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.
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