Frédéric Chopin's Impromptu No. 1 in A major, Op. 29, was composed in 1837.
The impromptu is in ternary form (ABA), the middle being in the key of F minor. A perpetuum mobile in triplets accompanies the piece.
In George du Maurier's novel Trilby, the title character, a singer who can perform only under the influence of hypnosis, performs the Impromptu in A major as a wordless vocalise to end her concerts.