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Broken

printing, frame, bromide and silver

BROKEN NEOATIVE.—With a little care and trouble passable prints may be made from broken negatives if the glass only is cracked or broken. If the film is broken, however, it is almost useless to endeavor to hide the defect. Even with a cracked negative it is usually less trouble to make a new negative than to print from the broken one. As this is not always possible, however, it will be well to give the two methods of printing so as to partially hide the defect. First method—Place the negative and sensitized paper in the printing frame as usual. Lay or attach a piece of tissue paper over the back of the negative or glass of the printing frame, and lay the frame on a board suspended by the four corners to a roasting jack. The object of this is to keep the printing frame continually turning round during the printing operation. If a meat jack is not obtainable the ingenuity of the operator will easily suggest some similar arrange ment. Second method—Lay the printing frame in a narrow box about two feet deep, having its sides blackened. Next drop a piece of tissue paper or lay a piece of ground glass over the frame. By this means only direct light from above will attack the silver paper, no side light being admissible, so that the crack or line of break in the glass will not be so distinctly defined.

BROMIDE.—The principal bromides used in photography are potassium and ammonium bromides. Of these two, potassium bromide is the most suitable, owing to its stability.

Ammonium bromide is hygroscopic, and discolors under the action of light. Nearly all bromides contain a slight trace of chloride. If the quantity does not exceed z per cent., however, and soluble bromide be in excess of the silver, its presence in emulsions is of little consequence; but if the bromide and silver be used in exactly their combining proportions, or if silver be in excess, silver chloride will be formed.

To detect a bromide in the presence of an iodide or chloride, first add a small quantity of sulphuric acid to the solution, then starch paste, and lastly, a few drops of nitric acid. Next gradually drop in chlorine water until the blue color formed by the starch paste is destroyed, and continue the addition of the chlorine water until it is present in slight excess. Lastly shake up with chloroform. This will dissolve any bromine present, forming a yellow or yellowish-brown precipitate.