226 
Proceedings of the Royal Society of Edinburgh. [Sess. 
Thus, so early as seven years before the establishment of Kekule’s 
benzene theory, Couper endeavoured to take account of the mode of union 
of the seven carbon atoms of salicylic acid. 
As I have pointed out in the preceding section, Couper, in his fuller 
paper in the Philosophical Magazine , “ On a New Chemical Theory,” 
everywhere replaces the brackets of his structural formulae by lines 
indicating the union of the atoms. If we carry this out in the case of the 
eight formulae given above, and represent, as has been done in later times, 
the double union by two parallel lines, we obtain the following eight 
forms, l c , II C , III C , IV C , and I„ II„ XIX d , IV, : — 
I, I’d (O = 16). 
C H 2 
Ci- 
VC H 
V 
C H 
C 
C 0 OH 
i o 2 
C r: " o OH 
IX C . 
C H 2 
c 
• ; :C H 
,.C -11 
c 
c o-o. 
o 2 PCI, 
C o--o 
.-■6C H 2 
5 ce: 
\ 4 c h 
.-• 3 C H 
.,0 OH 
j O 
C'- ; OH 
II, (0 = 16). 
, C H 2 
C 
■ C H 
, C H 
C 
C 0. 
: PCI, 
C ;> " 0 
IIIc 
C H 2 
c 
: C H 
III, (O = 16). 
C H 2 
C 
' C H 
C H 
c O' 
C 0 0 o 2 
C H 
C 
C 0 0 
0 2 
p 
0 P 
c- 
HI C' : O' -Cl 
0 0 
