A Manual Of Photography

84 HISTORY OF PHOTOGRAPHY. ing them over with a solution formed of one drachm of the ferro- cyanate of potash to an ounce of water. These papers, washed with the ferrocyanate, and dried in the dark, are, in this dry state, absolutely insensible, but they may at any moment be rendered sensitive by merely washing them with a little cold clean water. Papers thus prepared are rendered quite insensible by being washed over with the above hydriodic solution. They are, how- ever, best secured against the action of time by a solution of ammonia. The yellow colour of the paper militates against its being used as the original from which copies may be taken; but even this colour may be removed by employing hot hyposulphite of soda. Upon paper thus prepared the curious result of an impressed coloured spectrum was first obtained. Section V.—The Fluorotype, So called from the introduction of the salts of fluoric acid, con- sists of the following process of manipulation : — f Bromide of potassium, 20 grains. [Distilled water 1 fluid ounce. [Fluoride of sodium . . 5 grains. [Distilled water ... 1 fluid ounce. Mix a small quantity of these solutions together when the papers are to be prepared, and wash them once over with the mixture, and, when dry, apply a solution of nitrate of silver, sixty grains to the ounce of water. These papers keep for some weeks without injury, and become impressed with good images in half a minute in the camera. The impression is not suffi- ciently strong when removed from the camera for producing positive pictures, but may be rendered so by a secondary process. The photograph should first be soaked in water for a few minutes, and then placed upon a slab of porcelain, and a weak solution of tire proto-sulphate of iron brushed over it ; the picture almost immediately acquires an intense colour, which should then be stopped directly by plunging it into water slightly acidulated with muriatic acid, or the blackening will extend all over the paper. It may be fixed by being soaked in water, and then dipped into a solution of hypo-sulphite of soda, and again soaked in water as in the other processes. Mr. Bingham has the following remarks on tins process, and he gives a modified form, into which a new photographic element is introduced.