A Manual Of Photography

214 PRACTICE OF PHOTOGRAPHY. in warm water, but not warmer than may be borne by the finger ; this water is to be changed once or twice, and the pic- tures are then to be well drained, and either dried altogether, or pressed in clean and dry blotting-paper, to prepare them to imbibe a solution of the hyposulphite of soda, which may be made by dissolving an ounce of that salt in a quart of water. Having poured a little of the solution into a flat dish, the pictures are to be introduced one by one ; daylight will not now injure them : let them soak for two or three minutes, or even longer, if strongly printed, turning and moving them occasion- ally. The remaining unreduced salts of silver are thus thoroughly removed by soaking in water and pressing in clean blotting paper alternately ; but if time can be allowed, soaking in water alone will have the effect in twelve or twenty-four hours, according to the thickness of the paper. It is essential to the success of the fixing process, that the paper be in the first place thoroughly penetrated by the hyposulphite, and the sensitive matter dissolved ; and next, that the hyposulphite compounds be effectually removed. Unless these salts are completely washed out, they induce a destructive change upon the picture; they become opaque in the tissue of the paper, and unfit it for the operation of being copied. Being desirous, not merely of describing all those processes which have passed into common use, but those even which have been suggested merely upon the strength of a few experiments, where these appear likely to lead to any improved practice, under any circumstances, in the art, the following process of Reuben Phillips is introduced. Mr. Phillips found that the solvent power of any menstruum was increased by voltaic action. He therefore employed elec- trodes the size of the photographic picture to be fixed, and placing upon the under one a flannel wetted with the solvent— either common salt, ammonia, or hyposulphite of soda — he placed the impressed paper, wetted with the same solution, on it, and laid another wetted flannel upon it, covering the whole with the other electrode. Connection being made with a tolerably active battery, the metallic salt is rapidly removed to one pole, and thus the fixing process rendered comparatively short and easy, where a voltaic battery is at command. The hyposulphite of soda has been used for almost every photo- graphic process, from the facility it affords for removing the silver salts. The following is the process of Gustave le Gray, of Paris, which is valuable as being the directions of one who has produced most beautiful pictures: but it does not differ in any important particulars from the process already given :—