In many, and possibly in a majority of cases, the illuminating composition applied as a dry powder will give the most satisfactory results, in view of the tendency to chemical action between the paint and composition when intimately mixed; in view of the fact that by the addition to paint of any color of a sufficient quantity of the composition to render the product luminous, the original color of the paint will be modified or destroyed; and, also, in view of the fact that the illuminating composition is so greatly in excess of the paint, the proportions in which they are united being substantially ten parts of the former to one of the latter, it will be difficult to impart a particular color to the product of the union without detracting from its luminosity. On the other hand, the union of dry powder with a body already painted by the simple force of adhesion does not establish a sufficiently intimate relation between it and the paint to cause chemical action, the application of a light coat of powder does not materially change the color of the article to which it is applied; and, further, by the use of the powder in an uncombined state its greatest illuminating effects are obtained. Again, if the appearance in the daytime of the article which it is desired to have appear luminous at night is not material, it may be left unpainted and simply sized to retain the powder. In printing it is probable that the composition will be employed almost exclusively in the form of dry powder, as printing-ink, normally pasty, becomes too thick to be well handled when it is combined with powder in sufficient quantity to render the printed surface luminous. However, the printed surface of a freshly printed sheet may be rendered luminous by dusting the sheet with powder, which will adhere to all of the inked and may be easily shaken from the unmoistened surfaces thereof. I am aware that monosulphide of calcium and magnesia have before been used together in phosphorescent compounds. What I claim is a phosphorescent composition consisting of monosulphide of calcium, combined with carbonate of lime, magnesia, and silex, substantially as described. Orlando Thowless, of Newark, N.J., obtained a patent for a process of manufacturing phosphorescent substances dated November 8, 1881. The inventor says: The object of my invention is to manufacture phosphorescent materials of intense luminosity at low cost and little loss of materials.