Impromptu No. 1 (Chopin)

Frédéric Chopin's Impromptu No. 1 in A major, Op. 29 was composed in 1837.
Music.
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 popular culture.
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.