Reference : Sur la cause de l'absence de coloration de certaines eaux limpides naturelles
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Sur la cause de l'absence de coloration de certaines eaux limpides naturelles
[en] Cause of the Absence of Color in Certain Limpid Natural Waters
Spring, Walthère [Université de Liège - ULiège]
Recueil des Travaux Chimiques des Pays-Bas et de la Belgique. 2e série
[en] Color ; Waters, natural
[fr] Couleur ; Eaux naturelles
[en] Spring, W. Recueil des Travaux Chimiques des Pays-Bas (1898), 17, 359-75; SciFinder (Chemical Abstracts Service: Columbus, OH); (accessed July 8, 2010).

Compare Abstr., 1884, 259, and Bull. Acad. roy. Belg., 1886, [iii], 12, 814, and 1897, [iii], 34, 578. Although it is well recognised that pure water is blue when viewed through a thickness greater than 1 metre, the only natural waters which appear blue are those of mountain streams which have their origin in the ice and snow of great altitudes. Berzelius has stated (Jabresbericht, 1830, 9, 207) that the extraordinarily clear water of Lake Wettern, in Sweden, is perfectly colourless when viewed through a thickness of more than 32 feet, and has hence raised objection to the view that pure water is blue. The author has previously shown (loc. cit.) that if water contains one ten-millionth part of its weight of colloidal ferric hydroxide, it no longer appears blue, but green in colour; with quantities greater than this, the colour is yellow or brown. By macerating fragments of a red rock, such as a Devonian schist, during several weeks with frequently renewed hot caustic potash, and subsequently washing with water by repeated decantation, a point is ultimately reached when the red coloring-matter ceases to subside from the washing water, even after standing several months; the particles of suspended ferric oxide (haematite) are no longer visible under a magnifying power of 150 diameters, and probably correspond with the dust of the Devonian epoch. On adding a few drops of this turbid solution to a large volume of pure water, the latter is rendered perfectly clear and colourless when viewed through a thickness of 6 metres. When the proportion of ferric oxide, however, is increased, the water quenches more and more of the transmitted light, until it finally becomes opaque, although appearing red by reflected light. These observations explain the fact that terrestrial waters rarely appear blue. That the waters of Alpine streams are generally blue is probably due to their being entirely free from suspended anhydrous ferric oxide; the cosmic dust with which they are often contaminated consists principally of meteoric iron, which possesses different optical properties from haematite, and is incapable of destroying the natural blue colour of the water.

Reprinted with the permission of the American Chemical Society. Copyright © 2010. American Chemical Society (ACS). All Rights Reserved.
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