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The photographic news
- Bandzählung
- 7.1863
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- 1863
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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. 250, June 19, 1863
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Zeitschrift
The photographic news
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Band 7.1863
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- Register Index 619
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THE PHOTOGRAPHIC NEWS. Vol. VII. No. 250.—June 19, 1863. CONTENTS. Note on the Results of Mr claishc.. n, . . . , .. PaGI By John Spiller, F.C S Photometric Observations. Photographic Chemicals 280 OnsPevslopingathe Photographic Negative. By "ug"Testeli 290 NTCrophodigrapnd, Pry Processes., Dr. D.van Aonickhoven 292 Photographs:‘.on.th.Art.of taking Enlarged Copies of A Few Words on Portraiture .... 295 Dialysis 296 Aerial Photography 297 Annual Report of the South London Photographic Society 297 Correspondence 297 Proceedings of Societies 298 Photographic Notes and Queries 299 Talk in the Studio 300 To Correspondents 300 Photographs Registered during the past Week 300 NOTE ON THE RESULTS OF MR. GLAISHER’S PHOTOMETRIC OBSERVATIONS. by JOHN SPILLER, r.C.9. Apter reading the interesting account of Mr. Glaisher’s last balloon ascent, as given by him in the Times of the 22nd April last, I was induced to make some experiments with the view of imitating, if possible, the extraordinary con ditions under which that gentleman observed, at an altitude of three miles, and in the clear atmosphere above the clouds, that surfaces of sensitized photographic paper were not so much darkened in the course of half-an-hour’s exposure to direct sunshine as were similar sheets by one minute’s solar action within the grounds of the Royal Observatory, Green wich. Several causes have been assigned by way of account ing for these remarkable results, and some useful suggestions followed the announcement of the full particulars by Mr. Glaisher at the meeting of the London Photographic Society, on the 5th May. It was on this occasion stated that the thermometer indicated 21° Fahr., and that the dew point was below zero at the time of exposure. These con ditions, at the altitude mentioned, are indicative of an exceedingly dry and rare atmosphere, in which rapid evaporation must occur, and the cold would be sufficiently intense to freeze very quickly any traces of water still linger ing in the pores of the paper. Absence of hygroscopic moisture appears then the probable explanation of the facts observed. The verification of this opinion is, I believe, contained in the experimental results which have now to be described. Sheets of albumenized and plain salted paper were sensi tized respectively on nitrate of silver in the usual manner, and, when air-dried, were cut into slips for comparison. 1. Exposed to bright diffused daylight in a glass globe filled with air at the ordinary pressure. 2. The same arrangement; the air in the globe being exhausted by the aid of an ordinarily good air-pump, until the vacuum gauge stood within half an inch of the height of the barometric column. 3. Similar experiment to No. 2 in all respects, excepting that a piece of moistened filter paper was placed near, but not in contact with, the sensitized paper inside the glass globe. 4. Also similar to No. 2, but with a supply of chloride of calcium to absorb water from the rarefied air. twohours intpumping out the air the paper was kept for I n tne dark under a glass receiver, within which wassassna owdish containing sulphuric acid to absorb the mosdnaAt the end of that time, exposed to light beside the orinary paper under glass comparison. , nuicePaper were kept some time in an atmosphere dried y 7 Slim of then exposed to light as before. cation of heat, nPa then erodrie thoroughly by the appli- between two plates of duaxposed to light under pressure hygroscopic condition seving’fotmhaparapnrs in ordinary The results were as follows :— No. 2 darkened more slowly than No. 1, and exhibited, in the case of albumenized paper, a pale lilac tint, instead of a rich chocolate or purple brown. No. 3, in the moist vacuum, was affected by light in the same manner, and as quickly, as No. 1. No. 4. The action of light was very much retarded, more so than in No. 2. Nos. 5, 6, and 7, were but slowly affected, the colour of the papers being generally similar to No. 4. The plain chloride of silver paper, and other sheets pre pared with Swedish filtering paper, exhibited, in different degrees, the same general result as the albumenized surfaces. The effect of exposure to intense cold, or artificial freezing mixtures, remains yet to be investigated, and it cannot be said that the effects observed in the course of my experi ments were so decisively marked, although doubtless of the same character, as those described by Mr. Glaisher. The influence of moisture in increasing the sensitiveness of these photographic surfaces has been many times pointed out by others as well as myself, and was particularly alluded to in my “ Description of a Desiccating Box for Preserving Sen sitized Paper, ’ read on the 5th March, 1861, at a meeting of the London Photographic Society. In using this apparatus I found that the sheets of sensitized paper could not be employed for printing in the unusually dry state in which they were taken from the box, but that a short interval, for re-absorption of hygroscopic moisture, must be permitted before laying them in contact with the negative. The addition of nitrate of zinc as a deliquescent agent was tried under the impression that this substance would have furnished a more uniformly sensitive paper under all circumstances ; but the result of such admixture has not proved this to be the case. The use of a bath of fluoride of silver, instead of the nitrate, for sensitizing the paper ■would doubtless have the effect of retarding the evapora tion of water from the prepared surface, aud might thus afford a means of producing papers of more definite character. I am now engaged in investigating this point, and will, if successful, communicate the results. In the course of these experiments I have had many opportunities of noting the remarkable degree of expansion which coincides with the absorption of moisture. The di mensions of the paper frequently varied as much as one- fiftieth in the transition from moist to dry, a point which does not appear to have been sufficiently considered in attempting photometrical determinations upon paper tablets. Chemical Department, Royal Arsenal, Woolwich. June 9, 1863. • PHOTOGRAPHIC CHEMICALS: Their Manufacture, Adulteration, and Analysis. Uranium is of value in optical researches, not only on account of the sensitiveness of some of its salts to light, but
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