A Manual Of Photography

PRACTICE OF PHOTOGRAPHY. 290 removed from the paper. When the weaker solution of lead has been used, instead of the formation of an iodide the hydriodate exerts one of its peculiar functions in producing an oxide of the metal. . Muriate and Nitrate of Copper.—These salts, in any quant■ render the action of the hydriodates very quick ; and ^used in moderate proportions, they appeared to promise at first much assistance in quickening the process I have obtained ,wth papers into the preparation of which nitrate of copper has entered perfect camera views in ten minutes ; but experience has proved their inapplicability, the edges of the parts in shadow being destroyed by chemical action.,, oLn«..r ««M ...... Platinum act S1m?larly to each other They remain inactive until the picture is formed; then a rapid oxidation of these metals takes place, and all the bright parts of the picture are darkened. _, An extensive variety of preparations, metallic was used with like effects, and I am convinced that the only plan of obtaining a perfectly equal surface, Without impairs the sensitiveness of the paper, is careful manipulation with the ordinary muriates and silver solutions. which are Bv attention to the directions given at page 88, which are simple in their character, but arrived at by a long series of inquiries, any one may prepare photographic papers on w ie the hydriodic solutions shall act with perfect uniforml y. Hydriodates of Potash and Soda.—The former of these sas being more easily procured than any of the hydriodates, is the one generally employed. The strength of the solution of these salts best adapted for the general kinds of paper is thirty grains to an ounce of water. The following resu is will exhibit the different energies manifested by these solutions at severa strengths, as tried on the same paper by the same light: 120 grains of the salt to an ounce of i vater took) 12 minutes. 100 80 60 40 30 20 10 to whiten the paper do. do. do. do. do. do. do. do. do. do. do. do. do. do. to to to to to to to do. do. do. do. do. do. do. 10 9 7 6 4 6 12 do. do. do. do. do. do. do. The other hydriodic salts correspond nearly with these in their action ; a certain point of dilution being necessary with all.