A Manual Of Photography

FIXING THE DAGUERREOTYPE IMAGE. 251 into the air through proper ventilators, and the operator is thus protected from the injurious effects of the mercury. Section V.—FIXING the Daguerreotype Image. It lias already been stated that the solution of hyposulphite of soda is the most effective agent for removing all the unchanged iodide of silver, after the application of, and the development of the image by, the mercurial vapour. This being effected, greater permanence is given by the appli- cation of a solution of gold. The process, as described by M. Fizeau, to whom we are in- debted for its introduction, is as follows : — “ Dissolve eight grains of chloride of gold in sixteen ounces of water, and thirty-two grains of hyposulphite of soda in four ounces of water : pour the solution of gold into that of the soda, a little by little, agitating between each addition. The mixture, at first slightly yellow, becomes afterwards perfectly limpid. This liquid now contains a double hyposulphite of soda and gold. " To use this salt of gold, the surface of the plate should be per- fectly free from any foreign substance, especially dust ; conse- quentlv it ought to be washed with some precautions which might be neglected if it was tobe finishedby the ordinary mode of washing. “ The following manner generally succeeds the best : the plate being yet iodized, and perfectly free from grease on its two sur- faces and sides, should have some drops of alcohol poured on the iodized surface ; when the alcohol has wetted all the surface, plunge the plate into a basin of water, and after that into a solu- tion of hyposulphite of soda. “ Tins solution ought to be changed for eacli experiment, and to consist of about one part of the salt to fifteen of the water : the rest of the washing is done in the ordinary way, only taking care that the water should be as free as possible from dust. “The use of the alcohol is simply to make the water adhere perfectly all over the surface of the plate, and prevent it from quitting the sides at eacli separate immersion, which would in- fallibly produce stains. “When a picture has been washed, with these precautions, the treatment with the salt of gold is very simple. , It is sufficient to place the plate on a support, fig. 64, or fig. 66, y, and pour upon its surface a sufficient quantity of the salt of gold that it may be entirely covered, and heat it with a strong spirit-lamp; the picture will be seen to brighten, and become, in a minute