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The photographic news
- Bandzählung
- 27.1883
- Erscheinungsdatum
- 1883
- Sprache
- Englisch
- Signatur
- F 135
- Vorlage
- Hochschule für Grafik und Buchkunst Leipzig
- Digitalisat
- Hochschule für Grafik und Buchkunst Leipzig
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- SLUB Dresden
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- Public Domain Mark 1.0
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- urn:nbn:de:bsz:14-db-id1780948042-188300004
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- http://digital.slub-dresden.de/id1780948042-18830000
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- oai:de:slub-dresden:db:id-1780948042-18830000
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- LDP: Historische Bestände der Hochschule für Grafik und Buchkunst Leipzig
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- Parlamentsperiode
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- Bandzählung
- No. 1271, January 12, 1883
- Digitalisat
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Zeitschrift
The photographic news
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Band
Band 27.1883
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- Titelblatt Titelblatt I
- Register Index III
- Ausgabe Ausgabe 1
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- Ausgabe Ausgabe 817
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Band
Band 27.1883
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- Titel
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washed in a revolving cylinder apparatus with plenty of cold water, and afterwards exposed to the fames of burning sulphur in a wooden chamber. They are now squeegeed to expel the moisture, and finally converted into soluble gelatine by water in earthen vessels, enclosed in steam cases. The fluid gelatine is purified by straining it at a temperature of 100° or 120° F., allowed to set in thin sheets, and dried on nets. Properties.—Pure gelatine is a neutral transparent solid, without taste or smell. At the ordinary temperature it is somewhat soft and flexible, and contains from 15 to 20 per cent, of water. Dried over the water bath, it becomes hard and brittle, and may be powdered in a mortar. Immersed in cold water it swells up, absorbing a large quantity—from five to ten times it weight (Abney)—of water, and becoming very soft and flexible; it does not, however, dissolve. The swelled gelatine heated to about blood heat, 90° F., melts into a transparent liquid. On cooling this liquid again to about 70° F., it solidifies or sets into a tremulous jelly. The quantity of gelatine compared with water required to solidify in this way varies considerably with different samples, but is usually very small. A quarter of an ounce of a good sample will set with no less than a pint (20 ozs.) of water. Asa rule, 5 per cent, or one ounce of gelatine to the pint of water is a fair quantity to employ to form a firm jelly. The addition of a smallquantity of alum, or a still smaller quantity of chrome alum, hardens gelatine, and raises its setting and melting points. A solution of gelatine, by continued boiling or frequent setting and re-heating, undergoes a change in properties so that it refuses to set when cold, and dissolves readily in cold water. Free acids and alkalies, ammonia and ammonium salts, such as ammonium bromide and nitrate, greatly accelerate this change. In contact with water, gelatine putrefies in a few days, first becoming acid, and then strongly alkaline, with evolu tion of ammonia. The time taken for this putrefaction varies considerably according to the weather, the occur rence of a thunder storm frequently setting up very rapid putrefaction. Thymol, salycilic acid, carbolic acid, acetic acid, alcohol, alum, and some other substances, if added to gelatine, retard or prevent this decomposition. Dissolved in dilute hydrochloric acid, and dialysed, a solution of gelatine is obtained which does not putrefy (Graham). Chlorine, bromine, and iodine combine with gelatine. If chlorine or bromine be added to a solution of gelatine in excess, a precipitate is thrown down, insoluble in water ; if, however, the gelatine remain in excess, the free halogens disappear, but no precipitate occurs. Iodine combines with, but does not readily precipitate, gelatine. Many other powerful oxidizing agents, such as chromic acid, car bolic acid, &c., also precipitate gelatine if added in excess. Alcohol also precipitates gelatine by extraction of the water. Silver nitrate, if kept for any time in contact with a solution of gelatine, especially if the temperature be high, combines with it, the gelatine gradually assuming a reddish tinge, and the resulting compound is not decomposed by soluble bromides unless the solution be boiled. Gelatine is readily soluble in dilute acid or alkaline solutions, also readily soluble by the aid of the heat in glycerine and anhydrous acetic acid. Insoluble in alcohol, ether, and other spirituous liquids; soluble, however, in weak alcohol with the aid of acetic or other acid. Commercial Gelatines.—The best of commercial gelatines are anything but pure products, and vary very much in quality. They all contain more or less dirt or insoluble matter; some contain free acid, others free alkali ; some are practically colourless, others strongly coloured; some are very soft, others very hard; some contain grease, and others a quantity of sulphur. They also vary in other respects which are not so readily detected unless a trial emulsion be made. METHODS OF PURIFYING AND REMOVING SOLUBLE MATTER, GREASE, ETC., FROM GELATINE FOR EMULSION PROCESSES. A. Dirt and Insoluble Matter.—If the gelatine be not already acid, the addition of a small quantity usually dis solves up a large portion of the insoluble matter. The larger particles can be removed by straining through fine flannel several times. It is entirely removed by the follow ing method :—Soak the gelatine in water and liquefy it. For every ounce weight of gelatiue take the white of one egg, well beaten up, and thoroughly incorporate with the former at a moderate temperature ; this is best done in a deep beaker. Now place in a bath consisting of a satu rated solution of calcium chloride or sodium sulphate, and heat until the gelatine solution boils ; simmer for a minute or two, and, while still hot, strain through fine flannel. The albumen of the egg, in coagulating, imprisons the insoluble matter, and when the gelatine boils, rises in a scum to the surface, leaving a perfectly transparent solu tion. B. Removal of Soluble Matter, Grease, ^c.—Add methy lated alcohol to the liquid gelatine, stirring during the operation until the whole of the gelatine is precipitated ; pour off the liquid containing the impurities, and add a little more alcohol to remove the last traces. Break up the precipitated clot into small pieces, and allow to swell in clean water. The albumen method also removes every trace of grease. PHOTOGRAPHIC EXHIBITION IN BRUSSELS. Rules of the International Photographic Exhibition, to take Place in Brussels in 1883. The Belgian Association of Photography will organise, in the galleries of the Palais des Beaux Arts, Brussels, the second public exhibition of works appertaining to all branches of the art. All photographers, amateur or professional, and instru ment manufacturers—Belgian and foreigners—are invited to contribute, and are requested to note the following rules and conditions adopted by the committee of administra tion at the meeting on October 10 th, 1882. 1. The exhibition will take place in the Palais des Beaux Arts on the 15th August next, and will close on the 1st of October. 2. All intending exhibitors are requested to notify their intention to the Secretary of the Association as soon as possible, and before June 1st. They are at the same time to state what amount of space will be required, following the conditions indicated below. 3. All exhibits should be addressed, carriage paid, to Mons. A. Geruzet, Secretary to the Association, Palais des Beaux Arts, Rue de la Regence, and sent in between July 15th and August 1st. 4. The exhibits must be accompanied by a letter giving the number of objects sent, and signed by the exhibitor. 5. Exhibitors are recommended to protect their works by frames or passepartouts. In order to avoid breakage and the difficulty of transport which frames occasion to foreign exhibitors, the committee recommend them to send their prints to any correspon dent in Brussels, to have them put under glass, and taken to the Palais des Beaux Arts before August 1st. In such cases exhibitors should give particulars of what has been sent to Mons. A. Geruzet, at the Secretary’s office of the Association, Rue de 1’Ecuyer, 27 bis, according to rules 4 and 8. . Exhibitors having no correspondent in Brussels may send their prints to the Secretary, Palais des Beaux Arts, who will undertake to put them under glass with as much care and as little outlay as possible. In this case it is
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