Impromptu in E-flat minor
Movements and Duration
There is one movement: Allegro furioso (E-flat minor, 150 bars), lasting around 7 minutes in performance.
Nothing is known of the process of composition, except that it was written while Tchaikovsky was a student at the Saint Petersburg Conservatory.
The Impromptu found its way into print accidentally. Nikolay Kashkin recalled that it had been "set down in the middle of Pyotr Ilyich's other Petersburg work, and in this notebook were some blank pages on which a new work [the Scherzo à la russe] was written... When P. I. Jurgenson wanted to print the Scherzo à la russe, Rubinstein took him the whole notebook, but P. I. Jurgenson did not receive any instructions, and so he had engraved all the pieces he found. When Tchaikovsky saw the proofs of both pieces, he was at first surprised and annoyed that the Impromptu had also been engraved, but he later became reconciled to this irreversible fact" 
The autograph score of the Impromptu has been lost.