The relation between the crystal symmetry of the simpler organic compounds and their molecular constitution. —Part II

In this paper the experimental results concerning the crystalline properties of the unsaturated aliphatic hydrocarbons, the simpler oxygen- and sulphur-compounds of carbon, the halogen-compounds, and the simpler aromatic hydrocarbons are given. Ethylene. —Ethylene, prepared from alcohol and sulphuric acid, was purified by liquefying it and distilling it twice. It crystallises very well, large prisms being formed. Two distinct cleavage systems occur, one parallel to a prism and the other parallel to the basal plane (or an orthodome). The doublerefraction is of middle strength; the extinction is in some sections parallel to the prismatic cleavage, in others it is not. The angle of the optical axes is large, and the optical character negative. These optical observations show that ethylene crystallises in the monoclinic crystal system.