[ 515 ] 



LXI. Some Thermodynamical Relations. — Part I. 

 By William Ramsay, Ph.D., and Sydney Young, D.Sc* 



rj^HE relations to be considered in the following pages are, 

 -A- we believe, well founded ; but we hope to confirm them 

 by more exact experiments than have as yet been made. 



It appears advisable here to state the share which each of 

 the authors has had in this work. For our purpose, the 

 equation 



L __dp t 



will be employed. The relations of the first term of this 

 equation were the subject of a communication to the Chemi- 

 cal Section of the Philosophical Society of Glasgow in the 

 year 1877 by Dr. Ramsay, which, however, he considered too 

 incomplete to be published ; while the application of the last 

 term of the equation to the vapour-pressures of substances, 

 which formed the subject of a joint Tesearch by both authors, 

 was independently discovered by Dr. Young. It is also right 

 here to mention that some of the relations discovered by Dr. 

 Ramsay have been pointed out subsequently and independently 

 by Troufcon (Phil. Mag. 1884, vol. xviii. p. 54). 



The term (where L represents the heat of vaporiza- 



Sj S 2 



tion of a liquid or solid substance at its boiling- or volatilizing- 

 point, and where s 2 * s the volume of the liquid or solid at 

 these temperatures, and s x that of the gas into which one or 

 other is converted), if stated in words, denotes the heat ex- 

 pressed in units required to produce unit increase of volume 

 of substance at the temperature of ebullition of the liquid or 

 volatilization of the solid. 



Two laws have been discovered, representing certain rela- 

 tions between different liquids. 



The first law may be stated thus : — The amount of heat re- 

 quired to produce unit increase of volume in the passage from 

 the liquid to the gaseous state at the boiling-point under normal 



pressure is approximately constant for all bodies ; or 



= C. 5 l~^2 



The data on which this law is based are imperfect. The 

 heats of vaporization of but few bodies have been determined 



* Communicated by the Physical Society : read November 28. 



