1908-9.] Life and Chemical Work of Archibald S. Couper. 
IV. 
1 T c • 
. C H 2 
227 
IV, (O = 16). 
C H 2 
C 
'C- 
C 
C 
' c- 
II 
H 
•o- 
O 2 
o 2 
OP 0 -O H 
0....0 ...H 
c- 
•o OH 
c 
c- 
c 
c 
c- 
0 
c- 
H 
H 0 
OP’ ..Oil 
OH 
•OH 
As I said some time ago, in discussing these formulae * : — “ If my recon- 
struction of Couper ’s formulae is justifiable, these formulae clearly show 
what Couper lacked for the discovery of the benzene theory. Four carbon 
atoms — I have numbered them in formula I, ; they are 2, 3, 4, and 5 — are 
represented by Couper in the same state of combination with one another 
as Kekule’s formula gave them at a later date.” Couper had only to take 
one step more, to unite the carbon atoms 6 and 1, and close the ring: this 
would have involved the transference of a hydrogen atom from 6 to 5, and 
of the hydroxyl from 1 to 2. And Couper had already arrived at the 
assumption of the union of multivalent atoms in ring form, as is shown by 
the formula, given in an earlier part of this paper (p. 216, and Appendix, 
p. 265), by which Couper expressed the constitution of cyanuric acid. 
“ Undoubtedly Archibald Couper was, at that time, August Kekule’s most 
dangerous rival.” 
Of the three chemists whose work was criticised in Couper ’s salicylic 
acid paper, Gerhardt was gone (having died August 19, 1856, in Strassburg, 
soon after his settlement there), Chiozza said nothing, and only Drion 
attempted to defend himself and Gerhardt. t He maintained that the 
existence of the salicyl chloride observed by Gerhardt, although not isolated 
in a pure state owing to its non volatility, was indubitably proved by the 
readiness with which it reproduced the ethers of salicylic acid when 
treated with alcohols. It will be seen that Drion makes his task too easy : 
he tries neither to refute Couper ’s description of the course of the reaction 
nor to explain what became of the phosphorus oxychloride, which must 
have been produced in the formation of salicyl chloride, but which neither 
he nor Couper had observed. 
It is remarkable that Couper and Kekule encountered one another not 
only in the theoretical but also in the experimental field. Kekule, in 
* Liebig’s Annalen , cccxlvi. 290. 
t Comptes rendus , xlvi. 1238, seance du lundi, 21 juin 1858. 
