ll>4 Mr. M. M. P. Muir on Isomerism*. 



each of the three, are nevertheless not arranged in the same 

 manner in each, is, I think, not opposed to but is in keeping 

 with known tacts. 



4. Granting, then, that change in the form of energy and 

 change of molecular structure are correlated in isomeric bodies, 

 the inquiry into the facts of isomerism would naturally branch 

 out into two directions. 



Chemists would seek to determine what are the atomic ar- 

 rangements in isomeric molecules, and what are the differences 

 in the energies of these molecules. 



The first part of this inquiry has been approached by a 

 method which seems to present the most probable chances of 

 success, viz. by studying the reactions of formation and of 

 decomposition of isomers. These reactions have been in many 

 instances generalized, and the results have been embodied in 

 appropriate formulae. From the generalizations so reached 

 some slight idea of the atomic arrangement (granting, of 

 course, that such arrangement has an actual existence) of 

 many isomeric bodies has been attained to. 



But even in this part of the inquiry we have still very 

 much to learn. Attention has not, it appears to me, been 

 sufficiently paid to the fact that atomic structure involves 

 atomic motion of some kind. 



In the second part of the inquiry (that, namely, which relates 

 to changes of energy) little or no progress has been made. 

 The subject is beset with many difficulties ; but in this field 

 many of the future triumphs of chemical science will doubtless 

 be achieved. 



5. As a preliminary investigation it would be well that the 

 data concerning the physical properties of isomers should be 

 more carefully observed. Something has, it is true, been done 

 in this direction. Thus we know that the boiling-points of 

 isomeric compounds, which have, so far as we can judge from 

 their reactions, a similar molecular structure, are nearly iden- 

 tical ; whereas when the molecular structure of isomeric com- 

 pounds is essentially different we find a marked difference 

 between the boiling-points of these compounds. We are 

 indeed in some cases able to trace a somewhat regular altera- 

 tion in the boiling-points of the members of an isomeric series 

 and to correlate this with a regular alteration in molecular 

 structure ; thus the boiling-points of the four butylic alcohols 

 differ by about 11°. By comparing the structural formulas of 

 these compounds (i. e. formulae which generalize the reactions 

 of formation and of decomposition which these bodies exhibit) 

 a gradual closing-up, so to speak, of the molecular structure 

 becomes apparent. 



