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The photographic news
- Bandzählung
- 29.1885
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- 1885
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- Bandzählung
- No. 1400, July 3, 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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JULr 3, 1885.J THE PHOTOGRAPHIC NEWS. 421 K H minimum (a perfectly clear space), which corresponds with the maximum of absorption of eosine gelatine (curve 5, fig. 13). It is thus proved that the maximum of sensitiveness of dyed gelatino-bromide of silver is not identical with the maximum of absorption of dyed gelatine, but that the colour of bromide of silver itself must be taken into account. Fig. 13.—1. Spectrum picture upon byumide of silver iu gel tiue eosine. 2. Absorption spectrum of sheet gelatine stained with eosine. 3 Spec, trum picture upon bromide of silver in gelatine aniline red. 4. Ab sorption spectrum of sheet gelatine stained with aniline red. 5. Absorption spectrum of sheet gelatine stained with eosine, photographed upon a bro mide of silver plate stained with eosine. That the molecule of bromide of silver itself is, in fact, coloured, I have experimentally shown. To the interpre tation of the great lighting of the maximum, the law of Kundt may be applied, according to which, iu most cases, with an increase of refracting power of the medium, the absorption band of the dye therein contained is moved towards the red end. In an analogous case, Dr. E. Albert has made observations upon dyed collodion emulsion. From this consideration I also think that the behaviour of gelatino-bromide of silver which is exposed wet under a solution of a dye can be explained. The solution of dye acts then as a coloured medium. For instance, the spec trum picture upon a gelatino-bromide of silver plate covered with an aqueous solution of eosine resembles more the image 5 in tig. 13, than that of 1 in the same figure. The absorption baud of the aqueous solution of eosine near E keeps back the light from the sensitive silver bromide, and nai rows the action to the maximum of sensitiveness lying nearer D, which last lies nearly in the same place, for stained silver bromide, whether dry or wet. When gelatino-bromide of silver is stained with a mix- ture of dye-stuffs, the action of one is often hindered by that of the other, and not seldom oue is apparently sup pressed. This appears to happen particularly when the absorption band of oue of the compounds of the dyed gela tine falls upon the maximum of sensitising action of the other. E 0 C B * Solutions of dyestuffs give quite different absorption spectra from those of the dry dye. It would be best to employ thin films of well dyed bromide of silver in gelatin-, but as these are difficult to apply, I contented myself with dyed sheets of gelatine. t Following the suggestion of Kayser (Lehrbuch.der Spectralnnalgse, 1883, p. li), I have shown the wave-lengths in millionths of inm= Mu, of silver bromide contained in one case 0'45, and in another, i 0-52 parts of gelatine. 1 It is seen from this that bromide of silver which has I been precipitated in presence of gelatine takes up some of the latter, and retains it so obstinately that it caunot be < removed by washing with hot water ami the use of the i ceutiifugal machine. When to a gelatine emulsion eosine • or cyanine is added, and the same is then washed, the ; dye cannot be so completely driven off that the sensi tiveness to yellow does not appear in the spectrograph. When, however, the silver bromide is, by repeated treat ment (three times) in thecentrifugal machine, and washing, separated from an emulsion to which eosine had been added, at first the gelatine conies away stained red, afterwards the washing water comes off colourless. Nevertheless, whether the silver bromide, after separation from a strongly dyed emulsion, remain of a faint reddish colour, or, after the use of less eosine, can scarcely be seen to be tinted by it, in every ease the characteristic maximum of sensitiveness in the neighbourhood of D shows itself. This proves that the dye ho ds fast to the particles of bromide of silver, whether to bromide of silver as such, or to the gelatine retained in these particles. This fact appears to be of importance in researches on “ Optical Sensitizing.” Connection between the Absorption of Dyestuffs and their Sensitising Action upon Bromide of Silver. For the examination of the connection of the absorption of a dyestuff, with its sensitising action—which has beeu already referred to by H. W. Vogel—dried sheets of dyed gelatine are used, and their absorption compared with the spectrum photograph upon similarly dyed gelatino- bromide of silver plates.* In every case that I have ob served, the position of the absorption spectrum of the dried stained sheets of gelatine corresponds with that of the sensitising maximum upon the dyed bromide of silver ; there is, however, a shifting towards the red iu the latter case as compared with the former. This shifting is not always very important; with eosine the maximum of ab sorption of the dyed gelatine differs from that of the sensi tising of bromide of silver in the yellow given by 16 to 20 uut. J In fig. 12 the results of some of my experiments are exhibited. Spectrum 1 is the facsimile of the spectrum picture upon gelatino-bromide of silver which had been dyed with bluish eosine, obtained iu direct sunshine. Similar spectra upon yellowish eosine, as well as upon Bengal rose, have been shown in the curves previously given. In 2, the absorption spectrum of a sheet of gelatine dyed with the same eosine is given (obtained by photographic reproduction of the same upon a cyanine bromide of silver plate). 1 he maximum of sensitising action of eosine upon gelatino-bromide of silver lies more towards the red than that of the maximum of absorption in the dyed gela tine. The same occurs with aniline red,as is shown in 3 and 4, fig. 13), as well as with other dye-stuffs. The dyed gelatine also permits many rays to pass at the less refrangible end of the spectium, which rays act very strongly upon a bromide of silver plate dyed with the same substance. When the solar spectrum is passed through a sheet of gelatine dyed with eosine, there should be no pic ture iu the yellow green upon an eosine dyed bromide of silver plate, if the rays absorbed by the former are those which excite the sensitiveness of the latter. I obtained. , however, under these conditions, besides the customary spectrum picture iu the blue, an intense image in the yellow near D, which corresponds with the maximum of optical sensitising upon eosine of silver, and near to it a ON THE WORK OF A LOCAL PHOTOGRAPHIC SOCIETY. BY W. JEROME HARBISON, F.G.S.* During the last few days I have more than once had the enquiry made . “ What are the objects of your Society ? ” “ What do you propose to do ? ” and “ How will it benefit me to become a member ? ” I shall now attempt to briefly answer these questions. Within the last four or five years photography has made a new departure. The introduction of gelatine dry plates has made the process so clean, and, by comparison, so easy, that photographers have multiplied twenty-fold. 0 1 that we could bring Daguerre, with his costly silver plates which required such tremendous polishing ; Fox Talbot, with his collotypes ; and Scott Archer, with his silver bath and travelling tent, which • Head before the Birmingham Photographic Society.
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