Chemical Calculations Chlorophyll
present time. Many changing boxes and bags are figured and described in the older books on photography. The magazine portion of a camera, if detachable, is sometimes called a changing box.
Chemical Calculations, Reactions, and Equivalent Quan-tities. See Equivalence, Chemical, and Analysis.
Chemical Focus. See Chromatic Aberration.
Chemigraphy. Relief etching on metals, the resist being an original drawing on the metal, a transfer from another print, or a transfer obtained by photographic means. Zinc is the metal most used, and very weak nitric acid (about I to 40) the mordant. As the etching progresses, the lines are loaded with fresh ink and resin powder. This mixture being heated on the plate, runs down on the sides of the relief and affords protection against undercutting. (See list of references under Blocks for Print-ing.)
Chlorates. A class of salts derived from chloric acid ; the chlorate of potassium KC103 being used as a source of oxygen, which it readily yields when heated, especially if a small pro-portion of manganese dioxide is present.
Chlorides. A chloride is a compound of a metal or other element with chlorine, the most common chloride being sodium chloride, or common salt, NaCl. The so-called chloride of lime and chloride of soda or potash come under a different category, containing as they do a hypochlorite as the active constituent. (See Bleaching Powder ; also Eau de Javelle.)
Chloroform (Ger., Chloroform; Fr., Chloroforme; Ital., Chloroformio). CHC13. Prepared by the action of Bleaching Powder (q.v.) and water on alcohol or methylated alcohol. It is a heavy, colourless liquid of pleasant smell and sweet, hot taste. It dissolves in alcohol and ether in all proportions, and 1 volume in 200 of water. It evaporates very quickly, and leaves no residue. It is used in some varnishes.
Chlorophyll (Ger., Chlorophyll or Blattgriin; Fr., Chloro-phylle ; Ital., Clorofilla or Cromolo). This is the green colouring matter of plants and leaves, and is stated to be composed of two substances, phylloxanthine, of a yellow colour, and phyllo-