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The photographic news
- Bandzählung
- 12.1868
- Erscheinungsdatum
- 1868
- Sprache
- Englisch
- Signatur
- F 135
- Vorlage
- Hochschule für Grafik und Buchkunst Leipzig
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- Hochschule für Grafik und Buchkunst Leipzig
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- SLUB Dresden
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- Public Domain Mark 1.0
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- urn:nbn:de:bsz:14-db-id1780948042-186800009
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- http://digital.slub-dresden.de/id1780948042-18680000
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- LDP: Historische Bestände der Hochschule für Grafik und Buchkunst Leipzig
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- Bandzählung
- No. 500, April 3, 1868
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Zeitschrift
The photographic news
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Band
Band 12.1868
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- Titelblatt Titelblatt I
- Kapitel Preface III
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- Register The Index To Volume XII 619
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Band
Band 12.1868
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- Titel
- The photographic news
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APRIL 3, 1868.] THE PHOTOGRAPHIC NEWS. 161 paper,” you reply ; and your remark brings me to dwell for a few moments on the subject of weak baths. Probably no greater boon connected with photographic printing was ever presented than the suggestion offered by a certain “ Publi- cola,” who, I believe, was the first to propose the addition of a neutral salt as an adjunct to the silver bath. Since that time many are they who have ploughed with the heifer then provided, and numerous are the substances advised by the compounders of weak silver baths: nitrates of sodium, potassium, magnesium, and I don’t know the number of others that are marshalled as the possessors of some dis tinct virtues when added to the silver solution. My dear Telemachus. it is all “ bosh,” as Brother Jonathan quaintly hath it. What would you think of the wisdom of Mentor if he were to advise you to adopt a formula stated as follows :— Silver nitrate ... COgrains Rain water } ounce Aqua dist. t » Pump water ± „ Snow water ... ... ... j „ You certainly would imagine that much thinking had made him foolish; yet I must ask -pardon when I say that the additions often recommended as fit and proper for the office of silver-savers are marked with wisdom equal to the formula j ust rendered. Seriously, it matters not whether nitrate of potash, of soda, of magnesium, or any other nitrate applicable, is added to the printing bath. By abundant experiment I have satisfied myself that their operations are on the neutral side, passive, never active; and were I not ressed for space I could summon an array of argument that think would bear me out in the assertion. As matters stand, I simply describe the part played by the neutral salt. When an albumen surface is brought into contact with water the albumen dissolves, and a dried, unglazed paper-surface only remains. In a minor degree a similar result occurs when a small portion only of silver is present in solution. If, however, the density of the solution is increased, its solvent powers are diminished. Still silver must be present, or saturation itself will not suffice to render the concen trated neutral mixture capable of preserving the albumen intact. Yet it strangely happens that the most minute quantity of silver present will exercise an influence. I have secured a really tolerable print with 5 grains of nitrate of silver to the ounce of otherwise neutral saturated solution ; without the neutral salt the small amount of silver described would have been lost and useless. To cut a long story short: after a lengthened experience, I have arrived at a conclusion that no better formula for a sensitizing bath can be adopted than that given as my offering to the YEAn-BooK, and is there stated as follows :— Water ... ... 80 ounces. Silver nitrate ... 0 „ Soda nitrate (pure) ... ... 3 „ Loaf sugar 2 drachms. The reason why and the wherefore must, however, stand over until my next, as I am unwilling to trespass on space. And it to myself appears more prudent to cut short at once than to risk a clip of the editorial scissors that oft shows up in all its saddening disappointments that tantalizing sen tence, “ To be continued.” THE MAGIC LANTERN AND PHOTOGRAPHY. BY JAMES MARTIN. No. 9. As the single lantern is incapable of producing the beautiful dioramic and other effects possible with the dissolving view apparatus, I should advise my readers, if possible, to obtain the possession of the latter. It is not so complicated as might be supposed. It merely consists of two lanterns of the usual construction, mounted on a stand, and moving upon pivots in any direction, so that the disc of light from each lantern may be thrown on the screen one exactly upon the other, so as to appear as if there was but one. This is essentially necessary, as many of the changes (such as, for in stance, a summer scene to that of winter) are produced by two pictures, one in each lantern, the leading outlines of which are in every respect the same, except that one repre sents the scene as in summer, with foliage, running water, and green fields ; the other the same trees, but bare of leaves, the water frozen, and the fields covered with snow. In this case, should the two discs of light not be correctly superposed, the effect will be the same as if, when taking a photograph, the camera has by some accident been moved during the exposure, thus producing a double outline. The obscuration and melting of the views into each other, called dissolving, and from which effect the double lantern takes its name, is effected by an apparatus fixed in front. These are of various kinds ; the purpose of all is, that while the light is gradually shut off from one, that from the other is admitted by degrees. The following arrangement is one of the most simple and effective. Two pieces of sheet iron, out of each of which a semi-circular aperture has been cut, are placed before the tube ot each lantern, and arranged upon slips of wood in such a manner that, by means of a small winch, the two pieces can be made to move in contrary directions at the same time, so as to gradually close one aperture entirely while the other is progressively opened in the same ratio, until it admits the passing of the whole of the light from it. There are various kinds of dissolving view apparatus : such as the binocular, which is one lantern having two nozzles, one placed above the other; the dioptric, in which the light is thrown upon glass prisms, from thence upon the screen, and lighted by the oxycalcium light (by this contrivance only one light is required) ; and one gas bag (of this class is the opaque lantern, which is very ingeniously contrived). Lanterns have also been made with three sets of lenses ; but, taking into consideration the additional loss of light, ex pense, and complication of arrangement, I believe that a well-made pair of lanterns on the usual plan will be found the most generally useful. These, with a pair of good lamps, for small-sized pictures for parlour exhibitions, and an arrangement so that the hydro-oxygen light can be used for larger sizes, or when a stronger light is desirable, will leave little to be desired. A microscope should also be added, and will be found a most amusing and instructive addition. It should have two powers, a lower one for large objects and a high one for very small ones. This cannot be shown except by the hydro-oxygen light. I have so recently given instructions as to the management of the oil lamp that I need not here repeat them. I will there fore only add that dipping the wick in vinegar, and drying it before use, is said to cause it to burn free from smoke; but the size and height of the lamp-glass chimney has much to do with the clearness and brilliancy of the light. The hydro-oxygen light is composed of two gases, which require to be mixed in certain proportions, either before or while burn ing. The apparatus consists of a pair of india-rubber gas bags, generally of a wedge-shape, each of which should bo able to contain from 5 to 9 cubic feet of gas, according to the length of time of consumption and power of light required. These are furnished with stop-cocks, to which unions can be attached connected with the tubes which lead to the blow pipes. These tubes are better made of vulcanized india- rubber, which will not collapse when trod upon; about 12 feet in length each will be found sufficient; at the other ends these tubes arc attached to T unions, from which short tubes convey the gases to the blowpipes, which are of various construction. I have found those answer well that are com posed of two tubes, one within the other, carrying the gases on separately until within a short distance of the orifice of the blowpipe, where they become mixed, and so issue upon the heated lime cylinder. By this contrivance there is so little mixed gas that no explosion can be caused on that ac count. To these short tubesare affixed two small stop-cocks, by which the flow of each gas is regulated as required; before each blowpipe is a support, on which is placed the lime cylinder.
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