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The photographic news
- Bandzählung
- 6.1862
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- 1862
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- Hochschule für Grafik und Buchkunst Leipzig
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- Bandzählung
- No. 188, April 11, 1862
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Zeitschrift
The photographic news
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Band 6.1862
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- Ausgabe Ausgabe 73
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- Register Index 619
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Band 6.1862
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62. ormed th the black he ah ordi, nee of oil in under esence which Irogen rest is hi fre- f con- when .■n the nee of The erous, vith a ented, le two tered, easily oured, : dy be' les, is teavy, i very r the as a s un- satu i are of I shade ng to lamp at 0 been i fine le air and with lood. n an i the id in ydro- 1 by e by etate iy be d in iabar volu- ■ the n of I ie of dis- . the and I m of I ures, ards tage wise abat the tly, iera and It April 11, 1862.] THE PHOTOGRAPHIC NEWS. 173 may also he prepared by sublimation. In this way the beautiful Chinese cinnabar is prepared. 1 part of sulphur and 4 parts of mercury are sublimed in an earthen vessel, to which an iron cover, kept constantly moist, is luted. In twenty-four hours the vessel is allowed to cool and is broken; tne purer portion of the cinnabar is powdered up and sifted into water, and the fine sediment afterwards collected apart and dried. This cinnabar inclines to carmine colour, and is very expensive, lately, however, means have been found to imitate it in Europe by subliming common cinnabar with sulphide of antimony and then treating the product with solution of liver of sulphur. • ON SULPHATE OF IRON AS A DEVELOPING AGENT. BY M. ADOLPHE MARTIS. Many photographers now employ sulphate of iron as a developing agent for collodion negatives, because they prefer it to pyrogallic acid; nevertheless the latter is pre ferable in many circumstances. In studying the production of photographic pictures by the aid of sulphate of iron— in order to avoid the reduction that frequently occurs in the surface of the solution, and settles upon the film, from which it is impossible to remove it—I have been led to employ acetic ether, which sufficiently retards the appearance of the image, to avoid this reduction, and also the lines arising from the solution being poured on to the film in sufficient Quantity. I have already communicated the result to the French Photographic Society. But there remains another difficulty to be overcome. The sulphate of iron yields grey negatives which acquire suffi cient intensity in the high lights only on condition of a little opacity. This is due to the crystalline state under which the reduced silver is found; and the crystals are larger and better formed in proportion as the sulphate of iron bath is more or less acid. This state of the silver does very well for direct positives but not for negatives. I have thought by eliminating the free sulphuric acid and substituting for it an equivalent quantity of acetic acid, we might entirely avoid this inconvenience and secure to the developing solution the acidity required for it, so that the proof should not become stained by a reduction taking place in the interior of the solution. I have arrived at the compositio of the following developing solution, which is, perhaps, a little complicated, but which has during four months given me and others who have adopted it, the best results, and who have urged me to make it public. Dissglve 100 parts of sulphate of iron in 500 parts of WAten; and if the liquid be not perfectly clear, filter it. Pour Into It 25 parts of a very clear solutiou of acetate of lead, of the strength of 10 per cent, a precipitate is formed which must be allowed to subside. The liquid is then filtered, and 25 parts of acetic acid added; lastly, 450 parts of water con taining 5 parts of acetic ether, and 5 parts of commercial nitric ether, is added to the above. The liquid resulting from these mixtures may bo pre served for a considerable length of time in well stoppered bottles. The reaction is easily understood; by double decomposition sulphate of lead and acetate of iron are formed, which meeting with the free sulphuric acid, give rise to sulphate of iron again and free acetic acid. The proportion of 10 per cent of sulphate of iron, answers very well in the circumstances under which I work, but it may be modified to suit the wishes of the operator. ON THE ACTION OF IODINE IN THE SILVER BATH. BY M. L’ABBE’ LABORDE. I learn from the Society’s Bulletin that Messrs. Girard and Thouret have obtained results entirely different from those published in my note upon the action of iodine in the silver bath. I have therefore repeated my experiments, and again proved the accuracy of all that I have advanced, so long as I maintain things in the same condition. I could not attri bute to the impurities of the iodides dissolved in the nitrate of silver the neutrality it maintained, notwithstanding the presence of iodine; for I have always prepared the iodide of silver by precipitating it from a mixture of nitrate of silver and iodide of potassium, and washing it in several waters before saturating the silver bath with it* I then directed my attention to the solution of silver, which, as will be shown, exhibits a peculiar composition. Before undertaking this research, I found it much easier to prepare a solution of ordinary nitrate of silver, saturating it with iodide, and after proving its neutrality, to introduce the iodine. I repeated this experiment several times, and like MM. Girard and Thouret, I recognized that in these conditions the silver bath quickly becomes acid, notwith standing that it is saturated with iodine. As the effect of the iodine depends upon the solution I employ, I shall endeavour to omit nothing while describing its preparation. Those who have justly reproached me with being too laconic, will pardon me any superfluous details, and not forget that my aim is to prepare a silver bath capable of giving an impressionable film of the greatest possible sensitiveness. I dissolve some pieces of silver coin in nitric acid, and I then precipitate the silver by pure copper, such as the plates formed by the galvanoplastic process for daguerreotype pur poses. After simply decanting the nitrate of copper, I throw a little hydrochloric acid upon the silver powder, and allow it to act for about an hour, and then wash it in several waters. I next dissolve the silver powder in nitric acid, introducing small portions of the metal at a time in order to avoid too great liberation of gas, and when the cold acid will dissolve no more, I gently warm it, and continue adding the silver powder so long as it is dissolved. The solution is evaporated to dryness; but I never fuse the nitrate of silver; this operation has too many objections. In this way I obtain a very acid salt, 140 grains of which I dissolve in 1,000 grains of water. I neutralize it by freshly precipitated car bonate of silver, added in slight excess ; and I saturate this solution with iodide of silver, prepared in the way described above. I then add 1,000 grains of water, and filter. The method I have already advised for saturating the silver bath with iodide must be followed step by step. If the water it must finally contain be added in advance, it will never take up the quantity of iodide it ought to dissolve, even when we add iodide in excess. In fact, if we add a small quantity of water to a concentrated solution of silver, and which we believe is saturated because the iodide was added in excess, a yellowish cloud is formed, which is immediately redissolved; this fully proves that the solution was not saturated, since after having diminished its capacity for saturation by the water added, it is still capable of dissolving the iodide of silver thus presented to it in a state of minute division. Upon adding a further quantity of water, the weakened nitrate of silver finally rejects what it can no longer dissolve. The silver bath I employ, well saturated with iodide, contains then a feeble proportion of carbonate of silver, for this salt is slightly soluble in water. The part played by the carbonate of silver is easily understood: it neutralizes the acid in pro portion as it is produced by the influence of the iodine; but when its action is exhausted, the solution quickly becomes acid. We must then seek another cause. I have never employed iodine except in such silver baths as have already been in use, and which gave foggy negatives; for in practical photography, so long as a silver bath yields proofs entirely satisfactory, we should avoid “doctoring” it. 1 make use of a collodion iodized with iodide of cadmium; * We must remark on this head that the iodide of potassium of commerce is always alkaline, and frequently contains as much as three per cent, of carbonate of potassa.—(A. GIRARD.)
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