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
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• Sammlungen: Fotografie
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DECEMBER 21, 1885. | THE PHOTOGRAPHIC NEWS. 819 tube, as in the diagram, put some clean copper turnings, about one ounce of these being used for every four ounces of common carbonate of soda, or for crystal carbonate cool. The greater part of the impurities, which consis chiefly of chloride and sulphate, being more soluble than the sulphite, are left in the mother liquor, and the sulphite crystallizes out. The liquor should be poured off, and the crystals thrown on a filter to drain, after which they may be dried between blotting-paper. By this method I have made from common soda a sul phite containing over 90 per cent, of Na,SO3,7H,O ; but should greater purity be desired, the salt obtained as above described may be redissolved in water, and again crystallized. As this salt is so very liable to oxidise, care should be taken to expose it to the air as little as possible, and all the water used in its preparation should have been boiled recently, as ordinary water contains a considerable quantity of dissolved oxygen. Before using, test the sul phite as directed in the last paper of this series. about two ounces copper for four ounces soda. The cork should then be carefully' lilted into the flask, and the latter fixed in the retort stand. The delivery tube is con nected by a short piece of india-rubber tubing to another glass tube running through the cork to the bottom of a six- ounce bottle about half full of water. Thegas, after bubbling through the water, passes out of the washing bottle by a glass tube, which reaches only just inside the cork, and by this it is led nearly to the bottom of the beaker con taining the solution of soda. Having ascertained that the corks and joints are tight, run into the flask through the thistle funnel sufficient strong sulphuric acid to cover the copper turnings. Now apply a gentle heat with a Bunsen burner, using the rose top, as shown in the diagram. The copper decomposes the sulphuric acid, sulphate of copper and sulphur dioxide being the final products of the reaction, thus— 2H,S0,+Cu =CuSO,+SO, + 2H-0 If the heat is properly adjusted, the gas is given off in an even stream, and is washed, principally to catch any sulphuric acid that may be volatilized, by passing through the water in the intermediate bottle ; and finally, it is ab sorbed by the carbonate of soda in the beaker. When the action has properly commenced, the soda solu tion will be seen to effervesce, minute bubbles being con tinuously given off. Sulphur dioxide is passed through the solution for some time, when the effervescence will considerably diminish, and the liquid will have an acid re action, shown by its reddening blue litmus paper. When this happens, it is time to stop the flow of sulphur dioxide. This is done, not by removing the heat, which, by leaving the flask free to cool, would diminish the volume of gas con tained in the flask, and owing to the partial vacuum formed, the water would flow back from the wash bottle, and probably break the flask, or at the best cause great in convenience. First, disconnect the flask from the wash bottle, and then remove the Bunsen burner, and carry the retort stand with the flask into the open air to cool, before washing out. The solution in the beaker now consists of normal sul phite of sodium, NagSO,, with some bisulphite or acid sul phite of sodium, NaHSOa, which is formed, as shown by the equation, by the excess of SO, passed into the solu tion— NaSO3S0, +H,0= 2NaHSO 3 The solution will also contain some carbonic acid (car bon dioxide), and perhaps some free sulphur dioxide. The liquid is transferred to an evaporating basin, and boiled to expel all dissolved but uncombined gas. If, after this, a drop of the solution, taken out on the end of a glass rod, reddens litmus paper, some solution of soda must be added a little at a time, with boiling between each addition, and then testing with litmus till the reaction is neutral. We have now simply to boil down till a scum of crystals is formed on the surface when it is blown upon, and leave to COMMUNICATIONS FROM THE PHOTO-CHEMI CAL LABORATORY OF THE IMPERIAL HIGH SCHOOL OF BERLIN. BY DR W. H. VOGEL. CHRYSANILINE as Optical Sensitizer and Accelerator of Development. Dr. Lohse was the first to recognize the sensitizing action of chrysaniline and of diamidoabenzol. He found that the first mentioned substance raised the sensitiveness for green and yellow. Eder experimented with the same body, and discovered that it altered the spectrum of bromide of silver, inasmuch as it shifted the maximum of sensitive ness towards the green. Eder does not allude to a second maximum of sensitiveness beside that of pure bromide of silver, nor does Messerschmidt. The latter says: ‘‘Ac cording to Lohse ... it is all the same whether the plate is immersed in chrysaniline solution before or after expo sure.” Messerschmidt refers in these words to my theory of optical sensitizing by a dye-stuff. In fact, it would be remarkable in the highest degree, if chrysaniline possessed the property of raising the sensitiveness for green after, as well as before, exposure. As the subject is one of great interest to me, I made experiments with two of Sack’s and two Monckhoven plates, exposed side by side in the spectrum. One plate of each make was developed in the usual way, and the other after an immersion in a bath of chrysaniline before develop ment. The result was that chrysaniline greatly accele rated development (on this practically important point I shall have more to say further on), but the colour-sensi- tiveness was not altered in the slightest degree. The spectra (of which each plate bore five impressions, with exposures of }, 1, 2, 5, 10, and 15 seconds) showed the same increase and diminution of intensity, and extended just as far with the bathed, as with the unbathed plates. Colour-sensitiveness consequently is only given by chrys aniline—and it cannot be otherwise—when the plate is treated with the substance before exposure. Neverthe less, I have obtained, when experimenting with chrysani line, certain results which differ in some points from those reported by Lohse, Eder, and Messerschmidt. Herr Messerschmidt states that chrysaniline removes the ordinary maximum of photographic action towards the red, and adds, that since this dye-stuff has only an absorbing action in one portion, the characteristic referred to cannot be said to be in connection with an absorption band. I must, on the other baud, recall the fact that chrysaniline has an absorption band between F and b. I have referred to this in my hand-book of “ Spectrum Analysis, 1878.” This absorption band must, however, correspond with a photographic action. Such, neverthe less, does not appear to be present, according to Eder, Messerschmidt, and Lohse. In order to clear up this point 1 have made further experiments. In the result it