ll>8 Mr. M. M. P. Muir on Isomerism* 



saturated those which remain become weaker, if one may use 

 such an expression, and that in some instances the atom does 

 not exercise its total valency because of this weakening of the 

 unsaturated affinities. On this view the whole of the atoms 

 in a molecule must influence the total force exercised by that 

 molecule. Thus the group OH may, in certain compounds, 

 exchange its hydrogen for metals, while in others, or even in 

 the same compounds, an exchange of hydrogen of this group 

 can only be effected for alcoholic radicles. 



The group has thus two functions, an " alcoholic " and an 

 " acid " function. Now we cannot doubt that it is the com- 

 position of the remainder of the molecule which chiefly deter- 

 mines the function of the OH group ; the position of the 

 group will of course also exercise an influence. From these 

 considerations it becomes evident that in considering the phe- 

 nomena exhibited by a chemical molecule we may divide these 

 phenomena into two classes : — first, those which are dependent 

 on the nature of the atoms composing the molecule ; and, 

 secondly, those which are dependent on the linking-together 

 or the position of these atoms in the molecule *» The pheno- 

 mena of isomerism will be influenced by both of these factors; 

 and in endeavouring to explain these phenomena we must 

 overlook neither. 



8. We may, then, perhaps imagine the meeting of two 

 molecules, the result of which is to be the formation of new 

 molecules. Molecular dissociation is the first result ; for a 

 moment we may picture the atoms vibrating about certain 

 fixed points, at each of which these atoms are capable of 

 exercising their chemical affinity. 



Let us suppose that the atoms of molecule a vibrate about 

 four, and that the atoms of molecule b vibrate about two of 

 these points. Let us further suppose that the force exercised 

 at each of the four points by a atoms is different in amount, 

 but that b atoms exercise the same amount of force at each of 

 their two points. 



The atoms become associated and new molecules result, 

 which have a different atomic structure from that of the 

 original molecules a and b, and are possessed of an amount of 

 energy differing from that originally possessed by these mole- 

 cules. But suppose the atoms of molecule b had come within 

 the sphere of action of the atoms of molecule a, not at the two 

 positions at which they have, by supposition, actually come 

 within that sphere of action, but at the two remaining posi- 

 tions, we should have a second new set of molecules produced 



* See L. Meyer's Modcrne Theorien der Chemie, 2nd ed. pp. 138-217 ; 

 also Crum Brown, he. cit. 



