DRY PROCESS, in photography. Reference, to the article COLLODIONIZED PAPER PROCESS will show that the collodionized glass-plate, on being withdrawn from the bath, previous to, and during exposure in the camera, has mechanically adhering to its surface a quantity of solution of free nitrate of silver, and it is partly upon the presence of this salt that the extreme sensitiveness of wet collodion plates depends. This, how ever, is not the sole cause of sensibility to actinic rays; carefully conducted experiments fairly lead to the assumption, that the molecular arrangement of the ultimate particles of iodide of silver, and of the pyroxyline, forming, as it were, the network of the film while wet, materially affect this necessary condition; and it is the object of what is termed a dry process to preserve this molecular arrangement as far as possible unaltered, notwithstanding the disturbing influence which would necessarily be exerted by the desiccation of the film. This desirable end for traveling photographers is accomplished with more or less certainty by the employment of solutions of various substances, which are poured over the film after the adhering nitrate of silver has been removed by copious washing with water. The heterogeneous character of the substances so used
goes far to prove that their action is principally mechanical, they being selected from the animal, vegetable, and mineral kingdoms. Among the first may be mentioned honey, gelatine, glycerine, milk, and albumen; among the second, syrups, gum, wine, beer, balsams, and resins added to the collodion, and linseed tea; and among the third, chloride of calcium, nitrate of zinc, and nitrate of magesia. The plate, on its removal from the sensitizing bath, being well washed with water, any one of these substances is dissolved in water in suitable proportion, and applied to the surface of the plate by pour ing on and off several times. It is then set up to drain and dry on folds of bibulous paper in a dark closet or box. The plate is then ready for use. The pictures obtained on plates so prepared do not suffer by comparison with those taken by the collodion process; the only drawback to their use being a slight diminntion in the degree of sensi bility to light.