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December 17, 1880.J THE PHOTOGRAPHIC NEWS. 601 Ue Ahotographir Elebs, Herember 1880. PHOTOGRAPHY IN AND OUT OF THE STUDIO. Photo-Electricity of Fluor-Spar Crystals—Phosphor escent Substances for Lighting Mines—The Com position of Ammoniacae Silver Nitrate—New Inves tigations of the Action of Light on Plants— Pyroxylins Varnishes—Photographic Portraits, the Eyes of which SEES to Wink—THE Testing of Potassium Bromide. Photo-Eleclricity of Fluor-Spar Crystals.— Hantzel has communicated to the Saxon Royal Society of Science some interesting observations on the production of elec tricity by light in coloured fluor-spar. The centres of the fluor-spar cubes become negatively electric by the action, of light. The electric tension diminishes towards the edges and angles, and frequently positive po’arity is produced there. With very sensitive crystals a short exposure to daylight is sufficient; by a long exposure to light the electric current increases. The direct rays of the sun act much more powerfully than diffused day light, and the electric carbon light is more powerful even than sunlight. The photo-electric action of light belongs principally to the “ chemically active ” rays; this is shown by the fact that the production of electricity is extremely small behind a glass coloured with cuprous oxide, and behind a film of a solution of quinine sulphate ; while it is not appreciably diminished by a film of a solution of alum. The photo-electric excitability of fluor spar crystals is increased by a moderate heat (80° to 100° C.) Phosphorescent Substances for Lighting Mines.— Montigny has lately proposed to light mines by means of phosphor escent substances, the latter being made luminous in Geissler’s tubes. Balmain’s luminous paint spread upon moving endless bands has also been suggested. The Composition of Ammoniacal Silver Nitrate.—As is known, many methods have been proposed for the pre paration of bromide of silver gelatine emulsion, in which the silver nitrate must be mixed beforehand with enough ammonia to dissolve the precipitate first formed. The question now is, what reaction takes place by the addition of ammonia to silver nitrate ? According to Prescott, nearly two molecules of ammonia are required for the solution of the silver salt, under the most varied conditions of temperature and concentration. The reaction that takes place here is represented by the following equation : 2AgN0,+4NE,OH=(NH,Ag),0 + 2NH,NO-+3H,0. New Investigations of the Action of Light on Plants.— Hamiotzine has shown by a series of very interesting ex periments that plants decompose carbonic acid in diffused daylight quite as energetically as in direct sunlight, and sometimes even more so ; also in artificial light (a gas flame equal to about fifty candles) a decided decomposi tion of carbonic acid by the leaves of various plants takes place. Different plants behave differently, according to the degree of absorption of light by their exterior cell walls containing chlorophyll. From this it follows that with many plants a certain intensity of light acts most favourably on the carbonic acid decomposition. By fur ther increase of the intensity of light no greater quantity of carbonic acid is decomposed ; in some cases even a smaller quantity. A gas flame (with an intensity equal to that of fifty candles) causes the decomposition of about a third as much carbonic acid as daylight. Pyroxyline Varnishes.—Parkes, of Birmingham, has patented the manufacture of varnishes from pyroxyline. According to his method, pyroxyline is dissolved in a mix ture of carbon tetrachloride and camphor, which is also mixed with gum, resins, oils, colouring matters, &c. Car bon bisulphide and camphor form also a good solvent. A mixture of camphor with benzole or turpentine, with the co-operation of pressure and heat, also dissolves the pyroxyline quickly. These solutions make very good varnishes. Photographic Portraits, the Eyes of which Seem to IVink.— Bottzer describes the following pretty experiment. Two negatives are prepared of the same person—one when the person’s eyes are shut, the other when they are open. Both negatives are pasted on opposite sides of a piece of transparent paper, so as to cover one another perfectly. If the double picture is now held before a flickering lamp, or any other flame or source of light of rapidly changing intensity, the combined photograph shows quick changes of opening and shutting the eyes, producing a most remark able effect. The Testing of Potassium Bromide.—Silver iodide is almost insoluble in a 10 per cent, solution of ammonia, and silver bromide is insoluble in a 15 to 17 per cent, solu tion of ammonium carbonate. Hager recommends the following experiments for the examination of potassium bromide in the Pharmaceutischen Centralblatl: 5 to 6 grammes of potassium bromide are finely powdered, and 0-1 gramme ot the powder is dissolved in 10 to 12 cubic centimetres of ammonia; to this 1 drop of a solution of silver nitrate is added, and the mixture shaken. A tur bidity not disappearing indicates the presence of potassium iodide. The test is sufficiently delicate. To test for chloride, 0T gramme of the powdered potassium bromide is dissolved in 2 to 3 cubic centimetres of water, and a solution of about 046 grammes of silver nitrate in 2 to 3 cubic centimetres of water is added; then 10 to 12 cubic centimetres of a solution of ammonium carbonate are added, the mixture shaken, and filtered after about ten minutes. The formation of a turbidity in the filtrate after neutralizing with nitric acid indicates the presence of chloride. Et Zome, THE VAN DER WEYDE ELECTRIC STUDIO IN REGENT STREET. The lamps in Regent Street are lit, for the light fades early these short wintry days. It is still afternoon ; the Quadrant is full of life ; the gay costumes of the prome- naders, now veiled in the mist of twilight, now made res plendent by the vivid illumination of the shops, lose none of their attraction, but, on the contrary, seem enhanced rather “ between the dark and the daylight, when the night is beginning to low’r.” Longfellow is not alone in loving the period ; we believe every thorough-bred Cock ney rejoices in this time between the lights, and it is the one thing that reconciles him to winter when it comes upon us. There is a feeling of warmth, of cosiness, of brightness, of snugness prevailing at such times, which dwellers in great cities always delight in, and which may be considered a set-off against the many advantages our country cousins enjoy. “ I like to stroll down Regent Street,’’ says the song, and between afternoon and evening the sentiment appears to be a very popular one. It is Cattle Show week, and this may have something to do with augmenting the busy crowd of loungers that hustle one another upon the glimmering pavement before the bright shops and under the glittering lamps. It may not be “the season" in town; but London is full, for all that, and so bustling and animated a scene is rarely found at any other time of the year. It is hardly a seasonable hour to visit a photographic studio, one would think ; but we have purposely delayed our call. The card of invitation says any hour before 7’30 p.m., so we are in plenty of time. Mr. Van der Weyde's studio is in a magnificent position in the very centre of