Gerhardt's Organic Chemistry. 97 
each of them R represents a compound in which the carbon and 
hydrogen are in the proportion of 1:2. These bodies are homo- 
logues, and the relation of their elements is such that they may ev- 
idently be derived from each other by the abstraction of equal 
equivalents of carbonic acid CO, and water H,O. This is 
then the most simple ratio, and is selected as the term of com- 
parison. It is not however the most frequent; generally the hy- 
drogen is less than two, and when it exceeds it, the excess is 
seldom more than two equivalents. 
__. “When homologous bodies are decomposed into other homolo- 
gues, they lose or fix atomically the same quantities of carbonic 
acid, water, oxygen, &c.”’ This principle is illustrated by the 
group of alcohols so often referred to; when converted into hy- 
drocarbons, they give up one equivalent of water, and in the 
formation of acids they severally lose H, and fix O. From this 
it follows that a geometrical ratio between the elements of ho- 
mologous substances is not necessary ; bodies having the follow- 
‘Ing proportions of C and H may be homologues: 
PEAR Fs C 
1; 4= 1:( 242) 4g A= A; ( 8-4) 
2% G= 231442 ; 8= 6:(12-4) 
5:12= 5;(10+2) 8; 12= 8: (16-4) 
16 ; 34=16.: (32+2) 16 ; 28=16 : (32-4) 
pee preceded by the sign plus (+), and when its proportion is 
form R+? O, ‘and the acids derived from them by the abstraction 
he acids, oxalic 
O, and suberic 
C,H,N, 
les of the form RN, O, ; benzene C,H, and cumene CO Hs 
are expressed by R-*, and so on. To determine whether two bod- 
les having the same amount of oxygen, can be homologues, we as- 
Sume a number of equivalents of hydrogen equal to twice that of 
the carbon, (this being the proportion of 1: 2,) and observe whether 
the excess or deficiency of hydrogen is the same in both ; and con- 
sequently whether they can be expressed by the same formula. 
Srconp Serizs, Vol. [V, No. 10.—July, 1847. 13 
