Lenses, double-convex, concavo-convex, double-concave, 19. Lenses, forms of, 19, 20; combination of, for portraits, 27; chromatic aberration of, 23; spherical aberration of, 22. Leveling stands, 35. Light, decomposition of, 16. Litmus, 98. Manipulations of the positive collodion process, 129; negative process, 143. Measures and Weights, 210. Milk, 99. Mounting positives on paper, 157. Negatives for printing positives, 151, 169. Nitrate of potash, 102. Nitrate of silver, 116. Nitrate of silver bath, mode of preparing for positives, 64; for negatives, 147; for negatives and positives in Helio's process, 164. Nitrate of silver used in developing negatives, 145. Nitric acid, preparation and properties of, 100; use in nitrate bath, 65, 147; use in making soluble cotton, 46. Nitro-sulphuric acid used in preparing soluble cotton, 42, 51. Oxide of silver, preparation of, 109. Oxygen, 109. Oxymel, preparation of, 105. Paper, sensitive, for printing, 152; alcohol used in, 201. Patent for the use of camphor in combination with iodized collodion, 176; for sealing photographic pictures, 177; for the use of alcohol as a desiccating agent, 178; for the use of bromide of potassium in collodion, 178; for the use of japanned surfaces for taking positives, 179; for photographic pictures in oil, 181; for making transparent borders, 183; coloring positives, 185, 187; for albumenized collodion, 186. Plate-Holders, Lewis's patent, solid glass corners for, 137. Plato vices, 64. Portrait lenses, combination of, 27. Positives, (ambrotypes,) process for producing, 129; by the Helio process, 164; printing on albumenized paper, 192, 206; ammonio-nitrate of silver used in, 152; use of chloride of gold in toning, 155; fixing, 155; fixing and brightening, (ambrotypes), Humphrey's collodion gilding used in, 63; printing frames for, 36; collodion for, 58, 59; mica used for, 136. Positives, enlarging from negatives, 199. Potash, 105; carbonate of, 106. Practice of the positive collodion process, 129; negative process. 143; Helio's positive and negative process, 164; printing on paper, 151. Prism, 14; refraction of light by, 14. Protosulphite of iron used in developing positives. 62; negatives, 144. Pyrogallic acid, preparation of, 107. Sensitizing paper, use of alcohol in, 201. Silver, properties of, 107; removal of stains from the nitrate of, 161; recovery of from waste solutions, 203. Solar spectrum, 14. Soluble cotton, 42; Hadow on, 46. Spherical aberration, 22. Spots upon positives, 139. Stains and lines upon positives, 139.