Bach, Johann Christian (1735 - 1782)
Source of “Quartetto” Op. 18 is a ms. of separate parts online available at Giedde’s Collection, ms. IV,37 mu 6212.1645, The Royal Library, Copenhagen. It is a transcription of a quartet published posthumous as Op. 19 by Preston, London, 1783 and later published in Frankfurt as Op. 18.
The source is a 375 pages ms available at Conservatorio di musica S. Pietro a Majella, Napoli with Id no. Ms. DM02032101093. It includes several compositions by J. C. Bach and a “Concerto per Cembalo”. The sonata is in three separate parts. Caption title is: “Trio / A' Due Violini, é / Basso / Del Sig:r / Giovanni Cristiano Bach”.