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The photographic news
- Bandzählung
- 7.1863
- Erscheinungsdatum
- 1863
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- Englisch
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- Hochschule für Grafik und Buchkunst Leipzig
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- Hochschule für Grafik und Buchkunst Leipzig
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- Bandzählung
- No. 248, June 5, 1863
- Digitalisat
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Zeitschrift
The photographic news
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Band 7.1863
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- Register Index 619
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Band
Band 7.1863
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June 5,1863.] THE PHOTOGRAPHIC NEWS. 271 agitated us on this subject is M. Niepce de St. Victor, whose reputation certainly entitles him to a hearing. He gravely states that he has succeeded in obtaining a pure and perma nent black and white, with colours which were evanescent. Without questioning the correctness of this statement, or attempting here to account for the phenomena observed upon the principle of sympathetic molecular vibrations, it is safe to assert that the real problem is as far as ever from a satisfactory solution. It seems proper that practical photo graphers should have a clear comprehension of the proposed improvement and the difficulties attending all attempts to give it permanence. A few succinct statements may eluci date the subject. 1st. The action of light is through an undulating ethereal medium which produces three distinct kinds of effects, viz., colorific, calorific, and actinic. 2nd. The colorific effect resulting from the action of a single octave of waves, probably depends upon the harmonic relations arising from the ratio of the velocities of these waves. These waves produce the picture visible to the eye im the camera, but have little or no influence in producing the invisible effects made upon the prepared plate. 3rd. The waves of higher velocity possess actinic power, which is graduated by the sun of light sent from every point of the object to be copied. 4th. It is obvious that the actinic rays being the chief, if not the sole cause of chemical change, must impart their own characteristics to the chemical preparation to the exclu sion of those belonging to colorific action. 5th. The ratios of velocities of waves exciting the impres sion of color are generally lost the instant these waves impinge upon the plate, as the ratio of falling drops of water disappear when the drops are commingled. Yet should the atoms of the sensitive film take up the vibratory motion of the impinging waves, the action could not be of long duration, because the same kind of matter cannot have various rates of vibration, each normal and lasting. . oth. Besides a change in molecular motion, wo may imagine a change in the position and arrangement of mole cules, so as to.present a thin lamina, which may have the ettect of decomposing light and sending out such delicate tints as come from the shell of the pearl oyster. It is possible that this mechanical change might be quite as per manent as the chemical change produced by the actinic rays; yet who has proved by experiment that th-waves have the power of aggregating and dispersing molecules or atoms ? 7th. The chemical changes produced by light can differ only in degree, owing to the homogeneity of the substance covering the prepared plate; and in this view of the case the scientist is safe in asserting that the colours of nature cannot be imitated, until we have more perfectly under our control the materials with which she works. Thus far, the few ele ments she uses in producing the gorgeous colours found the in the vegetable kingdom have refused to acknowledge any other master. These colours are not superficial . they are the result of internal structure. The gradual and systematic arrangment of cells belongs alone to the power of growth. When man can weave atoms at his will, and combine elemen tary substances in ways which chemistry thus far has failed to do, he may construct the groundwork for a chromatic ex hibition. But to prepare a surface with any of the compounds now known to the chemist, which will give back the whole gamut of permanent colours, is a proposition that should not be seriously entertained. • Gorresyondence. FOREIGN SCIENCE. [FROM OUR SPEOIAL CORRESPONDENT.] Paris, June 3rd, 1863. Dr. Van Monckiioven, experimenting upon formic acid in developers, both sulphate of iron and pyrogallic acid, states the result to be as follows:—Sulphate of iron develops the negative more quickly than pyrogallic acid, whether the latter has acetic or formic acid added to it. It admits also of an exposure, one-third shorter, in the camera. Pyrogallic acid, with formic acid added to it, makes the image appear quicker than with acetic acid; but formic acid, reducing the silver from its nitrate without, however, concurring in making the image appear, fogging often results. Although the addition of formic acid, in the place of acetic acid, develops the picture in less time, the exposure in the camera cannot be diminished. Thus, it appears that Mr. Claudet’s formula does not possess the advantages he claims for it. On the other hand, Mr. Claudet assumes that the acid employed by Dr. Van Monckhoven was too con centrated. Possibly it was so. But as Mr. Claudet has not indicated the degree of concentration of the formic acid he employed, while Dr. Van Monckhoven, in the account of his experiments, took that precaution, the latter intends to repeat them, although he finds it difficult to admit that by diminishing the proportions of formic acid the exposure in the camera can be shortened. With reference to the composition of the positive image on paper, Dr. Schnauss has stated that non-albumenized positive paper simply toned with chloride of gold, either before or after fixing, contains gold only, without appre ciable traces of silver. But Dr. Van Monckhoven formally disputes this conclusion, at least, so far as relates to the words in italics. He maintains that only gold remains in the proof when it is toned before fixing, but silver remains in the state of chloride, if the picture is toned after fixing. This fact is explained in the following manner :— The image, upon paper simply salted, is composed for the most part of metallic silver. Immersed in the chloride of gold, one portion of the gold is precipitated upon the silver, while the chlorine of the chloride of gold combines with the silver, and forms white chloride of silver and violet chloride of silver. If, however, the chloride of gold acts for a long time, this violet chloride itself takes more chlorine and passes to the state of white chloride. Then the hyposulphite, acting upon it, leaves only the gold. But, on the other hand, the image first fixed, it is then wholly constituted by metallic silver, the chloride of gold acts in the same manner, and chlorides of silver and of gold are found in the proof. If, therefore, we do not have recourse to a second fixing, silver in the state of chloride remains in the proof. With albumenized paper, the reac tions are more complex. It must not be forgotten that in this case we operate with chloride of gold only, and not with the alkaline gold baths usually employed. Some of our photographers are busily occupied in pro ducing the photographic postage stamp. Cameras and objects are specially constructed for this purpose, by which four-and-twenty pictures are taken at one operation. Positives taken upon plain paper generally possess less brilliancy than those taken upon albumenized paper. It is not sufficient for the paper to contain chloride of silver with excess of nitrate; to obtain brilliant pictures, there must also be present an organic substance, capable of combining chemically with the nitrate of silver, just as the albumen does. The substances which accomplish this object, more or less, are gelatine, arrowroot, resin, gutta percha, caout chouc, sugar of gelatine, decomposed nitro-glucose, &c. Very good results are obtained by immersing the positive papers for a few moments in a warm solution of gutta percha, or caoutchouc in chloroform and benzine, and when dried, salting them in a solution of an alkaline chloride. Sensitizing, and the other operations, are performed in the usual manner. The pictures thus obtained are, it is true, less brilliant than those with albumenized paper, but on the other hand, the paper is more reliable for use. In any case, the picture is infinitely more brilliant than with ordinary salted papers. M. Testelin’s article on developing and strengthening with sulphate of iron, inserted in No. 239 of the Photographio News, is very complete and instructive ; and in our present
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