298 ORGANIC CHEMISTRY 



the electrons in definite parts of the carbon atoms, the four electrons 

 involved cannot approach as near to each other as is the case in a 

 single union. This is Baeyer's theory of strain, and is much better 

 in accord than is the theory of free valences with the fact that cyclo- 

 propane and propylene appear to be about equally unsaturated, as 

 evidenced by their heats of combustion and by their conduct toward 

 bromine. On the other hand, it seems to lead logically to conclusions 

 with regard to the addition of bromine to triple unions, which Pro- 

 fessor Michael has shown are contrary to the facts. (3) Without 

 a condition of strain, we may suppose that the presence of both a 

 positive and a negative electron in each of the atoms united by the 

 double union causes a lessening of the attraction of the electrons. 

 This would result in such a union being less stable than a single union. 

 The second and third views appear, at present, most in accord with 

 the facts possibly the truth lies in some combination of the two. 



Whatever view we may take, it is noteworthy that double unions 

 are usually formed by the loss of a positive and negative atom or 

 group from adjacent carbon atoms, as hydrogen and hydroxyl or 

 hydrogen and bromine. It is also true that in many double unions 

 one of the carbon atoms is more positive than the other, causing the 

 addition of halogen acids in a definite manner which may be pre- 

 dicted in accordance with Michael's "positive negative law." Apply- 

 ing this thought to conjugated double unions, we see that of the four 

 atoms involved the two central ones are likely to be positive and 

 negative respectively and neutralize each other's attraction for out- 

 side atoms, while an intensified attraction for outside atoms would 

 be found in the exterior atoms. The effect may be analogous to that 

 of the attractive forces of a magnet which exhibit themselves chiefly 

 at the ends. 



But I have permitted myself to wander much farther in the field of 

 speculation than was my first intention farther than is at all 

 profitable, I fear, for these questions furnish, at present, few points 

 for experimental study, and speculations divorced from experiment 

 have usually been profitless. I should be very sorry if what has been 

 said should give encouragement to such speculations. On the other 

 hand, I have a very firm conviction that we should not be content 

 with rounding out organic chemistry as a descriptive science, nor even 

 with adding to the number of empirical rules which enable us to predict 

 certain classes of phenomena. We must, instead, place before our- 

 selves the much higher ideal of gaining a clear insight into the nature 

 of atoms and molecules and of the forces or motions which are the 

 real reason for the phenomena which we study. When we consider the 

 progress which has been made and the knowledge of structure we 

 now possess, which would have appeared sixty years ago to lie be- 

 yond the limits of possible acquirement, it is not presumptuous to 



