The Dictionary Of Photography

A True Historic Record Of The Art & Practice Of Photography 100 Years Ago.

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perfectly dry. In no case should the box be opened till a reason-able time has elapsed, or else peculiar markings will be caused, due to unequal drying. When the calcium choride has once been used, it should be heated in an oven till it swells up and becomes perfectly dry. The disadvantage of drying by air alone is that the rate of drying is proportionate to the amount of moisture in the air, and that the unequal drying caused by a fall in tempera-ture may give rise to marks which are absolutely irremovable and show in the finished negative. To enter into all details of emulsion making would fill the greater part of the Dictionary ; but we may give reference to a few sources of information which may prove useful to any readers who may wish to break new ground, or to thoroughly study past investigations. Perhaps the most valuable and suggestive information is that contained in a volume (the fourth edition) of the late Dr. H. W. Vogel's comprehensive handbook of photography, which volume was published shortly before the death of that distinguished investi-gator (" Handbuch der Photographie," von Dr. H. W. Vogel, III. Theil, Abtheilung I., Vierte Auflage, 308 large octavo pages, Berlin, 1897, Gustav Schmidt). In this volume there is an account of the author's experiments on combined collodion and gelatine emulsion, experiments which are not unlikely to fructify some day, and here will be found much that is important in connection with orthochromatic plates. Other works which may be mentioned as likely to furnish valuable hints on collodion and gelatine emulsion are the following : - " Photographie mit Bromsilber-Gelatine," von David und Scolik, 148 pp.: Wien, 1885, Hartleben; " The Model Dry Plate Maker," by Abel M'Donald, 56 pp., price is.: Penrith, published by the author, Station Road; u Die Brom-silber Gelatine," von Dr. Paul E. Liesegang, various editions (1st 1882, 6th, 198 pp., 1889): Diisseldorf, Ed.Liesegang's Verlag; " Die Photographie mit Brom-silber Gelatine," von David & Scolik, Band I. (containing pre-paration of emulsion), 254 large octavo pages: Halle, 1889, Knapp. This work is far more than a new edition of that by the same author which is mentioned above. " Die Collodium Emulsion," von F. Von Hubl, 144 pp.: Halle, 1894, Knapp; "Photographie par Emulsion Seche," par A. Chardon, 70 pp.: Paris, 1877, Gauthier Villars; "The Practical Working of the Gelatine Process," by W. de W. Abney, 82 pp.: London, 1880, Piper & Carter;