A Manual of the Chemistry of the Carbon Compounds

THE CARBON COMPOUNDS. 313
the cornera where the carbon-atoms are supposed to be, we see at
once that three isomeric dime thy 1-beuzenes may exist :—
The methyl groups having the following positions:—
1:2
1:3
1:4
No further different positions of the two methyls are possible, for
1:5 = 1:3 and 1:6 = 1: 2,
The hydrocarbon C^HU, which we have represented in three
isomeric forms, can exist in eight different modifications. There are,
first of all, three trimethyl-benzenes:—
1:2:3
1:2:4
1:2:5
Further, there can exist three methyl-ethyl-benzenes and two
propyl-benzenes, one containing normal propyl, and the other
lsopropyl.
As the isomevio aromatic hydrocarbons have generally a great
resemblance in their physical properties, it is of the greatest importance
to have means for distinguishing them from each other. This
cau easily be done by studying their products of oxidations.
By heating an aromatic hydrocarbon with very dilute nitric acid,
one of the alcohol radicals is first oxidized to oarboxyl; methylbenzene,
ethyl-benzene, amyl-benzene, &c, yielding hnzoie add.
The formation of this acid, therefore, proves the existence of only one
alcohol radical in an aromatic hydrocarbon.
The three methyl-benzenes as well as ethyl-metbyl-benzene yield
isomerio methyl-lmoic adds C6H41 no OH' an ^ diethyl-benzene yields
f C H
as first product of oxidation, ethyl-benzoicaridGJUA QQ ^g. Besides
these monobasic acids, there is, at the same time, a bibasio acid
f CO OH
C6H4 j CO OH *° me( *> "which is obtained in larger quantity by using
stronger oxidising agents, such as a solution of potassium dicliromate
in dilute sulphuric acid, Tbis bibasic acid exists of course, also, in
three isomerio modifications, differing from each other by their physical
properties, as well as those of their salts. In the same way, a hydrocarbon
containing three alcohol-radicals will yield by successive