The Theory of Molecular Volumes. 345 



We divide the influences operating on molecular volumes 

 into : — 



(a) Ad ditive, 

 (/>) Constitutive. 



The first, as already stated, is an independent proof of the 

 atomic division of matter. The latter is an important factor 

 about which very little is known. An attempt is here made 

 to elucidate some of these constitutive influences. We 

 suppose that the acting forces are the repellent heat forces, 

 following possibly some simple law. In the opposite direction 

 are the conservative forces of chemical affinity. There will 

 always be a balance between the two. Constitutive influences 

 have the effect of modifying the latter according to the 

 structural and other features of the molecules. The result 

 is that a new equilibrium is obtained, and the molecular 

 volume is correspondingly modified. 



A Periodic Relation between the Atomic Volumes. 



Kopp thought that the atomic volumes of the members 

 of each family of elements have probably identical values 

 (Ann. Ch. Pharm. xcvi. p. 319). 



This is not so. Thorpe has shown (Trans. Chem. Soc. 

 1880, xxxvii. p. 141, ibid. p. 327_, and Kopp Memorial 

 Lecture) that the volume of an element is a function of its 

 atomic mass. 



The necessity for changing many of the values has brought 

 out this fact more clearly^ that a periodic relation seems to 

 exist between the atomic volumes according to the position 

 of the corresponding element in the series. There are, 

 however, remarkable divergences from the characters re- 

 vealed by the well-known Lothar Meyer Table for Solids. 



It will be seen that atomic volume variations occur at 

 the boiling-point which are dependent on general character- 

 istics of the molecules, but as a rule these do not influence 

 the relations betw r een their volumes. There are other cases 

 where the atomic volume of an element undergoes a radical 

 change according to its particular function. Thus hydroxylic 

 oxygen has a volume 2H(7*4) which is the same as the ester 

 oxygen —OR, and the phenolic oxygen. Ethereal oxygen 

 has a volume 3 H (11*0) and also carboxylic oxygen. When 

 is attached not to carbon but to S, P, or N, its volume 

 changes to 8'3. 



These facts lead us to suspect that the volume of an 

 element may vary within certain limits, according not only 

 to its position, but to its chemical function and relation to its 

 surroundings. 



