INTERMOLECULAR SPACE 41 



Thus for amylene 



2 CH = 



J/, 5x9-9 + 10x3-1 1-7 + 25-9 = 104-7 (obs. 105-1); 

 this equation may be used to determine molecular weights 

 if there are sufficient data for the constitution, and conse- 

 quently for the part played by constitutive influences. 

 Thus if we have a hydrocarbon whose analysis gives 



(CH 2 ),, 

 with a density 0-7977 at 15 we get 



0-7977 

 and on the other hand 



M v = 25-9 + 1 6-1 n 1-7 or 25-9 + 16-1^-8-1, 

 since the hydrocarbon may contain either a double linkage 

 or a hexamethylene ring. If the latter is excluded on other 

 grounds, then 



i4n 



- 25-94- i6.m 1-7, 

 0-7977 



whence n= 16-7, or probably 17, 



which indicates that the hydrocarbon is heptadecylene. 



Since, however, this rule is purely empirical, it must be 

 handled with the greatest discretion, particularly with 

 regard to molecular doubling in liquids, since, according to 

 p. 26, it is not probable that this exercises a large influence 

 on the volume of the liquid. 



6. The Volume in Solution. 



In order to extend the range of comparison, and so bring 

 out better the additive and constitutive relations, the volume 

 of a dissolved body has often been considered. In recent 

 times this has attained a higher interest in the case of 

 dilute solutions, on account of the insight which the new 

 theory of solutions gives as to the state of dissolved bodies. 

 Two chief points must be attended to in this connexion if 

 we first deal with aqueous solutions. In the first place, 

 the formation of double molecules, which (p. 26) occurs 

 in hydroxylic bodies, especially in formic and acetic acids, 



