It has been shown that substances which
do not associate, or do so only to a slight extent,
yield melting point curves for their optical isomers
which either definitely show the absence of a racemic
compound, or show that it is unlikely to be present
to any large extent.
Secondly, substances which are definitely
known to associate show the existence of a racemic compound from the investigation of their melting point curves, and the theoretical curves, which have been drawn, agree well with the assumption that the dextro isomer is associated with itself in the pure isomer to the same extent as it is associated with the laevo isomer in the racemic compound.