578 



Transactions. — Physics. 



(1.) The hydrocarbons themselves associate rapidly in 

 phenol solution. 



(2.) The ethereal salts of the lower fatty acids have a nega- 

 tive value for A, and show little or no association. But ethyl 

 laurate and ethyl palmitate associate rapidly, and the associa- 

 tion is greater for the compound with the longer carbon chain. 



(3.) The introduction of an ethylene linkage in stearic 

 acid breaks the continuity of the hydrocarbon chain, and the 

 rate of association is considerably reduced. 



(4.) Amongst the lower fatty acids — butyric acid, for ex- 

 ample — the introduction of a bromine atom in the a position 

 to the carboxyl reduces A to about half its original value ; 

 higher up the series this is not the case, a brompalmitic 

 acid associating almost as rapidly as palmitic acid itself. 



IVi+s>i*ber- of Carbon* aUvrna 



Various other properties of the fatty acids show a mini- 

 mum or maximum at the sixth member. The most charac- 

 teristic example is furnished by the melting-points. These 

 are graphically depicted with the values of A in fig. 1. The 

 minimum is reached in both cases at the same acid, and the 

 similarity between the two curves is readily noticeable. These 

 results show clearly to what an extent the melting-point of a 

 substance is dependent on its association. Further, they 

 confirm the conclusion already arrived at* — namely, that "a 

 maximum or minimum of a series is due to the molecular 

 complexity of one or more members of that series." 



»TraDS. N.Z. Inst., l l J02, p. 465. 



