I 



Gerhardtfs 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- 

 logies, 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 C0 2 and water 11,0. This is 

 i hen 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 : 



C H C H 



1 : 4= 1 :( 2+2) 4 



2: 6= 2 :( 4+2) ' 6 



5 : 12= 5 :(10+2) 8 



16:34=16 :(32+2) 16 



4= 4;( 8-4) 



8= 6 :(12-4) 



12= 8 :(16-4) 



28 = 16: (32 -4) 



and the same principle applies to any other proportions of these 

 elements. In the first group, each compound by losing in equiv- 

 alents of hydrogen is reduced to the normal ratio, and in the 

 second, the addition of four is required. 



1 o express these relations, the symbol II is preserved for the 

 ratio of 1:2; for those bodies in which the proportion of hydro- 

 gen is greater, the number of equivalents is indicated by an ex- 

 ponent preceded by the sign plus ( + ), and when its proportion is 

 less it is expressed by a similar exponent with the sign minus ( — ). 

 Wood-spirit CH,0, alcohol C 3 H„0, potato-oil C,H I2 

 andethal C ia H 34 "0, are by this notation, homologies of the 

 wrm R+2 o, and the acids derived from them by the abstraction 

 01 two equivalents of hydrogen and the addition of one of oxy- 

 gen are expressed by the formula R0„. The acids, oxalic 

 ^H 2 0„ succinic 0^,0. pimelic C 7 H 13 4 and suberic 



.< .«0« are homologues of the form R~» 4 ; • cannd 

 S H N, O, and succinamid C 4 H 8 N 8 0„ are homologous bod- 

 ies of the form RN 0„ ; benzene C e H e and cumene G 9 H 

 af e expressed by R- » and so on. To determine whether two bod- 

 ies having the same amount of oxygen, can be homologues, we as- 

 f" m e a number of equivalents of hydrogen equal to twice that ot 



Je carbon, (this being the proportion of 1 : 2,) and observe whether 

 "* excess or deficiency of hydrogen is the same in both ; and con- 

 ^quently whether they can be expressed by the same formula. 



8 *«*»» Ser, es , Vol. IV, No. lO.-July, 1847. « 



