American Hand Book of the Daguerrotype by S. D. (Samuel Dwight) Humphrey
page 60 of 162 (37%)
page 60 of 162 (37%)
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The various colors produced are owing to the thickness of the coating,
and the maximum sensibility of the coating, as generally adopted, is when it assumes a deep yellow, or slightly tinged with rose color. This compound is largely employed in most photographic processes on paper, and may be easily prepared by the following formula: By adding iodide of potassium to a solution of nitrate of silver, a yellowish-white precipitate of iodide of silver is obtained, which is insoluble in water, slightly soluble in nitric acid, and soluble in a small degree in ammonia, which properties seem easily to distinguish it from the chloride and bromide of silver. Chlorine decomposes it and sets the iodine free, and chlorohydric acid converts it into a chloride. It fuses below a red heat. Although the effect of light on the iodide is less rapid than on the chloride, the former sooner turning black, assuming a brown tinge; but when in connection with gallic acid and the ferrocyanate of potash, it forms two of the most sensitive processes on paper. Iodide of silver dissolves easily in a solution of iodide of potassium, and the liquid deposits in evaporation crystals of a double iodide. Iodide of Gold.--If a solution of potassium be added to a solution of chloride of gold, a precipitate of iodide of gold takes place, soluble in an excess of the precipitate. A little free potash should be added to combine with any iodide that may chance to be set free by the chloride of gold. Iodide of Lime is prepared by adding iodine to hydrate of lime (which will be referred to farther on) until the mixture assumes a light yellow shade, when wanted for combinations with accelerators, |
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