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
• URN: urn:nbn:de:bsz:14-db-id1780948042-188500006
• PURL: http://digital.slub-dresden.de/id1780948042-18850000
• OAI: oai:de:slub-dresden:db:id-1780948042-18850000
• 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

316 THE PHOTOGRAPHIC NEWS. [May 15, 1885. I had tried it some time previous to the publication of the red prussiate of potash solution which I saw advocated a few days ago in .luthony's Photojrnphic Bulletin, but which I have not yet employed. Curiously enough, however, I tried to develop the other day a plate of Wratten’s and one of Rouch’s by an ammonia formula very similar to their own, and could get no result, but on washing the plates well, and treating them to the solution given above, they came up fairly fast, and behaved altogether most satis factorily. Ernest BILBROUGH. Mexico City, April 20, 1885. DISTORTION IN PAPER POSITIVES. Dear Sir,—As albumenizers of long standing, we have read with interest the article on the above subject by Air. J. Harris in your last issue. We have always con demned any previous coating of the paper with gelatinous substances or any “mixtures” with the albumen of any kind, because it prevents the perfect coagulation of the albumen by the silver bath, and this, to a certain extent, must help the distortion. We do not know, of course, whether the paper manufacturers are treating their papers as formerly. We would willingly make trials and send samples to anyone who would correspond with us oa the subject.—We beg to remain, sir, yours, &c., A. RivOT & Co. abnormal behaviour or GELATINO- BROMIDE PLATES. Dear Sir,—-In your last issue you report a member of the Chicago Amateur Photographic Club to have dropped two 8 by 10 plates out of their holder on to the floor of a well-lighted room, which plates had previously been ex posed in the camera for one second on a out door subject, and were found on development to yield perfect pictures. The phenomenon is a very curious one, and may appear to many incredible. I may say, however, that I have had many experiences which, if not identical, certainly have a strong leaning in the same direction. I have many times found plates which had received a very long exposure— say ten times what was required—almost incapable of yielding any image whatever. The development has been continued for a long time with a developer at first normal, but afterwards gradually increased in strength until, after a great deal of forcing, rhe picture would suddenly flash out, to be quickly followed by a reduction of silver all over the plate. In such cases, one might expect fog to ensue, but hardly that greatly-diminished sensitiveness under the action of the developer, which has invariably occurred in my experience. I ought to say that these effects have only been observed in the case of very rapid plates where the emulsion has been carried far into the blue stage, and suggest to my mind the existence of a sort of neutral zone somewhere between the point of maximum sensitiveness and that at which complete reversal of the image takes place. At any rate, the matter is one of interest, and ought to be of practical utility to those who occasionally use plates the sensitiveness of which is carried further than is usually deemed expedient for ordinary work.—Yours truly, J. W. Hunter. Qroceedings of Sortettes. PHOTOGRAPHIC Society of Great Britain. The ordinary meeting of this Society was held on Tuesday, the 12th inst., at the Gallery, 5a, Pall Mall East, Mr. James Glaisher, F.R.S., President, in the chair. The minutes of the previous meeting were read and confirmed. The following gentlemen were then elected members of the Society:—Major-General J. Preston, Messrs. J. Francis Leese and George Walter Tyser. Captain W. de W. Abney, R.E., F.R.S., read a paper entitled “ On the Chemical Theory of the Photographic Image.” He commenced by saying that when light was allowed to act on ilver chloride, chlorine was given off, and if silver bromide be similarly acted upon, bromine would be liberated. Taking the silver bromide as an example, two atoms of bromide of silver after exposure would be represented thus:—Ag:Br-+Br. Text books, and some other sources of information, stated that silver was a monad, one atom of silver uniting with one atom of bromine. The opinion, however, that silver was a monad, was not confirmed by many able chemists. Captain Abney then touched on the theory set up in 1839 regarding the supposed action of light on the iodized Daguerreotype plate. Methods of forming argentous oxide were then spoken of, and Captain Abney said if it be granted that argentous oxide did exist, then it was possible to admit the sub-bromide and sub- chloride theory. Now the question arose whether the same effect could be brought about by the action of light. Tubes containing chloride and bromide of silver respectively both in the presence of nitric acid and water were shown, which had been exposed to light for some days. Those containing acid were found to be unaffected by light, the acid proving a solvent for the metallic silver. Captain Abney then mentioned the early experi ments of Guthrie, wherein it was found that metallic silver was formed in every case by a blackening of the tubes, which was afterwards amenable to the influence of nitric acid. Also that ammonia, acting on Ag 2 Cl, takes up one equivalent of silver and leaves the other behind. Some people, he thought, had not seen sub-chloride or sub-bromide of silver, so he had brought some prepared by Dr. Hodgkinson. Sub-bromide had been prepared by means of argentous citrate, and examples of each were passed round for inspection. The speaker, continuing, said it was usually considered that silver bromide, exposed to light, remained in the same physical condition—some thought a chemical action, and others a voltaic disturbance took place. Neither could take place without the other. With a delicate galvanometer it was thought possible to observe a deflection of the needle when the film was acted upon by light, and in some cases the deflection would be sufficient to cause the needle to swing out of the sphere of electric action. The use of bromine absorbents in collodion emulsion plates was then spoken of, whereby density was more easily attainable, as in the case of tannin, beer, and other similar substances. Blates were passed round showing the effect of heat on a sensitive plate, by which an image of the iron used for the purpose was produced. When, in other cases, the plates had been allowed to cool, no difference was observable, the normal condition having become again established. It was necessary for those who hold to the physical theory to explain why the increased amplitude of vibration dies away, and he would be glad to hear of any experiments that would explain the vibratory theory, which could not be explained by the chemical. The effect of the silver haloids on the spectrum was alluded to, and their power of absorption pointed out when mixed, as in the case of bromide and iodide. The keeping qualities of plates was also dealt with, before and after exposure ; in the latter the images had completely disappeared, in some cases, in two months. At the conclusion, The Chairman said that if anyone present had been working in a similar direction, he should be glad to hear of their results. Mr. W. E. Debenham thought the results with all three haloids were nearly equal. If films were of sufficient thickness to be opaque, they would absorb all the light in every part of the spectrum. Some experimenters had found a difference between iodide and bromide in certain parts of the spectrum, and others had found certain additions appeared to act as optical sensitizers. Drs. Vogel and Eder had been working in that direction. Mr. T. Sebastian Davis spoke of the changes which are effected in development. So far as wet collodion was concerned, an exposed and fixed but undeveloped plate was undistinguish- able from a plate fixed without exposure to light. Mr. A. Spiller mentioned that an Italian professor had shown that silver chloride was not acted upon by light at very low tem peratures ; about 12° F. he thought. Capt. Abney, in reply, said that Mr. Debenham was perfectly correct. Absorbtion in the case of a thin film would give the true colour in the spectroscope ; with a thick film it would be of a deep red. With regard to the colour of objects, white light boro a large percentage over any other. He did not quite follow Mr. Davis, but with regard to the fixing bath, there would be some;