Mr. M. M. P. Muir on Chemical Notation. 5 



circumstance s, how this body will react with other bodies_, 

 chemists seek to compress all they know of the doings of the 

 substance into that shorthand expression by which they dis- 

 tinguish it from all other bodies. To say that structural 

 formulae do not tell us much about the actual, and even the 

 possible, actions of the substances formulated is simply to 

 confess to ignorance of what these formulae exhibit. 



9. For proof of this statement I might refer to many 

 researches ; let one suffice. 



In a remarkable paper published in this Magazine*, Dr. 

 C. R. A. Wright examined the relations between affinity and 

 dissected or structural formulae in the case of certain groups 

 of compounds ; and he showed that the dissected formula of a 

 chemical compound may give us much information, not only 

 with regard to the method of formation, and decomposition 

 under the influence of various reagents, of that compound, but 

 also with regard to the transformations of energy which take 

 place during these actions. Thus, to take an example, it is 

 shown that when an operation, " symbolically represented by 

 the substitution of the group of symbols CH 3 for the symbol 

 H in some constituent hydrocarbonous radical (CH 3 , CH 2 , or 

 CH) in the dissected formula of the original substance," is 

 performed upon a given vapour, then " heat is evolved during 

 the performance of the operation," and the new and more 

 dense vapour produced has a higher " affinity-value " than the 

 original vapour. Here we have a most important generaliza- 

 tion with regard to homologous series of compounds : as the 

 series is ascended the " affinity-value " increases; and these 

 differences of affinity-values are " correlative with the differ- 

 ences between . . . dissected formulae indicating substances 

 chemically related together." 



On the other hand, Dr. Wright shows that substitution of 

 the group CH 3 for H in the OH group in the dissected 

 formula of a vapour is attended with absorption of heat, and 

 therefore with decrease in affinity-value : thus the conversion 

 of an acid into its methylic ether is attended with absorption 

 of heat. 



10. It may be urged that our formulae do not express such 

 relationships as those between transformations of energy and 

 chemical action. At present they do not ; but it would require 

 only the addition of a symbolic expression of some kind, not 

 the discarding of the formulae and the invention of entirely 

 new expressions, to enable us to express such relationships. 

 Dr. Wright's researches show (and this is the main point to 

 be insisted upon) that there is a connexion between the com- 

 * December 1874. 



