Stranica 150 [150]
OCR
88 LIGHT AND WATER deposited, as is the case with the Velino at Terni, and the Anio at Tivoli; but I doubt if pure saline matters, which are in themselves white, ever change the tint of water. “ ORNITHER.—On what then does the tint of the ocean depend, which has itself given name to a colour? “ HALIEUS.—I think probably on vegetable matter, and perhaps, partially, on two elementary principles, iodine and brome, which it certainly contains, though these are possibly the results of decayed marine vegetables. These give a yellow tint, when dissolved in minute portions in water, and this, mixed with the blue of pure water, would occasion sea screen. I made many years ago, being on the Mer de glace, an experiment on this subject. I threw a small quantity of iodine, a substance then recently discovered,’ into one of those deep blue basins of water, which are so frequent on that glacier, and, diffusing it as it dissolved with a stick, I saw the water change first to sea green in colour, then to grass green, and lastly to yellowish green; I do not however, give this as a proof, but only as a fact favourable to my con. jecture. “POIETES.—It appears to me to confirm your view of the subject, that snow and ice, which are merely pure crystallized water, are always blue, when seen by transmitted light. I have often admired the deep azure in crevices in masses of snow in severe winters, and the same colour in the glaciers of Switzerland, particularly at the arch where the Arve issues, in the Valley of Chamouni.” : Iodine was discovered by Courtois in 1811, and its elementary nature established by Davy towards the end of 1813.
