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The photographic news
- Bandzählung
- 6.1862
- Erscheinungsdatum
- 1862
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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. 203, Juny 25, 1862
- Digitalisat
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Zeitschrift
The photographic news
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Band 6.1862
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- Ausgabe Ausgabe 73
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- Register Index 619
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Band 6.1862
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3 in pho- ate years, dally pre- is strange micals it lend, only not B<® cal agents seems the dealers ol to prepan Amateurs at certais chemicils 1, in order of purity- establisk in ass'-* icturers d warrant the fl he solitaf by Mess- ne oft tense ligb g the B irpassed . Some' 4 are sho" er nub oromide is is a ve h,judgi0s itscolotf rofphol mmod"l rent so whentd have " paratioz, i collo ration P I aral very V/ ; cr ) st, a it beib sop® autif dy- b ceptb a. or " table 9 Is, sd®a it, plu, k, and if oft, ourc 2 gallpe 1edq thet stthelb he cot variebl 9 rema ew pr® y 0 1otos, , 0 pa •UIY 25,1862.] THE PHOTOGRAPHIC NEWS. 357 of a hitherto unused variety of tannin, when he can appear mpnnt as the discoverer of a new dry process. We may, perhaps, save much future discussion as to priority of dis covery, if we state that the tannin in general use is derived from the gall-nut, and is, therefore, known as gallo-tannic acid. . It is a pale, yellow crystalline body, soluble in water and dilute alcohol, but sparingly so in ether, it has decided acid reactions, reddening litmus paper, and dissolving carbon ates with effervescence. Its diluted aqueous solution slowly absorbs oxygen from the air, and is converted into gallic acid. Many salts, such as chloride of potassium and others, coagulate an aqueous solution of tannic acid. When sub jected to a temperature of about 620°, it is decomposed into Pyrogallic acid. The remaining chemicals in this case do not need detailed notice. They include a very nice sample of gallic acid, some sodio-chloride of platinum, ammonio- nitrate of silver in crystals, which have a suspiciously dark and fulminating appearance, the rather rare salt—chloride of lithium, and numerous other ordinary photographic chemicals. AWARDS OF JURORS IN CLASS XIII. [Wb here merely make such a selection of names in the class devoted to philosophical instruments as we think may be interesting to photographers, from having some connection, intimate or remote, with photography.] MEDAL. N’amt of Exhibitor. United Kingdom. Objects Awarded and Reasons jor the Award. Butters, T. E Mia, L. P. Chance, Brothers ... Dallmeyer, 3. It. Dancer, J. B Be la Rue, Grubb, T lighley, 8 "me and Thornthwaite "tretti and Zambra T Slyer, s. W., and Co. Smith, Beck, and Beck Wenham, F. It. Yoistlnder and Son ... Puboscq, L. J. Serrin, V. Robert, p. ... For his registering anemometer; and for the skilful execution of his photographs of the sun. For great excellence of workmanship of parallel glass for optical instruments. For his mercurial minimum thermometer and accuracy and excellence of construc tion of thermometers, &c. ... For improvements in dioptric lights and great excellence in optical glass. ... Equatorial telescopes. For his excellent . object glasses and equatorial mountings. ... For the general excellence of his microscopes and microscopic photographs. ... For the general excellence of his astronomical photographs. Large equatorial telescope. For general excellence ; with regard to his object glass no means of testing it has been afforded to the Jury. ... For students’ microscopes, combining cheap ness and good workmanship, and for excellence in other optical instruments. ... IIerapathites, and polarising apparatus. For general excellence. ... Meteorological instruments. For many im portant inventions and improvements, together with accuracy and excellence in objects exhibited. ... Microscopes and hand telescopes of large aperture. For great excellence of con struction. ... Conductors insulated with caoutchouc. For general excellence of manufacture. ... Microscopes and other optical instruments. For economy in the production of students’ binocular microscopes, and the excellence of their instruments generally. ... For improvements in his binocular micro scope. Austria. ... For general excellence in optical instru ments. France. ... Optical instruments for scientific researches. For great excellence. ... Self-regulating electric light. For novelty of construction and general excellence. Prussia. ... For the great skill displayed in the execu tion of his microscopic test lines. Aekland, w. HONOURABLE MENTION. United Kingdom. ... For the accurate construction of his straight line dividing engine. Name of Exhibitor. Buss. T. 0 Murray and Heath ... Reade, Rev. J. B. Objects Awarded and Reasons for the Award. ... For the accurate construction of his hydro meters. ... For good workmanship in his philosophical instruments. ... For novelty of construction in his hemi spherical condenser for microscopes.. STUDY OF THE WET COLLODION PROCESS. - BY E. REYNAUD.* 1 now proceed to study the cause of the failures that most frequently occur to the inexperienced operator, and by analyzing each in succession, determine their source, and the means of avoiding them. These failures may be classed as follows:— 1. Non-adherence of the collodion film, and cracking and scaling off while drying. 2. The formation of streaks, specks, &c. 3. Spots in the film produced during sensitizing. 4. The negative riddled with small holes produced during development, and also after intensifying and fixing. 5. A complete fogging of the picture. I will now proceed to examine each of these failures in succession, and determine as completely as possible their causes and remedy. 1. Non-adherence of the collodion film, and cracking and scaling ojf while drying. These two accidents often occur together, and are generally caused by imperfect cleaning of the glass plate; but they may be produced by another cause. Too large a proportion of iodine, for example, will destroy the adherence of a collo dion film. Examination of the negative will show whether it is to this excess of iodine, or to a bad cleaning of the plate, that this accident must be attributed. For, if the reverse of the image, that is, the side touching the glass plate is spotted with brilliant reductions of metallic silver, visible after the negative is fixed, we must attribute it to imperfect cleaning of the plate. The complete absence of these reductions, and the trans parency of the darkest portion of the picture vievted positively, indicate, on the contrary, sufficient cleanliness in the glass, and if, notwithstanding, the film does not adhere, if it allows the solutions to penetrate through it to the glass, this non-adherence must be attributed to the proportion of iodine in the collodion being too strong. It must be remarked in this place, that the quantity of iodine which the latter can contain with impunity depends on the thickness of the film, and, consequently, on the pro portion of pyroxylinc: the thinner the film, the less quan tity of iodine : it must be kept within the following limits:— Pyroxylinc 15 to 2 grains. Iodine ... 1'0 to 1'5 „ Mixture of ether and alcohol ... 100 „ The iodide of ammonium being that which, in equal weight, contains most iodine, must be employed in less pro portion.—1 grain to 100 of collodion is quite sufficient. The rapidity with which the collodion plate becomes tinted at the moment of immersion in the sensitizing bath, and the degree of opacity the film exhibits when the sen sitizing reaction is completed, appears, a priori, a certain means of recognizing the greater or lesser proportion of iodides contained in the collodion ; but these different phenomena being intimately allied to the state of the silver bath, and the nature of the iodides, we must examine these several questions, in order to arrive at a rational conclusion. The degree of concentration of the bath has a consider able influence upon the phenomenon of double decomposition, which, as we know, forms iodide of silver in the film ; thus, at the moment of the immersion of the plate, a certain * From the Mmiteur. Coatinucd from p. 332.
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