638 8ir J. A. Ewing on Specific Heat of Saturated Vapour 



From 0° to 180° the saturation line is nearly straight, 

 with a slight bend about 120° which may be due to irregular- 

 ities in the determination of L. The entropy diagram for 

 ethyl alcohol is clearly of the "normal" type, showing 

 negative values for the specific heat of the saturated vapour 

 throughout the whole range of temperature. 



This is also true of methyl alcohol, which has a diagram 

 of the same type, but with a wider spread of the two limbs, 

 on account of its possessing greater latent heat. 



The diagram for propyl alcohol is shown in fig. 2. It is 

 calculated in the same way from Ramsay and Young's 

 values of L, using Bose's formula for the specific heat of the 

 liquid, namely, 



0-5279 + 0001692^, 



from which 



^. = 0-1515 log 10 T -f 0-001692 T-0-8312. 

 The resulting numbers are given below. 





Propyl 



Alcohol. 





Temp. 



'W' 



L/T. 



*.• 



40° 



0767 





... 



80 



0-1523 



0-4899 



0-6422 



100 



0-1898 



0-4395 



0-6293 



120 



0-2270 



0-3892 



0-6162 



140 



0-2642 



0-3447 



0-6089 



160 



0-3011 



02979 



0-5990 



180 



0-3379 



0-2567 



0-5946 



200 



0-3746 



02160 



0-5906 



220 



0-4111 



01730 



0-5841 



240 



0-4476 



01236 



0-5712 



263-7 



(critical) ... 







0-52 (about) 



Here again the figure is of the " normal " type, bat there 

 is a distinct bend in the saturation line which, though 

 insufficient to make the specific heat of the saturated vapour 

 positive at any temperature, tends that way. 



Ether. — Turn now to a substance in which the specific, 

 heat of the saturated vapour is known to be positive at some 

 temperatures, namely ethyl ether. I have used Eamsay 

 and Young's values of L, along with Regnault's formula for 

 the specific heat of the liquid *, namely, 



0*529 -}- 0-0005917 1, 



* Regnault, Relation des Experiences, vol. ii. p. 175. 



