Pièce d'Orgue in G, BWV 572, also known as Fantasia in three parts, is written in a French style. It originated rather early in Bach's career (before 1712). The first part is entitled as Tres vitement (very fast), the second - Gravement (heavy) and the final part - Lentement (slow).
The Italians would call the introduction of 28 bars the Passagio which was also a common feature in the North German Praeludia. The cojncluding cadenza has a different form of the perfidia, the arpège figuré.
The Piece d'Orgue is structurally closely related to the Fantasia in A-minor BWV 922 and the Praeludium in D BWV 532a. The Piece d'Orgue is the most mature of the three compositions.
A likely model for the dominant middle section has been found in the Grand Plein Jeu Continu that opens Boivin's Premier Livre d'Orgue. The affinity are the Alla Breve metre, white notation and 5 part texture. It is possible it was originally written for pedal clavichord, the study instrument of choice for organists in those days, which had an extended pedal.
Here's the Boyvin recording:
These notes come from a few different sources.
I tried this piece once on St. Omer and was quite excited by the silvery 16' Plenum and the rolling 16' reeds in the middle pedal section. The complicated textures sounded clear throughout.
So I thought it a good idea to record it on this organ.