ON THE STUDY OF HYDRO-AROMATIC SUBSTANCES. 159 
This argument may account for the difficulty experienced in reducing 
isophthalic acid, and for the fact that tetrahydro derivatives, and not 
dihydro derivatives, are formed at once, because the free valencies, which 
cannot saturate one another, will naturally combine with hydrogen, and 
thus yield at once tetrahydroisophthalic acids. 
The substance! derived from the condensation product of ethyl 
dibromopropanetetracarboxylate and ethyl disodiopropanetetracarboxylate 
is not, as described in the last report,” a mixture of trans-hexahydro- 
benzenetetracarboxylic acid and the double anhydride of the cis-modifica- 
tion of the same acid, but is a mixture of cis- and ¢rans-trimethylenedi- 
carboxylic acid. The condensation takes place in accordance with the 
following scheme :— 
| | 
(CO,Et),.CNa.CH,.ONa(CO,Et); (CO,Et),.C.OH,.C(CO,Et), 
(CO,Et),.C — C(CO,Et), 
(CO, Et),.C — C(CO,Et), 
BA 
CH, 
Rosaniline Bases.—The trihydrochlorides of the rosaniline bases 
combine with four molecules of water* in acid solution to form tetra- 
hydroxyhexahydrobenzenerosanilines, analogous to the tetrachloro- and 
tetraminohexahydrobenzenerosanilines previously obtained by absorption 
of 4HClor 4NH;. To account for the formation of colourless solutions 
under the above conditions‘ it is assumed that four molecules of water 
are taken up, the quinonoid nucleus being transformed into a cyclohexane 
ring, which view is supported by thermo-chemical data. 
The Nature of Double Linkings.—F rom the observations of others on 
the addition of bromine to unsaturated substances,® Bauer is led to the 
following generalisations, which, though not drawn up with special reference 
to hydro-aromatic substances, may be of use to those working in this field. 
The capability of carbon atoms, united by a double bond, adding on 
bromine is lessened when both carbon atoms have attached to them the 
following groups : COOH, COOR, C,H; or Br. In certain cases alkyl 
residues in combination with the above groups behave in a similar 
manner. In the system R'R?C=CR*R‘, if R! be replaced by COOH, 
bromine is added on so long as R?R*R* are not replaced by bromine or 
bromine and methyl. Methyl groups without bromine atoms have no 
influence. For example, addition takes place in the case of acrylic, 
bromo- and dibromoacrylic crotonic, dimethyl- and trimethylacrylic acids, 
but not with tribromoacrylic or dibromocrotonic acids. 
When R! and R? are replaced by carboxyl groups, the addition takes 
place so long as R? and R‘ are not both replaced by Br or methyl: for 
example, fumaric, methylfumaric and bromomaleic acids form dibromides, 
whereas dibromo- and dimethylfumaric acids do not. 
If R! be replaced by C;H; and R?R*R*‘ by methyl groups, addition 
takes place ; but if R! and R* are replaced by C,H; and R® and R‘ by 
1 Perkin, J. C. S., 1905, 87, 358. 2 Reports, 1904, p. 62, 
8 Schmidlin, Compt. Rend., 1904, 189, 506. 
+ Ibid., p. 521. 5 Ber., 1904, 37, 3317. 
