Variation in the Pressure of Saturated Vapours. 65 



This table shows that from 0° to 110° the results of calcula- 

 tion and observation are sufficiently near to each other ; hence 

 the vapour of ether in a state of saturation diverges but 

 little between these temperatures from the laws of Boyle 

 and Gay-Lussac. 



Benzene, C 6 H 6 . 

 11. 1st Method. 



t 30° 55° 70° 75° 80° 85° 



x 93901 3-8215 2-7054 2-5321 2'5988 2*3905 



t 90° 95° 100° 105° 125° 



x 2-5563 2-6051 2-6575 2-7598 3-3561 



In this instance x has not a maximum value, as it has with 

 water and ether, but a minimum, whose exact position it is 

 unfortunately difficult to determine, probably owing to errors 

 (misprints ?) in the pressures. It may be said that the mini- 

 mum lies between 80° and 90° ; we will take 85°, and will 

 consider the minimum of x as the arithmetical mean of its 

 three values for temperatures 80°, 85°, and 90°, that is as 

 2-5152. Hence 



0-^=2-5152 x 4=^64492. 



to 



According to Wiedemann q = 0*3325, and Regnault gives 

 c = 0*43602, hence c — c 1 = '10352 ; the disagreement between 

 the above results is explained by the uncertainty of the 

 calorimetric measurements. If, however, we assume that 

 the error in c is small, and take c — c x = '064492 as found 

 by the 1st method, then we obtain Ci = 0*37153, which is 

 slightly greater than that determined by Wiedemann. To 

 calculate y, I made three replacements, in equation (9), 

 for x : 2 5988, 2'3905, and 2*5563, corresponding to tem- 

 peratures 80°, 85°, and 90°, and obtained three figures whose 

 mean was taken as the desired value of y. It appeared that 



y=3816*72 ; 

 whence 



r =3816-72x ^ =97-866. 



According to "Regnault r 85 = 90*75 *. 



* It is important to exactly calculate the amount of heat required to 

 heat a kilogram of the liquid from 0° to 85°, because observations were 

 not carried beyond 71°. 



Phil. Mag. S. 5. Vol. 37. No. 224. Jan. 1894. F 



