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A Powder Which Catches Fire When Exposed To The Air

Put three ounces of rock alum, and one ounce of honey or sugar, into a

new earthen dish, glazed, and which is capable of standing a strong

heat; keep the mixture over the fire, stirring it continually till it

becomes very dry and hard; then remove it from the fire, and pound it

to a coarse powder. Put this powder into a long-necked bottle, leaving

a part of the vessel empty; and, having placed it in a crucible, fill

the crucible with fine sand, and surround it with burning coals.

When the bottle has been kept at a red heat for about seven or eight

minutes, and no more vapour issues from it, remove it from the fire,

then stop it with a piece of cork; and, having suffered it to cool,

preserve the mixture in small bottles well closed.

If you unclose one of these bottles, and let fall a few grains of this

powder on a bit of paper, or any other very dry substance, it will

first become blue, then brown, and will at last burn the paper or

other dry substance on which it has fallen.