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The photographic news
- Bandzählung
- 7.1863
- Erscheinungsdatum
- 1863
- Sprache
- Englisch
- Signatur
- F 135
- Vorlage
- Hochschule für Grafik und Buchkunst Leipzig
- Digitalisat
- Hochschule für Grafik und Buchkunst Leipzig
- Digitalisat
- SLUB Dresden
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- Public Domain Mark 1.0
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- urn:nbn:de:bsz:14-db-id1780948042-186300004
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- http://digital.slub-dresden.de/id1780948042-18630000
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- oai:de:slub-dresden:db:id-1780948042-18630000
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- Bandzählung
- No. 227, January 9, 1863
- Digitalisat
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Zeitschrift
The photographic news
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Band
Band 7.1863
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- Titelblatt Titelblatt -
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- Register Index 619
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Band
Band 7.1863
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January 9, 1863.] THE PHOTOGRAPHIC NEWS. 17 lence of the book, and the appreciation in which it is held by photographers. It is also a satisfactory illustration of the fact that photographers generally are interested in a work which, besides containing technical instructions in the art of applying pigments, is also full of hints on the appli cation of art principles to photography, for we can scarcely suppose that there are many thousands of professional or amateur colourists, or that all who have bought the book, have done so simply for the purpose of learning to colour. The new edition contains, not only full instructions for every mode of colouring photographs, but a very lucid state ment of the general principles of harmonious colouring, and of the application of those principles to photography. Fresh chapters are added on the retouching in crayons of enlarged pictures, and also in colouring such pictures in pastel. A very useful chapter, containing “A Few Words on Por traiture,” ought to be read by every photographer, and espe cially by those engaged in the production of card pictures. COMPOSITION AND PROPERTIES OF GUN COTTON. BY AUG. TESTELIN. PrROXYIINE does not appear to be a chemical combination, in definite proportions, of cellulose with the oxygenic ele ments of nitrogen ; it appears to us too variable in its com position and most essential properties, not to appear rather a physical modification, effected by condensation more or less considerable andJperfect of a nitrogenous gas, which appears to be the protoxide of nitrogen. In our opinion, the capillary fibres of the ligneous sub stance operating upon these gaseous elements by an attrac tive action comparable, in some measure, to the catalytic force of the cellular interstices of carbon, platinum, sponge, and many other bodies, which present this peculiar property of condensing certain gaseous bodies, without in any way uniting with them, and permitting the disengagement of these gases by the action of influencing causes more or less energetic. Cotton, after undergoing the operations which transform it into pyroxyline, undergoes no change in its physical pro perties ; still, in the generality of cases, it becomes less soft to the touch, and appears considerably disaggregated. But a remarkable phenomenon presents itself in this product, which is, that it has assumed an extremely singular passive condition, which renders it unattackable by chemical agents as powerful as concentrated sulphuric acid, nitric acid, potassa, and most other substances which completely destroy organic matters. These different properties appear to us to be due to the fixation of a considerable quantity of protoxide of nitrogen in the organic cells, which exercise, like all capillary in terstices, a powerful influence upon certain gases, which they condense and solidify, becoming at the same time inac cessible to the influence of other bodies, with regard to which the modified substance becomes less attackable, and then establishes itself in a truly passive state, by a cause analogous, so to speak, to that which produces a similar phenomenon upon iron and other bodies. But when a more intimate cause comes to penetrate these spaces of the ligneous matter to destroy their cells, and dilate the gas which their attractive power concentrates, then the latter, spontaneously resuming their primitive normal state, i.e., an infinitely larger volume—by breaking the cells which still form an obstacle, and the provocative force act ing only upon a point—the vigorous action resulting pro ducesan enormous disengagement of heat, propagating itself in every direction with an extreme energy; the organic matter is burned in contact with protoxide of nitrogen, a burning gaspar excellence—the carbonic acid, spontaneously produced and dilated by heat, joins its expansion to that of the other gases from whence results a vivid explosion. The cellulose transformed into pyroxyline acquires the property of dissolving in a mixture of ether and alcohol ; it appears, nevertheless, that it is not a true solution so pro duced, but simply a separation of the ligneous particles, and, according to M. Davanne, a swelling of the fibres analogous to the swelling of the granules of starch, or of fish isinglass in water. For, upon precipitating a solution of pyroxyline in ether and alchol by water, we easily recognize the distinct remains of the organic tissue in the deposit formed, composed of elongated fibres which have preserved the principal pro perties of the nitrated cotton; that is to say, they can be redissolved, partially it is true, in the ethereal mixture, and be instantly decomposed, after drying, upon contact with a burning substance only: the material then fuses, on account of its compactness, the same as gunpowder when pulverized and compressed. This apparent solubility of pyroxyline in alcoholic ether, is therefore simply only the effect of a disaggregation of the fibres of the ligneous substance, but not of the compound cells of the organic body. The cells not being destroyed by the dissolving vehicle, and so remaining quite entire in the liquid, it is natural that they should preserve their principal properties in con tinuing to exercise their condensing action upon the nitro genous gas, until an influencing cause, such as heat or light, comes to provoke the more or less partial disengagement of the condensed gas, which is then liberated slowly, by reason of the little energy of the cause, and various other circumstances, favourable or unfavourable, amid which the phenomenon takes place. The protoxide of nitrogen, thus disengaged, combines with the elements of the solvent itself, changing it by forming more hyponitric acid, which concurs powerfully to the rapid destruction of all these sub stances. Whatever be the care employed in the preparation of nitrated cotton, after it is dried it instantly disengages a small portion of the protoxide of azote it contains, of which the oxygen of the atmosphere determines the con version into hyponitric acid, which is always found in large quantities in bottles in which gun cotton has been kept. When the vessel containing the gun cotton is hermeti cally closed, and the disengagement of the gas is very little favoured by any external influence, the hyponitric acid formed, withdraws the water from the ligneous matter and partially decomposes it; nitric acid is also formed ulti mately, the action of which upon the pyroxyline and the organic portion of the substance, disengages the oxygenic elements of the nitrogen, and ends by causing a more com plete destruction. A portion of the mass becomes liquid under the prolonged action of the nitric acid, and is con verted into a substance similar to xyloidine, which the water precipitates from its solution, and there remains in the liquid other matters, soluble and deliquescent, arising from a more advanced decomposition ; for these phenomena are slow to be produced, so that several different com pounds must be developed in succession. Nitric acid does not form a true combination with cellulose, hence a product, the elements of which are in definite proportions, cannot result ; and it is the diversity of these proportions which gives rise to the variety of pyroxy- lines, which may always be seen among the specimens arising from different manufactures. It is generally admitted that there are four varieties of pyroxyline, because analysis has sometimes afforded, accord ing to the species, 2, 3, 4, or 5, equivalents of a nitrogenous gas, which is considered to be hyponitric acid, but which is also oxygenized, finally only by the modifications it under goes during the reactions effected by the decomposition of the organic matter. Moreover, these numbers, which are taken to represent the equivalents of the composition of the fulminating matter, are rather only the two extremes, in some respects, that are most frequently found, and between which there may be an infinity of varied proportions. We are sustained in this supposition by the diversity of proportions found by every
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