XC
Malus in France 1808. Polarization may be caused by refrac
tion as well as by reflection. The light of the sun and of the
fixed stars is unpolarized light, that of comets, planets and the
moon is polarized.
G. Chemical effects of Light.
§ 220 According to the nature of bodies, light either
decomposes or composes them; f. e. mercury red oxide by
the agency of light is decomposed into mercury and oxygen;
fats and oils under the influence of light unite with the oxygen
of the air and form sebacic acids (froughy butter). Light
changes and increases the chemical affinity of a great many
substances, thus furthering the chemical exchange of matter
in vegetable life.
§ 221. The green parts of plants by the assistance of light
very easily decompose carbonic acid (green leaves with carbonic
water under a bell-jar, exposed to the light), cf. § 95 and Q. 223.
The richest vegetable growth we find, where the sun's light acts
the strongest. Shadows prolong the decomposition of carbonic
acid and the separating of oxygen in plants.
§ 222. If one part of chlorate and one part of hydrogen
gas are mixed in the dark, they remain a mechanical mixture;
as soon as one direct ray of light falls into the mixture, the gases
unite chemically causing a vehement explosion. That the chemi
cal effects of light may be even preserved, the art of Photogra
phy proves. (See § 201.)
