Crystals of L-aspartic acid are monoclinic (P21) with a=7.617, b= 6.982, c= 5.142/~, ,8=99.84 °, Z=2. The crystals are often more or less twinned. The structure was solved in the hOl projection by the Patterson vector shift method. The structure was refined with 602 diffractometer hkl data to a final R value of 0.04. The molecules are in the zwitterionic form. A rigid three-dimensional network of intermolecular 'hydrogen bonds' is found.

The microscopic equations for the polarization caused by a travelling light wave in an infinite crystal are brought into a form that is analogous to that of macroscopic optics. The role of the 'incident' field term in the elementary theory and that of a magnetic contribution to the optical rotatory power are discussed.