Mr. A. S. Couper on a New Chemical Theory. 109 



herent property, common to all the elements. It has been deno- 

 minated chemical affinity. It is discovered under two aspects : — 

 (I) affinity of kind ; (2) affinity of degree. 



Affinity of kind is the special affinities manifested among the 

 elements, the one for the other, &c., as carbon for oxygen, for 

 chlorine, for hydrogen, &c. 



Affinity of degree is the grades, or also limits of combination, 

 which the elements display. For instance, C^ 0^ and C^ 0* are 

 the degrees of affinity of carbon for oxygen. C^ 0^ may be called 

 the first degree, and C^ 0^ may be termed the second degree, 

 and, as a higher degree than this is not known for carl)on, its 

 ultimate affinity or combining limit. Affinity of degree in an 

 element may have only one grade. It may have, however, and 

 generally has more than one. Here then is an inherent property 

 common to all elements, by the removal of which the chemical 

 character of an element will be destroyed, and by virtue of 

 which an element finds its place marked out in a complex 

 body. 



It is such a property that is required to form the base of a 

 system. Nor would its suitableness for this purpose beaflPected 

 by the discovery that the elements are themselves composite 

 bodies, which view the chemist is perhaps not unwarranted to 

 adopt. For in such a case the necessity would doubtless still 

 be found to exist of adopting the principle of affinity, or some- 

 thing at least equivalent to it, as the basis of the explanation of 

 chemical combinates. In applying this method, I propose at 

 present to consider the single element carbon. This body is 

 found to have two highly distinguishing characteristics : — 



1. It combines with equal numbers of hydrogen, chlorine, 

 oxygen, sulphur, &c. 



2. It enters into chemical union with itself. 



These two properties, in my opinion, explain all that is cha- 

 racteristic of organic chemistry. This will be rendered apparent 

 as I advance. 



This second property is, so far as I am aware, here signalized 

 for the first time. Evidence as to its being a property of carbon 

 may therefore be required. 



It will be found in the following : — What is the link which 

 binds together bodies comjjosed of 4, G, 8, 10, 12, &c. equiva- 

 lents of carbon, and as many equivalents of hydrogen, oxygen, 

 &c. ? In these you may remove perhaps all the hydrogen or 

 oxygen, and substitute so many equivalents of chlorine, &c. It 

 is then the carbon that is united to carbon. Further, that it is 

 not the hydrogen that is the binding element in these combinates 

 is evident ; thus — 



