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The photographic news
- Bandzählung
- 27.1883
- Erscheinungsdatum
- 1883
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- Englisch
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- Hochschule für Grafik und Buchkunst Leipzig
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- Hochschule für Grafik und Buchkunst Leipzig
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- Bandzählung
- No. 1275, February 9, 1883
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The photographic news
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- Titelblatt Titelblatt I
- Register Index III
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FEBRTARY 9, 1883.] HE PHOTOGRAPHIC NEWS. 85 No. 2. No. 1. No 2, ounce ounces 1 3 5 grains 4 ounces 1 3 ounce ounces 1 drachm 9 drachms Ammonia Water * Hydrokinone Water To every four ounces of No. 1, thirty minims of No. 2 are added to obtain full intensity. As 1 will now show you, this is a most beautiful deve loper, giving negatives perfectly free from stain or fog, and of a good colour, which should make it invaluable for transparencies. At present it is expensive, but, should its price diminish, it will probably be preferred to either pyrogallic or ferrous oxalate. Potassium oxalate Water THE SOUTH LONDON PHOTOGRAPHIC SOCIETY’S POPULAR LANTERN MEETING, AND ITS LESSONS. BY WILLIAM BROOKS, t I must apologise for bringing this subject up again ; but I think a practical explanation of certain matters may be of service as a guide for contributors in the future. I think you will all agree with me when I say that the recent lantern meeting was by far the best we have ever had as regards the quality of the slides ; for you must be aware that many of our members who contribute, do all in their power to ensure its being a successful gathering, by preparing slides specially for the occasion. Some of those members know very little about making slides, but I am sure they do their best. This year we had fewer bad slides than in years gone by ; but I think there is still room for a little improvement. Several, I have no doubt, have seen their weak points, and have made an improvement in this year’s productions, which is a good lesson for them, for I believe there is nothing to equal a good untouched photograph when exhibited on a large screen. I may direct attention to one or two points which some do not seem to quite understand. One is as regards the size. The best size for a slide is 34 by 3}, but they must not be more than 34 high. They may be a little longer—say 44 inches—but the former size is the best. I regretted the case of one gentleman who brought me some slides of excellent quality, but they were mostly about seven inches in length. I was quite unprepared for this size, so had to pass them over, which I regretted very much. One gentleman asked me if I had one of those push- Ferrous sulphate Water • “ Instruction in Photography,” 5th edition. V A communication to the South London Photographic Society. The solutions are best made with hot water, and both should be slightly acidified—preferably the ferrous sulphate with sulphuric, and the oxalate with oxalic acid. To develop a plate, place three ounces of No. 2 in a measure, add half-an-ounca of No. 1, and pour over the plate as before described. If there is any tendency to fog, a small quantity of potassium bromide (say a quarter grain to the ounce) should be dissolved in the oxalate solution. To regulate the density, increase or diminish the ferrous sulphate, but never add more than one of ferrous sulphate to three of oxalate, or ferrous oxalate will be precipitated. In case of under-exposure, add one oi two drops of a dilute solution of hyposulphite, and in cases of over-rxposure add potassium bromide or sodium citrate [examples shown]. On mixing the two solutions to make a developer, it is found that they always become alkaline. This seems rather strange, getting an alkaline solution by mixing two acid ones together, but the reason is not far to seek: ferrous oxalate has a great tendency, we know, to combine with any acid it can get, and form a ferric salt, while potassium oxalate is naturally an alkaline substance ; hence the ferrous oxalate takes up the free acid which was added, forming a small quantity of ferric salt, and leaves the potassium oxalate in its normal alkaline condition. It may be asked, why acidify the solutions at all, since on mixing they become alkaline? In the case of the ferrous sulphate, it is to keep the solution clear; and in that of the potassium oxalate it is found that if it be alkaline before mixing, the resulting developer has a tendency to give thin images, and sometimes fog. After being left for some time, even if well stoppered, the oxalate developer becomes to a great extent inactive from the forma tion of a basic salt. Hudroklnone Developer.—Hydrokinone is an organic substance somewhat similar in properties to pyrogallic acid ; its use as a developer was suggested by Captain Abney, in 1880. It requires the addition of ammonia, but not bromide. The formula is as follows :— No. 1. potassium oxalates—one called neutral oxalate K,(C.0,), the other, salts of sorrel or acid oxalate, and which latter may be considered as a compound of one molecule of the neutral salt in combination with a molecule of oxalic acid, K2(C,0.)H2(C,0.). The former of these, or what is called neutral oxalate, is the one employed for development. It is prepared by neutralizing oxalic acid with potassium car bonate K,(C0a) +H,(C,0.)=K:(C:0+H:04+C0: The acid oxalate can also be readily converted into the neutral oxalate by neutralizing its oxalic acid with potassium carbonate. Neutral potassium oxalate is a white crystalline substance soluble in about three parts of cold water, its solution being slightly alkaline to test paper. It should be slightly acidified, preferably with oxalic acid before use. Its use in development is to dissolve the ferrous oxalate, which it does very readily, forming a double salt; beyond this it does not appear to have any effect, neither acting as a retarder or accelerator. Ferrous Oxalate, Fe(C,0,).—Iron forms two series of compounds, called respectively ferrous and ferric ; thus we have ferrous oxide, FeO ; ferrous bromide, FeBra ; ferrous oxalate, Fe(C,0,) &c. ; and with these same substances another series of compounds—ferric oxide, Fe,O, ; ferric bromide, FeBra ; ferric oxalate, Fe,(C,0,)a, &c. It will be noticed that all the ferric compounds contain half as much again of the other substance in combination with the same quantity of iron as the ferrous. All the ferrous compounds, and more especially ferrous oxalate, tend to combine with oxygen or other substance to form the ferric series of com pounds, and it is in virtue of this property that ferrous oxalate acts as a developer. It is prepared as a yellow powder, nearly insoluble in water, by adding ferrous sul phate to oxalic acid, and washing by decantation ; and in solution either by dissolving the yellow powder in a solu tion of potassium oxalate, or by adding 1 part of ferrous sulphate to a solution of 3 parts of potassium oxalate (Eder). Fe(SO,)--K,(C,0,)=Fe(C,0,)+K-(S0,) The action which takes place in development is very similar to that when pyrogallic is used. 2Ag„Br-2Fe(0.0,)+-K-(0.0,=Fe:(00)H4Ag-2KBr The silver sub-bromide is reduced by the ferrous oxalate, the bromine set free combining with some of the potassium oxalate, forming potassium bromide, and the iron forming ferric oxalate. The silver thus reduced combines with fresh silver bromide to form sub-bromide, which again becomes reduced until the image is built up. The ferrous oxalate really exists in solution, in combination with some of the potassium oxalate as a double salt, Ka(C.O,)Fe (C a O 4 ), but this does not affect the change which occurs. Potassium or Ammonium Bromide.—These have precisely the same effect as in pyrogallic development. Hyposulphite of Soda.—A small quantity of this substance added to the oxalate developer acts as a powerful accelerator, and promotes density ; although not essential as is ammonia in pyrogallic development, its action is very similar. Formula for Oxalate Development.—Prepare solution of the following strength :—
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