266 Mr. William Sutherland on the 



To make clear the two simple laws that rule these tabulaled 

 values, it will be advisable to confine our attention at first 

 only to those values obtained by the fifth method, using those 

 by other methods only to fill gaps. It will also be well to 

 consider first a single chemical family, such as the paraffins, 

 for which we have the following values : — - 



CH 4 . 2 H 6 . C 6 H U . C 8 H ]8 . C 10 H 22 . 



2-2 14-7 59-3 90'6 125*6 



These show that there is not a constant difference in the value 

 of M 2 / corresponding to the difference in the number of CH 2 

 groups contained. We can amplify this list of paraffins by 

 using the material furnished by Bartoli and Stracciati (Ann. de 

 Chim. et de Phys. ser. 6, t. vii.), who have determined the more 

 important physical constants for all the paraffins from C 5 H 12 

 up to C 16 H 34 . Their values of the capillary constants were 

 found at about 11 degrees in every case. To obtain those at 

 two thirds of the critical temperature, we have to use the 

 values of the critical temperatures calculated by them from 

 Thorpe and Rucker's convenient empirical relation (Journ. 

 Chem. Soc. xlv.), 



/ o/(2T -T) = constant, 



p being density at T. 



The following are the values of VI thus obtained : — 



C 5 H 12 . 



C 6 H U . 



C 7 H 16 . 





C 7 H 16 . 



C 8 H 18 . 



C 9 H 20 . 



C 10 H 22 . 



47-2 



58 1 



77-1 





79-6 



91-2 



110 



127 



C n H 24 . 



C 12 H 26 



0- 



L3 H 28 . 



'iAo- 



C 15 H 32 . 



1B H 34 . 



147 



171 





L92 





215 



230 



256 



Considering the assumptions involved in the. calculation of 

 these values and the difficulty of obtaining the paraffins pure, 

 the agreement for C 6 H U , 8 H 18 , and C 10 H 22 with Schiff's 

 numbers is excellent ; but the higher we go in the series the 

 larger is the temperature-interval for which we have to 

 extrapolate, and the more uncertain do the values become. 

 However, they are useful as giving a general idea of the 

 course of M 2 Z in an extended series. 



On plotting these numbers as ordinates with abscissas 

 representing the number of CH 2 groups in the molecule, 

 a curve was constructed which proved to be the parabola 



M 2 Z = 6S + -66S 2 , 



where S is the number of CH 2 groups. It is only necessary 

 then to determine on this curve the abscissa corresponding to 



