EFFECT OF LIGHT UPON CRYSTALLIZATION.
Place a solution of nitre in a small basin of water, in a room which has the light admitted only through a small hole in the window-shutter; crystals will then form most abundantly upon the side of the basin exposed to the aperture through which the light enters; and often the whole mass of crystals will turn towards it. This peculiar effect may also be seen in the crystals in camphor glasses in druggists’ windows, which are always most copious upon the side exposed to the light.
EFFECT OF LIGHT ON PLANTS.
Shut a plant up in a room into which light is only admitted through a small hole in the window-shutter, and set the plant out of the direction of this light; it will, in a short time, turn itself, and even grow downwards, that it may expose its leaves to the light.
If plants be kept in darkness, they will soon become bleached; then, if they be exposed to the sun for three, four, or five hours, the leaves and stalks will become as intensely green as if the plants had been reared in the sun. Again, if a lighted lamp be introduced into a dark room, wherein a plant has been shut up and bleached, it will become green, and direct itself towards the lamp. If such a plant be removed from the room, exposed for some time to the sun, and then returned to darkness, it will no longer support the privation of light, but will fade and perish.
INSTANTANEOUS LIGHT UPON ICE.
Throw upon ice a small piece of potassium, and it will burst into flame. In one experiment, the operator pressed the potassium on the ice with a penknife, when the whole length of the ice became ignited.
WHITE LIGHT FROM ZINC.
As a substance for light, zinc is far superior to any of the metals. The light which it yields on burning is as bright as that of the sun, and as white, so that the eye can scarcely endure it; and the effect is much increased by the great quantity of silvery smoke which reflects the fire, and thus widely increases the sphere of illumination. Zinc may be used in thin sheets, or in filings.