The photographic news

• Bandzählung: 29.1885
• Erscheinungsdatum: 1885
• Sprache: Englisch
• Signatur: F 135
• Vorlage: Hochschule für Grafik und Buchkunst Leipzig
• Digitalisat: Hochschule für Grafik und Buchkunst Leipzig
• Digitalisat: SLUB Dresden
• Rechtehinweis: Public Domain Mark 1.0
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• PURL: http://digital.slub-dresden.de/id1780948042-18850000
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• Sammlungen: LDP: Historische Bestände der Hochschule für Grafik und Buchkunst Leipzig
• Sammlungen: Fotografie
• Bemerkung: Seite I-II fehlen in der Vorlage. Paginierfehler: Seite 160 als Seite 144 gezählt.
• Strukturtyp: Band

• Digitalisat: SLUB Dresden
• Strukturtyp: Ausgabe

644 THE PHOTOGRAPHIC NEWS. [OcTOBER 9, 1885. members of it. I knew of one firm that got over the difficulty by taking as nearly as possible an equal hand in every picture made to exhibit under the name of the firm, and if either of them got ? particularly bright inspiration that could not be shared by his partner, the result was always exhibited in the name of the individual; the medals for other productions were divided. Notwithstanding what I have said above, I see no objection to a photographer accepting assistance in the production of his picture. The materials, tools, and the mechanical parts of production should be kept distinct from conception, and are only rational aids to results. This view of the matter was very ably put some years ago by an anonymous writer in the News, whose remarks I paraphrase. Both painters and sculptors have assistants ; in some instances it is well-known that these assistants have acquired such ability as almost to carry out the whole work of their masters from the sketch which illustrates the conception. Again, for the sculptor who has made his model in clay, a great part of the work is carried out by other hands than the artist’s, but under his guidance. For all that, on beholding the finished picture or statue, it is evident that both painter and sculptor are the Alpha and Omega in the production of these works. So also with photography as an art. To conceive and to carry out the production of the negative of his picture is, with the photographer, to produce and be the author of the work. It is no more necessary for him to have prepared his plates or mixed his developer, than for the painter to strain his canvas or grind his colours. To sum up : if a man wants safely and honourably to put his name on any photograph and call it his own, the subject and arrangement should be of his own conception. What he does by the hand of another should be under his own superintendence and guidance, and the delicate and important parts, such as exposing and developing, which require matured judgment, should be done by himself. RESEARCHES ON THE CHEMICAL ACTION OF LIGHT. BY PROFESSOR DR. J. M. EDER. 1 .—Behaviour to light of ferricyanide of potassium, and mixtures of the same with other substances. 2.—Relative light sensitive ness of ferri-cyan, nitro-prussic, and other iron compounds. 3.—Various copper compounds. 4.—Indigo sulphate of soda. 5 .—Molybdic acid. 6. Decomposition of chlorine and bromine water, and of tincture of iodine in the light, and the influence of organic substances upon this process. 7.—Decomposition of alco holic solution of chromate in the light. 8.—Decomposition of iodide of mercury by light. 1 .—Behaviour to Light of Ferricyanide of Potas sium, and of Mixtures of the Same. It is well known that an aqueous solution of ferri cyanide of potassium becomes decomposed in the light, with the formation of a blue precipitate, and of ferro cyanide of potassium. Upon the duration of this reaction, and the quantity of the decomposition products, however, nothing has appeared. For the study of these points, I placed solutions of various strengths in closed flasks from the 28th July to the 2nd November, 1884, where they received the action of the sun and daylight, and in the immediate neighbourhood of the same another sample of the same solution protected from light. The solation becomes at first dark brown, afterwards blue. After a time, a precipitate of Prussian blue was formed, in addition to ferrocyanide of potassium and free hydrocyanic acid. The Prussian blue was present as the so-called soluble Prussian blue ; when collected upon a filter and washed, the filtrate began to be coloured as soon as the greater part of the soluble salts had been removed. For the quantitative estimation of the precipitate, I washed towards the end of the operation with a very dilute solution of perchloride of * Communicated to the Imperial Academy of Vienna. iron, and finally with alcohol. The precipitate was then dried at 100° C., and weighed. The ferrocyanide of potassium in the filtrate, which gave neutral reaction, was estimated by precipitation with acetate of lead, and treatment of the precipitate with per manganate of potash.* The formation of hydrocyanic acid in the ferricyanide solution exposed to light makes itself evident by the smell. Old lighted solutions, by warming to 60° C., develop much hydrocyanic acid ; fresh solutions, on the other hand, yield very little. Similarly, the first, by distillation with bi carbonate of soda, give an easily recognisable amount of hydrocyanic acid in the distillate, but the latter an ex ceedingly small quantity. The quantities of decomposition products from 150 com. of solution was estimated in solutions of various concentra tions, as follows :— An eight per cent, solution of ferricyanide of potassium separated—: 0’041 grammes of Berlin blue, and 0703 grammes of ferrocyanide of potassium. A four per cent, solution of ferricyanide of potassium separated 0’017 grammes of Berlin blue, and 0-432 grammes of ferrocyanide of potassium. A one per cent, solution of ferricyanide of potassium separated 0 023 grammes of Berlin blue, and 0 322 grammes of ferrocyanide of potassium. From this it appears that for each part by weight of Berlin blue, there is formed from 7 to 25 parts of ferro cyanide of potassium (besides hydrocyanic acid). A one per cent, solution is relatively more quickly decomposed than an eight per cent, solution. Mixtures of solution of ferricyanide of potassium with sugar or oxalic salts are decomposed in the light more quickly. A solution (150 c.cm.) which contained: Eight per cent, of ferricyanide of potassium, and eight per cent, of sugar, gave 0 092 grammes of Berlin blue, and 1032 grammes of ferrocyanide of potassium. One per cent, of ferricyanide of potassium, and } per cent, of oxalate of ammonium, gave ’9 grammes of Berlin blue, and 064 grammes of ferrocyanide of potassium. E'ght per cent, of ferricyanide of potassium, and four per cent, of oxalate of ammonium, gave '9 grammes of Ber lin blue, and 0528 grammes of ferrocyanide of potassium. These mixtures, then, are decomposed quicker than pure ferricyanide of potassium. That the one per cent, solution gave on analysis a greater amount of ferrocyanide may be due to an inexactitude in estimation. Ferricyanide of potassium and citrate of potash behave similarly to the mixture with oxalate. A solution of ferricyanide of potassium, added to acetate of lead, gives in the light a bluish-white precipitate of ferrocyanide of lead, which can be extracted by means of hyposulphite of soda, as well as Prussian blue. Ferricyanide of potassium, and sulphate of uranium, is more sensitive, then, tha i the foregoing mixture ; it gives a reddish brown precipitate, which contains much ferro cyanide of uranium. Ferricyanide of potassium and bichloride of mercury mixed are much more sensitive to light than either alone. Chloride of mercury, Prussian green, and hydrocyanic acid are formed. 2 .—Relative Sensitiveness to Light of FERRICYAX, Nitroprusside, and other Iron Compounds. Dissolved ferricyanide of potassium is less sensitive to light than the ammonium salt. B th are, in the absence of light, very permanent. Solution of hydroferri- cyanogen becomes blue even in darkness, quicker however in the light. Pure ferricyanide of iron behaves with light like a mixture of ferricyanide of potassium and iron-alum. The last named decomposes in darkness with the formation of * The ferrocyanide of lead was first dissolved in caustic potash, and then acidified with hydrochloric acid.