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The photographic news
- Bandzählung
- 24.1880
- Erscheinungsdatum
- 1880
- Sprache
- Englisch
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- F 135
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- Hochschule für Grafik und Buchkunst Leipzig
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- Hochschule für Grafik und Buchkunst Leipzig
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- urn:nbn:de:bsz:14-db-id1780948042-188000001
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- http://digital.slub-dresden.de/id1780948042-18800000
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- oai:de:slub-dresden:db:id-1780948042-18800000
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- Bandzählung
- No. 1165, December 31, 1880
- Digitalisat
- SLUB Dresden
- Strukturtyp
- Ausgabe
- Parlamentsperiode
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- Wahlperiode
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Zeitschrift
The photographic news
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Band
Band 24.1880
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- Register Index 631
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Band
Band 24.1880
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THE PHOTOGRAPHIC NEWS. December 31, 1880.7 Take it out, shake up, remove stopper, and set bottle down on the table near your lamp, so that you can see what you are doing. Pour in, all at once, the four drachms of dilute silver solution. Put in the stopper, and shake up thoroughly, but not too violently, for about half-a-minute. Now pour in the strong silver solution in quantities of about half-an-ounce at a time, shaking, as before, after each addition, and, when all is added, give a final thorough shaking for (say) a couple of minutes. If the instructions have been so far accurately followed, there will be no coarse precipitate or grit in the finished emulsion. Now put the bottle into the pot of hot water, see that the stopper is not jammed in, and put on the lid. Light the gas, and boil up quickly as possible. If the water was previously boiling, and the gas only turned out for the mixing operation, it should boil up in less than five minutes ; then keep boiling for fifty-five minutes. At the end of this time turn out the gas, take off the lid, take out the bottle, and remove the stopper at once, or you will not get it out afterwards. The bottle must now be cooled down as quickly as is consistent with safety to the glass. In very cold weather it may stand on the table for ten minutes or so, and then be cooled with water ; or, in any weather, place it in a pan of nearly boiling water, and cool gradually by allowing cold water to trickle slowly in, shaking the bottle occasionally. Whatever method is adopted, it should be down to 90° Fahr., or lower, in fifteen or twenty minutes at most. It cannot easily be made too cold, as the gelatine has lost its power of setting. In a glass beaker (about twelve or fourteen ounce size) put one ounce of Nelson's No. 1 Photo, or “ X opaque ” gelatine, and pour over it ten ounces of clean, ordinary water. Leave to soak until the gelatine has absorbed four ounces of the water, pour off the surplus six ounces, melt the swelled gelatine by immersing the beaker in hot water, and pour it into the twenty ounce bottle containing the cooled emulsion. Shake up well, and pour all back into the beaker, draining out the bottle thoroughly. Leave to set in a cool place. The writer prefers to leave for twenty-four hours. It has next to be washed. For the washing, clean ordinary water, at a temperature not over 50° Fahr., should be used. The writer prefers, at all times, to use water cooled down to below 40°, by melting ice in it. By so doing, uniform results are obtained, and, where ice can be procured, the cost is trifling; three pounds of ice will be suffi cient for a pint lot of emulsion, in the hottest weather. In a glazed earthern pan, or other suitable vessel, put about three pints of cold water, and add three ounces of saturated solution of bichromate of potash, made by saturating ordinary water with bichromate (Hopkin and Williams’ re-crystallized, at Is. 4d. per pound). Having cooled the beaker of set emulsion down to 40? Fahr., run a bone spatula or paper-knife round and turn out the emulsion, or cut it out in lumps. If cold, it will come out almost quite clean from the glass. Place it on a piece of coarse straining-cloth or canvas, and squeeze through the meshes into the water, the operation being performed under the surface of the water. Leave it so for an hour. Lay the straining-cloth over the mouth of another pan, or large jar, and pour the mixture of emulsion threads and liquid on to it, so as to let the latter run through. Squeeze the emulsion a second time through the cloth into clean cold water, and immediately repeat the operation a third time, leaving the emulsion in the last water for half-an-hour. When strained for the last time, place cloth and all in a large beaker, and put the latter into hot Water until the emulsion is completely melted and warmed to about 115° Fahr.; i.e., not warmer than is pleasant to the hand. With a clean hand, take out the cloth and squeeze it: very little will be lost. The emulsion should now measure about sixteen or seventeen ounces. Add two ounces of aclohol, and mix thoroughly. The alcohol may be either pure ethylic alcohol sp. gr. about ’830, or good colourless methylated. The writer pre fers the former. If the emulsion now measure less than twenty ounces, make it up to that by adding clean water. The emul sion is now ready for use. It should be filtered into the coating cup through cotton-wool, to free from bubbles, and plates coated in the usual way, dried and used as usual for rapid gelatine plates, using about an ounce of emulsion for a dozen quarter plates. In drying arrangements, avoid the contact of gas, or of the products of combustion of gas, with the moist plates. The writer finds both to be very injurious. Exposure.—As usual for. good gelatine plates, say Wratten and Wainwright’s “instantaneous.” Development.—Either pyrogallic, ammonia and bromide, or ferrous oxalate. If the former, sufficient exposure and as little ammonia as possible will give best results, Note as to Gelatine.—The plates sent were made as above, "X opaque ” being used as described. This is necessary in hot weather, but the writer prefers to work in cold weather, and then uses only Nelson’s No. 1 Photo. Further Details and Explanations of Process sent by “ Eblana.” Dromide of Ammonium should be as nearly as possible neutral. It is usually more or less acid, even though otherwise pure, and frequently becomes strongly acid by keeping. It is then quite unfit for use, and will not give good results unless almost neu tral. Having a quantity of bromide of ammonia, which had by keeping grown acid and unfit for use, the writer tried to cure it by making a solution in water saturated at 100? C., adding liq. ammonia until the solution smelled strongly of ammonia, and leaving to crystallize out. When cold, before pouring off the mother liquor, a piece of blue litmus paper dipped into the latter showed it to be fully as acid as the salt had been before—a result which the writer is unable to explain. Since sending in the formula for competition, the writer has arrived at the con clusion that on the whole it is tetter to use bromide of potas sium. The latter is often alkaline, but may without much diffi culty be obtained neutral, and is free from tendency to alter. Nelson's No. 1 Photo. Gelatine unfortunately varies much in different samples. It should be absolutely free from the faint est smell or taste, and should dissolve clear, bright, and nearly colourless. Samples good for this purpose are very slightly acid with HC1 (i.e., contain a trace of it). Nitrate of Silver is usually (if good) slightly acid with excess of nitric acid. It may be so used, but the writer has recently found that better results are obtained if the silver solution be neutralized with carbonate of soda. A slight excess does no harm, as the resulting trace of carbonate of silver is converted into bromide; indeed, an emulsion may be made by mixing washed carbonate of silver with a soluble bromide. The uses of neutralizing the silver are twofold: one is, that as the amount of acidity of AgNOs varies with different samples, it en sures the same conditions in all cases; the other is, that the presence of nitric acid in emulsion produces a tendency to green and pink discolorations in the finished negative. The addition of atrace of HC1 to the soluble bromide and gela tine is recommended in formula given, for the following reasons. If the soluble bromide be absolutely neutral, and the gelatine a suitable sample (see ante), the HC1 is not necessary, and better omitted. If, however, the gelatine be ever so little alkaline or even apparently neutral, but yet does not dissolve clear, the acid is required. Its use is not to produce AgCl, but to ensure a fine precipitate of AgBr. According to the writer’s experience, a fine precipitate is hardly at all a question of thej method of mixing, and elaborate contrivances for the purpose he considers as quit e unnecessary. A fine precipitate is easily obtained, however rapidly the solutions be mixed, if two conditions exist, viz., if the bromized gelatine solution contain a trace of HC1, and the silver solution be not stronger than 110 grs. per oz. If it be 50 to 60 grs. per oz., it may be poured in all at once, or if a little weak solution be first poured in, the stronger may follow (as per for mula) . A good test for the suitability of a gelatine is to see if a fine precipitate can be obtained without having to add HC1. Too much HC1 retards or prevents the conversion of the AgBr into the sensitive form in cooking, a large excess destroys the gelatine. It will thus be seen that the addition of HOI m ust be made intelligently, according to the other materials accessible. It might be supposed that any acid would make the precipitate fine, and that therefore acid ammonium bromide would be good. Such is not the case, and moreover, the acid bromide has in some way a powerful effect in retarding the conversion of the AgBr into the sensitive form. The proportions of soluble bromide and Ag NO are very im portant. Contrary to usual statements, the larger the excess of soluble bromide the more quickly is the Ag Br converted; if there be but little excess, a very long cooking will be required ; and if exactly the equivalent quantities could be used, the writer believes that no amount of cooking would give the sensitive con dition. Too large an excess, on the contrary, produces a form of a tendency to fog, which is not to be afterwards got rid of by the use of bichromate, but which is more liable to occur with alkaline pyrogallic;developer than withferrous oxalate. Hence the amount of excess bromide must be proportionate to the time of cooking. The writer finds from 11G to 113 grains of Ag NOs to 70 grains NHi Br, and from forty-five to sixty mfutes’ boil ing, give him best results. If K Br be used, he rewommends 86
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