I first take clam shells and, after cleaning, place them in a solution composed of about one part of commercial nitric acid and three parts of water, in which the shells are allowed to remain about twenty minutes. The shells are then to be well rinsed in water, placed in a crucible, and heated to a red heat for about four hours. They are then removed and placed, while still red-hot, in a saturated solution of sea salt, from which they are immediately removed and dried. After this treatment and exposure to light the shells will have a blood-red luminous appearance in the dark. The shells thus prepared are used with sulphur and the phosphide and sulphide of calcium to produce a phosphorescent composition, as follows: One hundred parts, by weight, of the shells, prepared as above, are intimately mixed with twenty parts, by weight, of sulphur. This mixture is placed in a crucible or retort and heated to a white heat for four or five hours, when it is to be removed and forty parts more of sulphur, one and one-half parts of calcium phosphide, and one-half part of chemically pure sulphide of calcium added. The mixture is then heated for about ninety minutes to an extreme white heat. When cold, and after exposure to light, this mixture will become luminous. Instead of these two ignitions, the same object may be in a measure accomplished by the addition of the full amount of sulphur with the phosphide and sulphide of calcium and raising it to a white heat but once. The calcium phosphide is prepared by igniting phosphorus in connection with newly slaked lime made chemically pure by calcination. The condition of the shells when the sulphur is added is not material; but the heat renders them porous and without moisture, so that they will absorb the salt to as great an extent as possible. Where calcined shells are mixed with solid salt, the absorbing power of the shells is greatly diminished by the necessary exposure, and there will be a lack of uniformity in the saturation. On the contrary, by plunging the red-hot shells in the saline solution the greatest uniformity is attained.
Instead of using clam shells as the base of my improved composition, I may use other forms of sea shells--such as oyster shells, etc.