Indices of crystal faces, 11 Intercepts on crystal axes, 58 Interference colours due to double refraction, 177; figures of biaxial and uniaxial crystals, 189–191 Internal structure of crystals, 15, 111–120 Iodide of mercury, dimorphism of, 97 Isomerism, chemical and physical, 142, 143 Isomorphism, Mitscherlich’s conferment of the term, 81; doctrine of, 81, 82; limitations of, 85; recent clearer definition of, 121–132 Isotropic crystals, 206 John of Berlin’s discovery of racemic acid, 142 Kipping and Pope, definition of racemism and pseudo-racemism, 153, 154 Kopp, 100 Kundt’s powder, 149 Labile solutions, 241 Laurent and Nickle’s organic researches, 99 Lavoisier, 23 Law of rational indices, 24, 50, 57, 59 Le Bel and van t’Hoff’s explanation of optical activity, 151 Le Blanc, researches on alums, 77 Lehmann, researches on liquid crystals, 256–282 Liquid crystals, 255–282; and polymorphism, 138, 139; list of substances forming, 280, 281 Magnesium sulphate, 76, 78 Mallard and Le Chatelier on silver iodide, 256 Manganate, potassium, 96 Manganates, 84, 96 Manganese sulphate, 78 Marignac and isomorphism of tantalum and niobium compounds, 84; and morphotropy, 101 Mercury iodide, dimorphism of, 97 Metastable solutions, 240 Methyl triphenyl pyrrholone, 105, 106 Mica-sectors plate for testing sign of optical rotation, 212, 213 Microscope, Lehmann’s crystallisation, 256, 257, 276–280 Miers, H. A., researches on crystallisation, 238–243; on red silver ores, 109; on vicinal faces, 248–254 Millerian indices, 57 Mirror-image symmetry, 118, 119, 134, 135; illustrated by quartz, 231 Mitscherlich, experiment with gypsum, 90–94; work of, 70–97 Mixed crystals, 77, 86 Molecular compound, racemic acid a, 150 Molecular volume and distance ratios, 129, 130 Molecule, individuality and directive force of, 139, 269 Monochromatic illuminator, 192, 193 Monoclinic system, 39; axes and axial planes of, 53, 54 Morphotropy, 98–104 Muthmann, researches on permanganates, 123 Naphthalene tetrachloride, 99 Newton’s seven orders of spectra, 177 Nickel sulphate, 76, 78 Nicol prism, 174, 175, 187 Nitrobenzenes, von Groth’s researches on, 104 Noble, Sir Andrew, experiments on liquefaction of carbon, 138 Optical activity and mirror-image symmetry, 141; antipodes, characters of, 152; characters of crystals, 7 Optically active classes of crystals, 150, 151 Optic axes of biaxial crystals, 185; axis of uniaxial crystals, 165; axial angle, 191; axial angle of ethyl triphenyl pyrrholone for different wave-lengths, 107, 191; axial angle of gypsum at different temperatures, 90–94, 191 Ostwald’s predictions of crystallisation phenomena, 238, 240 Oxides of arsenic and antimony, isodimorphism of, 88 Para-azoxy-anisol, liquid crystals of, 259, 265; -benzoic acid, 263; -cinnamic acid, 263; -phenetol, 258, 259