VI. The Distribution of Crystal Faces in Zones, and the Mode of Constructing a Plan of the Faces 60 VII. The Work of Eilhardt Mitscherlich and his Discovery of Isomorphism 70 VIII. Morphotropy as distinct from Isomorphism 98 IX. The Crystal Space-Lattice and its Molecular Unit Cell. The 230 Point-Systems of Homogeneous Crystal Structure 111 X. Law of Variation of Angles in Isomorphous Series. Relative Dimensions of Unit Cells. Fixity of Atoms in Crystal 121 XI. The Explanation of Polymorphism and the Relation between Enantiomorphism and Optical Activity 133 XII. Effect of the Symmetry of Crystals on the Passage of Light through them. Quartz, Calcite, and Gypsum as Examples 162 XIII. Experiments in Convergent Polarised Light with Quartz, as an Example of Mirror-Image Symmetry and its accompanying Optical Activity 183 XIV. Experiments with Quartz and Gypsum in Parallel Polarised Light. General Conclusions from the Experiments with Quartz 201 XV. How a Crystal Grows from a Solution 236 XVI. Liquid Crystals 255 XVII. The Chemical Significance of Crystallography. The Theory of Pope and Barlow—Conclusion 283 Index 295 CRYSTALS (INCLUDING LIQUID CRYSTALS) CHAPTER I INTRODUCTION.