of Homologous Compounds. 



19 



the chlorine atom, and that the difference between the boiling- 

 points of the lower alcohols and of the corresponding chlorides 

 is entirely due to molecular association in the liquid state. 



With the acids there is association in the gaseous as well 

 as the liquid state, and since, according to the tables given 

 by Ramsay and Shields, the factor of association for a liquid 

 fatty acid at its boiling-point is rarely greater, and in most 

 cases is somewhat smaller, than for the corresponding liquid 

 alcohol, the molecular attraction to be overcome on vaporiza- 

 tion must be considerably less for the acid than for the 

 corresponding alcohol, and. the resulting rise of boiling-point 

 above the normal value must be less. 



The results for (1) non-associating liquids ; (2) esters ; 

 (3) associating substances are given in Table XI. 



Table XL ' 



Lower Members. 



No. of 



values of 



A. 



I Mean diff. 

 between 

 ! calc. & obs. 

 values of A. 



Xon-associating substances 

 Esters 



* 



30 



55 



Associating substances 10 



Higher Members. 



No. of 



values of 



A. 



+3-50 49 



+4-62 67 



+9-12 28 



Mean diff. 



between 



calc. & obs. 



values of A. 



o 

 0-05 



+V53 

 4-3-40 



The esters come between the non-associating substances 

 and those which are recognized as associating, and the con- 

 clusion previously arrived at that there is slight association 

 in the case of the esters is supported. 



Considering the data as a whole it may, I think, be con- 

 cluded that the values of A may be calculated from the formula 

 with an error rarely exceeding 1°*5 and generally less than 

 l c for the majority of organic compounds which contain one 

 or more C — CH 2 — C groups provided that their molecules 

 are not associated in the liquid state ; that is to say, for the 

 hydrocarbons and their halogen derivatives, the ethers, alde- 

 hydes, amines, hydrosulphides, and the higher esters, cyanides, 

 nitro-compounds, and ketones, probably also for all esters 

 which contain an iso-group in the variable alkyl radical, and 

 possibly for acids and even alcohols of very high molecular 

 weight. The calculated values of A are, however, too high 

 for the lowest members of nearly all homologous series, and 

 still more so for substances which are characterized by mole- 

 cular association. 



C 2 



