ALBUMEN. This, in photography, means the white of an egg, which is a pure form of it. It is used on paper for both negatives and positives, and on glass for negatives and dia-positives, as a vehicle for the sensitive silver salts. For negatives on paper, albu men is not often used, for the same reason that collodion negatives are seldom transferred to paper ; that is, because the advantages of the albumen and, collodion are then partly lost. It is not so sensitive as collodion, from its more horny nature and its being dry ; hut, for the same reasons, it will keep longer when sensitized. From its entering into combination with nitrate of silver, it gives a blacker image than collodion or gelatine, and one more inclined to become yellow : the image, from its organic character, is also more soluble in hypo and other solvents of the silver salts, and is there fore reddened and weakened more in fixing. The blackness of the image makes it the best material for transparencies on glass ; but its tendency in negatives is to give hard cutting pictures, and it is more troublesome than collodion in the manipulation. When applied to paper for printing, it gives the power of rendering the details of the negative with extreme sharpness and great transparency in the shadows ; but the smoothness is scarcely artistic; and when the glazed surface is perceived by the eye, it becomes offensive. That veil which sometimes covers pictures on plain paper is never seen on albumen ; but, on the other hand, plain paper gives good tones with greater ease and certainty.
Albumen retards the action in the camera or printing-frame, but increases the beauty and vigour of the image. It combines, like .other forms of organic matter, with bases and basic salts, which are then called albuminates. Thus, in the paper processes it unites with and is coagulated and rendered insoluble by the N. S., and the surface becomes a layer of chloride and albuminate of silver, which does not require any application of heat, as some suppose. It is this combi nation chemically with the silver salt which reddens the tone of the reduced silver; for those organic matters which have no combining have also no colorific power.
Albumen is, before coagulation, soluble in water, and is most fre quently more or less diluted with water in all the processes, to increase its fluidity. The entire destruction of the minute membra nous cells in which it exists in the egg, either by mechanical violence, as in whipping it, or by the addition of a small portion of alkali, which dissolves them, is necessary to the obtaining of a uniformly clean layer, and the alkalinity may be neutralized after the application of it, to the glass or paper, by acetic acid in the excit ing solution.