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. The intensity of the light emitted by this composition after exposure is considerable, and largely greater than the light produced by any of the substances heretofore known. The hereinbefore described substance may be ground with oil and used like ordinary paint; or it may be ground with any suitable varnish or be mixed in the manner of water colors; or it may be employed in any other suitable and well-known manner in which paints are employed. My improved luminous substance is adapted for a great variety of uses--for instance, for painting business and other signs, guide boards, clock and watch dials, for making the numbers on houses and railway cars, and for painting all surfaces which are exposed periodically to direct or indirect light and desired to be easily seen during the night. When applied with oil or varnish, my improved luminous substance can be exposed to the weather in the same manner as ordinary paint without suffering any diminution of its luminous property. I claim as my invention the herein described luminous substance, consisting of calcined chalk, sulphur, and bismuth, substantially as set forth. Merrill B. Sherwood, Jr., of Buffalo, N. Y., obtained a patent for a phosphorescent composition, dated August 9, 1881. The author says: My invention relates to an improvement in phosphorescent illuminants. I have taken advantage of the peculiar property which obtains in many bodies of absorbing light during the day and emitting it during the night time. The object of my invention is the preparation by a prescribed formula, to be hereinafter given, of a composition embodying one of the well-known phosphorescent substances above referred to, which will be applicable to many practical uses. With this end in view my invention consists in a phosphorescent composition in which the chief illuminating element is monosulphide of calcium.