The photographic news

• Bandzählung: 6.1862
• Erscheinungsdatum: 1862
• 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-id1780948042-186200003
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• Sammlungen: LDP: Historische Bestände der Hochschule für Grafik und Buchkunst Leipzig
• Sammlungen: Fotografie
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• Strukturtyp: Ausgabe

[JUNE 20,1861 I THE PHOTOGRAPHIC NEWS. 296 d these preparations, or they are associated with others wb carry them with them; therefore, an absolute fixity , photographic portraits will probably continue for a 1005 time problematical. Still, in the absence of clearly det PS facts, a kind of intuition, which may sometimes follow least worthy of examination; and then the caseweb" instanced is not the only one. There is at least one® I very similar kind. Pursuing our researches with the ad I the multiplicator, it has been easy for us to comparet. electric action of pyrogallic acid and sulphate of ironurSt nitrate of silver. We know that by means of the se® 1 1 reducing agent, the duration of the luminous action is g* rally diminished, in a word, it is a greater accelerator thss I pyrogallic acid. So we find that it is from its reaction upw nitrate of silver that the most energetic current resol With pyrogallic acid we obtained scarcely 45 degrees ® deviation, while with sulphate of iron, the needle, sum*! diverted from its position, makes almost the entire circuit ® the scale. We repeat, a correlation so manifest between t" such different classes of phenomena, seems to us worth)'” attention, and further researches in this direction wot perhaps not be without profit for the progress of art. In the preceding experiments, as well as in a host of otb® I analogous, the effects obtained are due to instantanedl ' electricity, or that acting by shocks. These effects, ah'P realizable at the pleasure of the observer, are, as may be P ceived, of ready appreciation and measure. But it is noty same with the effects caused by a slow electricity. Toooft the elements submitted to its action are inappreciable; mon over, if, during the intervals of electric action, these element 1 vary with respect to number and quality, combinations wb may be clearly defined for a moment may be destroyed give place, later, to new combinations. We can easily sound the latent elements upon which! force is exercised, as little understood as electricity still being made evident, effects will result which it will be 8 difficult to foresee as to prevent. We stated at the 0G mencement, that we were induced to think that the instabiill of photogenic preparation is due to this slow action of el tricity, either electricity acts upon the elements peculiar" PROGRESS OF PHOTOGRAPHY IN AMERIC Ar the annual meeting of the Photographic Societte America, the president, Professor Draper, gave aninteus ing address recalling and reviewing the photographic Gbo of the year. We commend the idea to presidents ofPs graphic societies in this country. We make some conw a extracts which will interest our readers. After some ge" attentive observation, may prove of great assistance;, 1 * thus, that positive paper which but lately changed very short time, may now be maintained in all their integ" since we have learned or divined that it was sufficiedt ’ preserve them from the action of moist air. It was" difficult to j udge a priori of the efficacy of these means, r now that this efficacy is no longer doubtful, it is, if certain, at least very probable, that in positive paper exp® to moist air, there is a decomposition of water by 1 nitrate of silver, and, consequently, electric action. 2 quote only this single example offered to us by the chob and preservation of positive paper, and it is sufficiebta seems to us, to prove that in referring these effects of cW, to an electric cause, we put forth a view which is not enti" void of probability. * We limit ourselves, therefore, to these general consid18 tions. The subject before us would furnish a cro"a others, interesting, without doubt, but, unfortunately, t or less vague, and not yet capable of furnishing us " rigorous conclusions. There is one, however, which j been our starting-point in this study, but which we do mention in this place, reserving it for the occasion who 11 speak of the sulphate of iron developing solution. (To be continued.) is to this second mode of electric action that we must attri bute the alteration, which ultimately manifests itself in the photographic preparation of proofs either negatives or posi tives. As may be seen, the question that now occupies us is full of interest, unfortunately, it is also full of mysteries. We repeat we have not the slightest pretension to explain them ; but persuaded that the path of experiment is that which must be preferred in advancing a science or an art, we proceed to indicate some of those which have more especially led ito the subject before us. These experiments, or other similar ones, are not new, they have been repeated by many physicists and chemists ; only as our mode of experimentation is very simple and very easily performed, we proceed briefly to explain it. The multiplicator we employ, although but slightly sensitive, is nevertheless sufficiently so to appreciate the electric forces to which it is submitted—it is Mellone’s thermo-electric multiplicator with astatic needles. Each end of the conducting wire of pure copper is terminated by a platinum wire six inches long armed at its free extremity with a plate of platinum one to one and a half inches square. If the copper wire terminates with these two plates there is a risk of developing by the mere warmth of the hand, a thermo-electric current sufficient to modify the results, but with a length of six inches of the platinum wire this incon venience is no longer to be feared, and, on the other hand, the platinum plates being unoxidizable, there is no other electricity except that developed by the combination of the bodies placed in contact. We first proceed to determine the direction of the current; this is ascertained by a plate of zinc being put in contact with one of the plates of platinum and separated from the other by some folds of blotting paper moistened with water acidulated with a few drops of sulphuric acid. When the circuit is complete, we shall perceive the system of needles, at first established parallel to the conducting wire, place itself at right angles with it, and always in the same direction every time the circuit is broken or renewed. The better to fix it in the mind, we call the current thus given by the zinc positive; and negative that of which the direction is opposite. We now proceed to experiment, electrically, with some of the ordinary and familiar combinations in photography. The platinum plates being superimposed, but separated by pieces of moistened bibulous paper of nearly twice their size, no electricity is developed, the needles remain fixed. Upon pouring on to the paper some drops of a solution of iodide of potassium, still no effect; but if, upon the paper being moistened with iodide, we let fall some drops of a solution of nitrate of silver, the needles are instantly diverted more than ninety degrees from their fixed position, and the direc tion proclaims a negative current. By causing the paper to imbibe first, nitrate of silver, and in the second place, pour ing upon it iodide of potassium, a current takes place as energetic as the first, but in an opposite direction to the first,that is, positive-, double decomposition being accom plished, that is to say, after the complete formation of iodide of silver all electric action ceases, and a stable equilibrium, for the minute at least, is definitely established. The results are identical if we operate in the same manner with hydro chlorate of ammonia and nitrate of silver; identical also with this latter salt and hydriodate of iron, except this difference, however, that in this last double decomposition the electric currents developed are much more energetic. The addition of iodide of iron to collodion with the view of obtaining greater sensitiveness is disapproved by some photographers ; for our own part, we have proved that the addition of this preparation to albumen is evidently accelerating. May we not be permitted to suppose that there is a certain correla tion between these two different phenomena, on the one hand, disengagement of more intense electricity, on the other, exaltation of photogenic sensitiveness. We cannot decide upon this point, but it seems to us at