Variation in the Pressure of Saturated Vapours. 85 



u 



Pressures. 



t 



Pressures. 



Calculated. 



Observed. 





Calculated. 



Observed. 





o 







20 

 40 

 50 

 60 



8-7 

 21-1 



47-8 



101-5 



7-6 

 189 

 44-1 

 66-0 

 97-4 



90 

 20-9 



42-2 

 67-5 

 97-4 



o 



70 



90 



100 



120 



140 



144-9 

 284-8 

 392-4 

 723-3 

 1285-5 



142-0 

 290-6 

 408-5 

 781-1 

 1931-3 



139-0 

 274-6 

 380-6 

 712-6 

 1293-5 



Finding the preceding calculations of the value of x un- 

 satisfactory, I repeated them at intervals of 10°. 



t .. 



50° 



60° 



70° 



80° 



90° 



100° 



X .. 



. -10-984 



-12-005 



-9-8238 



-11-094 



-9-5669 



-9-3295 



There is still an irregularity, but the position of the minimum 

 is clearer, it is equal to 12*005 and lies opposite 60°. Hence 



We then find 



c- Cl = 0-4002. 

 y = 4022-2; ^ = 130'7. 



I calculated the vapour-pressures of acetic acid from the new 

 values of x and y, and placed them in the fourth column of 

 the preceding table. 



24. There are some liquids to which our theory cannot be 

 applied, at least at present, owing to the insufficiency of ob- 

 servations on their vapour-pressures in a state of saturation. 

 Among these are : — 



C 2 H 5 I, PC1 3 , BCI3, SiCl 4 , CNC1 2 , C 2 H 4 C1 2 , and C 10 H 16 . 



With the first five liquids x increases with a rise of tempera- 

 ture, but with the last two x decreases. If the curve of x's 

 be constructed, it is easy to observe that it strives to attain a 

 maximum or minimum, and with the first six liquids it prob- 

 ably does so not far beyond the highest temperature at which 

 observations were made. In the case of turpentine this 

 temperature lies far beyond the temperatures observed. 



25. I have, as far as I know, reviewed all the liquids whose 

 vapour-pressures have been well determined ; there remain 

 the liquids produced by the liquefaction of gases under high 

 pressures. Our theory should not, however, be applied to 

 them, chiefly because the volume of the liquid presents a 



