254 
Proceedings of the Royal Society of Edinburgh. [Sess. 
manner that the combining energy of the complement (nM 4 , etc.) either potentially 
or actually does not extend beyond nC 2 . 
A secondary combinate is one in which the combining energy of the complement 
is not all expended upon nC 2 , but is extended further to one or more elements. 
On the same principle there are tertiary combinates, etc. 
These orders of complicity ought in reality to be subdivided. This, however, I 
do not think it necessary for the present to enter upon. It will now be understood 
why an alcohol belongs to the type nC 2 M 4 , and on the same principle why a free 
aether belongs to the same type, thus 
(02 0 *5 p 2 
*, while they are at the same 
C 2 • H 3 H 3 C 2 
time secondary combinates. 
A secondary combinate, that is to say, a body belonging to the second order of 
complicity, is, as will be understood from the principle which forms the ground of 
the rational theory, a direct consequence of an inherent property of one or more of 
the elements which form the complement to the carbon. 
In the instance before us, it is a certain property of the oxygen which is the 
cause of the secondary combinate. This property is the affinity which one atom of 
oxygen in combination always exerts towards another atom of oxygen likewise in 
combination. 
This affinity is modified by the electric position of the element to which the 
respective atoms of oxygen are bound. From this property results the fact, that in 
organic combinates the atoms of oxygen are always found double. 
For instance, the combining limit of oxygen being two, when two molecules of 
r;2""0"" 
^ — H 2 
are set at liberty, the free affinities of the oxygen instantly produce the 
C 2 "H 3 
union of these molecules. The cause of the union of two molecules of C 2 H 3 has 
been already remarked. In the two cases, the causes of the union of the respective 
molecules are in so far different, that the one is the result of a property of the 
carbon, while the other is the result of a property of the oxygen. 
The view here adopted of the nature of oxygen is, I am convinced, alone in 
conformity with the reactions where the properties of this body develope themselves. 
The vapour of anhydrous sulphuric acid, for instance, is conducted into anhydrous 
0 > 
aether. The following will then be the reaction : — S 2 
■ • O 2 
O 2 
cation with C 4 SL C 4 , the two atoms of the oxygen of the sulphuric acid 
'■■‘11° TP**’* 
entering 
into communi- 
* The vertical dotted line between these two “ C 2 ’s ” is omitted in the original. 
