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. 254, July 17, 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)
340 THE PHOTOGRAPHIC NEWS. [July 17, 1863. to, and mixing with it as little as possible, a layer of one of the above-named sulphates, an abundant precipitate of sulphate of silver is produced; if, after this, we mix the two by stirring with a glass rod, we perceive that the sulphate formed is re-dissolved. When the sulphate employed is the ferric sulphate, the experiment is modified in the following manner : before mixture, only a slight metallic reduction is produced between the layers of different liquids ; in propor tion as we effect the mixture by a slow agitation, the sul phate of silver is reduced and dissolved, but it does not undergo decomposition so long as it floats in the solid state. If we make use of sulphate of iron and ammonia, we per ceive that the metallic grain of the reduced- silver is much finer than that produced by the action of sulphate of iron alone. The proportion of ferrous sulphate varies greatly, accord ing to the various formula for the developing solution. Generally, for negatives, the extreme limits are from 1 to 10 per cent., with equally variable proportions of acetic acid. In our own practice we employ 3 per cent., increasing gradually to 5 in winter, with 1} per cent., of crystallizable acetic acid. Recently it has been proposed to employ the double salt of sulphate of iron and ammonia in preference to the simple sulphate, and, finally, it has been found that there is no great advantage in this substitution. Generally, the true value of this modification is not well appreciated. It is said that the double sulphate does not undergo peroxidation in contact with the atmosphere, like the single sulphate. True, in the crystallized state, the double sulphate is a very stable salt, with a clearly defined composition, but when dissolved, it absorbs oxygen just the same as the other salt; in this respect, therefore, there is no advantage; be sides, there is a simple sulphate of iron, well crystallized and very dry, which is as pure as the double salt; it is obtained by washing the crystals with alcohol at the moment when they are withdrawn from the mother waters. Few of the journals which have mentioned the employ ment of the double salt have shown photographers the equivalent quantities of the two salts ; for in preparing an iron solution of four per cent, of double salt, there would be only about three per cent, of ordinary sulphate. The formula of the ordinary sulphate gives us the following proportions:— SO’ Fe 0 + 7 H 0 is 16+ 8x3 +28 + 8 + 7 (1 + 8) = 139. The formula of the double sulphate is :— SO 3 Fe 0 + S 03 N H 4 0+6 H 0 is 16+8x3+28+8 + 16+8x3 + 14+1x4+8+6 (1+8)=196, so that 196 parts of double salt contain 139 parts of ferric sulphate. Dividing 196 by 139, we obtain 1 and 4-10ths per cent, of double salt, which should be substituted for the simple salt; for a bath of 3 per cent, it should be 4-2 per cent., and for a bath of 5 per cent, it should be 7 per cent, of double salt. The double salt is prepared by dissolving in water, with the aid of heat, 139 parts by weight, or an equivalent of crystallized sulphate of iron, and 66 parts by weight, or an equivalent of sulphate of ammonia. Filter the solution, and leave it to crystallize. According to the experiments published by some photo graphers, the action of the double salt will be less energetic, less subject to produce fogging. Our own experiments have taught us that the difference of action of the two salts, during the first period of development, is scarcely percep tible, but the employment of the double salt permits of keeping the iron solution upon the plate much longer, and even of renewing it without having to fear fogging with large crystallized particles, which are produced by leaving the iron solution to remain an unreasonable time on the plate while developing. It gives a certain advantage in producing more detail in the shades. There exists also another degree of hydratation of the ferric sulphate, which is the monohydrated sulphate. SO 3 Fe 0 + H 0 16+8 x 3 + 28 + 8 + 1 +8 = 85. It is very necessary to prepare an iron solution strictly proportioned : it is obtained by throwing some alcohol into a saturated solution of sulphate of iron; a white powder is precipitated which is the sulphate with an equivalent of water : it keeps well, its composition is always constant. 85 parts of this salt correspond to 139 of ordinary sulphate, or, in round numbers, 6 parts of monohydrated salt to 10 of ordinary sulphate. It can be easily weighed, because it is in very small crystals, and for the same reason it dissolves in water immediately, in the preparation of the developing solution.—Bulletin Bdge de la Pliotographie. PHOTOGRAPHIC COLLODION: THE SALTS IT SHOULD CONTAIN, AND THEIR PROPORTIONS. BY CILARLES HEISCH, F.C.S.* A good collodion should contain from five to eight grains of pyroxyline to the ounce. A pyroxyline, of which six grains cannot be dissolved in one ounce of mixed alcohol and ether without making it too thick to flow readily, will not make a really good collodion. The best proportions of ether and alcohol are, as a rule, equal quantities of each. Four drachms of ether and two of alcohol should be mixed, and the six grains of pyroxyline added, to make the plain collodion ; the requisite quantity of iodide, &c., should be dissolved in the remaining two drachms of alcohol, and the collodion, after getting clear, added to them, to make the ounce of prepared collodion. The nature and proportion of the iodides and bromides employed, should be regulated by the use to be made of the collodion. Where only black and white subjects, such as engravings, are to be copied, a simple iodide, or an iodide with a small quantity of chloride to increase the intensity of the blacks, is all that is necessary. Bromide of silver, being more readily affected by light of various colours than iodide, and giving also much greater delicacy of half-tone, a bromide should always be employed in conjunction with an iodide, either for landscape or portrait collodion where the best possible results are desired. The qualities which it is most desirable to unite in order to form a perfect collodion, are the maximum of sensibility to light, not only white but coloured, and the power of bearing an exposure sufficiently long to bring out the detail in the deepest shadows, without becoming solarised in the lighter parts. Much discussion has recently taken place, as to whether the presence of bromides increases the sensibility of collodion, and many contradictory assertions have been made on the subject. I believe these contradictions arc mainly owing to the fact, that but few of the experimenters have paid any attention to the proportion of the bromide to the iodide, or of both to the quantity of pyroxyline in the collodion. To attain the maximum of sensibility, the collodion should con tain, after being sensitized, as much silver (whether as iodide or bromide), as can be retained firmly by the film. If it contain less than this, the silver salts are so surrounded by pyroxyline, as to be comparatively insensible ; if it contain more, the silver salts wash out into the bath, and leave streaks on the film. It is universally admitted that in the daguerreotype process, bromide, in conjunction with iodide of silver, is far more sensitive than iodide alone. The reason of this universal admission I believe to be due to the fact, that a very slight difference in the proportions of iodide and bromide in this process renders a plate not only less sensi tive, but almost insensitive, so that daguerreotypists wen obliged to pay that strict attention to proportions, wine > the experimenters in collodion have many of them faded to do, and hence, I believe, has arisen the discrepancies in then opinions. r A careful consideration of the very slight difference * From “ The Elements of Photography.
- Aktuelle Seite (TXT)
- METS Datei (XML)
- IIIF Manifest (JSON)