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The photographic news
- Bandzählung
- 29.1885
- Erscheinungsdatum
- 1885
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- Englisch
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- Hochschule für Grafik und Buchkunst Leipzig
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- Hochschule für Grafik und Buchkunst Leipzig
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- Bandzählung
- No. 1400, July 3, 1885
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The photographic news
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Band
Band 29.1885
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- Register Index III
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420 THE PHOTOGRAPHIC NEWS. LJOLY 3, 1885. tunity presented to them for experimenting in aeronautc photography. The balloon VEtoHe, with its spacious ca capable of accommodating some twenty occupants, make? periodical ascents from a small enclosure near the Ex hibition, under the direction of M. Toulet. On the occasion upon which we had the pleasure of accompanying the able aeronaut, the day, though somewhat sultry, war delightfully clear, and eminently suited for an aerial ex cursion. As we slowly rose, the Exhibition ground gradually became beautifully less, and long ere we arrived at the maximum height of 350 metres, the whole seen, appeared like one gigantic map. The view was bounded on the north by the town of Malines, on the south by the winding and placid river Scheldt, while on our west the town of Antwerp, with its charming boulevards and the lofty towers of Notre Dame, completed, perhaps, the most magnificent bird’s-eye view it has been our good fortune to witness. After a period of twenty minutes we slowly descended, and a large crowd of anxious friends and inquisi tive loungers gathered to meet us, and cheered lustily as we again reached n other earth. Whilst the balloon was made taut, M. Raynaud, a local photographer, secured a picture of the car and its occupants. ACTION OE COLOURED SUBSTANCES UPON THE COLOUR SENSITIVENESS OF BROMIDE OF SILVER IN GELA TINE. BY DR. J. M. EDER.* When an ordinary gelatino-bromide of silver plate is im mersed in a very weak—and best, in a somewhat acid alcoholic—solution of nitrate of silver, t and dried, its sensitiveness to white light is increased from twice to three times. In the sun’s spectrum this effect is first noticed in a general increase of sensitiveness. Upon more exact observation, it is found that the relative sensitiveness to the less refrangible rays is somewhat increased. An ammoniacal solution of nitrate of silver acts similarly, and the picture is somewhat stronger. Plates thus prepared, however, do not keep good for more than a day, and do not approach dyed plates in sensitiveness to coloured rays. If a gelatino-bromide of silver plate that has been dyed with eosine be treated with a dilute (best an alcoholic) solution of nitrate of silver, eosine silvert is formed by the excess of silver nitrate. Plates of this kind are then more sensitive to light generally, and, at the same time, relatively more sensitive to the yellow-green. Other dyestuffs behave similarly. When gelatino-bromide of silver plates are immersed for some minutes in dilute ammonia (10 per cent, of liquid ammonia iu water), and dried, they appear about twice as sensitive to white light as before, and yield very intense pictures. Towards the sun’s spectrum such plates display increased sensitiveness in the same proportion throughout, without any special increase to the less refrangible rays being observable. The blackening, however, becomes very intense in the whole of the spectrum image. If a sensi tizing dyestuff be added to the dilute ammonia, the sensi tized band also becomes stronger. The action of the ammonia, which is entirely driven off by drying, can only be attributed to a molecular change in the bromide of silver, which influences powerfully the sensitiveness of the compound, as I have already shown in a former treatise. A solution of bromide of silver in ammonia deposits by evaporation microscopic crystals, as has been shown by Elsden.2 These are also formed by precipitation of bro- • Continual from page 357. + 100 cub. cents, of alcohol, and from 01 to 0 5 oub. cents, of a ten per cent, solution of nitrate of silver in water. + Eosine silver is itself, according to F. W. Vogel, sensitive to yellow’ (from D towards the green). This was first published by Robert Amory, in the American Academy, in January, 1878. 2 Photographic News, 1881, p. 174, I mide of silver in the presence of much ammonia. They take, according to the concenration of the solution, forms seen in fig. 11a,* or fig. 11bt, and range from a diameter a A©(O//C b Fiy. 11.—CRYSTALLIZATION OF SILVER BROMIDE WITH AMMONIA IN THE MICROSCOPE. of 0-02 to 0 2 m.m., and have a thickness of about 0001 m.m.. Such large crystals as these are not formed by immersing gelatino-bromide of silver in dilute ammonia, but by the evaporation of the ammonia from the wet plate; the bromide of silver doubtless becomes crystalline, and this may cause the increase of sensitiveness. Caustic and carbonated alkalies also increase sensitiveness by acting as bsorbents of bromine. Researches into the Chemical Condition of Bromide of Silver Mixed with Dye-stuff and Gelatine. For the estimation of the phenomena exhibited by dyed and undyed bromide of silver in the solar spectrum, as well as of the part played in this connection by gelatine, 'he decision of the following question is of importance: “ Does bromide of silver combine with these substances, or not? ” Here the same conditions must be observed as in the preparation of a sensitive bromide of silver emulsion. When bromide of silver gelatine emulsion, prepared in the usual manner, is washed, and then, whilst in a liquid state, submitted to the action of a centrifugal machine, the bro mide of silver can be separated from the gelatine. Mr. J. Plener has constructed a machine for the purifi cation for photographic purposes of bromide of silver, and kindly placed it at my disposal for the purpose of these investigations. Fig. 12 shows a vessel of gun-metal well c Fly. 12.—CENTRIFUGAL APPARATUS FOR THE SEPARATION OF BROMIDE OF SILVER FROM EMULSION. gilt upon the inner surface. Liquid emulsion being placed in this vessel, it is closed at C, and fixed upon a vertical axis, which is then caused to revolve with a speed of from 4,000 to 0,000 revolutions per minute. AU the silver bro mide is, by the action of centrifugal force, driven to the side of the vessel, and there forms a compact mass from which the gelatine solution can be poured off clear, and the bromide of silver washed free from gelatine.! Bromide of silver that has been, by repeated separations iu the centrifugal machine, and washings with hot water, completely freed from all soluble substances, contains, according to my analysis, after drying at 150° C., whereby much hygroscopic water is driven off, some organic matter. Ibis is estimated by heating to redness, and re-converting the resulting silver into bromile with bromine. lOOparts * By evaporation of a concentrated ammoniacal solution of bromide of silver after dilution with five parts of water. + Like the foregoing, after dilution with an equal quantity of water. t By treatment with a fresh solution of gelatine it becomes immediately divided into a fine emulsion of excellent photographic properties.
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