34 Mr. D. L. Hammick on Latent Heat 



(ii.) a T will be assumed to vary linearly with the tem- 

 perature up to the critical temperature, the temper- 

 ature coefficient ^yp- being -~ — p^. 



(iii.) Values of a T at various temperatures will be calcu- 

 lated from the temperature coefficient and the value 

 of a found from the surface energy from (1) and 

 substituted in the complete Bakker equation 



x < =a 4kS) 



Results are given in Table I. The surface-energy data 

 used are mainly from Jaeger (Zeit. Anorg. Chem. ci. pp. 1- 

 214 (1917)). Values of a are expressed as atmospheres 

 pressure x (volume of 1 gramme molecule of vapour at 

 N.T.P.) 2 . The gramme molecular volume is taken as 22*41 

 litres at N.T.P. The temperature at which a is calculated 

 from p, the surface energy, is shown by the suffix after a and p. 

 Young's data (Sci. Proc. Roy. Dubl. Soc. xii. p. 414 (1910)) 

 nave been used for specific volumes of liquid and vapour, 

 critical data (calculation of a c ), and latent heats. Values 

 of d, the molecular diameter, are those used in Part I. 



The connexion between internal and external latent heat 



RT 



has been taken as \ — \.-\- — - ? where M = molecular weight. 



Table I. 



Latent Heats from Surface Energy and the Critical Data. 



Benzene. 



a c =03822. T c = 288°-5 C. p 5 . 4 =30-9 ergsxcm. 2 d=4-88xI0- 8 cm. 



From equation (1) at 5°'4 C- c 5 . 4 = -05808. |^ = -"000070 



T 80C.° 100° C. 150 C°. 200° C. 250° C. 



<r T ........ -05286 -05146 -04796 -04446 -04096 



\ calc) 95-4 90-7 80-2 68-0 52-2 



Voung) - 95 '5 »1'4 80-9 08-8 [49-5] 



Ether. 



a c = -03551. T C =194°C. ,o = 19-2 ergs X cm. 2 ^=4-41 X 10-s em. 

 From equation (1) at 0° O. a = "05200. |^ = - -000085. 



T 35° C. 40° C. 60° C. 100° C. J50° C. 



a. T '04902 -04862 -04690 -04350 -03925 



X (calc) 84-2 82-6 77-6 67-2 51-5 



Voung)- 8 ^° 82 " 8 78-4 68-4 51-1 



