Sen′si-tizing.
（Photography.) Applied to paper or to films. The production on or in a surface or film of an insoluble salt of silver, generally chloride, iodide, or bromide of silver, which, under the actinic action of light, becomes colorably changed, or experiences such a change in its molecular constitution that, by a subsequent process of development, colorable changes are made to appear. In the former case, the image is at once apparent; in the latter, it is latent till the subsequent process has taken place. The process generally depends upon a double decomposition. For instance, paper charged with chloride of sodium being floated upon a solution of nitrate of silver, a film of chloride of silver, plus an excess of nitrate of silver, is formed upon the paper, the metal sodium uniting with nitric acid and passing into the bath. Or, in the case of the collodion film upon glass, the glass is floated with collodion containing bromides and iodides of the alkaline metals in solution, and the collodion “sets” upon the glass as a gelatinous film. It is then plunged into a bath of nitrate of silver, when a similar decomposition takes place, resulting in the production of insoluble bromides and iodides of silver, which become entangled in the film, while [2094] the nitrates of the alkaline metals pass into the bath. The collodion film thus prepared is sensitive to light. There are two exceptions where the double decomposition does not take place:— 1. In daguerreotyping. The production of a sensitive surface upon the plate by the action of the free vapors of iodine or bromine upon the surface of a clean metallic silver plate. 2. In the sensitizing of organic matter, such as gelatine, albumen, or gum, by the direct addition of salts of chromium, usually bichromate of potash.
