Axes and axial planes of crystals, 51, 55, 56 Axial ratios, 129 Babinet’s double-wedge quartz plate, 219 Bacteria, destruction of one enantiomorphous form by, 149 Barium nitrate, 152 Barker, researches on perchlorates, 123 Barlow, discovery of remainder of 230 point-systems, 118, 119, 140; and Pope’s theory, 285–292 Bartolinus, Erasmus, 17 Benzoic acid, screen experiment on crystallisation of, 229–231 Bergmann and Gahn’s laws of cleavage, 18 Berzelius and Mitscherlich, atomic weights and isomorphism, 80, 82, 83, 85 Beudant’s researches on the vitriols, 75, 76 Biaxial crystals, 60°-prisms and refractive indices of, 162, 163, 184; optic axes of, 185; optic axial angle of, 191 Biot’s researches on tartaric and racemic acids, 143 Biquartze, natural and artificial, 181, 211, 214, 216, 217 Black band of quartz twins, 216–218 Boisbaudran, Lecoq de, 238 Boyle, Robert, 17 Brauns, 254 Bravais, 114; space-lattices, 114 Brookite, 91 Cæsalpinus, 15 Cæsium alum, 42 Calcite, crystals of, 10–13, 38; amount of double refraction of, 174; in rock sections, 177, 178; uniaxial interference figure of, 189, 190; plate perpendicular to axis of, 209; refractive indices of, 174; 60°-prism of, 165, 168 Calcium carbonate, three habits of crystals of, 11 Calcium dextro-glycerate, optical activity and crystal form of, 155–160 Carangeot’s contact goniometer, 18–20 Carbonate, calcium, 11, 87; potassium sodium, 44 Carbonates of alkaline earths, 74 Carbon, dimorphism of, 137 Carbon dioxide, liquid in quartz cavities, 46 Cavendish, 23 Chemical significance of crystallography, 73, 283, 284; valency and crystalline form, 285–291 Cholesteryl benzoate, liquid crystals of, 258; acetate, spherical liquid crystals of, 281, 282 Chromate, potassium, 84 Chromates and manganates, isomorphism with sulphates, 84 Classes, the 32 crystal, 6, 33 Cleavage, 17; and glide-planes, 275, 276 Cobalt sulphate, 78 Conditions for growth of crystals, 240, 244, 245 Constancy of crystal angles, 6, 13, 14, 17, 23, 132 Convergent light experiments, 186, 188 Copper sulphate, 40, 76, 78 Coppet, de, 238 Crookes, Sir William, 138, 208 Crossed-axial-plane dispersion of optic axes, 89, 94, 95; of ethyl triphenyl pyrrholone, 106, 107, 108; of gypsum, 89 Crystal, definition of, 4; germs and their influence on crystallisation, 236, 237 Crystals, modes of formation of, 4, 5 Cube and its perfection of symmetry, 38; axes of, 52 Cubic system, 37 Cyanide, potassium cadmium, crystals of, 42 Dalton, 25 Dark field of polariscope, 188, 202 Davy, Sir Humphry, researches on ammonia, 82, 83 Delafosse and morphotropy, 101 Deville and Troost’s researches on tantalum chloride, 84, 85 Diamond, 8, 137, 138, 207, 208 Dibenzal benzidine, liquid crystals of, 264 Digonal axis of symmetry, 36 Dimensions of structural parallelepipeda, 129