|Reference : Sur la réalisation d'un liquide optiquement vide|
|Scientific journals : Article|
|Physical, chemical, mathematical & earth Sciences : Chemistry|
|Sur la réalisation d'un liquide optiquement vide|
|[en] Realization of an Optically Transparent Liquid|
|Spring, Walthère [Université de Liège - ULg]|
|Recueil des Travaux Chimiques des Pays-Bas et de la Belgique. 2e série|
|[en] Optical properties ; Liquids|
|[fr] Propriétés optiques ; Liquides|
|[en] Spring, W. Recueil des Travaux Chimiques des Pays-Bas (1899), 18, 153-68; SciFinder (Chemical Abstracts Service: Columbus, OH); https://scifinder.cas.org (accessed July 8, 2010).
Tyndall has assumed that when a beam of light passes through a gas its path is made evident by the illumination of minute solid or liquid particles present as impurities. Lallemand, however, from experiments with carefully distilled liquids, concluded that the illumination of a fluid medium by light is a specific property of the medium, and that each medium has a certain "coefficient of illumination", dependent on its nature. The author now shows that, although it is impossible to obtain a truly transparent liquid (that is, one which is not rendered luminous by the passage of a beam of light) by distillation or filtration, liquids can be rendered optically pure by means of a current of electricity; on passing, for example, a current through water containing a small quantity of silica or ferric hydroxide in suspension, the suspended matter is deposited at the cathode, and carries with it the minute particles which render the water capable of being illuminated. The same result is also obtained by adding clear lime water to a solution of silicic acid, and leaving the precipitate to subside in a stoppered vessel; on examining the liquid in a beam of light, care being taken that the vessel is not opened, it is found to be perfectly transparent. The subsidence of other gelatinous precipitates, such as the hydroxides of iron, aluminium, and zinc, from water renders the latter non-illuminable; the subsidence of crystalline precipitates, however, such as barium sulphate or calcium oxalate, gives no such result. It thus appears probable that the minute suspended particles can only be removed by being surrounded, during the precipitation, with a heavy, gelatinous envelope. The filtration of water through a layer of a gelatinous precipitate, out of contact with the air, renders it transparent; but if filtered in contact with air, this result is not obtained. The reason why distillation fails to yield transparent liquids is thus made evident. In the case of organic liquids, the author has not obtained such definite results; the subsidence of gelatinous precipitates from organic liquids is, as a rule, very incomplete, so that optical transparency cannot generally be obtained. It appears probable also, that many organic liquids become luminous on the passage of a beam of light, owing to fluorescence. The particles which are rendered luminous in water by a beam of light appear to consist largely of organic matter, but luminescence is also due to minute bubbles of gas; this is made clear by the increased illumination which occurs when the pressure in the space above the water is diminished, and by the fact that optically transparent water is rendered luminescent by passing air through it.
Reprinted with the permission of the American Chemical Society. Copyright © 2010. American Chemical Society (ACS). All Rights Reserved.
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