114 Dr. Carnelley on the Influence of Atomic Arrangement 



point of a pure compound is practically fixed and constant, 

 and hence depends solely on the nature of the compound, 

 whilst the boiling-point depends not only on the nature of the 

 compound, but also on the superincumbent pressure ; and, 

 further, given alterations of pressure by no means produce 

 corresponding alterations in the boiling-points of different 

 compounds. It is therefore far easier to trace the connexion 

 between melting-point and atomic arrangement than the con- 

 nexion between boiling-point and atomic arrangement. 



Such considerations as these induced me, about three years 

 ago, to commence the study of the influence of composition and 

 atomic arrangement on the melting-points of organic com- 

 pounds. And for this purpose I have made complete lists of 

 all the melting- and boiling-points which have been deter- 

 mined up to the present date. This tabulation has taken 

 three years, and was finished only a few weeks ago. During 

 this time I have collected not far short of 30,000 melting- and 

 boiling-points, about one half of which are melting-points. 

 The systematic arrangement of this enormous quantity of data 

 is now in progress; and I have already been able to trace cer- 

 tain relations between them, which I hope will throw light on 

 the influence of atomic arrangement. Some of these I now 

 propose to describe ; but at the same time I wish to say that, 

 though these conclusions have been verified in a very large 

 number of cases, I have not yet been able to test them in 

 every possible case, because the systematic tabulation of my 

 lists of melting-points is not yet completed. 



Of the compounds of carbon, the aromatic compounds are 

 perhaps the most important, and are certainly the most inter- 

 esting. These compounds may all be considered as derived 

 from benzene. 



Benzene has the formula C 6 H 6 ; and its constitution is gene- 

 rally represented as follows: — 



CH 



HC /A CH 



II I 

 HO CH 



Vh 



or it consists of a closed ring of six atoms of carbon united 

 alternately with one and two combining-powers, whilst the 

 fourth combining-power of each carbon atom is combined with 

 hydrogen. 



The aromatic compounds are derived from this ring by 



