The pages displayed here contain the first two movements of the third of the eleven sonatas, in C major. The first movement, maestoso assai, is stately and slow, with highly decorated solo passages. Its final dominant chord introduces the much faster allegro. The undated but almost certainly 18th-century manuscript is the work of a Venice firm of professional copyists, and it is likely that the composer had many of his works produced in this way for sale or for presentation to friends and patrons. Much of Boccherini's work was published in his lifetime, but six of these sonatas have evidently not been published. A gold-tooled inscription on the front cover of the manuscript reads 'The Dutchess of Hamilton', a title which Susan assumed after 1819 when her husband inherited the dukedom.

If a cellist, Duchess Susan would have had to have been reasonably accomplished to have played these sonatas. She certainly owned a piano but the solo parts, which are written mainly in the cello C-clef (the present-day tenor clef), could not be read easily by a pianist, though realisation of the unfigured bass line would not be a problem for an experienced keyboard player. The musicianship and knowledge of harmony which this required was not normally part of a lady's musical education, so perhaps unsurprisingly, the pages of this manuscript show little sign of the wear and tear of practical use. For Duchess Susan it may well have remained a handsomely bound (or re-bound) collector's item and a memento of her father's friendship with Boccherini.