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The photographic news
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- 29.1885
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- 1885
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- Bandzählung
- No. 1415, October 16, 1885
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The photographic news
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Band 29.1885
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- Register Index III
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662 THE PHOTOGRAPHIC NEWS. [October 16, 1885. have fallen into forgetfulness. The first observed* that he had found that chlorine water is not only by itself decom posed in the light, but that this decomposition is assisted when in combination with the chlorine water there is present a substance rich in hydrogen, which, for the most part, is the case with organic substances. Monheimt admitted that organic substances accelerate the photo chemical decomposition of chlorine water, but did not believe that the hydrogen itself played any part in this action. Monheim experimented with vegetable extracts. StadelerJ found that citric acid especially was quickly attacked by chlorine in the light. The photo-chemical reaction of gaseous chlorine upon acetic acid, &c., I will not treat further here, but only upon aqueous solutions of chlorine, bromine, and iodine. In the first place, I compared the relative sensitiveness of chlorine and bromine water, and alcoholic tincture of iodine* ; and then studied the acceleration of the process by the presence of organic substances. Chlorine, bromine, and iodine were dissolved in equivalent proportions, and exposed to light in vessels of similar form. Other quantities were, under like conditions, kept in darkness. After ex posure to light the remaining free chlorine was estimated by treatment in the known manner, with iodide of potas sium, starch, and hyposulphite of soda. No account was taken of the chloric acid which, according to Poppert, is formed in addition to hydrochloric acid and oxygen. The analyticalexamination was undertaken by me in conjunction with Herr Schlagenhaufen. The concentrated aqueous bromine solution contained ■ 8'000 grammes bromine in 1 litre ; the diluted, 0'800 grammes. Chlorine and iodine were dissolved in equivalent quantities. The chlorine and bromine water were further decomposed in the presence of the organic ' acids as mentioned. A Solution of Lost in the Light. In Darkness. Diferen ce. Time of Keeping. Chlorine water concentrated 53'95 % Cl 6-69 0/ Cl 47'26 0/o 30 days ,, ,, diluted 4187 „ 4 32 37'55 Bromine water concentrated 35 Br 12 Br 1'3 „ „ diluted 41 ,, 2'5 1'6 Iodine in alcohol 0'06 I 0 0'06 Chlorine water concentrated 5-0 Cl 0 5-0 2 hours in sunlight Bromine water concentrated 0'8 Br 0 08 Chlorine water + tartaric acid 60 Cl 7 Cl 53 1 hour 100 ,, 24 76 2 hours „ n „ 4-citric acid... 70 „ 46 34 1 hour 21 33 31 33 ••• Bromine water 4- tartaric acid 97 94 3 2 hours ., G7 Br 2 Br 65 1 hour „ 100 3 97 2 hours „ „ „ + citric acid 100 „ 5 , 95 1 hour „ It follows from the above that chlorine water decom poses in the light 6 to 12 times more quickly than bromine water, and that alcoholic tincture of iodine is about 1,000 times more stable in the light than chlorine water is. Chlorine and bromine water also decompose in darkness, and always the first-named more rapidly than the second. The presence of tartaric and citric acids accelerates de composition both in the presence and absence of light; but the presence of light greatly accelerates the action. Citric acid is more quickly attacked than tartaric acid by chlorine water, both in the presence and the absence of light. With bromine water the decomposition of these acids is slower in darkness than with chlorine water. On the other hand, in the light, the action is nearly as rapid with the former as with the latter. The chemical energy of chlorine is more strongly exalted by light in the case of citric than of tartaric acid. We find an example analogous to this with perchloride of iron, which is more sensitive to light with citric acid than with tartaric, as I have previously shown. An alcoholic tincture of bromine becomes coloured in darkness in a very short time (from half an hour to two hours). In direct sunshine the colouring is almost instan taneous. The rapidity of the photo-chemical decomposi tion of chlorine water, bromine water, and alcoholic tincture of iodine, is in the order of the increase of their atomic weights. 7. Decomposition of Alcoholic Chromate Solution in the Light. Saturated solutions of bichromate of ammonia were prepared in absolute alcohol, in alcohol of 50 per cent., and in that of 25 per cent., and exposed for three years at a sunny window. 1. The solution of bichromate of ammonium in absolute alcohol was changed in colour in three months time, and • Wochenschrift fur die gesammte Ileilkundc Von Camper in Berlin, 30th October, 1835. Bucher's Repertnriwn, f. d. Pharmacie, 1835, lie. 8. 355. + Bucher's Repertoriutn. Ibid. $ Annul, d. Chem. u. Pharm, Bd, iii., 8. 299. had deposited a slimy green precipitate of oxide of chromium. The solution contained acetic acid, aldehy de and acetic ether. 2. The solution in 50 per cent, alcohol had during this time deposited only a little brownish yellow precipitate of “ chromate of chromium,” and even after three years the liquid was dark red from the presence of chromate, and the precipitate was not perfectly converted into the oxide of chromium. 3. The solution in 25 per cent, alcohol behaved like that of 50 per cent., but at the end of the three years the de composition was still less advanced than in the other. It follows that in this case the alcohol accelerates the deoxidation of the bichromate by light, as, for example, is the case with nitrate of uranium and perchloride of iron, whilst, with increase of water, sensitiveness falls off. An aqueous solution of bichromate is not changed by light. 8.—Decomposition of Mercurous Iodide by Light. Mercurous iodide is a greenish yellow powder which claims a sensitiveness to light near to that of chloride of silver. Upon gum or gelatine paper which has been im pregnated with mercurous iodide, a photographic print may be obtained with a few minutes exposure to sunlight Upon the extent of the photo-chemical process nothing is known with certainty. According to Artus, darkening only takes place with moist mercurous iodide, and no iodine is given out, but hydriodic acid, from which Artus con cluded that suboxide of mercury was probably formed. According to Inglis, it decomposes in a few weeks when air is present, even in the absence of light, into mercury and iodine. I prepared by yellow light, mercurous iodide by precipi tation from nitrate of mercury with iodide of potash, washed the precipitate with alcohol, and placed it in glass tubes. One of these tubes I filled with moist air, another, * Aqueous solution of iodine is very permanent in the light, and experi ments with it under similar conditions to those observed with chlorine ana bromine water gave no results. + Liebig's Anna I, Bd. 227, S. 161.
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