A Manual Of Photography

DR. SCHAFHAEUTL’S PROCESS ON CARBONISED PLATES. 9/ drachms of distilled water), by merely drawing the paper over the surface of the solution contained in a large dish. In order to convert this nitrate into a chloride, the author exposed it to the vapours of boiling muriatic acid. A coating of a chloride of silver, shining with a peculiar silky lustre, was by this me- thod generated on the surface of the paper, without penetrating into its mass ; and in order to give to this coating of chloride the highest degree of sensibility, it was dried, and then drawn over the surface of the solution of nitrate of silver again. 2 ci having been dried, the paper was ready for use, and by no repe- tition of this treatment could its sensitiveness be improved. Even on the ordinary kinds of writing paper, I have found this manipulation produce extreme sensitiveness, but much exact attention is required to prevent any excess of muria ic acid, which, in the state of vapour, is rapidly absorbed by the paper. The whole of the nitrate of silver employed in the first instance must be converted into a muriate, and there the pro- cess should stop. . .. 1 1-IY» u „ Schafhaeutl’s method of fang is extremely difficult, lie drawing is to be steeped for five or ten minutes in alcohol and after removing all superfluous moisture by means of ok g paper, and drying it slightly before the fire the paper thus pre- pared is drawn through diluted muriatic acid, mixed with a few drops of an acid nitrate of quicksilver, prepared by dissolving quicksilver in pure nitric acid, and again dissolving the crystal- lised salt to saturation in water acidulated with nitric acid. The addition of the nitrate of mercury requires great caution, and its proper action must be tried first on slips of paper, upon which have been produced different tints and shadows y ex posure to light ; because, if added in too great a quantity, tue lightest shades entirely disappear. The paper having been drawn through the above-mentioned solution, is well washed in water, and then dried in a degree of heat approaching to about 158° Fahr., or, in fact, till the white places assume a very slight tinge of yellow. The appearance of this tint indicates that the drawing is fixed permanently. Section XI —Dr. Schafhaeutl’s Process on Carbonised PLATES. Metallic plates are covered with a layer of hydruret of carbon, prepared by dissolving pitch in alcohol, and collecting the resi- duum on a filter. This, when well washed, is spread as equally as possible over a heated even plate of copper. The plate is II