98 Gerhardt’s Organic Chemistry. 
The salicylic acid C,H,O,, and the anisic C,H, 0,, are 
monobasic and contain three equivalents of oxygen; in the first, 
the deficiency of hydrogen is 14—6=8, and the second = 16— 
8=8. Theseacid y then be represented by the formula R~*O,,. 
This proportion between the elements of a compound does 
not, however, necessarily imply a homology ; there are some ex- 
ceptions which depend in some way upon the peculiar grouping 
of the elements. Thus ordinary ether C, H, , O, is represented 
by the same general formula as alcohol R*? O, but the chemical 
characters of the two are entirely different and do not allow us to 
consider them homologues. It is then necessary to add as a con- 
dition of homology, a similarity of chemical characters, dependent 
upon a like arrangement of the molecules. Vol. i, pp. 29-35. 
This notation expresses in a beautiful and simple manner, the 
relations of homology which exist between different compounas. 
It is the peculiarity of this system that it is based upon the natu- 
ral affinities of bodies and not upon analogies; this is the only 
arrangement which will always be correct, because it is founded 
in the constitution of the substances themselves. 
The important relations which the combustible elements sus- 
tain, appear “to permit us to class homologous bodies according 
to their carbon,” and M. Gerhardt has accordingly constructed 
upon this basis a classification in which all organic substances 
are arranged in a tabular form. Those containing the same 
atomical proportion of carbon constitute a family which 1s de- 
signated by the number of equivalents of that substance. Each 
family is divided into the carburets of hydrogen and those con- 
taining oxygen and nitrogen, so that we have R, RO,, RN, &e. 
These divisions are found on the left of the table, while at the. 
top are marked at the head of their respective columns, the pro- 
portions of hydrogen. This will be better understood by a view 
of a part of the Ist and 2d families. 
Family.|Gen. formula. Rr2 R be 
\ C,H CoH 
“ wel wis olefant gas. 
O, 
| RO (a) aleohol. { cea 
ee (4) metl. ether. “a sgt 
RO C,H,0,, 
7 acetic acid. Mee 
( ms oxalic acid. 
R { CH,, 
marsh gas. 
1 RO M,O;, CO, oxyd 
wood-spirit. ae ‘ of carbon. 
CH,0., CO,, car- 
ete oie ee ee { formicatida { bonic acid gas.! 
