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The photographic news
- Bandzählung
- 24.1880
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- 1880
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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. 1159, November 19, 1880
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Zeitschrift
The photographic news
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Band 24.1880
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- Register Index 631
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Band
Band 24.1880
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November 19, 1880.] THE PHOTOGRAPHIC NEWS. 555 A NEW INSTANTANEOUS SHUTTER. The accompanying engravings represent an instantaneous shutter designed by Mr. S. P. Jackson, of Henley-on- Thames. Fig. 1. is a front view ; A A, two discs of card- Fig. 1. C C, mahogany frame, turned in two pieces, and joired at E E. The whole is enclosed, except the aperture in the middle. of ferric chloride and tartaric acid to the light, I found besides ferrous chloride and hydrochloric acid, a little formic acid, and that with continuous exposure carbonic acid is also given off. An aqueous solution of ferric chloride mixed with citric, acid is not so readily reduced by light as that with tartaric acid ; but the mixture which I found to surpass all those above-named in sensitiveness is that with oxalic acid. Marchand was therefore quite right in using a mixture of ferric chloride and oxalic acid for the construction of his “Photantipimeter,” an instrument intended to measure the intensity of light by the quantity of carbonic acid given off on exposure.* This mixture is principally acted on by the blue rays of the spectrum, and in a less degree by the violet rays ; but even the yellow and red rays have some slight effect; a long-continued exposure to gaslight is also sufficient to produce reduction. If the oxalic acid which is mixed with the ferric chloride contains nitric acid, nitric peroxide will be found in the carbonic acid set free by the luminous action. A solution of ferric oxalate in water is decomposed by light according to the equation— Fe> (C, 0,)3 = 2(Fe C2 0,) + 2C02. board, or ebonite, with an opening, B, cut in each, the size of the lens. In the position of the discs in the engraving the lens is open. Fig. 2 is a side view of the back; B B, Fig. 2. For focussing, the trigger is placed at the middle stud. two pulleys of hard wood ; C, a leather or steel baud con necting the two pulleys ; D, a brass handle and trigger; E E E, stud-pins to catch the handle ; F, an india-rubber band or spring. In the position of the trigger shown, the shutter is set for use, and on being released from the stud- pin the india-rubber band causes the two pulleys to revolve rapidly, the discs cross in opposite directions, and the expo sure of the plate takes place. With this shutter, various scenes at Henley Regatta, passing trains &c., have been taken; the marvellous swan pictures of Messrs. Marsh Brothers were secured by a shutter of the same construction, the exposure being about the 130th part of a second. As I could trace no other products of the decomposition except ferrous oxalate and carbonic acid. This decom position was first observed by Dobereiner in the year 1831, t and it was afterwards investigated by Suckow,# Draper,§ and Reynolds. The indigo blue part of the spectrum seems to be the most effective in producing this reaction. My own experiments have convinced me that the amount of ferrous chloride reduced from all these solutions increased considerably with the degree of con centration and the rise in temperature. Until these rela tions have been thoroughly studied it will not be possible to construct a photometer with these solutions, although Draper, Lipowitz, and Woods|| have all tried to do so. A mixture of ferric chloride with acetic acid or formic acid, as also a solution of ferric acetate or formiate, is non sensitive to light. With basic ferric oxalate I did not suc ceed in observing any decomposition under the influence of light. Potassic ferric oxalate, and the corresponding double salts of sodium and ammonium, are quickly reduced by light, whether they are in the solid state or dissolved in water ; this was first noted by Bussey,TT in 1838. The same reaction was also more closely investigated in an appendix to the treatise by Herr Valenta and myself on ferric oxa late and its double salts. Under the influence of light these crystals of these salts turn yellow on the surface and lose their lustre, but the action penetrates deeper very ON THE DECOMPOSITION OF IRON CHLORIDE AND OF SOME OF THE ORGANIC FERRIC SALTS BY THE ACTION OF LIGHT. BY DR. J. M. EDER.* Iron chloride, both in the solid state and when dissolved, does not change on exposure to light; but when mixed with certain organic substances it is rapidly reduced by luminous action. The first observation in this direction was made more than 200 years ago with a solution of iron chloride in ether, at that time known as Bestuschef’s nerve tincture ; this solution loses its yellow colour on ex- posure to light.t In 1804 Gehlen further investigated this phenomenon, and discovered that the ferric chloride is re ¬ duced to the ferrous chloride, inasmuch as some of the chlo rine is set free, and a little chloric ether is formed.+ Poite- viu found that a mixture of iron chloride with tartaric acid, glycerine, or alloxantin—more especially with the first of these substances—readily forms ferrous chloride under the action of light.§ When I myself also exposed a mixture * Read before the Vienna Academy of Science. + Macquer's Chemical Dictionary, 1790, vol. vi.,p. 548. 1 Gehlen's Journal, vol. iii., p. 666. { Comptei Rendus, 1861, vol. Iii., p. 94. slowly, probably because the yellow crust which forms is not readily permeated by actinic light. After being ex posed for some time to the continuous action of light, the crystals disintegrate. When the salts are pulverized they turn yellow much quicker, and in that state they contain, besides the undecomposed salt, an amount of ferrous oxalate, with (so soon as the atmospheric air is admitted) small quantities of basic ferric oxalate, and both of these latter substances remain undissolved on being treated with water. An aqueous solution of potassium-ferric oxalate decom poses more rapidly in the light than the solid salt. If the air be excluded the action is given by the equation— Fee (C: 0,)6 K, = 2Fe O 3 0 + 3K: C 2 0 + 2002. Part of the ferrous oxalate crystallises out, but the rest • Etude sur la force chimigue dans la lumiHre dn srliel, 1875. Mar- chand’s solution for his photometer consisted of 10 cub. centim. of ferric chloride solution, 20 cub. centim. of a 5 per cent, solution of oxalic acid, and about 70 cub. centim. of water. + Schweigaer'» Journal, vol Ixii., p. 90. t On the Chemical Action of Light, 1832, p. 27. % Philosophical Magazine, 1832, vol. li., p. 161. Dingier's Polytechnic Journal, vol. cxlvi., p. 29. II Kreuttcr^s Zeitschrift filr Photographic, 1860 and 1861. “I Journal de Pharmacie, 1838. Journal filr Practitche Chemie, vol, xvi., p. 345.
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