ALBUMEN (Fr., Albumins; Ger., Albumen) A very complex organic compound containing carbon, hydrogen, oxygen, and sulphur, which occurs both in the animal and vegetable kingdom. Animal albumen exists as the serum or white fluid of blood, but photographically the white of eggs is the only animal albumen used. To prepare it for photographic purposes the whites of eggs should be separated from the yolks and the germ, and thoroughly beaten to a froth, allowed to settle for twelve or twenty-four hours, and then filtered. Actually, the albumen is contained in minute cells, and the beating has the purpose of breaking the cell walls, which subsequently form the flocks or scum.
Albumen is coagulated by heat (i5o° F. or 65.5° C.), by alcohol, and most metallic and inorganic salts, the resultant precipitate with the latter being albumenates. It is an almost colourless, gummy liquid, which dries to a pale yellow solid. Seventy grains of the dried egg albumen dissolved in one fluid ounce of distilled water forms a solution equal to the fresh white of egg. The solution is extremely liable to decomposition, and should be either freshly pre pared or preserved with an antiseptic. It is used for albumenised paper, the albumen nega tive, beer, and positive processes.
Invert albumen is obtained from ordinary albumen by first treating with acid and then with alkali, by which treatment it is so altered in character that it becomes soluble in alcohol.
The following process has been suggested by Sanger Shepherd : White of eggs . 20 oz. I ,000 ccs.
Glacial acetic acid . 48 mins. 16.5 „ Beat up thoroughly, and allow to stand for one hour, then add a 20 per cent. solution of sodium hydrate drop by drop with constant stirring till the mixture thickens ; next allow to stand for one hour, break up into small pieces, and wash (see " Emulsion "), drain well, and dissolve in boiling alcohol. Invert albumen gives an extremely tough, structureless film, and was suggested for making colour filters.
In process work, albumen is used as a sub stratum, or for edging the glass plates in making wet plate negatives. Also, it is almost univers ally employed with potassium bichromate for sensitising the zinc plate for photo-etching. Albumen is also often mixed with fish-glue in making up the enamel solution for printing on zinc or copper from half-tone negatives. Dried albumen is frequently employed in preference to the liquid white of eggs. Varying opinions are expressed as to the quantity of dried albumen required to equal the albumen of one egg, but yo grs. to i oz. of water may be taken as a safe standard.