Latent Heat of Evaporation of Benzene. 37 



water ; for the critical point of benzene would fall at about 

 677° C, and that of water at about 990° C. It has, however, 

 been shown that in the case of water the curvature from 0° to 

 100° (that is, over a pressure-range of about 4 mm. to 760 mm.) 

 may be neglected (Paper W, pp. 316-321) ; and the above 

 Table would indicate that we cannot be far wrong in making 

 a similar assumption with regard to benzene, especially when 

 we consider that both the temperature-range (0° to 80 o, 2 C.) 

 and the pressure-range (26 mm. to 760 mm.) are in the latter 

 case diminished. 



We originally intended to perform a group of experiments 

 at 60°, which is about the highest temperature to which it is 

 advisable to expose the apparatus ; but before doing so it 

 would have been necessary to standardize a third mercury- 

 thermometer — a work which would have occupied at least a 

 week of the short time at our disposal. 



Assuming formula {a) to hold to 760 mm., and taking the 

 boiling-point at that pressure as 80°* 20 C. (Ramsay and Young, 

 Phil. Mag. 1887), we get 



When = 80-2, L = 94'37 (" thermal units at 15° C."). 



The results of the experimental work described in this 

 paper may be summarized as follows : — 



The Latent Heat of Evaporation of Benzene over the temperature- 

 range 20° to 50° C. (nitrogen-scale) is represented by the 

 equation 



L = 107-05- 0158 0, 



where L is expressed in terms of a "thermal unit at 15° C." 



Assuming this expression to hold over the range 50° to 80°, 

 the resulting value of L at 80 o, 2 C. (760 mm. pressure) is 

 9437. 



22. Historical. 



We have been unable to find records of any determinations 

 in addition to the following : — 



Regnault. Memoir es de PAcademie, 1862, vol. xxvi. 



P- 761 : L = 109-0. 



R. Schiff. Liebig's Annalen, 1886, vol. ccxxxiv. p. 338 : 

 L = 93-4 at 80°-35. 



K. Wirtz. Wiedemann's Annalen, 1890, vol. xl. p. 438 : 



L = 92-9 at 80°-l. 

 Jahn. Zeitschrift fur Physikalische Chemie, 1893, vol. xi. 

 P- 79 : L = 107-6. 



