COLLODION-ALBUMEN EMULSION.—A collodio-albumen emulsion. A process intro duced by Captain Abney, and thus described by him. The following is the mode of preparation: Sixteen grains of ordinary cotton are dissolved in 6 drachms of ether (.730) and 4 of alcohol (.805), and the plain collodion thus formed decanted. Twenty grains of zinc bromide are dis solved in a small quantity of alcohol, and enough bromine water added to tinge the solution with a pale yellow. This is added to the above amount of plain collodion. To each half-ounce of the above, one grain of dried albumen is taken and dissolved in the least possible quantity of water, or eight drops of the white of an egg may be dropped into a drachm of alcohol and thoroughly stirred. Either of these solutions is then carefully dropped into the collodion, placed in a jar, and well stirred up. This should form an emulsion of albumen in the collodion. Forty grains of silver nitrate are next added, after having been dissolved in the smallest possible quantity of water and boiling alcohol. A beautifully smooth emulsion should result from this. The amount of silver nitrate added ensures that there is an excess of at least two grains in each ounce of the emulsion. Instead of the emulsion being made entirely of zinc bromide, greater density can be obtained by omitting four grains of it and replacing this by four grains of calcium chloride. The
emulsion is next poured into a dish= andthe ordinary manipulation carried out.
After a couple of washings it may be advantageously covered with a weak solution of silver nitrate, and again washed till the traces of silver are very faint. The pellicle should be redissolved in equal quantities of ether and alcohol, and finally there should be about seven grains of the pyroxyline as originally used to each ounce of the mixed solvents. The emulsion when finished gives a tender blue by transmitted light, and is seemingly transparent. It may have a tendency to curl off the plate on drying, in which case the addition of a little ordinary washed emulsion will correct it. It will develop with plain pyrogallic acid, and can be intensified by pyrogallic and citric acid, with the addition of a few drops of silver nitrate solution, or it can be developed with the alkaline developer, the ferrous oxalate developer, or the hydrosulphite devel oper. If the developer be kept above a temperature of 6o deg. Fahr., the tendency to blister will be prevented.
The image obtained by this process is usually very delicate and thin, and the exposure required is a little less than for an ordinary wet plate.