678 SCIENCE PROGRESS 



The Molecular Volume {and A.V.), a Function of the Chemical 



Constitution of the Molecules 



The Law of Additivity has been suggested by the foregoing 

 Tables, and thus we notice the probability of the M.V.'s being 

 also functions of the Constitution of the Substances. We start 

 with a substance like Hexane, C 6 H 14 , and by a series of chemical 

 changes illustrate the different varieties of structure. 



I. Straight Chains : The Di-substitution of Hexane. 



Hexane CH 3 . CH 2 . CH 2 . CH 2 . CH 2 . CH 3 M.V. 139-93 observed. 

 3A.V. 6 x 147 + 14 x 37 = 140 o calculated, 



(i) CH 3 . CH 2 . CH 2 . CH 2 . CH 2 . CH 3 + Cl 2 



= CH 3 . CH 2 . CH 2 • CH 2 . CH 2 . CH 2 [5] 4- HC1 

 C 6 H 13 C1 M.V. 158-5 

 2A.V. 6XC + 13XH +C1= 1590 



This compound has thus a straight chain, like Hexane. 



(ii) CH 3 . CH 2 . CH 2 . CH 2 . CH 2 . CH 2 C1 4- Cl 2 



= |5| CH 2 . CH 2 . CH 2 . CH 2 . CH 2 . CH 2 . |a| + HC1 

 C 6 Hi 2 Cl 2 M.V. 162-4 (Extrapolated value) 



2A.V. 6 x CH 2 + 2CI = 177-4 



A — i5'o Possibly somewhat less 



There is thus a large difference in volume between the two 

 results. It has been shown by experiment that 1 : 1 di-substitu- 

 tion products are normal and involve no contraction. 1 : 2 

 compounds show a contraction of 3*0, and 1:3a contraction of 

 6 - o, and so on successively. (See paper read before Brit. Assoc. 

 Portsmouth, 191 1, Section B; and also Chemical News, vol. civ. 

 191 1, p. 151 et seq.) 



Such di-substituted compounds as the above, however, mark 

 a structure different from that of straight-chain compounds. 

 Owing to residual affinity, arising from the terminal chlorine 

 atoms, the curvature of the Hydrocarbon chain is effected and 

 a Partial Ring is formed. 



CHj — CHj — CHo — CI 



CI . CH 2 . Cri 2 . CH 2 . CH 2 . CH 2 . CH 2 C1 = 



Crl 2 — CH 2 — CH 2 — CI 



The difference, i5'o, is an expression of this change in con- 

 stitution. 



