Variation in the Pressure of Saturated Vapours. 83 



mistakes and correct the errors, rough as they may be, pro- 

 ceeding perhaps from misprints and mistakes in interpolation. 

 It is exceedingly remarkable that with the majority of acids 

 x has a negative value. Whether c— c x is negative depends 

 upon x being so when it attains a maximum or minimum 

 value. Acetic acid apparently offers less error, and I here 

 insert my endeavours to bring our theory into agreement with 

 Landolt's data for this acid. 



Acetic Acid, C 2 H 4 2 . 



Is* Method. 



In order to shorten the calculations, I calculated the nu- 

 merator of equation (8). Its different values are placed in 

 the second line of the following table ; the first line contains 

 the corresponding temperatures: — 



* 50° 55° 60° 65° 70° 75° 



x 0-225 0-405 0*417 0329 0206 0-303 



t 80° 85° 90° 95° 100° 105° 110° 



x 0-428 0-203 0'405 0-132 0-325 0-106 0-309 



On dividing these figures by the denominator of equation (8), 

 which is always negative, we find that all the tie's are also 

 negative, x increases with a rise of temperature above 110° 

 and a fall below 50°, hence its maximum value lies between 

 these temperatures ; but it is impossible to indicate the exact 

 corresponding temperature, owing to the disorder of the 

 figures. I take 80°, because in the preceding table the maxi- 

 mum quantity lies opposite it. To determine as accurately 

 as possible the minimum of x, it is necessary to divide the 

 figures of the second line by the corresponding numerators 

 and to take the arithmetical mean of the thirteen figures so 

 obtained. As the latter are too irregular it is impossible to 

 expect a great accuracy from the mean result ; I therefore 

 changed this method for another, which, although less accu- 

 rate, is simpler, counting that this would not render the 

 calculations less exact. I took the arithmetical mean of the 

 figures of the second line of the preceding table and divided 

 the number so obtained, 0*2848, by the numerator of equa- 

 tion (8) taken for the temperature 80°. I found 



#= -9-2657, 



whence 2 



c- Cl = - 9-2657 x t^t = -0-30886. 



According to Regnault, c=0'4599 (between 10° and 15°); 

 Ci is unknown. From these data we find 



Cl = 0'7688. 

 G2 



