[ 93 j 



VIII. 



ON THE BOILING-POINTS AND CRITICAL TEMPERATURES 

 OF HOMOLOGOUS COMPOUNDS. 



By SYDNEY YOUNG, D.Sc, F.R.S., 

 Trinity College, Dublin. 



[Read March 28. Published April 3, 1916.] 



In the year 1842 Kopp made the statement that in every homologous series 

 of organic compounds the boiling-point rises eighteen degrees for each 

 addition of CH 2 ; and although he afterwards modified his views to the extent 

 that he adopted different constants for different homologous series, he still 

 adhered to the conclusion that for each series the rise of boiling-point for 

 each additional CH 3 group was constant. 



The error into which Kopp fell was due partly to the limited number 

 and the uncertainty of the data available, but chiefly to the fact that the 

 very numerous compounds — alcohols and acids — which contain a hydroxyl 

 group exhibit abnormal physical properties. The same remark applies also, 

 although in lesser degree, to the esters derived from the aliphatic alcohols 

 and acids, and to certain other series of organic compounds. In all such 

 series the abnormality diminishes with rise of molecular weight. 



It is quite obvious that the paraffins and many of their derivatives are 

 very far indeed from following Kopp's rule ; and many attempts have been 

 made to find a formula applicable to the boiling-points of these compounds. 



In the earlier formulae it was sought to find a relation between the 

 boiling-points and the number of atoms in the molecule, but none of these 

 formulae gave satisfactory results, and it may be sufficient to mention that 

 references to the original papers are given in Smiles's " Relations between 

 Chemical Constitution and some Physical Properties," 1910, p. 222. 



90TENT. PROC. K.D.S., VOL. XV., NO. VIII. (J 



