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The photographic news
- Bandzählung
- 24.1880
- Erscheinungsdatum
- 1880
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- Englisch
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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. 1121, February 27, 1880
- Digitalisat
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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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FEBRUARY 27, 1880. | THE PHOTOGRAPHIC NEWS. 105 This is so well recognised that, where vitriol is required in large quantities, it is invariably made on the spot, and used, wherever possible, without concentiation. Another class of bodies in which increased purity often means in creased cost, is that in which substances are obtained by a change of conversion of other bodies ; such a case is that of pyrogallic acid. It by no means follows that a weaker sample has been wilfully adulterated ; still, for economy and accuracy of work, it is highly necessary that the acid should be valued. The writer has found the following method of valuation answer well, and therefore lays it before the readers of the Photographic News. Since it depends on the action of the pyrogallic acid on bromide of silver, it directly represents the value of the sample under examination for photo graphic purposes. Some bromide of silver is prepared and dried, and about one gram is introduced into a small flask with a few cubic centimetres of distilled water; 01 gram of the pyrogallic acid is then accurately weighed out and added to the bromide of silver and water ; five or six drops of a solution of pure caustic soda are then added, and the alkaline solation is allowed to act on the bro mide for a given time—say, ten minutes. This matter of time is of the utmost importance, and, having once been decided on, should be invariably adhered to, or the results obtained with different samples will not be comparable. At the end of the time fixed on the alkaline solution is carefully poured off, and the bromide, now partially re duced, is washed with distilled water until free from sodium bromide. This can be rapidly and easily per formed by decantation. A small quantity of pure dilute nitric acid is now poured into the flask and gently heated. The reduced silver is rapidly dissolved, and the solution of nitrate of silver, with excess of nitric acid, poured off into a stoppered bottle; the bromide left unacted on is washed, and the washings added. The silver can now be estimated with standard sodium chloride, as long ago described by Gay Lussac, or the chloride may be precipitated and weighed. If the volumetric method be used, the number of c. c. of solution required will give an arbitrary scale of value, but it is, of course, better to calculate from the amount of silver found in solution the amount of bromide reduced. The writer recently obtained the following results with four samples of pyrogallic acid :— Bromide of silver reduced in ten minutes by one part of pyrogallic acid— 12 3 4 335 367 2-68 2-66 Relative values— 1 2 3 4 Is. lOd. 2s. Is. 6d. Is. 5d. The above will show the necessity not only for accurate work, but for economy of correctly valuing pyrogallic acid. The Topic for next week will be " Carbon Pictures on Opal,” by Mr. J. R. Sawyer. Gorrespondente. EXHIBITION OF PICTORIAL PHOTOGRAPHS. Sir,—Will you allow me to state, in reply to a letter in last week’s News, that the results of the monthly artistic competition in photography are exhibited at each meeting of the Society. The Committee will, no doubt, in due time consider the exhibiting of the whole series at the end of the year; in the meantime the best way for “ A Dry-plate Learner,” or any one else who wishes to see the pictures, would be for them to join the Society.—Yours, &c., H. Garrett Cocking, Secretary, South London Photographic Society. THE ARCTIC PHOTOGRAPHS. Dear Sir,—In the News for February 13, I notice a paragraph in which it is said that during the recent Dutch Arctic Expedition I used wet collodion plates on land, and collodion emulsion at sea. Will you kindly allow me to correct this statement ? During the cruise of 1878, I used wet collodion when practicable, but nearly always the Liverpool dry plates ; while, during the cruise of 1879, I worked solely with gelatine plates prepared by the Liverpool Dry Plate Company. I took some collodio-bromide plates in case of accidents, but only exposed two of them.—Yours very truly, February 18. W. J. A. Grant. CONVEX AND CONCAVE MIRRORS. Dear Sir,—Would you or any of your correspondents kindly inform me, through the News, of the names of makers of convex and concave (silvered glass) mirrors, up to (say) two or three feet in diameter ? Also, what is the best way of cleaning spoilt dry plates, so that they may again be utilized ?—I am, dear sir, yours faithfully, W. T. Jackson. PHOTOGRAPHERS’ SPECIMENS. Sib,—I wish to call your attention to the very aggra vated way in which assistants, &c., are deceived by petty photographers, &c. When they see an assistant adver tising, they generally send for specimens, and these they generally forget to return, especially if good ones. Hoping you will find space for this in your valuable paper, An Assistant. PHOTOGRAPHY IN BED-ROOMS. Sib,—Your correspondent "Yalnif ” is a little too severe respecting my remarks on the above subject. In his letter to the News of 30th (not 10th) he asks Mr. Parkinson to give some directions how to proceed in taking portraits in sitting rooms ; therefore I hoped, quite as much as “ Yalnif,” that Mr. Parkinson would have done so. As, however, such is not the case, perhaps you will kindly allow me sufficient spate to give “ Yalnif ” my modus operandi, fully expecting my brother amateurs will silently laugh at my innocent simpli city. Having been asked by a portrait painter to oblige by taking a photograph of a child in a bed-room, I at first refused, saying I had never attempted such a thing before, and was veiy doubtful as to the resulting picture. However, by gentle persuasion, he induced me to try. 1 started at once, and found the room very small, with only one window about four feet by five. Imagine my nerves—how they trembled at the idea of securing a negative of a child about three years of age with so small an amount of light! I bad read of many wonderful pictures taken on gelatine plates, more especially theUniversity Boatrace, audlresolved to test their capabilities. The child was placed about three feet from the window on an easy chair covered with some light material. All being in readiness, I uncapped the lens, counted five seconds, then the child moved, and of course I recapped the lens at once, hoping to be able to expose longer next time, but was terribly disappointed, as the child moved at the third second. One more trial, but this time the little— what shall I say ?—laughed the moment I uncapped the lens. Having only three plates (W ratten’s) and all exposed, I packed up, feeling very angry with myself for having under taken such a hopeless task, and started off home, the painter intimating that he would call next morning to see how they turned out. After business was over for the day I reluc tantly repaired to my dark-room and commenced developing as per Wratten's instructions, but with a very forlorn hope as to the results. Imagine my surprise to find I had secured a very good, but slightly underexposed negative, a print from ' which I shall be pleased to send “ Yalnif,” together with any
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