XXI. Bakerian Lecture.— On the continuity of the gaseous and liquid states of matter

Abstract

In 1863 the author announced, in a communication which Dr. Miller had the kindness to publish in the third edition of his 'Chemical Physics,’ that on partially liquefying carbonic acid by pressure, and gradually raising at the same tune the temperature to about 88° Fahr., the surface of de­marcation between the liquid and gas became fainter, lost its curvature, and at last disappeared, the tube being then filled with a fluid which, from its optical and other properties, appeared to be perfectly homogeneous. The present paper contains the results of an investigation of this subject, which has occupied the author for several years. The temperature at which carbonic acid ceases to liquefy by pressure he designates the critical point, and he finds it to be 30°·92 C. Although liquefaction does not occur at temperatures a little above this point, a very great change of density is produced by slight alterations of pressure, and the flickering movements, also described in 1863, come conspicuously into view. In this communication, the combined effects of heat and pressure upon carbonic acid at temperatures varying from 13° C. to 48° C., and at pressures ranging from 48 to 109 atmospheres, are fully examined.