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The photographic news
- Bandzählung
- 35.1891
- Erscheinungsdatum
- 1891
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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. 1695, February 27, 1891
- Digitalisat
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The photographic news
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ALUMINIUM. BY G. L. ADDENBROOKE. To all those who take an interest in the brass and glass elements of photography, few things offer a more pleasing and hopefill field for speculation at present than the possibilities which the cheap production of this metal opens out. Great as have been the advances of metallurgy in other directions, they have, during the last few years, been simply astonishing in this. At the exhibition of 1851, some small bars of aluminium, reduced by the French chemist, Deville, at the cost of Napoleon III., formed one of the rarest and greatest curiosities. From that time the reduction of the metal has always been carried on commercially on a small scale, but until some four years ago the price remained steadily at about seven shillings and sixpence per ounce, while no method of soldering it satisfactorily was known, so that its use was limited to certain parts of scientific instruments, and to the best kinds of opera and field glasses, where its lightness was a sufficient set off against its expense and the difficulties of working it. The old method of reducing this metal, which forms the chief constituent in clay, and is, therefore, the most abundant metal in nature, consists in acting with metallic sodium on a kind of spar called cryolite, which is a fluoride of aluminium. The cryolite is pounded up and mixed with small pieces of sodium, and the whole brought to a red heat, and kept for some time at this temperature in a closed retort, during which the fluorine combines with the sodium, leaving the aluminium in a metallic state. The price of aluminium made by this process is, therefore, entirely dependent on the price at which the sodium needed for its reduction can be procured. The improve ments which have been made in the manufacture of aluminium by what is called the chemical process have chiefly lain in the direction of improved and cheaper methods of reducing the metal sodium. The Castner process is of this kind, and chiefly by its means the price of aluminium was brought down about three years ago from seven shillings and sixpence per ounce to twenty shillings per pound. But during the past three or four years a third process has been worked out by which, with the aid of electricity, the cost of producing aluminium has still further been reduced. By this process the aluminium is reduced in an electric furnace—that is, one in which the heat is generated by the passage of a current of electricity between two carbon rods, or between a carbon rod and a plumbago crucible. The heat is thus actually gene rated in the furnace itself in the midst of the materials to be operated on, and is not communicated from outside in the ordinary manner. The electric process, being a cheaper one to work than the chemical, when first introduced caused a sharp rivalry to spring up between the two, the result being that both processes have been still further perfected, and the price of aluminium is now brought down to eight shillings a pound, while there are prospects of still further considerable reductions. The price of the metal is now brought to a point which admits of its being employed for numerous purposes where its cost has hitherto been prohibitive. In com paring its price with that of brass, it must be remembered that it is only one-third the weight—the proportions being exactly 2-67 to 8-4—so that, bulk for bulk, a pound of aluminium goes three times as far as a pound of brass ; thus, at eight shillings per pound, the cost of aluminium is only about three times that of brass. Already we have lenses mounted in aluminium, and there is now no reason why tripod heads and some of the other metal parts of cameras should not be made of it. Its use for constructing shutters is obvious. It might advantageously be employed for the framework of dark slides and changing-boxes, and, finally, it would make excellent developing dishes, both light and indestructible. Aluminium has, therefore, a wide and useful field before it in connection with photographic apparatus, while the possibilities of its application in other ways are almost endless. THE SCIENCE OF COLOUR. Last Friday Captain W. de W. Abney delivered his second lecture on the above subject at the Society of Arts. He said that, as a standard light, he always used the most luminous portion of one of the poles of an arc lamp. It was sensibly the same at all times, as might be expected from its being at the temperature of the vaporising point of carbon. The variations in the brightness of daylight at various alti tudes of the sun above the horizon had been much worked at experimentally by Professor Tyndall, and Lord Rayleigh had worked out the law. Much of the variation is due to small particles floating in the atmosphere, and there are differences of opinion as to the nature of those particles. He (Captain Abney) believes them to be chiefly small fl nating particles of water. Such particles will float for a long time if small enough ; in fact, Stokes has proved that some of them do not fall more than one tenth of an inch in an hour ; coarser particles may sink as much as one foot in an hour. Lord Riyleigh says that the small particles in the air can discriminate between the waves of ether, and absorb some more than others. The lower the sun is on the horizon, through the more of these particles does its light have to pass. He then proceeded to make a “ mock sun ” upon the screen by projecting a bright beam from the electric lamp, and making the light pass through a weak solution of hyposulphite, of soda, into which he poured a little acid. Particles of sulphur were theieby slowly set free, and, as they increased, they more and more intercepted the light, so that the white disc on the screen slowly chinged to yellow, then to red, and passed through all the changes of colour presented by the sun as it approaches the horizon. He then described the sector photometer and the means of registering any colour the human eye can see. • Patent Xntellgence. Applications for Letters Patent. 2,880. T. R. Dallmeyer, 115, Cannon Street, London, “ Means and Devices for Obtaining Projectins of Photographs in Natural Colours.”—February 17th. 2,934. C. CLOAKLY, 13, Northumberland Place, Bath, “ Photo graphic Printing Frames.”—February 18th. 2,935. W. J. Lancaster, 6, Livery Street, Birmingham, “Plate Carriers and Cameras.”—February 18th. 2,956. W. G. Thomson and W. Ward, 8, Quality Court, London, “Photographic Focussing.”—February 18th. 3,024. Marion and Co., 22, Soho Square, London, “ Marion’s Glass-Roller Hot Rolling Press.”—February 19th. 3,042. J. Y. Johnson, 47, Lincoln’s Inu Fields, London, "Artificial Light for Photcgraphy ” (Paul Nadar, France). —February 19th. 3,071. Matthews and Son, St.John’s Road, Ryde, “ Frames for Exhibiting Photographs.”—February 20th.
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