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The photographic news
- Bandzählung
- 27.1883
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- 1883
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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. 1275, February 9, 1883
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- Titelblatt Titelblatt I
- Register Index III
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preparation in his book, but according to Schnauss (Der Lichtdruck und die Photo-Liihographie) it is as follows: — 1 part of the finest gelatine is dissolved in 24 parts of water ; rB, of a part of chrome alum dissolved in a little water is added. The mixture is filtered, and poured, while warm, into a large zinc tray, which is kept heated by spirit or petroleum to about 108° F. The surface is freed from froth, and the paper floated on it sheet by sheet, and hung up to dry. The paper is then coated a second time with the gelatine solution, and hung up to dry the reverse way to what it was at first. Finally, the dry gelatine paper is coated with a mixture of 1 part albumen to 2 parts water, and when dry is ready for use. For sensi tizing this paper Husnik recommends the following solu tion, which will be found useful with other papers :— Bichromate of potash 1 part Water... ... ... 15 parts Spirits of wine 4 „ Liquor ammonia is added to turn the colour of the solu tion yellow, and the bath should first smell of ammonia ; a little extra is of no consequence. This bath stands well if kept in a well-stoppered bottle in the dark. When required for use, the clear solution is decanted off into a flat dish. The paper is immersed in the solution, or, being held by two opposite corners, is just drawn through it face uppermost, and hung up to dry in the dark, in a place where there is a good current of air, so that the paper may dry rapidly. As soon as the requisite quantity of paper is sensitized, it is well to pour back the solution into the bottle at once, so that the spirit and ammonia may not evaporate. If the bath is in constant use, a little fresh spirit should be added to it as required, or it may be strengthened with fresh solution. According to Professor Husnik, the spirit is a very im portant ingredient of the sensitising solution. It makes the bath, in which by degrees organic matter is dissolved out of the paper, more durable,* and brings about a change in the coating of the paper which considerably facilitates the bringing out of the picture with the sponge. A bath without spirit gives no open parts in the heavy shadows of the picture, and causes a tint over the lights. The ammonia completely neutralises the bath, so that it cannot decompose in this condition, and consequently remains in good order. When the paper is dry, the ammonia evapo rates, and is replaced by a sensitive double salt. The immersion of the paper in the bath must be done with care, so that the prepared side is uppermost, and while wet it must not be touched with the finger or any solid substance, for it is very easily damaged, and such spots would appear as defects in the picture. If it is de sired to give a very smooth highly-glazed surface to the paper, a glass plate that has been rubbed over with a very thin solution of wax may be put into the sensitising bath, and the paper laid on it prepared side downwards. The paper and plate are drawn out together, and the paper lightly squeegeed down to the glass and allowed to dry. When stripped, the paper will have a fine bright surface. If this is not done, the paper should be glazed in a press before use. The prepared paper is very sensitive, so that it can be used in any weather and in any light. It will not keep in good order for more than a day or two, especially in hot weather. {To ie continued.) EXPERIMENTS ON THE DIRECT PHOTOGRAPHY OF SOUND VIBRATIONS. BY PROF. BOLTZMANN, t A SMALL thin platinum plate was attached perpendicularly to the centre of a thin iron plate, which, as in the telephone or * This is contrary to what one would expect, but experience with a similar bath for pigment printing shows that it keeps in good order longer than the simple bichromate solution. + fhxlosophical Uagazine, phonograph, was fixed on a wall-piece. It was first ascertained that the small platinum plate really repeated approximately unchanged the vibrations of the sound that arrived in the capsule. For this purpose a second small platinum plate was fixed immovably in the vicinity of the first. The resulting fine slit bstween the two was brought into the focus of a collecting lens, upon which sunlight fell. After passing through the slit, the rays reached a Breguet selenium cell, which, together with two telephones, was inserted in the closing circuit of twelve Leclanche cells. Single sounds and words spoken into the mouthpiece could be heard most distinctly in the telephones. When the rays, after issuing from the slit, were rendered aS nearly as possible parallel, and intercepted at a greater distance by a large collecting-lens to be concentrated upon the selenium cell, the apparatus could also be employed as a photophone. After these preliminary experiments, intense sunlight was again concentrated upon the vibrating platinum plate; and then, by means of a solar microscope, an image of the shadow of the platinum plate was thrown upon a screen. The bounding line of the shadow, as nearly as possible straight, was condensed by a cylindrical lens. In the place of the screen a glass plate, prepared with Vogel’s emulsion, was now moved rapidly across by a strong spring, so that the direction of its motion was perpendicular to the line of light produced by the cylindrical lens, while the mouthpiece was spoken into. Side light being duly kept off, a bounding line between light and shadow was then obtained on the prepared plate, forming a curve corres ponding to the sonorous vibrations. To the vowels pretty simple curves correspond, often approximately curves of sines, often interference-curves of two or three curves of sines. With the vowel a a period contains the greatest, with the vowel u the least number of indentations. To the consonants I, m, n, r, and also especially p and k, uncommonly multifarious curves correspond, having a resemblance to those found by Konig for r by means of his tone-flame, but showing in addition much finer details. The author intends to repeat the experiments by photography upon rotating discs in order to be able to take up a greater number of successive vibrations.—Kaiserl. Akad. der TFissensch. in Wien, math.-naturw. Classe, November 30, 1882. Hebieb. Physical Optics {Text-Books of Science). By K. P. Glazebrook, F.R.S. {Longman's, Green, § Oo.) It is the habit of photographers rather to neglect the optical aspect of their work, and to, perhaps, give an undue preponderance to the chemical side. Hence we find that almost every photographer has several chemical books on his shelves ; but very few works on optics find place in the library of the general photographer. For five hundred photographers who make emulsion or collodion for their own use, we do not meet with one who has ever made a lens, or even projected the making of one ; yet the diffi culties of the two positions are by no means so unequally balanced as one might imagine. The work before us presents a systematic course of theoretical optics, clearly and concisely explained, and we cannot help thinking that many of our readers might peruse Mr. Glazebrook’s book with pleasure and profit to them selves. The kinetic aspect of light, and its relation to other forces, is first brought under consideration, after which the fundamental ideas of wave motion are clearly explained, and the main subject is entered upon. Every page is rich with matter of interest to the photographer; but, as a sample, we extract a description of the direct vision spectroscope, a convenient apparatus which may often serve to give valuable indications to the photographic worker;— “ For many purposes the direct-vision spectroscope is a con venient and useful form. We have seen how it is possible to combine two prisms so as to produce deviation without disper sion. It is equally possible to combine a number of prisms. so_ as to produce dispersion of the extreme rays without deviation for some one given ray. On allowing, then, the light from •
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