I have found that chalk, which is composed of the shells of microscopic
animals, possesses the desired property in the highest degree; and my
invention consists, therefore, of a luminous substance composed of such
chalk, sulphur, and bismuth, as will be hereinafter fully set forth.
In preparing my improved composition I take cleaned or precipitated
chalk, and subject it to the process of calcination in a suitable
crucible over a clear coal or charcoal fire for three or four hours,
or thereabout. I then add to the calcined chalk about one-third of its
weight of sulphur, and heat the mixture for from forty-five to ninety
minutes, or thereabout. A small quantity of bismuth, in the proportion
of about one per cent, or less of the mixture, is added together with
the sulphur.
The metal may be introduced in the metallic form in the shape of
fillings, or in the form of a carbonate, sulphuret, sulphate, or
sulphide, or oxide, as may be most convenient.
The substance produced in this manner possesses the property of emitting
light in the dark in a very high degree. An exposure to light of very
short duration, sometimes but for a moment, will cause the substance
to become luminous and to remain in this luminous condition, under
favorable circumstances, for upward of twenty-four hours.
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