440 Mr. Grervaise Le Bas on the 



Refractive Power may be influenced to a slight extent by 

 Ring structure, but the evidence is inconclusive, and at any 

 rate no reliance can be placed on the conclusions arrived at. 



Magnetic Rotatory Power shows a much more marked and 

 reliable influence, but this development of Perkin's theory 

 has not been much exploited. 



The influence, such as it is, is positive for refractive power, 

 and negative for magnetic rotatory power. 



Perkin in Trans. Chem. Soc. 1902, xci. pp. 293-4, has, by 

 one method of calculation, found differences of varying mag- 

 nitude for different classes of rings, but has discarded this for 

 an alternative method, which apparently shows that the cor- 

 rection for ring structure is the same for simple rings of all 

 magnitudes. This is contrary to the observed effect on 

 molecular volume, for, as will be shown, the correction 

 depends on the size of the ring. Perkin did not realize the 

 significance of the result obtained by the first method of calcu- 

 lation, and so discarded it for the second. The latter result 

 is only arrived at by utilizing the first and second members 

 of series, such as formic and acetic acids, acetone, &c, which 

 are anomalous in respect of their molecular magnetic 

 rotations. The first is thus the correct method of calculation, 

 and the results obtained are the true ones. If this be so, then 

 we must conclude that both magnetic rotatory power and 

 molecular volume show effects due to ring structure, which 

 are dependent on the size of the rings. The first physical 

 property is so much affected by constitutive influences that it 

 is doubtful if sufficiently accurate results have been, or even 

 can be obtained by means of this property. This is not the case 

 with molecular volume. This property is much less subject 

 to constitutive influences, and the effects due to ring structure 

 are relatively and actually large. 



There does not thus appear to be any good method for 

 the elucidation of the Ring structure of a compound till we 

 turn to Molecular Volumes. 



The history of the subject can be briefly stated. Kopp 

 certainly recognized that the densities of benzene and its 

 derivatives were abnormal, but notwithstanding this he 

 adhered to his atomic values C = 11*0 H = 5*5, which were 

 derived from comparisons made between the volumes of 

 paraffin and benzene derivatives. This is unjustifiable. 



No reference was made to the possible effect of Ring- 

 structure on volume, till Traube (BericJde, xxviii. p. 2926) 

 deduced the fact, that a contraction of —8'2 exists for the 

 hexamethylene ring, and one of —13*2 for the benzene ring 



