The Relation between the Crystal Symmetry of the Simpler Organic Compounds and their Molecular Constitution.- Part III

The investigation of the crystalline properties of the simpler organic bodies, gaseous or liquid at Ordinary temperature, has been described in Parts I and II.* In this paper the experimental results will be discussed with regard to their bearing upon the problem of the relationship between molecular constitution and crystal symmetry. In order to facilitate a comparison the experimental results are summarised in the table on p. 2. As seen from the table, more than 50 per cent, of the substances investigated are polymorphic, and to this class nearly all the substances which contain only one carbon atom belong. The question therefore arises which one of the crystalline modifications of a substance is to be compared with the one or the other form of another substance, or with the crystals of a substance of which only one modification is known. In most of the cases investigated very little is known with regard to the modification stable at low temperature, and thus for practical reasons only the form crystallising directly out of the liquid state can be taken into account.