Concerto for flute in A Major No. 256 (QV 5:218)

J.J. Quantz: Concerto for flute in A Major No. 256 (cataloged as QV 5:218) was written around 1735-1736, at the time when Quantz was serving in the Hofkapelle (court orchestra) in Dresden.
While Quantz wrote nearly 300 concertos primarily for Frederick the Great, this specific work predates his official "Berlin" contract.
The concerto is uniquely linked to Quantz's invention of a second key (for D#) to improve the instrument's intonation. A famous portrait of Quantz from c. 1735–1736 shows him holding the autograph manuscript for this specific concerto (QV 5:218) while pointing to the additional key, suggesting the piece was written to demonstrate the technical ease of his new design.
In the tuning systems of the 1730s, D-sharp and E-flat were not the same pitch. According to the acoustic theories, Quantz detailed in his treatise Versuch, a major semitone (e.g., D to E-flat) was larger than a chromatic semitone (e.g., D to D-sharp). D-sharp needed to be approximately 22 cents lower than E-flat to sound perfectly in tune as a major third above B.
Standard flutes of the time had only one key, forcing players to use a single hole for both notes. This made D-sharp consistently too high and E-flat often too low. To resolve this, Quantz added a second, smaller key specifically for D-sharp. By using two separate keys with differently sized holes, a flutist could play a perfectly tuned D-sharp without having to manually adjust their embouchure or "shade" the hole with their finger.