198 
Proceedings of the Royal Society of Edinburgh. [Sess. 
discovery of glycol, by the treatment with caustic potash of the glycol 
diacetate obtained by the interaction of ethylene iodide and silver acetate. 
Couper’s first work, published in August 1857, is so closely connected with 
this discovery that one is led to surmise that Wurtz had suggested its 
subject to Couper — indeed, Couper’s paper, “ Recherclies sur la Benzine,” * 
immediately follows a paper by Wurtz, “Note sur la liqueur des Hollan- 
dais,” j- in the Gomptes reudus. 
Couper’s Investigations on Benzene. 
Couper started with the supposition that it is possible to convert 
benzene into the corresponding alcohol and the corresponding glycol. 
With this view, he treated boiling benzene with bromine vapour and thus 
discovered brombenzene (boiling point 150°), as well as the dibrombenzene 
fusing at 89° and boiling at 219°, our p dibrombenzene. He nitrated and 
sulphonised the monobrombenzene. He heated both the brombenzenes 
to 200° with silver acetate in sealed tubes. He ascertained that mono- 
brombenzene scarcely acts on silver acetate. With better hope of success 
he tried the action of silver acetate on dibrombenzene, but unfortunately 
lost his material by an explosion, and had to postpone the continuation of 
the experiment. 
In his communication Couper uses the small equivalents C = 6, 0 = 8, 
4 
as Wurtz also always did at that time, and wrote, for instance : — 
“ Bromobenzine C 12 H 5 Br 
Dibromobenzine C 12 H 4 Br 2 
ra 2 fj4 ) 
Phenylglycol diacetique / C 4 H 3 Q 2 ^ } ° 4 -” 
From this it will be seen that Couper was, at that time, by no means 
so much under the influence of Gerhardt’s type theory as Kekule was so 
early as April 1854 ; see his famous paper, “ On a New Series of Sulphurated 
Acids.” I He had not, like Kekule, had the opportunity of developing his 
scientific opinions by close scientific intercourse with Gerhardt in Paris, 
and then with Odling, and especially with Williamson in London. No 
doubt Couper uses for his expected “ phenylglycol diacetique ” a typical 
formula; but it is of a sort then generally used even in Germany, and 
derived from the multiple type of water H 2 0 2 , and not from the type H 2 0 
* Comptes rendus, xlv. 230-232. See Appendix to this paper, p. 235. 
t Ibid., xlv. 228-230. 
I Proceedings of the Royal Society of London, vii. 37-40. 
