Suche löschen...
The photographic news
- Bandzählung
- 7.1863
- Erscheinungsdatum
- 1863
- 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-id1780948042-186300004
- PURL
- http://digital.slub-dresden.de/id1780948042-18630000
- OAI-Identifier
- oai:de:slub-dresden:db:id-1780948042-18630000
- Sammlungen
- Fotografie
- LDP: Historische Bestände der Hochschule für Grafik und Buchkunst Leipzig
- Strukturtyp
- Band
- Parlamentsperiode
- -
- Wahlperiode
- -
- Bandzählung
- No. 236, March 13, 1863
- Digitalisat
- SLUB Dresden
- Strukturtyp
- Ausgabe
- Parlamentsperiode
- -
- Wahlperiode
- -
-
Zeitschrift
The photographic news
-
Band
Band 7.1863
-
- Titelblatt Titelblatt -
- Ausgabe Ausgabe 1
- Ausgabe Ausgabe 13
- Ausgabe Ausgabe 25
- Ausgabe Ausgabe 37
- Ausgabe Ausgabe 49
- Ausgabe Ausgabe 61
- Ausgabe Ausgabe 73
- Ausgabe Ausgabe 85
- Ausgabe Ausgabe 97
- Ausgabe Ausgabe 109
- Ausgabe Ausgabe 121
- Ausgabe Ausgabe 133
- Ausgabe Ausgabe 145
- Ausgabe Ausgabe 157
- Ausgabe Ausgabe 169
- Ausgabe Ausgabe 181
- Ausgabe Ausgabe 193
- Ausgabe Ausgabe 205
- Ausgabe Ausgabe 217
- Ausgabe Ausgabe 229
- Ausgabe Ausgabe 241
- Ausgabe Ausgabe 253
- Ausgabe Ausgabe 265
- Ausgabe Ausgabe 277
- Ausgabe Ausgabe 289
- Ausgabe Ausgabe 301
- Ausgabe Ausgabe 313
- Ausgabe Ausgabe 325
- Ausgabe Ausgabe 337
- Ausgabe Ausgabe 349
- Ausgabe Ausgabe 361
- Ausgabe Ausgabe 373
- Ausgabe Ausgabe 385
- Ausgabe Ausgabe 397
- Ausgabe Ausgabe 409
- Ausgabe Ausgabe 421
- Ausgabe Ausgabe 433
- Ausgabe Ausgabe 445
- Ausgabe Ausgabe 457
- Ausgabe Ausgabe 469
- Ausgabe Ausgabe 481
- Ausgabe Ausgabe 493
- Ausgabe Ausgabe 505
- Ausgabe Ausgabe 517
- Ausgabe Ausgabe 529
- Ausgabe Ausgabe 541
- Ausgabe Ausgabe 553
- Ausgabe Ausgabe 565
- Ausgabe Ausgabe 577
- Ausgabe Ausgabe 589
- Ausgabe Ausgabe 601
- Ausgabe Ausgabe 613
- Register Index 619
-
Band
Band 7.1863
-
- Titel
- The photographic news
- Autor
- Links
- Downloads
- Einzelseite als Bild herunterladen (JPG)
-
Volltext Seite (XML)
Pnorocnapm0 News, vol. vii. p. 5. albumen upon the surface; but this precaution is unnecessary, since the coagulation is perfectly effected by the nitrate of silver used in sensitizing; and it is doubtful whether a layer of dry albumen admits of coagulation by the simple application of a heated iron.” You will, no doubt, have noticed that he does not £ ay the application of the hot iron is useless for coagulation ; but, merely, that it is unnecessary, because it will bo effected by other moans, thus ignoring the beneficial effect produced by its desiccating the paper; and you must bo well aware that the statement, "it is doubtful" whether a thing can be done, is, in fact, an avowed acknowledgementthat it is not certain it cannot be done. M. Gaudin, in an article lately published,® alluding to albumen- ized paper, says that it will be sufficient to hang it in a cellar, or other damp locality, to coagulate the albumen by the passage of a hot iron across its surface ; and also that at the time of albumenizing if the hot iron be passed over it before it is dry enough to cease sticking to the fingers, the same effect will bo produced. Now, this statement is a very great fallacy, for the following reason:—Whatever moisture is imbibed will be duction is necessary. The vigour of the print is not, I think, duo to the chloride of silver, but to the albuminate ; to which is also due the richness of tone. So little is understood of the render it almost—if not wholly—incapable of being sensitized by the nitrate of silver bath. The belief in the fallacy that dried albumen could be coagu lated, or even rendered insoluble, naturally induced means to bo sought for to accomplish it; but, its being an impossibility, the beneficial effects produced by them were attributed to a cause which had no existence ; and thus attention was diverted from the real philosophy of their action. The rapidity with which a substance, soluble in water, is dissolved in it, is dependent upon its more or less hydrated state at the time it is submitted to the action of the solvent; thus, the passing a hot iron over the sur face of albumenized paper, by desiccating it, renders it more difficult of solution ; and, therefore, the nitrate of silver is en abled to be forming an insoluble compound before the solvent power of the water can come much into play. Unfortunately, in making the sensitizing bath as wo do at present, we use a solvent for the nitrate of silver, which is also a solvent of dried albumen; and thus, with respect to the albu menized surface of our paper, we have two antagonistic forces in operation at the same time—one having power to dissolve, and the other to form an insoluble compound. This being the case, we can diminish the power of either of them by increasing that of the other ; and therefore it is perfectly possible, by suffi ciently increasing the quantity of nitrate of silver, to almost (if not entirely) neutralize the solvent power of the water. The stronger the sensitizing bath the quicker will be its action, and the more will the albumenized surface of the paper be able to maintain its brilliancy ; and I believe it to be possible to make the nitrate bath strong enough to render a mere drawing of the paper across its surface quite sufficient to form the albuminate and chloride of silver with the requisite quantity of free nitrate ; and, from the solution not having time to penetrate the sub stance of the paper, that the prints will have all the brilliancy which albumen is capable of affording; and, moreover, that less silver will be wasted than at present, and less washing required; we should also, I believe, then receive the full benefit of colouration which the nitrates of the bases of the salting chlorides would give us. As alcohol is not a solvent of dried albumen its addition to the nitrate bath, by mixing with the water it contains, mitigates its solvent power in proportion to the strength and quantity added; hence the addition of alcohol to the sensitizing bath, and the desiccation of the paper by a hot iron, are beneficial because the solvent action of the water has been decreased by their means, and the albumenized surface is enabled to retain more of its brilliancy than it can do without their employment. It is scarcely necessary, perhaps, to say that alcohol must not bo added in sufficient quantity to cause precipitation of the nitrate of silver. In printing upon albumenized paper, it is usually considered that wo have present three compounds of silver ; the albuminate, chloride, and nitrate ; and that the chloride is the most important of them. I do not hold this opinion myself, but believe that if the chloride be not deserving of being degraded to the lowest rank, it only holds a secondary one. That the chloride is not of that paramount importance usually attributed to it, is fully evidenced by th© beautiful effects produced by the use of low salting formulae. The almost universally accepted theory respecting the production of the image, is, that the action of the light decomposes the chloride of silver, liberating the chlorine ; and silver having a greater affinity for chlorine than it has for nitric acid, the silver of the free nitrate combines with this liberated chlorine, setting free in its turn the nitric acid and oxygen with which it had previously been combined; this decomposition and recomposition of the chloride of silver going on during the whole time of printing: the vigour and intensity of the print being due to this constant and continued re-com position of the chloride of silver. According to this theory, the presence of the albuminate of silver is entirely ignored, and the free nitrate—as such—p\wgs no part whatever in the production of the imago. Wore this the case, we could produce the same result by giving al once the same amount of chloride of silver as this additional re-composition has afforded, and dispensing entirely with any free nitrate ; but experience tells us that this will not produce the same effect. I therefore hold the opinion that the nitrate of silver plays an important part itself in the production of the image : for surely it is too much to ask us to believe that the chloride can only produce a good effect when the nitrate is present; that is to say, that its continued re-pro same term. In what way heat coagulates albumen chemists have not yet determined; but no additional substance enters into combination with it; it is simply the same albumen in another state ; it is not so, however, when chemical agents are employed to produce insolubility; the generality of them enter into combination with it, and an insoluble precipitate is formed, which is not albumen alone, but a compound substance, and no one has any right to mis-call it coagulated albumen. I have said the generality of these chemical agents enter into combination with albumen, because I believe that alcohol simply unites with the water of the albumen, and causes an insoluble precipitate to be formed, with which it does not enter into combination ; this may, perhaps, bo the case with the coagulating acids, as it is not yet satisfactorily determined whether they form any defi nite compound with albumen ; it is, however, otherwise with such metallic salts as nitrate of silver—here a direct chemical combination takes place. I have also said, we have no means whatever of rendering dried albumen insoluble; for I maintain • that when normal albumen is coagulated by any agents, without their entering into chemical combination ■with it, these same agents, as they cannot coagulate dried albumen, do not render it insoluble, the insolubility of the normal albumen being due to its coagulation. From what I havo now stated I leave you to judge whether it be not want of knowledge which can alone induce any one to use the term coagulation in any way whatever when applied to dried albumen. I need, perhaps, scarcely say to those who havo paid any attention to the subject, that this fallacious notion of dried albu men being capable of coagulation, even by heat, is very preva lent, notwithstanding it is at variance with the dictates of com mon sense. In a pretty extensive and varied course of reading, I have never yot mot with any author, bo he photographer or chemist, who has over stated tiro impossibility of so coagulating it; the most that any of them has advanced is, that it is not coagulated up to a certain temperature. Mr. Hardwich, in the last edition of his Manual of rhotogra- phic Chemistry, leads his readers to suppose it to bo a possibility. At page 470 ho says:—“A layer of dried albumen cannot easily be coagulated by the mere application of heat.” Now, we all know that when a person says a certain thing cannot easily be done the inference to be drawn from his statement is, that it cun be done with difficulty. Again, in speaking of albumenized paper, at page 371, he says:—“Some havo recommended to press it with a heated iron, in order to coagulate the layer of evaporated by the application of the hot iron before it can arrive at sufficient temperature to coagulate the albumen. The same will also bo the case with tho albumen in its sticky state. Moreover, as I stated nearly two years ago, no amount of dry heat will coagulate or render insoluble a mere film of albumen, even in its normal state—it simply dries the albumen ; therefore, the albumenized surface of a sheet of paper, whether it be rendered damp after being dried, or bo taken before the albumen has ceased to be sticky, cannot be rendered insoluble by the application of a hot iron. By tho aid of steam and boiling water, the albu menized surface of the paper may perhaps bo made to imbibe sufficient moisture for coagulation to take place, but it becomes a question whether this coagulated moist albumen would return to a sufficiently dried state to be fit for photographic printing; but, oven if it did so, I believe that this very insolubility would
- Aktuelle Seite (TXT)
- METS Datei (XML)
- IIIF Manifest (JSON)