THE

LONDON, EDINBURGH, AND DUBLIN

PHILOSOPHICAL MAGAZINE

AND

JOURNAL OF SCIENCE.

[FIFTH SERIES.]

JANUARY 1894,

I. Note on the Generalizations of Van der Waals regarding "Corresponding" Temperatures, Pressures, and Volumes. By SYDNEY YOUNG, D.Sc., F.R.S., Professor of Chemistry, University College, Bristol*.

I

N a paper read before the Physical Society in November 1891, and published under the above title in the Philosophical Magazine for February 1892 (xxxiii. p. 153), the absolute temperatures and the molecular volumes (as liquid and saturated vapour) of eleven compounds were compared with those of fluorbenzene at a series of corresponding pressures.

It was pointed out, however (p. 155), that a better mode of procedure in many respects would have been to give the temperatures, pressures, and volumes of each of the twelve substances in terms of its critical constants; but as the critical volumes of several of the compounds had not been directly determined, and as none of them were known with accuracy, the method had to be abandoned.

Since then it has been shown by M. Mathias that the critical densities—and therefore the volumes-may be determined with great accuracy by the method of Cailletet and

* Communicated by the Physical Society: read November 10, 1893. Phil. Mag. S. 5. Vol. 37. No. 224. Jan. 1894.

B

Mathias, and as the values calculated by M. Mathias differed very slightly from those obtained independently by the same method by myself, I accepted these values as correct (Phil. Mag. Dec. 1892). It appears, however, that there were a few small errors in the calculations, and I have therefore adopted my own values in the tables that follow. The new critical molecular volumes and those previously accepted as correct are given below; it will be seen that the alterations are very small.

The vapour-pressures, molecular volumes, and critical constants of ten esters [methyl formate, acetate, propionate, butyrate, and isobutyrate; ethyl formate, acetate, and propionate; propyl formate and acetate] have recently been determined by Mr. G. L. Thomas and myself, and the absolute temperatures, pressures, and volumes of each substance have been given in terms of its critical constants (Trans. Chem. Soc. Ixiii. p. 1191).

In order to allow of a comparison being made, pressures corresponding" with the previous ones (with a few omissions) were taken, and I now propose to give the absolute temperatures and volumes of the substances previously studied in terms of their critical constants. As the data for the esters are published in full in the Trans. Chem. Soc., it is unnecessary to reproduce them here, and it will be sufficient to give the extreme values for the ten esters in each case.

of Critical C,H,F. C,H,Cl. C,H,Br. C.H,I. CH. OCl. SnCl. (C,H),O CH2OH. C2H2OH. C2H,OH CH,COOH