Suche löschen...
The photographic news
- Bandzählung
- 35.1891
- Erscheinungsdatum
- 1891
- Sprache
- Englisch
- Signatur
- F 135
- Vorlage
- Hochschule für Grafik und Buchkunst Leipzig
- Digitalisat
- Hochschule für Grafik und Buchkunst Leipzig
- Digitalisat
- SLUB Dresden
- Lizenz-/Rechtehinweis
- Public Domain Mark 1.0
- URN
- urn:nbn:de:bsz:14-db-id1780948042-189100009
- PURL
- http://digital.slub-dresden.de/id1780948042-18910000
- OAI-Identifier
- oai:de:slub-dresden:db:id-1780948042-18910000
- Sammlungen
- Fotografie
- LDP: Historische Bestände der Hochschule für Grafik und Buchkunst Leipzig
- Strukturtyp
- Band
- Parlamentsperiode
- -
- Wahlperiode
- -
- Bandzählung
- No. 1725, September 25, 1891
- Digitalisat
- SLUB Dresden
- Strukturtyp
- Ausgabe
- Parlamentsperiode
- -
- Wahlperiode
- -
-
Zeitschrift
The photographic news
-
Band
Band 35.1891
-
- Ausgabe Ausgabe 1
- Ausgabe Ausgabe 17
- Ausgabe Ausgabe 37
- Ausgabe Ausgabe 57
- Ausgabe Ausgabe 77
- Ausgabe Ausgabe 97
- Ausgabe Ausgabe 117
- Ausgabe Ausgabe 137
- Ausgabe Ausgabe 157
- Ausgabe Ausgabe 177
- Ausgabe Ausgabe 197
- Ausgabe Ausgabe 217
- Ausgabe Ausgabe 237
- Ausgabe Ausgabe 257
- Ausgabe Ausgabe 277
- Ausgabe Ausgabe -
- Ausgabe Ausgabe 313
- Ausgabe Ausgabe 329
- Ausgabe Ausgabe 345
- Ausgabe Ausgabe 361
- Ausgabe Ausgabe 377
- Ausgabe Ausgabe 393
- Ausgabe Ausgabe 409
- Ausgabe Ausgabe 425
- Ausgabe Ausgabe 441
- Ausgabe Ausgabe 457
- Ausgabe Ausgabe 473
- Ausgabe Ausgabe 489
- Ausgabe Ausgabe 505
- Ausgabe Ausgabe 521
- Ausgabe Ausgabe 537
- Ausgabe Ausgabe 553
- Ausgabe Ausgabe 569
- Ausgabe Ausgabe 585
- Ausgabe Ausgabe 601
- Ausgabe Ausgabe 617
- Ausgabe Ausgabe 633
- Ausgabe Ausgabe 649
- Ausgabe Ausgabe 665
- Ausgabe Ausgabe 681
- Ausgabe Ausgabe 697
- Ausgabe Ausgabe 713
- Ausgabe Ausgabe 729
- Ausgabe Ausgabe 745
- Ausgabe Ausgabe 761
- Ausgabe Ausgabe 777
- Ausgabe Ausgabe 793
- Ausgabe Ausgabe 809
- Ausgabe Ausgabe 825
- Ausgabe Ausgabe 841
- Ausgabe Ausgabe 857
- Ausgabe Ausgabe 873
-
Band
Band 35.1891
-
- Titel
- The photographic news
- Autor
- Links
- Downloads
- Einzelseite als Bild herunterladen (JPG)
-
Volltext Seite (XML)
September 25, 1891.] THE PHOTOGRAPHIC NEWS. 679 into their constituent molecules by appropriate treatment. But the “ photo-salt ” cannot be resolved by any such treat ment, since all solvents which dissolve the normal haloid appear to decompose the darkened product, leaving only a trace of metallic silver. On the other hand, metallic silver cannot be extracted from the “photo-salt ” by any of the ordi nary methods. In answer to the question which the inquiring student would naturally put, “ what is the photo-salt ?" it can only be said that these products must be regarded as indefinite mole cular compounds of the silver haloids with coloured unstable products of photo-chemical decomposition, the composition of the latter being as yet unknown. That the coloured products are unstable appears from the fact that they cannot exist apart from an excess of the normal haloid. In the same way that a solvent will take up a solid till the point of saturation is reached, so the silver haloid, on exposure to light, becomes decomposed up to a certain point—i.e., the point when the haloid is saturated with the coloured product of photo-decom position. Beyond this point the action of light produces no further effect unless a reducing agent is present capable of com bining with the liberated halogen as fast as the latter is liberated. It is advisable to let the student observe for himself that silver iodide prepared with excess of potassium iodide undergoes no change of colour on exposure to light, but that in the presence of silver nitrate or reducing agents, darkening occurs. Let him observe also that the darkened chloride yields no appre ciable quantity of silver to dilute nitric acid, but that in the pre sence of a strong reducing agent, even when the latter is gaseous, such as hydrogen, the reduction may proceed up to the complete liberation of the metallic silver. This last point can be demonstrated very conveniently by placing some finely- divided silver chloride (prepared by precipitation) into a glass tube through which a current of moist hydrogen is kept passing, the gas being made to bubble through a solution of silver nitrate containing free nitric acid. On exposing the contents of the tube for some time to strong light, silver chloride is precipitated from the solution of the nitrate, the chloride in the tube (which should be shaken from time to time in order to expose fresh portions) gradually becoming dark coloured. An equal quantity of the chloride may be exposed in air at the same time for comparison. The two lots of darkened chloride are then treated with equal quantities of dilute nitric acid, the clear solution filtered off, and the filtrates tested for silver. If the experiment has been properly conducted, the solution from the chloride darkened in hydrogen will be found to con tain distinct traces, while that from the chloride darkened in air will be free from silver. Having arrived at the conclusion that the silver haloids, when exposed to light under suitable conditions, lose a small quantity of their halogen, and become converted into coloured compounds, the course of instruction will here naturally diverge along two lines :— (1) The nature of the coloured product combined with the excess of unaltered haloid ; and— (2) The part played by the associated substance or sensitiser. With regard to the first, it must be pointed out that, although we have no positive information of a conclusive character, many views have been advanced which are more or less worthy of consideration ; and an excellent exercise in the use of scientific judgment might be given to the advanced student by sub mitting the current notions respecting the composition of these products, and requesting him to prepare a critical essay em bodying his own views. (To be continued.) Richmond Camera Club.—At the meeting on the 18th inst., a proposal to admit ladies to membership on certain conditions was adopted, subject to the approval of the forthcoming annual meeting ; and a circulating library was started. London and Provincial PHOTOGRAPHIC Association.— October 1st, “A Perfect Emulsion by a New Method ” ; demon strated by Mr. A. L. Henderson ; visitors invited. October 3rd, final outing of the season to Hampstead, in place of September 26th ; tea at “Bull and Bush,” 6.30. patent Intelligent. Applications for Letters Patent. 15,544. Alfred Morgan Gillham, Oak Lodge, Wellington Road, Wanstead, “Improvements in and in Connection with Cameras. ’ September 14th. 15,553. George Wilson Morgan, 30, Gladstone Place, Aber deen, “ Improved Movable Graduated Backgrounds for Portrait Photography.”—September 14th. 15,615. William Phillips Thompson, 6, Lord Street, Liverpool, “ Improvements relating to Photographic Apparatus or Devices for Automatically Registering and Indicating the Number of Exposures.” (Ellis Elmer Moore, United States.) —September 15 th. 15,657. Fox Shew and Lorenzo Henry, 23, Southampton Buildings, London, “Improvements in Photographic Cameras.”—September 15th. 15,700. Rose Mary Shawcross, 15, Water Street, Liverpool, “Improvements in and Connected with Sensitised Surfaced Paper, Woven or Tissue Fabrics, or other Material for the Production of Copies of Drawings, Designs, Pictures, Photo graphs, Writings, and the like, by the Action of Light.”— September l&th. 15,861. Thomas Rudolph Dallmeyer, 24, Southampton Buildings, London, “ Improvements in Photographic and Telescopic Apparatus.”—September 18th. 15,908. William Alfred Smith, 186, Fleet Street, London, “An Improved Photographic Shutter.”—September Ihth. Specifications Published. 5,860. April 11th, 1890.—“ Detective Cameras and Change- Boxes.” H. Ransom, 122, Newington Butts, London. The sensitised plates are placed in clip sheaths or backings, which are hinged to a cylinder within the camera. By rotat ing the cylinder from the outside, the plates are brought in succession to the focus, being there held between flexible guards and a stop. The cylinder is also arrested at this stage by a spring pawl, which engages a ratchet on the cylinder. The pawl is disengaged by a rod. The indicator numbers on the end of the cylinder are observed in succession through an aper ture in the camera. In a modification a segment of a cylinder replaces the cylinder. A disc shutter actuated by band gear ing is described. 6,028. April 21st, 1890. — “ Lenses.” P. Rudolph, Jena, Saxe-Weimar, Germany. The principal object in these lenses is to remove the indis tinctness of the marginal portions of the field. They consist mainly of dissymmetrical combinations of lenses, composed of two distinct systems of lenses cemented together. In one of the two distinct systems the positive number (the collecting lens) has a smaller, in the other system a greater, refractive index than the negative number (the dispersing lens) cemented thereto, and each system is in itself approximately achro matic. In one form of the lens the front combination is composed of a dispersing lens and a collecting lens, while the back combination is made up of a collecting lens and a dis persing lens. Tables giving the radii of curvature of the different lenses, and the refractive indices and relative dispersive power of the different kinds of glass to be used, are given in the specification. In another form of the lens the back combination consists of three lenses cemented together. 6,029. April 21st, 1890. — “Lenses.” E. Abbe and P. Rudolph, Jena, Saxe-Weimar, Germany. The combination consists of two single collecting lenses and a compound system consisting of three lenses cemented together, for correcting the spherical and chromatic aberration of the lens without perceptibly altering its focal length. Tables are given showing the radii of curvature of the lenses, and the refractive indices, and dispersive power of the glass to be used in particular cases. • PHOTOGRAPMIC Club.—Subject for Sept. 30th, “Mounting and Framing”; Oct. 7 th, “ The Influence of Development on the Colour of the Deposit.” Last outing of the season, Satur day, October 3rd, Hampstead ; tea at “ Bull and Bush ” at 6.
- Aktuelle Seite (TXT)
- METS Datei (XML)
- IIIF Manifest (JSON)