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.