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LX VII. The Influence of the Relative Volumes of Liquid and 

 Vapour on the Vapour-Pressure of a Liquid at Constant 

 Temperature. By Sydney Young, D.Sc., F.R.S.j Univer- 

 sity College. Bristol*. 



THE question whether the vapour-pressure of a liquid at a 

 given temperature depends on the relative volumes of 

 liquid and vapour has been frequently discussed, and has been 

 the subject of many experimental investigations. Within 

 recent years extended researches on the relations between the 

 temperatures, pressures, and volumes of several liquids have 

 been carried out by Prof. Battelli, and he arrives at the con- 

 clusion that when, in a tube containing a perfectly pure liquid 

 and its vapour, the volume is diminished and the vapour 

 caused to condense, the vapour-pressure rises : in other words, 

 that the smaller the relative volume of vapour the higher is 

 the vapour-pressure. 



These results are entirely opposed to those obtained by 

 Dr. Ramsay and myself and, while referring to this question 

 in a letter to the ' Philosophical Magazine ' last February, we 

 ventured to characterize the conclusions of Prof. Battelli as 

 incorrect, and to suggest that the error was due to the pre- 

 sence of small quantities of air or other impurity in the liquid 

 examined and to the employment of insufficiently purified 

 substances for heating-purposes. 



In a letter published in the August number of the l Philo- 

 sophical Magazine ' Prof. Battelli adheres to the conclusion 

 previously stated, and does not admit the existence of either 

 of the sources of error suggested. " I would rather observe," 

 he writes, " that, in order to observe such a phenomenon, an 

 apparatus is necessary which enables us — as in my case — 

 slowly to compress the vapour, and to maintain it for a time 

 under constant pressure." 



There can be no doubt, I think, that such an apparatus is 

 required in order to decide the question whether the pheno- 

 menon exists, but it seems hardly necessary to point out that 

 the conditions described are fulfilled in the apparatus em- 

 ployed by Dr. Ramsay and myself. 



During the present year I have been engaged in an inves- 

 tigation of the thermal properties of isopentane — a liquid, 

 boiling at 28°, which can, by suitable treatment, be obtained 

 in a pure state f« 



* Communicated by the Physical Society : read November 9, 1894 

 t Full details of the method of purification adopted will be described 

 later when the research is completed. 



Phil. Mag. S. 5.- Vol. 38. No. 235. Dec. 1394. 2 Q 



