Mr. M. M. P. Muir on Isomerism. 167 



in eacli of its periodic movements there are four positions in 

 which it can exercise such force. Now if this be granted we 

 are in no way necessitated to suppose that the valency and 

 the total chemical affinity are dependent on one another, nor 

 that the force exercised in one of the four directions or posi- 

 tions is equal in amount to that exercised in each of the other 

 three directions or positions. On this supposition the equi- 

 valents or affinities of an atom may differ in value ; and the 

 existence of isomers becomes possible, the difference between 

 which is to be traced to the directions in which the chemical 

 force of the constituent atoms of the molecule is exercised. 



Such a theory as this has commended itself to several 

 chemists, among others to Crum Brown, who has discussed 

 some of its consequences in a paper published in the ' Journal 

 of the Chemical Society' [2], vol. iii. p. 230. 



But, on the other hand, it may be supposed that the equi- 

 valents of a given atom have equal values, and, nevertheless, 

 that, owing to the positions of the atoms with respect to each 

 other, 'isomeric bodies may arise which shall exhibit differences 

 of behaviour towards the same reagents. Thus, of the isomeric 

 amylic alcohols (C 5 H n OH), that whose reactions are best 

 expressed by the constitutional formula 



CH 3 — CH— CH 2 — CH 2 — OH 



CH 3 



is stable at temperatures at which that having the constitu- 

 tional formula 



CH 3 — CH— CH— CH 3 



CH 3 OH 



undergoes dissociation into water and amylene. 



The most plausible explanation of this fact appears to be, 

 that, although the affinities of the carbon atoms are all of 

 equal value, yet the group OH is related in one case to a 

 carbon atom a large number of whose affinities are already 

 " saturated" (to use a common term) with other carbon 

 affinities ; whereas in the other case the same group is related 

 to a carbon atom whose affinities are not to so great an extent 

 " saturated " with carbon. Hence, from the different positions 

 occupied by the OH group, it is possible, during the excursions 

 of the molecule, for those forces which tend to produce mole- 

 cular disintegration more readily to act upon the OH group 

 in the one case than in the other. 



Again we may suppose that the affinities of any given 

 atom are of equal value, but that as they are successively 



