89 



on the conductivity of boric acid, would lose all signiticance for (he 

 determination of the configuration. 



Therefore, if this improbability be excluded and if we assume that 

 an attack of the valencies somewhere in tlie molecule leaves unaltered 

 the arrangement around the atoms, which are not immediately 

 concerned, then we shall be able to obtain a solution in some 

 apparently hopeless cases. 



We have seen that with the two isomeric hexahydro-terephtalic 

 acids a comparison of the dissociation constants does not answer 

 the purpose; neither is resolvable into optical antipodes and besides 

 from neither an anhydride could be obtained. 



Of the A'-tetrahydro-terephtalic acids (see accompanying diagrams) 



COOH COOH COOH 



COOH H H 



Fig. 2. 



the trans acid should be resolvable into optical isomerides and it is there- 

 by to be distinguished from the cis acid, which caimot be resolved. 

 Now it should oe possible to change these acids into tlie corre- 

 spondent hexahydro-terephtalic acids by catalytic reduction, without 

 altering the arrangement of the carboxyl groups and therefore the 

 configuration of the last mentioned acids may be definitively established. 

 A case bearing an essential relation to this one, is: 

 Benzoquinone furnishes maleic acid by careful oxidation ; from 

 this we may conclude with rather great certainty, tliat this acid 

 has the cis configuration, as this arrangement is contained, in the 

 quinone molecule and because at the elimination of the — CH = CH- 

 group, the bonds that bear the isomerism, are not interfered with; 

 if in the case of maleic and fumaric acid we were as badly equipped 

 as with the hexahydro-teiephtalic acids, then this mode of formation 

 would have been of preponderant importance for the determination 

 of the configuration. 



