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The photographic news
- Bandzählung
- 27.1883
- Erscheinungsdatum
- 1883
- Sprache
- Englisch
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- 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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- 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
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Band
Band 27.1883
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- Titel
- The photographic news
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THE PHOTOGRAPHIC NEWS. 27 indeed much to do in making the high reputation of the text-book. We are glad to see, too, that the present editor, in deal ing with the chemical aspect of photography, has confined himsell to plain and, one might almost say, homely language. Photographic students may be chemists, or they may not; but, in any case, they are only students, and should be regarded as such in a hand-book that pro fesses to deal as much with the practical as the theoretical. The main features of Hardwich’s photographic chemistry are unchanged. Regarded by the light of the present state of photographic practice, there is doubtless much it might have included, but the rapid and sudden pro gress of our art is responsible for this, rather than editor or publisher, who must, perforce, set down a fixed date for a new edition. Thus, the paragraph dealing with gelatine, now that this substance is the body, if not the soul, of our sensitive emulsions, might well have been enlarged, for we cannot know too much about the history and properties of a substance we have now to deal with every day. The same may be said of such salts as the oxalates of iron and potash, whose role in photography has been of late so widely extended. In fact, as we have said, the gelatino-bromide process deserved more space than has been accorded to it. The dark room described is that adapted to wet collodion rather than gelatine plates. The optics of photography are, however, adequately treated, and there is much valu able information about the chemicals employed in every day photography. Collotype or Lichtdruck printing might, with advantage, have been treated at greater length ; and while Willis’ aniline method for printing plans is given, no mention is made of Pellet’s iron process, that is most extensively employed in such work now-a-days. On page 368 we note a hint of some practical import ance, viz., how to make a stirrer or beater for mixing gelatine solutions ; here it is. “ There are various appliances by which the admixture may be thoroughly made, and much ingenuity has been expended in devising such appliances ; but one of the best consists in having a piece of a tolerably coarse and long toothed vulcanite comb, of a length somewhat less than the diameter of the beaker, attacked to a round wooden handle ten or twelve inches in length, much in the fashion of a miniature garden rake, with this difference, that the teeth will be standing in the same direction as the handle. This is placed in the gelatine solution, and by rolling the handle between both hands a twirling motion is imparted by which the silver solution is rapidly incorporated with the gelatine. After this addition allow the beaker to remain undisturbed for about a minute, then add the remainder of the silver in four or five doses, with out diluting it as in the case of the first silver added, and with a vigorous application of the agitator after each addition.” NOTES ON PHOTOGRAPHY. BY E. HOWARD FARMER. Lecture VII.—The Gelatine Process—History. Gelatine has been employed as a vehicle in which to sus pend sensitive salts since the earliest days of photo graphy. 1853. In a paper of this date, by Gaudin, we have, how ever, the first account of its employment for emulsion ■ purposes. 1871. Dr. Maddox introduced the first workable emul sion process with gelatine, and showed some negatives produced by his process to Mr. Traill Taylor. He added an excess of silver nitrate to a solution containing gelatine and cadmium bromide, and coated plates with the result ing mixture. When dry they were exposed and developed '* with plain pyrogallic acid. 1873. Mr. Burgess advertised gelatine emulsion for sale s d in the photographic journals. The method of preparation was not published. Mr. King pointed out the necessity for removing the useless products in emulsions, and described the use of dialysis for that purpose. He also pointed out the bene ficial property possessed bv alcohol of assisting the pro duction of the silver bromide in a fine state of division. Mr. Johnston, also in this year, recommended that the soluble bromide should be in excess of the silver salt, a recommendation which is now universally adopted. 1874. Mr. Kennett gave a great impetus to the new pro cess by the introduction of his gelatino-bromide pellicle ; and in June of the same year published bis method of pre paring the pellicle. His process differed from Dr. Mad dox’s, in that he kept the soluble bromide in excess, and. after allowing the emulsion to set, scraped it into small pieces, which were allowed to soak in water, to dissolve out the soluble products ; it was then dried and preserved for use. 1878. Mr. Bennett (an amateur) generously published his discovery that, by prolonged digestion at a moderate temperature—about 90° F.—gelatine emulsions containing excess of soluble bromide increased in sensitiveness to a most remarkable extent. He also exhibited some wonder ful results he had obtained with very short exposures on plates coated with emulsions which had been digested, in some instances, as long as seven days. 1879. Captain Abney published his simplified process by precipitation from aqueous solutions, and washing by decantation. This is the most simple process known, and, with a little care, yields satisfactory results. Dr. Monckhoven published his process with silver carbonate and hydrobromic acid, and his discovery of the accelerating action of ammonia. Mr. Mansfield discovered that by boiling an emulsion for a short time, the same effect is obtained as by prolonged digestion at a lower temperature; finally, Mr. Bolton described a practical process utilizing Mansfield’s dis covery, and which process forms the basis of most of the methods now employed. 1880. Captain Abney pointed out the advantages derived by employing a small quantity of silver iodide in conjunc tion with the bromide. Mr. W. J. Wilson (winner of the Paget prize) showed the important part which the excess of soluble bromide plays during digestion, and the necessity for keeping the emulsion slightly acid during the same period. gelatine. Gelatine being the all important substance in this pro cess, its properties and peculiarities should be very care fully studied. Gelatine is a complex organic substance composed of four elements : carbon, hydrogen, oxygen, and nitrogen, united, according to Scherer, in the following proportions:— Carbon 50-4 Hydrogen 6-9 Oxygen 238 Nitrogen 18.9 100 0 It is obtained as a product when bones, hoofs, skins, and various other kinds of animal matter are heated for some time with water, more especially if the water contain free acid or alkali. There are many different methods employed in the arts for the extraction of gelatine; thus in England Nelson employs caustic soda, and Swinburne water only; while in France, hydrochloric acid is generally employed; they are all, however, in practice somewhat complicated. Dr. Ure thus described the method employed by Nelson. After washing the parings, &c., of skins, he scores their surfaces, and then digests them in dilute caustic soda lye during ten days. They are next placed in an air-tight vat lined with cement, kept at a temperature of 709 F., then
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