64. REPORT—1904. 
in a continuous state of oscillatory motion. In the case of a substance such 
as butadiene, the formation of the dibromide BrCH, -CH=CH—CH,Br, 
is explained by supposing the swinging motion of the carbon atoms to be 
taking place first in one direction and then in the opposite, as indicated in 
the accompanying diagram (fig. 1). 
Continuous motion in one direction only is prevented by the hydrogen 
atoms attached to the terminal carbon atoms, which come into the plane 
of rotation. It is quite another matter in the case of benzene, where 
alternate carbon atoms are supposed to rotate continuously in opposite 
directions, because none of the valencies which pass into the plane of 
rotation have hydrogen atoms attached to them ; the result is that the 
double linkings change their position and travel round the ring (fig. 2). 
HTGa. Fig. 2. 
oO | S So) Po Qa S 
Such a theory indicates the possibility of new types of isomerism, 
more subtle even than optical isomerism, and it is pointed out that cases 
of supposed polymorphism, ¢.g., the quinols and benzophenone, may be 
in reality manifestations of structural differences of the above type. 
Knoevenagel supports Lehmann’s view,' that substances exhibiting 
difference in crystalline form afford evidence of difference in chemical or, 
perhaps better, physical constitution. 
It is also suggested that bodies of the type of ethyl +*:°-dihydro- 
terephthalate should be particularly liable to lose a molecule of hydrogen, 
(+) 
HC . COOCH, 
Ars 
HO CH 
| ll 
HC CH 
ay 
HC . COOCH, 
(+) 
since the two hydrogen atoms marked (+) would be in a continuous state 
of bombardment, due to the swinging motion of the carbon atoms con- 
nected by a double bond. On increasing the temperature this state of 
things would become sufficiently intense to cause the partial dissociation 
of the molecule with evolution of hydrogen. This actually happens in the 
case of the above ethereal salt on heating? in an atmosphere of carbon 
dioxide, especially in presence of platinum black. The evolved hydrogen 
is much smaller in amount than required by theory, only 18 c.c. being 
obtained by heating one gram of the salt instead of 113 c.c. This is 
1 Molehularphysih (2), 413. ? Ber,, 1903, 36, 2857. 
