Heats with Temperature and Density. 529 



general outline with that deduced from van der Waals's 

 equation. 



■— for Ether. 



By a well-known thermodynaniical relation 

 _ C p _ E, 



where E,, and E T are the adiabatic and isothermal elasticities 

 respectively ; and 



E_ ^ 



where S is the velocity of sound in the vapour, and Y is its 

 specific volume ; then 



S 2 



*4) 



V3V. 



This equation was used for the calculation of 7, values of 

 S 2 being taken from the data given by Ramsay and Perman 

 (Joe. cit.). 



The following table (p. 530) gives the results as obtained. 



Fig. 3 (p. 531) represents these results graphically, and, with 

 the exception of the left branch of the curve for T = 200°C, 

 they are fairly regular. 



It is evident that as the temperature increases while the 

 volume is kept constant, the value of 7 falls ; as the density 

 increases at constant temperature, 7 also increases at first 

 slowly and then more rapidly ; at volumes smaller than 

 the critical volume 7 decreases rapidly with increase of 

 density. 



The general resemblance between the Cp — C B and 7 

 diagrams is marked, and must be due to the comparative 

 smallness of the variation of C P . 



Phil Mag. S. 6. Vol. 13. No. 76. April 1007. 2 



