Stranica 150 [150]
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 yel¬
low 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 crystal¬
lized 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.