used in printing to give purple tones, 128; formula for preparing paper with, 246. Cleaning glass plates, theory of, 39; details of, 213. Collodion, its discovery, 10; chemistry of Pyroxyline, 75; physical effect of Ether and Alcohol in, 83; of water in, 85; glutinosity of, 83; coloration of iodized, explained, 85; sensitiveness and intensity affected by the change, 97, 99; details of manufacture of Collodion, 185; Positive Collodion, theory of, 108; formula for, 201; Negative Collodion, theory of, 113; formula for, 208; Collodion for copying engravings, 231; for keeping processes, 298; for hot climates, 210; for working by artificial light, 238; to remove the brown colour from Collodion, 86. Collodion film, the proper time for immersing it in the Bath, 219; a thin film often good for direct Positives, 109; a thicker film for Negatives, 113; cause of the film falling away from the glass, 83, 293; spots and markings on, 281; conditions which affect its sensitiveness to light, 92; causes influencing its behaviour with the developer, 98; mode of preserving sensitiveness of film, 289. Collodio-Albumen process, theory of, 181; practical details of, 294. Colours, their nature explained, 47; their chemical action on sensitive film, 64; their photographic action assisted by reflection of white light, 66. Combination, laws of, 307. Conjugate foci, explained, 52, 272. Crookes, Mr., remarks upon chemical spectrum, 63; upon waxed paper process, 180; preservative process for Collodion films, 289. Curvature of luminous image formed by lens, explained, 53. Cyanide of Potassium, its fixing action explained, 44; preparation of solution of, 207; used to remove stains, 377. Daguerreotype, its invention, 8; theory of the process, 171. Development of invisible image, explanation of, 34-40; second, or intensifying stage explained, 37; details of developing glass Positives and Negatives, 221-223; development of paper Positives, 259; conditions which increase or diminish rapidity of development, 98; irregularities of development, 103. Developers, their preparation and properties, 26; comparative strength of, 98; theory of, for Positives, 111; for Negatives, 117; formulæ for Positive developers, 205; for Negative, 211. Diagrams, mode of copying, 232. Diaphragms for lenses. _See_ Stops. Double decomposition, illustrated, 14; explained, 314. Dry Collodion process, 298.