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The photographic news
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- 27.1883
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- 1883
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- Hochschule für Grafik und Buchkunst Leipzig
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The photographic news
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Band
Band 27.1883
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- Titelblatt Titelblatt I
- Register Index III
- Ausgabe No. 1270, January 5, 1883 1
- Ausgabe No. 1271, January 12, 1883 17
- Ausgabe No. 1272, January 19, 1883 33
- Ausgabe No. 1273, January 26, 1883 49
- Ausgabe No. 1274, February 2, 1883 65
- Ausgabe No. 1275, February 9, 1883 81
- Ausgabe No. 1276, February 16, 1883 97
- Ausgabe No. 1277, February 23, 1883 113
- Ausgabe No. 1278, March 2, 1883 129
- Ausgabe No. 1279, March 9, 1883 145
- Ausgabe No. 1280, March 16, 1883 161
- Ausgabe No. 1281, March 22, 1883 177
- Ausgabe No. 1282, March 30, 1883 193
- Ausgabe No. 1283, April 6, 1883 209
- Ausgabe No. 1284, April 13, 1883 225
- Ausgabe No. 1285, April 20, 1883 241
- Ausgabe No. 1286, April 27, 1883 257
- Ausgabe No. 1287, May 4, 1883 273
- Ausgabe No. 1288, May 11, 1883 289
- Ausgabe No. 1289, May 18, 1883 305
- Ausgabe No. 1290, May 25, 1883 321
- Ausgabe No. 1291, June 1, 1883 337
- Ausgabe No. 1292, June 8, 1883 353
- Ausgabe No. 1293, June 15, 1883 369
- Ausgabe No. 1294, June 22, 1883 385
- Ausgabe No. 1295, June 29, 1883 401
- Ausgabe No. 1296, July 6, 1883 417
- Ausgabe No. 1297, July 13, 1883 433
- Ausgabe No. 1298, July 20, 1883 449
- Ausgabe No. 1299, July 27, 1883 465
- Ausgabe No. 1300, August 3, 1883 481
- Ausgabe No. 1301, August 10, 1883 497
- Ausgabe No. 1302, August 17, 1883 513
- Ausgabe No. 1303, August 24, 1883 529
- Ausgabe No. 1304, August 31, 1883 545
- Ausgabe No. 1305, September 7, 1883 561
- Ausgabe No. 1306, September 14, 1883 577
- Ausgabe No. 1307, September 21, 1883 593
- Ausgabe No. 1308, September 28, 1883 609
- Ausgabe No. 1309, October 5, 1883 625
- Ausgabe No. 1310, October 12, 1883 641
- Ausgabe No. 1311, October 19, 1883 657
- Ausgabe No. 1312, October 26, 1883 673
- Ausgabe No. 1313, November 2, 1883 689
- Ausgabe No. 1314, November 9, 1883 705
- Ausgabe No. 1315, November 16, 1883 721
- Ausgabe No. 1316, November 23, 1883 737
- Ausgabe No. 1317, November 30, 1883 753
- Ausgabe No. 1318, December 7, 1883 769
- Ausgabe No. 1319, December 14, 1883 785
- Ausgabe No. 1320, December 21, 1883 801
- Ausgabe No. 1321, December 28, 1883 817
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43 determining cause, and, as before stated, the granular con dition is the most sensitive. The finer modifications, if present in any quantity, reduce the sensitiveness. The sensitiveness also apparently varies somewhat according to the method of preparing the granular bromide; thus the granular bromide prepared by the action of ammonia is never so sensitive as that prepared by boding (Abney). b. Gelatine, by its affinity for oxygen aid the halogens, acts as a sensitizer to the bromide; to exert its most favourable action in this respect it should be as pure as possible. c. The gelatine should be as soft as is consistent with safety. d. F inished gelatine emulsions, when kept for a few days, frequently increase considerably in sensitiveness. This, Captain Abney believes to be due to the fact that the particles of silver bromide, to be in the most sensitive state, must be placed entirely beyond any state of strain. During preparation, a strain is probably given to the particles of silver bromide, and by subsequent keeping the emulsion in the state of jelly, this strain wears off. e. The excess of soluble bromide employed should be very thoroughly washed out. The presence of one per cent, excess of ammonium bromide reduces the sensitive ness to one-half (Eder). The cause of this energetic retarding action of the solu ble bromides has been fully explained by Captain Abney (Cantor lectures) ; he showed that at the same time that light reduces the silver bromide to sub-bromide, it also decomposes any ammonium (or other) bromide present, with the result of re-converting the silver sub-bromide to bromide ; thus the sensitiveness obtained is only the diffe rence between these opposite actions. f. Alkaline carbonates and alkalies, especially ammonia, added in small quantities to emulsions increase their sensi tiveness (Eder). Fuming a dry plate with ammonia in creases its sensitiveness (Col. Wortley). Treating a plate with very dilute silver nitrate and thorough washing before development, increases its sensitiveness (Eder). g. Free halogens, oxidizing agents, acids, soluble bro mides, iodides, oxidized organic matter, &c., reduce the sensitiveness to a greater or less extent, and in some cases destroy it altogether. Silver Chloride.— 1 This substance is not so sensitive as silver bromide, and is therefore not employed alone for producing negatives. A small quantity in conjunction with the silver bromide in a t emulsion gives density on development, an I increases the sensitiveness somewhat (Bolton). Silver Iodide—This body is very insensitive, and very difficult to develop alone with gelatine. Captain Abney, however, in 1880, pointel out that a small quantity in con junction with the silver bromide in an emulsion confers very valuable properties upon it without reducing the sensi tiveness. In the first place, it takes away the sensitiveness which pure granular bromide has to red light, and so enables a comfortable light to be employed in develop ment ; in the second place, it acts as a restrainer of fog, giving brighter images with clearness in the shadows; thirdly, it allows greater latitude in exposure ; and finally, by producing a more opaque film, prevents halation. Dr. Eder’s experience it reduces the sensitiveness slightly, has a tendency to give thin images, and prolongs the time of development. METHODS OF PREPARING EMULSIONS. Extremely sensitive silver bromide in conjunction with gelatine can be prepared in many ways ; thus, it may be prepared by careful precipitation from aqueous solutions, washing by decantation, and subsequent emulsification in gelatine (Abney); or by producing the fine orange bromide by double decomposition in a solution of gelatine, digestion with an excess of the soluble bromide, and subsequently washing the set emulsion (Bennett) ; or by precipitating a solution of bromide of ammonium in gelatine with ammonia nitrate of silver, and subsequent washing (Obernetter), &c. They nearly all, however, arrange themselves under one or other of three principal types, viz.:— 1. Precipitation processes. 2. Boiling or acid processes. 3. Ammonia processes. And of which the above three methods are examples. In some cases these methods are combined together, as in Mr. Burton's recent process. They may again be divided into those which contain silver bromide only, silver bromide and iodide, and silver bromide, iodide, and chloride, respectively. In England the second of these types, or the boiling methods containing silver bromide and iodide, seem in most general favour, and will, therefore, be employed by us. — GREEN FOG. BY C. RAY WOODS.* The experiments I wish to bring before your notice this evening are somewhat imperfect in their scope, but may, in connection with the experience of others and the discussion I wish to open this evening, be possibly of a little value. I should like first to give a few of my experiences in the preparation of gelatine plates. In the first emulsion giving green fog, that I prepared, I omitted to put in the two drops of hydrochloric acid that the formula required. I stopped the boiling considerably before the proper time, and have no doubt I checked the evil to some extent. Since then I was not troubled with green fog for some time, until I began to use a fresh sample of bromide, when I had some difficulty to prepare plates in which this pest did not appear. Proceeding to examine the two samples of potassium bromide, I noticed this :— Old Sample. Neutral, containing a trace of bromate. On addition of a drop of hydrochloric acid a trace of bromine was set free, which was rendered more apparent by the addition of potassic iodide, due to the consequent liberation of iodine. The emulsions in which I used the above samples of bromide contained chloride, bromide, and iodide. Emulsions of exactly similar character, but preparel entirely with salts of ammonium, gave no green founder ordinary circumstances. The chloride and bromide were both perfectly neutral, but became acid on boiling, and therefore no free acid was added in the mixing. The iodide was old, of a dark yellow tint, containing a certain amount of free iodine. In addition to these facts, I have noticed, so far as my own experience goes, that green fog seems to occur more frequently when the gelatine and silver are mixed first, than when the gelatine and haloid salts are mixed and then the silver added. I very much prefer the first method of mixing, and have tried to persuade myself that it is not more liable to bring about green fog. In spite of my wishes, however, I have not been able to bring myself to believe this is the case ; while very far from asserting that the bromide into silver plus gelatine has more tendency to bring about green fog, my own experience tends towards this view. It may be asked, if nitrate of silver added to gelatine tends to green fog, how can green fog occur when the silver is added to gelatine plus bromide where the haloid salt is ready to receive it ? It must be recollected that the bromide is surrounded by the gelatine, and combination between gelatine and silver may in this case also take place, the boiling with excess of bromide being unable to undo the mischief. I have also noticed, in connection with some experiments of another character, that if a plate coated with emulsion be treated with a solution of nitrate of silver, washed well after a short time, placed in a dilute solution of bromide to destroy all trace of free silver nitrate, and then developed, a fog is found on the plate, somewhat resembling what is known as green fog. This fog is the more intense the longer the plate has been in contact with the nitrate of silver ; and is this a sort of slow cooking ? • Read before the Photographic Society of Great Britain. New Sample. Very faintly alkaline. No bromate present.
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