A Manual Of Photography

PRACTICE OP PHOTOGRAPHY. 292 then add another fluid ounce and a half of water. It is now a so- lution of hydriodic acid and phosphoric acid. By adding carbona of barytes to it, a phosphate of barytes is formed, which being insoluble falls to the bottom, whilst the soluble hydriodate or barytes remains dissolved. Make up the quantity of the solution to nine ounces with distilled water, and carefully presene it in a1633 ^ ^° camera obscura. With a very soft flat brush apply the hyfe odic solution on both sides of the prepared paper, .untilit appears equally absorbed ; place it in close contact with the ^ect to be copied, and expose it to sunshine. The exposure so continue until the parts of the paper exposed to uninterrupted light, which first change to a pale yellow, are seen to row little The observance of this simple rule will be found of y great advantage in practice. Immersion for -*" water removes the brown hue, and renders the bright parts o the picture clearer than they would otherwise have been Engravings to be copied by this process,—which they are most beautifully,—should be soaked in water and ^perimposed on the photographie papers quite wet. Il the M^smt dd to be used in the camera, it is best to soak it m the tounoam solution until a slight change is apparent, from ehemcal actio on the silver: it is then to be stretched on a slight frame of wood which is made to fit the camera, and not allowed to touch in any part but at the edges ; placed in the dark chamber of the camera at the proper focus, and pointed to the object of whicha cony is required, which with good sunshine is effected in about twenty minutes, varying of course with the degree of sensibility manifested bv the paper. If the wetted paper is placed upon ™y powus body, itU be found, owing to the capillary com- munication established between different points, that the Solution is removed from some parts to others, and different states of sensitiveness induced. Another advantage of the frame is the paper being by the moisture rendered semi-transparent, the light1 penetrates and acts to a greater depth ; thus cutting out fine lines which would otherwise be lost. However, if the camera is large, there is an objection to the frame ; the solution is apt to gather into drops, and act intensely on small spots, to the miury of the general effect. When using a large sheet, the safest course is to spread it out when wetted upon a piece of glals are in close® contact. The picture is not so slightly retarded. The adm-