERSITY.

THERMODYNAMIC PROPERTIES OF LIQUID WATER TO 80° AND 12000 KGM.

BY P. W. BRIDGMAN.

CONTRIBUTIONS FROM THE JEFFERSON PHYSICAL

LABORATORY, HARVARD UNIVERSITY.

THERMODYNAMIC PROPERTIES OF LIQUID WATER TO 80° AND 12000 KGM.

Pressure Coefficient, (37)

Specific Heat at Constant Pressure, Cp
Specific Heat at Constant Volume, Co

Эт

Thermal Effect of Compression, (3),

Adiabatic Compressibility, (3%),

Volume of Kerosene as a Function of Temperature and Pressure
Compressibility and Dilatation of Ice VI

348

349

351

352

354

355

356

359

INTRODUCTION.

THIS paper is in the nature of a supplement to a former paper on the properties of water in the liquid and the solid forms.1 The solid forms were studied over a range of 20,000 kgm./cm.2, and from -80° to +76°, but the study of the liquid reached only from the lowest temperature of its existence to about +20°. Above 0°, measurements were made on the liquid at only 20°. The two measurements, at 0° and 20° were sufficient to give the mean dilatation between 0° and 20°, but not the variation of dilatation with temperature. It was assumed in the earlier paper that the variation of dilatation with temperature became negligible at high pressures, since this seemed to be the most plausible assumption in view of all the data then available.

In this present paper the study of the liquid has been continued from 20° to 80°, and to 12000 kgm. The pressure range is greater than that of the preceding paper by about 2,500 kgm. The range is not great enough to entirely cover the region of stability of the liquid, but it is as great as it was convenient to cover with the method used here, which is different from that of the former work. It has the advantage of very much greater rapidity of operation, but since it depends on the complete elastic integrity of the steel pressure cylinders it is not possible to reach so high pressures with it as with the former method. [The former limit of 9500 kgm. was set by the freezing of the liquid and was not due to any limitation of the method.] Nevertheless, it may be hoped that the present temperature and pressure ranges are both wide enough to give a fairly complete idea of the nature of the effects to be expected at high pressures with varying tempera

ture.

Measurements of the dilatation have been made at four temperatures, so that it has been possible to find the variation of dilatation with temperature at any pressure. Perhaps the most unlooked for feature disclosed by the measurements is the fact, contrary to the assumption of the first paper, that the variation of dilatation with temperature does not become vanishingly small at high pressures, but reverses in sign. This means that while at low pressures the volume increases more and more rapidly with rising temperature, at high pressures the expansion becomes more slow at high temperatures. The data of this paper are sufficient to completely map out the p-r-t surface over the domain in question: Both the first and second

1 Bridgman, These Proceedings, 47, 439–558 (1912).

derivatives are therefore completely determined, so that we now have all the data at hand for the determination of any one of the thermodynamic properties of the liquid. This means that we are in a position to find such quantities as the specific heats, change of internal energy, adiabatic temperature rise etc., as well as the more easily determined compressibility and thermal dilatation. The latter part of the paper, after the discussion of the method and the presentation of the data in the first part, is occupied with the computation of these various thermodynamic quantities. The accuracy of some of these is probably not very great, because the error in the second derivative of an experimental quantity may be considerable. It has, therefore, seemed best to give the general view of the nature of the quantities which is offered by a graphical representation, rather than to give tables, with the tacit assumption of greater accuracy which usually goes with a set of tables. In spite of the lower order of accuracy of some of these thermodynamic quantities, it has still seemed well worth while to give them, since even the general trend of some of the quantities, such as the specific heats, has not been hitherto known with relation to pressure.

The data presented here are only the beginning of a projected study of the characteristic surface under high pressures for a number of liquids. The measurements have already been carried through for twelve other liquids beside water. The purpose of this study is ultimately the development of a theory of liquids, since it would seem that a much more intimate grasp of the nature of the forces at work in a liquid would be afforded by a study over a wide pressure range, than over the comparatively low pressures hitherto used. It must be admitted, however, that this broader purpose is not particularly furthered by this work on water, because of the well known abnormalities of this substance. In the previous paper several abnormalities had been shown to exist at low pressures. In this paper, new abnormalities are found at higher pressures. Water gives the appearance of becoming completely normal only at the higher temperatures and pressures of the range used here, but of course whether this is really normal or not cannot be told until the behavior of normal liquids has been discovered. The full significance of the present data, in their bearing on such questions as the polymerization of the liquid, for example, cannot appear until after the discovery of the laws for entirely normal liquids. The investigation of water before that of normal liquids was undertaken for two reasons; firstly because of the desire to complete the work for water already begun, and