A lovely little piece!
I found this brief description on t'internet. You might find one or two useful comments here :-
"In 1815, Schubert composed the Adagio in G major D. 178. Though there are two known versions of this work, the second is extant only as a fragment. The first version of 8 April 1815 was cast in a tripartite song form (A-B-A) and boasts not only interesting harmonics, but also pianistic brilliance provided by dazzling interjections which the Schubert biographer Alfred Einstein once called 'little virtuoso coquetries'. "