210 Proceedings of the Royal Society of Edinburgh. [Sess. 
comes to the conclusion that the equivalent, atom or molecule (be does not 
distinguish between these terms), of oxygen must be taken as 8 and not 
as 16. It seems to me that Couper, still entangled in the doctrine of 
Berzelius, considered the hydrates of the oxygen acids and the salts of 
these acids as composed of two electrically opposite components. He takes 
a hydrated acid as a compound of the anhydride and water. In the for- 
mation of a salt from a hydrated acid and a basic hydroxide, according to 
him, it is not the hydrogen of the acid which changes place with the metal 
of the basic hydroxide, but the hydrogen takes with it an atom of oxygen 
(0 = 8) from the acid, and the metal carries an oxygen atom from the 
basic hydroxide into the salt. The oxygen atom of the acid radical, with 
which is united the oxygen atom combined with the metal, is negative, 
while the latter oxygen atom is rendered positive by its union with the 
metal. The reaction between hydrated acid and basic hydroxide is possible 
because the affinity between the positive and the negative oxygen is less 
than that between metal and oxygen, hydrogen and oxygen, and acid 
residue and oxygen. “ A consequence of this truth is, that it is impossible 
to double the equivalent of oxygen, if the chemical equivalents are to be 
understood as not being in direct contradiction to any chemical truth or 
essential feature in the properties of an element. Carbon differs entirely 
in this respect from oxygen.” 
If Couper had not been so fundamentally opposed to Gerhardt’s type 
theory he would no doubt have freed himself from these untenable views. 
Butlerow, too, thought Couper’s adherence to the equivalent 8 for oxygen 
unfounded. He sets against Couper’s notion of double decomposition that 
of Kekule, according to which the two interacting molecules, in the first 
moment of the reaction, unite, and then the resulting complex splits in a 
new direction. 
In Couper’s three papers there are to be observed some variations in 
the mode of writing the examples of constitutional formulae of carbon 
compounds. In the first short note in the Comptes rendus, dotted lines 
and brackets are used to indicate the bonds. Brackets are also used in 
the fuller paper in the Annates de chimie et de physique, with continuous 
instead of dotted lines. In the use of brackets we can well see a 
concession to the French and German chemists, who had been accustomed 
to their use by Gerhardt. In the English paper in the Philosophical 
Magazine the dotted lines are retained and the brackets are altogether 
discarded. 
I here give Couper’s constitutional formulae for carbon compounds 
containing oxygen, from the Comptes rendus paper, in which he takes 
