Steep a loosely twisted cotton skein in a solution of nitre; dry it,
and it will readily kindle by the sparks produced from the flint and
steel. If, however, the cotton be further prepared by coating portions
of it, at regular intervals, alternately with sulphur and white wax,
and the sparks be struck upon the sulphur, it will readily kindle, and
as readily light the wax; and the flame will endure long enough for
sealing a letter.