MANDELIC ACID (Phenylglycollic Acid), C 8 H 8 O 3 or C 6 H 5 CH(OH) COOH, an isomer of the cresotinic and the oxymethylbenzoic acids.
According to the above formula the critical temperature is given by 8aA/54b, and as the critical temperature is approximately proportional to the boiling-point, both being estimated on the absolute scale of temperature, we may conclude that the larger value of b corresponds to the lower boilingpoint, and indeed the isomer corresponding to the left-hand formula boils at 74°, the other at 114°.
An isomer of cinnamic acid known as allo-cinnamic acid is also known.
Phenazone is an isomer of phenazine, to which it bears the same relation that phenanthrene bears to anthracene.
Consequently, of each pair of isomers we may establish beforehand which is the more stable; either in particular circumstances, a direct change taking place, as, for instance, with maleic acid, which when exposed to sunlight in presence of a trace of bromine, yields the isomeric fumaric acid almost at once, or, indirectly, one may conclude that the isomer which forms under greater heat-development is the more stable, at least at lower temperatures.