Form

Binary (in terms of tonality)
AA'BA""
sonata "principle"
sonata and variation hybrid (e.g. "repeat" of exposition is actually a variation)

Theme (B-flat major)

Secondary Key (F major)

Cadenza

In bar 73, one copy of the quartet included a brief cadenza for 1st violin

Notes

This is a lovely, bright song for the 1st violin.
This is the first in a very long line of exquisite adagios in Haydn's quartets.